Distribution of Living Benthic Foraminifera in the Baffin Bay and Nares Strait in the Summer and Fall Periods: Relation with Environmental Parameters

<jats:p>Arctic climate warming leads to drastic changes in sea ice dynamics, hence impacting primary productivity but also the benthic communities. Therefore, to assess the response of living benthic foraminifera to contrasting Arctic environments, surface sediments from nine stations were collected during the summer of 2014 and fall of 2015 in the Baffin Bay and Nares Strait. Living standing stock are systematically low in the eastern and western Baffin Bay and much higher in the North Water Polynya and the Kane Basin located at the entrance and in the center of Nares Strait, respectively. High living benthic foraminiferal densities in the NOW reflect higher TOC while the highest density in the Kane Basin coincides with lower TOC but higher C/N and higher δ13Corg. The contribution of agglutinated species is on average very high for the whole study area and dominated by the species Adercotryma glomeratum, Lagenammina arenulata, and Reophax scorpiurus. Calcareous species, dominated by Nonionellina labradorica and Melonis barleeanus, are more abundant in the North Water Polynya and the Kane Basin. The very high living standing stock observed in the Kane Basin might be related to the northern position of the ice arch that summer during 2014 and therefore a particularly scarce sea ice cover might have allowed massive phytoplankton production during that season. In this study, the distribution of living benthic foraminifera is discussed according to several environmental parameters such as water masses, phytoplankton productivity, and organic matter fluxes.</jats:p>

section_content: Warming of the Arctic regions observed in recent decades impacts physical, biological, and human systems [1] [2] [3] [4] [5]. The Baffin Bay, located on the west of Greenland and connected to the Arctic Ocean by the narrow Nares Strait, experiences rapid and continuous environmental changes with a warmer and wetter atmosphere, shortened snow cover periods, and a decreased in Greenland ice sheet and sea ice thickness [6, 7]. These environmental changes potentially impact ocean circulation and mixing [8, 9]. Ecosystems of the Baffin Bay are therefore strongly dependent on atmospheric and hydrological regimes and sea ice dynamics that are influenced by the contrast between relatively warm Atlantic water and cold Arctic water. These environmental parameters influence the primary productivity at the surface of the water column but also have an impact on the benthic communities. 

The distribution of modern benthic foraminifera in the Baffin Bay and the surrounding regions has been investigated by few authors during the last few decades. Early works [10] [11] [12] [13] provided some data on the distribution of benthic foraminifera in the sediment and some basic ideas on the ecology of those organisms in the environments of the Baffin Bay and the Canadian Arctic Archipelago. All studies revealed the omnipresence of agglutinated benthic foraminifera in the cold waters of the Canadian Arctic Archipelago and Baffin Bay continental shelves. The nature of the water masses is shown to be the main factor controlling the distribution of benthic foraminifera observed in these studies. This hypothesis was also developed by Hunt and Corliss [14]. More recently, the study of modern (living and dead) benthic foraminifera in the Baffin Bay and Labrador Sea [15, 16] showed that the main parameters controlling benthic foraminifera distribution in those environments are processes of carbonate dissolution and the physical characteristics of water masses. However, Schroder-Adams et al. [17] suggest that sea ice exerts a more important control on the distribution of benthic faunas in the Canadian Arctic Archipelago. The abundance of agglutinated benthic foraminifera compared to calcareous species would be linked to the seasonal dynamic of sea ice, accentuating processes of carbonate dissolution in sediments. Calcareous benthic foraminifera appear to be preserved in environments where sea ice cover is permanent. Based on a study of the central Arctic, Wollenburg and Kuhnt [18] showed that the critical environmental parameter influencing the distribution of benthic foraminifera in terms of density, diversity, and foraminiferal associations is episodic food supply derived from seasonal primary productivity which in turn is closely related to sea ice dynamics. 

Benthic foraminifera are frequently used as paleoenvironmental proxy in the Baffin Bay and Nares Strait [19] [20] [21] [22] [23], but interpretations made from the paleo-records rely on solid knowledge of the benthic foraminifera ecology in those particular environments. The Baffin Bay and adjacent Nares Strait are locations of very active sea ice dynamics with highly contrasted environments between the deep Baffin Bay, the narrow and relatively shallow Nares Strait, and the North Water Polynya (NOW) that connects those two regions. This study therefore aims at better understanding the distribution of living benthic foraminifera in summer and fall periods in those regions in relation to water depth and water masses, sea ice cover, and primary production.
section_name: Introduction

section_content: The Baffin Bay is a marginal sea of the North Atlantic Ocean surrounded by Baffin Island to the west, Greenland to the east, and Ellesmere Island to the north (Figure 1 ). This semi-enclosed basin has an average depth of 2400 m [16]. To the west, the shelf is narrow, steep, and cut by several deep trenches. To the east, the shelf is wider and cut by glacial paleovalleys. Sedimentation in the Baffin Bay is mainly controlled by terrigenous detrital inputs owing to debris flows, turbidite events, and ice-rafted material [24, 25]. One of the features of the Baffin Bay is the shallow depth of the carbonate compensation depth (CCD). Aksu [26] suggested that the CCD occurs at a depth of between 600 to 900 m and the foraminiferal lysocline may be as shallow as 100-300 m. 

