deep-water foraminifera communities of the arctic ocean

9
ISSN 00014370, Oceanology, 2011, Vol. 51, No. 1, pp. 60–68. © Pleiades Publishing, Inc., 2011. Original Russian Text © Kh.M. Saidova, 2011, published in Okeanologiya, 2011, Vol. 51, No. 1, pp. 65–73. 60 INTRODUCTION The investigated regions are located in the arctic biogeographical province of the Arctic Ocean [5]. The negative average multiannual radiative balance [3]; the yearround presence of ice; the negative tempera tures of the whole water column lower than the surface Atlantic and Pacific waters; the high salinity of the waters; the low primary production; and the sufficient saturation of the benthal waters and ground with О 2 , СаСО 3 , and C org for the lives of the benthic foraminifera at all the depths are the basic features of this province. A relatively low amount of research works are devoted to the investigation of the quantitative content of the bathyal and abysmal species of benthic foramin ifera and their ecology in the Arctic Ocean. Four of the most important indicator species spe cific to some depths—Cassidulina teretis (433–510 m), Valvulineria arctica (619–1142 m), Eponides tumidulus (1532–2000 m), and Eponides tener horvathi (2250– 2760 m)—were specified by K.E. Green [27] accord ing to their relative percent content at the continental slope of North America near Lake Ellesmere at depths of 600–2800 m. Biofacies of Cassidulina teretis specific to the Atlan tic water and biofacies of Stetsonia horvathi specific to the benthal waters were found by M.B. Lagoe [28, 29] using the relative number of foraminifera in the region of the southern end of the Mendeleev ridgelet and the Chukchee upheaval at depths of 300–900 m and 900– 4000 m, respectively. The quantitative predominance of the living and dead examples of the Eponidеs tumidulus and Oridorsalis tener species was revealed by T.A. Khusid [20] at the base of the continental slope of the Canadian archipel ago at depths of 2710–3580 m. The community of Lernina neoteretis, which is found everywhere, and the communities of Saccam mina sphaerica, Recurvoides contortus, Oridorsalis umbonatus, and Stetsonia horvathi, which are found at some areas of the bottom, were isolated based on the dominance of the species by Kh.M. Saidova [14] in the upper part of the continental slope at a depth of 300– 800 m near the Queen Elizabeth archipelago. Oridorsalis umbonatus, Eponides tumidulus, and Plan ulina wuellerstorfi dominated in number and were detected by D.B. Scott and G. Vilks [32] at the Lomonosov ridgelet near the North Pole at a depth of 1570–1980 m. In Amundsen bolson near Greenland, the following dominating species were isolated: Stetso nia arctica at a depth of 3825–4060 m; at the continen tal slope of the Spitzbergen archipelago at depths of 795–1100 m species of genera Reophax and Trocham mina were dominant, while Hyperammina friabilis was dominant at a depth of 4214—4225 m. The analysis of the relative content of the living for aminifera in the various granulometric fractions of the ground was performed by H. Bergsten [25], J.E. Wol lenberg [33], and J.E. Wollenberg and Mackensen [34]. These data showed a misalignment of the domi nating species in those fractions during the summer time in the Eurasian sector of the Arctic Ocean. The assemblies of species that may serve as indicators of the water masses, the productivity of the waters, and the directions of ice drifting were marked. The biogeography and ecological features of the foraminifera communities revealed according to the dominating species and the distribution of these com munities in other regions of the World Ocean were considered in the present work. MATERIALS AND METHODS The data on the absolute or relative content of the foraminifera species in the surface layer (0–1 cm) of the ground published in 254 pages as well as data on DeepWater Foraminifera Communities of the Arctic Ocean Kh. M. Saidova Shirshov Institute of Oceanology, Russian Academy of Sciences, pr. Nakhimovskii 36, Moscow, 117997 Russia Received February 4, 2009; in final form, October 9, 2009 Abstract—Sixteen foraminifera communities were distinguished on the basis of the quantitative analysis of the composition of the benthic foraminifera in the bottom sediments sampled at 254 stations at depths from 200 to 4411 m in the Arctic Ocean. The distribution of these communities is controlled by the environmental factors, which depend on the latitude and bathymetric zones of the Arctic Ocean, the currents, the water masses, and the content of calcium carbonate and organic carbon in the bottom water and in the sediments. DOI: 10.1134/S0001437011010152 MARINE BIOLOGY

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Page 1: Deep-water foraminifera communities of the Arctic Ocean

ISSN 0001�4370, Oceanology, 2011, Vol. 51, No. 1, pp. 60–68. © Pleiades Publishing, Inc., 2011.Original Russian Text © Kh.M. Saidova, 2011, published in Okeanologiya, 2011, Vol. 51, No. 1, pp. 65–73.

