foraminifera as paleoceanographic and paleoclimatologic ... · 577 foraminifera as...

577

Foraminifera as Paleoceanographic andPaleoclimatologic Proxies

Chaired by Wolkfgang Kuhnt and Holger Gebhardt

Foraminiferal studies provide a fundamental contribution to ourunderstanding of past and future ocean and climate systems. Mostreconstructions of paleotemperature, paleosalinity, carbon dioxide content ofatmosphere and oceans, sea-level fluctuations, paleoproductivity and carbonexport flux rates rely entirely on analyses of foraminiferal test geochemistryand assemblage composition. In this session, we want to focus on innovativeapplications of foraminifera as proxy indicators in paleoceanography andpaleoclimatology. This may include (but is not restricted to) stable isotope andgeochemical analyses of foraminiferal tests, transfer functions for planktic andbenthic assemblage counts, biometric and other quantitative approaches toreconstruct physical, chemical and biological oceanographic processes. Thesession is not restricted to more recent periods of Earth’s history and extendsto the entire Phanerozoic. Contributions which try to overcome the lack ofmodern analogues for pre-Pleistocene times were particularly encouraged.

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol . 29 - 1 / 2006

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579

Reconstructing changes in upper water habitats during thelate Maastrichtian global warm event based on stable isotopes

Sigal Abramovich1; G. Keller2; Z. Berner3 & D. Stüben3

1Department of Geological and Environmental Sciences,Ben Gurion University of the Negev, P.O.B 653, Beer Sheva 84105, Israel

[email protected] of Geosciences, Princeton University, Princeton, NJ 08544-1003 U.S.A.

3Institute für Petrographie und Geochemie, Universitat Karlsruhe,Karlsruhe 76128, Germany

Oxygen and carbon stable isotope measurements of individual speciesof planktic foraminifera are a valuable tool for reconstructing habitats pattern,water mass stratification paleofertility, and for tracing special vital effects (e.g.,photosymbiosis). This study presents a stable oxygen and carbon isotopedatabase for several Maastrichtian species that provides insight into changesin upper water habitats and vital activities during the global greenhouse warmingnear the end of the Maastrichtian.

The South Atlantic DSDP Site 525A was chosen for this study becauseit provide the most detailed record of this warm event. Previous studies indicatethat the warming occurred between 65.45 and 65.11 Ma, raised deep-watermasses temperatures by about 3-4°C, was associated with significant decreasein planktic foraminiferal diversity and the appearance of dwarfed morphologies(Li & Keller, 1998; Abramovich & Keller, 2003).

Eleven sample intervals were selected from the uppermost Maastrichtiansediments of Hole 525A representing the climatic periods that predated (65.7,65.67, 65.6 Ma), coincided with (65.32, 65.3, 65.28, 65.26, 65.15 Ma), andfollowed the warm event (65.1, 65.04 Ma). Stable isotope measurements weretaken from 20-30 adult specimens of each species from the > 250 µm sizefraction from each sample interval. In addition, ~50 specimens of dwarfedforms from the < 150 µm size fraction were measured to assess possibleecological divergence in this group in the warm intervals.

In the intervals that predate warming, δ18O values of the surface dwellerPseudoguembelina hariaensis averaged -0.98‰ and the deep dwellerAbathomphalus mayaroensis averaged -0.58‰ indicating temperatures of16°C and 14.2°C, respectively. Peak warming was at 65.32 and 65.3, whereδ18O values of P. hariaensis averaged -1.1 ‰ (17.1°C) and δ18O values ofAbathomphalus mayaroensis averaged -0.96‰ (15.9°C) suggesting that

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol. 29 - 1 / 2006 p. 579-580

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580Anuário do Instituto de Geociências - UFRJISSN 0101-9759 - Vol. 29 - 1 / 2006 p. 579-580

FORAMS 2006Reconstructing changes in upper water habitats during the

late Maastrichtian global warm event based on stable isotopesSigal Abramovich; G. Keller; Z. Berner & D. Stüben

maximum surface and sub-thermocline temperatures increased by about 1.1°Cand 1.7°C, respectively. Thus, surface waters warmed at the same time as thedeeper water masses, but not by the same amount. This warming eventterminated at 65.15 Ma, with the return of average Late Maastrichtianpaleotemperatures values.

Enriched δ13C values in Racemiguembelina fructicosa are attributedto a strong photosymbiotic signal occurring during cool intervals pre- andpostdating the warm event. Average δ13C values of 3.1‰ for R. fructicosaare typically > 0.5‰ more enriched than other species from the same sample.However, during the 65.32-65.3 Ma intervals δ13C values of this species decreaseto an average of 2.5‰, which is similar to the δ13C signal of non-symbioticspecies. This change suggests that photosymbiotic activity was significantlyreduced during the warmest intervals.

Oxygen and carbon signals of dwarfed specimens to date do not showany significant deviation from the signals of coeval normal-sized adult forms,which suggest that they lived in the same temperatures and in similar habitats.Unless better sampling of peak warming and cooling intervals modify theseresults, a different explanation for the dwarfing feature, such as reproductivestrategy, must be invoked.

581

Modern distribution of benthic foraminifera fromthe Tagus Prodelta and Estuary, Portugal

Helga Bára Bartels-Jónsdóttir1,3; Karen Luise Knudsen1;Joachim Schönfeld2 & Jón Eiríksson3

1Department of Earth Sciences, University of Aarhus, DK-8000 Aarhus C, [email protected]

2Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Dienstgebaeude Ostufer,Wischhofstr. 1-3, D-24148 Kiel, Germany

3Earth Science Institute, Askja, University of Iceland, IS-101 Reykjavík, Iceland

The Tagus Prodelta on the Iberian Margin is located in an area, wherethe productivity and local oceanography is controlled by the Tagus river inputand seasonal coastal upwelling. The Tagus river is the longest river of theIberian Peninsula and extreme flood events lead to major discharge ofsuspended and bed load sediments, especially during the winter months.

The modern distribution and microhabitat of 21 different benthicforaminiferal taxa (15 calcareous and 6 agglutinated) have been studied in theTagus Prodelta and Estuary in order to obtain a better understanding of thespecies dynamics and their trophic preferences. In addition, the stable oxygenand carbon isotopes were analyzed for eight different species from six surfacesamples from the Tagus Prodelta and Estuary. The results are discussed inrelation to the oceanography of the area.

At the box core stations, most of the living foraminifera are concentratedin the oxygenated top centimetre of the sediment. They generally show shallow-infaunal behaviour. Some infaunal taxa inhabit the presumably anoxic sedimentdown to 10 cm depth. The deep infaunal species are suggested to feed selectivelyon refractory organic matter or on the bacterial stocks, while the opportunisticshallow-infaunal species presumably feed on fresh phytodetritus or labile organicmatter. The highest abundance of living benthic foraminifera was found insediments close to the Tagus river plume, where the sediments had a relativelyhigh organic carbon content.

The variation in the isotopic values for the different species is partlycontrolled by the chemical and physical properties of the water masses andpartly by differences in their microhabitats. The spatial distribution of the ä13Cvalues reflects relatively high organic flux at the site which is closest to thecoast and to the Tagus river plume. Low ä18O values for foraminiferal shells inthe Tagus Estuary, compared with the values obtained in the Prodelta, reflectreduced salinity and higher temperatures in the Estuary.

Anuár io do Inst i tu to de Geociências - UFRJISSN 0101-9759 Vol. 29 - 1 / 2006 p. 581

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582

Signature of the Brazil-Malvinas confluence in the isotopiccomposition of planktonic foraminifera from core top sediments

Cristiano Mazur Chiessi1,*; Shannon Ulrich2; Stefan Mulitza1;Jürgen Pätzold1 & Gerold Wefer1

1Research Center Ocean Margins, University of Bremen, Postfach 330440, 28334 - Bremen, Germany

[email protected]* CNPq-Brazil Research Fellow

2Bryn Mawr College, Bryn Mawr, Pennsylvania, U.S.A.

The upper-level circulation in the southwestern Atlantic is dominated bythe Brazil-Malvinas Confluence (BMC), that emerges from the encounter ofsouthward-flowing warm, saline, and nutrient-depleted Brazil Current (BC)and northward-flowing cold, fresh, and nutrient-rich Malvinas Current (MC).At the junction both currents are deflected from the continental margin andflow south-eastward. Dramatically steep gradients in sea-surface temperatureand sea-surface salinity are found in the confluence, reaching 1oC km-1. TheBMC migrates north and south seasonally, lying farther south during australsummer than during the winter. This oscillation is triggered by the change intransport of both the BC and the MC.

The main factors controlling calcite oxygen isotope composition (ä18Oc)of planktonic foraminifera are the temperature and the isotopic composition ofthe water in which calcification takes place, both factors being biased to someextent by the species specific vital effects. Nevertheless, äc of planktonicforaminifera records the temperature, latitudinal temperature gradient, andstratification of upper-water masses and has the potential to deliver importantinformation about past environments.

We measured the ä18Oc of planktonic foraminifera from a latitudinaltransect of core tops from the continental slope off Brazil, Uruguay, andArgentina between 20 and 49oS to test its potential use as a proxy for theposition of the BMC. The species measured cover a wide range of waterdepths, comprising surface dwellers like G. ruber (pink) and G. sacculifer,subsurface species like G. bulloides, and deep dwellers like G. truncatulinoides(dextral) and G. inflata.


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FORAMS 2006Signature of the Brazil-Malvinas confluence in the isotopic composition of planktonic

foraminifera from core top sedimentsCristiano Mazur Chiessi; Shannon Ulrich; Stefan Mulitza; Jürgen Pätzold & Gerold Wefer

The lowest values of ä18Oc are found for G. ruber (pink) and G.sacculifer, in which the latter show slightly higher values than the former. Theshallow water low ä18O anomaly characteristic of the Rio de la Plata outflowis registered just on the ä18Oc of G. ruber (pink). The ä18Oc values of the otherthree species were considerably higher, and the values of G. bulloides and G.inflata show a strong decrease associated with the BMC. These are the onlyspecies available across the confluence. ä18Oc values of G. truncatulinoides(dextral) are available north of the BMC where they are remarkably stable.

Our data associated to the biogeographical distribution of the speciesmeasured show that G. ruber and G. sacculifer reflect surface water conditionsnorth of the BMC, whereas G. truncatulinoides (dextral), G. bulloides, andG. inflata reflect subsurface conditions north (e.g. G. truncatulinoides dextral),and south (e.g. G. bulloides, G. inflata) of the confluence. The combinationof G. truncatulinoides (dextral) and G. inflata turned out to be the most reliableindicator for the position of the BMC and can therefore be used to define thepast migration of the front.

584

Foraminiferal evidence for the intensification of theEast Australia current during the LGM

Li Chung-Leong; Stephen Gallagher & John Bye

School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, [email protected]

Reconstructions of paleoceanographic conditions for the Last GlacialMaximum (LGM) from foraminiferal proxy data have sparse data coverage inthe oceans of southern and southeastern Australia. Results from the planktonicforaminiferal analyses of sediment cores from the Murray Canyon (Core MD03-2611G) and Bass Canyon (Core FR 11/98 PC-26) have been used to interpretmodern and LGM paleoceanographic conditions. These results were comparedwith other planktonic foraminiferal data in southeast Australia to obtain anoverview of paleoceanographic change from the LGM to today. The greateramount of subantarctic species and the decrease in transitional and subtropicalspecies during the LGM suggest lower sea surface temperatures during theLGM compared to the modern ocean. The less transitional and moresubantarctic water mass was associated with the more northerly location ofthe Subtropical Front during the LGM compared to today, similar to otherpublished records in the region. While there is evidence of recent upwelling inthe cores from high abundances of Globigerina bulloides, the marked increasein this species at the LGM level suggests an increase in the intensity of upwelling.This indicates a stronger Flinders Current possibly due to the stronger Tasmanoutflow from the Pacific. Results from the Bass Canyon core also suggest thecontinued and perhaps intensified flow of the East Australia Current during theLGM, due to a stronger gyral wind field in the Pacific Ocean, which in turnwould have been responsible for the intensification of the Tasman outflow.


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585

Planktic foraminiferal assemblages and stable isotoperecords of the southern Japan Sea during the last 27,000 years

Hanako Domitsu1; Motoyoshi Oda1; Naokazu Ahagon2;Shinji Tsukawaki3; Ken Ikehara4 & Hajime Katayama4

1Institute of Geology and Paleontology, Graduate School of Science,Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan

[email protected] of Earth and Planetary Sciences, Graduate School of Science,

Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo 060-0810, Japan3Division of Eco-Technology, Institute of Nature and Environmental Technology,

Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan4Institute of Geology and Geoinformation, Geological Survey of Japan,

AIST, Higashi 1-1-1, Tsukuba 305-8567, Japan

Planktic foraminiferal faunal and oxygen isotope changes during the last27 cal kyr BP were examined using two well-dated cores KT96-17 P-2 andGH87-2 K-B recovered from the southern Japan Sea. Thirteen species belongingto six genera were identified in down-core samples. Dominant species withmaximum percentages greater than 10% in at least one sample wereNeogloboquadrina pachyderma, Globigerina bulloides (thick-walled form),Globigerina umbilicata, Globigerina quinqueloba, Globigerinita uvula,and Neogloboquadrina incompta. These six species accounted for 95.5% ofthe planktic foraminiferal assemblage in each sample of core KT96-17 P-2and 94.7% in each sample of core GH87-2 K-B. In addition to these species,Globigerinoides ruber, Neogloboquadrina dutertrei , Pulleniatinaobliquiloculata, Globigerinoides tenellus, and Globigerinita glutinata, withmaximum percentages of less than 3%, were also recognized. Since 27 cal kyrBP, planktic foraminiferal faunas have exhibited major changes in both fluxand abundance, suggesting three major paleoenvironmental stages consistingof the last glacial period, the subsequent deglacial period, and the postglacialperiod. In the last glacial stage, surface water in the Japan Sea was coveredby cold, nutrient-rich, and less-saline water because circulation through shallowerstraits was probably restricted due to the eustatic sea level lowering. Low-salinity water was stratified in the water column, preventing deep ventilation inthe sea and leading to anoxic bottom conditions. During the subsequent deglacialstage when exchange with the open ocean was renewed, coastal water from


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FORAMS 2006Planktic foraminiferal assemblages and stable isotope records of the southern Japan Sea

during the last 27,000 yearsHanako Domitsu; Motoyoshi Oda; Naokazu Ahagon; Shinji Tsukawaki; Ken Ikehara & Hajime Katayama

the East China Sea flowed into the Japan Sea through the Tsushima Strait.Low-salinity surface water of the last glacial maximum disappeared, and deepconvection began again, leading to oxic bottom conditions. After low-salinityand eutrophic surface water declined, the Oyashio Current probably flowedinto the Japan Sea through the Tsugaru Strait. The cold and dense OyashioCurrent water enhanced deep ventilation actively. However, deep circulationdriven by the East China Sea coastal water or Oyashio Current water wasweaker than that at present. In the postglacial stage, the warm Tsushima Currentbegan to flow into the Japan Sea. The modern deep circulation system wasformed in association with the Tsushima Current. We will discuss the timing ofabove mentioned events based on the tephrochronology and AMS 14C datingof 14 horizons of the two cores.

