a multi-proxy analysis of late quaternary ocean and ... - cpby changes in the ventilation of both...

Clim. Past, 13, 1791–1813, 2017https://doi.org/10.5194/cp-13-1791-2017© Author(s) 2017. This work is distributed underthe Creative Commons Attribution 3.0 License.

A multi-proxy analysis of Late Quaternary ocean andclimate variability for the Maldives, Inner SeaDorothea Bunzel1, Gerhard Schmiedl1, Sebastian Lindhorst1, Andreas Mackensen2, Jesús Reolid1, Sarah Romahn1,and Christian Betzler11Center for Earth System Research and Sustainability (CEN), Institute for Geology,University of Hamburg, 20146 Hamburg, Germany2Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research,27568 Bremerhaven, Germany

Correspondence: Dorothea Bunzel ([email protected])

Received: 24 March 2017 – Discussion started: 3 April 2017Revised: 25 August 2017 – Accepted: 30 October 2017 – Published: 13 December 2017

Abstract. As a natural sediment trap, the marine sedimentsof the sheltered central part of the Maldives Inner Sea repre-sent an exceptional archive for paleoenvironmental and cli-mate changes in the equatorial Indian Ocean. To evaluatethe complex interplay between high-latitude and monsoonalclimate variability, related dust fluxes, and regional oceano-graphic responses, we focused on Fe /Al, Ti /Al and Si /Caratios as proxies for terrigenous sediment delivery and totalorganic carbon (TOC) and Br XRF counts as proxies for ma-rine productivity. Benthic foraminiferal fauna distributions,grain size and stable δ18O and δ13C data were used for eval-uating changes in the benthic ecosystem and changes in theintermediate water circulation, bottom water current velocityand oxygenation.

Our multi-proxy data record reveals an enhanced dust sup-ply during the glacial intervals, causing elevated Fe /Al andSi /Ca ratios, an overall coarsening of the sediment and anincreasing amount of agglutinated benthic foraminifera. Theenhanced dust fluxes can be attributed to higher dust avail-ability in the Asian desert and loess areas and its transport byintensified winter monsoon winds during glacial conditions.These combined effects of wind-induced mixing of surfacewaters and dust fertilization during the cold phases resultedin an increased surface water productivity and related organiccarbon fluxes. Thus, the development of highly diverse ben-thic foraminiferal faunas with certain detritus and suspensionfeeders was fostered. The difference in the δ13C signal be-tween epifaunal and deep infaunal benthic foraminifera re-veals intermediate water oxygen concentrations between ap-

proximately 40 and 100 µmol kg−1 during this time. The pre-cessional fluctuation pattern of oxygen changes resemblesthat from the deep Arabian Sea, suggesting an expansion ofthe oxygen minimum zone (OMZ) from the Arabian Sea intothe tropical Indian Ocean with a probable regional signal ofstrengthened winter-monsoon-induced organic matter fluxesand oxygen consumption further controlled by the varyinginflow intensity of the Antarctic Intermediate Water (AAIW).In addition, the bottom water oxygenation pattern of theMaldives Inner Sea reveals a long phase of reduced venti-lation during the last glacial period. This process is likelylinked to the combined effects of generally enhanced oxygenconsumption rates during high-productivity phases, reducedAAIW production and the restriction of upper bathyal envi-ronments in the Inner Sea during sea-level lowstands. Thus,our multi-proxy record reflects a close linkage between theIndian monsoon oscillation, intermediate water circulation,productivity and sea-level changes on orbital timescale.

1 Introduction

Sedimentation and biogeochemical processes in the tropicaland subtropical northern Indian Ocean are closely linked tothe intensity and seasonal changes of the Indian monsoonsystem. From June to October, the region is dominated bythe south-western (SW) monsoon, while the north-eastern(NE) monsoon operates from December to April (Wyrtki,1973; Schott and McCreary, 2001). During the SW monsoon,

Published by Copernicus Publications on behalf of the European Geosciences Union.

1792 D. Bunzel et al.: A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives

coastal and open-ocean upwelling results in maximum sur-face water productivity and related organic matter fluxes inthe Arabian Sea (Nair et al., 1989; Rixen et al., 1996). At thesame time, the South-west Monsoon Current (SMC) trans-ports high-saline surface waters from the Arabian Sea intothe equatorial region (Schott and McCreary, 2001). The SWsummer monsoon variability is strongly coherent over theprecessional band and reveals a close but lagged response toNorthern Hemisphere summer insolation maxima (Clemensand Prell, 2003). In comparison, during the NE winter mon-soon the ocean current system reverses and the North-eastMonsoon Current (NMC) transports lower-saline surface wa-ters from the Bay of Bengal into the western Indian Ocean.Thus, during the NE monsoon, elevated chlorophyll a con-centrations are mainly restricted to the Indian western coastand the Maldives area, while chlorophyll a strongly de-creases in the Arabian Sea at the same time (Sasamal, 2007;de Vos et al., 2014; NASA Goddard Space Flight Center,2014).

Evaluations of deep-sea sediment archives from the Ara-bian Sea deliver not only comprehensive information on thepacing and intensity of the Indian summer monsoon on or-bital timescales (Clemens and Prell, 1990, 2003; Clemenset al., 1991, 1996; Ziegler et al., 2010; Caley et al., 2011a),but also show variance within orbital bands to more rapidclimate shifts on suborbital timescales (Schulz et al., 1998;Altabet et al., 2002; Gupta et al., 2003; Pichevin et al., 2007;Böning and Bard, 2009; Caley et al., 2013; Deplazes et al.,2013). Records from the equatorial Indian Ocean provide amore diverse and partly contradictory picture since this re-gion is not only influenced by the summer and winter mon-soons but also by the strength of Indian Ocean EquatorialWesterlies (IEW), which are stronger during the intermon-soon seasons in spring and fall and are inversely related tothe Indian Ocean Dipole (Hastenrath et al., 1993; Beaufortet al., 2001). Variations in surface water properties at a siteclose to the Maldives platform revealed maximum produc-tivity at times of enhanced winter monsoon winds associ-ated with precessional maxima in ice volume (Rostek et al.,1997). By contrast, an upper bathyal benthic foraminiferalrecord from the Maldives Ridge suggests that Late Quater-nary changes in organic matter fluxes are either driven bysummer monsoon winds (Sarkar and Gupta, 2009) or linkedto changes in the IEW strength (Sarkar and Gupta, 2014).The precessional variability in productivity records from theequatorial Indo-Pacific Ocean has been attributed to the in-fluence of low-latitude insolation on the IEW strength andon the long-term dynamics of the El Niño–Southern Oscilla-tion (ENSO; Beaufort et al., 1997, 2001).

The seasonally reversing circulation pattern of the mod-ern monsoon system was established∼ 12.9 Ma, as indicatedby the onset of drift deposition in the Maldives Inner Sea(Betzler et al., 2016). However, early aeolian dust deposits atthe Maldives between ∼ 20 and 12.9 Ma can be attributed toa weak proto-monsoon when prevailing wind systems were

strong enough to transport dust material into the northern In-dian Ocean, but not sufficiently strong to promote the watercurrents that generate drift deposits (Aston et al., 1973; Guoet al., 2002; Grand et al., 2015; Betzler et al., 2016). Since theearly Miocene, the deposition of aeolian particles to the Mal-dives increased stepwise, coinciding with the onset of Asiandesertification derived from loess deposits in northern China(Guo et al., 2002; Betzler et al., 2016). On a regional scale,these changes in aridity were caused by various factors, in-cluding the Tibetan–Himalayan plateau uplift, which inten-sified 25–20 Ma and changed wind circulation patterns dueto the uplifted topography (Ruddiman and Kutzbach, 1989;Manabe and Broccoli, 1990; Harrison et al., 1992; Guo etal., 2002). However, little detailed information is availableabout the variability of aeolian dust delivery or its prove-nance and linkage to prevailing monsoon circulation patternsin the Maldives area since the Late Quaternary.

In addition to the aeolian influx, sea-level fluctuations andbottom currents played a significant role in the evolution ofthe sedimentary system of the Maldives (Betzler et al., 2009,2013a, 2016; Lüdmann et al., 2013). Relative sea-level high-stands caused a flooding of the carbonate platforms and anexport of shallow-water carbonate sediments into the adja-cent basins, whereas sea-level lowstands caused an exposureof the platforms and likely a strengthened restriction of theInner Sea area (Schlager et al., 1994; Paul et al., 2012; Lüd-mann et al., 2013; Betzler et al., 2013b, 2016). Moreover,previous studies have shown that during times of restrictedwater circulation in the Inner Sea, the deposition of organicmatter was likewise facilitated (Betzler et al., 2016). In re-cent times, the decay of organic matter in the water columnand the generally reduced ventilation of regional subsurfacewaters in the Indian Ocean results in the development ofa strong oxygen minimum zone (OMZ) between 200 and1200 m of water depth (Reid, 2003; Stramma et al., 2008).This oxygen depletion is fostered by the semi-enclosed na-ture of the northern Indian Ocean, the long pathway of in-termediate water from its main formation sites at 40◦S inthe central South Indian Ocean (Antarctic Intermediate Wa-ter, AAIW) and Indonesia (Indonesian Intermediate Water,IIW; Olson et al., 1993; You, 1998), and the contribution oflow-oxygen outflow waters from the Red Sea and the Per-sian Gulf (Jung et al., 2001; Prasad and Ikeda, 2001). TheOMZ extends from the Arabian Sea into the equatorial In-dian Ocean. While oxygen concentrations in the Arabian Seacan be as low as 0.1 mL L−1 (or 5 µmol kg−1; Reid, 2003),they still reach low oxic values of around 1 mL L−1 (or45 µmol kg−1) in 500 to 1000 m of water depth in the Mal-dives region (Weiss et al., 1983; Reid, 2003). Phases of anintensified OMZ in the northern Indian Ocean are controlledby changes in the ventilation of both intermediate- and deep-water masses (Schmiedl and Leuschner, 2005; Ziegler et al.,2010; Das et al., 2017) and by regional oxygen consump-tion responding to monsoon-driven upwelling and high sur-face productivity (e.g. Reichart et al., 1998; Den Dulk et al.,

Clim. Past, 13, 1791–1813, 2017 www.clim-past.net/13/1791/2017/

D. Bunzel et al.: A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives 1793

2000; Das et al., 2017). This addresses the ongoing debateson whether fluctuations of the OMZ in the Maldives area canbe linked to a basin-wide change in the composition of inter-mediate waters and/or super-regional oceanic processes, re-spectively. And what is the role of regional sea-level changesin this context?