The Baffin Bay is connected to the north to the Arctic Ocean through several narrow channels of the Canadian Arctic Archipelago and Nares Strait and to the south to the Atlantic Ocean via the Davis Strait. Ocean circulation is cyclonic and comprises two main currents (Figure 1 ). To the east of the bay, the West Greenland Current (WGC) transports modified Atlantic water mass that is relatively warm and salty [27]. Several branches of this current carry Atlantic water in the middle of the Baffin Bay. Along the Canadian coast, a colder and less salty Arctic water mass flows southward by the Baffin Current (BC). This ocean circulation affects the dynamic of sea ice [28]. In winter, the bay is entirely covered with sea ice. The sea ice extent is maximal in February and March. From April to August, the sea ice extent decreases progressively reaching a minimum in August and September. The retreat of sea ice occurs from south-east to north-west owing to the presence of a relatively warm water mass coming from the Atlantic Ocean to the north along the Greenland coast. During springtime and summertime, the annual melt of sea ice influences phytoplankton blooms and therefore benthic ecosystems. Intense blooms are observed near the ice edges during the melting period [30, 31]. Several factors, such as solar energy, input of fresh water, and nutrients, tend to stimulate primary productivity in these areas. This phytoplankton production constitutes a major supply of food for benthic organisms including benthic foraminifera [32] [33] [34]. In the Baffin Bay, annual primary production varies from 60 to 120 gC•m -2 [35, 36].
section_name: Environmental Settings 2.1. Baffin Bay

section_content: Nares Strait, narrow and 530 km long, separates the north-west of Greenland from Ellesmere Island (Figure 1 ). It extends from the north of the Baffin Bay to the Lincoln Sea in the Arctic Ocean and constitutes the major connection in the region between the Arctic Ocean and the Atlantic Ocean via the Baffin Bay. Ocean circulation flows to the south from the Arctic Ocean [37, 38]. A powerful north wind also affects the region [39] [40] [41]. Arctic water carried through Nares Strait is less salty than Atlantic water found in the Baffin Bay. This arctic water is largely composed of nutrient-rich Pacific-origin water and freshwater During springtime and summertime, the annual melt of sea ice influences phytoplankton blooms and therefore benthic ecosystems. Intense blooms are observed near the ice edges during the melting period [30, 31]. Several factors, such as solar energy, input of fresh water, and nutrients, tend to stimulate primary productivity in these areas. This phytoplankton production constitutes a major supply of food for benthic organisms including benthic foraminifera [32] [33] [34]. In the Baffin Bay, annual primary production varies from 60 to 120 gC•m -2 [35, 36].
section_name: Nares Strait

section_content: Nares Strait, narrow and 530 km long, separates the north-west of Greenland from Ellesmere Island (Figure 1 ). It extends from the north of the Baffin Bay to the Lincoln Sea in the Arctic Ocean and constitutes the major connection in the region between the Arctic Ocean and the Atlantic Ocean via the Baffin Bay. Ocean circulation flows to the south from the Arctic Ocean [37, 38]. A powerful north wind also affects the region [39] [40] [41]. Arctic water carried through Nares Strait is less salty than Atlantic water found in the Baffin Bay. This arctic water is largely composed of nutrient-rich Pacific-origin water and freshwater from rivers and melting ice [39]. Pacific water is twice as rich in nitrogen and phosphorus and seven times richer in silicate than Atlantic water [42]. These features lead to the rise of primary production especially during sea ice melting and so there is a rise of benthic productivity. A part of the Atlantic water mass coming from the Baffin Bay is carried along the Greenland coast and penetrates into Nares Strait until the Kane Basin [39, 43, 44]. The Kane Basin with an area of 27,000 km 2 is relatively large (120 km maximum) and not very deep (220 m). Many icebergs coming from the Humboldt Greenland glacier discharge in the Kane Basin. From September to June, more than 80% of Nares Strait is covered by sea ice [45]. One of the distinctive features of this strait is the presence of ice arches blocking the ice drift to the Baffin Bay, as well as promoting the formation and the preservation of the NOW [44].
section_name: Nares Strait

section_content: Between the north of the Baffin Bay and the southern entrance of Nares Strait, the NOW is considered to be the largest and the most productive Arctic polynya (Figure 1 ). The polynya starts to grow during the months of March and April and reaches its maximal extent in July with a surface area between 80,000 and 90,000 km 2 [45] [46] [47]. In summer, the NOW is opened on the Baffin Bay and is no longer strictly a polynya. The presence of the NOW is due to the combination of atmospheric and oceanic factors. The formation of ice bridges to the north allows the blockage of ice drift from the north and brakes the strong north winds, letting the area be ice-free [48] [49] [50]. 

The NOW is important for primary productivity and biodiversity. This ice-free area makes it possible to produce premature spring phytoplankton blooms compared to the Baffin Bay region [51]. The high productivity observed in the polynya is due to the combined action of many physical factors such as the penetration of sunlight, an effective mixing of surface waters by the wind, and the supply of nutrient-rich Pacific water [52] [53] [54]. Annual primary productivity reaches 150 gC•m -2 in the polynya [52, 53]. However, the ecosystem of the polynya is subject to a high inter-annual and seasonal variability [55]. Since the last decade, annual productivity in the polynya has declined significantly [56]. A study by Bergeron and Tremblay [57] showed a reduction of 65% of the net biological productivity between 1997 and 2011 which was attributed to the freshening and increased stratification of surface waters. The extent of the phytoplankton bloom would also have decreased in 10 years [51]. According to Blais et al. [58], this drop of the phytoplankton productivity and the abundance of diatoms is due to changes in sea ice dynamics and the stratification of the water column.
section_name: North Water Polynya (NOW)

section_content: This study is based on interface sediment cores, collected during two oceanographic cruises as part of the ArcticNET program and the ANR GreenEdge project on board the Canadian research vessel NGCC Amundsen (Table 1 ; Figure 1 ). The first oceanographic expedition, AMD14, led to the acquisition of five cores at five different stations between 27 July and 4 August 2014. Three other cores were sampled during the cruise AMD15 from 1 October to 1 November 2015. 

Sediment was collected from boxcores that were subsampled using push cores of 9 cm in diameter during the AMD14 cruise and 15 cm in diameter during the AMD15 cruise. Upon recovery, sediment cores were sliced from the surface down to 5 cm, every 1 cm for the cores from the AMD14 cruise and every 0. 5 cm for the ones of the AMD15 cruise. For each station, one sediment core was used for benthic foraminiferal analysis and another one for sedimentological and geochemical analyses. Temperature and salinity profiles over the whole water column were measured at each station using a conductivity temperature depth (CTD) profiler.
section_name: Materials and Methods

section_content: The phytoplankton biomass distribution range in the study area during the sampling periods is illustrated with average monthly chlorophyll a concentrations (Chl a in mg•m -3 ) in July 2014 and September 2015, derived from satellite data collected by the spectroradiometer MODIS installed on the Aqua satellite. Composite images have a resolution of 4 km and come from NASA's application "Giovanni" [59].
section_name: Satellite Data

section_content: For each station, one core was dedicated to sedimentological and geochemical analyses. Between 0. 5 and 100 mg of dry sediment was used, depending on the sample and the type of analysis. 