587

Distribution of planktonic foraminifera: A modeling approach

Igaratza Fraile1; Michael Schulz1,2; Stefan Mulitza2 & Gerald Ganssen3

1Department of Geoscinces, University of Bremen, Bremen, [email protected]

2Research Center of Ocean Margins, University of Bremen, Bremen, Germany3Institut of Earth Sciences, Free University of Amsterdam, Amsterdam, Netherlands

Planktonic foraminifera are widely used for paleoceanographicreconstructions. Their assemblages are a good proxy to quantify pastenvironmental conditions, such as sea-water temperature, stratification, andbiological productivity. In general, all estimation procedures are based on thecorrelation between modern sea-surface temperature and the observedforaminiferal fauna (“transfer function”). The estimation process is, however,complicated by different ecological needs (season, depth of habitat and foodrequirement) of the employed foraminifera species.

Any change in the timing of the maximum in foraminiferal flux withrespect to, say, summer temperature, that may have occurred in the past, maylead to a bias in estimated paleotemperature. This bias arises, because thesedimentary record will ultimately reflect the convolution of foraminifera fluxthroughout the year with the annual temperature cycle. Moreover, differencesin seasonality hinder comparison of reconstructed temperatures based onassemblages of planktonic foraminifera with those derived by other sea-surfacetemperature proxies (e. g. prymnesiophyte-based Uk

37 ratio).Climate changes could induce variations in the seasonal succession of

the planktonic foraminifera typically used in transfer functions. This variationsneed to be quantified to understand corresponding proxy-based reconstructions.

To study the seasonal variations of planktonic foraminifera species atglacial-interglacial timescales, we developed a foraminiferal distribution model.This model is forced with a global hydrographic dataset (e.g. temperature,mixed layer depth) and with biological information taken from an ecosystemmodel (e.g. “food type”, zooplankton abundance) to predict monthlyforaminiferal fluxes of the most common species used in transfer functions.The sensitivity of each species with respect to temperature (optimal temperatureand range of tolerance) is derived from sediment trap studies.

We present results for the global distribution of the most important modernplanktonic foraminifera used in transfer functions. The model output is comparedwith measured foraminiferal fluxes of globally distributed sediment traps.


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588

Foraminiferal and facies evidence for the onset of the Leeuwincurrent in the Pleistocene, northwest shelf, Australia

Stephen J. Gallagher; Malcolm W. Wallace; Chung Leong Li;Tiffany Gourley; Belinda Kinna & Guy R. Holdgate

School of Earth Sciences, University of Melbourne, Vic 3010, [email protected]

The Leeuwin Current is the only south flowing western boundary currentsystem in the southern hemisphere. The current presently transports warmlow salinity nutrient deficient water from the equatorial West Pacific WarmPool southwards along the west coast of Australia. This current extends modernreefal development to 29°S and the tropical to subtropical transition as farsouth as Rottnest Island (33°S) where large foraminifera are common. Thestrata of the Northwest Shelf preserve a detailed Mio-Pleistocene record ofoceanographic change and reef growth related to the development of theLeeuwin Current. Our study focuses on the Carnavon Basin (18 to 21°S) andincorporates foraminiferal, facies and seismic analyses. Subtropical oligotrophicplatform carbonates with abundant large foraminifera, regressive barrier sandfacies, submarine canyon and slope deposits typify Miocene deposition in theregion. The overlying transgressive Pliocene to early Pleistocene plankton-rich strata (with common Globoturborotalia rubescens, Neogloboquadrinadutertrei and Globigerina falconensis) were deposited in nutrient-enrichedsubtropical platform to slope environments. After the middle Pleistocene (1Ma) oligotrophic subtropical to tropical platform to slope conditions developedassociated with the first reefal and oolitic facies. This phase of deposition isassociated with an upward increase in tropical to subtropical planktonic speciessuch as Globigerinoides ruber, Globigerinoides sacculifera andPulleniatina obliquiloculata. Foraminiferal evidence and absence of reefsand ooids in the Early Pleistocene and older strata suggest that the LeeuwinCurrent initiated after 1 Ma. Indeed, the planktonic foraminiferal assemblagein strata from 1 Ma to 450 kyr typically have a higher tropical component thanthe present plankton assemblages from 18 to 21°S. We suggest the initiation ofLeeuwin Current was associated with a more intense outflow of equatorialwaters along the Western Australian coastline and sometime after 450 kyrreached it present equilibrium.


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589

Foraminifera and the tephrochronology of marine sedimentsaround the Island of Montserrat, Lesser Antilles volcanic arc

Malcolm B. Hart1; Christopher W. Smart1; Emily J. Lock1;Jodie K. Fisher1 & Melanie J. Leng2

1School of Earth, Ocean & Environmental Sciences, University of Plymouth,Drake Circus, Plymouth PL4 8AA, U.K.

[email protected] Isotope Geosciences Laboratory, British Geological Survey,

Keyworth, Nottingham NG12 5GG, U.K.

The Soufrière Hills Volcano, Montserrat, has undergone cyclic domegrowth and collapse events since the present phase of eruption began in 1995.Over 90% of the pyroclastic deposits avalanched down the volcano flanks andwere deposited into the ocean. The coarse components (pebbles to boulders)are deposited in dense slurries to form steep-sided, near linear ridges proximallythat intercalate and amalgamate to form a submarine fan. The finer ash gradecomponents are mixed into the overlying water column to form turbidity currentsthat flow distances in excess of 30 km from source. The present on-goingeruption began in 1995 but marine sediment coring has recovered a record ofintermittent volcanic activity over the last ~350,000 years. Using foraminiferalbiostratigraphy (Globorotalia menardii ratios, etc.) and stable isotopestratigraphy we have identified significant eruptive events at 330,000 yearsBP, 240,000 years BP, 182,000 years BP, 137,500-120,000 years BP, 77,500years BP and 20,000 years BP. The most interesting record is the 17,500 yearsof eruption activity between 137,500 and 120,000 years BP which agrees withthe date for the origin of the Soufrière Hills volcanic centre.

Work on the marine cores is on-going and will provide further informationon the distribution of both planktic and benthic foraminifera, the impact of thevolcanic sedimentation on the benthic faunas and a detailed analysis of thepteropods distribution in the samples, which appears to be recording a distinctclimatic signal as well as a record of the movement of the AragoniteCompensation Depth within the water column.


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590

Estimating species distribution along an environmentalgradient using morphological characters

Johann Hohenegger

Institut für Paläontologie, Universität Wien, Althanstrasse 14, A-1090 Wien, [email protected]

The species-characteristic combination of morphological characters thatdepend on an environmental gradient can be used to determine the frequencydistribution of the species along the gradient. The gradual change in charactercomposition along the gradient is called a ‘morphocoenocline’. Transformingthe empirical frequency distributions of characters and character states alongthe gradient to probability distributions enables calculating a probability densityfunction of any subset of characters of the morphocoenocline. Since a speciesis distinguished by a specific combination of characters that are functionallyrelated to the gradient, the distribution of this species along the gradient can beestimated using the probability density functions of combined characters.Assuming ‘functional uniformitarianism’ this estimation can be extended intothe geologic past for all fossil species, as long as their functional characters arehomologous or analogous to those found among Recent forms. When amorphocoenocline is based on a compound environmental gradient, such asdepth, which represents a combination of single environmental factors, thegradient estimation reflects only a specific combination of the singleenvironmental factors.

A morphocoenocline for test characters of symbiont-bearing benthicforaminifera from the West Pacific was established for water depth. Depthdistributions based on probability density functions were compared withempirical distributions to prove the accuracy of this method, and were used toestimate the depth distribution of other living species that had not been includedin the determination of the morphocoenocline because they live in other regions.The method was also applied to fossil species that are closely related to Recentforms (Nummulites, Assilina from the Eocene), and to fossil species that are moredistantly related to the living species (Orbitoides from the Upper Cretaceous).


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591

Planktic foraminiferal assemblages and oxgen isotope recordsof the northwest Arabian Sea over the last 215,000 years

Satoko Ishikawa1; Motoyoshi Oda1; Masafumi Murayama2;Hidenori Kagawa2 & Tomohide Oayma3

1Institute of Geology and Paleontology, Graduate School of Science,Tohoku University, Sendai 980 8578, Japan

[email protected] for Advanced Marine Core Research, Kochi University, Nankoku 783 8502, Japan

3Department of Geosystem Engineering Graduate School of Engineering,Tokyo University, Bunkyo-ku, 113-8654, Japan

Planktic foraminiferal faunal and oxygen isotope changes have beenstudied in well-dated core GOA 6 recovered from the northwest Arabian Seato reconstruct variations in southwest (SW) and northeast (NE) monsoonsover the past 21,5000 years. The foraminireral census counts were performedon > 125µm fractions. Foraminiferal composition and total number of plankticforaminiferal shells (#/g) were determined.

In the northwest Arabian Sea the SW monsoon causes upwelling offOman in summer and the NE monsoon induces convective mixing in winter.This seasonal change in oceanography is reflected in planktic foraminiferalcomposition and foraminiferal productivity. We focused here onoceanographically important species, Globigerinita glutinata Globigerinabulloides, Neogloboquadrina incompta, Neogloboquadrina dutertrei, G.ruber and G. sacculifer, the sum of which contributs to as much as 70 % ofthe total planktic foraminiferal assemblage. Relative abundance of upwellingindex species (G. bulloides and G. glutinata) were high during marine isotopestages (MIS) 1, 5 and 7. This result suggests that SW monsoon was intensifiedduring these periods. In contrast, dominance of species related to deepconvective mixing (N. incompta, N. duterteri, G. ruber and G. sacculifer)during MIS 2, 3, 4 and 6 implies that the NE monsoon was intensified duringMIS 2, 4 and 6.

In addition, the time series of the total number of shells is dominated bya cyclicity of 22 kyr. The total number of shells was compared with the insolationcurves of January and July at 45°N. The comparison revealed that threedifferent causes led to eight peaks recognized in the total number of shells:

1) The peak of total number of shells during MIS 5 is related to themaximum insolation in July. Planktic foraminiferal assemblages during


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FORAMS 2006Planktic foraminiferal assemblages and oxgen isotope recordsof the northwest

Arabian Sea over the last 215,000 yearsSatoko Ishikawa; Motoyoshi Oda; Masafumi Murayama; Hidenori Kagawa & Tomohide Oayma

this stage are characterized by upwelling species. This result suggeststhat the SW monsoon was intensified when summer insolation washigh during this period.

2) The two peaks of total number of shells during MIS 6 are associatedwith insolation minima in January. These peaks correspond toabundant winter convective mixing index species during this stage.This indicates that developed NE monsoon resulted in weakwinter insolation.

3) The peaks of total number of shells at the glacial-interglacial boundaries(MIS 6/5, 4/3 and 2/1) seem to coincide with rapid increase of δ18Orecords. These boundaries were characterized by an increase ofupwelling species and fewer convective mixing index species. Thisresult may imply that the development of SW monsoon and the declineof NE mosoon are related to abrupt global warming at glacial-interglacial boundaries.

593

Ecological studies of benthic foraminifera based onthe stable isotopic dispersions of individual tests

Toyoho Ishimura1; Urumu Tsunogai1; Shiro Hasegawa2 & Fumiko Nakagawa1

1Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, [email protected]

2Graduate School of Science and Technology, Kumamoto University, Japan

Stable carbon and oxygen isotopic compositions of foraminiferalcalcareous tests are useful as indicators of the paleoenvironment, such aspaleotemperature, global deep-sea circulation, and huge methane release eventsfrom seafloor. To analyze the stable isotopic compositions of foraminiferal tests,however, calcium carbonates at least over 20~400 microgram is needed todetermine stable carbon and oxygen isotopic compositions at the useful accuracyand precision. That is to say, we have had to prepare several to several tens offoraminiferal tests to determine the stable isotopic compositions, and the reportedisotopic data of individual foraminiferal tests are limited to the taxa those havelarge and thick calcareous test.

Recently, Ishimura et al. (2004. Rapid Commun. Mass Spectrom. 18,2883-2888. DOI: 10.1002/rcm.1701.) developed the high-precise analyticalsystem for determining stable carbon and oxygen isotopic compositions of sub-microgram quantities of calcite, which is less than 1/100 of the conventionalanalytical methods. By using this system, we can determine the stable carbonand oxygen isotopic compositions of CO2-gas with standard deviations of +/-0.05 permil (for both stable carbon and oxygen), and 1 grains of NBS-19 (5.6~ 10.9 microgram) within the standard deviations of +/-0.05 permil for carbonisotopes and +/-0.11 permil for oxygen isotopes. Thus, we can apply the isotopicstudies of foraminifera to seafloor in which limited numbers of small-sizedtests are available, and could construct the innovative applications of foraminiferaas proxy indicators in paleoceanography and paleoclimatology.