Here we present a multi-proxy data set on the links be-tween the climate variability, ocean circulation, sedimenta-tion and biogeochemical processes of the Maldives InnerSea. Specifically, our study addresses the following ques-tions: (1) what impact did orbital-scale changes in the In-dian monsoon have on the dust fluxes and marine environ-ments of the Maldives? (2) How did global sea-level changesinfluence the sedimentation processes and benthic ecosys-tems of the Maldives Inner Sea? (3) Can we trace the influ-ence of changes in the configuration of intermediate waters,and how are these changes related to super-regional oceano-graphic processes? The Maldives Inner Sea is ideally situ-ated to answer these questions because it lies in the centralpart of the Indian Ocean and is therefore situated in a re-gion influenced by the different processes introduced above.The Maldives also appear as an ideal place to trace back pa-leoceanographic variations in time, as seismic surveys haveshown that the Maldives are comparable to a large naturalsediment trap with a continuous succession since the Neo-gene (Betzler et al., 2009, 2013a, b, 2016; Lüdmann et al.,2013).

2 Material and methods

2.1 Sediment cores and material descriptions

For this study, two sediment cores were retrieved from differ-ent sites in the Inner Sea of the Maldives (Fig. 1). The 5.97 mlong sediment core SO236-052-4 was obtained by means of agravity corer in the framework of R/V SONNE cruise SO236in August 2014, east of the North Ari Atoll in the centralpart of the Inner Sea (03◦55.09′ N; 73◦08.48′ E) from a wa-ter depth of 382 m. The 12.94 m long sediment core M74/4-1143 is a piston core from R/V METEOR cruise M74/4, ob-tained in 2007 from east of the Goidhoo Atoll (04◦49.50′ N;73◦05.04′ E) at a water depth of 387 m (Fig. 1). For compar-ison with the gravity core, this study is focused on the first6.00 m of core M74/4-1143.

The sediment of core SO236-052-4 consists of an al-ternation of non-lithified fine-grained ooze with abun-dant pteropods, sponge spicules, planktonic and benthicforaminifera, and echinoid remains, with minor otolites andfragments of gastropods and bivalves. There are some lo-cal intervals that present up to 4 cm of bioclast includingsolitary corals and thin-shelled bivalves. The entire succes-sion is intensely reworked by bioturbation. Just a few pri-mary structures, usually the main boundaries between fa-cies, are preserved (i.e. the sharp contacts at 2.35 m be-low sea floor, m b.s.f., and at 3.90 m b.s.f.). Discrete bur-

50

0

40

0

30

0

400

40

0

30

0

1 0 0 02 0 0 0

2 0 01 0 05 0 0

30

0

40

0

30

0

2 0 0 010 0

0

5 00

4 0 0

2000

10

00

5 0 0

0 °

2 °

4 °

6 °

7 3 °

SO236/052

M74/4-1143

SOUTH MALÉATOLL

MALÉ ATOLL

GOIDHOOATOLL

SOUTHMAALHOSMADULU

ATOLL

RASDHOOATOLL

ARI ATOLL

FELIDHE ATOLL

FAADHIPPOLHUATOLL

20 km

IndianOcean

MaldivesStudy area

N

N

5°0

0´

4°0

0´

7 3 ° 0 0 ´

IN

NE

R

SE

A

IN

NE

R

SE

A

(a)

(b)

(c)

(c)

Figure 1. Location maps of the Maldives archipelago in the IndianOcean (a, b) and the setting of the study area (c) (modified afterBetzler et al., 2013a), showing the location of sediment core M74/4-1143 in the Kardiva Channel and core SO236-052-4 in the centralpart of the Inner Sea (red circles).

rows are scarce. The succession recovered at site M74/4-1143 has been described by Betzler et al. (2013b). The coremainly consists of periplatform ooze containing planktonicforaminifera, pteropods, otoliths, mollusc remains, benthicforaminifera, sponge spicules, and echinoid debris. Down thecore, light and dark coloured greenish to olive grey intervalsalternate (Betzler et al., 2013b).

2.2 Geochemical analyses

Scanning X-ray fluorescence (XRF) element analysis of coreSO236-052-4 was carried out at the MARUM, Universityof Bremen, using an Avaatech XRF Core Scanner II. Ele-ment analysis was performed at 1 cm intervals using gener-ator settings of 50 kV (1.0 mA current), 30 kV (1.0 mA) and10 kV (0.2 mA) and a sampling time of 20 s per measure-ment. Raw data spectra were processed using the softwarepackage WIN AXIL. Element ratios (Fe /Al, Ti /Al, Si /Ca,Sr /Ca) were calculated and used for environmental interpre-tations following Martin et al. (1991), Zhang et al. (1993),Boyd et al. (2000), Gao et al. (2001), Lourens et al. (2001),Jickells et al. (2005), Itambi et al. (2009) and Croudace andRothwell (2015). Bromine (Br) XRF counts were used as an

www.clim-past.net/13/1791/2017/ Clim. Past, 13, 1791–1813, 2017


indicator of variability in the marine organic carbon (MOC)content (Ziegler et al., 2008; Caley et al., 2013).

The total inorganic carbon (TIC, calcium carbonate) andtotal organic carbon (TOC) contents of core SO236-052-4were measured at 5 cm spacing. The carbon content of thegrain size fraction < 63 µm was determined using a LECODR144 carbon analyser. All samples were freeze-dried. Sub-sequently, one subsample was measured at 1350 ◦C to ob-tain the total carbon (TC) content. A second subsample washeated to 550 ◦C for 5 h to remove the organic carbon priorto measurement in the LECO; this gave the TIC content. Thedifference between the TC and TIC contents is regarded asthe TOC content. The calcium carbonate contents were thencalculated from the total inorganic carbon content as follows:CaCO3 (%)= (TC−TOC)× 8.33, where 8.33 is the atomicproportion of carbon in CaCO3 (e.g. Müller et al., 1994; diPrimio and Leythaeuser, 1995; Romero et al., 2006).

2.3 Grain size analyses

For bulk grain size analysis, core SO236-052-4 was sampledequidistantly (1.5 cm3 every 1 cm). Samples were wet-sieved(2000 µm) to remove very coarse particles and subsequentlysuspended in water with the addition of a 0.05 % solution oftetrasodium diphosphate decahydrate as a dispersant.

The mean grain size of the non-carbonate fraction between10 and 63 µm, the sortable silt, has been shown to be a reli-able proxy for paleocurrent strength in predominantly silici-clastic sediments (Manighetti and McCave, 1995; McCaveet al., 1995a, b; Hall et al., 1998; Bianchi et al., 1999; Mc-Cave and Hall, 2006). The method makes use of the non-carbonate fraction only and is therefore expected to be unaf-fected by primary carbonate production and burial diagene-sis. Samples for the determination of the sortable silt com-ponent (ca. 20 cm3 each) were taken equidistantly (in coreM74/4-1143 at 5 cm intervals down to 1 m of core depth andat 10 cm intervals underneath, and at 5 cm downcore inter-vals in core SO236-052-4). Subsequently to wet-sieving, thefraction < 63 µm was cooked in H2O2 to remove the organicportion and treated with 1 M Ca3COOH to dissolve the car-bonate. Biogenic opal was removed with 2 M NaHCO3. Theremainder was dispersed in water for grain size determina-tion.

Bulk grain size and sortable silt measurements were doneusing a Helos KF Magic Laser particle size analyser andmeasuring ranges of either 0.5/18–3500 µm (for bulk grainsize) or 0.25–87.5 µm (for the non-carbonate fraction). To en-sure the accuracy of the measurements and the absence of along-term instrumental drift, an in-house grain size standardwas measured regularly. Grain size statistics are based on thegraphical method (Folk and Ward, 1957) and were calculatedusing the software GRADISTAT (Blott and Pye, 2001).

2.4 Foraminiferal faunal and stable isotope analyses

For stable isotope analyses, core SO236-052-4 was sam-pled at 5 cm spacing, and for benthic foraminiferal fau-nal analysis at 10 cm spacing. All samples were wet-sievedover a 63 µm screen and the residues were subsequentlydried at 38 ◦C. The benthic foraminiferal analysis was car-ried out on the > 125 µm size fraction and based on allocatesplits in order to obtain approximately 300 tests. Genus andspecies identifications were mainly based on Loeblich andTappan (1988), Hottinger et al. (1993), Jones (1994), Debe-nay (2012), Milker and Schmiedl (2012) and Holbourn etal. (2013). The genera Cymbaloporetta and Tretomphaloideswere summarized as meroplanktonic benthic foraminifera(BF) since they are known to have planktonic drift phasesas part of their dispersal strategy (Banner et al., 1985; Alve,1999). For analysis based on the test material, all individualsof the foraminiferal orders Astrorhizida, Lituolida and Tex-tulariida were summarized as agglutinated BF.

Benthic foraminiferal assemblages were defined by Q-mode principal component analysis (PCA) with varimax ro-tation using the software SYSTAT version 5.2.1. FollowingSchmiedl et al. (1997), only foraminiferal taxa with per-centages of ≥ 1 % in at least one sample and/or taxa whichoccur at least in two samples were used for the statisticalanalysis. Loadings ≥ 0.5 were defined as significant (Back-haus et al., 2008). The Shannon–Wiener diversity indexH (S)was calculated after Murray (2006) based on the functionH (S)= (−1)

∑Si=1pi×ln(pi), where S is the species number

and pi is the relative abundance of the ith species.Stable oxygen and carbon isotope records were gener-

ated for planktonic and benthic foraminifera. Approximately10 tests of the planktonic foraminifer Globigerinoides ru-ber (white) were selected from the 250–350 µm size frac-tion of core SO236-052-4. Stable isotope data for G. ru-ber (white) of core M74/4-1143 were taken from Betzleret al. (2013b). In addition, approximately 2–5 tests of theepibenthic foraminifera Cibicides mabahethi and the deep in-faunal species Globobulimina affinis s.l. were selected fromthe size fraction > 125 µm of core SO236-052-4. Stable oxy-gen and carbon isotope analyses were performed with aFinnigan MAT253 gas mass spectrometer coupled to the au-tomatic carbonate preparation device Kiel IV. The mass spec-trometer was calibrated to the PDB scale via internationalstandard NBS19, and results are given in δ notation versusVPDB. Based on measurements of an internal laboratorystandard (Solnhofen limestone) together with samples overa 1-year period, precision was better than 0.08 ‰ for δ18Oand 0.06 ‰ for δ13C.

For core SO236-052-4 changes in bottom water oxygenconcentrations were estimated based on the δ13C differencebetween the epifaunal (C. mabahethi = Cm) and deep in-faunal (G. affinis s.l. = Ga) benthic foraminifera using thefunction 1δ13C= 0.00772×[O2] + 0.41446, wherein [O2]concentrations between 55 and 235 µmol kg−1 have shown



a strong linear relationship between bottom water [O2] and1δ13C (Hoogakker et al., 2015). We also applied this func-tion to the low [O2] values ([O2] < 55 µmol kg−1) becausesuch a relationship may also exist for low [O2] valuesand 1δ13C, although this is not investigated by Hoogakkeret al. (2015). For [O2] reconstruction two δ13C values ofcore SO236-052-4 (at 0.17 and 130.92 ka) have not beenconsidered due to the weak validity in the δ13CGa signal.For comparison, oxygen concentration changes in a deep-sea sediment core from an Arabian Sea site (GeoB3004;1803 m of water depth) were taken from Schmiedl and Mack-ensen (2006). These data are based on the difference betweenthe epifaunal Cibicidoides wuellerstorfi (Cw) and G. affinis(Ga). Further, the δ13C gradient between G. ruber (white;Gr) and C. mabahethi (Cm) of core SO236-052-4 was esti-mated to assess the sea surface and bottom water stable car-bon isotope difference and water column mixing.