60

INTRODUCTION

The investigated regions are located in the arcticbiogeographical province of the Arctic Ocean [5]. Thenegative average multi�annual radiative balance [3];the year�round presence of ice; the negative tempera�tures of the whole water column lower than the surfaceAtlantic and Pacific waters; the high salinity of thewaters; the low primary production; and the sufficientsaturation of the benthal waters and ground with О2,СаСО3, and Corg for the lives of the benthic foraminiferaat all the depths are the basic features of this province.

A relatively low amount of research works aredevoted to the investigation of the quantitative contentof the bathyal and abysmal species of benthic foramin�ifera and their ecology in the Arctic Ocean.

Four of the most important indicator species spe�cific to some depths—Cassidulina teretis (433–510 m),Valvulineria arctica (619–1142 m), Eponides tumidulus(1532–2000 m), and Eponides tener horvathi (2250–2760 m)—were specified by K.E. Green [27] accord�ing to their relative percent content at the continentalslope of North America near Lake Ellesmere at depthsof 600–2800 m.

Biofacies of Cassidulina teretis specific to the Atlan�tic water and biofacies of Stetsonia horvathi specific tothe benthal waters were found by M.B. Lagoe [28, 29]using the relative number of foraminifera in the regionof the southern end of the Mendeleev ridgelet and theChukchee upheaval at depths of 300–900 m and 900–4000 m, respectively.

The quantitative predominance of the living anddead examples of the Eponidеs tumidulus and Oridorsalistener species was revealed by T.A. Khusid [20] at thebase of the continental slope of the Canadian archipel�ago at depths of 2710–3580 m.

The community of Lernina neoteretis, which isfound everywhere, and the communities of Saccam�

mina sphaerica, Recurvoides contortus, Oridorsalisumbonatus, and Stetsonia horvathi, which are found atsome areas of the bottom, were isolated based on thedominance of the species by Kh.M. Saidova [14] in theupper part of the continental slope at a depth of 300–800 m near the Queen Elizabeth archipelago.

Oridorsalis umbonatus, Eponides tumidulus, and Plan�ulina wuellerstorfi dominated in number and weredetected by D.B. Scott and G. Vilks [32] at theLomonosov ridgelet near the North Pole at a depth of1570–1980 m. In Amundsen bolson near Greenland,the following dominating species were isolated: Stetso�nia arctica at a depth of 3825–4060 m; at the continen�tal slope of the Spitzbergen archipelago at depths of795–1100 m species of genera Reophax and Trocham�mina were dominant, while Hyperammina friabilis wasdominant at a depth of 4214—4225 m.

The analysis of the relative content of the living for�aminifera in the various granulometric fractions of theground was performed by H. Bergsten [25], J.E. Wol�lenberg [33], and J.E. Wollenberg and Mackensen[34]. These data showed a misalignment of the domi�nating species in those fractions during the summertime in the Eurasian sector of the Arctic Ocean. Theassemblies of species that may serve as indicators of thewater masses, the productivity of the waters, and thedirections of ice drifting were marked.

The biogeography and ecological features of theforaminifera communities revealed according to thedominating species and the distribution of these com�munities in other regions of the World Ocean wereconsidered in the present work.

MATERIALS AND METHODS

The data on the absolute or relative content of theforaminifera species in the surface layer (0–1 cm) ofthe ground published in 254 pages as well as data on

Deep�Water Foraminifera Communities of the Arctic OceanKh. M. Saidova

Shirshov Institute of Oceanology, Russian Academy of Sciences, pr. Nakhimovskii 36, Moscow, 117997 RussiaReceived February 4, 2009; in final form, October 9, 2009

Abstract—Sixteen foraminifera communities were distinguished on the basis of the quantitative analysis ofthe composition of the benthic foraminifera in the bottom sediments sampled at 254 stations at depths from200 to 4411 m in the Arctic Ocean. The distribution of these communities is controlled by the environmentalfactors, which depend on the latitude and bathymetric zones of the Arctic Ocean, the currents, the watermasses, and the content of calcium carbonate and organic carbon in the bottom water and in the sediments.