In this study, we determined both the stable carbon and oxygen isotopiccompositions of calcareous tests for individual small benthic foraminiferasampled at normal surface sediment to estimate the microhabitat based on thedispersion of the isotopic compositions within each taxa, as well as their absolutevalues. The isotopic values of each calcareous benthic foraminiferal chamberreflect each environmental parameter in which they have grown, such as thesea/pore water chemistry and the temperature. While both the isotopic


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FORAMS 2006Ecological studies of benthic foraminifera based on the stable isotopic dispersions of individual tests

Toyoho Ishimura; Urumu Tsunogai; Shiro Hasegawa & Fumiko Nakagawa

compositions and the temperature are homogeneous for bottom water, theyare heterogeneous for pore water. Therefore, we could clarify whether theylives within sediment or at sediment surface by determining the isotopiccompositions, especially for using the dispersions within a taxa living in asame environment.

The stable carbon isotopic values of Bulimina aculeata are close tothose of the bottom water, accompanying small dispersions. They must beliving and growing within the surface sediment, so that we conclude that wecan apply them as the paleoindicator of bottom water. On the other hand, thestable carbon isotopic values of Stainforthia sp. and Brizalina pacifica areextremely lower than those of bottom water, accompanying large dispersions.They must be living and growing within the sediment, so that it must be difficultto use them as the paleoindicator of bottom water. Besides, Globocassidulinasp. exhibits the 13C-enrichment in proportion to the individual weight. Thus,while juvenile individuals might grow within the sediment, adult individuals mightgrow at the surface. From the isotopic compositions and their dispersions oftests, Brizalina pacifica, Stainforthia sp., and juvenile Globocassidulinasp., all of which have thin/small hyaline clear test, seem to be infauna, reflectedby pore water related with decompositions of organic matter. These estimationscorrespond with their reported microhabitat. By using dispersions in the stablecarbon and oxygen isotopic compositions of each benthic foraminiferal taxa, aswell as their average values, we can choose suitable paleoindicators for futurestudies by estimating the microhabitat.

595

Holocene paleoceanography of an Arctic fjord ofSvalbard as recorded

by stable isotopes, foraminifera and macrofauna

Sergei Korsun1; M. Hald2; L. Khomenko3; M. Forwick2; Ho-Ii Yoon4 & Seung-Il Nam5

1Shirshov Institute of Oceanology, Moscow, [email protected]

2Geological Institute, Univ. of Tromsø, Tromsø, Norway3Biol. Dept., St.Petersburg Univ., St.Petersburg , Russia

4Korea Ocean Research and Development Institute, Ansan, Korea5Korea Institute of Geoscience & Mineral Resources, Daejeon, Korea

Fjords accumulate thick sediment packages providing high-resolutionpaleoceanographic records. Core MD99-2305 retrieved in Van Mijen Fjord ofSvalbard has penetrated a complete, uninterrupted package of 16 m thickHolocene sediments. The western coast of Svalbard, where the fjord opens tothe Greenland Sea, meets a terminal branch of the Gulf Stream system andthus is potentially sensitive to the influx of Atlantic heat to the Arctic.

The fjord basin is 50km long, 10km wide and 115 m deep. Water exchangewith the open sea is much restricted at present owing to a 25 mwd sill at themouth. Seasonal ice stays 8 months a year. A local water mass with negativetemperatures and slightly reduced salinities (34.0-34.5‰), which forms in thefjord during the freeze-up, fills the basin and is removed partially during summer.A major tidewater outlet glacier feeds meltwater and small icebergs into thefjordhead, ca. 40km upfjord from the coring location. The chronology isconstrained by 23 AMS 14C dates.

Deglaciation of the fjord took place at about 11.2 cal kyr BP. The ablationwas dominated by iceberg calving, whereas meltwater production was small,as suggested by a moderate sedimentation rate, the absence of laminateddeposits and a lack of the typical meltwater-affected foraminiferal assemblages.Due to postglacial rebound, the depth of the sill was decreasing rapidly fromplus 45-50 mwd at 11.2 kyr to plus 15 mwd at 8.8 kyr, as compared to themodern 25 mwd (the uplift dates are adapted from Landvik et al., 1987. PolarResearch 5: 29–44). The decreasing sill depth resulted in progressive isolationof the fjord basin.

Seasonal ice, interpreted from the occurrence of winnowed subtidalforaminifera, nearly disappeared at 10.7 kyr, resumed at ca. 9.0 kyr, and hasbeen present in the fjord since. The cold, brine-injected local water probably


FORAMS 2006


FORAMS 2006Holocene paleoceanography of an Arctic fjord of Svalbard as recorded by stable isotopes,

foraminifera and macrofaunaSergei Korsun; M. Hald; L. Khomenko; M. Forwick; Ho-Ii Yoon & Seung-Il Nam

started to accumulate in the deep basin since ca. 6 kyr, as suggested by thechange of the ä18O trend toward lighter values.

Productivity (inferred from calcareous benthic foram accumulation rate,mollusk occurrences, C/N ratio and ä13C) was generally high between 10.5 to7.5 kyr, peaking at 9.5 kyr. Productivity kept decreasing from 7.5 to 3.5 kyrand has stayed low afterwards. Our explanation of the increased productivitybetween 10.5 and 7.5 kyr is that the summer stratification of the water columnin the fjord was maintained by temperature rather then by salinity, as it is today.

Temperature of the bottom water in the fjord seems to have been stableand low over the Holocene. There has been no invasion of boreal foraminiferaltaxa into the fjord. Bivalves in the core occur predominantly in the earlyHolocene. Unlike the shallow-water thermophilous blue mussel of Svalbard(Salvigsen, 2002. Nor Geograf Tidskrift 56: 56–61), to which our bivalves arecontemporaneous, they are not thermophilous and do not reveal any temperatureincrease in the basin at ca. 100 m depth. We infer that bottom temperature inthe fjord even during the local thermal optimum at 9.5 kyr was only slightlyhigher than today, perhaps, 0°C to 2°C year-round.

Planktonic foraminifera are predictably rare in this silled fjord. Theyoccur throughout the Holocene but are most frequent between 10.3 and 8.7kyr. This interval coincides with the Holocene temperature maximum in theeastern Norwegian-Greenland Sea (Sarnthein et al., 2003. Boreas 32: 447–461; Hald et al., 2004. Quaternary Science Reviews 23: 2075–2088). Probably,at this time the influx of warm water was largest and the surface temperaturewas at its maximum.

Overall, in the studied fjord of Svalbard, the Holocene climate changehas been small and gradual. Soon after the deglaciation at 11.2 kyr BP, thetemperature and, driven by it, productivity reached a maximum at ca. 9.5 kyrBP. After that, both temperature and productivity have been decreasing reachingminimal values in the Late Holocene.

597

Paleoclimatic changes through the last 67,000 years in thenortheastern Caribbean derived from planktonic foraminifera

Dominika Kozakiewicz1; Björn A. Malmgren1; Ulysses Ninnemann2;Antoon Kuijpers3 & Anna-Lena Krantz Eilola1

1Department of Earth Sciences-Marine Geology, Göteborg University,Box 460, SE-405 30 Göteborg, Sweden - [email protected]

2Bjerknes Centre of Climate Research, Allegaten 55 5007 Bergen, Norway3Geological Survey of Denmark and Greenland (GEUS), Oster Voldgade 10, DK-1350

Copenhagen K, Denmark

A climate reconstruction through the last 67,000 years of the northeasternCaribbean is presented. The study is based on a 12.75 m long piston core(MD02-2582) retrieved immediately to the south of Puerto Rico at 17º51.20’Nand 66º36.00’W (water depth of 380 m). A major hiatus (17,000 yrs long)occurs between 95 and 100 cm depth in the core that might be caused by amass wasting event during the Last Glacial Maximum (LGM) sea-level low-stand. The upper 100 cm of the core shows the lowest sedimentation rate, 1.5to 11.1 cm/kyr, while the interval between 345 and 900 cm is marked by aconsiderably higher sedimentation rate, about 59 cm/kyr. Samples were takenat 5 cm intervals along the core, providing a nominal temporal resolution in therange of 450-3,200 years (800AD – 17,500 BC) in the post-LGM part of therecord, and 85-700 years (37,200 – 67,000 BP) in the pre-LGM record. Seasurface-water temperature (SST) fluctuations are derived from planktonicforaminifer census data, together with oxygen isotope analysis of the planktonicforaminifer species Globigerinoides ruber (pink variety). Past warm- andcold season SSTs are reconstructed using artificial neural networks (ANN)based on fluctuations in the relative abundance of 26 species of planktonicforaminifera. The dominant species in the core are Globigerinoides ruberand G. sacculifer. Warm season SSTs range between 27.5 - 29.0ºC, and coldseason values fluctuate between 24.5 - 27.0ºC, through the major parts of therecord, except for two cooling events at 44,600 - 44,000 BP and 36,000 –36,400 BP, which are predominantly observed in the warm-season SST recordwhen the SSTs were ~2ºC lower. The paleo-SST record is highly statisticallysignificantly correlated with the δ18O record (r=-0.397, p<0.001). Thepaleoclimatic record at this site can be correlated with changes seen in theGISP ice core from Greenland, including the warming events, known asDansgaard-Oeschger (D-O) events, initially recognized in the Greenland ice-core record during the MIS 3 period.


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598

Origin of intraspecific morphological variability inplanktonic foraminifera

Michal Kucera1 & Kate Darling2

1Institute of Geosciences, Eberhard Karls Universität Tübingen, Tübingen, [email protected]

2Grant Institute of Earth Science/Institute of Evolutionary Biology,University of Edinburgh, Edinburgh, U.K.

Compared to other groups of marine microzooplankton, planktonicforaminifera show a surprisingly low diversity. On the other hand, all of theabout 40 living species exhibit a remarkable degree of morphological plasticity.The significance of this morphological plasticity has been a matter of debate,with the prevalent view attributing the variability to ecophenotypy. However,recent molecular genetic studies demonstrated a high level of genetic diversityamong morphospecies of planktonic foraminifera, opening up the possibilitythat some of the phenotypic plasticity could be genetically controlled. Mostpaleoecological applications of planktonic foraminifera rely on species-specificempirical calibrations. An understanding of the origin of intraspecific variabilityin planktonic foraminifera is therefore essential for the development of ameaningful species concept and consequently for any application of theseorganisms as paleoceanographic proxies.

We review existing data on the nature of intraspecific morphologicalvariability in planktonic foraminifera and present the first rigorous assessmentof the respective contributions of ecophenotypic and genotypic control on themost common species of modern planktonic foraminifera, Globigerinabulloides. We combine measurements on genetically identified individuals fromplankton samples from the North Atlantic, the South Atlantic and the NorthPacific with sediment trap material and coretop material. An analysis of thisdataset supports the presence of a significant genetic component in themorphological variation of this species. Combined with growing evidence fromgeochemical calibrations, it is increasingly obvious that lumping of cryptic genetictypes of planktonic foraminifera has been an underestimated source of noise inpaleoceanographical reconstructions. Conversely, an understanding of the originand significance of the morphological variation in individual species has a greatpotential for increasing the capacity of planktonic foraminifera to produceaccurate and reliable information on past sea surface conditions.


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599

Late Glacial to Holocene variability of the deep Aegean Seaas revealed by benthic foraminifera

Tanja Kuhnt & Gerhard Schmiedl

Institute of Geophysics and Geology, University of Leipzig, Talstrasse 35, 04103 Leipzig, Germany - [email protected]

To reconstruct the paleoceanographic and paleoclimatic variability ofthe Eastern Mediterranean during the past 25 kyr, we studied benthicforaminiferal faunas and stable isotopes of two sediment cores from the deepnorthern and southern Aegean Sea. During the last glacial maximum and thetransition to the Holocene elevated benthic foraminiferal numbers and highlydiverse faunas indicate enhanced organic matter flux rates and well-ventilateddeep-water masses. Highest organic matter availability is observed in thesouthern Aegean Sea. The organic matter is likely derived from a combinationof elevated marine productivity as response to wind-induced mixing and thetransfer of degraded organic matter from continental sources and with bottomcurrents. During the formation of sapropel S1, drops in benthic foraminiferalnumbers and diversity are more significant at the shallower site in the southernAegean Sea when compared to the deeper site in the northern Aegean Sea.This suggests the persistence of local deep-water formation in the northernAegean Sea during sapropel formation. In addition, faunal fluctuations at bothsites suggest the repeated influence of short-term climate changes on re-ventilation and re-colonization of deep-sea ecosystems in the whole AegeanSea. During the middle and late Holocene the faunas point to a clear spatialdifferentiation of Aegean deep-sea environments. While the North AegeanSea is characterized by mesotrophic conditions combined with varying oxygenconcentrations in the pore and bottom water, the faunas at the southern sitereflect an oligotroph and well-ventilated benthic ecosystem. Further, stableoxygen and carbon isotope records from the northern Aegean Sea suggestvariations in the freshwater and nutrient input derived from adjacent rivers andthe Black Sea outflow. These fluctuations are likely caused by short-termchanges between cold/dry and warm/wet periods. Particularly cold and dryintervals are observed around 4.2 and 1.5 kyr. At the southern site, stablecarbon isotopes reveal an increase of eutrophication with an onset atapproximately 2 kyr. This is corroborated by the occurrence of Uvigerinaperegrina that is considered to feed on degraded organic material with a slighttolerance to dysoxic conditions. The elevated organic matter availability is likelya response to deforestation causing enhanced erosion and terrestrial organicmatter input into the South Aegean Sea.


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600

Paleoclimatic changes during the Holocene of the St Jonesestuary, Delaware (USA): Foraminiferal proxies for sequence

stratigraphy reconstruction

Eduardo Leorri1; Ronald E. Martin2 & Peter P. Mclaughlin3

1Laboratoire d’Etude des Bio-indicateurs Actuels et Fósiles, Université d’Angers-UFR Sciences,2 Boulevard Lavoisier, 49045, Angers Cedex, France

[email protected] of Geology, University of Delaware, Penny Hall, 101 Academy street, Newark,

DE, 19716, U.S.A.3Delaware Geological Survey, University of Delaware, DGS Building, Newark, DE 19716, U.S.A.