2.5 Spectral analyses

For the evaluation of periodic temporal variability,Blackman–Tukey spectral analyses were performed forTOC, Fe /Al and Ti /Al ratios, Br XRF counts of coreSO236-052-4, the reconstructed oxygen concentrationsof core SO236-052-4 and Arabian Sea core GeoB3004(Schmiedl and Mackensen, 2006), and the 1-insolation at30◦ N. The analyses were carried out with the AnalySeriessoftware 2.0 version 05/2005 (Paillard et al., 1996). Prior tothe analyses, the records of SO236-052-4 were rescaled with1t = 2 ka (TOC, oxygen) and 1t = 0.5 ka (Fe /Al, Ti /Al,Br XRF counts), and the oxygen record of GeoB3004 wasrescaled with 1t = 1 ka.

2.6 Radiocarbon dating and compilation of the agemodel

Accelerator mass spectrometry (AMS) radiocarbon dat-ing was carried out at the Beta Analytic RadiocarbonDating Laboratory on mixed surface-dwelling planktonicforaminifera from 35 cm, 80 cm and 140 cm of depth incore SO236-052-4 (Table 1). Due to the contrasting avail-able reservoir age correction values (varying between 301and 544 years; Dutta et al., 2001; Southon et al., 2002), theAMS 14C ages were corrected for the global reservoir ageof 400 years in order to minimize potential errors and con-verted to calendar years using the radiocarbon calibrationprogram CALIB (version 7.0.4; Stuiver and Reimer, 1993)and the calibration curve Marine13 (Reimer et al., 2013).Additional age tie points were derived from graphical corre-lation of the benthic δ18O record of core SO236-052-4 withthe LR04 standard benthic stack (Lisiecki and Raymo, 2005)using the software AnalySeries 2.0 (version 5/2005; Paillardet al., 1996). The age model of core M74/4-1143 (Betzleret al., 2013b) was revised by graphical correlation with theplanktonic δ18O record of core SO236-052-4 (Fig. 2).

3 Results

3.1 Age model and sedimentation rate

Based on the radiocarbon ages and the alignment of thestable oxygen isotope stratigraphy, core SO236-052-4 iscomprised of sediments from the past 207.7 kyr (Fig. 2).The top 6 m of sediment core M74/4-1143 is comprisedof the past 242.3 kyr. Average sedimentation rates variedbetween 3.5 cm ka−1 in SO236-052-4 and 4.4 cm ka−1 inM74/4-1143. Maximum sedimentation rates occurred dur-ing interglacial intervals, with 6.8 cm ka−1 (SO236-052-4) and 8.4 cm ka−1 (M74/4-1143) for the Eemian and7.1 cm ka−1 (SO236-052-4) to 3.0 cm ka−1 (M74/4-1143)for the Holocene (Fig. 2).

3.2 Foraminiferal stable oxygen and carbon isotoperecords

The δ18O values of core SO236-052-4 vary between −3.09and −0.68 ‰ in the planktonic G. ruber, between 0.91 and2.51 ‰ in the epibenthic C. mabahethi, and between 1.10 and5.02 ‰ in the deep infaunal G. affinis (Fig. 3). Generally, theδ18O records reveal a consistent picture with relatively highervalues during glacial intervals and lower values during in-terglacial intervals. The δ13C values of core SO236-052-4vary between 0.12 and 1.25 ‰ in G. ruber, between 0.22 and0.91 ‰ in C. mabahethi, and between −0.84 and 0.27 ‰ inG. affinis (Fig. 3). Despite considerable short-term variabil-ity, all records reveal a stepwise increase in δ13C values withlowest values during the Marine Isotope Stage (MIS) 6 andhighest values during the Holocene (Fig. 3).

Considering the past bottom water oxygen concen-tration reconstruction for core SO236-052-4 by us-ing the 1δ13CCm-Ga estimation, the [O2] values var-ied between 10.43 µmol kg−1 (=̂ 0.50 ‰ 1δ13CCm-Ga)and 139.45 µmol kg−1 (=̂ 1.49 ‰ 1δ13CCm-Ga) with aver-age values of approximately 67.10 µmol kg−1 (=̂ 0.93 ‰1δ13CCm-Ga). In addition, a long-lasting oxygen depletionwas observed, starting from the end of MIS 5 to the endof MIS 3 (duration of ∼ 50 kyr), with average oxygen con-centrations of approximately 52.50 µmol kg−1. The oxygenconcentration of sediment core GeoB3004 (western Ara-bian Sea) showed an average oxygen content of approxi-mately 81.75 µmol kg−1 (=̂ 1.05 ‰ 1δ13CCw-Ga), with vari-ations between 22.04 µmol kg−1 (=̂ 0.58 ‰ 1δ13CCw-Ga)and 133.87 µmol kg−1 (=̂ 1.45 ‰ 1δ13CCw-Ga) (Schmiedland Mackensen, 2006). Spectral analyses of the oxygenrecords of cores SO236-052-4 and GeoB3004 reveal strongpower in the precession band (Fig. 4a). Error estimationsat the 95 % confidence level on the power spectrum of theoxygen records are 0.49


Table 1. Accelerator mass spectrometry (AMS) radiocarbon dating results based on mixed surface-dwelling planktonic foraminifera (Gr =Globigerinoides ruber, white; Gs = Globigerinoides sacculifer) from 35, 80 and 140 cm of sediment depth in core SO236-052-4. Conven-tional radiocarbon ages were calibrated using the radiocarbon calibration program CALIB (version 7.0.4; Stuiver and Reimer, 1993) and thecalibration curve Marine13 (Reimer et al., 2013).

No. Sample ID Lab ID Material Core depth 12C/13C 14C age Calibrated age (1R0)[m b.s.f.] o/oo ya BP cal BP (2 s ranges, 95.4 % probability)

range rel. area median of[years] u. distr. prob. [ka]

1 SO236-052-035 Beta-418574 Gr, Gs 0.35 +1.4 7940± 30 8330–8480 1.00 8.4± 0.082 SO236-052-080 Beta-418575 Gr, Gs 0.80 +1.6 12890± 40 14310–15020 1.00 14.7± 0.363 SO236-052-140 Beta-418576 Gr, Gs 1.40 +1.8 23930± 100 27480–27850 1.00 27.7± 0.19

-0.8

-1.6

-2.4

-3.2

18O

plan

ktic

0 50 100 150 200 250Age [ka BP]

600

400

200

0

Dep

th [c

m]

3.5 cm ka- 1

2.2 cm ka- 1

6.8 cm ka- 1

1.3 cm ka- 1

4.6 cm ka- 1

7.1 cm ka- 13.6 cm ka- 1

2.6 cm ka- 1

2.3 cm ka- 1

2.2 cm ka- 1

MIS: 1 2 3 4 5 6 7

(a)

(b)

SO236-052-4M74/4-1143

Cal. 14C age [ka BP]3.0 cm ka- 1

1.7 cm ka- 1

8.4 cm ka- 1

5.9 cm ka- 13.8 cm ka- 1

2.4 cm ka- 1

2.9 cm ka- 1

Figure 2. Full-resolution stable oxygen isotope records of theplanktonic foraminifer G. ruber (a) and age–depth plots for the sed-iment cores SO236-052-4 (light blue) and M74/4-1143 (grey). Or-ange triangles indicate radiocarbon dates and circles indicate agecontrol points derived from correlation with the LR04 benthic iso-tope stack of Lisiecki and Raymo (2005). Sedimentation rates arederived from linear interpolation between age data. MIS denotes themarine stable oxygen isotope stages.

glacial period at site SO236-052 is not observed at siteGeoB3004.

The 1δ13CGr-Cm calculation for site SO236-052 showedmaximum differences in the planktonic and epibenthic sta-ble δ13C values (0.68 ‰) during the full interglacial periodsof MIS 7, 5 and 1, coinciding with global sea-level high-stands. Accordingly, minimum differences (−0.54 ‰) weredocumented for the glacial periods MIS 6 and 2 and sea-levellowstands.

3.3 Sedimentological and geochemical records

The detailed sedimentological and geochemical data of coreSO236-052-4 reveal a glacial–interglacial pattern but alsoconsiderable short-term variability (Figs. 4c–f, 5). Sortablesilt records are available for both sites and in generalthey show coarser means during interglacial times, up to14 µm during the Holocene and >13 µm during the Eemian(Figs. 5a, 6). However, absolute values and variability aremuch greater in core M74/4-1143, which is located in thedrift of the Kardiva Channel (see Betzler et al., 2013b) com-pared to core SO236-052-4 from the more sheltered part ofthe Inner Sea. In core M74/4-1143, sortable silt shows anincrease towards the MIS 6–5 transition (Termination II) fol-lowed by generally elevated values during the Eemian (maxi-mum 27.17 µm), whereas there is much less variability at thesame time in the data from core SO236-052-4. Both coresshow a coarsening of the sortable silt towards the MIS 1.

Bulk mean grain size shows a pronounced glacial–interglacial variability of up to 57 µm during the MIS 2 andMIS 6 and values between 10 and 30 µm for the remainder(Fig. 5a). The finest sediments occur during the early MIS 5and the MIS 1 (10 µm).

The total organic carbon (TOC) and calcium carbon-ate (CaCO3) contents of core SO236-052-4 reveal reverseglacial–interglacial trends with maximum TOC content dur-ing glacial and maximum carbonate contents during inter-glacial periods. TOC varies between 0.85 wt % (interglacial)and 2.06 wt % (glacial), whereas the carbonate content variesbetween 77.03 wt % (glacial) and 89.40 wt % (interglacial)(Fig. 5b).



-1

-2

-318

Opl

ankt

ic

5

4

3

2

1

18O

bent

hic

-1

0

1

13

0 50 100 150 200Age [ka BP]

-0.5

0

0.5

1

1.5

13

MIS: 1 2 3 4 5 6 7

G. ruberC. mabahethiG. affinis s.l.

13CGr-Cm13CCm-Ga

(a)

(b)

(c)

Figure 3. (a, b) Stable oxygen and carbon isotope records of planktonic and benthic foraminifera in sediment core SO236-052-4. Displayedare the planktonic species G. ruber (light blue), the epibenthic species C. mabahethi (dark blue) and the deep infaunal species G. affiniss.l. (red). Also shown are the full-resolution data of the 1δ13CGr-Cm and 1δ13CCm-Ga signals (c) as a result of the difference between the1δ13C values of G. ruber and C. mabahethi, as well as C. mabahethi and G. affinis s.l. MIS denotes the marine stable oxygen isotope stages.