Grain size analysis was performed at Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC, Bordeaux, France) using a laser diffraction particle size analyzer (Malvern Mastersizer 2000 hydro G, Palaiseau, France). The analytical error was on average ± 0. 02 µm. Grain size was measured on freeze-dried sediment for each core every centimeter from the surface down to 5 cm. 

Freeze-dried samples were also used for measuring different geochemical parameters at EPOC. Sedimentary total carbon (TC) and total organic carbon (TOC) contents were measured by dry combustion in a LECO CS-125 carbon analyzer (LECO Corporation, St Joseph, MI, USA) [60]. The total nitrogen (TN) content as well as stable carbon isotope ratios of the organic fraction (δ 13 C org ) and stable nitrogen isotope ratios (δ 15 N) were determined by an elemental analyzer isotope ratio mass spectrometer (EA-IRMS, ThermoFisher Flash 2000 + Isoprime, Thermo Fisher Scientific, Dreieich, Germany). TOC and δ 13 C org were analyzed on carbonate-free sediment after HCl (10%) treatment. The isotopic ratios were reported using the conventional δ notation in per mil (‰) and calibrated according to the international references (standards), with these being V-PDB for δ 13 C org values and atmospheric nitrogen (AIR) for δ 15 N values [61]. TOC and TN contents are expressed as a percentage of weight of sediment (wt. %). The analytical errors were on average ± 0. 1 wt. % for TN and TOC contents and ±0. 1‰ for δ 13 C org and δ 15 N. The C/N ratio was calculated by dividing TOC by TN.
section_name: Sedimentological and Geochemical Analyses

section_content: Samples used for living benthic foraminifera analyses were preserved for several months prior to the study in a 1. 5 g•L -1 solution of Rose Bengal in 96% ethanol in order to stain the endoplasm of benthic foraminifera living at the time of coring [62, 63]. At the EPOC laboratory, samples were wet sieved through 63 and 125 µm meshes sieves. Only the >125 µm fraction was considered for this study. For all stations, all stained individuals in the sediment > 125 µm were hand-sorted under wet conditions (ethanol + Milli-Q water) from the surface down to 5 cm. The pink coloration of living faunas is generally clear by transparency through the tests of the organisms. However, this coloration could display differences between species, varying from light pink to dark red or brownish violet [64]. Moreover, the Rose Bengal staining method may also stain the protoplasm of well-preserved dead organisms in deep and anoxic environments [65, 66]. Nevertheless, this method shows reliable results and remains the most appropriate method to study living benthic foraminifera [63]. Strict criteria were applied in order to collect only living individuals: only specimens with all of the chambers coloured, except the last one, were considered to be living [67, 68] and some non-transparent tests (miliolids and agglutinated taxa) were broken, after identification, to ensure that the protoplasm was stained. Tubular species such as Saccorhiza ramosa were often found fragmented but remained recognizable [16]. Each fragment over 1 mm coloured with Rose Bengal was counted as one individual. Otherwise, we considered five coloured fragments as one individual. 

We considered species representing at least 5% of the foraminiferal assemblage to be major species. Major species are shown in Figure A1. Faunal densities for each sample were standardized for a sediment volume of 50 cm 3. For each sample, a theoretical volume of sediment was calculated based on the core diameter and the slice thickness. Living standing stock represents the total number of living individuals > 125 µm counted per station, normalized for a 100 cm 2 sediment area.
section_name: Living (Stained) Benthic Foraminiferal Analysis

section_name: Results

section_content: Water masses in the Baffin Bay have two origins, the Arctic Ocean and Atlantic Ocean. Figure 2 shows temperature and salinity profiles measured at each station allowing us to differentiate water masses in the area. In the Kane Basin, cold and low salinity Arctic water mass (<0 • C; <34) dominates. This Arctic water mass reaches 300 m depth to the northern and the western parts of the Baffin Bay but is shallower in the east, affecting the 200 first meters of the water column. 

Moreover, the Rose Bengal staining method may also stain the protoplasm of well-preserved dead organisms in deep and anoxic environments [65, 66]. Nevertheless, this method shows reliable results and remains the most appropriate method to study living benthic foraminifera [63]. Strict criteria were applied in order to collect only living individuals: only specimens with all of the chambers coloured, except the last one, were considered to be living [67, 68] and some non-transparent tests (miliolids and agglutinated taxa) were broken, after identification, to ensure that the protoplasm was stained. Tubular species such as Saccorhiza ramosa were often found fragmented but remained recognizable [16]. Each fragment over 1 mm coloured with Rose Bengal was counted as one individual Otherwise, we considered five coloured fragments as one individual. 

We considered species representing at least 5% of the foraminiferal assemblage to be major species. Major species are shown in Figure A1. Faunal densities for each sample were standardized for a sediment volume of 50 cm 3. For each sample, a theoretical volume of sediment was calculated based on the core diameter and the slice thickness. Living standing stock represents the total number of living individuals > 125 µm counted per station, normalized for a 100 cm 2 sediment area.
section_name: Environmental Settings