Foraminiferal assemblages in the sedimentary successions of marsheslocated along St. Jones Estuary (western Delaware Bay, USA) reflect sea-leveland paleoclimate change during the Holocene. The sedimentary sequence comprisesa range of foraminiferal assemblage zones (FAZ) that can be organized intoparasequences, and grouped into systems tracts. During late glacial to earlyHolocene low sea-level conditions, sedimentation was represented by fluviatilegravels and coarse sands (lowstand systems tract-LST) that do not occur in thesubestuaries. During the marine transgression in the tributaries (depending on theirproximity to the mouth of the estuary and coastal geomorphology 6,000-3,000 yearsBP) the initial sediment consists of unconsolidated sand that corresponds to thepre-Holocene coastal plain. Sedimentological and micropaleontological criteriatogether with radiocarbon dates indicate that overlying sediments represent mid-Holocene fluvial deposits with fresh water marshes established around 4,000 yrBP. The subsequent sea-level transgression occurred sufficiently slowly, sothat freshwater marshes alternated with salt marshes at the same sites to around3,000 yr BP. Those sediments correspond to the Transgressive Systems Tract(TST). The Highstand Systems Tract (HST) deposited during the upper Holocene(3,000 years BP to 20th century) is represented by the establishment of salt marshesthat alternate with fresh water marshes in the middle estuary and brackish intertidalsediments in the lower estuary. In general, cores exhibit a transition from mud(barren of foraminifera) at the bottom to peat or muddy peat at the top, with variationsin mud content in the middle (alternating between peat, muddy peat, and peatymud). Middle core sediments show an increase in abundance and diversity offoraminifera that increases downstream. Mainly fresh water marsh sediments weredeposited in the middle estuary, while brackish sediments accumulated in the lower


FORAMS 2006


FORAMS 2006Paleoclimatic changes during the Holocene of the St Jones estuary, Delaware (USA):

Foraminiferal proxies for sequence stratigraphy reconstructionEduardo Leorri; Ronald E. Martin & Peter P. Mclaughlin

estuary during the transgression. The absence of foraminifera (which live in brackishto marine environments) is characteristic of the upper estuary, whereas increasinglymuddy sediments and increasing brackish-to-marine sediments are typical of thelower estuary. This general pattern is in agreement with results from other coastalsedimentary sequences studied in Delaware Bay and elsewhere (Gulf of Mexico,Bay of Biscay).

Locally another two transgressions are identified at 1,800 and 1,000 yr BPrespectively. Marine influence increased in the estuaries until 600 yr BP (the LittleIce Age), when regression occurred. Sea-level began to rise again during the mid-19th Century at the end of the Little Ice Age about 150-180 years ago coupled withanthropogenic straightening of the channel in 1913. This infill resulted in a sharpboundary and a transgressive sequence represented by salt marsh foraminiferalassemblages in the upper part of the cores.

The parasequences defined by foraminiferal assemblages appearcorrelative with rapid Holocene climate changes that are of worldwidesignificance: 6,000-5,000, 4,200-3,800, 3,500-2,500, 1,200-1,000, and 600 cal yrBP. Variations in sea level recorded by Delaware marshes may act as proxy forocean circulation and thus as climatic proxies.

602

Development of a foraminiferal-based transferfunction in the Basque marshes, N. Spain:

Implications for sea-level studies in the Bay of Biscay

Eduardo Leorri1; Benjamin P. Horton2; Alejandro Cearreta3 & Maria Alday4

1Laboratoire d’Etude des Bio-indicateurs Actuels et Fósiles, Université d’Angers-UFR Sciences,2 Boulevard Lavoisier, 49045, Angers Cedex, France

[email protected] Level Research Laboratory, Department of Earth and Environmental Science,University of Pennsylvania, 240 South 33rd Street, Philadelphia, PA, 19104, U.S.A.

3Departamento de Estratigrafía y Paleontología, Facultad de Ciencias,Universidad del País Vasco/E.H.U., Apartado 644, 48080 Bilbao, Spain

4Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa,Bloco C6, Campo Grande, 1749-016 Lisboa, Portugal

Assemblages of saltmarsh foraminifera on temperate coastlines exhibita strong correlation with altitude above mean tidal level. Although many localhabitat factors influence the composition of foraminiferal assemblages, studiesfrom North America, South America and Europe indicate that the strongcorrelation between foraminiferal assemblage zones distribution and marshelevation can be recognized worldwide. Various authors have used foraminiferaas precise sea-level indicators, allowing the generation of high-resolution recordsof relative sea-level change. Recently, it has appeared a quantitative way tocalculate paleo-marsh surface changes from fossil marsh sequences throughthe use of foraminiferal-based transfer functions. This technique providesobjective, quantitative and reproducible estimates of paleomarsh-surfaceelevation associated with explicitly stated error terms. The foraminiferal transferfunction approach has been successfully applied to salt-marsh cores, but spatialvariability in surface and sub-surface foraminiferal assemblages may result inerroneous reconstructions when these data are applied elsewhere. Therefore,the development of similar quantitative techniques suitable for application innew areas is important in order to understand the Holocene sea-level and climateevolution. In this study we have developed transfer functions using an unimodal-based technique known as WA-PLS (weighted averaging partial least squares)based on the 59 samples and 23 species (> 2%) obtained from the moderndistribution of foraminifera recorded in four Basque marshes: Axpe-Busturiamarsh (Urdaibai estuary), Muskiz marsh (Barbadun estuary), and Ostrada andTxipio marshes (Plentzia estuary) in the southern Bay of Biscay. Unimodal-based methods of regression and calibration were used based on the results


FORAMS 2006


FORAMS 2006Development of a foraminiferal-based transfer function in the Basque marshes, N. Spain:

Implications for sea-level studies in the Bay of BiscayEduardo Leorri; Benjamin P. Horton; Alejandro Cearreta & Maria Alday

obtained from the detrended canonical correspondence analysis (DCCA) withthe elevation as the only environmental variable. The performance of eachtransfer function was assessed in terms of the root-mean square of the errorof prediction (RMSEP) and the squared correlation (r2) of observed versuspredicted values. The reliability of elevation reconstructions of fossil depositswas evaluated using a modern analogue technique (MAT). The basic idea ofMAT is to compare numerically, using an appropriate dissimilarity or similaritymeasure, the biological assemblage in a fossil sample with the biologicalassemblages in all available modern samples that have associated environmentaldata. The transfer function produces results for six components. The choice ofcomponent depends upon the prediction statistics (RMSEP and r2) and theprinciple of parsimony, i.e. choosing the lowest that gives an acceptable model.Therefore, we have chosen component three because it performs significantlybetter than components one and two when jack-knifed errors are considered:prediction errors (RMSEP and maximum-bias) are lower and squaredcorrelations (r2) are higher. Using component three the relationship betweenobserved and foraminifera-predicted elevation is very strong and illustrates thestrong performance of the transfer function (r2

jack = 0.79). Indeed, these resultsindicate that precise reconstructions of former sea levels are possible(RMSEPjack = 0.33 m). The transfer function is used to calibrate the fossilforaminiferal assemblages collected from a core obtained in the Ostrada marsh(Plentzia estuary). We identified a total of 12 foraminifera species (> 2%)from 35 samples. To illustrate fully the potential application of the transferfunction technique, we place the foraminiferal-based reconstructions from theOstrada core into a temporal framework to produce a relative sea-level curve,where the chronology is established from the 210Pb-derived sedimentaccumulation rates.

604

Benthic foraminifera as proxies for climate andoceanographic changes in the Holocene off southern Chile

Melissa K. Lobegeier1; Carina B. Lange2 & Ulysses S. Ninnemann3

1Centro FONDAP-COPAS, Universidad de Concepción, Casilla 160-C, Concepción, [email protected]

2Departamento de Oceanografía y Centro FONDAP-COPAS,Universidad de Concepción, Casilla 160-C, Concepción, Chile

3Department of Earth Sciences and Bjerknes Centre for Climate Research,University of Bergen, Allegaten 41, 5007 Bergen, Norway

The eastern South Pacific Ocean is one of the least explored and mostproductive regions of the global ocean. Circulation along much of the Chileancoastline is controlled by the West Wind Drift (WWD) which approaches thecoast at 45°S, where it splits into two unequal water masses, the Peru-ChileCurrent (PCC) and the Cape Horn Current (CHC). The PCC flowsequatorward from 42°S up to 4°S where it turns westward. The CHC flowspoleward from 43°S along the southernmost coast of Chile until it rounds thetip of the continent. South of 52°S in the Magellan Strait, Atlantic, Pacific, andAntarctic waters interact. Latitudinal shifts in the WWD have been noted duringthe Holocene.

Recent studies have used various proxies, e.g., alkenones, isotope ratiosof planktonic foraminifera, biogenic opal, and organic carbon, to study changesin temperature, salinity, and productivity along the Chilean continental margin(23-41°S) during the Holocene and late Quaternary. None of these studieshave used benthic foraminifera as a proxy for oceanographic or climatic changeor focused upon the region south of 42°S. Little is known of thepaleoceanographic history of the CHC.

The present study utilizes cores taken during leg 3 of the R/V MIRAIMRO3-KO4 cruise, which was part of the BEAGLE (Blue Earth Global OceanExperiment) 2003 program and developed by JAMSTEC. We are working ontwo cores taken from station 3 at the entrance to the Magellan Strait at latitude52°52’S and longitude 74°05’W and 560 m water depth. The cores include amulticore which is 26 cm in length and estimated to encompass 345 years ofsedimentation (based on 210Pb) and a piston core which is 964 cm in length andestimated by preliminary 14C data to be ~12,000 years old at the base. The aimof this study is to use a multiproxy approach to reconstruct changes oftemperature, salinity, and productivity to determine the effect of the latitudinal


FORAMS 2006


FORAMS 2006Benthic foraminifera as proxies for climate and oceanographic changes in the Holocene off southern Chile

Melissa K. Lobegeier; Carina B. Lange & Ulysses S. Ninnemann

shifts of the WWD and changes in the Patagonian Icefields at the entrance tothe Magellan Strait.

Data to be collected from these cores will include benthic and planktonicforaminiferal assemblages, Mg/Ca ratios and ä18O from one species of benthicforaminifera, Cibicides dispars, and Mg/Ca ratios and ä18O from two speciesof planktonic foraminifera, Globigerinoides bulloides and Neogloboquadrinapachyderma. Mg/Ca ratios in benthic foraminiferal calcite are used as a proxyfor bottom water temperatures and Mg/Ca ratios in planktonic foraminiferalcalcite are used as a proxy for sea surface temperatures. We will use thesetemperature proxies in combination with foraminiferal ä18O to reconstructvariations in salinity, temperature, and past oceanic circulation. Changes inpaleotemperature and paleosalinity reconstructions will be compared with otherproxies including alkenones, biogenic opal, and organic carbon.

Preliminary results indicate the benthic foraminiferal assemblage in themulticore is a diverse assemblage with Globocassidulina subglobosa,Discorbis peruvianus, Cibicides dispars, and Bolivina minuta the dominantspecies. A decrease in the number of benthic foraminifera per volume ofsediment in the last 50 years is apparent. Trace element and isotopegeochemistry should serve to clarify the cause of the recent decreases inbenthic foraminiferal abundance.

606

On the use of benthic foraminiferal δδδδδ13C in paleoceanography:Constraints from primary proxy relationships

Andreas Mackensen

Alfred Wegener Institute for Polar and Marine Research, 27568 Bremerhaven, [email protected]

I review recent findings from observations in the field on the generationof the δ13C signal in shells of live (Rose Bengal stained) benthic foraminifera,and end up with implications for the interpretation of fossil signatures. Theδ13C values of calcite tests of preferentially epibenthic foraminifera principallyreflect the δ13C of dissolved inorganic carbon (DIC) of ambient seawater,whereas endobenthic species record a porewater signal, both with an offsetfrom equilibrium calcite. Species occupying the deepest average living depth inthe sediment usually exhibit lowest δ13C test values, but δ13C values ofconspecific specimens at a single site do not decrease with increasing subbottomdepth and decreasing porewater δ13CDIC. Organic carbon fluxes to the sedimentsurface are generally reflected by infaunal species such that lowered δ13Cvalues coincide with high fluxes, but even strictly epibenthic species may reacton seasonally pulsed phytodetritus supply by depleted test δ13C. In high-productivity environments, however, where dissolved oxygen and sedimentarycarbonate contents are low, benthic foraminiferal tests show 13C enrichmentprobably due to carbonate-ion undersaturation. Ontogenetic enrichment in δ13Cvalues of certain endobenthic species suggests a slow-down of metabolic ratesduring test growth and decreasing fractionation with age. At sites of activemethane discharge δ13C values of endobenthic species reflect low pore waterδ13CDIC values, documenting active methane release in the sediment, whereaslowered δ13C values of strictly epibenthic species are most probably the resultof incorporation of 13C depleted methanotrophic biomass.


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607

Paleoproductivity at the NW Iberian continentalslope during the last 31.5 kyr

Virgínia Martins1; E. Salgueiro2; J. M. A. Dias3 & F. Rocha1

1Unidade de Investigação em Minerais Industriais e Argilas (MIA), Universidade de Aveiro,Campus Universitário de Santiago, 3810-193 Aveiro, Portugal

[email protected] Nacional de Engenharia, Tecnologia e Inovacao I.P., Dept. Geologia Marinha,

Estrada da Portela, Apartado 7586, Alfragide 2721-866, Portugal3Universidade do Algarve, Campus de Gambelas, 8000 Faro, Portugal

In order to investigate the productivity conditions at the Galicia continentalslope during the last 31.5 kyr, the OMEX (Ocean Margin Exchange Project)core PE 109-13 (540 cm of length) recovered at 42.572º N, 9.690º W, and 2000m water depth was studied. Today hydrographic conditions at this site arecharacterized by recurrent seasonal upwelling and by the southward coldPortugal Coastal Current during April to October, and by the poleward warmPortugal Coastal Countercurrent during the rest of the year. The upwellingcold and nutrient rich Eastern North Atlantic Central Water is the most importantphenomenon to enhance the oceanic productivity in this region.

The age model of the studied core is based in five AMS 14C ages and inthe synchronization of the planktonic ä18O (G. bulloides) record from the PE109-13 sediment core with the ä18O record from the GISP2 ice core. In theproximity of the Heinrich Events (HE) the age model was improved using therelative abundance of polar species, N. pachyderma (sinistral), and sea surfacetemperature (SST). Planktonic foraminifera assemblages are used to estimateSST with the modern analogue technique SIMMAX 28, as described inPflaumann et al. (1996. Paleoceanography, 11: 15-35), using as referencethe Portuguese margin database added to the North Atlantic surface samplesused by the MARGO project (Salgueiro et al., in prep. Paleoceanography).