Both the Fe /Al and Ti /Al records show similar pat-terns with relatively higher values during glacial periodsand slightly increasing values towards today. The Br XRFcounts and the Si /Ca ratio show similarly distinct glacial–interglacial patterns comparable to the TOC record, with gen-erally higher values during glacial periods and lower val-ues during interglacial periods (Fig. 5d). Further, the Si /Carecord is characterized by an abrupt and short-lasting max-imum at Termination II (Fig. 5d). Inverse patterns are ob-served for the Sr /Ca record, which follows the inversedδ18O curve and shows higher values during interglacial andlower values during glacial periods (Fig. 5d).

Spectral analyses of TOC, Ti /Al and Br reveal substantialbut considerably weaker variability in the precession bandwhen compared to the reconstructed oxygen records (Fig. 4c,e). The Fe /Al record lacks substantial precessional variabil-ity but is rather dominated by long-term glacial–interglacialchanges (Fig. 4e). Error estimation at the 95 % confidencelevel on the power spectra of TOC, Fe /Al, Ti /Al and Br is0.49


100 ka 23 ka

0 0.05 0.1 0.15 0.20

0.2

0.4

0.6

0.8

1

Nor

mal

ized

pow

er

Bandwidth

[O2] SO236/052[O2] GeoB3004

(a)

0 50 100 150 200

200

240

280

320

360

-2]

40

60

80

100

120

O2

[µm

ol k

g-1 ]

(b)

0 0.05 0.1 0.15 0.20

0.2

0.4

0.6

0.8

1

Nor

mal

ized

pow

er

Bandwidth

Br XRF countsTOC

(c)

200

240

280

320

360

-2]

0 50 100 150 2000.8

1.2

1.6

2

TOC

[wt.

%]

600

800

1000

Br X

RF

coun

ts

(d)

0 0.05 0.1 0.15 0.2Frequency [cycles ka-1]

0

0.2

0.4

0.6

0.8

1

Nor

mal

ized

pow

er

Bandwidth

Ti/AlFe/Al

(e)

200

240

280

320

360

-2]

0

20

40

60

80

Fe/A

l0 50 100 150 200

Age [ka BP]

0

4

8

12

Ti/A

l

(f)

Figure 4. Records and normalized Blackman–Tukey power spectra of (a, b) the oxygen reconstructions of core SO236-052-4 (blue) andGeoB3004 (purple), (c, d) productivity proxies TOC (green) and Br XRF counts (pink), and (e, f) dust proxies Ti /Al (light blue) and Fe /Al(dark blue) in comparison to the 1-insolation at 30◦ N (black dashed line). Grey bars indicate the 23 kyr period of the 1-insolation and itsbandwidth. Oxygen and TOC records represent 5-point running averages; Br XRF counts and Ti /Al and Fe /Al records represent 15-pointrunning averages.

3.4 Benthic foraminiferal record

In sediment core SO236-052-4, a total of 256 differentbenthic foraminiferal species were distinguished, with 51to 93 different species per sample. The diversity H (S)is relatively high and varies between 3.3 and 4.0, witha slight long-term decrease towards today (Fig. 7a). Theforaminiferal fauna at the Inner Sea is dominated by hya-line taxa. In comparison, agglutinated individuals were lessabundant, but with increasing relative abundances up to ap-proximately ≥ 20 % of the entire fauna during the glacial pe-riods (Fig. 8e). The three-component model of the Q-modePCA explains 89.14 % of the total variance (Table 2). Assem-

blage 1 (PC1) explains 31.54 % of the total variance and isdominated by Neouvigerina proboscidea and Discorbinellaaraucana, with Hyalinea inflata, Cymbaloporetta squam-mosa, Bulimina marginata and Rosalina vilardeboana as as-sociated taxa (Table 2). This assemblage occurred mainlyduring the late MIS 7 and 5 and is less pronounced dur-ing MIS 4 to early MIS 2 (Fig. 7b). Assemblage 2 (PC2)explains 30.54 % of the total variance and is dominated byCibicides mabahethi, with Discorbinella bertheloti, Sipho-generina columellaris, Gyroidina umbonata, Reophax sp., H.inflata and D. araucana as associated taxa (Table 2). As-semblage 2 occurred mainly during MIS 6 and 1 (Fig. 7c).



MIS 2 MIS 4 MIS 6

0.8

1.2

1.6

2

TOC

[wt.

%]

0 50 100 150 200

88

84

80

76

CaC

O3 [

wt.

%]

MIS 2 MIS 4 MIS 6

0 50 100 150 200

Age [ka BP]

5

10

15

20

Ti/A

l

0

50

100

150

Fe/A

l

MIS 2 MIS 4 MIS 6

10

20

30

Sorta

ble

silt

[µm

]

0 50 100 150 2000

20

40

Bulk

sed

imen

t [µm

]

12

13

14

Sorta

ble

silt

[µm

]

MIS 2 MIS 4 MIS 6

600

800

1000

Br (

XR

F co

unts

)

0

0.005

0.01

Si/C

a

0 50 100 150 200

Age [ka BP]

0.008

0.01

0.012

0.014

Sr/C

a

(a) (b)

(c) (d)

SO236/052M74/1143

Figure 5. Sedimentological and geochemical records of sediment core SO236-052-4 from the central part of the Maldives Inner Sea.(a) Sortable silt (black) in comparison with the data of core M74/4-1143 (brown) and bulk sediment (grey) mean values, (b) total organiccarbon (TOC) (dark green) and calcium carbonate (light green) content of the sediment, (c) iron (dark blue) and titanium (light blue) inrelation to the aluminium XRF counts and (d) bromine XRF counts (pink), and silicon (dark purple) and strontium (light purple) in relationto the calcium XRF counts. Thin lines represent full-resolution data, bold lines in panels (a) and (b) indicate 5-point running averages,whereas all XRF counts in panels (c) and (d) are displayed as 15-point running averages (bold lines). MIS denotes the marine stable oxygenisotope stages.

Assemblage 3 (PC3) explains 27.06 % of the total varianceand is dominated by N. proboscidea and Hoeglundina ele-gans, with D. bertheloti, Cibicidoides subhaidingeri, Discor-bis sp., Spiroplectinella sagittula s.l. and C. mabahethi as as-sociated taxa (Table 2). Assemblage 3 occurred during MIS 4to 2 (Fig. 7d). The distribution of the most important benthicforaminiferal species, which characterize the three faunal as-semblages, is displayed in Fig. 7e–g. The most abundantspecies include C. mabahethi (maximum relative abundanceof ∼ 17 % during MIS 6), the weakly hispid N. proboscidea(maximum of ∼ 16 % at the end of MIS 5) and D. araucana(maximum of ∼ 11 % during the onset of MIS 5). Mero-planktonic benthic foraminifera (genera Cymbaloporetta andTretomphaloides) occurred in elevated numbers during inter-glacial periods (maximum of 10.88 %), particularly duringMIS 5 (Figs. 6d, 7e).

4 Discussion

4.1 Dust fluxes, marine productivity and monsoonvariability

The Ti /Al and Fe /Al in core SO236-052-4 were used asproxies for terrigenous sediment delivery, reflecting changesin the deposition of aeolian dust and thus in the aridity of thehinterland as the source area of the dust (Zhang et al., 1993;Lourens et al., 2001; Itambi et al., 2009). Local sources ofFe-rich sediments can be excluded since the sediments of theMaldives archipelago and adjacent shallow- to deep-waterenvironments are characterized by carbonates comprised ofreef and lagoon carbonates of the islands and pelagic deep-water carbonates (Betzler et al., 2013b; Reolid et al., 2017).This is also reflected by the calcium carbonate content, whichis very high at site SO236-052 throughout the past 200 kyr(Fig. 5b). Studies on modern aerosols in the North Pacific re-



MIS: 1 2 3 4 5 6 7

10

20

30

Sorta

ble

silt

[µm

]

12

13

14

Sorta

ble

silt

[µm

]

0 50 100 150 200 250Age [ka BP]

0

4

8

12

Mer

opla

nkto

nic

BF

[%]

(b)NW Kardiva Channel

(M74/1143; 387 m)

(c)Central Inner Sea

(SO236/052; 382 m)

(d)Centr. Inner Sea

(SO236/052;382 m)

5

4

3

18O

LR04

2.5

2

1.5

1

18O

Cm

(a)

Bottom watercurrent intensity

+

-

Sea level

+

-

Figure 6. (a) Epibenthic stable oxygen isotope record of core SO236-052-4 (dark blue) in comparison with the LR04 benthic stable isotopestack (orange; Lisiecki and Raymo, 2005). (b, c) Comparison of the sortable silt records of sediment cores M74/4-1143 and SO236-052-4 and(d) relative abundance of meroplanktonic benthic foraminifera (BF; including the genera Cymbaloporetta and Tretomphaloides) in sedimentsof core SO236-052-4. Thin lines represent full-resolution data, bold lines indicate 5-point running averages. MIS denotes the marine stableoxygen isotope stages.

Table 2. Species composition of benthic foraminiferal assemblages.Principal component number, dominant (bold) and important asso-ciated species with principal component scores (Q-mode) and ex-plained variance in percent of total variance are given.

Q-mode principal Species Scores Explainedcomponents variance [%]

PC1 Neouvigerina proboscidea 5.812 31.54Discorbinella araucana 3.948Hyalinea inflata 2.562Cymbaloporetta squammosa 1.913Bulimina marginata 1.729Rosalina vilardeboana 1.595

PC2 Cibicides mabahethi 7.466 30.54Discorbinella bertheloti 1.756Siphogenerina columellaris 1.622Gyroidina umbonata 1.589Reophax sp. 1.387Hyalinea inflata 1.214Discorbinella araucana 1.109

PC3 Neouvigerina proboscidea 4.608 27.06Hoeglundina elegans 3.952Discorbinella bertheloti 3.004Cibicidoides subhaidingeri 2.311Discorbis sp. 2.161Spiroplectinella sagittula s.l. 1,808Cibicides mabahethi 1,084

gion indicate that most of the oceanic iron input is derivedfrom atmospheric transport after mobilization from the cen-tral Asian deserts and Chinese loess plateau (Duce and Tin-dale, 1991). Accordingly, the most likely dust sources for theobserved Fe in the sediments of the Maldives are the Indiansubcontinent and the Asian desert and loess areas (Roberts etal., 2011), although a minor contribution from north-easternAfrica and Arabia cannot be excluded (Chauhan and Shukla,2016). The latter regions rather have been identified as ma-jor dust sources in the Arabian Sea based on specific claymineral composition and the magnetic susceptibility of thelithogenic fraction (deMenocal et al., 1991; Sirocko andLange, 1991). North-west winds over the Arabian Peninsulablow dust into the Arabian Sea when the Arabian source ar-eas undergo aridification during high-latitude ice cover (de-Menocal et al., 1991; Sirocko and Lange, 1991). In the north-western Arabian Sea, associated dust fluxes are in phase withmaximum ice volume but also vary in the precessional band,suggesting a likewise strengthening of the SW summer mon-soon as an important regional driver (Clemens and Prell,1990; Clemens et al., 1996). In contrast, in the eastern equa-torial Indian Ocean the majority of dust is transported via theNE monsoon, coinciding with the prevailing wind system,which blows during Northern Hemisphere winter. Therefore,elevated Fe /Al and Ti /Al ratios at site SO236-052 indicate