section_content: Water masses in the Baffin Bay have two origins, the Arctic Ocean and Atlantic Ocean Figure 2 shows temperature and salinity profiles measured at each station allowing us to differentiate water masses in the area. In the Kane Basin, cold and low salinity Arctic water mass (<0 °C; <34) dominates. This Arctic water mass reaches 300 m depth to the northern and the western parts of the Baffin Bay but is shallower in the east, affecting the 200 first meters of the water column. The Atlantic water mass is warmer (>0 °C) and saltier (>34). To the eastern part of the Baffin Bay, the WGC transports Atlantic water to the north. The Atlantic water mass occupies a more important volume of the water column in the south than in the northern part of the bay. Indeed, the Atlantic water mass extends to 1200 m water depth at station 200 then becomes progressively less important to the north of the Baffin Bay and reaches 600 m depth at station 115. The temperature of this water mass is higher in the south (around 3 °C) than the north (around 1 °C). Under the Atlantic water mass, there is a colder deep water mass (around 0. 5 °C). Salinity is uniform at around 34. 5. The differences of the distribution of water masses observed between the stations is reflected in the ocean circulation in the Baffin Bay. Warm and salty water is brought from the Atlantic Ocean along the The Atlantic water mass is warmer (>0 • C) and saltier (>34). To the eastern part of the Baffin Bay, the WGC transports Atlantic water to the north. The Atlantic water mass occupies a more important volume of the water column in the south than in the northern part of the bay. Indeed, the Atlantic water mass extends to 1200 m water depth at station 200 then becomes progressively less important to the north of the Baffin Bay and reaches 600 m depth at station 115. The temperature of this water mass is higher in the south (around 3 • C) than the north (around 1 • C). Under the Atlantic water mass, there is a colder deep water mass (around 0. 5 • C). Salinity is uniform at around 34. 5. The differences of the distribution of water masses observed between the stations is reflected in the ocean circulation in the Baffin Bay. Warm and salty water is brought from the Atlantic Ocean along the Greenland coast to the north, and cold and less salty Arctic water is brought from the Canadian Arctic Archipelago and Nares Strait to the south, along the Canadian coast. These results are in line with the observations of [28], which describe the circulation and the distribution of water masses in the Baffin Bay. 

Phytoplankton biomass in the studied area mainly gathers to the western and northern parts of the Baffin Bay, in the NOW area, and in Nares Strait (Figure 3 ). Chl. a concentrations in these areas reach 2 mg•m -3. Figure 3 shows that in July 2014, phytoplankton biomass seems to be more important than in September 2015. The NOW is the most productive zone of the studied area [53, 54, 69]. Following a significant phytoplankton bloom that grows during the months of May and June, the phytoplankton biomass starts to decrease in July and August, then fades slowly from September [51]. 

x FOR PEER REVIEW 7 of 23

Greenland coast to the north, and cold and less salty Arctic water is brought from the Canadian Arctic Archipelago and Nares Strait to the south, along the Canadian coast. These results are in line with the observations of [28], which describe the circulation and the distribution of water masses in the Baffin Bay. Phytoplankton biomass in the studied area mainly gathers to the western and northern parts of the Baffin Bay, in the NOW area, and in Nares Strait (Figure 3 ). Chl. a concentrations in these areas reach 2 mg•m -3. Figure 3 shows that in July 2014, phytoplankton biomass seems to be more important than in September 2015. The NOW is the most productive zone of the studied area [53, 54, 69]. Following a significant phytoplankton bloom that grows during the months of May and June, the phytoplankton biomass starts to decrease in July and August, then fades slowly from September [51]. Sedimentological and geochemical settings of the sediment measured for this study are shown in Figure 4. Grain-size spectra show all unimodal distribution. In addition, the grain size distribution is consistent for each level of each core. Therefore, we consider the median diameter of the particle size distribution D50 as a reliable measurement of the mean grain size in the sediment cores investigated in the present study. The sediment is mainly muddy-silty. The >125 µm size fraction used for benthic foraminiferal analyses is largely composed of lithic sand, expressing the importance of the ice-rafted transport process in the study area. Only stations 101 and BC1 located in the NOW contain many frustules of diatoms reflecting high primary productivity at the surface. Sedimentological and geochemical settings of the sediment measured for this study are shown in Figure 4. Grain-size spectra show all unimodal distribution. In addition, the grain size distribution is consistent for each level of each core. Therefore, we consider the median diameter of the particle size distribution D50 as a reliable measurement of the mean grain size in the sediment cores investigated in the present study. The sediment is mainly muddy-silty. The >125 µm size fraction used for benthic foraminiferal analyses is largely composed of lithic sand, expressing the importance of the ice-rafted transport process in the study area. Only stations 101 and BC1 located in the NOW contain many frustules of diatoms reflecting high primary productivity at the surface. 