DOI: 10.1134/S0001437011010152

MARINE BIOLOGY

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DEEP�WATER FORAMINIFERA COMMUNITIES OF THE ARCTIC OCEAN 61

the benthal temperature, the water salinity, and thecontent of СаСО3 and Corg [14, 20, 25, 27, 28, 29, 32,33, 34] served as the material for the isolation of thesecommunities.

These stations on the field traverse (Fig. 1) weredistributed as follows: field traverse 1—4 stations atdepths of 192–562 m; field traverse 2—67 stations atdepths of 1069–3812 m; field traverse 3—70 stationsat depths of 200–3580 m; field traverse 4—10 stationsat depths of 1570–4225; field traverse 5—3 stations atdepths of 3825—4060 m; field traverse 6—10 stationsat depths of 795—3675 m. Along the profiles, 76 sta�tions were located (Fig. 2), and 11 stations werelocated separately (Figs. 1, 2).

The communities of benthic foraminifera weredetected and titled according to the species dominat�ing by number. At that, their shells with and withoutplasma that passed a cycle of reproduction were sum�

marized. The species forging ahead after the dominantones were referred to subdominant ones.

The taxonomic accessory of these species is pre�sented in agreement with the recent systems for fora�minifera [10, 11, 30].

ENVIRONMENT

Underwater topography. The continental slopes ofEurasia, North America, and Greenland are relativelysharp and narrow. In places, the slopes are stair�stepped and complicated with boundary plateaus andgorges. The width of the continental base reaches inplaces 150–300 km. At the sea floor, bolsons separatedwith ridgelets are marked. The Nansen bolson is rela�tively narrow with a champaign bottom and a maximaldepth of 5449 m. The bottom of the Amundsen bolsonis smooth�faced, but, in the Greenland sector, it iscomplicated with a longitudinal upheaval. The maxi�

Greenland

Fram gat

North

Bering Strait

No

rth

Am

eric

a

Q u e e n E l i z a b e t h

Pole

Spitzbergen

Eurasia

90°E 180°

1

2

3

4

56

Am

undsen bolson

Makarov bolson

Nansen bolson

The Canadian bolson

Fig. 1. The location of field traverses 1–6 and the separate stations in the Arctic Ocean where the foraminifera communities werestudied. 1—The continental slope at Laptev Sea; 2—the continental slope and the Canadian bolson at the Chukot plateau; 3—the continental slope at the archipelago of Queen Elizabeth and Beaufort Sea; 4—the slope of the Lomonosov ridgelet and theMakarov bolson; 5—the Amundsen bolson in the Greenland sector; 6—the continental slope at the Ermak plateau; isolines—depths of 2000 m; black points—the separate stations.

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mal depth of the bolson is 4425 m. The bottom of theMakarov bolson (including Podvodnikov’s bolson) isshallow, champaign, and with a maximal depth of 4007 m.The bottom of the Canadian bolson is slightly slopingand billowy with a maximal depth of 3879 m. Themaximal depths of the bottom in all bolsons arelocated in the western sector of the ocean.

Gakkel ridgelet is a narrow separated with lateralruptures. The slopes of the Lomonosov ridgelet aresharp and slightly dissected. Mendeleev’s ridgelet isbroad; in the middle part, it is narrow and buried [2, 6].

Grounds. Two milliards of aqueous terrigenousdeposits are introduced annually into the ArcticOcean. The main part of the deposits subsides at theshelf and at the upper part of the continental slope [1].At the continental slopes and ridgelets, the depositsare represented by aleurites gradually transforminginto aleurite–pelites. In the bolsons, pelites are pre�dominantly accumulated [1, 2, 6].

The amount of СаСО3 in the deposits at the conti�nental slope of Eurasia accumulates in dependence onthe depth (from 2% to 11%), while at the ridgeletslopes, it reduces from 12% to 5.5%. In the bolson ofthe sea floor, the content of СаСО3 varies in the rangeof 1.7–10.7%. The amount of Corg in the deposits atthe continental slope of the Canadian archipelagoreduces in dependence on the depth from 0.8% to

0.2% [27]. In the western part of the Eurasian conti�nental slope, the amount of Corg in the deposites isabout 0.3–0.9%. At the ridgelets and in bolsons of thesea floor, its content is 0.2–1.9% [33].