3.2

3.6

4

Div

ersi

ty H

(S)

0

0.5

1

Load

ings

Q-P

C 1

(3)

Assemblage 1

0

0.5

1

Load

ings

Q-P

C 2

(3)

Assemblage 2

0

0.5

1

Load

ings

Q-P

C 3

(3)

Assemblage 3

0

4

8

12

D. a

rauc

ana

Mer

opla

nkto

nic

BF

B. m

argi

nata

0

8

16

C. m

abah

ethi

H. i

nfla

taG

. um

bona

ta

0

8

16

N. p

robo

scid

eaH

. ele

gans

C. s

ubha

idin

geri

0 50 100 150 200Age [ka BP]

1 2 3 4 5 6 7MIS:

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Figure 7. Comparison of benthic foraminiferal faunal records of core SO236-052-4 from the central part of the Maldives Inner Sea.(a) Shannon–Wiener diversity index H (S), (b–d) Q-mode benthic foraminiferal assemblages, including the N. proboscidea and D. arau-cana fauna (assemblage 1), the C. mabahethi fauna (assemblage 2), and the N. proboscidea and H. elegans fauna (assemblage 3). Loadings≥ 0.5 are defined as significant after Backhaus et al. (2008). (e–g) Distribution of selected important and associated benthic foraminiferaltaxa, given in percent. The meroplanktonic benthic foraminifera (BF) are comprised of the genera Cymbaloporetta and Tretomphaloides.

the combined effects of enhanced glacial dust availability inthe source areas and dust transport to the Maldives with gen-erally strengthened NE monsoon winds during the glacial in-tervals of MIS 6 and MIS 4–2. On a global scale, the gener-ally colder and drier glacial conditions resulted in a twofoldto fivefold increase in dust fluxes (Maher et al., 2010).

The observed response of the winter circulation in theMaldives to glacial conditions is in line with the finding ofa general strengthening of the NE Indian monsoon after theinitiation of the Northern Hemisphere glaciation (Gupta andThomas, 2003). But our dust proxies show little (Ti /Al) tono (Fe /Al) variability at the precessional band (Fig. 4e),which should be expected if the dust fluxes were directlyproportional to the intensity of the winter monsoon (Caleyet al., 2011a, b). For a statistically more robust evaluationof the full orbital variability (including the long-wave com-ponents) considerably longer time series would be required.Nevertheless, graphical comparison of our data series reveals

a dominant eccentricity component in the dust proxies withpronounced glacial-to-interglacial changes, suggesting a linkto high-latitude climate and environmental changes (Fig. 8).Therefore the dust records of the Maldives Inner Sea aremainly driven by the generally enhanced dust availabilityduring glacial intervals. As a major dust source, the Chineseloess plateau is strongly influenced by the East Asian mon-soon (EAM). During the Late Quaternary, EAM and relatedvegetation changes are characterized by predominant eccen-tricity cycles associated with the advance and retreat of theboreal ice sheets (Ding et al., 1995; Liu et al., 1999; Sunet al., 2006; Hao et al., 2012). Our conclusion is also in linewith the lithogenic flux reconstructions from the Arabian Sea(e.g. site ODP722; Clemens et al., 1996), which show strik-ing changes on the glacial-to-interglacial timescale (in theeccentricity band) and suggest a close relation between high-latitude climate and the aridity of the dust source areas. Onthe Chinese loess plateau, the onset of glacial conditions led



MIS: 1 2 3 4 5 6 7

200

240

280

320

30°

N [W

m-2

]

1

1.2

1.4

1.6

1.8

TOC

[wt.

%]

600

700

800

900

1000

Br X

RF

coun

ts

20

30

40

50

60

70

Fe/A

l

12

16

20

24

Agg

lutin

ated

BF

[%]

0.6

0.8

1

Load

ings

Q-P

C

0 50 100 150 200 250Age [ka BP]

Assemblage 3 Assemblage 2

(a)

(b)

(c)

(d)

(e)

(f)

Indi

an m

onso

on

Arid,NE winds

Humid,SE winds

Dus

t sup

ply

+-

Pro

duct

ivity

+-

Weaker NH radiation Weaker NH radiation

Figure 8. Variation in the insolation difference between the June and December solstice at 30◦ N (after Laskar et al., 2004; calculated withAnalySeries 2.0: Paillard et al., 1996) (a) in graphical correlation with geochemical and benthic foraminiferal productivity records of coreSO236-052-4. (b) Total organic carbon (TOC) content and (c) bromine as derived from XRF scanning count data as a tracer for marine organiccarbon (MOC), (d) Fe /Al ratio and (e) relative abundance of agglutinated benthic foraminifera as an indicator for enhanced dust supply.(f) Principal components (PCs) show the C. mabahethi fauna (assemblage 2) and N. proboscidea and H. elegans fauna (assemblage 3). Thiscomparison reveals coherent glacial-to-interglacial changes in all proxy records with elevated values during glacial stages MIS 6 and MIS 4–2 and during a weaker Northern Hemisphere solar radiation amplitude (yellow bars). Thin lines represent full-resolution data, bold lines inpanels (b) and (e) indicate 5-point running averages and bold lines in panels (c) and (d) indicate a 15-point running average. MIS denotesthe marine stable oxygen isotope stages.

to an abrupt increase in atmospheric dust loadings (Zhanget al., 2002), suggesting the operation of climate–vegetationfeedbacks. Enhanced deposition of terrestrial particles at siteSO236-052 led to a general coarsening of the glacial sed-iment and fostered the distribution of agglutinated benthicforaminifera, which reached a relative abundance of up to∼ 20 % during the last glacial period (Figs. 5, 8e). Most ag-glutinated foraminifera in core SO236-052-4 belong to theTextulariida, such as Spiroplectammina sagittula, Textulariacalva and Textularia pala. These and related taxa are oftenassociated with relatively coarse-grained substrates and theypreferentially use siliciclastic grains for building up their testwalls (Allen et al., 1999; Murray, 2006; Armynot du Châteletet al., 2013).

The modern equatorial Indian Ocean is limited in the mi-cronutrient iron (Wiggert et al., 2006; Maher et al., 2010),and therefore enhanced aeolian Fe fluxes to the ocean duringglacial periods likely have a direct impact on the seasonalsurface productivity (Martin et al., 1991; Boyd et al., 2000;

Gao et al., 2001; Jickells et al., 2005), which also influencesthe deep-sea benthic ecosystems through seasonal phytode-tritus pulses. Similar relations between Fe fluxes and surfaceocean productivity have been reported from the SouthernOcean (Anderson et al., 2014; Martínez-García et al., 2014)and the equatorial Pacific Ocean (Costa et al., 2016). TheTOC and Br contents of marine sediments are widely usedas proxies for organic matter fluxes and surface water pro-ductivity (Müller and Suess, 1979; Rühlemann et al., 1999;Ziegler et al., 2008, 2009; Caley et al., 2013). But the ap-plicability of both proxies in quantitative reconstructions islimited by the specific sedimentological and biogeochemicalprocesses at the sediment–water interface, including the bulkaccumulation rate and bottom water oxygenation (Möbius etal., 2011; Schoepfer et al., 2015; Naik et al., 2017). How-ever, elevated TOC and Br values in core SO236-052-4 sug-gest generally enhanced organic matter fluxes during glacialperiods, which may reflect the influence of Fe fertilization(Fig. 8b–d).



The benthic foraminiferal fauna at site SO236-052 reveala marked glacial–interglacial pattern (Figs. 7, 8f). The di-versity, microhabitat partitioning and species composition ofdeep-sea benthic foraminiferal faunas are mainly controlledby the combined influences of the quantity and quality offood supply and oxygen content of the bottom and pore wa-ters (Jorissen et al., 1995; Fontanier et al., 2002). The di-versity of the fauna is high, with H (S) values always > 3.2throughout the studied time interval, suggesting the absenceof extreme environmental conditions at the sea floor of thestudy site. Therefore, the observed faunal changes likely re-flect variations in the amount and quality of food supply. Themost abundant species of the three benthic foraminiferal as-semblages are C. mabahethi, N. proboscidea and D. arau-cana, all with PC scores > 3 in at least one assemblage (Ta-ble 2). Microhabitat studies demonstrated that most speciesof the genera Cibicides and Cibicidoides live as suspensionfeeders on or elevated above the sea floor (Lutze and Thiel,1989; Linke and Lutze, 1993); therefore we assume a sim-ilar microhabitat preference for C. mabahethi. In the RedSea, this species is adapted to relatively high oxygen con-tents and low organic matter fluxes (Edelman-Furstenberg etal., 2001; Badawi et al., 2005). The cosmopolitan N. pro-boscidea inhabits an epifaunal to very shallow infaunal mi-crohabitat (Fontanier et al., 2002; Licari et al., 2003) and hasbeen described as a detritus feeder from various bathyal andabyssal environments. In the South Atlantic Ocean, N. pro-boscidea is associated with well-ventilated and oligotrophicconditions (Schmiedl et al., 1997). This species thrives undermoderate to high organic matter fluxes and oxygen-depletedintermediate waters in the Indian Ocean (Murgese and DeDeckker, 2007; De and Gupta, 2010) and was used as a proxyfor the strength of the SW monsoon (Gupta and Srinivasan,1992; Gupta and Thomas, 2003; Sarkar and Gupta, 2014).These observations and the high relative abundance of N.proboscidea in core SO236-052-4 during the last glacial in-tervals MIS 4–2 and the interglacial interval MIS 5 suggestan adaptation to a wide range of trophic conditions and con-firms its tolerance to moderate oxygen depletion. Little in-formation is available on the ecology of D. araucana, butits flat trochospiral test morphology and its distribution inthe North Atlantic Ocean suggest an epifaunal microhabi-tat and adaptation to suspended food sources (Corliss andChen, 1988; Koho et al., 2008). Similar to the closely relatedD. bertheloti, it may prefer oxic conditions (Duleba et al.,1999; Smith and Gallagher, 2003), with a tolerance for mod-erate oxygen depletion (Edelmann-Furstenberg et al., 2001).The shallow infaunal Hoeglundina elegans, which mainly oc-curs together with N. proboscidea in assemblage 3 duringMIS 4–2, is commonly associated with low to moderate or-ganic matter fluxes, fresh phytodetritus and high oxygen con-tents (Corliss, 1985; Koho et al., 2008).