The NOW area stands out from the rest of the study area with higher TOC and TN contents in the surface sediment. In the Baffin Bay and Nares Strait, the TOC values vary around 1 wt. % and the TN values range from 0. 10 to 0. 20 wt. % (Figure 4 ). In the NOW, the TOC contents are >2 wt. % and the TN contents are >0. 20 wt. %, reaching 0. 33 wt. % at station 101. These values are in line with those measured during the summers of 1998 and 1999 in the same zone by Hamel et al. [70] so we consider them to be representative of average values in this region. Moreover, this study indicates that TOC contents in the surface sediment of the NOW area are significantly higher than those measured in other Arctic or subarctic environments. Our results show that the C/N ratio is equal to eight and nine for all stations except Kane2B where values reaching twelve were measured (Figure 4 ). Organic matter in surface sediments of the Baffin Bay and Nares Strait mainly originates from primary productivity but includes a little part of terrigenous supply as suggested by the values of the C/N ratio, which are slightly higher to those representatives of marine organic matter (five to seven; [71] ). This part is more important in Nares Strait where Holocene sediments are rich in carbon particles from Paleogene series present on the coast of Ellesmere Island [72]. The NOW area stands out from the rest of the study area with higher TOC and TN contents in the surface sediment. In the Baffin Bay and Nares Strait, the TOC values vary around 1 wt. % and the TN values range from 0. 10 to 0. 20 wt. % (Figure 4 ). In the NOW the TOC contents are >2 wt. % and the TN contents are >0. 20 wt. %, reaching 0. 33 wt. % a station 101. These values are in line with those measured during the summers of 1998 and 1999 in the same zone by Hamel et al. [70] so we consider them to be representative o average values in this region. Moreover, this study indicates that TOC contents in the sur face sediment of the NOW area are significantly higher than those measured in other Arc tic or subarctic environments. Our results show that the C/N ratio is equal to eight and nine for all stations except Kane2B where values reaching twelve were measured (Figure 4 ). Organic matter in surface sediments of the Baffin Bay and Nares Strait mainly origi nates from primary productivity but includes a little part of terrigenous supply as sug gested by the values of the C/N ratio, which are slightly higher to those representatives o marine organic matter (five to seven; [71] ). This part is more important in Nares Strai δ 13 C org is used to indicate the relative importance of marine vs. terrigenous inputs [73] but also changes in CO 2 concentration in surface waters [74] [75] [76]. In general, marine organic matter is isotopically heavier compared to C3 angiosperm plants (tundra and taiga), which constitute the major part of the Arctic vegetation. The C4 terrestrial plants do not grow in high northern latitudes and so do not contribute to carbon inputs in the Arctic region [77, 78]. Our results show that δ 13 C org is quite constant in the studied area with values oscillating around -22 and -21‰ (Figure 4 ). At station Kane2B, δ 13 C org is slightly higher, with a value of -19. 5‰. Studies by Naidu et al. [79] on carbon stable isotopes in sediments of the Amerasian continental shelf (Bering, Chukchi, Siberian, and Beaufort Seas), allowed us to determine values of terrigenous δ 13 C org around -27‰, and -24 to -21‰ for marine δ 13 C org. According to Pomerleau et al. [80], marine δ 13 C org is estimated to be -21‰ in the Baffin Bay region. This value is deduced from the average of δ 13 C org of dominant zooplankton species, primary consumers, in the Baffin Bay. According to our results, δ 13 C org values measured in the sediments of the Baffin Bay and NOW stations show a marine origin of organic matter with a slightly terrigenous input similar to what was shown by the s C/N data. Station Kane2B is special, with a higher δ 13 C org value (-19. 5‰; Figure 4 ). In the Arctic, algae proliferating under sea ice is a specific element, which can take part in the δ 13 C org of the sediment. Indeed, the weak CO 2 concentration dissolved in water covered by sea ice leads to an increase in δ 13 C org of ice algae. δ 13 C org derived from sea ice algae fluctuate around -18‰ [81, 82]. The δ 13 C org value measured at station Kane2B strongly suggests the presence of sea ice for most of the year in the Nares Strait. 

δ 15 N measured in sediments is used to trace the relative use of nitrogen (NO 3 -) in surface waters, an essential nutrient for primary production [83] [84] [85]. It depends on nitrogen isotopic composition in the surface water mass and isotope fractionation from phytoplankton assimilation of nitrogen nutrients. In the photic zone, phytoplankton uses preferentially isotopically weak nitrogen ( 14 NO 3 -). In addition, Fox and Walker [86] indicate that sinking particulate organic matter reaches the deep ocean within a few days in the Baffin Bay. We can consider that N is well preserved in surface sediments and that δ 15 N provides direct information on primary productivity and nutrient availability in the surface ocean. Our results indicate that δ 15 N is slightly different between the Baffin Bay, with values of 7 to 9‰, and the NOW and Nares Strait areas, with weaker values of 5 to 6‰ (Figure 4 ). Despite it being an intense biological activity in the polynya, nutrient-rich Pacific water from the Arctic Ocean allows the maintenance of relatively weak δ 15 N values. On the other hand, δ 15 N values measured in sediments of the Baffin Bay are higher, suggesting a lower availability in nutrients in surface waters from the North Atlantic.
section_name: Environmental Settings

section_content: The Arctic, particularly in the Baffin Bay, is known to contain numerous species of agglutinated benthic foraminifera [15, 17, 18, 87]. Results of this study are no exception to this rule. Indeed, all studied stations present at least 50% of agglutinated individuals except station BC1 with only 26% (Figure 5A ). Stations BC3, 200, 210, 115, and 101 contain the most agglutinated individuals in their respective assemblages (>75%, Supplementary Materials). Station 210 is entirely composed of agglutinated benthic foraminifera. Densities of living fauna for each core expressed in number of individuals per 100 cm 2 are shown in Figure 5B and in the middle of the pie charts in Figure 6A. The weakest densities are noticed in the Baffin Bay (150 to 324 ind. /100 cm 2 ) and at station BC1 (260 ind. /100 cm 2 ). Densities are higher in NOW, with a density higher than 1000 ind. /100 cm 2 Densities of living fauna for each core expressed in number of individuals per 100 cm 2 are shown in Figure 5B and in the middle of the pie charts in Figure 6A. The weakest densities are noticed in the Baffin Bay (150 to 324 ind. /100 cm 2 ) and at station BC1 (260 ind. /100 cm 2 ). Densities are higher in NOW, with a density higher than 1000 ind. /100 cm 2 at station 115. The highest density is noticed at station Kane2B with 1754 ind. /100 cm 2. Densities of living fauna for each core expressed in number of individuals per 100 cm 2 are shown in Figure 5B and in the middle of the pie charts in Figure 6A. The weakest densities are noticed in the Baffin Bay (150 to 324 ind. /100 cm 2 ) and at station BC1 (260 ind. /100 cm 2 ). Densities are higher in NOW, with a density higher than 1000 ind. /100 cm 2 at station 115. The highest density is noticed at station Kane2B with 1754 ind. /100 cm 2. For all stations, the relative abundance of major species is illustrated in Figure 6A. Station Kane2B, located in Nares Strait, is dominated by an agglutinated species, Adercotryma glomeratum (44%, Figure A1 ). Another agglutinated species, Lagenammina arenulata, is present with a relative abundance of 11%. Calcareous species also compose the assemblage of station Kane2B, such as Nonionellina labradorica (15%) and to a lesser extent, Cribroelphidium subarcticum and Melonis barleeanus (6% each). Species A. glomeratum and N. labradorica represent a high proportion in the NOW, in cores BC1 (16% and 62%, respectively) and 101 (26% and 11%, respectively). Recurvoides contortus (26%) and Reophax fusiformis (6%) are associated to these two species in the core 101. The assemblage of station 115 located in the NOW is different from those of the two close stations, 101 and BC1. Major species are similar to those observed in the cores of the Baffin Bay. Lagenammina arenulata (32%) is the dominant species at this station. Three other agglutinated species Reophax scorpiurus (16%), R. contortus (6%), and Trochammina inflata (5%), as well as one calcareous species, M. barleeanus (13%), complete the assemblage of station 115. In the Baffin Bay, observed species of living benthic foraminifera are largely agglutinated. Therefore, the assemblages are composed of a mix of agglutinated species without any particular trend between the stations. Among others, Lagenammina arenulata, R. scorpiurus, and Hormosinelloides guttifer are found in several cores. Melonis barleeanus is the only calcareous species being part of a major species of the Baffin Bay. Species A. glomeratum present at stations Kane2B, BC1, and 101 is also found at station BC4, representing 29% of the assemblage. 