Hydrology. The warm Atlantic waters with a tem�perature of 1.5–2.0°С are introduced into the ArcticOcean with the Norwegian–Spitzbergen flow throughthe Fram gat. With advancing along Eurasia to theEast, the temperature of these waters is reduced to0.5°С. Warm Pacific waters with surface temperaturesof 2–3°С are introduced into the Ocean through theBering Strait with the Alaska flow. These waters aredirected to the East along Alaska.

The Atlantic waters and a part of Pacific waters atthe longitudes of the Chukchee Sea change theirdirection to the West, and, in the eastern sector of theOcean with the recurrent trans�Arctic flow, they areredirected to the Fram gat. The temperature of thesewaters is 0.5–1.0°С at a depth of 300 m. In the westernsector of the Ocean, the Atlantic and Pacific watersform an anticyclonic circulation with the water tem�perature being –1 to 0°C [4, 8, 24, 35].

The circulation of the deep layers of the oceanicwaters is poorly investigated. It is suggested that, in thebolsons of Nansen and Amundsen, the circulation hasa cyclonic character, while, in the Canadian bolson,an anticyclonic one as at the surface [19].

82° 84° 86° 88°N

W

10°

10°

20°

40° 70°E

130°

100°

I

II

III

IV

V

Fig. 2. The location of profiles I–V and the stations in the Arctic Ocean [33] where the communities of benthic foraminifera wereinvestigated.

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DEEP�WATER FORAMINIFERA COMMUNITIES OF THE ARCTIC OCEAN 63

Four water masses (w.m.) may be pointed out in theabyssal arctic province of the ocean according to thepublished data [4, 7, 22, 23, 26]. The underwater sur�face arctic w.m. occupies depths less than 50–100 m.Its temperature increases from –1.5 to 1.7°С, whilethe salinity is from 32.2 to 34.0‰. Up to the 750–1000 m depth, there is the warm Atlantic w.m. Its tem�perature increases gradually with the depth from 0 to1.5°С, while the salinity increases from 34.5 to34.9 per mille. Up to the 1500 m depth, in the Green�land sector of the ocean, there is the cooled recurrentAtlantic water, with a temperature below 0°C. Thebottom w.m. is situated deeper than the intermediatew.m. to the maximal depths of the sea floor. Its temper�ature reduces to –0.96°C, while the salinity increasesto 34.95‰.

The content of oxygen in the water column in theArctic province reduces with the depth from 0.8 to0.59 mg�atm/l, and to 0.55 mg�atm/l in the Canadianbolson. The water saturation with Ca СаСО3 rarelyreaches 100% [9].

Biota. The phytoplankton biomass in the waters ofthe arctic province in the vegetation period may reach0.6 g/m2 owing to the cryopelagic biotic communities.

The data on benthos biomass in this province is frag�mentary. It is suggested that it may reach 5 g/m2 [18].

BIOGEOGRAPHY AND ECOLOGY OF THE FORAMINIFERA COMMUNITIES

The benthic foraminifera in the abysmal arcticprovince are represented by 360 species. At the conti�nental slopes and the slopes of the underwater ridge�lets, the biodiversity of the foraminifera reduces withthe depth, and, at the bottom of the deep bolsons, only20 species were found.

In this province, 16 communities of benthic fora�minifera were revealed. The dominating species in thecommunities represent 30–50%. In the regions withunfavorable conditions, the predominance of the prin�cipal species may increase to 60–80% and more.

The taxonomic content of the communities is pre�sented in the table. Their distribution area is shown byFigs. 3–7.