The bottom paleoproductivity was assessed by benthic foraminifera highproductivity (BFHP) proxy, considering that deep sea benthic foraminiferaassemblages are controlled mainly by variations in oceanic primary productivityand dissolved-oxygen levels in the water/sediments.

Heavy (2.94-3.3 ‰VPBD) planktonic foraminifera ä18O, the high (41-89 %) relative abundance of polar species, and low summer SST (5-8 ºC)allow the identification of the three youngest HE and some cold Dansgaard-Oeschger (D-O) events. The BFHP suggests a higher deposition of organicmatter, related probably to an increase in the productivity or the exportation of


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FORAMS 2006Paleoproductivity at the NW Iberian continental slope during the last 31.5 kyr

Virgínia Martins; E. Salgueiro; J. M. A. Dias & F. Rocha

organic matter during the HE3, HE2, and HE1, between the Last GlacialMaximum (LGM), the early Holocene, and probably during some D-Ointerstadials (1-7). The low productivity during the LGM is also suggested bythe drop in foraminiferal abundance (200-900/g of bulk sediment; with nosignificant signals of dissolution) in spite of the expected high productivity duringthe LGM due to the westerlies strengthening. Sediments deposited during thisperiod are also characterized by an increasing in fine fraction and detritalminerals. But between the LGM and 5 Kyr sand fraction, foraminiferalabundance and calcite content increased significantly whereas detrital mineralsdecreased. These results agree with a strong influence of sea level changes inthe sedimentation and probably in the upwelling pattern in the NW IberianMargin since the last 31.5 kyr.

609

Mediterranean humid periods and sapropel formationduring the last four climatic cycles

Tarek Melki1; Frans Jorissen2; Nejib Kallel1; Laurent Labyeyrie3;Jean-Claude Duplessy3 & Michel Fontugne3

1Department of Geology, Faculty of Science, University of Sfax, BP :802, Sfax 3018, [email protected]

2Lab d’étude des Bio-indicateurs Actuels et Fossiles, University of Angers,UPRES EA, 49045 Angers, France

3CNRS-CEA, Lab. Des Sciences du Climat et de l’Environnement, 91198 Gif-sur-Yvette, France

We have analyzed the benthic foraminiferal fauna at high-resolutionalong the core MD84-641 (33°02’ N ; 33°38’ E) recovered in the EasternMediterranean Sea and covering the last four climatic cycles. For each sapropel,the succession of benthic foraminifera assemblages displays that the decreasein the oxygen content of the eastern Mediterranean deep water was gradual.This contrasts with the abrupt decrease of the Sea Surface Salinity (SSS)associated with sapropel formation. It is now well established that the organicmatter preservation on the bottom of the eastern Mediterranean Sea andsapropel formation were linked to the slowing in the deep water circulation ofthe Mediterranean Sea. This can only be possible when the MediterraneanSea received an enhanced freshwater supply that was able to equilibrate thewater loss by evaporation transforming the Mediterranean Sea into a nonconcentration basin. However, hydrological conditions responsible for organicmatter preservation events, seems to be different from one sapropel to another.This is indicated by differences in the duration and the installation rhythm ofanoxic conditions. Benthic foraminifera did not disappeared completely duringsapropels S10, S9, and S4 suggesting that anoxia was never reached duringthese episodes. On the other hand, anoxia occurred for short duration duringcold sapropels S8 and S6. This suggests that climatic conditions conducing tothe wet epochs, associated with sapropels, were not identical for all the easternMediterranean sapropels.


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610

Paleoproductivity changes in the southeastern Braziliancontinental margin:

Benthic foraminifera and stable isotope evidences

Renata Hanae Nagai1,*; Silvia Helena de Mello e Souza1;Michel Michaelovitch de Mahiques1,** & A.V. C. Moura2

1Instituo Oceanográfico, Universidade de São Paulo, USP, São Paulo, SP, [email protected]

2Centro de Geociências, Universidade Federal do Pará, Belém, PA, Brazil

The aim of this study is to comprehend the environmental changes duringthe Holocene on the southeastern Brazilian upper slope, based onsedimentological, isotopical and foraminiferal parameters The study area islocated in the São Paulo Bight, where the sedimentary processes of the uppermargin are greatly influenced by the southward displacement of the BrazilCurrent (BC).

A sediment core (7486 core) 96 cm in length, collected on the upperslope (44º19.80´W and 24º24.24´S), at 233 m depth, was analysed for grainsize, calcium carbonate content, stable isotopes (ä18O and ä13C), benthic andplanktonic foraminifera (G. ruber /G. bulloides rate). Specimens ofGlobigerinoides ruber (white) and Globigerinoides ruber (pink), with >250 µm size, were used for stable isotopes analyses. Benthic foraminiferaanalysis was carried on > 125 µm size fraction. At least, 300 specimens werecollected from the sediment, identified and counted.

An upward increase in the calcium carbonate content and in the G.ruber/G. bulloides rate was observed. This fact allied with the decrease ofä18O values in both species and in Islandiella sp. frequencies seems to indicatethe occurrence of warmer superficial and bottom waters towards the Recent.

Sandy sediments are predominant on the top of the core. This isaccompanied by an increase in the frequency of Globocassidulina subglobosaand by a decrease of Bulimina marginata and Uvigerina peregrina, whichare considered as detritivore feeders and preferentially infaunal species andalso good markers of food availability. The high number of specimens ofGlobocassidulina subglobosa may be related to the intensification of bottomcurrents. Apparently, the trend of the increase of ä13C values reveals lowersuperficial water productivity towards the Recent. This may explain the lownumber of species within the infauna at the top of the core.


FORAMS 2006


FORAMS 2006Paleoproductivity changes in the southeastern Brazilian continental margin:

Benthic foraminifera and stable isotope evidencesRenata Hanae Nagai; Silvia Helena de Mello e Souza; Michel Michaelovitch de Mahiques & A.V. C. Moura

The correlation of the studied core with a well radiocarbon dated core,also located in the study area, allows us to assume that it corresponds to thedeposition of Holocene sediments, probably spanning the period after 8,000years BP. Our results indicate a progressive onshoreward displacement ofwarm and oligotrophic waters of the Brazil Current, leading to an intensificationof the bottom currents on the upper margin as well as a decrease in waterproductivity.

*FAPESP Proc. Nº 04/12693-1. **FAPESP Projeto Nº01/13490-9.

612

Closure of the Indonesian seaway and ocean circulationduring the middle to late Miocene (~13.6-5.6 Ma): Early

history of the western Pacific warm pool

Stephen A. Nathan & R. Mark Leckie

Department of Geosciences, University of Massachusetts, 611 N.Pleasant St., Amherst, Massachusetts 01003, U.S.A.

[email protected]

The Western Pacific Warm Pool (WPWP) is an important facet of thetropical ocean-climate system, including the El Niño/Southern Ocean climatecycle. The origin of the WPWP is due to the constriction of IndonesianThroughflow (ITF) and the piling up of warm waters in the western tropicalPacific by the Trade Winds. The eastward flowing Equatorial Undercurrent(EUC) is a consequence of WPWP development. This narrow jet deliversnutrient-rich thermocline waters to the central and eastern equatorial Pacificwhere the mixed layer is thinner and the thermocline shoals high into the photiczone. Previous data and modeling studies have suggested that the modernWPWP-EUC became established during the Pliocene with the prospect ofearlier development in the Miocene.

Here we studied the middle to late Miocene (~13.6-5.6 Ma)paleoceanography of the western equatorial Pacific (WEP) and present datadocumenting the on again/off again history of a “proto-warm pool” and EUCbased on changes in planktic foraminiferal assemblages and multispecies stableisotope data from ODP Site 806 (Ontong Java Plateau). Times of proto-warmpool development are distinguished from other intervals by relatively low numbersof thermocline-dwelling species of planktic foraminifers relative to mixed layerspecies, and by the sharply reduced oxygen isotope gradient between a deepthermocline species (Globoquadrina venezuelana) and a mixed layer species(Globigerinoides sacculifer; ∆δ18ODTH-ML). We hypothesize that the presenceor absence of a proto-warm pool in the WEP, caused by the progressive tectonicconstriction of the Indonesian Seaway and modulated by sea level fluctuations,created El Niño/La Niña like alternations of tropical climate and hydrographic


FORAMS 2006


FORAMS 2006Closure of the Indonesian seaway and ocean circulation during the middle to late Miocene

(~13.6-5.6 Ma): Early history of the western Pacific warm poolStephen A. Nathan & R. Mark Leckie

conditions during the late Miocene. This hypothesis is based partially on a generalantithetical relationship observed between carbonate productivity andpreservation in the western and eastern equatorial Pacific, which we suggestwas caused by these alternating ocean-climate states.

Development of a proto-warm pool ~11.6-10.0 Ma coincides with icesheet expansion (Miocene isotope events Mi5 and Mi6), a sea level fall of ~50m, and production of Northern Component Water. It also marks the initiation ofa more modern equatorial current system as La Niña like conditions becameestablished across the tropical Pacific. This situation sustained carbonateproductivity in the eastern equatorial Pacific (EEP) at a time when carbonatepreservation sharply declined in the Caribbean. Proto-warm pool weakeningafter ~9.8 Ma may have contributed to a similar “carbonate crash” in the EEP.Decay of the proto-warm pool and resultant El Niño like conditions broughthigher but variable productivity to the WEP, particularly ~9.4-9.0 Ma coincidentwith a major perturbation in tropical nannofossil assemblages. At ODP Site806, increased productivity is registered by marked increases in the relativeproportion of thermocline species, radiolarian abundances, carbonate massaccumulation rates, and by a sharp increase in the oxygen isotopic valuesbetween the deep thermocline and mixed layer taxa. This broad interval ofincreased productivity across the Indo-Pacific records the initial phases of the“biogenic bloom”. Resurgence of a later proto-warm pool in the WEP after~6.7-6.3 Ma may have spurred renewed La Niña-like conditions and a stronglate phase of the “biogenic bloom” in the EEP.

614

Reconstruction of paleo-SST in the eastern Mediterraneanduring marine isotopic stage 11 by transfer functions

Lea Numberger; Michal Kucera & Christoph Hemleben

Tübingen University, Tübingen, [email protected]

Marine isotopic Stage 11 (MIS11), some 400,000 years ago, providesthe closest analogue to the Holocene in terms of the configuration of the Earth’sorbit around the Sun and the resulting strength and variability of solar insolation.Understanding the climate of MIS11 will thus aid in assessment of the humanimpact on global climate and of the future of the present warm period. Climaticreconstructions for this period are facing two significant challenges: high-resolution correlation of marine sequences is hampered by the lack of absolutedating and evolutionary changes in marine plankton potentially complicateinterpretation of microfossil-based paleoproxies. The Mediterranean Sea offersa good opportunity to overcome at least the first limitation. High-resolutioncorrelations can be achieved in the Eastern Basin, through identification ofregional bottom-water dysoxic events. In addition, the semi-enclosedMediterranean is known to amplify climatic forcing and is thus particularlysuitable for studies of climate variability during apparently stable intervals, likeMIS11. We have identified the MIS 11interval in a series of ODP- and pistoncores from the eastern Basin and are conducting a multi-proxy investigation ofthe regional climate variability through time and in space. As a main proxy, weare using artificial neural network based transfer functions that describequantitatively the relationship between assemblages of planktonic foraminiferaand sea-surface temperature. Planktonic foraminifera are well preserved in allstudied sections and our first results indicate that assemblage composition duringMIS11 and adjacent glacials mirror that of the Holocene and the Last Glacial.Despite the considerable amount of time separating the Holocene and MIS11,combined with the potentially non-analog warmth during MIS11, it appears thatthe same species have inhabited the Basin throughout the last 0.5 Ma, and theirassemblages have good analogs in modern sediments. With respect to themagnitude of MIS11 warmth in the eastern Mediterranean, first calculationssurprisingly indicate SST values similar, or slightly cooler (< 1°C) than at present.


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615

Sediment trap results from the Japan trenchin the Kuroshio domain:

Seasonal variations in the planktic foraminiferal flux

Motoyoshi Oda1 & Makoto Yamasaki2

1Institute of Geology and Paleontology, Graduate School of Science, Tohoku University,Sendai 980-8578, Japan

[email protected] of Applied Earth Sciences, Faculty of Engineering and Resoruce Science,

Akita University, 1-1 Tegata-Gakuencho, Akita, 010-8502, Japan

Time series sediment traps were deployed at two depths at Station JT(Japan Trench) along the northern margin of the Kuroshio domain from March1991 to May 1992. Total foraminiferal fluxes ranged from 334 to 1028 shells/m2/day in the shallow trap (1200 m), and from 657 to 2130 shells/m2/day in thedeep trap (3700 m). A total of 35 planktic foraminiferal species belonging to 13genera were identified. The assemblage was dominated by Globigerinabulloides, Globigerinita glutinata , Globigerinoides ruber, andNeogloboquadrina dutertrei, whose fluxes varied seasonally. Globigerinabulloides along with Globigerina quinqueloba occurred during the earlyspring phytoplankton bloom. These taxa were replaced by G. ruber,Globigerinoides sacculifer, N. dutertrei, and Pulleniatina obliquiloculataduring the late spring to early autumn, with the development of a sharpthermocline and a deep chlorophyll a maximum just below the thermocline.The maximum shell flux of G. glutinata, Globigerina falconensis,Globorotalia inflata, and Globorotalia truncatulinoides occurred duringthe winter near the 18°C isotherm in well-mixed surface water that resultedfrom the extensive vertical mixing induced by the winter monsoon.

