Pauline Depuydt
email: pauline.depuydt@univ-angers.fr

Meryem Mojtahid

Christine Barras

BOUHDAYAD Fatima Zohra

Samuel Toucanne

Intermediate ocean circulation and cryosphere dynamics in the Northeast Atlantic during Heinrich Stadials: benthic foraminiferal assemblage response

Keywords: Intermediate water masses, AMOC, European Ice Sheet, Glacial Eastern Boundary Current (GEBC), Channel River, Benthic foraminifera

The interaction between ocean circulation and ice-sheet dynamics plays a key role in the Quaternary climate. Compared to the surface and deep compartments of the Atlantic Meridional Overturning Circulation (AMOC), the study of intermediate depths during key time periods, such as Heinrich Stadials (HSs), remains poorly documented, especially in the northeast Atlantic. Here we use benthic foraminiferal assemblage data to trace paleoenvironmental changes from ~32 to 14 ka cal BP at ~1000 m depth in the Bay of Biscay.

Our results highlight the high sensitivity of foraminifera, with species-specific responses, to continental (European Ice Sheet dynamics) and marine (AMOC) forcing factors during the last three HSs. In general, HSs were characterized by the concomitant presence of mesooligotrophic and anoxia indicator species and the low abundance of high-energy indicator species. This confirms an overall sluggish intermediate circulation during the three HSs in the northeast Atlantic. HS1 is distinctive by the abundance of high-organic flux indicator species during its early phase. This is consistent with the fact that HS1 was, by far, the most important period of ice-sheet retreat and meltwater release to the ocean over the studied time interval.

Finally, foraminifera depict the mid-HS2 re-ventilation event due to regional glacier instabilities.

Introduction

The last glacial-interglacial cycle is a critical period to understand the natural climate variability and its abrupt transitions (e.g. [START_REF] Bond | Correlations between climate records from North Atlantic sediments and Greenland ice[END_REF][START_REF] Waelbroeck | A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from Hulu Cave[END_REF][START_REF] Clark | Pattern and timing of retreat of the last British-Irish Ice Sheet[END_REF][START_REF] Denton | The Zealandia Switch: Ice age climate shifts viewed from Southern Hemisphere moraines[END_REF]. Orbital forcing (solar radiation), and the feedbacks implying the atmosphere, the ocean, and the cryosphere are the main factors explaining the recorded centennial to multi-millennial climate variability over this period [START_REF] Broecker | The role of ocean-atmosphere reorganizations in glacial cycles[END_REF][START_REF] Mcmanus | A 0.5-Million-Year Record of Millennial-Scale Climate Variability in the North Atlantic[END_REF][START_REF] Denton | The Last Glacial Termination[END_REF][START_REF] Lynch-Stieglitz | The Atlantic Meridional Overturning Circulation and Abrupt Climate Change[END_REF]. In the Northern Hemisphere, the climate of the last glacial period was punctuated by cold (stadials) and warm intervals (interstadials), that were coeval with periods of weakened and accelerated Atlantic Meridional Overturning Circulation (AMOC), respectively (e.g. [START_REF] Kissel | Millennialscale propagation of Atlantic deep waters to the glacial Southern Ocean[END_REF][START_REF] Böhm | Strong and deep Atlantic meridional overturning circulation during the last glacial cycle[END_REF][START_REF] Henry | North Atlantic ocean circulation and abrupt climate change during the last glaciation[END_REF][START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. Amongst the cold intervals, the most drastic are certainly the Heinrich Stadials (HSs), encompassing the Heinrich events (HEs), i.e. armadas of icebergs discharge issued from the dislocation of the Hudson Strait Ice stream of the Laurentide Ice Sheet (LIS) that ultimately caused the deposition of ice-rafted debris (IRD) rich sediments in the subpolar North Atlantic [START_REF] Hemming | Heinrich events: Massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint[END_REF]. It is hypothesized that HEs were triggered by sub-surface heat (700-1100 m depth), 1-2 ka after the decline of the AMOC [START_REF] Shaffer | Ocean subsurface warming as a mechanism for coupling Dansgaard-Oeschger climate cycles and ice-rafting events[END_REF][START_REF] Marcott | Ice-shelf collapse from subsurface warming as a trigger for Heinrich events[END_REF][START_REF] Alvarez-Solas | Iceberg discharges of the last glacial period driven by oceanic circulation changes[END_REF]. The initial AMOC slowdown likely requires precursor melting of North Atlantic-adjacent ice sheets and it is now accepted that the European Ice sheet (EIS) was a critical source for AMOC destabilization and the initiation of HSs conditions [START_REF] Peck | High resolution evidence for linkages between NW European ice sheet instability and Atlantic Meridional Overturning Circulation[END_REF][START_REF] Eynaud | New constraints on European glacial freshwater releases to the North Atlantic Ocean[END_REF][START_REF] Boswell | Enhanced surface melting of the Fennoscandian Ice Sheet during periods of North Atlantic cooling[END_REF][START_REF] Toucanne | Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate[END_REF][START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF][START_REF] Toucanne | Chapter 25 -Abrupt (or millennial or suborbital) climatic variability: Heinrich events/stadials[END_REF].

The present work investigates the evolution of northeast Atlantic intermediate water depth environments and their interaction with EIS dynamics during the last glacial and deglaciation periods, with a focus on HSs. This is achieved through the study of marine sediment core BOBGEO-CS05 retrieved at ~1000 m water depth in the northern Bay of Biscay (BoB) (Figure 1a & 1c). This record covers the past ~32-14 ka cal BP, thus encompassing the last three HSs (HS1, HS2 and HS3). During the last glacial period and the last deglaciation, BOBGEO-CS05 site was located off the Channel River, that drained EIS sediment-laden meltwaters to the northern BoB [START_REF] Zaragosi | Initiation of the European deglaciation as recorded in the northwestern Bay of Biscay slope environments (Meriadzek Terrace and Trevelyan Escarpment): a multi-proxy approach[END_REF][START_REF] Bourillet | Morphology and Seismic Stratigraphy of the Manche Paleoriver System, Western Approaches[END_REF][START_REF] Toucanne | Timing of massive 'Fleuve Manche' discharges over the last 350kyr: insights into the European ice-sheet oscillations and the European drainage network from MIS 10 to 2[END_REF][START_REF] Toucanne | The first estimation of Fleuve Manche palaeoriver discharge during the last deglaciation: Evidence for Fennoscandian ice sheet meltwater flow in the English Channel ca 20-18ka ago[END_REF] (Figure 1b). At the time, the core site was also on the pathway of the Glacial Eastern Boundary Current (GEBC), the glacial analogue of the northward-flowing European Slope Current, that represents the easternmost portion of the upper branch of the AMOC [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF] (Figure 1b). As such, core BOBGEO-CS05 is ideally located to track EIS melting episodes and evaluate their impact/relation to the upper branch of the AMOC.

The present study focuses on fossil benthic foraminifera as one of the very few biological indicator groups that are able to record the history of events on the seafloor by integrating the cumulative impacts of the changing physico-chemical habitats (e.g. Schmiedl and Mackensen, 1997;[START_REF] Wollenburg | Changes in Arctic Ocean paleoproductivity and hydrography during the last 145 kyr: The benthic foraminiferal record[END_REF][START_REF] Rodriguez-Lazaro | Deep-sea benthic response to rapid climatic oscillations of the last glacial cycle in the SE Bay of Biscay[END_REF]. A particular interest is found in documenting HS2 and HS3, which are not covered by the nearby recent foraminiferal studies [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF][START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF]. In addition, our aim is to establish to what extent information previously obtained from sedimentary, geochemical and surface water proxies on the interaction between the AMOC and the EIS during the HSs are consistent with our benthic biotic data. More specifically, the approach uses here foraminiferal diversity and density, and the ecological requirements of specific species to interpret several aspects of the environment on the seafloor (e.g. organic matter flux, bottom-water oxygenation, current, transport, water masses properties). Our findings highlight strong foraminiferal species-specific responses, particularly during HSs, with some species associations able to discriminate between EIS/continental impact and ocean circulation changes.