The Lobatula lobatula community is distributednear the archipelagos of Spitzbergen and Queen Eliz�abeth (Figs. 6, 7) at depths less 500 m at sand–aleuritegrounds containing 5–38% СаСО3 and 0.3—2.2%

Taxonomic content of the deep�water communities of benthic foraminifera of the Arctic Ocean

Dominating species Subdominating species

Lobatula lobatula Astrononion gallowayi, Pullenia osloensis, Buccella tenerima, Lernina neoteretis

Pseudobolivina torquata Spiroplectammina earlandi, S. biformis, Morulaeplecta arctica, Ammodiscus sp.,Lagenamina arenulata, Saccorhiza ramosa

Lernina neoteretis Melonis zaandami, Peschongia arctica, Valvulineria arctica, Ioanella horvathi, Reophanus guttifer, Pseudobolivina torquata

Proteonella laguncula R. guttifer, Hyperammina sp., L. neoteretis

Oridorsalis tenerus Triloculina frigida, P. arctica, I. horvathi, Placopselinella aurantiaca, Adercotryma glomerata

Adercotryma glomerata P. arctica, I. horvathi, L. neoteretis,Buliminella elegantisima, Oridorsalis tenerus, P. aurantiaca, Stetsonia horvathi

Fontobotia wuellerstorfi O. tenerus, Quinqueloculina arctica, Q. akneriana, Miliolinella sp.

Peschongia arctica A. glomerata, I.horvathi, P. aurantiaca, L. neoteretis, O. tenerus

Reophanus guttifer Cribrostomoides gr. subglobosus, A. glomerata, Fontobotia wuellerstorfi, Ioanella tu�midula, T. frigida

Triloculina frigida I. horvathi, A. glomerata, R. guttifer, S. horvathi

Placopsilinella aurantiaca S. horvathi, Alabamminoides exiguus, Sorosphaera depressa, T. frigida, F. wuellerstorfi, O. tenerus, I. tumidula

Ioanella tumidula O. tenerus, F. wuellerstorfi, S. horvathi, A. exiguus, T. frigida, L. neoteretis

Stetsonia horvathi Aschemonella scabra, S. depressa, Hippocrepina flexibilis, P. aurantiaca, A. exiguus, O. tenerus

Stetsonia horvathi – Sorosphaera depressa A. scabra, Reophax fusiformis, Lagenammina tubulifera

Sorosphaera depressa S. horvathi, A. scabra, H. flexibilis, R. fusiformis, Subreophax aduncus

Hyperammina friabilis S. depressa, Rhizammina algaeformis, Psammosphaera fusca, Pseudonodosinella nodulosa, S. horvathi

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Corg with the temperature of the benthal water beingnear 0°С with salinity of 34.6–34.8‰.

In other regions of the World Ocean, this commu�nity is represented at shelves of the arctic seas and sub�arctic and boreal shelves of the Atlantic Ocean [14, 15,21, 31].

The Pseudobolivina torquata community is found atthe external shelf and in the upper part of the conti�nental slope of the Laptev Sea and the archipelagos ofSpitzbergen and Queen Elizabeth (Fig. 1—fieldtraverse 1; Figs. 3, 4) at depths less 700 m at aleuritegrounds containing 3.7–12.7% СаСО3 and 0.8–0.9%Corg with the temperature of the benthal water being0.5–1.0°C with salinity of 34.8–34.94‰.

In other basins, this community is found at theshelf and in the upper part of the continental slope ofthe Atlantic Ocean [14].

The Lernina neoteretis community is distributed inthe upper part of the continental slope at depths downto 1024 m at the archipelago of Spitzbergen, near theBeaufort Sea, and at archipelago of Queen Elizabethdeeper than the community of Pseudobolivina torquataat aleurite grounds containing 2.4–2.0% СаСО3 and0.5–1.6% Corg with the temperature of the benthalwater being 0.9–1.0°С with salinity of 34.92–34.94‰(Fig. 1—field traverse 3; Figs. 3, 4, 6, 7).

This community is found on the upper part of thecontinental slope of the Scandinavian Peninsula at theslopes of the Faroe–Iceland ridge and in the easternpart of the Fram gat [21].

The Proteonella laguncula community is distrib�uted deeper than the Lernina neoteretis community onthe upper part of the continental slope of Eurasia at

М

1000

2000

3000

42°54′ 40°26′E

1

2

3

4

Th

e N

anse

n b

ols

on

82°12′ 82°76′N

2

Fig. 3. Communities of benthic foraminifera of the conti�nental slope of Eurasia in the Barents Sea (profile I).(1) Pseudobolivina torquata; (2) Lernina neoteretis;(3) Reophanus guttifer; (4) Triloculina frigida.