Temporal changes in the path of the Kuroshio caused by its meanderingappeared to be the dominant flux control factor, based on the correlation betweenthe meander types of the Kuroshio and the timing of large fluxes in the deeptrap. During the trap experiments, major meanderings of the Kuroshio wereobserved from September to October 1991 and from mid April to May 1992.During these two periods, prominent flux peaks of t:G. bulloides andNeogloboquadrina incompta were observed in both shallow and deep traps.The major meander of the Kuroshio was near Station JT during these periods,and the nearshore side of the Kuroshio Front, which is characterized by high


FORAMS 2006


FORAMS 2006Sediment trap results from the Japan trench in the Kuroshio domain:

Seasonal variations in the planktic foraminiferal fluxMotoyoshi Oda & Makoto Yamasaki

productivity in the euphotic zone, was very close to Station JT. These resultssuggest that these two species were produced on the nearshore side of theKuroshio Front and collected in the sediment trap. The temporal occurrencesof N. incompta at Station JT associated with the meanders of the Kuroshioare consistent with the high abundance of N. incompta in the surface sedimentrecord from beneath the modern cold water mass off Kishu and Enshu-nada,between the Japanese coast and the axis of the Kuroshio.

617

Planktic and benthic foraminiferal assemblage responses toglacial-interglacial sea level fluctuations in tropical mixed

siliciclastic-carbonate margins: Belize and the Gulf of Papua

Brooke Olson1; R. Mark Leckie2; André W. Droxler1; Gerald R. Dickens1;Sam Bentley3; Larry Peterson4 & Bradley Opdyke5

1Department of Earth Science, Rice University, Houston, TX 77005, [email protected]

2Department of Geosciences, University of Massachusetts, Amherst, MA 01003, [email protected]

3Coastal Studies Institute, Louisiana State University, Baton Rouge LA 70803, U.S.A.4Rosenstiel School of Marine and Atmospheric Science – MGG, University of Miami,

4600 Rickenbacker Causeway, Miami, FL 33149, U.S.A.5Department of Earth and Marine Science, The Australian National University, Canberra

ACT 0200, Australia

Foraminiferal abundances and distributions yield a wealth of paleoecologicand biostratigraphic information, providing excellent tools to interpret the geologicrecord and date sediments. In purely siliciclastic systems, analysis of preservedforaminiferal sediment assemblages has proved invaluable in paleoenvironmentand sea level history reconstruction, as well as sequence identification. However,many fewer studies have investigated the utility of foraminiferal proxies inmixed siliciclastic-carbonate environments. The Belize margin and the Gulf ofPapua represent two modern tropical mixed siliciclastic-carbonate systemswhere significant volumes of terrigenous sediments interact with shallow waterneritic and pelagic carbonates. In this study, planktic and benthic foraminiferalpopulations are used to investigate foraminiferal response to glacial-interglacialcycles relative to sea level, water masses, and sequence stratigraphic principles.The Quaternary is an ideal interval to accomplish these objectives, as the timingand amplitude of Quaternary sea level fluctuations are well establishedindependent of sequence stratigraphic principles.

This study is based on the analyses of a 37.7 m long piston core (MD02-2532) taken 3 km offshore the central Belize Barrier reef and two shorterpiston cores (MV24-0407 07JPC, 11.3 m and MV26-0403 74JPC, 11.3 m)taken in Ashmore Trough, Gulf of Papua. MD02 2532, was collected on thedistal slope of Gladden Basin at 333 m of water depth by the R/V MarionDufresne (IPEV). MV24-0407 07JPC and MV26-0403 74JPC were collectedon the basin and slope, respectively, of southern Ashmore Trough by the R/V


FORAMS 2006


FORAMS 2006Planktic and benthic foraminiferal assemblage responses to glacial-interglacial sea level

fluctuations in tropical mixed siliciclastic-carbonate margins: Belize and the Gulf of PapuaBrooke Olson; R. Mark Leckie; André W. Droxler; Gerald R. Dickens;

Sam Bentley; Larry Peterson & Bradley Opdyke

Melville. Robust chronologies are established using radiocarbon ages and highresolution planktic oxygen isotope stratigraphy, A robust chronology is establishedusing radiocarbon ages and high resolution planktic oxygen isotope stratigraphy,and demonstrates that MD02-2532 represents approximately the last 850 kyr,while MV24-0407 07JPC and MV26-0403 represent approximately the last 80kyr.y: Planktic foraminiferal assemblage variations typically corresponding tothe oxygen isotope record, glacial/interglacial cycles, likely reflecting watermass changes (e.g., temperature, salinity). Benthic assemblages are morecomplicated, reflecting water depth and paleoenvironmental changes (watermass, productivity), as well as varying influences of carbonate and siliciclasticprovinces. Associations of various species can be used as proxies for sea levelfluctuations and/or glacial/interglacial cycles in both locations.

619

Guembelitria: Proxies for major oceanic catastrophes

Alfonso Pardo1 & Gerta Keller2

1Universidad San Jorge, Alcalde Sainz de Varanda, 1-3, E-50009 -Zaragoza, Spain - [email protected]

2Department of Geosciences, Princeton University, Princeton, NJ08544, U.S.A. - [email protected]

Biotic responses and strategies by opportunistic species to environmentalcrises, in particular during major ecological perturbations, have been widelystudied in modern and ancient ecosystems. Those studies revealed a pattern ofresponse that appears to be universal.

During the late Maastrichtian and the Cretaceous-Tertiary (K-T)transition planktic foraminiferal fossil assemblages reflect a similar biotic patternin response to major environmental catastrophes. A global data analysis revealsthat blooms of the disaster opportunist Guembelitria seem to be excellentmarkers for environmental catastrophes, whether due to impact, volcanism orrapid climate changes, leading to severe biotic crises that may range fromtemporary exclusion of ecological specialists and generalists to mass extinctions.The fossil record indicates that the most intense Guembelitria blooms tookplace in shallow continental shelf areas, slope/shelf margins, and volcanicprovinces of the Indian Ocean. All these areas experienced eutrophicenvironments during the late Maastrichtian to early Paleocene interval, eitherfrom volcanic input, continental runoff, or upwelling currents alongcontinental margins.

The paleoecological succession and recovery phases of fossil plankticforaminiferal assemblages that followed a major biotic perturbation can besummarized in a simple model. Data show that eutrophication - a toxic conditionfor planktonic foraminifera - is the most critical factor in mass mortality, leadingto phytoplankton blooms. As soon as phytoplankton consume the excessnutrients, the first opportunistic foraminifera, the Guembelitria appear andgraze on phytoplankton. These triserial species have a wide fundamental nichethat enables adaptation to variable environmental conditions and permits theniche drift that guarantees survival of these stress-tolerant species. Theiradaptation to high-stress disturbed environments includes dwarfing, which takesadvantage of the nutrient supply by means of heterochronic acceleration (i.e.,early sexual maturation and faster reproduction). Without interference from


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FORAMS 2006Guembelitria: Proxies for major oceanic catastrophes

Alfonso Pardo & Gerta Keller

competitors, triserial r-strategists rapidly reproduce and increase theirpopulations exponentially, taking full advantage of stressed and disturbed habitats.

Once nutrient levels decrease, Guembelitria populations decline, openingecologic niches for other generalists and a slow ecosystem recovery begins.Small low O2 tolerant heterohelicid blooms mark this second stage, followed bysmall trochospiral and planispiral species. With further environmental upturn,increasing ecological competition, niche development, and restoration of a well-stratified watermass, oligotrophic conditions are restored opening habitats forthe K-strategists and a return to politaxic communities.

This ecological succession pattern seems to be related to mantle plumevolcanism in the Indian Ocean, Andean volcanism in Argentina and shallowinland seas in Egypt and Madagascar during the late Maastrichtian, and the K-T impact and volcanism during the early Paleogene.

621

Planktonic foraminifera and stable oxygen isotopes as tools topaleoceanography of the South Brazilian continental margin

Rodrigo da Costa Portilho-Ramos1; Aristóteles de Moraes Rios Netto2 &Cátia Fernandes Barbosa1

1Programa de Pós-Graduação em Geoquímica Ambiental - Departamento de Geoquímica - UFF,Universidade Federal Fluminense, Outeiro de São João Batista s/no ,

Centro, Niterói 24020-007, RJ, Brazil - [email protected]ório de Bioestratigrafia, Paleoambientes e Paleoclima (LabMicro) - Depto. de Geologia -

Instituto de Geociências - UFRJ, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil

The frequent climatic oscillations during the past two million years havecaused great changes in biodiversity, on ocean circulation patterns and in thephysico-chemical properties of seawater. Since the precipitation of CaCO3occurs in equilibrium with the water environment, it is possible to evaluate thepaleoceanography and paleoclimatic variations through the biogenic calcareousisotopic composition of marine sediment. Among others, planktonic foraminiferaare important paleoclimatic proxies in the ocean due to their highly sensitivitiesto temperature variations of sea water masses. These changes are evident ondiversity and relative abundance of the species, and therefore it’s possible tocorrelate the stable isotopic records with the changes on planktic foraminiferalpopulations. The sediment studied, in order to delineate the paleoceanographyand paleoclimatic changes that occurred on the southwest Atlantic alongBrazilian border, were from the core JPC-95, collected during cruise on the R/V KNORR 159-5 from Woods Hole Oceanographic Institution (WHOI, USA)in 1998, which was retrieved from the slope of Santos Basin at coordinates 270

52.73’ S and 460 55.25’ W. The core was collected at 1,485 meters depth, inwhich the piston core JPC 95 reached 18 meters length with a recovering of16.4 meters, which were analyzed in a total of 164 samples at each 10 cm. Atthe laboratory the samples were washed through meshes sieves of 62 µm anddried on environmental temperatures. Each sample was dry splitted throughmeshes sieves of 125 µm and 250 µm. Following this procedure the pickingwas done counting about 300 specimens per sample selecting significant speciesof foraminifera for paleoceanography study. Stable oxygen isotope wasmeasured on Cibicides spp. Three to five individuals were selected, immersedin ethanol, gently crushed with a glass rod, and measured by mass spectrometry.The measurements were made at WHOI. The foraminifera show that the


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FORAMS 2006Planktonic foraminifera and stable oxygen isotopes as tools to

paleoceanography of the South Brazilian continental marginRodrigo da Costa Portilho-Ramos; Aristóteles de Moraes Rios Netto & Cátia Fernandes Barbosa

interval among base of the core and samples 920-921 cm was deposited underwarm conditions (last interglacial interval or Marine Isotopic Stages 5, MIS-5,)due to the presence of menadiform plexus, which include Globorotalia tumidaflexuosa, characteristic species of this interval adapted to warm conditions.The interval among samples 910-911 cm and 20-21 cm was deposited undercold-water conditions (glacial) due to the absence of menadiform plexus.Therefore two top samples of the core (10-11 and 3-4 cm) were depositedunder warm conditions (post glacial) due to the presence of menadiform plexus.These intervals can be correlated with biozones X, Y and Z, respectively. Basedon variable percentages of menardiform plexus and Pulleniatina plexus, itwas possible to subdivide the last interglacial and glacial intervals fromPleistocene, which correspond to X1 to X6 and Y1 to Y5. The low values ofδ18O at the top of the sedimentary succession (8.5 cm) show a close correlationwith species frequency indicating an elevation on oceanic water temperatures.This tendency toward low values can be explained by the input of 18O from theice melting on high latitudes expressed on the tropics, showing a transitionalperiod between the last glacial age (Marine Isotopic Stages 2, MIS-2) and theRecent (Marine Isotopic Stages 1, MIS-1). The highest values recorded onsample 16.5 cm was recognized as the Last Glacial Maximum (LGM). Theseresults are coherent to absolute age from o:14C data (unpublished data from D.Oppo, WHOI/USA) that shows an age of 21,800 years to this sample.

623

Paleoclimate recorded in foraminiferal assemblages,isotopes, and lithofacies in an Iceland fjord

Ursula Quillmann; John T. Andrews & Anne E. Jennings

University of Colorado at Boulder and INSTAAR, Colorado, [email protected]

Icelandic fjords are ideal locations for investigating Holocene marineclimate. Fjords accumulate thick sediment packets composed of marine andterrigenous sediments that provide insights into land and ocean processes. Icelandlies in a sensitive location relative to the polar oceanic and atmospheric fronts.The oceanic polar front between the warm and saline Atlantic Water carriednorthward by the Irminger Current (IC) and the cold, low salinity Polar Watercarried southward by the East Greenland Current has shifted throughout thelate Quaternary and Holocene. The fronts influence not only the climate inIceland but also the climate in the North Atlantic. Today, the waters of therelatively warm and saline IC overlie the study site. We are presenting dataobtained from a marine sediment core, B997-339, from Skotufjordur, a NWIcelandic fjord in the Vestfirdir peninsula. The core is 527 cm long and wasretrieved at a water depth of 104 m. We are using biologial, geochemical, andsedimentological proxies to reconstruct Holocene climate variations. An agemodel is based on 12 radiocarbon dates and the 10,180 cal yr Saksunarvatntephra. The core spans the time interval 11,500 to 1,000 cal yr BP. Stratigraphybased on foraminiferal assemblages, benthic δ18O composition, and lithofaciesagree. Stratigraphical boundaries divide the record into 3 intervals: 11,550-10,600,10,600-8900, and 8900-1000 cal yr BP. The first interval from 11,550 to 10,600cal yr BP is interpreted as a glacial marine environment, characterized by anElphidium excavatum f. clavata – Cassidulina reniforme assemblage, bothspecies that are indicators of glacial marine environments. Other characteristicsof this interval are high amounts of ice rafted debris, low total organic carbon%and total inorganic carbon%, little bioproductivity, and heavy isotopes with lightspikes. The light spikes are likely to be caused by melt water pulses. We interpretthe second interval from 10,600 to 8,900 cal yr BP to be a transitional periodbetween glacial marine and modern environments. A Cibicides lobatulus –Elphidium albiumbilicatum assemblage with the accessory speciesAstrononion gallowayi is associated with sandy substrate often to be inferredas high bottom-current indicating. E. albiumbilicatum is a shallow water


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FORAMS 2006Paleoclimate recorded in foraminiferal assemblages, isotopes, and lithofacies in an Iceland fjord

Ursula Quillmann; John T. Andrews & Anne E. Jennings

species. These species are interpreted to be reworked from shallower adjacentareas along the fjord margin, because neither is the substrate at the study sitesandy nor shallow. Interpreting this assemblage in context of increased energythat can be seen in the x-radiographys occurring in this interval, we can inferthat relative sea level (RSL) was lower. Increasing current energy caused byRSL can explain the presence of these allochtonous species at the study site.At the same time, lighter δ18O and declining arctic, glacial marine species C.reniforme and E. excavatum f. clavata, suggest warmer temperatures. Weinterpret the third interval from 8,900 to 1,000 cal yr BP to representenvironmental conditions approaching those of the modern environment. A C.reniforme assemblage dominates (up to ~80%) in this interval. This species iscommon today in the study site, where water masses of the IC are present yetthe faunal assemblage indicates arctic conditions. This apparent paradox canbe resolved by the formation of winter water. The modern hydrological datashow ~< 1°C bottom waters in February and March. This cooled winter watersuggests that the fjord water masses are overturned by cooled surfacewaters formed during the polar winter. A fully Boreal fauna cannot establishitself in the fjord.