Core location, present and past sedimentological and hydrographical settings

Core BOBGEO-CS05 (46°18.850'N, 5°56.988'W, 1473 cm length, 1015 m water depth) was extracted from the upper continental slope of the northern BoB (northeast Atlantic) during the BOBGEO cruise (doi.org/10.17600/9030060; R/V Pourquoi pas?; [START_REF] Bourillet | BOBGEO cruise[END_REF] (Figure 1).

Core BOBGEO-SC05 is mostly composed of contourite deposits [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF], i.e.

sediments deposited or substantially reworked by the persistent action (e.g. selective deposition, winnowing, erosion) of bottom currents (Facies 1 and 2; Fig. 2). Silty-clayey laminations characterized the early part of the deglaciation (early HS1), ca. 18-16.7 ka (Facies 3; Figure 2), and IRD (Facies 4; Figure 2) allowed the recognition of the Heinrich layers (cf. Supplementary material S1 for the complete X-Ray radiographs).

Today, the sedimentation on the slope is governed by the European Slope Current (ESC), flowing along the upper slope (~500-2000 m water depth) from the northern Iberian Peninsula to the Faroe-Shetland Channel [START_REF] Marsh | Large-scale forcing of the European Slope Current and associated inflows to the North Sea[END_REF][START_REF] Clark | Weakening and warming of the European Slope Current since the late 1990s attributed to basin-scale density changes[END_REF][START_REF] Moritz | Volume Transport Time Series and Variability of the North Atlantic Eastern Boundary Current at Goban Spur[END_REF] (Figure 1a). This current, driven by both the steep topography of the European margin and large-scale meridional density gradients [START_REF] Huthnance | Slope Currents and "JEBAR[END_REF][START_REF] Pingree | Structure, strength and seasonality of the slope currents in the Bay of Biscay region[END_REF][START_REF] Friocourt | A regional numerical ocean model of the circulation in the Bay of Biscay[END_REF], is largely recruited from the eastern North Atlantic and is connected, north of ~55°N (i.e. Rockall Trough), to the upper part of the North Atlantic Current (NAC; that is the eastern limb of the subpolar gyre). This forms the bulk of the upper branch of the AMOC (down to ~1500 m; [START_REF] Lozier | A sea change in our view of overturning in the subpolar North Atlantic[END_REF][START_REF] Huthnance | Oceanic Density/Pressure Gradients and Slope Currents[END_REF]. The latter (to which the ESC contributes by ~25 %; [START_REF] Berx | Combining in situ measurements and altimetry to estimate volume, heat and salt transport variability through the Faroe-Shetland Channel[END_REF] finally reaches the Nordic Seas convection region, where it cools and sinks to form a deeper southward return flow, the North Atlantic Deep Water (NADW), mainly found along the eastern continental margin of North America and transported by the Deep Western Boundary Current (e.g. [START_REF] Dickson | The production of North Atlantic Deep Water: Sources, rates, and pathways[END_REF] (Figure 1a).

The main water mass transported by the NAC into the BoB forms the Eastern North Atlantic Central Water (ENACW), found down to ~600 m water depth [START_REF] Pollard | Structure and circulation of the Upper Atlantic Ocean northeast of the Azores[END_REF]. Below, the Mediterranean Outflow Water (MOW) is present between ~600 and 1500 m, flowing northward from the Gulf of Cadiz and largely entrained by the ESC north of ~45°N (e.g. [START_REF] Pingree | Seasonality of the European slope current (Goban Spur) and ocean margin exchange[END_REF][START_REF] Van Aken | The hydrography of the mid-latitude Northeast Atlantic Ocean: II: The intermediate water masses[END_REF]. Deeper, the Labrador Sea Water (LSW), centered at ~2000 m water depth and corresponding to the upper NADW, dominates (van Aken, 2000a). fcapture of the (southward-flowing) LSW by the above (eastward-flowing) Gulf Stream -NAC system in the north-western North Atlantic [START_REF] Buckley | Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: A review[END_REF][START_REF] Zou | Observed and modeled pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic[END_REF] (Figure 1a).

During the last glacial maximum (LGM) ca. 23-18 ka cal BP [START_REF] Mix | Environmental processes of the ice age: land, oceans, glaciers (EPILOG)[END_REF], the Gulf Steam -NAC system and more generally the upper branch of the AMOC certainly had a different geometry (i.e. positioned southward) because of the (southward) expansion of ice sheets over North America [START_REF] Keffer | The Position of the Gulf Stream During Quaternary Glaciations[END_REF][START_REF] Otto-Bliesner | Last Glacial Maximum and Holocene Climate in CCSM3[END_REF][START_REF] Brady | The role of meltwater-induced subsurface ocean warming in regulating the Atlantic meridional overturning in glacial climate simulations[END_REF][START_REF] Löfverström | Evolution of the largescale atmospheric circulation in response to changing ice sheets over the last glacial cycle[END_REF] (Figure 1b). The NADW was likely replaced by a shallower, northern-sourced nutrient-poor water mass, namely the Glacial North Atlantic Intermediate Water (GNAIW), dominant above 2000 m depth and overlaying a more nutrientrich water of southern origin below 2000 m (i.e. a glacial analog of Antarctic Bottom Water) (e.g. [START_REF] Lynch-Stieglitz | Atlantic Meridional Overturning Circulation During the Last Glacial Maximum[END_REF]. The recirculation of the GNAIW by the glacial Gulf Stream -NAC system certainly explains GNAIW signatures recorded in the NE Atlantic basin and the BoB basin during the last glacial period [START_REF] Zahn | Thermohaline instability in the North Atlantic during meltwater events: Stable isotope and ice-rafted detritus records from Core SO75-26KL, Portuguese Margin[END_REF][START_REF] Peck | High resolution evidence for linkages between NW European ice sheet instability and Atlantic Meridional Overturning Circulation[END_REF]Peck et al., , 2007a;;[START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. At the same time, the Mediterranean-Atlantic water exchange was reduced by ~50 %, and the MOW was certainly restricted to the southern Iberian margin (e.g. [START_REF] Rogerson | Paleoceanography of the Atlantic-Mediterranean exchange: Overview and first quantitative assessment of climatic forcing[END_REF]. On the other hand, the presence of Antarctic Intermediate waters (AAIW) along the European margin as far north as the South Iceland Rise was hypothesized [START_REF] Rickaby | Evidence from the high-latitude North Atlantic for variations in Antarctic Intermediate water flow during the last deglaciation[END_REF][START_REF] Thornalley | Intermediate and deep water paleoceanography of the northern North Atlantic over the past 21,000 years[END_REF] but the recent studies of [START_REF] Thornalley | A warm and poorly ventilated deep Arctic Mediterranean during the last glacial period[END_REF] then [START_REF] Crocker | Geochemical response of the mid-depth Northeast Atlantic Ocean to freshwater input during Heinrich events 1 to 4[END_REF] concluded that mid-depth in the NE Atlantic was never ventilated by southern-sourced waters during the last glacial period. During late HS1 (~17 ka cal BP), and the near shutdown of the AMOC [START_REF] Mcmanus | Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes[END_REF][START_REF] Ng | Coherent deglacial changes in western Atlantic Ocean circulation[END_REF], [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF] recorded low foraminiferal Sr/Ca ratios (i.e. carbonate system proxy; [START_REF] Yu | Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene[END_REF][START_REF] Allen | Trace element proxies for surface ocean conditions: A synthesis of culture calibrations with planktic foraminifera[END_REF][START_REF] Keul | Exploring foraminiferal Sr/Ca as a new carbonate system proxy[END_REF], indicative of a change in water mass chemistry and origin in the BoB. At the same time, [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF] recorded increasing benthic foraminiferal Mg/Ca ratios, indicating a warming of intermediate water masses. This is interpreted as the northward conveyance of the subsurface warming originating from the low latitudes [START_REF] Rühlemann | Intermediate depth warming in the tropical Atlantic related to weakened thermohaline circulation: Combining paleoclimate data and modeling results for the last deglaciation[END_REF][START_REF] Shaffer | Ocean subsurface warming as a mechanism for coupling Dansgaard-Oeschger climate cycles and ice-rafting events[END_REF] by the glacial NAC (GNAC) and the GEBC (Figure 1b) [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. This reinforces the view that the water mass structure in the glacial NE Atlantic could have changed rapidly through time.