31°29′

30°31′

60°14′

69°20′

108°

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2000

3000

4000

5000

81°46′

83°95′

84°88′

86°44′

87°59′

87°71′

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kel r

idge

let

Am

un

dse

n b

ols

on

Lom

on

oso

v ri

dge

let

Makarov bolson

2 3

4

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134°

85′

144°

48′

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68′E

88°04′

87°57′

87°63′N

5

6

7

8

9

5

9

8

77

5

55

5

Nan

sen

bo

lso

n

Fig. 4. Communities of benthic foraminifera in the ArcticOcean in the region of profile II.

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DEEP�WATER FORAMINIFERA COMMUNITIES OF THE ARCTIC OCEAN 65

the Ermak plateau (Fig. 1—field traverse 6) at a depthof 803–1085 m at aleurite grounds with the tempera�ture of the benthal waters being 0–5°С with salinityof 35‰.

The Oridorsalis tenerus community was detected onthe upper part of the continental slope at the archipel�ago of Queen Elizabeth (Fig. 1—field traverse 3) at adepth of 879—1698 m, in Greenland at the plateau ofMirris–Jessup (Fig. 6) at a depth of 1072, and at theslope of the Gakkel ridgelet (Fig. 4) at a depth of1911–2004 m at sand–aleurite grounds containing 7–11% СаСО3 and 0.2–1.0% Corg with the temperatureof the benthal water being –0.4 to –0.8°С with salinityof 34.91–34.93‰.

The Adercotryma glomerata community is founddeeper than the Oridorsalis tenerus community at thecontinental slope of Greenland at the plateau of Mir�ris–Jessup (Fig. 1—field traverse 5; Fig. 6) at a depthof 1099 m at aleurite grounds containing 26–8%СаСО3 and 0.34% Corg with the temperature of thebenthal water being –0.4°С with salinity of 34.91‰.

In other regions of the World Ocean, this commu�nity is distributed in the Baffin Sea near the Canadianarchipelago at a depth of 100–800 m at the externalshelf of North America in the region of the Labradorcold current [14, 15] and in the Bering Sea at thenorthern shelf [12].

The Fontobotia wuellerstorfi community is found onthe upper part of the continental slope of Greenlandnear the plateau of Mirris–Jessup (Fig. 6) at a depth of1614 m at sand–aleurite grounds containing 12.2%СаСО3 and 0.3% Corg with the temperature of thebenthal water being –0.6°С with a salinity of 34.93‰.

In other basins, this community is revealed in theNorwegian Sea near the Scandinavian Peninsulanorthward at the latitude of 63°N at a depth of 1600–2900 m [17] and in the eastern part of the deep�waterbolson of the Gulf of Mexico at a depth of 2200 m [16].

The Peschongia arctica community is distributed atthe slopes of the Lomonosov ridgelet (Fig. 1—fieldtraverse 6; Fig. 4) at a depth of 1051–1980 m, on theupper part of the continental slope in the region of theChukot plateau (Fig. 1—field traverse 2) at a depth of1051–1980 m, and at the archipelago of Queen Eliza�beth (Fig. 1—field traverse 4) at a depth of 740–1142 m.This community is developing at aleurite and aleu�rite–pelite grounds containing 5.4–9.2% СаСО3 and0.5–0.62% Corg with the temperature of the benthalwater being –0.5°С with salinity of 34.91–34.93‰.

The Reophanus guttifer community is distributeddeeper than the Lernina neoteretis community at thearchipelagos of Spitzbergen and Franz Joseph Land inthe upper and in the middle part of the continentalslope (Fig. 1—field traverse 6; Fig. 3, 4, 6, 7) at adepth of 1394–2439 m at sand–aleurite and slitgrounds containing 5.0–13.6% СаСО3 and 0.55–1.75% Corg with the temperature of the benthal waterbeing from –0.5 to –0.9°С with salinity of 34.91–34.93‰.

The Triloculina frigida community is found on thelower part of the continental slope in the Barents Sea(Figs. 3, 4) deeper than the Reophanus guttifer com�munity at a depth of 2875–2994 m at aleurite–peliticgrounds containing 5.70–8.83% СаСО3 and 1.85–1.89% Corg with the temperature of the benthal waterbeing from –0.94°С and with a salinity of 34.94‰.