The vertical distribution of living benthic foraminifera at each station is presented in Figure 6B. The density and the richness are always more important in the first 2 cm of the sediment. The station Kane2B presents the highest surface density with 457 ind. /50 cm 3. Adercotryma glomeratum is found at 5 cm, whereas N. labradorica dominates between 1 and 3 cm sediment depth. At station BC1, N. labradorica is abundant at the surface then its density decreases to 3 cm. Adercotryma glomeratum and R. contortus are the most abundant species at station 101. Their densities decrease with depth. The density of N. labradorica is more important between 1 and 2 cm. At station 115, L. arenulata is the dominant species observed at 5 cm sediment depth. Melonis barleeanus is mainly abundant between 2 and 3 cm sediment depth, producing an increase in the density in this sample. Station 210 shows the lowest density together with station BC3. The surface density only reaches 46 ind. /50 cm 3. The majority of taxa are contained in the first centimeter of the sediment. At station 204, the layer with higher density is found within the 1-2 cm interval contrary to other stations. This observation is due to the presence of M. barleeanus, abundant from 1 to 3 cm sediment depth. The three major species of station 200 are grouped together in the topmost layer and the density is raised to 101 ind. /50 cm 3. Reophax scorpiurus is found down to 5 cm. Station BC3 shows a low surface density with 51 ind. /50 cm 3. Living benthic foraminifera are very rare under 3 cm sediment depth. Station BC4 contains the most important surface density of the Baffin Bay stations with 129 ind. /50 cm 3. Melonis barleeanus is present from the surface to 2 cm sediment depth. A slight increase is visible between 3. 5 and 4. 5 cm due to the presence of the species A. glomeratum.
section_name: Distribution of Living Benthic Foraminifera

section_content: This study covers a large geographical area, extending from the relatively deep environments of the lower slope in the western and eastern areas of the Baffin Bay to the shallower Kane Basin in Nares Strait, and the unique environment of the NOW connecting those two environments. Environmental settings of the Baffin Bay and Nares Strait appear to be contrasted in term of water masses, phytoplankton productivity, and organic matter fluxes [88] (and references therein). Some authors have already demonstrated the importance of these parameters on the distribution of benthic foraminifera in the Baffin Bay and Canadian Arctic [10] [11] [12] [13] [14] [15] [16] [17]. The different water masses and the quantity of organic matter measured in the study area constitute some important features, in addition to some specific features as well as CO 2 concentrations in the pore water of the sediment and in the water column, in relation to the export and the degradation of the produced organic matter. This specific environmental context allows an explanation of the repartition of living benthic foraminifera in the region in terms of both richness and density or the assemblage's composition.
section_name: Discussion

section_content: Agglutinated benthic foraminifera are widely present on the shelves of the Arctic Seas and in the Baffin Bay [18, 87]. Several studies reported the dominance of these species in the Canadian Arctic [10] [11] [12] [13] [14] [15] [16] [17]. According to these different studies, sea ice cover and properties of water masses would be responsible for the particular distribution of agglutinated benthic foraminifera, establishing a hostile environment for the development of calcareous species as a result of carbonate dissolution in corrosive bottom waters. The shallow CCD in the study area induces carbonate dissolution in the Baffin Bay from 300 m water depth [26]. The sea ice seasonal dynamic favors the absorption of atmospheric CO 2 in cold surface waters but also primary productivity therefore increasing the flux of organic matter reaching the ocean floor. Dense and well-oxygenated cold high-latitude waters flowing in the deep ocean oxidize this organic matter leading to a rise of the partial pressure of CO 2 in sediment pore waters. High CO 2 content at the water-sediment interface causes carbonate dissolution [25, 89]. However, in the core BC1 located in the NOW, at approximately 700 m water depth, agglutinated benthic foraminifera only represent 26% of the total of observed living individuals. One calcareous species is largely dominant, N. labradorica (62%). This opportunistic species, typical of North Atlantic waters, is a good indicator of high surface productivity which constitute animportant source of organic matter for the benthic community [90] [91] [92]. Despite corrosive waters, a number of calcareous individuals (N. labradorica and M. barleeanus notably) was observed in the cores of the NOW and Kane Basin (200-700 m water depth) but also in the deep environments of the Baffin Bay (to 1000 m water depth). The presence of calcareous species under the CCD could be explained by a seasonal variation of the CCD. At station 204, east of the Baffin Bay, tests of M. barleeanus present important marks relating to dissolution (Figure 7 ). Despite an intense Rose Bengal staining, it could be possible that these individuals have calcified during a period where waters were less corrosive and were later partly dissolved. Considering the depth of station 204 (995 m), the CCD position in the region and the absence of other calcareous species in the core, it would seem that calcification occurs in corrosive conditions. A recent study shows that this species could integrate sedimentary particles during the formation of the calcareous test to strengthen it and to reduce carbonate dissolution [93]. Despite a priori negative conditions, some calcareous species, typically infauna living between 1 and 3 cm sediment depth, can survive and represent an important part of the assemblage of benthic foraminifera in the considered sample (Figure 6 ). 