The ecological preferences of the dominant taxa suggestthat faunal changes at site SO236-052, although pronounced,were driven by rather subtle changes in the amount of organic

matter fluxes. Instead, the faunal changes likely reflect varia-tions in the lateral suspension of food particles, the substrate-specific development of infaunal niches and the influence ofoxygen changes on the quality of the organic matter. Thehigh dominance of the detritus feeders N. proboscidea andH. elegans in assemblage 3 reflects the highest organic mat-ter fluxes during the last glacial MIS 4–2 (Fig. 8f). In con-trast, the dominance of the epifaunal suspension feeder C.mabahethi in assemblage 2 during the penultimate glacial(MIS 6) suggests relatively lower organic matter fluxes. TheN. proboscidea and D. araucana assemblage 1 of MIS 5 re-veals some similarity to assemblage 3, but the high abun-dance of D. araucana suggests an overall lower food fluxwith a considerable amount of suspended particles. In addi-tion, the relatively finer-grained substrate likely opened in-faunal niches as indicated by the presence of the shallow todeep infaunal Bulimina marginata during the MIS 5 (Joris-sen and Wittling, 1999) (Fig. 7e). Contrasts in the bound-ary conditions between different glacials and interglacialsmay account for the inconsistent association of certain as-semblages to either glacial or interglacial periods. For in-stance, glacial boundary conditions during MIS 6 were dif-ferent from MIS 4–2, in which the latter was characterizedby a relatively higher global ice volume, a related lower sealevel (Rohling et al., 2009) and pronounced millennial-scalevariability (Dansgaard et al., 1993). Previous studies showedsimilar patterns, with certain benthic foraminiferal assem-blages occurring during both glacial and interglacial peri-ods, e.g. in the Red Sea (Badawi et al., 2005). At the Mal-dives Inner Sea, glacial-to-interglacial changes in food fluxeswere likely not extreme and therefore ecological thresholdsfor certain species and faunas may not have always beenpassed during glacial–interglacial transitions. A detailed in-spection of assemblage 2 (C. mabahethi fauna) actually dis-plays faunal differences between their occurrences in MIS 1and MIS 6, although C. mabahethi is the dominant taxon inboth intervals.

While the benthic foraminiferal fauna basically varies onthe glacial–interglacial timescale, the TOC, Br and Ti /Alrecords reveal additional variability in the precessional band(Fig. 4). This suggests that marine environmental conditionsin the Maldives are linked to high-latitude climate variabil-ity and regional monsoonal changes. The surface water pro-ductivity of the northern Indian Ocean is driven by wind-induced mixing of the upper water column and upwelling ofnutrient-rich subsurface waters and thus reveals a close as-sociation with seasonal changes in the monsoonal wind sys-tem (Nair et al., 1989). Accordingly, productivity changesin the northern and north-western Arabian Sea are coherentwith the strength of the SW monsoon (Ivanova et al., 2003;Leuschner and Sirocko, 2003; Singh et al., 2011) and alongthe Indian western coast with the strength of the NE mon-soon (Rostek et al., 1997; Singh et al., 2011). The elevatedTOC and Br values at site SO236-052 during phases of re-duced Northern Hemisphere summer insolation suggest a di-



Plankton

Epifauna (a)

(b)

(c)

MIS: 1 2 3 4 5 6 7

200

240

280

320

-2]

0 50 100 150 200 250Age [ka BP]

40

60

80

100

O2

[µm

ol k

g-1 ]

0.8

1

1.2

13C

Cib

.-Ga

[O2] depletion

Oxy

gena

tion

+-

Ver

tical

mix

ing

+-

0.4

0.6

0.8

1

13

13CCw-Ga)13CCm-Ga)

0

0.2

0.4

13C

Gr-

Cm

Figure 9. Water mass circulation changes obtained from the stable δ13C data of core SO236-052-4 (Indian Ocean) in comparison to ven-tilation changes in the Arabian Sea; (a) δ13C records of the planktonic G. ruber (light blue) and the epibenthic C. mabahethi (dark blue),(b) difference between the planktonic and epibenthic stable carbon records (1δ13CGr-Cm) and (c) differences between epibenthic and deependobenthic δ13C records of SO236-052-4 (dark blue) from the intermediate Maldives Inner Sea in comparison to those of GeoB3004(purple) from the deep Arabian Sea (Schmiedl and Mackensen, 2006). Changes in intermediate- and deep-water oxygen concentrations arecalculated by the linear regression between 1δ13C and [O2] < 235 µmol kg−1 after Hoogakker et al. (2015). The minimum significancelevel of [O2]= 55 µmol kg−1 is shown as a dashed line (Hoogakker et al., 2015). Variation in the insolation difference between the Juneand December solstice at 30◦ N (yellow) was estimated after Laskar et al. (2004) with AnalySeries 2.0 (Paillard et al., 1996). All linesindicate 5-point running averages. MIS denotes the marine stable oxygen isotope stages. Cib. is Cibicides, Cm is Cibicides mabahethi, Cwis Cibicides wuellerstorfi, Ga is Globobulimina affinis, Gr is Globigerinoides ruber.

rect influence of the Indian winter monsoon on productivityand related organic matter fluxes of the Maldives Inner Seaduring the past 200 kyr (Fig. 8), which is consistent with thepresent-day situation (de Vos et al., 2014). The link betweenthe winter monsoon intensity and surface water productiv-ity in the study area is confirmed by the difference betweenthe δ13C values of the epipelagic G. ruber and the epiben-thic C. mabahethi (Fig. 9). Low 1δ13CGr-Cm values indicateenhanced vertical mixing of the water column, which is asso-ciated with an increased supply of nutrients from subsurfacewaters into the photic zone based on enhanced surface waterproductivity.

4.2 Sea-level changes, sedimentation processes andbenthic ecosystem dynamics

The close association of changes in sediment composition(i.e. bulk grain size, carbonate content) at site SO236-052with the LR04 stable benthic isotope stack (Lisiecki andRaymo, 2005) suggests a dominant influence of sea-levelchanges on the depositional environments of the MaldivesInner Sea. This is also corroborated by the Sr /Ca variationsin the core. In periplatform ooze, i.e. areas around shallow-water carbonate banks and higher Sr contents are a conse-quence of a higher input of shallow-water aragonite (Dunbarand Dickens, 2003), which is produced in the neritic parts ofthe platforms and exported to the areas around the platformby currents.



As shown by previous studies, variations in the total or-ganic carbon content in the Inner Sea sediments are con-siderably triggered by sea-level and ocean current changes(Betzler et al., 2016). Thus, the observed changes in bottomcurrents likely influenced the lateral transport of suspendedorganic particles, as is suggested by variations in the rela-tive abundance of suspension feeders in the different benthicforaminiferal assemblages (Figs. 7, 8, Table 2). The domi-nance of D. araucana during MIS 5 and C. mabahethi duringMIS 6 and MIS 1 indicates phases of enhanced lateral foodsupply, which for the interglacial periods (MIS 5, MIS 1) cor-relate with reconstructed higher current velocities and sea-level highstands (Fig. 6). This is shown by the higher sortablesilt data at site SO236-052, implying higher bottom currentvelocities, which is also supported by the higher amplitude ofchange and the sortable silt values of the drift deposits recov-ered by core M74/4-1143. The different sortable silt ampli-tudes of both settings in the Maldives are due to the restric-tion of the central part of the Inner Sea (core SO236-052-4), whereas in comparison the deposition area in the KardivaChannel (core M74/4-1143) is known to be exposed by muchstronger current regimes since the Late Pleistocene (Betzleret al., 2013b; Reolid et al., 2017).

The interglacial intervals (mainly MIS 5 and MIS 7;Fig. 6) contain high abundances of meroplanktonic ben-thic foraminifera (Cymbaloporetta, Tretomphaloides), whichbuild floating chambers for dispersal (Banner et al., 1985;Alve, 1999). These taxa are commonly found in shelf envi-ronments (Milker and Schmiedl, 2012). Their acme duringthe last interglacial maximum at upper bathyal depth in theMaldives Inner Sea coincides with an almost absence of otherdisplaced species from reef and lagoon environments, such asElphidium, Amphistegina and Operculina (Parker and Gis-chler, 2011). This implies a repeated colonization of upperbathyal environments with meroplanktonic taxa from sub-merged neritic environments during sea-level highstands andconditions of strengthened bottom water velocity.

4.3 Changes in intermediate water circulation andoxygenation

The epibenthic stable carbon isotope record of core SO236-052-4 lacks a coherent glacial–interglacial pattern but re-veals an overall δ13CCm increase of ∼ 0.5 ‰ over the past200 kyr (Fig. 10). Long-term trends of similar magnitudehave been recorded from sites in the south-western Pa-cific Ocean, which were particularly bathed by the well-oxygenated Antarctic Intermediate Water mass (AAIW) dur-ing warm intervals (Thiede et al., 1999; Pahnke and Zahn,2005; Elmore et al., 2015; Ronge et al., 2015; Fig. 10).The general resemblance of relative changes in epibenthicδ13C records from different regions suggests a significantand super-regional role of the AAIW in ventilation of the up-per bathyal environments in the Maldives Inner Sea, which

is consistent with the modern oceanographic situation (You,1998).

Following the approach of Hoogakker et al. (2015) we es-timated the changes in the oxygen content of the interme-diate water mass of the Maldives Inner Sea based on the1δ13CCm-Ga signal, i.e. the difference between the δ13C val-ues of the epifaunal C. mabahethi and the deep infaunal G.affinis s.l. The resulting [O2] concentrations display signifi-cant power in the precession band (23 kyr period), with oxicand low oxic conditions related to Northern Hemisphere in-solation maxima and minima, but they never dropped sub-stantially below 45 µmol kg−1 (≈ 1 mL L−1; Fig. 9). More-over, the oxic to low oxic conditions did not seem to posestress to the benthic foraminiferal fauna. Instead, the pro-portion of the deep infauna increases exponentially underdysoxic conditions, i.e. at [O2] values significantly below1 mL L−1 (Jorissen et al., 2007). The lack of dysoxic con-ditions at site SO236-052 at any time in the past 200 kyr iscorroborated by the persistently high diversity across glacialand interglacial periods and the low abundance of deep in-faunal taxa. However, the reconstructed [O2] changes in in-termediate waters at site SO236-052 resemble those from thedeep OMZ of the western Arabian Sea, which is influencedby the advection of oxygen-rich North Atlantic Deep Wa-ter (NADW; Schmiedl and Mackensen, 2006). The depen-dence of oxygen changes in Indian Ocean water masses onthe inflow of Atlantic and Antarctic water masses is corrob-orated by a number of recent observations from the north-western and south-eastern Arabian Sea (Pattan and Pearce,2009; Das et al., 2017; Naik et al., 2017). We therefore as-sume that the OMZ variability in the Maldives Inner Seais influenced by the overall strength and lateral southwardexpansion of the Arabian Sea OMZ and by local monsoon-related organic matter fluxes and oxygen consumption, butit is additionally controlled by the ventilation of southern-derived oxygen-rich intermediate water (AAIW). The ocean-wide linkage of intermediate water ventilation can be as-sumed due to the general resemblance of our epibenthic sta-ble carbon isotope record to comparable records from otherareas. On the other hand, the significant variability of ournew oxygen reconstruction from the Maldives Inner Sea inthe precession band and its resemblance to the reconstruc-tion from the Arabian Sea suggests an additional influenceof monsoon-driven biogeochemical processes. The resultingchanges in the biogeochemical processes at site SO236-052are illustrated by the establishment and long-term persistenceof the benthic foraminiferal assemblage 3 underlining thepositive response of N. proboscidea and associated speciessuch as H. elegans and D. bertheloti to moderately reducedoxygen and increased food levels.