The Ioanella tumidula community is found on thelower part of the continental slope at the Chukot

W 11°09′ 9°47′ 127°21′ 140°36′ 138°16′E

М

1000

2000

3000

4000

500087°53′ 88°00′ 89°96′ 88°76′ 88°51′ 88°02′N

110°82′

Gakkel ridgelet

Amundsen bolson

Lomonosov ridgelet

Mak

arov

bo

lso

n

1

2

3

4

1 1

Fig. 5. Communities of benthic foraminifera in the Arctic Ocean in the region of profile III. (1) Sorosphaera depressa; (2) Pla�copsilinella aurantiaca; (3) Stetsonia horvathi; (4) Hyperammina friabilis.

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upheavel and at the archipelago of Queen Elizabeth(Fig. 1—field traverse 2, 3; Fig. 4) at a depth of 1700–3580 m at aleurite–pelite grounds containing 5.7–8.8% СаСО3 and 0.20 –1.89% Corg with the tempera�ture of the benthal water being from –0.4 to 0.94°Сwith salinity of 34.94–35.00‰. This community iswidely distributed in the eastern deep�water part of theGulf of Mexico at a depth of 3000–3800 m [16].

The Placopsilinella aurantiaca community is widelydistributed in the bolson of Nansen at the western end ofthe Gakkel ridgelet at a depth of 2993–3806 m anddeeper than the Peschongia arctica community at theslopes of the Lomonosov ridgelet at a depth of 1674–2619 m (Figs. 4–6) at aleurite–pelite grounds con�taining 6.5–10.5% СаСО3 and 0.21– 0.87% Corg withthe temperature of the benthal water being from –0.5to –0.94°С with salinity of 34.93–34.95‰.

The Stetsonia horvathi community is distributed inthe bolson of Nansen (to the East and deeper than thePlacopsilinella aurantiaca), and the bolsons ofAmundsen and Makarov and the Canadian bolson(Fig. 1—field traverses 2 and 4–6; Figs. 4–6) at adepth of 3418–4427 m at aleurite–pelite and pelitegrounds containing 5.1–10.7% CaCO3 and 0.21–1.12% Corg with the temperature of the benthal waterbeing from –0.55 to –0.94°C with salinity of 34.94‰.

The Stetsonia horvathi–Sorosphaera depressa com�munity is found in the Amundsen bolson deeper thanthe Stetsonia horvathi community (Fig. 4) at a depth of4083–4411 m at aleurite–pelite grounds containing2.8–5.9% СаСО3 and 0.68–0.87% Corg with the tem�perature of the benthal water being –0.95°С with salin�ity of 34.94– 34.95‰.

18°50′

15°72′

10°09′

4°60′

0°2°

51′

6°77′

13°03′

14°01′W

E

85°56′N

85°06′

84°64′

84°28′

83°64′

83°04′

82°06′

81°03′

Nan

sen

bo

lso

nA

mu

nd

sen

bo

lso

n

Gak

kel r

idge

let

Erm

ak p

late

au

plateau of Mirris–Jessup

М

1000

2000

3000

4000

5000

1

2

33

4

4

4

5

6

7

89

Fig. 7. Communities of benthic foraminifera at the continentalslope of Eurasia at the Fram gat in the region of profile V.(1) Lobatula lobatula; (2)Peschongia arctica; (3) Lerninaneoteretis; (4) Reophanus guttifer.

12°25′ 8°13′ 5°34′E

80°05′ 80°47′ 79°70′N

Fram gat

1

23

4

М

1000

2000

3000

0

Fig. 6. Communities of benthic foraminifera in the ArcticOcean in the region of profile IV. (1) Lobatula lobatula;(2) Lernina neoteretis; (3) Reophanus guttifer; (4) Placops�ilinella aurantiaca; (5) Sorosphaera depressa; (6) Stetsoniahorvathi; (7) Fontobotia wuellerstorfi; (8) Adercotrymaglomerata; (9) Oridorsalis tenerus.

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DEEP�WATER FORAMINIFERA COMMUNITIES OF THE ARCTIC OCEAN 67

The Sorosphaera depressa community is distributedin the Amundsen bolson westward of the Stetsonia hor�vathi–Sorosphaera depressa community (Figs. 5, 7) ata depth of 3828–4411 m at pelite grounds containing1.7–8.5% СаСО3 and 0.5–1.7% Corg with the temper�ature of the benthal water being –0.95°С with salinityof 34.95‰.