Materials and Methods

Chronology

The chronostratigraphic framework of core BOBGEO-CS05 (Figure 2) is detailed in [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. In short, the final age model is based on XRF-Ca/Ti data synchronization with the nearby well-dated core MD95-2002 (Figure 2a). Twenty-one XRF tiepoints based on the recognition of millennial-scale oscillations were determined. The final age model indicates that core BOBGEO-CS05 covers a period extending from ca. 32 to 14 ka cal BP (Figure 2), thus encompassing the end of MIS 3 (ca. 57-29 ka cal BP) and MIS 2 (ca. 29-14.7 ka cal BP). The accuracy of the age model is supported first by the good match between the percentages of the polar planktonic taxon N. pachyderma in core BOBGEO-CS05 and MD95-2002 (Figure 2c), and second, by the overall concordance with the new radiocarbon dates (n=12; Table 1; Figure 2b). The top core 14 C dates show older ages (~15.7 cal ka BP) than the final XRF-Ca/Ti based age model (~14 cal ka BP) (Figure 2b). The low percentages of the polar taxon N. pachyderma at the core top (Figure 2c) indicate that we are out of the Heinrich Stadial, making the core top 14 C ages unreliable. Such incoherencies in 14 C dates (including the few outliers; Figure 2b) are certainly linked to physical sediment mixing and bioturbation that are common in contourite deposits.

The final age model clearly shows a sedimentary hiatus after ~14 cal ka BP, in concordance with previous studies in similar environments in the BoB [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF][START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. The lack of sedimentation is due to increased erosion of the shelf deposits in response to the significant sea-level rise and the embayment of the English Channel (e.g., Bourillet et al., 2003;[START_REF] Toucanne | External controls on turbidite sedimentation on the glacially-influenced Armorican margin (Bay of Biscay, western European margin)[END_REF].

Core BOBGEO-CS05 shows sedimentation rates of 50-150 cm.ka -1 (Figure 2b). As such, core BOBGEO-CS05 offers a unique opportunity to study at high time resolution the later part of the last glacial period and the last three HSs.

Foraminiferal analyses

For benthic foraminiferal analyses, 56 samples were investigated (~320 years resolution).

The samples were washed through 63 and 150 µm mesh size sieves. The >150 µm fraction was splitted with a dry Otto microsplitter (when necessary) until obtaining at least 250-300 specimens in the final split. Then, all foraminifera were picked out from the split and mounted on Plummer cell slides for taxonomic determination. To verify the relevance of smallsized benthic species, 16 out of the 56 samples were investigated from the 63-150 µm size fraction. Foraminifera were picked out from 3 out of the 16 samples, put in Plummer cell slides and determined taxonomically. For the rest of the 63-150 µm samples, foraminifera were counted and determined directly under the stereomicroscope. Similarly to the >150 µm fraction, samples (63-150 µm) were splitted with a dry Otto microsplitter until obtaining at least 250-300 specimens in the final split. The benthic foraminiferal accumulation rate (ind.cm -2 .ka -1 ) (BFAR), used as paleo-productivity proxy [START_REF] Herguera | Paleoproductivity from benthic foraminifera abundance: Glacial to postglacial change in the west-equatorial Pacific[END_REF]Herguera, 1992;[START_REF] Gooday | Benthic foraminifera (protista) as tools in deep-water palaeoceanography: Environmental influences on faunal characteristics[END_REF][START_REF] Jorissen | Chapter Seven Paleoceanographical Proxies Based on Deep-Sea Benthic Foraminiferal Assemblage Characteristics[END_REF], was calculated for both the >150 µm and >63 µm (63-150 + >150 µm) fractions as: number of individuals per gram of dry sediment × linear sedimentation rate (cm.ka -1 ) × Dry Bulk Density (g.cm -3 ) [START_REF] Herguera | Paleoproductivity from benthic foraminifera abundance: Glacial to postglacial change in the west-equatorial Pacific[END_REF]. The Dry Bulk Density (DBD) was calculated following the relation: DBD = 2.65 x (1.024 -Dwet)/(1.024-2.65), where 2.65 g.cm -3 is the grain density and 1.024 g.cm -3 is the interstitial water density [START_REF] Auffret | Terrigenous fluxes at the Celtic margin during the last glacial cycle[END_REF]. Wet bulk densities (Dwet) were derived from gamma-ray attenuation density measurements obtained from a 'Geotek Multi Sensor Core Logger' (MSCL).

The relative abundances of benthic species (% of the total foraminiferal abundances) were calculated for the >150 µm fraction for the 56 samples and for the >63 µm fraction (63-150 µm + >150 µm) for the selected 16 samples. The error bars of the relative abundances were computed with the binomial standard error √(p(1-p))/n [START_REF] Buzas | Another look at conhdence limits for species proportions[END_REF][START_REF] Fatela | Seasonal variability of benthic foraminiferal faunas at 1000 m depth in the Bay of Biscay[END_REF], where p is the species proportion estimate (number of counted individuals for a given species/n). The diversity of the 56 samples (>150 µm) was calculated with the Shannon index (entropy, H; Hayek and Buzas, 1997) using the PAST software (PAleontological STatistics; Version 2.14; [START_REF] Hammer | PAST: Paleontological Statistics Software Package for Education and Data Analysis 9[END_REF]. Error bars representing 95 % confidence interval were computed with a bootstrap procedure. In this study, we discuss mainly the most dominant species with relative abundance >10 % showing the highest variability. All species with relative abundance between 5 and 10 % in at least one sample are presented in supplementary material S2, and their ecological interpretations summarized in Table 2. The complete raw data set is available as supplementary material S3 and in SEANOE data repository (https://doi.org/10.17882/88029). Scanning Electron Microscope (SEM) photographs were obtained at LPG (Angers University, France) using a Tabletop Microscope Hitachi TM4000Plus.

For the counts of the planktonic taxon N. pachyderma, the >150 µm fraction were used and the relative abundances were determined using a minimum of 300 planktonic foraminiferal tests from single sample splits. Counting was performed at University of Bordeaux (France).

Results

Average BFAR values from the >150 µm fraction are ~12.10 3 ind.cm -2 .ka -1 and from the >63 µm are ~7.5.10 6 ind.cm -2 .ka -1 (Figure 3a). The values from the >150 µm fraction are minimal during the three HSs (~1.10 3 ind.cm -2 .ka -1 ) and are more important during the interstadial periods (~30.10 3 ind.cm -2 .ka -1 ). From ~32 to 14 ka cal BP, the Shannon (H) index (Figure 3b) shows an overall increase of diversity, with values ranging from ~2 to 3.2.

