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Modern Benthic Foraminifer Distribution in the Amerasian Basin, Arctic OceanAuthor(s): Scott E. Ishman and Kevin M. FoleySource: Micropaleontology, Vol. 42, No. 2 (Summer, 1996), pp. 206-220Published by: The Micropaleontology Project, Inc.Stable URL: http://www.jstor.org/stable/1485871Accessed: 26/04/2010 19:45

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Modern benthic foraminifer distribution in the Amerasian Basin, Arctic Ocean

Scott E. Ishman and Kevin M. Foley U.S. Geological Survey, 926A National Center, Reston, Virginia 22092

ABSTRACT: A total of 38 box cores were collected from the Amerasian Basin, Arctic Ocean during the U.S. Geological Survey 1992 (PI92-AR) and 1993 (PI93-AR) Arctic Cruises aboard the U.S. Coast Guard Icebreaker Polar Star. In addition, the cruises collected geophysical data, piston cores and hydrographic data to address the geologic and oceanographic history of the western Arctic Ocean. This paper reports the results of the quantitative analyses of benthic foraminifer distribution data of the total (live + dead) assemblages derived from 22 box core-top samples. The results show that a distinct depth distribution of three dominant benthic foraminifer assemblages, the Textularia spp. - Spiroplectammina biformis, Cassidulina teretis and Oridorsalis tener - Eponides tumidulus Biofacies are strongly controlled by the dominant water masses within the Canada Basin: the Arctic Surface Water, Arctic Intermediate Water and Canada Basin Deep Water. The faunal distributions and their oceanographic associations in the Canada Basin are consistent with observations of benthic foraminifer distributions from other regions within the Arctic Ocean.

INTRODUCTION

There has been considerable interest in Arctic paleoceanography-paleoclimatology over the past several decades. This interest is primarily the result of the importance placed on the Arctic Ocean to North Atlantic Deep Water production throughout the Pleistocene (Broecker and Denton 1989). Much of the late Neogene paleoceanographic history for the Arctic to date has been derived either through the interpretation of foraminifers from marine cores (Clark et al. 1990; O'Neill 1981; Pak et al. 1992; Scott et al. 1989) or from coastal marine sections (Lagoe et al. 1989). To improve the accuracy of interpretations based on these biotic data, a better understanding of their moder distributions is essential.

This paper presents a benthic foraminifer data set derived from box core surface samples taken from a transect down the Northwind Ridge into the Canada Basin and onto the Beaufort Sea shelf (48m to 3808m water depth) (text-figs. 1 and 2). Previous studies of modem Arctic benthic foraminifer distributions have focused on the deep Canada Basin and Alpha Ridge (Green 1960; Lagoe 1977; Schroder-Adams et al. 1990; Scott and Vilks 1991). These studies were based on the distribution of benthic foraminifers collected from gravity core-top and Shipek grab samples from water depths ranging from 433m to 4225m. More recently Bergsten (1994) described total and living benthic foraminiferal populations recovered from box core samples collected from the Eurasian Basin, Arctic Ocean. Other benthic foraminiferal studies on Arctic marginal seas (Loeblich and Tappan 1953; Schroder-Adams et al. 1990; Todd and Low 1966; Vilks 1969) have also contributed to our knowledge of modem Arctic benthic foraminifer distributions. The data presented in this paper will provide benthic foraminiferal distribution data from undisturbed core tops in the Arctic from regions not heavily studied. The results of these data are compared with results of previous studies on Arctic benthic foraminifers to determine the consistency of benthic foraminifer distributions throughout the Arctic basin.

MODERN ARCTIC OCEAN PHYSIOGRAPHY AND OCEANOGRAPHY

The oceanographic setting of the Arctic Ocean is controlled by the interaction of water masses produced in adjacent seas and the continental margins of the Arctic Ocean, and Arctic Basin physiography. The Arctic Basin is partitioned into two major basins separated by the Lomonosov Ridge (-1000m depth), the Eurasian Basin and the Amerasian Basin, which includes the

TEXT-FIGURE 1 Map showing the major physiographic features of the Arctic and regions of previous benthic foraminifer core-top studies (solid circles). The inset is the region of the Amerasian Basin presented in text-figure 2.

micropaleontology, vol. 42, no. 2, pp. 206-220, text-figures 1-7, plates 1-2, tables 1-3, 1996 206

Micropaleontology, vol. 42, no. 2, 1996

155? 150? 145? 140?

TEXT-FIGURE 2 Inset map from text-figure 1 showing the locations of box core sites from cruises PI92-AR ( o ) and PI93-AR ( ), and hydrocast localities PI92-AR (A) and PI93-AR (A) referred to in the text from the Amerasian Basin.

Canada Basin (text-fig. 1). The water masses that occupy these basins originate through the mixing, by thermohaline driven circulation, of water masses generated in the Greenland and Iceland Seas and on the continental shelves (Aagaard and Carmack 1989; Aagaard et al. 1985). This mixing results in the formation of the dominant Arctic water masses; the Arctic Surface Waters (ASW), Upper and Lower Arctic Intermediate Waters (UAIW and LAIW), and several Arctic Deep Water (ADW) masses (Aagaard et al. 1985). The ASW and AlW's are widely distributed throughout the Arctic Ocean with distinct temperature and salinity minimums and maximums. Separate

deep water masses are recognized within the sub-basins of the Arctic Ocean, identified by their distinct temperature and salinity characteristics, as well as their basin residence time (Aagaard et al. 1985; Ostlund et al. 1987).

The Eurasian Basin is occupied by Eurasian Basin Deep Water (EBDW). The EBDW is formed by the mixing of Norwegian Sea Deep Water (NSDW) with resident Eurasian Basin water (Aagaard et al. 1985; Ostlund et al. 1987), which results in the cooling and reduction in salinity of the EBDW. This relatively high density water mass (a>41.98) is restricted from the Canada

207

Scott E. Ishman and Kevin M. Foley: Modern benthicforaminifer distribution in the Amerasian Basin, Arctic Ocean

TABLE 1 List of box cores selected for this study including, longitude, latitude and water depths in meters below sea level (mbsl) from which they were collected.