625

Micromilling technique applied to foraminifer testsfor sample preparation of geochemical analysis

Saburo Sakai

Institute for Frontier Research on Earth Evolution (IFREE),Japan Agency for Marine Science & Technology, Yokosuka, Japan

[email protected]

The oxygen and carbon isotopes of shallow-water carbonates and theirfossil components can be important tools for understanding paleoceanographicconditions of open- to marginal- seas, including coral reef regions. However,most previous paleoceanographic studies using isotopes have been based onpelagic or hemipelagic sediments, because the original δ18O and δ13C values ofshallow-water carbonates are normally altered by post-depositional diagenesis.To avoid the problem of diagenesis, low-Mg calcite, which is stable despite thediagenetic alteration has been used for the analysis. Recent study reportedthat the original isotopic signals are preserved in carefully picked low-Mg calciticplanktic foraminifers of shallow-water carbonates, even the isotopic values ofthe carbonate host rock have been altered by meteoric fluids. Therefore,paleoceanographic studies using planktic foraminifers (or originally low-Mgcalcitic components) are possible in shallow-water carbonates as the studiesof deep-sea core sediments.

However, this approach is limited in unconsolidated shallow-watercarbonate sediments, because the foraminifer tests are difficult to be extractedfrom lithified shallow-water carbonate rocks. Applying to lithified limestone,micromilling technique is expected to become an effective tool in order toextract samples from µm-order areas where the original isotopic signals areexpectedly preserved. In this study, new developed micromilling equipmentadapts for extracting specimens of foraminifer tests from lithified Pleistocenecarbonate rocks. The equipment is computer-controlled micro positioningtechnology with ~1 µm spatial resolution, is able to be extracted samples froma chamber scale. The spatial resolution of micromilling is equivalent to orsurpasses that of laser ablation, and preserves the benefits of conventionalphosphoric acid sample processing. δ18O and δ13C values of the milled low-Mg calcitic foraminifers are much heavier than diagenetically depleted valuesof micritic / sparitic cements and high-Mg calcitic benthic foraminifer tests,and correspond to the isotopic values of foraminifer tests in modern shallow-water carbonate worldwide. The results reasonably imply preservation of the


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FORAMS 2006Micromilling technique applied to foraminifer tests for sample preparation of geochemical analysis

Saburo Sakai

original isotopic signals in low-Mg calcitic foraminifer tests, and confirm thatthe method used in this study is applicable to lithified limestone. However, incase of foraminifer tests for microsampling, the exposed chambers are restrictedon thin section, thick section, or polished chips. So the isotopic data for a chamberusing the micro-milling system must examine carefully the ontogenetic effects(e.g., shell size, parts of chambers, vital effects) on isotopic values.

627

d18O of a shallow water benthic foraminifer Marginoporaand paleotemperature calibration

Pratul Kumar Saraswati1; Kenji Iwao2; Karyne Rogers3 & Ramalingam Raja1

1Department of Earth Sciences, IIT-Bombay, Powai 400076, [email protected]

2Akajima Marine Science Laboratory, Aka, Zamami-son, Okinawa, 901-3311 Japan3Rafter Stable Isotope Laboratory, Institute of Geological and Nuclear Sciences, PO Box

31312, Lower Hutt, New Zealand

Research in chemical proxies of past ocean water temperatures, aspreserved in skeletal carbonates of marine organisms, has witnessed aphenomenal growth in recent years. Oxygen isotopic composition (expressedas ä18O) of the foraminiferal carbonates is the principal proxy used forpaleoclimate reconstruction. It is known that inorganic equilibrium precipitationis not valid for biogenic carbonates and therefore, species specific calibrationsare emphasized for paleoceanographic and paleoclimate studies. Planktonicand deep water benthic foraminifera are commonly analyzed to estimatetemperatures of sea surface and bottom waters to reconstruct ocean watercirculation. There are, however, very few studies on ä18O of shallow water,symbiont-bearing, benthic foraminifera, popularly known as larger foraminifera.These foraminifera are important contributors to modern reef sediments andhave been the most abundant constituent of shallow water carbonates of theCenozoic times. It necessitates developing a paleotemperature scale based onshallow water benthic foraminifera. In the present, work we analyze ä18O ofseasonally collected, symbiont-bearing benthic foraminifer, Marginopora, fromAkajima (Okinawa), Japan. The specimens were picked live from the reef flat(depth < 2 m) and the analysis was carried on:

1) whole-test and2) outer-most chambers.It is found that the oxygen isotopic values are in equilibrium but if

correction for MgCO3 is made then all the values are depleted by 0.4 to 0.6‰.A second order polynomial is fitted between (ä18O)foram – (ä18O)water and monthlyaverage temperature of the sea water for the month of collection. It is found


FORAMS 2006


FORAMS 2006δδδδδ18O of a shallow water benthic foraminifer Marginopora and paleotemperature calibration

Pratul Kumar Saraswati; Kenji Iwao; Karyne Rogers & Ramalingam Raja

that the correlation (R2=0.98) improves in outer chamber values relative to thewhole test data (R2=0.84). The best correlation is found when the average ofseveral outer-most chamber data are considered for fitting the curve (R2=0.998).We suggest the following calibration for use in shallow water carbonatesuccessions containing larger foraminifera: T = 19.05 – 1.09 (äf – äw) + 0.85 (äf– äw)2. It is also observed that the difference in maximum and minimum valuesrespectively of ä18O between the several species analyzed is perfectly correlatedlinearly with the difference in maximum and minimum temperatures during themonth the samples were collected. This indicates that the scatter in values ofä18O of a set of samples may be an indicator of seasonal temperature variation.The ontogenic variation in ä18O of carefully dissected Marginopora also recordsseasonal variation in sea-surface temperature. But it is cautioned that whileusing this approach, the depth habitat of the analyzed species must be known.The deeper shelf genus Cycloclypeus shows subdued cyclical variation inä18O composition, corresponding to smaller variations in temperature at thisdepth. It is suggested that the best sampling procedure for paleoclimatic studyis to analyze a fixed portion of the specimen, preferably the initial part, andtake the average values of several observations.

629

Cabo Frio upwelling variability during the Holoceneinferred by planktonic foraminifera

Alice Cruz Candido da Silva¹; Ana Luiza Spadano Albuquerque¹; Michelle Moratade Andrade¹; Eliza Cristina Celis Correia¹; Paulo Sérgio de Oliveira da Silva¹;

Bruno Jean Turcq¹,² & Abdelfettah Sifeddine²

1Departamento de Geoquímica Ambiental, Universidade Federal Fluminense.Outeiro de São João Batista, s/no, Centro, Niterói, RJ, 24020-007, Brazil

[email protected] de Recherche pour le Development/IRD, Université de Versailles, Yvelines, France

Planktonic foraminifera have been used in paleoenvironmental andpaleoceanografic studies, including upwelling areas. Cabo Frio is a peculiarplace of the Brazilian coast (State of Rio de Janeiro), due to the occurrence ofa coastal upwelling. Several studies were already accomplished on the biologicaland physical-chemical aspects of such oceanographic process. However, studiesabout the behavior of the upwelling during a long time scale are very recent.The goal of this study is reconstruct the upwelling variability during the Holoceneusing planktonic foraminifera as the main tool. In oceanographic terms, CaboFrio is characterized by the presence of different water masses, among them,the hot and oligotrophic waters of the Brazil Current (BC) and the cold andnutrient-rich waters of South Atlantic Central Water (SACW) that arise onthe continental shelf during periods of upwelling. The formation of this watermass occurs in the Zone of Subtropical Convergence, where there is confluenceof the Brazil Current with the Falklands Current. Located where the orientationNE-SW of the Brazilian coast it is interrupted to be predominantly E-W, CaboFrio presents a trade winds predominantly of direction of the E quadrant, morefrequently NE. The intensity of such winds allied to the topographical featuresof the area result in the upwelling coastal, which is interrupted during the passageof cold fronts that reach the coast of the State of Rio de Janeiro. For this study,two marine sedimentary profiles of the Cabo Frio continental shelf were collected(23ºS and 42’W) using a gravity corer. The studied cores are 268 cm (locatedCF02-01B to 23º11’S and 41º47’W) and 274 cm-long (located CF02-02B to23º15’59S and 41º48' 01W). Core lithology was descripted and sub-sampledfor each centimeter. The radiocarbon chronology has been performed fromsamples of organic matter and biogenic carbonate. The profile presentapproximately 4,000 and 12,000 years cal BP, respectively. Sixteen foraminifera


FORAMS 2006


FORAMS 2006Cabo Frio upwelling variability during the Holoceneinferred by planktonic foraminifera

Alice Cruz Candido da Silva; Ana Luiza Spadano Albuquerque; Michelle Morata de Andrade; Eliza CristinaCelis Correia; Paulo Sérgio de Oliveira da Silva; Bruno Jean Turcq & Abdelfettah Sifeddine

species were identified: G. aff glutinata, Globigerina bulloides, G.quinqueloba, Globigerina falconensis, Globigerina rubescensGlobigerinoides ruber, G. sacculifer, G.conglobatus, Neogloboquadrinadutertrei, Globigerinella siphonifera; G. obesa.; G. callida; Globorotaliamenardi;G. truncatulinoides; Orbulina universa; Tenuitella ambitacrena.Among them, the most abundant along the profile were Globigerina bulloides(Gb), typical from cold waters, usefull as indicator of variations in the upwellingintensity and Globigerinoides ruber(Gr), typical from hot waters, thatrepresents the predominance of the BC. The ratio Gb/Gr allowed theconstruction of a curve of temperature variation of the surface waters. It showeda variation of the upwelling intensity along the studied profiles. Besides, it waspossible to identify with two patterns of upwelling variability, suggesting itsintensification with low-frequency in direction to the core top. The interconectionocean-atmosphere allows to suggest that during the early-middle Holocenethere was a prevalence of the BC waters suggesting a pattern of weaknessupwelling which can be related the decrease of the NE winds intensity and/orincrease of the frequency of passages cold fronts during the summer. By theother hand, during mid-late Holocene an alteration in the upwelling variabilitypattern was observed. We suggest that this variability pattern change can beattributed to the intensification of the ENSO event after 5,000 yrs BP.

631

Enigmatic early Miocene biserial foraminifera

Christopher W. Smart1 & Ellen Thomas2

1School of Earth, Ocean and Environmental Sciences, University of Plymouth,Drake Circus, Plymouth, Devon, PL4 8AA, U.K.

[email protected] of Geology and Geophysics, Yale University. New Haven, CT 06520-8109,

U.S.A.

In the early Miocene, ocean circulation may have been a factor inmaintaining global warmth at a time when global temperatures were higherthan today’s at pCO2 levels which were probably similar to pre-industrial ones.Information on the distribution of benthic and planktic foraminifera may assistin understanding oceanic circulation in such a world, having only one polar icecap (Antarctica). Abundant, small (mainly <150 µm) biserial foraminifera arepresent in lower Miocene deposits (calcareous nannofossil Zone NN3 abovethe lowermost occurrence of Sphenolithus belemnos into lower NN4, ~ 19.0-17.5 Ma) over a range of bathyal depths in the eastern Atlantic and westernIndian Ocean, but they are absent in coeval strata in the equatorial westernAtlantic, eastern Indian Ocean and equatorial Pacific Ocean. They are mostabundant at northeastern Atlantic DSDP Site 608 (Rockall Plateau region), co-occurring with abundant sphenoliths in nannofloral assemblages and high valuesof the carbon isotopic composition of alkenones, indicating high growth ratesof haptophyte algae. These biserial foraminifera have been assigned to thebenthic genus Bolivina. Their very high abundances in benthic assemblages(up to 90% at Site 608), occurring in sedimentary deposits without indicationsof low oxygen conditions (lamination, high organic carbon) in which such highabundances are common, have been difficult to explain. New data on details oftheir apertural morphology, their absolute abundance and accumulation rates,and the carbon and oxygen isotope values of their tests document that theseforms were not benthic, but planktic, and constitute as yet undescribed speciesthat should be assigned to the planktic genus Streptochilus. The temporal andspatial distribution of Streptochilus species in the present oceans is little known,but they occur in variable, highly productive, commonly coastal waters withintermittent upwelling conditions. The widespread but not global high abundanceof Streptochilus may reflect variable environmental conditions with overallhigh nutrient supply and phytoplankton growth rates, although there is noevidence that the produced organic material reached the sea floor in view of


FORAMS 2006


FORAMS 2006Enigmatic early Miocene biserial foraminifera

Christopher W. Smart & Ellen Thomas

the low benthic foraminiferal accumulation rates. These conditions may haveoccurred when nutrient-enriched waters upwelled periodically within a deepthermocline, possibly because Subantarctic Mode waters started to form atthat time, bringing nutrients to large areas in the eastern Atlantic and westernIndian Oceans. The circulation of nutrient-enhanced waters at mid-depth mayhave been the result of the start-up of a deep-reaching Antarctic CircumpolarCurrent and vigorous vertical mixing within the Southern Oceans.