The eight most dominant species (>10 %) showing the highest variability are illustrated in Plate 1 and their relative abundances are presented in Figure 3 (c-j). Elphidium spp., Cassidulina crassa and Cibicides lobatulus are dominant along the record and account together for 12.7 to 74.3 % of the total fauna. In this study, Elphidium spp. includes mainly E. excavatum (i.e. E. excavatum f. clavatum) with pyritized shells (Plate 2a) and other species of the genus Elphidium (e.g., E. gerthi, E. macellum). Elphidium spp. show maximum values (>30 %) between 30.7 and 28.9 ka cal BP (i.e. HS3) and minimum values (<10 %) between 17.5 and 16.5 ka cal BP (i.e. Early HS1; Figure 3c). Before HS2, C. crassa accounts in average for about ~21 % of the total fauna (Figure 3d). The highest values are recorded during HS2, with maximum percentages (40 %) just before HE2 followed by a sharp decrease. After HS2, the relative density of this species remains stable around ~8 %. Cibicides lobatulus exhibits a different pattern in comparison with the previously mentioned species. Generally, this species is present with lower proportions during HS periods (around 5-10 %), except at 24.2 ka cal BP (during HE2) and 17.2 ka cal BP (during HS1). Between HS3 and HS2 (ca. 29-26 ka cal BP) and during the LGM (ca. 23-18 ka cal BP), C. lobatulus accounts for ~22 % of the total fauna (Figure 3e). Trifarina angulosa shows the same trend as C. lobatulus (Figure 3f) but with overall lower proportions (maximum values around 10 %). The remaining dominant species (>10 %) present a discontinuous evolution. Cassidulina carinata, Bolivina spp. and Globobulimina spp. exhibit high relative abundances (up to 42 %, 24 % and 18 % respectively), with high variability, during early HS1 (Figure 3g,3h & 3i). Before HS1, Globobulimina species are almost absent except in samples from HS3 and HS2 (average of ~5 % and 7.5 %, respectively). Cibicidoides pachyderma is also present mainly during the three HSs reaching 12.5 % at 29.3 ka cal BP (i.e. during HS3), 20 % at 25.3 ka cal BP (i.e. during HS2) and varying around 10 % at ~HS1 (Figure 3j). The evolution through time of the minor species (i.e. present only few times with percentages >5 %) is represented in Erreur ! Source du renvoi introuvable.. Gavelinopsis praegeri and Planorbulina mediterranensis mainly appear just after 24.2 ka cal BP, between HE2 and the end of HS2. Chilostomella oolina, Pullenia quinqueloba, Textularia sagittula occur just one time with relative densities >5 % at 16.8 ka cal BP, 16.5 ka cal BP, 17.2 ka cal BP respectively while Hoeglundina elegans occurs only at 14 ka cal BP. Nonionella turgida become dominant only after HE1 (~6 %).

In the small fraction (63-150 µm), the identified species were similar to the ones found in the larger size fraction (>150 µm). When considering the small and large fractions together (>63 µm), six major species >5 % are present: Elphidium spp., C. crassa, C. lobatulus, C. carinata, Bolivina spp. and T. angulosa. These species, also identified as major species when considering only the >150 µm size fraction, exhibit approximately similar trends (black dashed line; Fig. 3 c-h). Only C. crassa presents much higher proportions in the >63 µm fraction with abundances ranging from 15 to 60 % of the total fauna.

Discussion

Regional inter-comparison of benthic foraminiferal faunas

Most of the dominant foraminiferal taxa in core BOBGEO-CS05 (e.g. C. pachyderma, C. carinata, C. crassa, Bolivina spp., Globobulimina spp.) inhabit the modern upper slope environments of the BoB (e.g. [START_REF] Murray | Foraminifers of the Western Approaches to the English Channel[END_REF]Fontanier et al., 2006;[START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF][START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF][START_REF] Dorst | Diversity of benthic foraminifera on the shelf and slope of the NE Atlantic: analysis of Datasets[END_REF], and/or are found in the regional benthic fossil (i.e. last glacial) records of intermediate waters depths (Figure 1c; [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF][START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF]. However, some discrepancies are observed and detailed hereafter:

High-energy indicator species

Cibicides lobatulus (also known as Lobatula lobatula) is highly dominant in our record (~4-30 %). This species is also present, but with overall lower percentages (~10 %), at site MD99-2328, north of our study site (Figure 1), that covers the time interval from 23 to 16 ka cal BP [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF] (Figure 3). However, this epibenthic species is absent today from the BoB modern foraminiferal communities at ~1000 m depth (e.g. [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF]Fontanier et al., 2006;[START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF][START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF]. This discrepancy can be explained by different environmental conditions (e.g. food source, hydrodynamics) during the last glacial period allowing their settlement at intermediate water depths in the area. Indeed, C. lobatulus is a suspension-feeder that inhabits moderate-to-strong hydrodynamic environments of the modern northeast Atlantic. These include shelf environments (e.g. Basque shelf; [START_REF] Pascual | A survey of the benthic microfauna (foraminifera, Ostracoda) on the Basque shelf, southern Bay of Biscay[END_REF] and upper slope settings swept by strong bottom currents and characterized by coarse substrate and/or cold-water coral mounds and reefs trapping abundant food particles (e.g. Gulf of Cadiz, Porcupine and Rockall Banks; [START_REF] Schönfeld | The impact of the Mediterranean Outflow Water (MOW) on benthic foraminiferal assemblages and surface sediments at the southern Portuguese continental margin[END_REF]Schönfeld, , 2002aSchönfeld, , 2002b;;[START_REF] Margreth | Benthic foraminifera as bioindicator for cold-water coral reef ecosystems along the Irish margin[END_REF]Spezzaferri et al., 2015). As such, the high presence of C. lobatulus in the BOBGEO-CS05 glacial record might indicate stronger currents than today. The depicted link between C. lobatulus and strong energy environments is further supported in our record by its co-variation with: i) the abundance of Trifarina angulosa (r² = 0.78) (Figure 3e & 3f) which is commonly associated with shelf-edge to upper-slope areas swept by vigorous bottom currents (e.g. southwest Norway, Rockall Trough ; [START_REF] Mackensen | The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway[END_REF][START_REF] Austin | NE Atlantic benthic foraminifera: modern distribution patterns and palaeoecological significance[END_REF][START_REF] Gooday | Foraminifera associated with phytodetritus deposits at a bathyal site in the northern Rockall Trough (NE Atlantic): seasonal contrasts and a comparison of stained and dead assemblages[END_REF], and ii) the "sortable silt" mean size 𝑆𝑆 ̅̅̅ (i.e. the mean grain size of the carbonate-free terrigenous silt fraction) at BOBGEO-CS05 (Figure 4f; [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF] that provides a direct constraint on the rate of past bottom flows [START_REF] Mccave | Circulation in the glacial North Atlantic inferred from grain-size measurements[END_REF]. As such, our biotic data independently support the presence of strong bottom currents on the upper slope of the BoB, and by extent the presence of the GEBC along the French Atlantic margin [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. Based on the above, we summed the percentages of C. lobatulus and T. angulosa to constitute the group of high-energy indicator species. The latter will be used to examine the hydrodynamics variability in the study area throughout the ca. 32-14 ka cal BP interval, and more specifically during the HSs (cf. Section 5.2).

Glacier-proximal species

The high dominance (up to ~40 % in the late MIS 3 and ~20 % thereafter) of elphidiids in core BOBGEO-CS05 is peculiar as this group is presently found in coastal, shelf and estuarine environments of the northeast Atlantic (e.g. [START_REF] Pujos | Ecologie des foraminifères benthiques et des thecamoebiens de la Gironde et du plateau continental Sud-Gascogne: application à la connaissance du quaternaire terminal de la région Ouest-Gironde[END_REF][START_REF] Murray | Ecology and Palaeoecology of Benthic Foraminifera[END_REF][START_REF] Mojtahid | Spatial distribution of living (Rose Bengal stained) benthic foraminifera in the Loire estuary (western France). Journal of Sea Research, Recent and past sedimentary, biogeochemical and benthic ecosystem evolution of the Loire Estuary[END_REF].

In the modern benthic foraminiferal assemblage of the upper Whittard region (northern BoB, ~1000 m depth; [START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF], Elphidium spp. are found only in the dead faunas, and as such, were considered as transported from shallower settings. [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF] report high abundances of Elphidium spp. in core MD99-2328 especially during the late HS1 (16.7-16 ka cal BP; up to ~70 %) and hypothesized their transport to these intermediate depths by the EIS icebergs and/or shelf ice. This would be also a possibility for BOBGEO-CS05 since Elphidium shells show pyritization marks (Plate 2a) that may indicate a potential reworking and transport. However, it is interesting to note that modern elphidiids may extend their habitats to deeper settings (several hundred meters) in cold, arctic environments, usually in connection with freshwater river outflow (e.g. [START_REF] Bergsten | Recent benthic foraminifera of a transect from the North Pole to the Yermak Plateau, eastern central Arctic Ocean[END_REF][START_REF] Polyak | Benthic foraminiferal assemblages from the southern Kara Sea, a riverinfluenced Arctic marine environment[END_REF]. Therefore, another explanation for the high abundance of elphidiids in the glacial BOBGEO-CS05 record could simply be an adaptation to cold glacial conditions and meltwater inputs in the BoB. This is supported by the presence of E. excavatum f. clavatum, the dominant elphidiids species in our assemblages (~75 %), frequently found today in glacier-proximal environments (e.g. [START_REF] Jennings | Modern foraminiferal faunas of the southwestern to northern Iceland Shelf: oceanographic and environmental controls[END_REF][START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF][START_REF] Darling | The genetic diversity, phylogeography and morphology of Elphidiidae (Foraminifera) in the Northeast Atlantic[END_REF][START_REF] Fossile | Benthic foraminifera as tracers of brine production in the Storfjorden "sea ice factory[END_REF]. The modern conditions in the polar regions where this species lives today are close to the conditions prevailing during the last glacial period in our study area since the EIS invaded the western European shelf (cf. icesheet and polar fronts limits in Figure 1) and the Channel River channeled huge amounts of meltwaters to the northern BoB.