Box Core No. Latitude Longitude Water Depth (mbsl)

P192-AR-B1 72?24.2' N 164?18.2' W 49 m

P192-AR-B2 72023.8' N 164?16.2' W 48 m

P192-AR-B3 73041.6' N 162?39.8' W 201 m

P192-AR-B4 74000.0' N 161?23.7' W 447 m

P192-AR-B5 74030.58' N 159058.63' W 585 m

P192-AR-B7 74049.22' N 157033.48' W 1055 m

P192-AR-B8 74049.42' N 157?25.54' W 1402 m

P192-AR-B9 74049.5' N 157?12.3' W 2120 m

P192-AR-B12 74049.46' N 156052.37' W 3811 m

P192-AR-B15 75?44.05'N 160?51.63' W 2135 m

P192-AR-B16 75043.75' N 160005.54' W 1388 m

P192-AR-B17 76?05.19' N 164?50.15' W 402 m

P193-AR-B2 74045.33' N 157053.22' W 893 m

P193-AR-B4 74044.40' N 157?23.51' W 1779 m

P193-AR-B8 74043.97' N 157?17.10' W 2560 m

P193-AR-B11 74?44.19' N 157009.46' W 3482 m

P193-AR-B15 75020.30' N 150000.42' W 3808 m

P193-AR-B17 73?52.43' N 140036.47' W 3498 m

P193-AR-B18 72008.55' N 141 ?08.10' W 2940 m

P193-AR-B19 71?17.01' N 147?20.79' W 2089 m

P193-AR-B20 71003.73' N 147?19.88' W 1190 m

P193-AR-B21 71 00.89' N 147021.46' W 401 m

Basin by the presence of the Lomonosov Ridge where its residence time is estimated at 10 to 100 years (Ostlund et al. 1987).

The Canada Basin is occupied by the Canada Basin Deep Water (CBDW), a water mass relatively warmer, more saline and older than the EBDW (Aagaard and Carmack 1989; Aagaard et al. 1985; Ostlund et al. 1987). The CBDW forms by the mixing of AIW with cold, saline shelf water. The residence time of this water mass is estimated at approximately 500 years, making it consistently older than the EBDW because it is not regularly ventilated by GSDW (Aagaard et al. 1985; Ostlund et al. 1987). The CBDW is confined to the Canada Basin by the Lomonosov Ridge (-1000m). The AIW and ASW are the sources of Arctic intrabasin communication for the Canada Basin.

MATERIALS AND METHODS

Core top samples were collected from twenty-two box cores, PI92-AR-B1, -B2, -B3, -B4, -B5, -B7, -B8, -B9, -B12, -B15, -B16, -B17, and PI93-AR-B2, -B4, -B8, -Bll, -B15, -B17, -B 18, -B 19, -B20 and -B21 taken from depths ranging from 48 meters below sea level (mbsl) to 3811 mbsl, down the east side of the Northwind Ridge into the Canada Basin and up the

Beaufort Sea slope (text-fig. 2; table 1). The samples were not fixed upon collection for identification of the living assemblage, therefore the census data represent total assemblage (live+dead) data. Scott and Medioli (1980) suggest that the use of total assemblage data more accurately estimates modem environmental conditions than living assemblages. Approximately 50 cm3 of sample from each surface sample was disaggregated, using a gentle flow of water, and dried at 50?C. The PI92 samples were split into four size categories, >63gm to 106gm, >106gm to 125gm, >125gm to 150gm and >150,gm for analysis of size fraction variability within assemblages. The PI93 samples were split into >63gm to 125gm and >125[gm size frac- tions. Census counts of benthic foraminifers were done for all of the PI92 splits, the >63gm and >125gm data is presented herein (table 2). Quantitative analyses of the split data demon- strates that the 2125gm size fraction contains species significant to the identification of discrete water masses in the Canada Basin (Poore et al. 1994). Therefore, census counts for the PI93 samples includes only the >125gm size fraction.

Because of the variability in the abundance of the foraminifers between samples and splits, the data was standardized as proportional data (% of the total sample). All of the >125gm splits were used in the quantitative analyses except from samples PI93-AR-B19 and PI93-AR-B20, which were excluded due to their low foraminiferal abundance (<100 specimens). Quantita- tive analyses using 30 species (table 2) were used to determine benthic foraminifer associations in the Amerasian Basin. How- ever, the occurrence and relative abundance of species occurring in the >63gm to 125gm size fraction were noted.

Q- and R-mode cluster analyses of the benthic foraminifer data were used to provide groupings of the samples and assemblages, respectively. Here a hierarchical clustering method, complete linkage of the Pearson correlation similarity coefficient was used to identify biotopes (Q-mode) and biofacies (R-mode). This is similar to the methodology used by Lagoe (1979) to quantify benthic foraminifer distributions in the Arctic. Q-mode varimax principal component analysis of the Pearson correlation similarity matrix was used to determine the robustness of the sample groupings defined in the cluster analysis and quantify the data in multi-dimensional space to place environmental constraints on the faunal distributions.

BENTHIC FORAMINIFERAL RESULTS

A total of 49 genera represented by 59 species were identified from the Amerasian Basin box core-top samples (table 2 includes only the most frequently occuring benthic foraminifers with a majority of the Nodosariidae grouped). The fauna represents both agglutinated and calcareous benthic forms. Total species diversities (species number) range from 6 to 24.

Results of the quantitative analyses of benthic foraminifer data are shown in text-figures 3 and 4. Q-mode cluster analysis defines three sample groups or biotopes (text-fig. 3). R-mode cluster analysis of the benthic foraminifer data delineate 3 major groupings of taxa or biofacies (text-fig. 4).