face causes carbonate dissolution [25, 89]. However, in the core BC1 loc at approximately 700 m water depth, agglutinated benthic foraminife 26% of the total of observed living individuals. One calcareous specie nant, N. labradorica (62%). This opportunistic species, typical of North A good indicator of high surface productivity which constitute animpor ganic matter for the benthic community [90] [91] [92]. Despite corrosive wa calcareous individuals (N. labradorica and M. barleeanus notably) was obs of the NOW and Kane Basin (200-700 m water depth) but also in the de of the Baffin Bay (to 1000 m water depth). The presence of calcareous CCD could be explained by a seasonal variation of the CCD. At statio Baffin Bay, tests of M. barleeanus present important marks relating to d 7). Despite an intense Rose Bengal staining, it could be possible that these calcified during a period where waters were less corrosive and were later Considering the depth of station 204 (995 m), the CCD position in the r sence of other calcareous species in the core, it would seem that calci corrosive conditions. A recent study shows that this species could integ particles during the formation of the calcareous test to strengthen it a bonate dissolution [93]. Despite a priori negative conditions, some calcar ically infauna living between 1 and 3 cm sediment depth, can survive important part of the assemblage of benthic foraminifera in the consider 6). The Baffin Bay and Nares Strait present a high diversity of agglutinated species also classically found in the studies about benthic foraminifera in this region of the Canadian Arctic. In this study, species such as R. scorpiurus, L. arenulata, or H. guttifer are largely present in the Baffin Bay, from north to south and from east to west. However, two species appear to have a particular spatial distribution. Recurvoides contortus is present in the north of the Baffin Bay, at stations 210, 115, and 101. In some previous studies, this species was observed in the Baffin Bay and Canadian Arctic Archipelago. According to Schröder-Adams and Van Rooyen [16], R. contortus would be typical of Atlantic waters of the Baffin Bay. In our study, this species seems to be compatible with particularly cold Atlantic waters north of the Baffin Bay. Adercotryma glomeratum is a recurrent species in Nares Strait at stations Kane2B, 101, and BC1 as well as west of the Baffin Bay at station BC4. Schröder-Adams and Van Rooyen [16] observed this species in deep environments of the Baffin Bay particularly (>2000 m water depth) where waters were the coldest. Adercotryma glomeratum is a common species, in the high latitudes and in cold waters of the North Atlantic and Arctic Oceans [14] [15] [16] 94]. In our study, this species is primarily present in Nares Strait and the western part of the Baffin Bay, as a consequence of the inflow of cold waters from the Arctic Ocean. 

In good agreement with previous observations, a large part of living benthic foraminifera observed in this study are agglutinated. The association of different parameters such as seasonal sea ice cover as well as the flux of organic matter and cold temperatures lead to the corrosive nature of water masses in the region. Carbonate dissolution appears to be an important controlling factor on benthic fauna but cannot totally explain the distribution of living benthic foraminifera in the study area.
section_name: Influence of Carbonate Dissolution Process on Assemblages of Benthic Foraminifera

section_content: The distribution of living benthic foraminifera is influenced by various biotic and abiotic parameters among which the oxygenation of deep waters and the supply of organic matter exert important control on fauna [95] [96] [97] [98]. In Arctic environments, in areas of dense water formation, the oxygenation of deep waters is rarely a restricting factor. Therefore, the flux and the quality of organic matter are dominant factors controlling the distribution of benthic foraminifera. 

The highest densities of living benthic foraminifera in this study were observed in the Kane Basin with 1456 ind. /100 cm 2 and in the NOW (1487 ind. /100 cm 2 ). The highest densities in the NOW are consistent with observations of high productivity in this area [52, 53, 99] related to a combination of physical factors such as light availability, water masses stratification, and vertical mixing, and nutrient advection in the photic layer. However, it is worth noting that a certain disparity between the densities of living fauna was observed at the three stations of the NOW. On the one hand, there is a clear difference in faunal density between station 115 on the east (1487 ind. /100 cm 2 ) and station 101 on the west( 607 ind. /100 cm 2 ) of the polynya, although they were bothsampled in July 2014. This observation confirms the disparity of primary productivity, being earlier and more active to the east [57, 100] due to particular physical conditions (e. g., SST, sea ice, and stratification). Burger et al. [100], presenting the results of chlorophyll a measurements collected during the same scientific cruise in July 2014, explains the observed summer phytoplankton bloom by deep-water upwelling phenomena providing nutrients to fuel the bloom. On the other hand, station BC1, in the central part of the polynya, presents the lowest density observed in the NOW area (260 ind. /100 cm 2 ). This is probably related to the sampling period. Indeed, sediments of the station BC1 were collected early in the fall when the polynya, largely open on the Baffin Bay, is no longer really a strict polynya [53]. In fall, primary productivity is lower than in summer due to water masses stratification and a drop in solar irradiance at the surface of the water, significantly restricting the export of food to the bottom. Regarding station Kane2B, environmental conditions are different as the Kane Basin is located beyond the ice bridge marking the northern limit of the NOW. Nevertheless, a maximum density of living benthic foraminifera in this study can be observed here. While the TOC content remains rather low at this station, the C/N ratio reveals labile properties. Nutrient availability brought by cold Artic water leads to relatively important productivity in this region. Moreover, δ 13 C org measured in the surface sediment of this core indicates an export of sea ice algae feeding the benthic food chain in the Kane Basin. MODIS Terra satellite images (Figure 8 ) show that the situation in the Kane Basin in July 2014 is quite atypical compared to the same period in 2013 and 2015. Indeed, sea ice broke up earlier during the summer of 2014, resembling conditions of polynya type. Burgers et al. [100] also observed a sub-surface phytoplankton bloom in the Kane Basin during summer of 2014 above a topographic feature causing the formation of a localized upwelling and a supply of nutrients that fed the bloom. In the Baffin Bay, observed densities of living benthic foraminifera in surface sediments do not present notable variations between the east and west despite contrasting environmental features in terms of water masses, sea ice cover, or phytoplankton biomass. However, densities of living benthic foraminifera are significantly lower than in Nares Strait. δ 15 N measurements in the sediment indicate lower nutrient availability in North Atlantic waters flowing in the Baffin Bay. Primary productivity is less intense than in the NOW and this is reflected in recorded densities in this study. lynya type. Burgers et al. [100] also observed a sub-surface phytoplankton bloo Kane Basin during summer of 2014 above a topographic feature causing the form a localized upwelling and a supply of nutrients that fed the bloom. In the Baffin served densities of living benthic foraminifera in surface sediments do not presen variations between the east and west despite contrasting environmental features of water masses, sea ice cover, or phytoplankton biomass. However, densities benthic foraminifera are significantly lower than in Nares Strait. δ 15 N measurem the sediment indicate lower nutrient availability in North Atlantic waters flowin Baffin Bay. Primary productivity is less intense than in the NOW and this is refl recorded densities in this study. As well as faunal densities, assemblages of benthic foraminifera show som geographical disparities. Two main assemblages characterize the populations of foraminifera in this study. The first assemblage is dominated by the species N. la As well as faunal densities, assemblages of benthic foraminifera show some large geographical disparities. Two main assemblages characterize the populations of benthic foraminifera in this study. The first assemblage is dominated by the species N. labradorica and A. glomeratum. The second assemblage is essentially composed of an assortment of agglutinated species sometimes associated with the calcareous species M. barleeanus. In the Kane Basin, the major species, A. glomeratum, indicates the presence of cold Arctic waters, while the species N. labradorica and M. barleeanus highlight the export and the availability of organic matter in the benthic environment [97, 98, 101, 102]. Observed species of living benthic foraminifera in the cores of the NOW distinguish themselves by two different assemblages between the east and west of the polynya, at the mouth of Nares Strait. Indeed, stations BC1 and 101, to the east, are characterized by the abundance of species A. glomeratum and N. labradorica, while station 115, to the west, shows a more important number of species but that are mostly agglutinated. Adercotryma glomeratum highlights cold waters flowing down to the south along Ellesmere Island in Nares Strait. The NOW is considered to be the most productive region of the Arctic despite a drastic reduction in productivity and phytoplankton biomass revealed by several recent studies [51, [56] [57] [58]. The spring bloom starts at the end of April or the beginning of May, and east of the polynya, along the Greenland coast, due to the early sea ice retreat generated by relatively warm Atlantic water moving through the WGC [51]. The living benthic foraminiferal assemblage at station 115 is mostly composed of agglutinated species also found in the cores of the Baffin Bay, highlighting the influence of this corrosive Atlantic water mass. The presence of the intermediate infauna M. barleeanus, indicates that the organic matter available in this area and during that period is relatively degraded [91, 97, 98, 101, 103]. The phytoplankton bloom occurs later, west of the polynya, at the beginning of June [51]. At stations BC1 and 101 sampled in October and July, respectively, N. labradorica is abundant. This species is associated with episodic production of fresh phytodetritus in areas of high seasonal productivity [102, 104, 105], indicating the existence of a spring phytoplankton bloom then a less intense fall bloom. 