Cassidulina crassa occurs concomitantly to E. excavatum f. clavatum in our record (r 2 = 0.85). Similarly to Elphidium spp., modern upper slope foraminiferal studies from the BoB reported that C. crassa is either only encountered in the dead faunas or very rarely present in the living faunas (e.g. [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF]Fontanier et al., , 2006;;[START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF][START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF].

It is therefore probable that this species has been transported to the study site, although C. crassa tests are rather intact (Plate 1) compared to E. excavatum f. clavatum (Plate 2a). It must be noted that the morphospecies identified here as C. crassa (d'Orbigny, 1839) has a variant that is very close morphologically and was described first as Cassidulina crassa var. reniforme Nørvang, 1945, and later elevated to the species rank as C. reniforme. Cassidulina reniforme morphospecies is mainly reported from arctic regions as typical of near-glacier environments [START_REF] Hansen | Recent foraminiferal distribution in Freemansundet and Early Holocene stratigraphy on Edgeøya, Svalbard[END_REF][START_REF] Korsun | Recent foraminifera in glaciomarine sediments from three arctic fjords of Novaja Zemlja and Svalbard[END_REF][START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF]. Thus, it is highly possible that C. crassa from BOBGEO-CS05 is actually the same morphospecies than the one reported from arctic regions. We therefore assume that the C. crassa -E. excavatum f. clavatum association in our record is coherent with near-glacier environments. This is further corroborated by the absence of these species in the upper slope glacial record PP10-12 from the southeast BoB [START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF], far from both the ice sheet extent limit and the Channel River mouth. Based on the above, we summed the percentages of E. excavatum f. clavatum and C. crassa to constitute the group of glacier-proximal indicator species. The latter will be used to examine the EIS dynamics (cf. Section 5.2).

Holocene indicator species

One of the most striking features of our benthic foraminiferal record is the absence of uvigerinids (e.g. U. peregrina, U. mediterranea), whereas they dominate the modern benthic foraminiferal assemblages of the BoB between ~500 and 2000 m water depth (e.g., [START_REF] Schönfeld | Taxonomy and distribution of the Uvigerina peregrina plexus in the tropical to northeastern Atlantic[END_REF][START_REF] Barras | A comparison of spatial and temporal variability of living benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF][START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF][START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF]. This absence is also the case in the glacial part of the MD99-2328 record [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF]. We assume therefore that uvigerinids might not be tolerant to the glacial-related conditions on the BoB seafloor [START_REF] Mojtahid | High resolution Holocene record in the southeastern Bay of Biscay: Global versus regional climate signals[END_REF][START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF][START_REF] Rodriguez-Lazaro | Deep-sea benthic response to rapid climatic oscillations of the last glacial cycle in the SE Bay of Biscay[END_REF]. [START_REF] Schönfeld | Late Glacial to Recent distribution pattern of deep-water Uvigerina species in the north-eastern Atlantic[END_REF] hypothesized a widespread change from glacial to modern surface productivity configuration (e.g. nature of primary producers, seasonality in phytoplankton blooms) that may have triggered the Holocene settlement of U. peregrina in the northeast Atlantic. It is also interesting to note that U. peregrina and U. mediterranea are very abundant in bathyal depths (~200-1500 m) of the Mediterranean and the BoB bathed by the MOW (e.g.

De [START_REF] De Rijk | Organic flux control on bathymetric zonation of Mediterranean benthic foraminifera[END_REF][START_REF] Schmiedl | Trophic control of benthic foraminiferal abundance and microhabitat in the bathyal Gulf of Lions, western Mediterranean Sea[END_REF][START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF]. The possible link between water masses and specific fauna has been progressively abandoned in favor of organic matter and oxygen as major controlling environmental parameters [START_REF] Jorissen | Chapter Seven Paleoceanographical Proxies Based on Deep-Sea Benthic Foraminiferal Assemblage Characteristics[END_REF]. Yet, the settlement of uvigerinids in the BoB in the end of deglaciation -early Holocene [START_REF] Garcia | Benthic and Planktic Foraminifera as Indicators of Late Glacial to Holocene Paleoclimatic Changes in a Marginal Environment: An Example from the Southeastern Bay of Biscay[END_REF][START_REF] Mojtahid | High resolution Holocene record in the southeastern Bay of Biscay: Global versus regional climate signals[END_REF][START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF] seems to coincide with the significant increase in the influx of the MOW into the North Atlantic and along the European margin [START_REF] Rogerson | Paleoceanography of the Atlantic-Mediterranean exchange: Overview and first quantitative assessment of climatic forcing[END_REF][START_REF] Lebreiro | Paleoceanographic and climatic implications of a new Mediterranean Outflow branch in the southern Gulf of Cadiz[END_REF]. This is coherent with what [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF] observed in core MD99-2328 where they record the appearance of uvigerinids (although with low abundances) only in the Holocene portion of the record.

In summary, we have shown that the upper slope benthic foraminifera assemblage found at site BOBGEO-CS05 reflect the complex, highly dynamic and variable environmental conditions in the northern BoB during the last glacial period, including high bottom water currents, glacier-proximal settings, and southern retreat of the MOW. Since benthic foraminifera respond greatly to these various environmental parameters, they present a great potential to better constrain glacial intermediate bottom water characteristics during HSs.

Environmental particularities of Heinrich Stadials depicted by benthic foraminifera

What do the last three Heinrich Stadials have in common in the Bay of

Biscay?

In general, HS3 (~31-29 ka cal BP), HS2 (~26-23 ka cal BP) and HS1 (~18-15.5 ka cal BP) in core BOBGEO-CS05 are characterized by a systematic drop in BFAR values (Fig. 3a). This may indicate unfavorable conditions (e.g. low quality/quantity of the organic matter, low oxygenation) for the growth and reproduction of foraminifera. In the same intervals, we record the highest occurrence of Cibicidoides pachyderma and Globobulimina spp. (Figure 3j & 3i).

Cibicidoides pachyderma is usually found in meso-oligotrophic open-slope environments, as in the modern BoB [START_REF] Schmiedl | Trophic control of benthic foraminiferal abundance and microhabitat in the bathyal Gulf of Lions, western Mediterranean Sea[END_REF][START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF][START_REF] Duros | Live and dead benthic foraminiferal faunas from Whittard Canyon (NE Atlantic): Focus on taphonomic processes and paleo-environmental applications[END_REF].

Globobulimina spp., on the other hand, are deep infaunal species that tolerate hypoxia and anoxia [START_REF] Risgaard-Petersen | Evidence for complete denitrification in a benthic foraminifer[END_REF][START_REF] Pina-Ochoa | Widespread occurrence of nitrate storage and denitrification among Foraminifera and Gromiida[END_REF][START_REF] Koho | Vertical migration, nitrate uptake and denitrification: survival mechanisms of foraminifers (Globobulimina turgida) under low oxygen conditions[END_REF]. Hence, we interpret the C. pachyderma -Globobulimina spp. association (i.e. meso-oligotrophic species; see Figure 4h) during HSs, together with the low BFAR, as indicating meso-oligotrophic conditions, with moderate to low export of organic matter to the seafloor, and reduced bottomwater ventilation. The latter is supported by the concomitant decrease in the proportions of high-energy indicator species T. angulosa and C. lobatulus during each of the HSs (Figure 4g).

The weak hydrodynamics during the HSs is independently supported by the low 𝑆𝑆 ̅̅̅ values at BOBGEO-CS05 and at many sites along the French Atlantic margin [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF].