The distribution of the samples from the Q-mode cluster analysis closely corresponds with the bathymetric distribution of the samples. This analysis places shallow water samples from cores PI92-AR-B 1 (49 mbsl), -B2 (48 mbsl) and -B3 (201 mbsl) into a group, intermediate water depth samples from cores PI92-AR-B17 (402 mbsl), -B4 (447 mbsl), -B5 (558 mbsl) and PI93-AR-B21 (401 mbsl) into a group, and all samples from

208


1.00 2.00 !

I I I I I

P192B2

P192B1

P192B3

P192B15

P193B1 1

P192B16

P193B8

P193B18

P193B4

P192B9

P192B8

P193B17

P192B12

P193B15

P193B2

P192B7

P193B20

P193B21

P192B17

P192B5

P192B4

Shallow Water Biotope

Deep Water Biotope

Intermediate Water Biotope

TEXT-FIGURE 3 Q-mode dendrogram showing the results of the cluster analysis of the PI92-AR and PI93-AR box core top data based on 30 species. Shaded regions

highlight major sample groups.

water depths greater than 800 mbsl (PI92-AR-B7, -B8, -B9, -B12, -B15, -B16, and PI93-AR-B2, -B4, -B8, -Bll, -B15, -B17 and -B18) into a group (text-fig. 3). Q-mode principal component analysis shows similar results with high component 3 scores for shallow water samples PI92-AR-B1, -B2, -B3, -B4 and PI93-AR-B21, high component 2 scores for intermediate depth samples PI92-AR-B17, -B5 and -B7, and high component 1 scores for deep water samples PI92-AR-B8, -B9, -B15, -B16, -B12 and PI93-AR-B2, -B4, -B8, -Bll, -B15, -B17 and -B18 (table 3).

Results of the R-mode cluster analysis are used to describe three distinct benthic foraminiferal biofacies, the Textularia spp. - Spiroplectammina biformis Biofacies, Cassidulina teretis Biofacies, and Oridorsalis tener - Eponides tumidulus Biofacies (text-fig. 4), described below.

Textularia spp - Spiroplectammina biformis Biofacies

The Textularia spp - Spiroplectammina biformis Biofacies (T-S Biofacies) is dominated by the agglutinated species Textularia torquata, Textularia kattagatensis and Spiroplec- tammina biformis. Other associated species include the calcareous benthic foraminifers Elphidium excavatum, Buccella frigida, Fursenkoina fusiformis and Nonionellina labradorica (text-fig. 4). Principal component analysis shows samples containing this assemblage to have high component 2 scores (table 3).

Cassidulina teretis Biofacies

Cassidulina teretis is the dominant species in the Cassidulina teretis Biofacies (C Biofacies). Supplementary species to this assemblage include Cassidulina norcrossi and the aggluti-

209

0.00 I I

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TABLE 2 Benthic foraminifer relative abundance data (%) of species having 1% occurence or greater in one or more samples. Numbers presented in parentheses indicate the relative abundance in the 263gm size fraction. All other values represent the >125gm size fraction. Also included is the total number of foraminifers counted in the 2125gm size fraction (* indicates species used in the quantitative analyses).

c .o 8 o o o o o _ o o o o o o o o o o o o o o88 8888 88 8888 8888 8 888 8

0

(uC0 0oo o ooCoo oooC oooooo0 o ooo oo

1 0000|-00 8 88 0 o 8 8288 0 0 o 8 8 8888 8 C 88 8o

g? 60oooooooo ooooooooooooddoddddddddoddddddddd66 d66 -

a,

tnoooooo~oooooo6o66ooo6

43<V 8 U o o o o o o o o o o o o o8 8o .8... 88 oo o8 88 8 8 8 o88 8 a.

i ? ? o O ooo oooo o? g 8 o 8 8 8d o 8 o 8 8' 8 , 8 8 0

888888888888 ?88888 8888888888888588888888

|N ( g 0 0 g N 0Q g 0g0 8O g g g CY0 8>

N -N'ooooo-oQ oooo.ooooooooo C') 00 o-o000ooo-Oo o0

? 8 ? 88 88 88 8S 8 8 8 8 8 8 8 888 888 8 8 8 8 8 8 8 8

aw ooo-oooo o ooo oo .,ooooooooooooddddddd o

8888S88'88S888 888888 oo8888oo 8 88s 88888?g88?88 0. 00d0000ooooodooocoddddddddddooddodd'8o o868688688ddddd60o8

', c 'p '\'rrj~9, ~ c

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210

Sample P193B4 P193B19 PI92B9 P192B15 P193B8 PI93B18 P193B11 P193B17 P193B15 P192B12

Spedes \Water Depth (meters) 1779 2069 2120 2135 2560 2940 3482 3498 3808 3811

Adercotyma glomerata 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Alveophragmium rassimargo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ammodiscus catinus 0.00 27.59 0.00 0.29 0.00 0.69 0.00 0.00 0.00 0.00 Ammotium cassis 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Astrononion gallowayi 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Bolivina arctca* 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Buccella frigida' 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 0.00 1.33 Cassidulina teretis 0.43 0.00 0.00 0.00 0.00 0.00 0.64 0.00 0.00 0.00 Cassidulina norcrossi 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Cassidulina reniforme* 0.00 0.00 0.21 0.00 0.30 0.00 0.32 0.00 0.00 0.00 Cibicdes Iobatulus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Elphidlum bartletti 0.00 0.00 0.00 0.00 0.00 0.00 1.59 0.00 0.00 0.00

Elphdium clavatum' 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.33

Elphidium excavatum 0.43 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Cribrostomoddes sp. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Dentalina pauperata 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Eggerella advena' 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Eponides tumidulus' 0.00 0.00 1.27 2.63 0.30 0.23 0.96 0.00 11.71 10.67 Fontbotia wuellerstorfi 6.29 0.00 6.78 39.47 13.31 8.97 8.60 0.35 0.00 0.00 Fursenkoina fusiformis 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Glandulina laevlgata 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Glomosplra gordlalls 0.00 13.79 0.21 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Haplophragmnodes obscurus 0.00 34.48 0.00 0.00 0.00 2.76 0.96 0.35 0.45 0.00