The long period of lowered [O2] values below60 µmol kg−1 centred at MIS 4–3 coincides with a markedmonsoon and upwelling maximum in the Arabian Sea(Hermelin and Shimmield, 1995; Clemens and Prell, 2003;Leuschner and Sirocko, 2003; Caley et al., 2011a, b), which



0 50 100 150 200Age [ka BP]

-0.5

0

0.5

1

1.5

13C

bent

hic

MIS: 1 2 3 4 5 6 7SO236/052 (382 m; this study)MD06-2990, SO136/003 (943 m, 958 m; Thiede et al., 1999; Ronge et al., 2015)DSDP593 (1068 m; Elmore et al., 2015)MD97-2120 (1210 m; Pahnke and Zahn, 2005)MD06-2986 (1477 m; Ronge et al., 2015)

Study area

(a)

(b)PacificOcean

IndianOcean

Figure 10. Comparison of epibenthic δ13C records from intermediate water depth in the equatorial Indian and temperate south-westernPacific oceans; (a) δ13C record of C. mabahethi (blue) from the Maldives Inner Sea (SO236-052) in comparison to δ13C records from thesouth-western Pacific Ocean, which were mainly generated from Cibicidoides wuellerstorfi, C. cicatricosa and C. kullenbergi and representdifferent water depths (Thiede et al., 1999; Pahnke and Zahn, 2005; Elmore et al., 2015; Ronge et al., 2015). Data of MD97-2120 were tracedafter Pahnke and Zahn (2005). All lines represent 5-point running averages. (b) Simplified map of the Indian Ocean and the south-westernPacific Ocean with the location of the study sites.

caused a strengthening and deepening of the OMZ (Almogi-Labin et al., 2000; Den Dulk et al., 2000; Schmiedl andLeuschner, 2005). The expansion of the Arabian Sea OMZsouthward into the equatorial region likely preconditionedthe oxygen levels of intermediate waters in the MaldivesInner Sea. There, oxygen minima were further lowered bythe reduced glacial advection of the oxygen-rich AAIW andenhanced regional microbial oxygen consumption, reflectinga superposition of high- and low-latitude climate signals.Additionally, an abrupt [O2] drop occurred at the end of thelast glaciation, suggesting a short phase of reduced AAIWadvection or increased surface water productivity and relatedoxygen consumption at depth (Fig. 9).

The present OMZ in the north-western Indian Ocean ex-tends from the northern Arabian Sea into the tropical IndianOcean (Reid, 2003), reflecting the reduced ventilation of in-termediate water masses (due to its remote position) and thebiogeochemical processes related to monsoon-induced or-ganic matter fluxes and microbial oxygen consumption. In-deed, the oxygen concentrations in the Indian Ocean displaya gradient with very low values in the northern Arabian Seaand increasing values to the south. This gradient illustratesa clear relation to the monsoon-related biogeochemical pro-cesses in the Arabian Sea, but it is also a reflection of the re-mote position of the Arabian Sea in terms of intermediate wa-ter ventilation. Nevertheless, a monsoon-induced strengthen-

ing of the OMZ in the Arabian Sea (as during MIS 3) will re-sult in an increase in the north–south oxygen gradient in theentire north-western Indian Ocean, which should then alsobe detected in the Maldives Inner Sea at a lower amplitude.

Evaluations of calcareous nanoplankton records, whichare used as indicators for surface productivity, from sedimentcores of the equatorial Indian and Pacific Ocean reveal sig-nificant variability in the precession band and are coherentand in phase with February equatorial insolation (Beaufort etal., 1997, 2001). This orbital pattern suggested a close linkof equatorial Indian Ocean productivity to the strength of theIndian Ocean Equatorial Westerlies (IEW) and an ENSO-like forcing of equatorial surface ocean productivity duringthe Late Quaternary (Beaufort et al., 2001). Accordingly, re-gional productivity and organic matter fluxes in the widerMaldives area may have also been influenced by changes inthe strength of the IEW. However, a strong IEW influencein the Maldives Inner Sea is questioned by the low preces-sional variability observed in our productivity proxies andthe close association of modern phytoplankton blooms in thisregion with the NE monsoon (Sasamal, 2007; de Vos et al.,2014). To summarize, our new results imply that on orbitaltimescales changes in the winter monsoon and AAIW advec-tion seem to exert the dominant influence on upper bathyalenvironments in the Maldives Inner Sea.



5 Conclusions

The integrated evaluation of sedimentological, geochemicaland micropaleontological proxy records from the MaldivesInner Sea (tropical Indian Ocean) furthers our understand-ing of links between equatorial climate variability, sea-levelchanges, changes in intermediate water ventilation and ben-thic ecosystem dynamics on orbital timescales during thepast 200 kyr. The main conclusions are the following.

1. Aeolian dust fluxes were considerably enhanced dur-ing glacial intervals (MIS 6 and MIS 4–2) as indicatedby increased Fe /Al, Ti /Al and Si /Ca ratios, generalcoarsening of the bulk sediment and increased abun-dance of agglutinated benthic foraminiferal taxa, whichuse the siliciclastic grains for test formation. The en-hanced dust input was linked to phases of generally in-creased atmospheric dust loads and NE winds, suggest-ing a close linkage of Maldives marine environmentsto the aridity of the central Asian loess areas and thestrength of the Indian winter monsoon.

2. Increased vertical mixing during glacial phases of in-tensified winter monsoon resulted in enhanced surfacewater productivity and associated organic carbon fluxesto the sea floor as indicated by TOC values and thecomposition of the benthic foraminiferal fauna. TheCibicidoides mabahethi (assemblage 2) and Neouvige-rina proboscidea (assemblage 3) faunas dominate dur-ing MIS 6 and MIS 4–2, respectively, suggesting differ-ences in the amount and quality of food delivery for thetwo glacial intervals. The Br XRF counts and the TOCrecord reveal additional variability in the precessionalband (as shown with the Blackman–Tukey spectral anal-ysis; Fig. 4), which is inversely correlated with NorthernHemisphere summer insolation underlining a close linkof the regional vertical mixing of the water column andmarine productivity to the Indian winter monsoon.

3. Glacial–interglacial changes in sea level controlled thedownslope transport of sediment from the Maldivesarchipelago to the deep-sea environments and influ-enced the current strength at the benthic boundary layerof the Inner Sea, resulting in different grain sizes andsubstrates. The drift deposits recovered by core M74/4-1143 have shown that the highest current intensities oc-curred during and after the glacial terminations (Fig. 6).Bottom currents in general were stronger during inter-glacials than during glacials, although core SO236-052-4 shows lower current velocities and a lower amplitudeof change. Stronger current intensities at the sea floorlikely favoured the distribution of certain suspension-feeding benthic foraminiferal taxa, such as D. araucana.

4. The long-term trend in the benthic δ13C record mirrorsthe basin-wide change in the composition of intermedi-

ate waters, implying a close linkage to the main forma-tion sites of the AAIW in the Southern Ocean. The pre-cessional changes in the estimated oxygen concentra-tions of intermediate waters are coherent with changesin the deep Arabian Sea. This suggests an influence ofthe lateral expansion of oxygen minimum waters fromthe Arabian Sea into the equatorial intermediate IndianOcean and modulation by inflowing AAIW from thesouth. The predominance of N. proboscidea during along phase of reduced oxygen concentrations (with av-erage oxygen concentrations around 50 µmol kg−1) dur-ing late MIS 5 to late MIS 3 suggests an adaption of thisspecies to the particular biogeochemical conditions andfood quality associated with low oxic conditions.

Data availability. All data records of core SO236-052-4 used anddiscussed in this paper are accessible at https://doi.pangaea.de/10.1594/PANGAEA.882514 (Bunzel et al., 2017).

Competing interests. The authors declare that they have no con-flict of interest.

Acknowledgements. We thank the masters, crews and theshipboard scientific parties of the R/V SONNE SO236 andR/V METEOR M74/4 cruises for their excellent collaboration.Jutta Richarz is thanked for her support during grain size analyses,and Lisa Schönborn and Günther Meyer are thanked for technicalsupport during stable isotope measurements. Aurora Elmoreand Thomas Ronge are thanked for providing the stable car-bon isotope records of the south-western Pacific Ocean (coresDSDP593, MD06-2986, MD06-2990/SO136/003), and we thankYvonne Milker for the many helpful discussions. We acknowledgethe two anonymous reviewers who helped to considerably improvethis paper with detailed comments and suggestions. This researchused data acquired at the XRF Core Scanner Lab at the MARUMCenter for Marine Environmental Sciences, University of Bremen,Germany. This study was supported by grant 03G0236A fromthe Federal Ministry of Education and Research. The Ministry ofFisheries and Agriculture of the Maldives is thanked for grantingthe research permit for Maldivian waters.

Edited by: Luc BeaufortReviewed by: two anonymous referees

References

Allen, K., Roberts, S., and Murray, J. W.: Marginal marine aggluti-nated foraminifera: affinities for mineral phases, J. Micropaleon-tol., 35, 183–191, https://doi.org/10.1144/jm.18.2.183, 1999.

Almogi-Labin, A., Schmiedl, G., Hemleben, C., Siman-Tov, R.,Segl, M., and Meischner, D.: The influence of the NE wintermonsoon on productivity changes in the Gulf of Aden, NW Ara-bian Sea, during the last 530 ka as recorded by foraminifera, Mar.


https://doi.pangaea.de/10.1594/PANGAEA.882514https://doi.pangaea.de/10.1594/PANGAEA.882514https://doi.org/10.1144/jm.18.2.183


Micropaleontol., 40, 295–319, https://doi.org/10.1016/S0377-8398(00)00043-8, 2000.

Altabet, M. A., Higginson, M. J., and Murray, D. W.: Theeffect of millennial-scale changes in Arabian Sea den-itrification on atmospheric CO2, Nature, 415, 159–162,https://doi.org/10.1038/415159a, 2002.

Alve, E.: Colonization of new habitats by benthicforaminifera: a review, Earth-Sci. Rev., 46, 167–185,https://doi.org/10.1016/S0012-8252(99)00016-1, 1999.

Anderson, R. F., Barker, S., Fleisher, M., Gersonde, R., Goldstein,S. L., Kuhn, G., Mortyn, P. G., Pahnke, K., and Sachs, J. P.: Bi-ological response to millennial variability of dust and nutrientsupply in the Subantarctic South Atlantic Ocean, Philos. T. R.Soc. A, 372, 1–17, https://doi.org/10.1098/rsta.2013.0054, 2014.

Armynot du Châtelet, E., Bout-Roumazeilles, V., Coccioni, R.,Frontalini, F., Guillot, F., Kaminski, M. A., Recourt, P.,Riboulleau, A., Trentesaux, A., Tribovillard, N., and Ven-talon, S.: Environmental control on shell structure and com-position of agglutinated foraminifera along a proximal-distaltransect in the Marmara Sea, Mar. Geol., 335, 114–128,https://doi.org/10.1016/j.margeo.2012.10.013, 2013.

Aston, S. R., Chester, R., Johnson, L. R., and Padgham, R. C.: Eo-lian dust from the lower atmosphere of the eastern Atlantic andIndian Oceans, China Sea and Sea of Japan, Mar. Geol., 14, 15–28, https://doi.org/10.1016/0025-3227(73)90040-6, 1973.

Backhaus, K., Erichson, B., Plinke, W., and Weiber, R.: MultivariateAnalysemethoden, Springer, Berlin, Heidelberg, New York, 1–575, 2008.

Badawi, A., Schmiedl, G., and Hemleben, C.: Impact of late Qua-ternary environmental changes on deep-sea benthic foraminiferalfaunas of the Red Sea, Mar. Micropaleontol., 58, 13–30,https://doi.org/10.1016/j.marmicro.2005.08.002, 2005.

Banner, F. T., Pereira, C. P. G., and Desai, D.: “Tretomphaloid” floatchambers in the Discorbidae and Cymbaloporidae, J. Foramin.Res., 15, 159–174, https://doi.org/10.2113/gsjfr.15.3.159, 1985.

Beaufort, L., Lancelot, Y., Camberlin, P., Cayre, O., Vincent, E.,Bassinot, F., and Labeyrie, L.: Insolation cycles as a major con-trol of equatorial Indian Ocean Primary Production, Science,278, 1451–1454, https://doi.org/10.1126/science.278.5342.1451,1997.

Beaufort, L., de Garidel-Thoron, T., Mix, A. C., and Pisias,N. G.: ENSO-like forcing on oceanic primary produc-tion during the Late Pleistocene, Science, 293, 2440–2444,https://doi.org/10.1126/science.293.5539.2440, 2001.

Betzler, C., Hübscher, C., Lindhorst, S., Reijmer, J. J. G.,Römer, M., Droxler, A. W., Fürstenau, J., and Lüdmann,T.: Monsoonal-induced partial carbonate platform drown-ing (Maldives, Indian Ocean), Geology, 37, 867–870,https://doi.org/10.1130/G25702A.1, 2009.

Betzler, C., Fürstenau, J., Lüdmann, T., Hübscher, C., Lind-horst, S., Paul, A., Reijmer, J. J. G., and Droxler, A. W.:Sea-level and ocean-current control on carbonate-platformgrowth, Maldives, Indian Ocean, Basin Res., 25, 172–196,https://doi.org/10.1111/j.1365-2117.2012.00554.x, 2013a.

Betzler, C., Lüdmann, T., Hübscher, C., and Fürstenau, J.: Cur-rent and sea-level signals in periplatform ooze (Neogene,Maldives, Indian Ocean), Sediment. Geol., 290, 126–137,https://doi.org/10.1016/j.sedgeo.2013.03.011, 2013b.

Betzler, C., Eberli, G. P., Kroon, D., Wright, J. D., Swart, P. K.,Nath, B. N., Alvarez-Zarikian, C. A., Alonso-García, M., Bia-lik, O. M., Blättler, C. L., Guo, J. A., Haffen, S., Horozal, S.,Inoue, M., Jovane, L., Lanci, L. Laya, J. C., Mee, A. L. H.,Lüdmann, T., Nakakuni, M., Niino, K., Petruny, L. M., Pratiwi,S. D., Reijmer, J. J. G., Reolid, J., Slagle, A. L., Sloss, C.R., Su, X., Yao, Z., and Young, J. R.: The abrupt onset ofthe modern South Asian Monsoon winds, Sci. Rep., 6, 29838,https://doi.org/10.1038/srep29838, 2016.

Bianchi, G. G., Hall, I. R., McCave I. N., and Joseph, L.: Mea-surement of the sortable silt current speed proxy using the Sedi-graph 5100 and Coulter Multisizer IIe: Precision and accuracy,Sedimentology, 46, 1001–1014, https://doi.org/10.1046/j.1365-3091.1999.00256.x, 1999.

Blott, S. J. and Pye, K.: GRADISTAT: a grain size distri-bution and statistics package for the analysis of unconsol-idated sediments, Earth Surf. Proc. Land., 26, 1237–1248,https://doi.org/10.1002/esp.261, 2001.

Böning, P. and Bard, E.: Millennial/centennial-scale thermo-cline ventilation changes in the Indian Ocean as reflected byaragonite preservation and geochemical variations in ArabianSea sediments, Geochim. Cosmochim. Ac., 73, 6771–6788,https://doi.org/10.1016/j.gca.2009.08.028, 2009.

Boyd, P. W., Watson, A. J., Law, C. S., Abraham, E. R., Trull, T.,Murdoch, R., Bakker, D. C. E., Bowie, A. R., Buesseler, K. O.,Chang, H., Charette, M., Croot, P., Downing, K., Frew, R., Gall,M., Hadfield, M., Hall., J., Harvey, M., Jameson, G., LaRoche,J., Liddicoat, M., Ling, R., Maldonado, M. T., McKay, R. M.,Nodder, S., Pickmere, S., Pridmore, R., Rintoul, S., Safi, K., Sut-ton, P., Strzepek, R., Tanneberger, K., Turner, S., Waite, A., andZeldis, J.: A mesoscale phytoplankton bloom in the polar South-ern Ocean simulated by iron fertilization, Nature, 407, 695–702,https://doi.org/10.1038/35037500, 2000.

Bunzel, D., Schmiedl, G., Lindhorst, S., Mackensen, A., Reolid, J.,Romahn, S., and Betzler, C.: Benthic foraminifera census countsand compilation of the isotope, grain size, TOC, CaCO3 andXRF data records of sediment core SO236_052-4, PANGAEA,https://doi.org/10.1594/PANGAEA.882514, 2017.

Caley, T., Malaizé, B., Zaragosi, S., Rossignol, L., Bourget, J., Ey-naud, F., Martinez, P., Giraudeau, J., Charlier, K., and Ellouz-Zimmermann, N.: New Arabian Sea records help decipher or-bital timing of Indo-Asian monsoon, Earth Planet. Sc. Lett., 308,433–444, https://doi.org/10.1016/j.epsl.2011.06.019, 2011a.

Caley, T., Malaizé, B., Revel, M., Ducassou, E., Wainer, K.,Ibrahim, M., Shoeaib, D., Migeon, S., and Marieu, V.: Orbitaltiming of the Indian, East Asian and African boreal monsoonsand the concept of a “global monsoon”, Quaternary Sci. Rev.,30, 3705–3715, https://doi.org/10.1016/j.quascirev.2011.09.015,2011b.

Caley, T., Zaragosi, S., Bourget, J., Martinez, P., Malaizé, B., Ey-naud, F., Rossignol, L., Garlan, T., and Ellouz-Zimmermann,N.: Southern Hemisphere imprint for Indo-Asian summer mon-soons during the last glacial period as revealed by Ara-bian Sea productivity records, Biogeosciences, 10, 7347–7359,https://doi.org/10.5194/bg-10-7347-2013, 2013.

Chauhan, O. S. and Shukla, A. S.: Evaluation of the influence ofmonsoon climatology on dispersal and sequestration of conti-nental flux over the southeastern Arabian Sea, Mar. Geol., 371,44–56, https://doi.org/10.1016/j.margeo.2015.10.018, 2016.


https://doi.org/10.1016/S0377-8398(00)00043-8https://doi.org/10.1016/S0377-8398(00)00043-8https://doi.org/10.1038/415159ahttps://doi.org/10.1016/S0012-8252(99)00016-1https://doi.org/10.1098/rsta.2013.0054https://doi.org/10.1016/j.margeo.2012.10.013https://doi.org/10.1016/0025-3227(73)90040-6https://doi.org/10.1016/j.marmicro.2005.08.002https://doi.org/10.2113/gsjfr.15.3.159https://doi.org/10.1126/science.278.5342.1451https://doi.org/10.1126/science.293.5539.2440https://doi.org/10.1130/G25702A.1https://doi.org/10.1111/j.1365-2117.2012.00554.xhttps://doi.org/10.1016/j.sedgeo.2013.03.011https://doi.org/10.1038/srep29838https://doi.org/10.1046/j.1365-3091.1999.00256.xhttps://doi.org/10.1046/j.1365-3091.1999.00256.xhttps://doi.org/10.1002/esp.261https://doi.org/10.1016/j.gca.2009.08.028https://doi.org/10.1038/35037500https://doi.org/10.1594/PANGAEA.882514https://doi.org/10.1016/j.epsl.2011.06.019https://doi.org/10.1016/j.quascirev.2011.09.015https://doi.org/10.5194/bg-10-7347-2013https://doi.org/10.1016/j.margeo.2015.10.018


Clemens, S. C. and Prell, W. L.: Late Pleistocene variabil-ity of Arabian Sea summer monsoon winds and conti-nental aridity: Eolian records from the lithogenic compo-nent of deep-sea sediments, Paleoceanography, 5, 109–145,https://doi.org/10.1029/PA005i002p00109, 1990.

Clemens, S. C. and Prell, W. L.: A 350 000 year summer-monsoonmulti-proxy stack from the Owen Ridge, Northern ArabianSea, Mar. Geol., 201, 35–51, https://doi.org/10.1016/S0025-3227(03)00207-X, 2003.

Clemens, S. C., Prell, W. L., Murray, D. W., Shimmield, G., andWeedon, G.: Forcing mechanisms of the Indian Ocean monsoon,Nature, 353, 720–725, 1991.

Clemens, S. C., Murray, D. W., and Prell, W. L.: NonstationaryPhase of the Plio-Pleistocene Asian Monsoon, Science, 274,943–948, 1996.

Corliss, B. H.: Microhabitats of benthic foraminiferawithin deep-sea sediments, Nature, 314, 435–438,https://doi.org/10.1038/314435a0, 1985.

Corliss, B. H. and Chen, C.: Morphotype patterns of Norwe-gian Sea deep-sea benthic foraminifera and ecological impli-cations, Geology, 16, 716–719, https://doi.org/10.1130/0091-7613(1988)0162.3.CO;2, 1988.

Costa, K. M., McManus, J. F., Anderson, R. F., Ren, H., Sig-man, D. M., Winckler, G., Fleisher, M. Q., Marcantonio, F.,and Ravelo, A. C.: No iron fertilization in the equatorial Pa-cific Ocean during the last ice age, Nature, 529, 519–522,https://doi.org/10.1038/nature16453, 2016.

Croudace, I. W. and Rothwell, R. G.: Micro-XRF Studies of Sed-iment Cores: Applications of a non-destructive tool

a multi-proxy analysis of late quaternary ocean and ... - cpby changes in the ventilation of both...

Documents