As such, biotic and sedimentological data indicate reduced near-bottom flow speed (i.e.

weakened GEBC) and, by extension, a sluggish AMOC during the three HSs.

The glacier-proximal species (E. excavatum f. clavatum. and C. crassa), although present all along the BOBGEO-CS05 record, display the highest percentages during the HSs, especially during HS3 and HS2 (Figure 4b). In their modern habitats in the Arctic fjords, these species are impacted by seasonal melting of marine-terminating glaciers [START_REF] Schroder-Adams | Recent Arctic shelf Foraminifera: seasonally ice covered vs. perennially ice covered areas[END_REF][START_REF] Wollenburg | Living benthic foraminifers from the central Arctic Ocean: faunal composition, standing stock and diversity[END_REF][START_REF] Wollenburg | The response of benthic foraminifers to carbon flux and primary production in the Arctic Ocean[END_REF][START_REF] Wollenburg | High-resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal Arctic Ocean[END_REF].

Since enhanced EIS meltwaters influx to the BoB are described during HSs [START_REF] Toucanne | Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate[END_REF], increased densities of these species might be indicative of such meltwater inputs. The concomitant presence of meso-oligotrophic species (e.g. C. pachyderma) indicates a low to moderate export of organic matter to the seafloor, especially during HS2 and HS3. This will be further discussed when addressing the specificities of each HS (cf. Sections 5.2.2. and 5.3).

The difference between the early HS1 and the other HSs

In core BOBGEO-CS05, HS1 is very distinct from HS2 and HS3 by displaying a high presence (~60 %) of opportunistic and high-organic flux indicator species (C. carinata and Bolivina spp.; Schmiedl et al., 1997;[START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF] during its early phase ca. ~18-16.7 ka cal BP (Figure 4d). This is coherent with the findings of Mojtahid et al.

(2017) at the same time period at site MD99-2328. Conversely, during HS2 and HS3, these species were present with much lower abundances (< 10 %; Figure 4d). Thus, we assume that limited organic material inputs reached the BOBGEO-CS05 site during HS3 and HS2, then substantially increased during the early HS1. This difference is further corroborated by the positive correlation between the abundance of the high-organic flux indicator species during early HS1 at our site and both the BIT index at site MD95-2002 (Figure 4c;[START_REF] Ménot | Early Reactivation of European Rivers During the Last Deglaciation[END_REF] and the turbidite (i.e. flood-related deposits) flux in the deep BoB [START_REF] Zaragosi | The impact of the last European deglaciation on the deep-sea turbidite systems of the Celtic-Armorican margin (Bay of Biscay)[END_REF][START_REF] Toucanne | Activity of the turbidite levees of the Celtic-Armorican margin (Bay of Biscay) during the last 30,000 years: Imprints of the last European deglaciation and Heinrich events[END_REF][START_REF] Toucanne | External controls on turbidite sedimentation on the glacially-influenced Armorican margin (Bay of Biscay, western European margin)[END_REF]. It has been suggested that these differences in organic material inputs through time could result from complex interactions between climate conditions, and ice and vegetation cover [START_REF] Ménot | Early Reactivation of European Rivers During the Last Deglaciation[END_REF]. Our data cannot resolve this issue, but it certainly highlights the paroxysmal phase of EIS melting in response to increasing boreal insolation during HS1, and the concomitant rapid progradation of a large outer-shelf delta that ultimately improved the connection between the BOBGEO-CS05 site and the Channel River system [START_REF] Toucanne | External controls on turbidite sedimentation on the glacially-influenced Armorican margin (Bay of Biscay, western European margin)[END_REF]. That said, because C. carinata and Bolivina spp. are very abundant in shallower settings in the BoB (140-550 m depth; [START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF][START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF], we cannot discard that their presence in our record is a result of downslope transport. Even so, the abundance of these species still indicates increased organic fluxes in their source habitats.

Interestingly, in the upper slope BOBGEO-CS05 and MD99-2328 cores, the dominance of the anoxia indicator species (representing the sum of Globobulimina spp. and Chilostomella oolina) at HS1 occurs early within this interval, before HE1 event sensu stricto (Figure 4i).

According to [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF], the presence of these indicator species during early HS1 is indicative of organically-enriched and/or oxygen-depleted benthic environments, and their absence during HE1 event, together with high 𝑆𝑆 ̅̅̅ (Figure 4i & 4f) indicate well-ventilated intermediate waters. In deeper sediment cores from the BoB (>2000 m depth), the HE1 event is characterized by the presence of authigenic carbonates indicating anoxic bottom waters (e.g. [START_REF] Auffret | Identification of Heinrich Layers in core KS 01 North-Eastern Atlantic (46 °N, 17 °W), implications for their origin[END_REF][START_REF] Toucanne | Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate[END_REF]. Because these anoxia markers are not observed in the shallower cores BOBGEO-CS05 and MD99-2328 and because all proxies (𝑆𝑆 ̅̅̅ and foraminifera; Figure 4) indicate well-ventilated bottom waters, we can hypothesize a decoupling between a vigorous intermediate water depth circulation during HE1 and a still sluggish circulation at >2000 m in the northeast Atlantic, as reported by the Bermuda rise 231 Pa/ 230 Th data from the deep northwest Atlantic (Figure 4e). A similar pattern is found in the equatorial Atlantic where a better ventilation of mid-depth waters in late HS1 is recorded while the deep sites remained poorly ventilated [START_REF] Chen | Synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation[END_REF].

Foraminiferal evidence for mid-HS2 re-ventilation event

During HS2 (Figure 5), the overall meso-oligotrophic conditions and the low bottom-water ventilation depicted by both the low BFAR and the C. pachyderma -Globobulimina spp. association (i.e. meso-oligotrophic species) were interrupted around 24.3 ka cal BP (Figure 5d & 5e). At the same time, low percentages of the polar planktonic species N. pachyderma (Figure 5a) indicate a a warming of the sea-surface conditions and therefore a cessation of meltwater input in the northern BoB. This surface water warming is recorded in several sedimentary records along the European margin (e.g. [START_REF] Scourse | Growth, dynamics and deglaciation of the last British-Irish ice sheet: the deep-sea ice-rafted detritus record[END_REF][START_REF] Austin | The synchronization of palaeoclimatic events in the North Atlantic region during Greenland Stadial 3 (ca 27.5 to 23.3 kyr b2k)[END_REF]Waelbroeck et al., 2019). This warm event interrupting HS2 seems to be coeval with a well-known atmospheric decrease in dust flux at high latitudes [START_REF] Rasmussen | Synchronization of the NGRIP, GRIP, and GISP2 ice cores across MIS 2 and palaeoclimatic implications[END_REF][START_REF] Austin | The synchronization of palaeoclimatic events in the North Atlantic region during Greenland Stadial 3 (ca 27.5 to 23.3 kyr b2k)[END_REF].

During this sea-surface warming event, the re-appearance of the high-energy indicator species (Figure 5c) and the drop in the anoxia indicator species (Figure 5f) strongly suggests a reactivation of bottom water currents at site BOBGEO-CS05. This is supported by the increase in the 𝑆𝑆 ̅̅̅ values at our site and, more generally, in the northern part of the French Atlantic margin (Figure 5b). Our biotic data, although covering this millennial-scale event at low sampling resolution, thus indicate, together with the 𝑆𝑆 ̅̅̅ proxy, enhanced vigor of the GEBC and, by extension, of the AMOC during the mid-HS2. This re-acceleration of the GEBC continues to about100 yrs before the iceberg debacle of the LIS (i.e. HE2 sensu stricto at 24.2 ka cal BP), when our biotic and sedimentological proxies show a rapid return to mesooligotrophic conditions at the sea-floor and weak bottom currents.

Conclusions

Benthic foraminiferal assemblage data allowed us to reconstruct the paleoenvironmental evolution of the upper slope of the BoB (site BOBGEO-CS05) over the ca. 32-14 ka cal BP period. In general, species-specific responses reflect the complex, highly dynamic and variable environmental conditions in the northern BoB during the last glacial period, including fluctuations in the bottom water current and the GEBC, changes in organic matter fluxes and Channel River discharges, and latitudinal changes of the MOW.