Hap/ophragmoides pakerae 0.00 3.45 0.00 0.00 0.00 0.92 0.00 1.41 2.25 0.00

Hyperamnna ekvgata 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Melonis badeeanum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mliammina arenacea 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Nodosarlids 1.30 0.00 0.42 2.05 1.48 0.46 8.60 6.71 3.15 10.67 Nonionellbna labradorica 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ordorsalis tener' 80.91 0.00 79.87 44.15 80.77 84.37 57.32 78.09 64.41 73.33 Oridorsalls umbonatus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Portatrochanmmna bpolads 0.00 6.90 0.00 0.00 0.00 0.23 0.00 0.00 0.00 0.00

Pyrgo wIlamsonl 0.00 0.00 0.00 0.00 0.00 0.00 2.23 0.00 0.00 0.00 Qulnquebculina akneriana 0.00 0.00 1.06 8.48 0.00 0.00 0.00 0.00 0.00 0.00 QuinquekcuLna arctica 5.64 0.00 2.12 0.00 0.59 0.00 0.00 0.00 0.00 0.00 Recurvoldes sdtulus 0.00 0.00 0.21 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Reophax scorpurus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Reopha spp. 0.00 13.79 0.00 0.00 0.00 1.15 0.00 1.06 14.41 0.00 Roberhdes charlottensis 0.22 0.00 0.21 1.17 0.00 0.00 0.00 0.00 0.00 0.00 Saccammina difflugifomis 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Spiropkectammina bIfacrms 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.33 Stainfortha concava 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Stetsonia arctca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Textujaria kattagatensis 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Textulari torquata' 0.00 0.00 0.00 0.00 0. .00 0.00 0.00 0.00 0.00 Trdflocuna frgida' 4.34 0.00 7.63 1.75 2.66 0.23 18.47 12.01 3.60 1.33 Trodnlamina globigerintformis 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Trodammna pseudoinflata 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Vahvulneria arctIca 0.43 0.00 0.00 0.00 0.59 0.00 0.00 0.00 0.00 0.00 Total percent 100 100 100 100 100 100 100 100 100 100 Total number of foraminifers 461 29 472 342 338 435 314 283 222 75

I II IIIIIIIIIlII I I I IIIIII iiiiiiiiiiiiiiiii III II IMI II II III I IIIII --

Scott E. Ishman and Kevin M. Foley: Modem benthicforaminifer distribution in the Amerasian Basin, Arctic Ocean

0.00 1.00 2.00 I i I I I

Buccella frigida Fursenkoina fusiformis

Spiroplectammina biformis

Ammotium cassis

Cribroelphidium excavatum

Eggerella advena

Textularia torquata

Textularia kattagatensis

Nonionellina labradorica

Cassidulina teretis

Cassidulina reniforme

Cribroelphidium clavatum

Cassidulina norcrossi

Adercotryma glomerata

Portatrochammina bipolaris Trochammina globigeriniformis

Reophax spp. Recurvoides scitulus

Bolivina arctica

Glomospira gordialis

Quinqueloculina ankeriana

Fontbotia wuellerstorfi

Oridorsalis tener

Triloculina frigida

Quinqueloculina arctica

Valvulineria arctica

Haplophragmoides obscurus

Haplophragmoides parkerae

Eponides tumidulus

TEXT-FIGURE 4 R-mode dendrogram showing the results of the cluster analysis of the PI92-AR and PI93-AR box core top species. Shaded regions highlight major assemblage associations. Textularia spp.-Spiroplectammina biformis Biofacies (T-S Biofacies), Cassidulina teretis Biofacies (C Biofacies), and Oridorsalis tener - Eponides tumidulus Biofacies (O-E Biofacies).

nated foraminifera Portatrochammina bipolaris and Trocham- mina globigeriniformis (text-fig. 4). High component 3 scores are associated with samples that contain this assemblage (table 3).

Oridorsalis tener - Eponides tumidulus Biofacies

The Oridorsalis tener - Eponides tumidulus Biofacies (O-E Biofacies) is dominated by the calcareous benthic species Oridorsalis tener with the ancillary occurrence of Eponides

tumidulus. Other minor but important species in this assemblage are Fontbotia wuellerstorfi, Triloculina frigida and Valvulineria arctica (text-fig. 4). The samples containing this assemblage have high component 1 scores (table 3). In addition, qualitative analysis of samples containing this assemblage shows a high abundance of the species Stetsonia arctica, a species most common in the 263gm to 125gm size fraction. Therefore we recommend qualitative observation of the >63gm to 125gm size fraction.

212


ARCTIC OCEANOGRAPHY AND BENTHIC FORAMINIFERA

The benthic foraminifer distributions from the Amerasian Basin show depth relationships correlating with the vertical distribution of water masses in the Canada Basin. The results from our analyses are used to illustrate this. Temperature and salinity hydrographic profiles from PI92-AR and PI93-AR cruise sites from the Canada Basin (from Perkin, unpublished data 1993) define vertical water column structures common to the Arctic Ocean: Arctic Surface Water (ASW), Arctic Intermediate Water (AIW), and Arctic deep water, in this case Canada Basin Deep Water (CBDW) (text-fig. 5).

The T-S Biofacies is restricted to the ASW layer (text-fig. 6). Textularia spp., Spiroplectammina biformis and Nonionellina labradorica, dominant taxa in the T-S Biofacies do not occur in our samples at depths greater than 447 mbsl. The calcareous benthic Elphidium excavatum, of secondary importance to this assemblage, is a shallow water species common to shelf settings. In addition, the faunal composition of this biofacies is greatly variable. The T-S Biofacies closely resembles the Amerasian Basin Subfacies A of Lagoe (1979) (17 to 45 mbsl) that was dominated by agglutinated foraminifera having a maximum abundance of Spiroplectammina biformis and Textularia torquata. The T-S Biofacies is also similar to the Elphidiidae-Tex- tulariidae fauna (Polyak 1990) that is common to Arctic water depths up to 400 mbsl. The T-S Biofacies is similar to a mix of the assemblages from the inner and outer Lancaster Sound, Baffin Island that Schroder-Adams et al. (1990) describe as an inner agglutinated assemblage dominated by Spiroplectammina biformis and Adercotryma glomerata, and an outer assemblage dominated by Cassidulina laevigata, C. reniforme, Buccella frigida and Cribroelphidium excavatum. Schroder-Adams et al. (1990) also describe an agglutinated assemblage from the margin of Baffin Bay that is very similar to the T-S Biofacies in the Amerasian Basin. They attribute the dominance of agglutinated foraminifera in these regions of the Arctic to extended periods of seasonal ice free conditions and increased meltwater input inhibiting carbonate preservation. A benthic foraminifer assemblage from 3 to 223 mbsl off of Point Barrow, Alaska (Loeblich and Tappan 1953) contains many of the agglutinated taxa described as part of the T-S Biofacies from the Northwind Ridge.

Our second assemblage, the C Biofacies occurs at intermediate depth (402 to 1055 mbsl) on the Northwind Ridge, consistent with the results of Green (1960), Lagoe (1979), Polyak (1990) and Scott et al. (1991) who show maximum abundance of Cassidulina teretis from 300 to 1500 mbsl in the Arctic Ocean. The depth distribution of this assemblage correlates with the occurrence of the AIW (text-fig. 6) in the western Arctic Ocean, and is analogous to the association of the Cassidulina teretis Biofacies (Lagoe 1979) with the Intermediate Atlantic Layer in the Arctic Ocean. Bergsten (1994) reports a Eurasian Basin intermediate water fauna (552-2500m water depth) characterized by species typical of the North Atlantic, including C. teretis. Bergsten (1994) interprets the distribution of the intermediate water fauna as representing the zone of mixing of North Atlantic water in the Arctic down to -2500m. However, our data indicates a strong North Atlantic influence to -1500m, demon- strating a distinction between the Amerasian and Eurasian basins at intermediate depths.

TABLE 3 Results of the Q-mode varimax principal components analysis. Listed are the varimax scores (PC1, PC2, and PC3) for the box core samples.

Box Core PC Score 1 PC Score 2 PC Score 3 P192-B9 0.997 0.04 0.027 P192-B8 0.996 -0.047 0.021 P193-B4 0.995 0.025 0.034 PI93-B8 0.994 0.045 0.028 PI93B-18 0.992 0.04 0.029 PI93B-17 0.986 0.037 0.029 PI92-B12 0.981 0.04 0.035 P192-B16 0.978 -0.037 0.006 P193-B11 0.97 0.048 0.011 P193-B15 0.957 0.038 -0.018 P192-B15 0.802 0.101 -0.025 PI93-B2 0.794 -0.558 -0.023 P192-B7 0.71 -0.621 -0.042 PI92-B17 0.005 -0.967 -0.046 PI92-B5 -0.001 -0.923 -0.135 PI93-B20 -0.083 -0.226 0.018 P192-B1 -0.088 -0.008 0.938 P192-B2 -0.119 0.031 0.929 P192-B3 -0.089 0.013 0.324 PI92-B4 -0.075 0.001 -0.249 PI93-B21 -0.069 -0.025 -0.157 Percent of total variance explained = 76.42%

Samples from water depths 1388 to 3811 mbsl in the Amerasian Basin contain the O-E Biofacies, dominated by Oridorsalis tener and Eponides tumidulus (>50%) with a high qualitative abundance of Stetsonia arctica. This biofacies is associated with the CBDW in the Canada Basin (text-fig. 6). Our data show that at depths >1000m in the Amerasian Basin the distribution of O. tener (>125gm size fraction) represents the distribution of S. arctica (>63gm size fraction). The distribution of this biofacies in the Amerasian Basin is consistent with the depth distribution of similar faunas throughout the western Arctic basin. The Apron and Abyssal Facies of Green (1960) are characterized by the dominance of Eponides tumidulus var. arctica and Eponides tener, respectively, and occupy depths from 1532 to 2760 mbsl. Lagoe (1977, 1979) shows maximum abundance of Stetsonia arctica from 900 mbsl to -3700 mbsl. Scott et al. (1991) report the dominance of Stetsonia arctica at depths >1370 mbsl. Polyak (1990) shows the distribution of the Oridorsalis tener - Eponides tumidulus var. arctica fauna at depths from 900 mbsl to -3500 mbsl. Fontbotia wuellerstorfi occurs in small but significant percentages from the Northwind Ridge at depths from 1055 mbsl to 2135 mbsl. It is also reported from depths ranging from -1500 mbsl to 2700 mbsl (Polyak 1990, Scott and Vilks 1991) throughout the Arctic Ocean. Polyak (1990) sug- gests its occurrence may reflect increased water mobility within this depth range, however, its presence in the Norwegian Sea and North Atlantic may indicate the strong influence of the Atlantic Layer on the formation of the CBDW.

Deep water (>2500m) benthic foraminiferal faunas (>63gm size fraction) from the Eurasian Basin are dominated by Stetsonia arctica and lack significant numbers of Oridorsalis umbonatus (Bergsten 1994). The absence of 0. umbonatus, a dominant deep water species in the Canada Basin, may reflect the differences in origin, and temperature and salinity characteristics between the CBDW and EBDW.

213


Cast 92-4

Sal (%.) 25 26 27 28 29 30 31 32 33 34 35

o A AW 00-

CBDW

1. -1 -0.5 0 0.5. 2 -1.5 .5 0 0.5

Toerp (C)

Cast 92-16 Sal (Oo)

26 27 28 29 30 31 32 33 34 . . . . . . . . .

Temp (C)

Cast 92-9 Cast 92-12

Sal (Co) Sal (O?o)

25 26 27 28 29 30 31 32 33 34 35 25 26 27 28 29 30 31 32 33 34 35

Temp (C) Temp ()C)

Cast 93-21

Temp ('C)

Cast 93-24

Tenp ("C)

Cast 93-26 Salt (?)

25 26 27 28 29 30 31 32 33 34 35 0

ASW s 500 -<

-e

1000-

1500- CBDW

2000

3000 T S

3500

4000 i i | ' ...',...,...,.l ... -2 1 0 1 2 3 4

Temp ("C)

Cast 93-27 Cast 93-29 Sal (%?) Sal (0)

25 28 27 28 29 30 31 32 33 34 35 25 2 27 28 29 30 31 32 33 34 35

I

-r - ----

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-T ^

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1000

1500

T -2000

2500

3500

IIIYTY ..,A.b.al .-. .. l . ... i Ih.' i i., ?'1..J l.....*I.l",...........? ..w 4000 -2 -1.5 -1 -0.5 0 0.5 1 .51. 5 2 2.5-1.5 -1 .5 0 0.5 1 1.5 2 2.5 3

Temp ('C) Temp ("C)

TEXT-FIGURE 5 Conductivity, Temperature and Depth profiles along a depth transect of the Canada Basin from Arctic cruises PI92-AR (Cast 92-X) and PI93-AR (Cast 93-X) showing the major water mases, Arctic Surface Water (ASW), Arctic Intermediate Water (AIW), and Canada Basin Deep Water (CBDW), in the Canada Basin.

214

10 10(

1500-

2000-

2500-

3000-

3500-

4000-

CL 2500 -

0 2500

a

0 c

a

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I


Cast 92-16 Sal (/oo)

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Benthic Foraminifer Biofacies

T-S Biofacles

C Biofacles

O-E Blofacles

Temp (?C)

TEXT-FIGURE 6 Correlation between Canada Basin water masses, Arctic Surface Water (ASW), Arctic Intermediate Water (AIW), and Canada Basin Deep Water (CBDW), and benthic foraminifer assemblages, Textularia spp.-Spiroplectammina biformis Biofacies (T-S Biofacies), Cassidulina teretis Biofacies (C Biofacies), and Oridorsalis tener - Eponides tumidulus Biofacies (O-E Biofacies).

SUMMARY AND CONCLUSIONS The biofacies described above and their association with distinct water masses within the Canada Basin provide significant additional information on the benthic foraminiferal distributions within the Arctic Ocean, particularly the Amerasian Basin region. Our study confirms earlier work that the distribution of Arctic benthic foraminifers is strongly controlled by the major water masses in the Arctic Ocean. Three major benthic foraminifer biofacies are recognized from modem surface samples from the Amerasian Basin in the Arctic Ocean, the Textu- laria spp. - Spiroplectammina biformis Biofacies, Cassidulina teretis Biofacies, and Oridorsalis tener-Eponides tumidulus Biofacies. These assemblages are distributed with depth and are closely associated with the three major water masses in the Canada Basin, the Arctic Surface Water (ASW), Arctic Interme- diate Water (AIW) and Canada Basin Deep Water (CBDW) respectively. The assemblages are characteristic in their species composition and distribution of faunas described from throughout the Arctic Ocean (Green 1960; Lagoe 1977; Lagoe 1979; Polyak 1990; Schroder-Adams et al. 1990; Scott and Vilks 1991; Bergsten 1994). However, distinct differences in species occurrence between the Eurasian and Amerasian basins emphasizes the oceanographic uniqueness of each of these Arctic regions.

ACKNOWLEDGMENTS

This research was funded by the U.S. Geological Survey Global Change and Climate History Program. We would like to thank Richard Z. Poore, Thomas M. Cronin, Harry J. Dowsett, Lisa E. Osterman and David B. Scott for their reviews and helpful comments on the manuscript.

SYSTEMATIC LIST

Adercotryma glomerata (Brady) = Lituola glomerata Brady 1878 Ann. Mag. Nat. Hist., ser. 5, 1, p. 433, pl. 20, figs. 1 a-c. (Plate 1, fig. 6)

Alveophragmium crassimargo (Norman) = Haplophragmium crassimargo Norman 1892, Museum Normanianum, pt.8, p.17

Ammodiscus catinus Hoglund 1947, Zoologiska Bidrag Fran Uppsala, 26, p. 122, pl. 8, figs. 1 and 7; pl. 28, figs. 19 - 23; text Figs. 82 - 84, 105 - 107, 109

Ammotium cassis (Parker) = Lituola cassis Parker 1870, in Dawson, Can. Nat., n. s., 5, pp. 177, 180, fig. 3.

Astrononion gallowayi Loeblich and Tappan 1953, Smith- sonian Misc. Coll., 121, no. 7, p. 90, pl. 17, Figs. 4-7.

Bolivina arctica Herman 1973, Jour. Foram. Res., 3, p. 140, pl. 1, figs. 1-7, text fig. 3.

215

Water Mass

500-

1000o

1500-

E 2000-

S 2500-

3000-

3500-

ASW

AIW

CBDW

0.5


Buccellafrigida (Cushman) = Pulvinulinafrigida Cushman 1921, Results of the Hudson Bay Expedition, 1920, 1. The foraminifera: Contributions to Canadian Biology, 9, p. 135- 147.

Cassidulina norcrossi (Cushman) = Islandiella norcrossi Cushman 1933, Smithsonian Misc. Coll., 89(9), p. 7, pl. 2, fig. 7.