The Hyperammina friabilis community is found inMakarov bolson at the Lomonosov ridgelet deeperthan the Sorosphaera depressa community (Fig. 1—field traverse 4) at a depth of 4212–4225 m at pelitegrounds with the temperature of the benthal waterbeing –0.55°C with salinity of 34.95‰.

CONCLUSIONS

By the present time, 360 species of benthic fora�minifera have been detected in the Arctic Ocean.Their specific biodiversity reduces with increasingdepth and with removing from firm land.

The average number of foraminifera on the upperpart of the continental slopes at depths circumfluouswith the Atlantic warm and the recurrent Atlantic coldwaters changes in the range of 20–100000 copies per10 cm2 of the ground. On the lower part of the conti�nental slopes and ridgelets circumfluous with theintermediate water mass, their average number variesin the range of 2–6000 copies per 10 cm2. At the bot�tom of the deep�water bolsons at the benthic arcticwater mass, their number changes from 100 to 500copies per 10 cm2.

Agglutinized foraminifera with sandy shells—Pseudobolivina torquata, Proteonelia laguncula, Adercot�ryma glomerata, Reophanus guttifer, Placopsilinellaaurantiaca, Sorosphaera depressa, Hyperammina friabi�lis–are dominated among the 16 benthic foraminifera.

In the upper part of the continental slope of Eur�asia, communities of Lobatula lobatula, Pseudobolivinatorquata, Lernina neoteretis, and Proteonella lagunculaare distributed (from the top to down). These commu�nities are found at temperatures of the bottom watersof more than 0°С, and their area is influenced by theaction of the warm Atlantic water entering the ArcticOcean with the Norwegian–Spitzbergen flow throughthe Fram gat and directed along Eurasia.

In the upper part of the continental slope of Green�land at the temperature of the bottom waters from–0.4°C to –0.6°C, the following communities are dis�tributed (from the top to down): Oridorsalis tenerus,Adecotryma glomerata, and Fontobotia wuellerstorfiwhose area is directed by the action of the cold recur�rent waters of the Transarctic flow going to the Green�land Sea with the Eastern�Greenland flow through theFram gat.

The above�mentioned alternation in depth at theArctic continental slopes of the cold�resistant com�

munities of agglutinized foraminifera with more ther�mophilic communities of secretion carbonaceous for�aminifera is connected with the running off the coldwinter waters, which may resist the warm bottomwaters at some depths. A similar phenomenon takesplace in the Southern Ocean at the continental slopeof Antarctica [13].

On the lower part of the continental slopes at the tem�perature of the bottom waters from –0.4°C to –0.94°C,communities of Reophanus guttifer and Triloculinafrigida are distributed, while a community of Placops�ilinella aurantiaca is present at the slopes of the oce�anic ridgelets. The area of these communities is medi�ated by the influence of the intermediate water mass.

In the deep�water bolsons of the sea floor at tem�peratures from –0.55°C to –0.95°C, communities ofStetsonia horvathi, Stetsonia horvathi–Sorosphaeradepressa, and Hyperammina friabilis are distributed(from the top to down). These communities are morecold�resistant and specific to the regions with the arc�tic bottom water mass.

Among all the deep�water communities of benthicforaminifera of the Arctic Ocean, the communities ofthe continental slopes—Lobatula lobatula, Pseudobo�livina torquata, Lernina neoteretis, Fontobotiawuellestorfi, and Ioanella tumidula—are detected inother oceans. These communities are found in thenorthern part of the Atlantic Ocean and its marginalseas [14, 15].

SYNONYMY

Alteration of the taxonomic location of the speciesin the cited studies [20, 27–29, 31–34].

Alabaminoides exiguus = Epistominella exigua.Fontobotia wuellerstorfi = Planulina wuellerstorfi.Ioanella tumidula = Eponides tumidulus.Ioanella horvathi = Eponides tumidulus horvathi.Lernina neoteretis = Cassidulina “teretis”, Islandi�

ella teretis (part of the species).Lobatula lobatula = Cibicides lobatulus.Morulaeplecta arctica = Verneuilina arctica.Oridorsalis tenerus = Oridorsalis umbonatus (part of

the species), Eponides tener.Peschongia arctica = Epistominella arctica, Stetso�

nia arctica, Stetsonia horvathi (part of the species).Proteonella laguncula = Saccammina diflugiformis.Reophanus guttifer = Reophax guttifer,Pseudonodosinella nodulosa = Reophax nodulosa.

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