The three HSs (HS3, HS2 and HS1) present some common features. They are all characterized by an overall low proportion of high-energy indicator species (i.e. Cibicides lobatulus and Trifarina angulosa), and a significant presence of meso-oligotrophic indicator species (Cibicidoides pachyderma), anoxia indicator species (Globobulimina spp. and C. oolina), and glacier-proximal species (E. excavatum f. clavatum and Cassidulina crassa). In agreement with previously published sedimentological and geochemical proxies, this reflects overall low organic matter fluxes to the seafloor and a low bottom water ventilation during the HSs.

Detailed investigation of the benthic foraminifera reveals some specificities of the HSs in the northeast Atlantic. First, the high abundance of high-organic flux indicator species (Cassidulina carinata and Bolivina spp.) during early HS1, compared to their near absence during HS2 and HS3, reveals a millennial-scale peak in terrestrial organic material in the BoB resulting from the significant EIS melting and Channel River meltwater floods. Second, benthic foraminiferal species depict a short-term mid-depth re-ventilation event during HS2, indicated by a decrease in the proportions of anoxia indicator species and an increase in the abundance of high-energy indicator species. This short-term reactivation of the GEBC along the French Atlantic margin, and of the AMOC, is coherent with the cessation of the EIS meltwater input in the northern BoB, and more generally, with a warming of the sea-surface conditions in the northeast Atlantic. This result strongly emphasizes the connection between the intermediate ocean circulation and the cryosphere dynamics in the northeast Atlantic during the Heinrich Stadials. Bolivina spp. have opportunistic behaviour [START_REF] Schmiedl | Trophic control of benthic foraminiferal abundance and microhabitat in the bathyal Gulf of Lions, western Mediterranean Sea[END_REF] and ecological preferences for phytodetritus enriched deposits [START_REF] Duros | Benthic foraminiferal response to sedimentary disturbance in the Capbreton canyon (Bay of Biscay, NE Atlantic)[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF] 5-6

Cassidulina carinata Silvestri, 1896 Phleger et al. (1953), p1. 9, Figs. 32-37 Epifaunal to shallow infaunal [START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF][START_REF] Altenbach | Scaling percentages and distributional patterns of benthic Foraminifera with flux rates of organic carbon[END_REF] Cassidulina carinata is an opportunistic species [START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF] [START_REF] Fontanier | Live foraminiferal faunas from a 2800m deep lower canyon station from the Bay of Biscay: Faunal response to focusing of refractory organic matter[END_REF] In our case, Cassidulina crassa could be a morphospecies of Cassidulina reniforme. This latter is often transported from the continental shelf, and redeposited on glacial marine sediments [START_REF] Mackensen | The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway[END_REF], until 1000m water depth in Arctic [START_REF] Wollenburg | The ecology and distribution of benthic foraminifera at the Håkon Mosby mud volcano (SW Barents Sea slope)[END_REF].

8

Cibicides lobatulus

Walker and Jacob, 1798

Jones and Brady (1994), pl. 93, Fig. 1 Epifaunal (John W. [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] Cibicides lobatulus live at shallow depth, attached on seagrass and algae [START_REF] Vénec-Peyré | Les Foraminifères épiphytes de l'herbier de Posidonies de Banyuls-sur-Mer (Méditerranée occidentale): étude des variations spatiotemporelles du peuplement[END_REF]John W. Murray, 2006). Even if, they were described as transported species, they can be found alive in deep and high energy environments (e.g. [START_REF] Schönfeld | The impact of the Mediterranean Outflow Water (MOW) on benthic foraminiferal assemblages and surface sediments at the southern Portuguese continental margin[END_REF]Schönfeld, , 2002bSchönfeld, , 2002a;;[START_REF] Margreth | Benthic foraminifera as bioindicator for cold-water coral reef ecosystems along the Irish margin[END_REF]Spezzaferri et al., 2015) 13 Cibicidoides pachyderma Rzehak, 1886 [START_REF] Jones | The challenger foraminifera[END_REF], pl. 94, Fig. 9 Shallow infaunal [START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF][START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF] Cibicidoides pachyderma live in meso-oligotrophic conditions [START_REF] Fontanier | Seasonal and interannual variability of benthic foraminiferal faunas at 550m depth in the Bay of Biscay[END_REF][START_REF] Mojtahid | Spatial distribution of live benthic foraminifera in the Rhône prodelta: Faunal response to a continental-marine organic matter gradient[END_REF]. They prefer low nutrients waters [START_REF] Schmiedl | Trophic control of benthic foraminiferal abundance and microhabitat in the bathyal Gulf of Lions, western Mediterranean Sea[END_REF].

11-12 b

Chilostomella oolina Schwager, 1878 Jones and Brady (1994), pl. 55, Fig. 12-14 Deep Infaunal [START_REF] Corliss | Distribution of rose bengal stained deepsea benthic foraminifera from the Nova Scotian continental margin and Gulf of Maine. Deep Sea Research Part A[END_REF][START_REF] Bernhard | Benthic foraminiferal distribution and biomass related to porewater oxygen content: central California continental slope and rise. Deep Sea Research Part A[END_REF]Jorissen et al., 1998) Chilostomella oolina is adapted to anoxic or suboxic conditions [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF][START_REF] Bernhard | Foraminifera of oxygen-depleted environments[END_REF]. They may be replaced by Globobulimina spp. when the degraded OM quality decreases [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF] Infaunalepifaunal (John W. [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] Elphidium clavatum is a widespread taxon, mainly distributed in the Arctic, and frequent in glacierproximal environments. It is found living down to several hundreds of meters depths in the Arctic and in the Baltic [START_REF] Jennings | Modern foraminiferal faunas of the southwestern to northern Iceland Shelf: oceanographic and environmental controls[END_REF]John W. Murray, 2006;[START_REF] Darling | The genetic diversity, phylogeography and morphology of Elphidiidae (Foraminifera) in the Northeast Atlantic[END_REF][START_REF] Fossile | Benthic foraminifera as tracers of brine production in the Storfjorden "sea ice factory[END_REF]. In the nearby study of [START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF], Elphidium species found at 1000 m depth during the last deglaciation were interpreted as being possibly transported from shallower settings. Stage (MIS). The vertical dashed grey line represents the limit between early HS1 (ca. 18.2 -16.7 cal ka BP) and late HS1 (ca. 16.7 -14.7 cal ka BP). To better highlight the variations of the different species groups, the scale of the ordinate axis is not constant. for AMOC export at >2 000 m depth [START_REF] Mcmanus | Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes[END_REF][START_REF] Böhm | Strong and deep Atlantic meridional overturning circulation during the last glacial cycle[END_REF][START_REF] Henry | North Atlantic ocean circulation and abrupt climate change during the last glaciation[END_REF]. f) XRF-Zr/Rb (violet line) and 𝑆𝑆 ̅̅̅ (pink line) composite records from the northeast Atlantic including BOBGEO-CS05 as proxies for the reconstruction of GEBC flow speed changes [START_REF] Toucanne | The North Atlantic Glacial Eastern Boundary Current as a Key Driver for Ice-Sheet-Amoc Interactions and Climate Instability[END_REF]. g) Relative abundances of high-energy indicator species (% C. lobatulus + % T. angulosa) in core BOBGEO-CS05. h) Relative abundances of mesooligotrophic indicator species (% C. pachyderma) in core BOBGEO-CS05. i) Relative abundances of anoxia indicator species (% Globobulimina spp. + % C. oolina). To better highlight the variations of the different species groups, the scale of the ordinate axis is not constant. The main events and climatic phases are reported similarly to Figure 3.

  Here, C. pachyderma encompasses several morphotypes spanning from C. pachyderma sensu stricto (pronounced carina) to Cibicidoides kullenbergi sensu stricto (less pronounced carina) (Plate 2b). The presence of several intermediate morphotypes hampered the taxonomical differentiation between C. pachyderma and C. kullenbergi, and as such were lumped together as C. pachyderma.