Cassidulina reniforme (Norvang) = Cassidulina crassa d' Or- bigny var. reinforme Norvang 1945, The zoology of Ice- land. Foraminifera 2(2): 1-79. (Plate 2, fig. 5)

Cassidulina teretis Tappan 1951, Contr. Cushman Found. Foram. Res., 2, pt. 1, p. 7, pl. 1, fig. 30. (Plate 2, fig. 4)

Cibicides lobatulus (Walker and Jacob) = Nautilus lobatulus Walker and Jacob, in Kanmacher 1798, p.642, pl. 14, fig. 36.

Cribrostomoides sp. Dentalina pauperata d'Orbigny 1846, Foraminiferes fossiles du

Bassin Tertiaire de Vienne, Paris, p. 46, pl. 1, figs, 57-58. Discorbis squamata Parker 1952, Bull. Mus. Comp. Zool.,

106, p. 418, pl. 6, figs. 10a, 10b, 11. Eggerella advena (Cushman) = Verneuilina advena Cushman

1922, Results of the Hudson Bay Expedition, 1920, I. The foraminifera: Contributions to Canadian Biology, 9, p. 135- 147.

Elphidium clavatum (Cushman) = Elphidium incertum (Wil- liamson) var. clavatum Cushman 1930, United States Na- tional Museum Bulletin, 104, p. 20, pl. 7, fig. 10..

Elphidium excavatum (Terquem) = Polystomella excavata Ter- quem 1876, Societd Dunquerquoise, Memoires, 19 (1874- 75) p. 429.

Eponides tumidulus (Brady) = Truncatulina tumidula Brady 1884, Rept. Voy. Challenger, vol. 9 (Zoology), p. 666, pl. 95, figs. 8a-d. (Plate 2, fig. 10)

Fontbotia wuellerstorfi (Schwager) = Anomalina wuellerstorfi Schwager 1866, Fossile foraminiferen von Kar-Nicobar, Geol. Theil, 2, no. 1, Geologische Beobachtungen, no. 2, Palaontologische Mitteheilungen, p. 258, pl. 7, figs. 105, 107. (Plate 2, fig. 6)

Fursenkoina fusiformis (d'Orbigny) = Bulimina pupoides d'Or- bigny var. fusiformis Williamson,1858, On the Recent Foraminifera of Great Britain: Roy. Soc. Pub., p. 64, pl. 5, figs. 129-130.

Glandulina laevigata (d'Orbigny) = Nodosaria laevigata d' Orbigny 1826, Ann. Sci. Nat., ser. 1, 7, p. 252, pl. 10, figs. 1-3.

Glomospira gordialis (Jones and Parker) = Trochammina squamata var. gordialis Jones and Parker 1860, Quarterly Jour. Geol. Soc. London, 16, p. 304. (Plate 1, fig. 12)

Haplophragmoides obscurus O'Neill 1981, Journal of Paleon- tology, 55(6), p. 1160, pl. 2, figs. 13, 17.

Haplophragmoides parkerae (Uchio) = Recurvoidella parkerae Uchio 1960, Cushman Foundation for Foraminiferal Research Special Publication, 5, p. 53, pl. 1, figs. 18-19.

Melonis barleeanum (Williamson) = Nonionina barleeana Williamson 1858, On the Recent Foraminifera of Great Britain: Roy. Soc. Pub., p. 32, pl. 3, figs. 68-69.

Miliammina arenacea (Chapman) = Miliolina oblonga (Mon- tagu) var. arenacea Chapman 1916, Report on the Foraminifera and Ostracoda out of marine muds from soundings in the Ross Sea: British Antarc. Exped. 1907- 1909, Geology, 2(3), p. 59, pl. 1, fig. 7.

Nodosariids. Includes a variety of unilocular calcareous benthic species.

Nonionellina labradorica (Dawson) = Nonionina labradorica Dawson 1860, Canadian Naturalist, 5, p. 191, fig. 4.

Oridorsalis tener (Brady) = Truncatulina tenera Brady 1884, Rept. Voy. Challenger, 9 (Zoology), pl. 95, figs. 11. (Plate 2, fig. 9)

Oridorsalis umbonatus (Reuss) = Rotalina umbonatus Reuss, 1851, Zeitschrift der Deutschen Geoligischen Gesell- schaft, Berlin, 3, p. 75, pl. 5, figs. 35 a-c.

Portatrochammina bipolaris (Brady) = Haplophragmium nanum Brady 1881, Ann. Mag. Nat. Hist., 5(8), p. 406, pl. 21, figs. la-lc. (Plate 1, fig. 8)

Pyrgo williamsoni (Silvestri) = Biloculina williamsoni Sil- vestri 1923, Accad. pontif. Nuovi Lincei 76, p. 73, pl. 6, figs. 169-170.

Quinqueloculina akneriana d' Orbigny, 1846, Foraminiferes fossiles du Bassin Tertiare de Vienne, p. 290, pl. 18, figs. 16-21. (Plate 2, fig. 7)

Quinqueloculina arctica Cushman 1933, New Arctic Foraminifera collected by Capt. R.A. Bartlett from Fox Ba- sin and off the northeast coast of Greenland: Smithsonian Misc. Collection, 89(9), p. 2, pl 1, fig. 3 a-c.

Recurvoides scitulus (Brady) = Haplophramium scitulum Brady 1881, Konigliche Akademie der Wissenschaft Wein, Denkschriften, 43, p. 50. (Plate 1, fig. 10)

Reophax spp. Reophax guttifer (Brady) = Lituola (Reaphax) guttifera Brady

1881. Ueber einige arktische Tiefsee-Foraminiferen gesam- melt wihrend der osterreichisch-ungarischen Nordpol-Ex- pedition den Jahren 1872-74: Denjschriften der Kaiserlichen Akademie der Wissenschaften Wein Mathe- matisch-naturwissenschaftlichen Classe, 43, p. 9-110. (Plate 1, fig. 2 in this paper)

Plate 1 Scanning electron micrographs of selected species described from the Amerasian Basin box core-tops. Vertical scale bars represent

100Igm except where noted that they represent 10Igm.