633

The Danian/Selandian transition in Tunisia:Paleoenvironment and sea level

Jorinde Sprong1; Christian Dupuis2; Etienne Steurbaut3;Jimmy Van Itterbeeck4; Johan Yans5 & Robert P. Speijer1

1Department of Geography and Geology, K.U.Leuven, B-3001, Leuven, BelgiumH:[email protected]

2GFA, Faculté Polytechnique de Mons, 9000 Mons, Belgium3Royal Belgian Institute of Natural Sciences, 1000 Brussel, Belgium

4SIPM, Rijswijk, Netherlands5GFA, Faculté Polytechnique de Mons, 9000 Mons, Belgium

The Danian/Selandian (D/S) transition (~60 Ma) is marked by a hiatusin its type area Denmark. This level has been considered a sequence boundaryresulting from eustatic sea-level change (Hardenbol et al., 1998. Society forEconomic Paleontologists and Mineralogists, Special Publication, 60: 3-13) or tectonics (Nielsen et al., 2005. Nature, 435: 195-198). If eustasy wasthe cause, then similar expressions of sea-level change should also have beenrecorded on other continental margins. Tunisia provides great opportunities forstudying the D/S transition, because lower Paleogene deposits are widespread,expanded and well exposed. In the northern Tunisian basin (“Tunisian trough”),the El Haria Formation consists of an up to 500 m thick marl sequence ofMaastrichtian to early Ypresian age. In all studied sections (Sidi Nasseur, GarnHalfaya, El Kef, Elles), the rather monotonous succession of hemipelagic marls,is interrupted by a glauconitic bed with an unconformable base within the D/Stransition. In order to investigate the stratigraphic, paleoenvironmental and,sea-level record across the D/S transition in the Tunisian trough, we’re studyingthe micropaleontology, sedimentology, clay-mineralogy and stable isotopes. Inthis presentation we focus on the microfaunal records. The studied intervalsspan planktic foraminiferal Zones P2-P3 (p.p.), corresponding to calcareousnannoplankton Zone NP4. Quantitative analysis of the benthic foraminiferaland ostracod data demonstrate gradual faunal changes, punctuated at theglauconitic marker bed (P3a/P3b zonal boundary). These changes reflect anincrease in paleoproductivity concomitant with an overall shallowing of thebasin. The unconformable glauconitic bed further suggests a superimposedsea-level fluctuation, separating a late highstand systems tract from atransgressive systems tract. Despite difficulties correlating the boreal Danish


FORAMS 2006


FORAMS 2006The Danian/Selandian transition in Tunisia: Paleoenvironment and sea level

Jorinde Sprong; Christian Dupuis; Etienne Steurbaut;Jimmy Van Itterbeeck; Johan Yans & Robert P. Speijer

basin and the subtropical Tunisian basin, the lithologic and faunistic changes atthe P3a/P3b boundary in Tunisia seem to correspond to the D/S boundary inthe type region (Clemmensen & Thomsen, 2005. Palaeogeography,Palaeoclimatology, Palaeoecology, 219 (3-4): 351-394; Van Itterbeeck etal., submitted. Danian/Selandian boundary stratigraphy and ostracodrecords from Sidi Nasseur, Tunisia).

635

Paleoenvironmental and sea-level change of the Nile ValleyBasin (Egypt) at the Danian/Selandian transition

Jorinde Sprong1; Elisa Guasti2; Eliana Fornaciari3; Peter Schulte4;Mohamed Youssef5 & Robert P. Speijer1

1Department of Geography and Geology, K.U.Leuven, B-3001, Leuven, Belgiumum:[email protected]

2Fugro Robertson Limited, Llandudno, LL30 1SA North Wales, U.K.3Department of Geology, Palaeontology and Geophysics, University of Padua, Padova, Italy

4Institute for Geology and Mineralogy, University of Erlangen-Nürnberg,91054 Erlangen, Germany5Geology Department, Faculty of Science, South Valley University, 83523 Qena, Egypt

The Danian and Selandian are the two lowermost stages of the Paleogene.In their type region in Denmark a hiatus marks the Danian/Selandian (D/S)transition (~60 Ma). This level has been considered a sequence boundaryresulting from eustatic sea-level change or regional tectonics. If eustasy wasthe cause, then similar changes in sea-level should also have been recorded onother continental margins. Egypt provides great opportunities for studying theD/S transition, because lower Paleocene deposits are excellently exposed alonga neritic to upper bathyal depth transect across the Nile basin.

At the D/S transition, a prominent 5-25 cm thick dark-brown bedfrequently is intercalated in the monotonous marls and shales of theMaastrichtian-Paleocene Dakhla Formation in the Nile basin. This bed is richin coarse detritus, organic carbon and fish-remains, and shows anomalouslyhigh planktic/benthic foraminifera ratios (Speijer, 2003. GSA Special Paper.Geological Society of America, Boulder Colorado: 275-290). We providehigh-resolution micropaleontological, sedimentological, mineralogical, and stableisotope studies of four locations in the Nile basin (Gebel Duwi, Qreiya, Aweinaand Aras) across the D-S transition in order to understand stratigraphy,paleoenvironment, and sea-level changes. The studied intervals span part ofplanktic foraminiferal Zones P2-P3, corresponding to calcareous nannoplanktonZone NP4. Planktic foraminiferal assemblages show two main patterns acrossthe anomalous bed (P3a/P3b zonal boundary). Within this bed an increase ofAcarinina and Parasubbotina suggests lowered salinity and increased nutrientsupply through enhanced river discharge, causing stronger water columnstratification in the central part of the Nile basin (Qreiya and Aweina). In theeastern part of the basin (Duwi), flourishing of Morozovella and blooming of


FORAMS 2006


FORAMS 2006Paleoenvironmental and sea-level change of the Nile Valley Basin (Egypt)

at the Danian/Selandian transitionJorinde Sprong; Elisa Guasti; Eliana Fornaciari; Peter Schulte; Mohamed Youssef & Robert P. Speijer

small Prinsius martinii suggests increased upwelling during the D/S transition.The disappearance of outer neritic benthic foraminifera taxa at the end ofBiozone P3, including Angulogavelinella avnimelechi and Anomalinoidesaffinis, indicates shallowing (late HST). At the P3a/P3b zonal boundary invasionof opportunistic middle neritic Neoeponides duwi and disappearance of almostall other benthic taxa occurs likely as a response to eutrophic conditions andpoor seafloor oxygenation during the subsequent transgression. As sea-levelrose further, N. duwi disappeared and normal outer neritic assemblagesrecovered. Consequently, our results provide evidence for rapid sea-levelchanges across the D/S transition in Egypt. Moreover, our stratigraphic resultssuggest that the D/S marker bed in Egypt correlates well with a glauconiticmarker bed encountered in basinal sections in Tunisia (Van Itterbeeck et al.,submitted. Danian/Selandian boundary stratigraphy and ostracod recordsfrom Sidi Nasseur, Tunisia), which in turn correlates with the D/S boundary inthe type region of the Danish Basin (Clemmensen & Thomsen, 2005.Palaeogeography, Palaeoclimatology, Palaeoecology, 219 (3-4): 351-394).Therefore, the D/S sea-level changes may be of eustatic rather than of regionaltectonic origin.

637

Application of foraminiferal biostratigraphyto the assessment of submarine geohazards

Marco Aurélio Vicalvi & Renato Oscar Kowsmann

PETROBRAS-CENPES, Cidade Universitária, Ilha do Fundão, 21941-598Rio de Janeiro, RJ, Brazil

[email protected]

The safety of production facilities on the seafloor of the continental slopehas been a paramount concern of oil companies working in the deep offshoreenvironment. The continental slope region is characterized by steeper gradients,cohesive fine-grained sediments and strong geostrophic currents. Slide scars,erosional terraces and mass-movement deposits are common features inthis region.

Geohazard assessment is accomplished by integrating sea-floormorphology, structure and stratigraphy, obtained from geophysical data, withgeotechnical and sedimentological information obtained from direct sampling.Dating events of sediment instability is a critical aspect of this assessment.

At PETROBRAS, this dating is achieved by using the climaticallycontrolled biozonation of planktonic foraminifera for the Quaternary, tied to thestandard oxygen isotopic and sealevel curves. This biozonation is based mainlyon the relative abundance of the warm water Globorotalia menardii complex.The ratio of this complex with the cold water species Globorotalia inflataand Globorotalia truncatulinoides and the control of the appearance anddisappearance of the Pulleniatina complex provide a reliable control of theQuaternary climatic events.

The application of this methodology in the Southeast Brazil continentalslope has demonstrated that the great majority of the mass-movement eventsoccurred during glacial periods associated with low-stands of sea-level.


FORAMS 2006

638

The onset of northern hemisphere glaciations (Gelasian, latePliocene) as reflected in the North Sea Eridanos Delta

Kris Welkenhuysen1; Marloes Kloosterboer2; Lucas Lourens2;Roel Verreussel3 & Robert P. Speijer1

1Department of Geography and Geology, K.U.Leuven, 3001 Leuven, [email protected]

2Faculty of Geosciences, Utrecht University, 3508 TA Utrecht, Netherlands3TNO/NITG, 3508 TA Utrecht, Netherlands

In the North Sea basin, the base of the Gelasian (upper Pliocene) ischaracterized by an important turnover in different fossil groups. This turnoverreflects the first build ups of ice sheets in Scandinavia and the accompanyingblocking of the warm Proto-Gulf stream past Scotland. The presence of shallowgas in sediments of Gelasian age in the North Sea, initiated the retrieval ofplenty core material spanning this interval.

The upper Pliocene – lower Pleistocene succession is virtually continuousand very expanded, being located in the prograding part of the former Eridanosriver delta flowing from the Baltic region into the North Sea. The deposits arerich in various microfossil groups, providing excellent proxies for temperature,sea-level changes, nutrient availability, etc. The succession is well calibratedthrough magnetostratigraphic and biostratigraphic data. Cyclicity in the gammaray logs and palynologic data suggest 40 kyr obliquity cycles, linking variationsin surface water temperature to lithologic changes. The cycles correspond tomarine isotope stages 102 to 95. In the studied interval, two cold-warm cycles(isotope stages 98-95) have been recognized, with fine grained sedimentsrepresenting cold periods, and coarser grained sediments the warmer periods(Kuhlmann, 2004. Geologica Ultraiectina, 245: 205, Thesis, University ofUtrecht). By selecting multiple sets of samples from the cores (foraminifers,dinoflagellates, pollen, stable carbon and oxygen isotopes) we aim at obtainingbetter insight in the relationships between surface water temperature, nutrientavailability, paleodepths, changes in vegetation, etc. This research is focusedon high-resolution foraminiferal records of the lowermost climatic cycle (stages98-97) and it is part of an ongoing master study (to be completed Spring 2006),on quantitative foraminiferal records (P/B ratios and benthic foraminifera).The results from this study provide a first impression of benthic foraminiferalchanges on the slope of the Eridanos delta. The overall preservation of theforaminifera is fairly good, although some samples contain re-crystallized


FORAMS 2006


FORAMS 2006The onset of northern hemisphere glaciations (Gelasian, late Pliocene)

as reflected in the North Sea Eridanos DeltaKris Welkenhuysen; Marloes Kloosterboer; Lucas Lourens; Roel Verreussel & Robert P. Speijer

specimens. Occasionally severe dissolution occurred, judging from the fewpoorly preserved foraminifera remaining. Diversity in all sampllv:es is verylow, with only 2 to 9 species per 100 specimens >125 ìm. The dominant species(up to 95%) are Cassidulina laevigata and C. teretis. There is a strongcorrelation between the gamma-ray data (cold-warm cycles) and the occurrenceof Cassidulina spp. This genus constitutes up to 95% of the entire assemblagein cold periods and only 15-20% in warmer periods. Higher numbers of Buliminaaculeata, Elphidium spp. and Trifarina sp. are typical for the warmer periods.In the anticipation of culminating data it remains to be established to whichparameters (temperature, nutrients, sea level) are directly responsible for thetight relationship between the foraminiferal data and the orbital/lithological cycles.P/B ratios are very low throughout the whole range (average about 1% P),with an exception at the top of warm isotopic stage 95. These low values couldin part be due to dissolution of the smaller and thinner tests of planktonicforaminifera. However, smaller benthonic forms do not seem to have beenparticularly affected by dissolution. The semi-enclosed North Sea Basin wasnot a hospitable place for planktic foraminifera but also bottom life on the deltafront did not flourish during the Gelasian.

640

Environmental perturbations in the latest Maastrichtian based onplanktic foraminiferal assemblages from the Negev, Israel

Shlomit Yovel; S. Abramovich & Ch. Benjamini

Department of Geological and Environmental Sciences,Ben Gurion University of the Negev, P.O.B. 653, Beer Sheva 84105, Israel

[email protected]

Recent discoveries that Chicxulub impact considerably predated the K-T event, and was broadly coincident with a volcanism-induced greenhousewarming event, calls for clarification of the record of global change towardsthe K-T boundary. We focus here on biotic effects in the oceans in the lateMaastrichtian as reflected in changes in planktic foraminiferal faunas.

The hemipelagic section at Hor Hahar, Negev, Israel, was chosen forthis study. A relatively high sediment accumulation rate at Hor Hahar affordeda detailed evaluation of the timing of environmental change during the lateMaastrichtian, particularly during the last million years of the Maastrichtian.Samples were taken at 10-20 cm intervals, or on average one sample every 20kyr, for the last 3.3 Ma of the Maastrichtian, and planktic foraminifera wereidentified and counted. The planktic foraminiferal populations were found tobe typical for Tethyan outer shelf and upper slope pelagic environments.

The late Maastrichtian commences with the Pseudoguembelinahariaensis-Racemiguembelina fructicosa Zone (CF-3-4), represented by 15m of section, covering approximately 2.35 Ma. At the top of this zone, there isa distinct terminal bloom of Gansserina gansseri (8-15% of the faunalpopulation), after which it becomes extinct. This bloom is exceptional becauseglobotruncanids in the late Maastrichtian are much rarer (generally 30% less)than in the Early Maastrichtian. It is also identified in Tunisia and Egypt, butapparently absent in high latitude sections, and therefore represents an eventconfined to the tropical Tethys.

The next 9.4 m, representing 150 kyr, belong to the Pseudoguembelinapalpebra Zone (CF-2). The uppermost 8 m belong to the Plummeritahantkeninoides Zone (CF-1), estimated at 300 kyr. It is characterized by anextreme (up to 80%) bloom of Guembelitria spp. The massive occurrences ofGuembelitria in this interval indicate major environmental perturbations thatmay have been related to the greenhouse warming event near the end ofthe Maastrichtian.


FORAMS 2006

foraminifera as paleoceanographic and paleoclimatologic ... · 577 foraminifera as...

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