8

 8 Elphidium gerthi is a subtidal to intertidal species, very coommon along the western European coasts . In the nearby study of[START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF], Elphidium species found at 1000 m depth during the last deglaciation were interpreted as being possibly transported from shallower settings. of core BOBGEO-CS05; Blue bands: Heinrich Stadials (HSs); Gray bands: Heinrich Events (HEs); Greenland Interstadial (GI); Last Glacial Maximum (LGM); Marine Isotope Stage (MIS).

Figure 3 .

 3 Figure 3. Benthic foraminiferal data from core BOBGEO-CS05. a) Benthic ForaminiferalAccumulation Rates (BFAR; ind.cm -3 .ka -1 ) for the >150 µm (full line) and the >63 µm fraction (dashed line). b) Shannon index (H). c-j) Relative abundances (%) of the eight most representative benthic foraminiferal species (>10 %). Full lines and dashed lines represent respectively the > 150 µm and >63 µm fractions. Brown lines represent data from the >150 µm fraction of core MD99-2328[START_REF] Mojtahid | Changes in northeast Atlantic hydrology during Termination 1: Insights from Celtic margin's benthic foraminifera[END_REF]. Yellow bands: Greenland Interstadials (GI); gray bands: Heinrich Events (HEs); blues bands: Heinrich Stadial (HSs). Marine Isotope

Figure 4 .

 4 Figure 4. Benthic foraminiferal response to ice-sheet/AMOC dynamics. a) Relative abundance of N. pachyderma in core BOBGEO-CS05. b) Relative abundances of glacier-proximal indicator species (% Elphidium excavatum f. clavatum + % C. crassa) in core BOBGEO-CS05. c) BIT-index at site MD95-2002 as a proxy for continental-derived material input (Ménot et al., 2006). d) Relative abundances of high-organic flux indicator species (% C. carinata + % Bolivina spp.) in core BOBGEO-CS05. e) Bermuda Rise 231 Pa/ 230 Th compilation as a proxy

Figure 5 . 1 .

 51 Figure5. Focus on HS2. a) Relative abundances of the planktonic species N. pachyderma in core BOBGEO-CS05 (black line; this study) andMD95-2002 (blue line;[START_REF] Grousset | Were the North Atlantic Heinrich events triggered by the behavior of the European ice sheets?[END_REF].

Table 1 .

 1 14 C dates of core BOBGEO-CS05. 1047

									14 C
	Core label	Depth (cm)	Lab. Number a	Species	14 C age (yr BP)	err or (1σ )	Reserv oir correct ion b ( 14 C yr)	err or b (1σ )	age correc ted for reserv oir c ( 14 C	err or d (1σ )	Calenda r age range e (yr BP, 2)
									yr BP)
	BOBGEO-CS05	0	Poz-73846	N. pachyder ma	1410 0	80	970	200 13130		15133-16357
	BOBGEO-CS05	10	Poz-42911	bulk planktonic	1477 0	70	970	200 13800		16132-17333
	BOBGEO-
	CS05

Table 2 .

 2 Taxonomic reference list, microhabitat and ecological preferences for the 1049 dominant benthic species (>5 %) and the corresponding bibliographic references. 1050

	Species	References with images	Microhabitat	Ecological preferences	Plate 1	Plate 2
			Shallow
			infaunal
	Bolivina spp.		(John W.
			Murray,
			2006)

Acknowledgments

This study was funded by the CNRS-INSU-LEFE-IMAGO program (STING project), the ARTEMIS 14 C AMS French INSU project, and the Region Pays de Loire program (Rising Star project TANDEM). S.T. was funded by French National Research Agency (ANR) via the LabexMER program (ANR-10-LABX-19-01) and the PIA TANDEM project (ANR-11-RSNR-00023-01). Salary and research support for the PhD student (First author) were provided by the French Ministry of Higher Education and Research. We thank S. Le Houedec for core sampling, and L. Rossignol and S. Zaragosi (University of Bordeaux) for planktonic foraminifera counting, respectively. Finally, the authors warmly acknowledge J.-F. Bourillet (Ifremer), P.I. of the BOBGEO cruise (doi.org/10.17600/9030060), for his strong support on this research project

Species

References with images

Microhabitat Ecological preferences

Plate 1

Plate 2 Globobulimina spp.

Deep infaunal (John W. [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] Globobulimina spp. live in organically-enriched and/or oxygen-depleted sediments (e.g. [START_REF] Jorissen | Benthic foraminiferal microhabitats below the sediment-water interface[END_REF][START_REF] Schmiedl | Benthic foraminiferal record of ecosystem variability in the eastern Mediterranean Sea during times of sapropel S5 and S6 deposition[END_REF][START_REF] Mojtahid | Live benthic foraminiferal faunas along a bathymetrical transect (140-4800m) in the Bay of Biscay (NE Atlantic)[END_REF]. They can live in anoxic sediments by respiring nitrates [START_REF] Risgaard-Petersen | Evidence for complete denitrification in a benthic foraminifer[END_REF].

3 Gavelinopsis praegeri Heron- Allen & Earland, 1913Jorissen (1987), pl. 3, Fig. 13 Epifaunal [START_REF] Jorissen | The distribution of benthic foraminifera in the Adriatic Sea[END_REF] Gavelinopsis praegeri is an epiphytic species living in a wide range of water depths in marine environments (John W. [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF]. They are found down to 1200m water depth [START_REF] De Stigter | Recent and fossil benthic foraminifera in the Adriatic Sea: distribution patterns in relation to organic carbon flux and oxygen concentration at the seabed[END_REF] and prefers more oxic conditions [START_REF] Dorst | Recent benthic foraminiferal assemblages from the Celtic Sea (South Western Approaches, NE. Atlantic)[END_REF].

16

Hoeglundina elegans d'Orbigny, 1826

Milker and Schmiedl, (2012), pl. 19, Fig. 15 Epifaunal; shallow infaunal (Jorissen et al., 1998;[START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF] Hoeglundina elegans is described as indicator of low organic carbon environments [START_REF] Fontanier | Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats[END_REF][START_REF] Morigi | Benthic foraminiferal faunas in surface sediments off nw africa: relationship with organic flux to the ocean floor[END_REF]. Jones and Brady (1994), pl. 92, Fig. 1 Epifaunal [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] Planorbulina mediterranensis is an epiphytic species and lives at shallow depths [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF]. 15 Pullenia quinqueloba Reuss, 1851 [START_REF] Jones | The challenger foraminifera[END_REF], pl. 84, Fig. 14 Intermediate infaunal [START_REF] Corliss | Morphology and microhabitat preferences of benthic foraminifera from the northwest Atlantic Ocean[END_REF][START_REF] Fontanier | Stable oxygen and carbon isotopes of live (stained) benthic foraminifera from cap-ferret canyon (bay of biscay)[END_REF] Pullenia quinqueloba can live in low-organic carbon conditions [START_REF] Gupta | Latest Pliocene through Holocene paleoceanography of the eastern Indian Ocean: benthic foraminiferal evidence[END_REF]. 18

Textularia sagittula Defrance, 1824 Jorissen (1987), pl. 3, Fig. 12 Epifaunal [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF] Textularia sagittula is an agglutinated species [START_REF] Murray | Ecology and Applications of Benthic Foraminifera[END_REF]. They are dominant in shallow water depths, on sandy sediments [START_REF] Murray | Ecology and Palaeoecology of Benthic Foraminifera[END_REF] 1

Trifarina angulosa Williamson, 1858

Jones and Brady (1994), pl. 74, Fig. 15 Shallow infaunal [START_REF] Hess | Distribution patterns of living benthic foraminifera from Cap Breton canyon, Bay of Biscay: Faunal response to sediment instability[END_REF] Trifarina angulosa have been observed in phytodetritus-enriched sediment (e.g. [START_REF] Hess | Distribution patterns of living benthic foraminifera from Cap Breton canyon, Bay of Biscay: Faunal response to sediment instability[END_REF][START_REF] Duros | Live (stained) benthic foraminifera in the Whittard Canyon, Celtic margin (NE Atlantic)[END_REF]. They are often associated with C. lobatulus to strong bottom currents and can be observed until 1000m water depth [START_REF] Mackensen | The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway[END_REF].

14