1 Reophax nodulosus, PI-92-AR-B4.

2 Reophax guttifer PI-92-AR-B4.

3 Textularia torquata, PI-92-AR-B4.

4 Spiroplectammina biformis, PI-92-AR-B4.

5 Eggerella advena, PI-92-AR-B4.

6 Adercotryma glomerata, PI-92-AR-B4.

7 Ammodiscus catinus, PI-92-AR-B 15.

8 Portatrochammina bipolaris, PI-92-AR-B4.

9 Trochammina globigeriniformis, PI-92-AR-B4.

10 Recurvoides scitulus, PI-92-AR-B4.

11 Haplophragmoides parkerae, PI-92-AR-B5.

12 Glomospira gordialis, PI-92-AR-B 15.

13 Elphidium excavatum, PI-92-AR-B3.

216

Scott E. Ishman and Kevin M. Foley

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micropaleontology, vol. 42, no. 2, 1996

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Scott E. Ishman and Kevin M. Foley: Modem benthicforaminifer distribution in the Amerasian Basin, Arctic Ocean

Reophax nodulosus Brady 1879, Quarterly Journal of Micro- scopical Science, 19, p. 52, pl. 4, figs. 7-8. (Plate 1, fig. 1)

Reophax scorpiurus Montfort 1808, Conchyliologie syst6ma- tique, 1, p. 330-331.

Robertinoides charlottensis (Cushman) = Cassidulina charlottensis Cushman 1925, Contr. Cushman Lab. Foram. Res., 1, pt. 2, p. 41, pl. 6, figs. 6, 7.

Saccammina diflugiformis (Brady) = Reophax difflugiformis Brady 1879, Notes on some of the Reticularian Rhizopoda of the Challenger Expedition: Quarterly Journal of Micro- scopial Science, n. series, 19, p. 20-62.

Spiroplectammina biformis = Textularia agglutinans (d' Or- bigny) var. biformis Parker and Jones 1865, Philos. Trans. Roy. Soc. London, 155, p. 370, pl. 15, figs. 23-24. (Plate 1, fig. 4)

Stainforthia concava H6glund 1947, Zoologiska Bidrag Fran Uppsala, 26, p. 257, pl. 23,figs. 3, 4; pl. 32, figs. 4-7; text fig. (plate 2, fig. 2 in this paper)

Stetsonia arctica (Green) = Epistominella arctica Green 1960, Micropaleontology, 6, no. 1, p. 71, pl. 1, figs. 4a, 4b. (Plate 2, fig. 11)

Textularia kattagatensis Hogland 1948, Cushman Found. Foram. Res., 24, p. 45-46.

Textularia torquata F. Parker 1952, Bull. Mus. Comp. Zool., 106, no. 9, p. 403, pl. 3, figs. 9-11. (Plate 1, fig. 3)

Triloculinafrigida Lagoe 1977, Jour. Foram. Res. 7, no. 2, p. 120, pl. 1, figs. 12, 17, 18; text figs. 6D, 6E. (Plate 1, fig. 8)

Trochammina globigeriniformis (Parker and Jones) = Lituola nautiloidea Lamark var. globigeriniformis Parker and Jones 1865, Philos. Trans. Roy. Soc. London, 155, p. 407, pl. 17, fig. 96. (Plate 1, fig. 9)

Trochammina pseudoinflata Scott and Vilks 1991, Jour. Foram. Res, 21, no. 1, p. 35,pl. 2, figs. 3-6.

Valvulineria arctica Green 1960, Micropaleontology, 6, no. 1, p. 71, pl. 1, fig. 3a - c. (Plate 2, fig. 12)

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, 1979. Recent benthic foraminiferal biofacies in the Arctic Ocean. Micropaleontology, 25: 214-224.

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POLYAK, L. V., 1990. General trends of benthic foraminiferal distribution in the Arctic Ocean. In: V. M. Kotlyakov and V. E. Sokolov, Arctic Research: Advances and Prospects: Proceedings of the Conference of Arctic and Nordic Countries on Coordination of Research in the Arctic. Leningrad, Nauka, 447.

Plate 2 Scanning electron micrographs of selected species described from the Amerasian Basin box core-tops. Vertical scale bars represent

100gLm except where noted that they represent 10,gm.

1 Buccellafrigida, PI-92-AR-B3.

2 Stainforthia concava, PI-92-AR-B3.

3 Cassidulina norcrossi, PI-92-AR-B3.

4 Cassidulina teretis, PI-92-AR-B7.

5 Cassidulina reniforme, PI-92-AR-B7.

6 Fontbotia wuellerstorfi, PI-92-AR-B 15.

7 Quinqueloculina akneriana, PI-92-AR-B9.

8 Triloculinafrigida, PI-92-AR-B9.

9 Oridorsalis tener, PI-92-AR-B9.

10 Eponides tumidulus, Pi-92-AR-B9.

11 Stetsonia arctica, PI-92-AR-B9.

12 Valvulineria arctica, PI-92-AR-B9.

218

Scott E. Ishman and Kevin M. Foley

-A 'gt

r

micropaleontology, vol. 42, no. 2, 1996

Plate 2

. ,

, _a

: :g; X I

219


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SCOTT, D. B. AND MEDIOLI, F. S., 1980. Living vs. total foraminiferal populations: their relative usefulness in paleoecology. Journal of Paleontology, 54: 814-831.

SCOTT, D. B., MUDIE, P. J., BAKI, V., MACKINNON, K. D. AND COLE, F. E., 1989. Biostratigraphy and late Cenozoic paleoceanography of the Arctic Ocean: Foraminiferal, lithostratigraphic, and

isotopic evidence. Geological Society of America Bulletin, 101: 260-277.

SCOTT, D. B. AND VILKS, G., 1991. Benthic foraminifera in the surface sediments of the deep-sea Arctic Ocean. Journal of Foraminif- eral Research, 21: 20-38.

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Manuscript received June 28, 1994 Manuscript accepted April 28, 1995

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