The distinctive characteristic of the benthic assemblages of the Baffin Bay, south of the NOW, is the dominance of agglutinated species. The only living observed calcareous species in the cores of this region is M. barleeanus, an indicator species of relatively degraded organic matter in the sediment of the Baffin Bay. Between the east and the west of the Baffin Bay, faunas do not show any clear differences in terms of species or abundance. This is attributable to the fact that at the sampling depth of the cores in the Baffin Bay (from 689 m depth to 1448 m depth), the Atlantic water mass is dominant. However, the presence of the cold-water indicator species, A. glomeratum, at station BC4 would indicate the influence of Arctic waters carried by the BC. Environmental conditions in the Baffin Bay are relatively stable in summer and fall. A sampling earlier in the season might have allowed us to highlight changes in the composition of benthic foraminiferal assemblages, following sea ice retreat initiated from the east and later to the west of the Baffin Bay. 

Living benthic foraminiferal assemblages in general appear to be closely linked to the different dominant water masses in the Baffin Bay and Nares Strait. Faunal density and diversity, as well as assemblages, reflect the relation between pelagic and benthic environments in this high-latitude environment, despite the presence of sea ice for most of the year. Particularly, high densities in Nares Strait (NOW and Kane Basin) highlight the connection between primary productivity, the flux of organic matter, and the quality of the available organic matter and the benthic life in such extreme environments. Some benthic foraminifera taxa clearly respond better to food supply in those environments.
section_name: Relation between Primary Productivity and Distribution of Benthic Foraminifera

section_content: This study provides some important information about the ecology of benthic foraminifera in the Baffin Bay and Nares Strait. Assemblages of living benthic foraminifera are associated with specific environments of the studied area. Features of water masses and especially their corrosive nature, as well as primary productivity and the associated flux of organic matter, are essential parameters influencing the distribution of benthic foraminifera. Carbonate dissolution is also a major influencing factor on faunas of benthic foraminifera in the Baffin Bay and explain the dominance of agglutinated taxa over calcareous taxa in the area. Living faunal density is closely linked with the flux of organic matter produced in surface water. This phenomenon is clearly illustrated with regard to the important differences between the lowest density measured in the Baffin Bay and those observed in the NOW. Moreover, particular species are sensitive to the quantity and quality of available organic matter in benthic environments. In particular, species N. labradorica responds quickly and massively to episodic food supply, while M. barleeanus tolerates environments where organic matter is more degraded.
section_name: Conclusions

section_name: Acknowledgments:

section_content: We thank the captain, officers and crew of the NGCC Amundsen for their support during the 2014 and 2015 ArcticNet cruises.
section_name: Acknowledgments:

section_content: Data Availability Statement: All relevant data are shown in the Supplementary Materials.

section_name: Supplementary Materials:

section_content: More knowledge on the ecology of benthic foraminifera living in complex environments subject to seasonal sea ice cover is essential for optimal use of these fauna as a paleoenvironmental proxy in Arctic regions.

section_content: The following supporting information can be downloaded at: https: //www. mdpi. com/article/10. 3390/jmse11112049/s1. Raw counting data for benthic foraminifera (>125 µm) in all stations.
section_name: Supplementary Materials:

section_name: Author

section_content: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
section_name: Conflicts of Interest: