# Shifts in Fossil Benthic Foraminiferal Community Trajectories During the Last Deglaciation Along the European Margin

R. Fentimen, A. Sturbois, M. Mojtahid

► To cite this version:

R. Fentimen, A. Sturbois, M. Mojtahid. Shifts in Fossil Benthic Foraminiferal Community Trajectories During the Last Deglaciation Along the European Margin. Paleoceanography and Paleoclimatology, 2026, 41 (1), pp.e2025PA005238. 10.1029/2025PA005238. [hal-05448693](https://hal.science/hal-05448693v1)

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Paleoceanography and Paleoclimatology®

## RESEARCH ARTICLE

10.1029/2025PA005238

**Key Points:**

* Ecological Trajectory Analysis (ETA) is applied to fossil benthic communities

* ETA satisfyingly describes shifts in foraminiferal fossil assemblages temporally and spatially at the scale of the community

* Fossil benthic foraminiferal ETA highlights heterogeneities in community change during the last deglaciation along the European margin

**Supporting Information:**

Supporting Information may be found in the online version of this article.

**Correspondence to:**

R. Fentimen, robin.fentimen@univ-angers.fr

**Citation:**

Fentimen, R., Sturbois, A., & Mojtahid, M. (2026). Shifts in fossil benthic foraminiferal community trajectories during the last deglaciation along the European margin. *Paleoceanography and Paleoclimatology, 41*, e2025PA005238. https://doi.org/10.1029/2025PA005238

Received 3 JUN 2025
Accepted 16 DEC 2025

**Author Contributions:**

**Conceptualization:** R. Fentimen, A. Sturbois, M. Mojtahid

**Formal analysis:** R. Fentimen

**Investigation:** R. Fentimen, A. Sturbois, M. Mojtahid

**Methodology:** R. Fentimen, A. Sturbois, M. Mojtahid

**Validation:** M. Mojtahid

**Visualization:** R. Fentimen, A. Sturbois

**Writing – original draft:** R. Fentimen

**Writing – review & editing:** R. Fentimen, A. Sturbois, M. Mojtahid

© 2026. The Author(s). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

## Shifts in Fossil Benthic Foraminiferal Community Trajectories During the Last Deglaciation Along the European Margin

R. Fentimen¹ ID, A. Sturbois², and M. Mojtahid¹ ID

¹Laboratoire de Planétologie et Géosciences LPG UMR 6112, Université D'Angers, Nantes Université, Le Mans Université, CNRS, Angers, France, ²Laboratoire des Sciences de L'Environnement Marin (LEMAR), UMR 6539 CNRS/UBO/IRD/IFREMER, Plouzané, France

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**Abstract** Constraining how faunal communities vary over time and space in response to environmental change has long been a major goal of paleoecologists. Among fossilized organisms, few yield a better and greater detailed record than foraminifera to understand past marine conditions. The analytical frameworks used to build palaeoenvironmental reconstructions have progressed over the years, providing new perspectives within the field. One of these proposed frameworks, Ecological Trajectory Analysis (ETA), offers the possibility to compare geometric properties of trajectories to understand temporal changes within communities. We provide here an application of ETA to the fossil record by comparing benthic foraminiferal data sets from three previously studied cores from the French Atlantic margin. The three cores are each separated by approximately 350 km and cover the last deglaciation, thus allowing a comparison of community dynamics at spatial and temporal scales. A major perturbation in fossil benthic communities was identified in ETA metrics at the onset of Heinrich Stadial 1, with a twofold departing and recovering trend of communities. The three sites along the French Atlantic margin also show spatial differences during the deglaciation, testimony to a contrasting response of benthic foraminifera to ice sheet dynamics and fluctuating fluvial discharges. In this instance, the application of ETA allows to compare multiple fossil foraminiferal records. At a broader scale, the use of trajectory metrics within one unique multivariate space of community resemblance stands out as a powerful tool to compare many other fossil records within the field of paleoecology.

## 1. Introduction

The Last Glacial Maximum (26.5–19 ka according to Clark et al., 2009, 27.54–23.34 ka according to Hughes & Gibbard, 2015) corresponds to the maximum in global ice volume during the last glacial cycle. This period was marked by millennial-scale climate variability (i.e., Dansgaard-Oeschger oscillations), driven by changes in the Atlantic meridional overturning circulation (AMOC; Dansgaard et al., 1993; Hoogakker et al., 2007; Böhm et al., 2015; Waelbroeck et al., 2019; Menviel et al., 2020; Toucanne et al., 2021). During the Last Glacial Maximum, extensive ice-sheets covered the Northern hemisphere, namely the north American Laurentide Ice Sheet (LIS) and the Eurasian Ice Sheet Complex (Figure 1; Ives et al., 1975; Patton et al., 2016). The Eurasian Ice Sheet Complex was a composite of three distinct and initially independent ice sheets: the Fennoscandian Ice Sheet, the Barents Sea Ice Sheet, and the southernmost marine-terminating British-Irish Ice Sheet (BIIS; Patton et al., 2016). At its largest between 23 and 27 ka, the BIIS covered all of Ireland and northern Britain, extending offshore to approximately 50°N (Figure 1; Clark et al., 2012). The melting of the LIS and Eurasian Ice Sheet Complex during the last deglaciation, which began at 19 ka (according to Clark et al., 2012), is marked by the shedding of numerous icebergs and the transport of associated meltwater and sediment (such as Ice Rafted Debris) within the North Atlantic (Bond & Lotti, 1995; Hemming, 2004; Peck et al., 2006; Ruddiman, 1977). Periodic thick layers of Ice Rafted Debris, sourced from fast-flowing terrestrial ice, are found in North Atlantic sediment cores (Bond et al., 1992; Heinrich, 1988). These Ice Rafted Debris-rich intervals, named Heinrich events (HE), are part of longer cold phases: Heinrich Stadials (HS; Sanchez-Goni & Harrison, 2010; Barker et al., 2015). The most recent of these (HS1) occurred between approximately 18.2 and 14.6 ka and shows two distinct climatic phases in the North Atlantic (Hodell et al., 2017; Naughton et al., 2023). The first and most significant of the two (HS1a; ~18.2–16.2 ka) is linked to freshwater discharges from the Eurasian Ice Sheet Complex, whilst the second (HS1b; ~16.2–14.7 ka) is related to a vast ice rafting event from the LIS (HE1 per se; Zaragosi et al., 2001; Hemming, 2004; Denton et al., 2010; Toucanne et al., 2010, 2015; Hodell et al., 2017; Andrews & Voelker, 2018;
<figure><img src="image_3.png" /><figcaption>**Figure 1.** (a) Schematic map (adapted from García-Ibáñez et al., 2015, Daniault et al., 2016; Toucanne et al., 2021) illustrating the modern North Atlantic Ocean circulation and the ice-sheet extension at 30 ka (gray filled areas), 45 ka (red dashed line), and during MIS 4 (black dashed line) according to Batchelor et al. (2019). The modern-day Polar Front (PF) and Subpolar Front (SPF) are given according to Mokeddem and McManus (2016), together with the last glacial extents of the Laurentide Ice Sheet (LIS), British-Irish Ice Sheet (BIIS), and FIS (Fennoscandian Ice Sheet). The main currents and water masses are also indicated: North Atlantic Current (NAC), European Slope Current (ESC), Deep Western Boundary Current (DWBC), Levantine Intermediate Water (LIW), Western Mediterranean Deep Water (WMDW), Mediterranean Outflow Water (MOW), Labrador Sea Water (LSW), Iceland-Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW). Light brown, red, and blue arrows illustrate respectively Greenland currents, surface currents (i.e., the Gulf Stream and NAC), and deep-sea circulation (North Atlantic Deep Water-NADW: i.e., LSW, DSOW and ISOW). Dashed dark blue arrows mark the eastward recirculation of NADW (following Toucanne et al., 2021). Both Subtropical and Subolar gyres are indicated (STG and SPG). (b, c) Holocene (b) versus Last Glacial (c) bathymetric maps of the study area. The BIIS ice maximum extents at 23 ka BP (light blue contour lines) and 18 ka (pink contour lines) are based on Clark et al. (2012) and represent a –120 m sea level. The paths of the ESC and Glacial East Boundary Current (GEBL) are indicated by the green lines. The locations of the studied cores MD99-2328, BOBGEO-CS05 and SU81-44, together with cores MD95-2002 and MD13-3438 which are discussed in the text, are indicated. The maps are constructed using the CGIAR-CSI SRTM (Version 4) 30-m resolution topography, together with EMODnet and GEBCO bathymetry.</figcaption></figure>

Naughton et al., 2023). Sea-surface temperatures were especially cold at mid- and high latitudes in the Northeast Atlantic during HS1a (Bard et al., 2000; Hodell et al., 2013; Martrat et al., 2007; Salgueiro et al., 2014; Zaragosi et al., 2001), whilst the climatic pattern during HS1b was more complex with a relative warming followed by cooler conditions, as demonstrated by records from the French and Iberian margin (Bard et al., 2000; Fersi et al., 2021; Naughton et al., 2016; Penaud et al., 2024). Furthermore, the transition between HS1a and HS1b has
<table><caption>**Table 1**
Details of the Three Selected Cores</caption><thead><tr><th>Core</th><th>Naming</th><th>Latitude</th><th>Longitude</th><th>Depth (m)</th><th>Cruise (year)</th><th>Study</th></tr></thead><tbody><tr><td>MD99-2328</td><td>North</td><td>48°04.62′N</td><td>09°30.35′W</td><td>942</td><td>INTERPOLE MD99-114/IMAGESV (1999)</td><td>Mojtahid et al. (2017)</td></tr><tr><td>BOBGEO-CS05</td><td>Central</td><td>46°18.850′N</td><td>5°56.99′W</td><td>1,015</td><td>BOBGEO (2009)</td><td>Depuydt et al. (2022a)</td></tr><tr><td>SU81-44</td><td>South</td><td>44°15.4′N</td><td>2°41.7′W</td><td>1,173</td><td>CEPAG (1981)</td><td>Depuydt et al. (2024)</td></tr></tbody></table>

Note. The naming (North, Central, South) corresponds to the names given in the text.

been associated with a sharp strengthening of the upper branch of the AMOC at ~1,000 m depth along the European margin, resulting in increased bottom-current speeds (Henry et al., 2016; Toucanne et al., 2021).

These profound and rapid changes in water column properties and ocean circulation had an impact on benthic foraminiferal communities in the North Atlantic (Baas et al., 1998; Caralp, 1987; Depuydt et al., 2022a, 2024; Grunert et al., 2015; McKay et al., 2014; Mojtahid et al., 2017; Pascual et al., 2020; Rasmussen et al., 1996, 2002, 2017; Rodriguez-Lazaro et al., 2017; Schönfeld et al., 2003; Schönfeld & Zahn, 2000) but also as far as the western and eastern Mediterranean Sea (Melki et al., 2009; Angue Minto'o et al., 2015; Cornuault et al., 2016), Arabian Sea (Singh et al., 2015), and Southeast Atlantic (Barker et al., 2009; Romahn et al., 2015). Benthic ostracods were also affected by HS1-linked changes in the Northwest Atlantic (Yasuhara et al., 2008) and western Mediterranean (Bassetti et al., 2010; Angue Minto'o et al., 2015). At intermediate depths along the French margin (~1,000 m), benthic foraminiferal communities show distinct differences between the first and second phase of HS1 (Depuydt et al., 2022a, 2024; Mojtahid et al., 2017; Pascual et al., 2020). However, these findings are currently based on analyses from single sediment cores, using bivariate plots (Depuydt et al., 2022a, 2024; Mojtahid et al., 2017; Pascual et al., 2020) and more rarely Principal Component Analyses (PCA; Depuydt et al., 2022a). They thus provide a site-specific assessment of benthic communities, which remains limited at a wider regional level (i.e., along the European margin). We aim to fill this knowledge gap by applying the Ecological Trajectory Analysis (ETA) framework (formerly known as Community Trajectory Analysis; De Cáceres et al., 2019) to fossil benthic foraminiferal data sets. Specifically, we analyze a compilation of previously published data from three sediment cores along the French margin at depths ranging between ~940 and ~1,170 m (Figure 1 and Table 1; Mojtahid et al., 2017; Depuydt et al., 2022a, 2024).

Like other multivariate analysis applied in ecology, ETA focuses on comprehending community dynamics over time (Buckley et al., 2021; De Cáceres et al., 2019). A key strength of ETA is that it assesses the geometric resemblance between trajectories within the space of similarity, allowing an accurate quantification of community dynamics (De Cáceres et al., 2019; Sturbois, Cormy, et al., 2021). While ETA is a relatively novel approach (De Cáceres et al., 2019; Sturbois, Cormy, et al., 2021), it has gained increasing attention and has been applied to modern terrestrial and marine faunal and floral communities (Darragh et al., 2023; Hopper et al., 2024; Lamy et al., 2021; Neely et al., 2023; Smith et al., 2024; Sturbois, De Cáceres, et al., 2021; Sturbois et al., 2023; Toumi et al., 2023), bacterial communities (Barnett & Shade, 2024), and stable isotopes (De la Casa et al., 2025; Espinasse et al., 2022; Sturbois, Cucherousset, et al., 2022; Sturbois, Riera, et al., 2022). Yet, to our knowledge, ETA has never been applied to downcore fossil communities, despite its potential to capture environmental changes over time and space, particularly when multiple cores are considered. The major climatic and environmental shifts of the last 20 ka offer an ideal time window to test the applicability of ETA to fossil benthic foraminifera. The goal of this study is hence twofold: (a) to test the benefits of applying ETA to downcore fossil benthic foraminiferal communities, and (b) to evaluate quantitatively the response of fossil benthic foraminiferal communities to shifting environmental conditions along the French margin during the last Termination, noticeably during HS1.

## 2. Study Area

### 2.1. Core Locations

This study focuses on three sediment cores (SU81-44, BOBGEO-CS05, and MD99-2328), collected along a ~700 km transect between 44°N and 48°N, situated on the continental slope at depths between ~940 and ~1,170 m (Figure 1; Table 1). They consist of muddy to fine-sandy contouritic sediments, reflecting the persistent action of dynamic bottom currents in the area (e.g., Depuydt et al., 2024; Toucanne et al., 2021). The analyzed
samples date from ~23 to ~14 ka BP, thus fully covering the entire deglaciation period and HS1. The southernmost core, SU81-44, was retrieved from the Landes Plateau in the Bay of Biscay at 1,173 m depth during the CEPAG campaign in 1981 (Figure 1; Table 1; Duplessy, 1981). Core BOBGEO-CS05, located 350 km north of SU81-44, was collected at 1,015 m depth during the BOBGEO cruise in 2009 (Figure 1; Table 1; Bourillet et al., 2009). The northernmost core, MD99-2328, was retrieved 330 km farther north at 942 m depth on the Brenot Spur during the INTERPOLE MD99-114/IMAGESV cruise (Figure 1; Table 1; Labeyrie, 1999). For simplicity, these cores will be referred to as South, Central and North cores throughout this study (Table 1). Benthic foraminiferal assemblages were previously documented and published by Mojtahid et al. (2017) for the North core, and by Depuydt et al. (2022a, 2024) for the Central and South cores.

## 2.2. Paleogeography and Hydrographic Setting

Glacial and deglacial sediments on the Celtic margin are mainly sourced from the Irish Sea Ice Stream (ISIS) and the Channel River (Figure 1). The ISIS drained the BIIS and extended approximately 750 km from its feeder catchment in northern Britain down to the shelf break of the Celtic Sea during its maximum extent at 25.5 ka BP (Figure 1; Clark et al., 2012; Scourse et al., 2021). After 23 ka BP, the BIIS experienced a considerable shrinkage, with the ISIS retreating accordingly (Figure 1; Auffret et al., 2002; Clark et al., 2012, 2021; Scourse et al., 2021). At their maximum extent during the Last Glacial Maximum, the Fennoscandian Ice Sheet and the BIIS (named the European Ice Sheet when zipped together) formed a 2.5 × 10⁶ km² catchment area drained by the Channel River (Gibbard, 1988; Patton et al., 2017; Toucanne et al., 2009, 2010). During the last glacial and deglacial periods, the Channel River was a major path for meltwater and sediment transport to the Northeast Atlantic (e.g., Auffret et al., 2002; Eynaud et al., 2007, 2012; Penaud et al., 2009; Toucanne et al., 2009, 2010, 2015; Zaragosi et al., 2001). During HS1, extreme variations in fluvial input drove abrupt changes in planktic and benthic communities (e.g., increase in opportunistic benthic foraminifera abundance, changes in dinocyst assemblage composition; Mojtahid et al., 2005, 2017; Fersi et al., 2021; Depuydt et al., 2022a, 2024; Penaud et al., 2024).

Besides fluctuating fluvial influence, the deglaciation was characterized by important hydrological changes. At present, intermediate depths of the mid-latitude Northeast (NE) Atlantic, including the three core locations, are under the influence of the Mediterranean Outflow Water (MOW) which circulates between approximately 600 and 1,500 m water depth (Figure 1; Van Aken, 2000). Above the MOW, the Eastern North Atlantic Water dominates, while the Labrador Sea Water prevails below it (Van Aken, 2000). The European Slope Current (ESC) is the dominant current along the European continental margin (Figure 1) and forms the easternmost portion of the upper branch of the AMOC, flowing from the Iberian margin (~40°N) toward the Faroe-Shetland Channel (60°N) (Booth & Ellett, 1983; Huthnance, 1986; Kenyon, 1986). It is a major conveyor of particulate organic matter, whilst also controlling slope sedimentation over extensive time periods (Hernández-Molina et al., 2011; McCave et al., 2001; Thomsen & Van Weering, 1998) and thus shaping benthic habitats and faunal communities (Flach et al., 1998; Hebbeln et al., 2016; Saupe et al., 2023; Schönfeld, 2002). During the Last Glacial Maximum and deglaciation, the strength of the ESC, referred to as the Glacial Eastern Boundary Current (GEBC; Figure 1) during this time interval, exhibited variability in response to Dansgaard-Oeschger oscillations (Depuydt et al., 2024; Toucanne et al., 2021). It weakened significantly during Dansgaard-Oeschger and Heinrich Stadials, mirroring the temporal pattern observed within the lower branch of the AMOC (Böhm et al., 2015; Henry et al., 2016; Toucanne et al., 2021). Benthic foraminiferal communities responded to these velocity changes in the ESC, with fluctuations in the abundance of species resistant to winnowing such as the infaunal *Trifarina angulosa* (Depuydt et al., 2024).

# 3. Materials and Methods

## 3.1. Data Selection and Chronology

Benthic foraminiferal assemblages from the three cores were all counted from the >150 µm fraction. Raw data sets are available in Mojtahid et al. (2017) and Depuydt et al. (2022a, 2024) (see Data availability section). An identical size fraction was essential to ensure that foraminiferal counts were comparable between each core, since fraction size has a major influence on species composition (Weinkauf & Milker, 2018). For all three cores, the identification of benthic foraminifera was carried out at the University of Angers following the same taxonomic framework (Jones, 1994). This consistency helps minimizing taxonomical differences within the final merged data set.
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Original input data for the three cores (North, Central and South) compared to the final linear interpolation used for fossil benthic foraminiferal Ecological Trajectory Analysis (ETA).</figcaption></figure>

The age models of the North, Central and South cores were developed by Mojtahid et al. (2017), Toucanne et al. (2021), and Depuydt et al. (2024), respectively. These models were constructed by aligning XRF-Ti/Ca ratios and *Neogloboquadrina pachyderma* counts with those from the well-dated neighboring reference core MD95-2002 (Figure 1; Figure S1, Table S1 in Supporting Information S1; Grousset et al., 2000; Toucanne et al., 2015). The chronology of the reference core MD95-2002 was established by Toucanne et al. (2015, 2021) based on 26 monospecific planktonic foraminifera $^{14}$C ages (Table S1, Figure S1 in Supporting Information S1). Toucanne et al. (2015) corrected planktonic foraminifera $^{14}$C ages for reservoir ages according to each stratigraphic unit: ~400 ± 200 (1σ) $^{14}$C years for pre-HS1 and Holocene periods, and 970, 680 and 875 ± 200 (1σ) $^{14}$C years for HS1, the Bølling-Allerød and Younger-Dryas, respectively (Table S1 in Supporting Information S1; Toucanne et al., 2015). Radiocarbon ages were then calibrated to calendar ages using the IntCal13 calibration curve (Reimer et al., 2013). The final age-depth model is a smooth spline generated through 40,000 iterations using the Clam software (Blaauw, 2010) and reported with 95% confidence intervals (the final 2σ calendar age range of corrected $^{14}$C ages is ±500 years BP; see Toucanne et al., 2015, Figure S1 in Supporting Information S1). Finally, Toucanne et al. (2015) added control-points to the age model by tuning the *N. pachyderma* abundance to the NGRIP $\delta^{18}$O ice core record (Figure S1 in Supporting Information S1; Andersen et al., 2006).

After correlation with the reference core using Ti/Ca and *N. pachyderma* counts, the chronologies of the North, Central and South cores were validated using planktonic foraminifera $^{14}$C ages by Mojtahid et al. (2017) and Depuydt et al. (2022a, 2024), respectively (Table S1 in Supporting Information S1). These authors applied identical reservoir ages to foraminifera $^{14}$C ages and utilized the same calibration curve (IntCal13; Reimer et al., 2013) as in the reference core (Toucanne et al., 2015; Table S1 in Supporting Information S1). The use of a consistent chronological framework across all cores, together with their comparison to the same reference core, allows us to confidently use a unique age model to compare benthic foraminiferal assemblages. Yet, given that all three cores are aligned to one single reference core, themselves tuned to the NGRIP $\delta^{18}$O ice core record (Andersen et al., 2006), genuine small phase lags between the three locations may be smoothed out. Because the chronologies of the North, Central and South cores derive directly from the age model of the reference core, the same age uncertainties apply to these.

The selected samples from the three cores span the time interval 23–14 cal ka BP (Figure 2). Within this time window, we used all 78, 27, and 36 previously investigated samples, from the North, Central and South cores, respectively (Figure 2; Mojtahid et al., 2017; Depuydt et al., 2022a, 2024). To ensure temporal consistency across data sets, benthic foraminifera relative abundances were linearly interpolated every 200 years using the approxTime

function from the deSolve package in *R* (Soetaert et al., 2010, Figure 2). This time step was chosen as it represents the average time resolution of the three cores over the considered time window. It is also the same as the age uncertainties (1σ) of the corrected $^{14}$C ages of the reference core MD95-2002 (i.e., ±0.2 ky; Toucanne et al., 2015; Table S1 in Supporting Information S1). This 200 years time-step is finer than the ±500 years BP final calendar age range (2σ) of corrected $^{14}$C ages (Figure S1 in Supporting Information S1). As such, interpretations of fine-scale temporal changes may be influenced by the age uncertainties of the age-model. Due to sample absence, only the 23–16 and 23–15.2 cal ka BP intervals are considered for the North and South cores, respectively. To limit overplotting and potential misidentification of rare species, only dominant species (>5% of the relative abundance in at least one sample) were considered in this study. To further test for possible taxonomic discrepancies between
data sets, a second data matrix was built at the genus level, applying the same >5% threshold. Different *Elphidium* species were grouped together within the taxa data table because of identification discrepancies in the original data sets. To highlight differences in benthic foraminiferal assemblages, the 23–14 cal ka BP interval was subdivided into four periods: preHS1 (23–18.3 cal ka BP), HS1a (18.2–16.2 cal ka BP), HS1b (16.1–14.7 cal ka BP) and postHS1 (14.6–14 cal ka BP) (Naughton et al., 2023, Figure 2). The North and Central cores only cover pre-HS1, HS1a and the first 100 and 900 years of HS1b, respectively (Figure 2).

## 3.2. Statistical Analyses

Dissimilarity matrices using Euclidean distances on Hellinger transformed data were calculated for fossil benthic foraminiferal assemblages at both species and genus levels. All resulting matrices were then analyzed for ETA using the *R* package *ecotraj* (De Cáceres et al., 2019; Sturbois, Cormy, et al., 2021; Sturbois et al., 2023) to investigate the dynamics of benthic foraminiferal assemblages within and between time periods and cores. Results are displayed in the two first dimensions of the Principal Coordination Analysis (PCoAs). A color code is applied to highlight different areas (i.e., cores) and time periods (preHS1, HS1a, HS1b and postHS1), and is used throughout the different figures.

The benthic foraminiferal species ETA was used to calculate trajectory metrics which were utilized to compare community dynamics spatially (from the three cores) and temporally (from 23 to 14 ka BP). First, the segment lengths (SL) were calculated between consecutive ecological states (i.e., samples) for each core, using the oldest sample as the first state and the most recent as the last state (see De Cáceres et al., 2019 for details). For example, the first segment length (S1) corresponds to the distance between the samples taken at 23.0 and 22.8 ka. This SL proportionally translates the distance between ecological states: greater distance amounts to lower similarity. We then calculated the total trajectory path length for each core, which is the sum of all segment lengths. Given that the time interval between each state is identical (0.2 ka), SL corresponds to the speed of community change. Both segment speeds and lengths can help qualify the resilience of communities (De Cáceres et al., 2019). In addition to SL, we calculated net changes (NC) for all three cores. The NC corresponds to the distance between a given ecological state and an initial state and provides information about the overall change in communities (Sturbois, Cormy, et al., 2021). We calculated NC twice with two different initial states: the first at the base of the cores (i.e., 23.0 ka) and the second at the onset of HS1a (18.4 ka). For instance, the third net change corresponds to the distance between the third ecological state (22.6 ka) and the initial state (23.0, when taking the base of the core as the initial state). NC provides information about the temporal stability of communities relative to an initial state. The recovering or departing trajectory metric (Recovering Departing Trajectory (RDT)) was also calculated to determine if benthic foraminiferal communities were returning toward the defined initial state (i.e., the community at 23.0 ka when taking the base of the core as the initial state) or if they were rather departing from it. The RDT is the difference between $NC_{n-1}$ and $NC_n$ (Sturbois, Cormy, et al., 2021). Negative and positive RDT values respectively indicate departing and recovering trends. We defined the two same initial states as for NC: the first at the base of the cores (i.e., 23.0 ka) and the second at the onset of HS1a (18.4 ka) to precisely assess the impact of HS1-driven changes on benthic foraminiferal communities. Finally, we calculated the ratio between SL and NC to evaluate the correlation between the two metrics.

# 4. Results

## 4.1. Fossil Benthic Foraminiferal Assemblages

Fossil benthic foraminiferal ETA carried out on genera demonstrates three distinct trajectory groups that correspond to the three studied areas indicating some differences in taxonomic composition and dynamics inherent to sampling locations (Figure 3). Trajectories belonging to the North core show the highest scatter, predominantly following the first axis of the PCoA (Figure 3). The same distribution pattern is observed on fossil benthic foraminiferal ETA using the species matrix, with each trajectory group corresponding to a different area (Figure 3). The North trajectory group is essentially driven by the abundance of *Elphidium* spp. and Cassidulinids (*Cassidulina carinata*), whereas high *Cibicides pachyderma* abundance characterizes the South (Figure 3). In contrast, the Central trajectory group is rather driven by *Cibicides lobatulus*, *Trifarina angulosa*, and *Cassidulina crassa* (Figure 3).
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Fossil benthic foraminiferal Ecological Trajectory Analyses (ETA) performed on dominant (>5% relative abundance) genera (a) and species (b). The main genera and species that drive trajectory distribution are indicated (minor contributing species and genera are not shown to avoid overplotting).</figcaption></figure>

## 4.2. Core-Specific Fossil Benthic Foraminiferal Trajectories

In the North, preHS1 trajectories show a stronger variability following the seconds axis of the PCoA, essentially driven by *C. carinata* and *Sigmoilopsis schlumbergeri* (Figure 4a). HS1a trajectories mostly vary following the first axis of the PCoA and are driven by *Bolivina albatrossi* and *Elphidium* spp. (Figure 4a). The HS1a trajectory path shows a departing/recovering pattern from the preHS1 trajectory group, which follows the first axis of the PCoA (Figure 4a).

PreHS1 trajectories in the Central area demonstrate low trajectory path lengths (Figure 4b). In contrast, path lengths increase during HS1a and show a two-step departing/recovering pattern from the preHS1 trajectory group following the first and second axes of the PCoA. *Cassidulina carinata* and *B. albatrossi* stand out as the two main driving species behind this HS1a trajectory path (Figure 4b), whilst HS1b and postHS1 trajectory groups are essentially driven by *Elphidium* spp. and *C. pachyderma*. Moreover, considerably lower trajectory path lengths characterize HS1b and postHS1 in comparison to HS1a (Figure 4b).

Similarly to the Central area, preHS1 trajectories in the South demonstrate little variability characterized by lower trajectory path lengths than during HS1a and HS1b (Figure 4c). *Cibicides pachyderma* and *S. schlumbergeri* are the main species driving the preHS1 trajectory group, whereas HS1a and HS1b are characterized respectively by *Globobulimina affinis* and *Uvigerina* spp (*U. peregrina* and *U. mediterranea*; Figure 4c). In the same way as for the North, the HS1a trajectory path shows a departing trend from the preHS1 period (Figure 4c). This departing trend appears to be maintained during HS1b (Figure 4c).

## 4.3. Trajectory Metrics

Total trajectory path length is the highest in the North (15.6 in the North, 9.47 in the Central area, and 12.0 in the South; Figure 5). This is noticeable in the cumulative SL, with rapidly increasing values in the North compared to the Central and South areas (Figure 5). A similar but less acute trend is noticeable for the cumulative NC. During preHS1, SL are low and stable in the Central and South areas (between 0.1 and 0.4), whilst SL in the North stand out with important variations (between 0.2 and 0.6), with four increasing and decreasing phases (Figure 5). The latter increase in SL (ca. 18.5 ka BP) corresponds to a peak in *N. pachyderma* relative abundance (Figure 5). The preHS1 trend in NC in the South and Central areas follow those of SL. In contrast, in the North, the preHS1 NC trend does not follow SL, this is particularly noticeable for the 20.0–22.0 ka period, with an important NC spike at approximately 22.0 ka (from 0.4 to 0.6; Figure 5). The preHS1 RDT shows little variability in the Central and South areas with values close to 0, which is consistent with the stable NC values (ca. 0.25). In contrast, the North
<figure><img src="image_6.png" /><figcaption>**Figure 4.** Fossil benthic foraminiferal Ecological Trajectory Analyses (ETA) performed on dominant (>5% relative abundance) species for each core taken separately (a. North; b. Central, c. South). The main species that drive trajectory distribution are indicated (minor species are not shown to avoid overplotting). The different time periods are indicated by the color code at the bottom right corner of each panel.</figcaption></figure>

RDT demonstrates greater variability. The preHS1 SL/NC essentially demonstrates values <1 in the Central area, whilst the South and North regions show excursions toward more positive values (Figure 5).

Overall, SL and NC increase between preHS1 and HS1a (Figure 6). At the onset of HS1a, a sharp threefold increase characterizes SL in the Central and South areas (from ca. 0.2 to 0.6). This is followed by a decrease and another sharp increase during the mid-HS1a (ca. 17.0 ka BP; Figure 5). NC follows a similar pattern with a two-step increase/decrease during HS1a (from ca. 0.3 to 0.8). The choice of the initial state (defined at 23.0 ka or at 18.4 ka) does not change the observed trend. In the North, HS1a is overall characterized by high SL values (ca. 0.75), with a sharp decrease followed by an increase in the later phases of HS1a (Figure 5). In contrast with the South and Central areas, NC does not follow SL variations, with a sharp increase in NC at the onset of HS1a which does not correspond to an equivalent increase in SL, despite matching the sharp spike in NC observed in the Central and South regions (Figure 5). In all areas, the onset of HS1a is marked by a sharp decrease (ca. 0 to -0.4) followed by an increase (ca. -0.4 to 0.2) in the RDT, which coincides with an important increase in *N. pachyderma* numbers (Figure 5). The Central area is characterized by another RDT decreasing and increasing trend in the second phase of HS1a (between ca. 0.3 to 0.8), which follows changes in NC and SL, and is also mirrored by the SL/NC ratio (Figure 5). This RDT pattern is observed at a lesser extent in the South, whereas it is unnoticeable in the North where values fluctuate following a see-saw pattern between negative and positive values across HS1a.

In the Central area, SL decreases at the end of HS1a and remains low and stable during HS1b and postHS1 (ca. 0.2; Figure 5). Other trajectory metrics (NC, RDT, SL/NC) demonstrate the same trend (Figure 5). In contrast, in the South, the SL decreases at the end of HS1a is followed by a sharp SL increase from 0.2 to 0.6 during the early phases of HS1b (from 16.0 to 15.2 ka BP). This is mirrored by rapidly increasing NC values from 0.5 to 1.0 and a negative excursion in the RDT, and to a minor extent by an increase in the SL/NC ratio (Figure 5).

# 5. Discussion

## 5.1. Regional Community Differences Drive Trajectory Groups

The ETA carried out on both genera and species similarity matrices highlight contrasted trajectories between areas (North, Central and South; Figure 3). Thus, spatial differences in species composition, rather than any temporal discrepancies common to the three considered locations, explain the dissimilarity between groups. The species driving this spatial heterogeneity are *Elphidium* spp. and *C. carinata* (associated with the North), *C. lobatulus*, *C. crassa* and *T. angulosa* (associated with the Central area), and *C. pachyderma* (associated with the South; Figure 3b). These observations match those made by Mojtahid et al. (2017) and Depuydt et al. (2022a, 2024) who studied each core separately. A differing composition of fossil benthic foraminiferal assemblages between the three studied regions of the French Atlantic margin during the 23–14 ka BP time interval is not unexpected. Indeed, benthic foraminiferal communities are widely recognized to show a patchy distribution in proximal and distal settings (Gooday & Rathburn, 1999; Schönfeld et al., 2023). Spatial variability among deep-sea benthic foraminiferal communities can be observed at metric to centimetric scales due to changing habitats (Bernstein et al., 1978; Griveaud et al., 2010; Lejzerowicz et al., 2014). A disparate distribution of food and macrofauna (burrowers, predators, and/or bioconstructors), together with changes in substrates, can explain this heterogeneous distribution of macro and microhabitats (De Stigter et al., 1996; Fontanier et al., 2002; Schönfeld, 2002; Schönfeld et al., 2011). The dispersal of benthic foraminifera
<figure><img src="image_7.png" /><figcaption>**Figure 5.** Relative abundance of the subpolar planktic taxon *Neogloboquadrina pachyderma* (%) according to Mojtahid et al. (2017, North core), and Depuydt et al. (2022a, Central core; 2024, South core), Segment length/Net change ratio (SL/NC; green line), Recovering Departing Trajectory calculated with the initial state defined at 23.0 ka BP (full blue line) and at the onset of HS1a (18.4 BP ka; dashed blue line), Net changes (NC) calculated with the initial state defined at 23.0 ka BP (full orange line) and at the onset of HS1a (18.4 BP ka; dashed orange line), and Segment lengths (SL; filled black curve) for all three areas of interest (the top, central and lower panels correspond to the North, Central and South areas, respectively). Cumulative Net change (NC) and Cumulative Segment length (SL) are indicated for all three areas. The different time periods (preHS1, HS1a, HS1b, and postHS1) discussed in the text are highlighted by the shaded areas (the color code follows that of Figure 4).</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Figure 6.** Kernel distribution approximation and boxplots of Segment lengths (top panel) and Net changes (lower panel) in the North, Central and South areas during preHS1 and HS1a. The yellow dots indicate the mean values.</figcaption></figure>

and the transport of species from more proximal settings by sea-ice or gravity flows also play an important role in their geographic distribution (De Stigter et al., 1999; Duros et al., 2012; Fentimen et al., 2020; Murray, 2006).

The North area was situated just south (ca. 50–100 km) of the maximum extent of the BIIS at 23 ka BP, downstream of the ISIS, and within the path of Channel River discharges (Figure 1; Clark et al., 2012). Mojtahid et al. (2017) suggested that the numerous *Elphidium* spp. found in the area were transported by sea-ice and deposited on the seafloor through melting of ice rafts. The more southern Central and South areas, situated at a greater distance of the ISIS termination and Channel River mouth, would have been less subject to the transport of foraminiferal species from the shelf. The greater presence of the opportunistic *C. carinata* in the North (Figure 3), a species known to appreciate high organic matter input (Dessandier et al., 2018; Duchemin et al., 2008; Fontanier et al., 2003; Hess et al., 2005; Martins et al., 2015), is also probably linked to a stronger influence of terrestrial input due to the proximity of the Channel River mouth and ISIS termination (Figure 1). Additionally, the grain size of seafloor sediments has an impact on both infaunal and epifaunal benthic foraminiferal assemblages, particularly at bathyal depths (Gooday & Jorissen, 2012; Jorissen et al., 2007; Lutze & Thiel, 1989; Schönfeld, 2002; Venturelli et al., 2018). The grain size distributions of the three sites differ, which essentially reflects variations in bottom-water hydrodynamics, further explaining the observed trends in trajectory groups (Figure 7; Mojtahid et al., 2017; Toucanne et al., 2021; Depuydt et al., 2024). Given the afore mentioned benthic foraminiferal assemblage differences, it is necessary to evaluate changes between areas at the scale of communities by measuring the amount and speed of change (Segment lengths), together with the amount and direction of change relative to an initial state of the community (Net change and recovering or departing trajectory metrics).

## 5.2. Response of Benthic Foraminiferal Communities to Heinrich Stadial 1

NC, SL and RDT values during the preHS1 period indicate that benthic foraminiferal communities were stable in the Central and South areas, whereas they showed greater variability in the North (Figures 5 and 6). We suggest that the latter is linked to the proximity of the ISIS termination and Channel River mouth, which governed the fluctuating input of meltwater and associated organic matter in the area (Figure 1). Benthic foraminiferal communities in the North experience a change followed by a return to the initial

state at approximately 22 ka BP, as demonstrated by the departing/recovering trend in RDT (decrease and increase of RDT values; Figure 5). The deglaciation, noticeably after 23 ka BP, was discontinuous and marked by phases of rapid meltwater release through the Channel River due to the EIS retreat (Figure 1). One of these meltwater releases took place between approximately 22.5 ± 0.2 and 21.3 ± 0.2 ka BP (Toucanne et al., 2015) and may explain the observed changes in NC and RDT in the North at this time. The absence of any clear trends in the South and Central NC and RDT during the preHS1 period suggests that benthic foraminiferal communities were considerably less impacted at these lower latitudes than in the North, where the influence of abrupt episodes of ice calving from the ISIS would have been greater.

The sharp increase in NC combined with a departing trend in RDT (decrease in RDT) in all three areas at the onset of HS1a indicates that benthic foraminiferal communities experienced a rapid change, which contrasts with the more stable community structure that characterizes the preHS1 period, particularly in the Central and South areas (Figures 4–6). Interestingly, SL and NC suggest that benthic foraminiferal communities showed greater variability in the North during the 2,000 years before the onset of HS1a than in the South and Central areas (Figure 5). This can be linked to the arrival of cold meltwater brought by the Channel River between ±20 and 19 ka, as
<figure><img src="image_9.png" /><figcaption>**Figure 7.** (a) Temporal distribution of Sortable Silt Mean Size (Mean SS, i.e. mean of the carbonate-free 10–63 µm silt fraction) in the North (blue line), Central (gold line), and South (pink line); (b) Kernel distribution approximations and box plots of mean SS (µm) for the three areas. The yellow dots indicate the mean values. The plots use data previously published by Mojtahid et al. (2017; MD99-2328), Toucanne et al. (2021; BOBGEO-CS05); and Depuydt et al. (2024; SU81-44).</figcaption></figure>

indicated by an increase in the relative abundance of *N. pachyderma* (Figure 5; Zaragosi et al., 2001; Mojtahid et al., 2017; Fersi et al., 2021), the BIT-index (Ménot et al., 2006), the abundance of the freshwater algae *Pediastrum* (Zaragosi et al., 2001), and turbidite flux records from the area (Toucanne et al., 2010, 2012). In contrast, the relative abundance of *N. pachyderma* is low in the Central and South between ±20 and 19 ka (Figure 5; Mojtahid et al., 2017; Depuydt et al., 2022a, 2024), indicating a reduced input of meltwater which may in turn explain the stability of benthic foraminiferal communities within this time interval in these more southern locations.

The departing trend (decrease in RDT) of benthic foraminiferal communities at the onset of HS1a mirrors the sudden increase in *N. pachyderma* percentages at all three sites, which is also concurrent with quantitative SST records (Figure 5; e.g. Ménot et al., 2006; Eynaud et al., 2007; Salgueiro et al., 2014). Large quantities of meltwater entered the North Atlantic during the first phase of HS1, triggering a slowdown of the AMOC and a southward displacement of oceanic and atmospheric fronts (e.g., Bard et al., 2000; McManus et al., 2004; Naughton et al., 2016; Zaragosi et al., 2001). The vegetation from the French and North Iberian land masses record cool-humid conditions during HS1a (Naughton et al., 2016; Penaud et al., 2024), which would also have bolstered the watershed of the Channel River. The HS1a laminated sediments along the French margin are testimony to an important seasonality, characterized by considerable river ice discharges during winters and EIS melting during summers (e.g., Fersi et al., 2021; Mojtahid et al., 2005; Toucanne et al., 2015; Zaragosi et al., 2001). The HS1a climatic changes triggered a rapid response of benthic foraminiferal communities (Depuydt et al., 2022a, 2024; Mojtahid et al., 2017). Yet, their response is not identical across all three sites (Figures 4 and 5). Indeed, communities in the Central and South areas show a twofold departing/recovering trend during HS1a, which is especially noticeable in the Central area and less pronounced in the North (Figures 4 and 5). This observation reveals the instability of benthic foraminiferal communities during the turmoil of HS1a. The recent study of core MD13-3438 (Figure 1) at a sub-centennial time resolution suggests that HS1a can be divided into 5 sub-phases (HS1a1 to HS1a5; Fersi et al., 2021; Penaud et al., 2024). HS1a2 and HS1a4 would have been char-

acterized by enhanced EIS retreat and Channel River runoff, whereas HS1a1, HS1a3, and HS1a5 were rather marked by a reduced retreat of the EIS and hence weaker Channel River runoff (Fersi et al., 2021). Because of the considerably lower resolution (200-year resolution) of our study when compared to the 20-year resolution over HS1a presented by Fersi et al. (2021) and Penaud et al. (2024), correlations of benthic foraminiferal trajectory metrics to these subdivisions remain tentative. However, we propose that the twofold departing/recovering trend observed in the RDT and NT in the Central and South areas could correspond to variations in meltwater release, as proposed by Fersi et al. (2021) and Penaud et al. (2024). Indeed, departing trajectories are associated with *B. albatrossi*, *G. affinis* and *C. carinata* (Figure 4). As described previously (Section 5.1), the opportunistic *C. carinata* can be related to enhanced organic matter from fluvial systems. The deep infaunal *G. affinis* is known to tolerate anoxia in highly productive areas (Corliss, 1985; Koho et al., 2011; Rathburn & Corliss, 1994), whilst the infaunal *B. albatrossi* is documented for its opportunistic behavior and inclination toward phytodetritus (Duros et al., 2011; Schmiedl et al., 2000). Thus, the relationship between these three species and departing trajectories may indicate that HS1a instability in benthic foraminiferal communities is related to fluctuating meltwater input, which is in turn driven by marine and terrestrial climatic conditions. If the two departing trajectories in the Central and South areas are indeed related to phases of enhanced Channel River runoff, the absence of a clear twofold departing/recovering trend in the North, which is rather defined by a seesaw pattern in NC and RDT (Figure 4a), may indicate that benthic foraminiferal communities were more regularly confronted with fluctuations in river runoff due to the proximity of the Channel River mouth and ISIS termination. Secondary pulses of river runoff, which would not have impacted benthic communities at lower latitudes along the French Atlantic margin, could
drive community change at a more local scale. In addition, we propose that the instability of benthic foraminiferal communities in the North prior to HS1, noticeably between ±19 and 20 ka BP (Figure 4), may have resulted in a contrasting response of communities to the events of HS1a when compared to more southern settings.

Unlike HS1a, the response of benthic foraminiferal communities in the South and Central areas during the first half of HS1b (16.1–15.2 ka BP) shows clear differences (Figure 4). In the Central area, SL, NC and RDT suggest that benthic foraminiferal communities were stable and showed little variability after HS1a until the end of our record (14 ka BP), although species composition before and after HS1a changed (Figure 3b). This change in benthic foraminiferal communities is also observed in the South before and after HS1a (Figure 3c). Yet, HS1b in this area is also characterized by a sharp increase in SL and NC, together with a decrease in RDT, which suggests a rapid change in benthic foraminiferal communities between approximately 15.2 and 15.8 ka BP (Figure 4). This trend is essentially driven by an increase in the abundance of the infaunal *U. peregrina* and *U. mediterranea* (Figure 3b). These two species are dominant since the deglaciation and during the Holocene along the North European Atlantic margin at intermediate water depths (between ca. 500 and 200 m depth; e.g. Schönfeld & Zahn, 2000; Rüggeberg et al., 2007; Mojtahid et al., 2017; Depuydt et al., 2022a, 2024). Depuydt et al. (2024) propose that this increase in *Uvigerina* spp. was driven by a strengthening of the GEBC along the slope of the Bay of Biscay. However, the Central area does not demonstrate any similar shift in benthic foraminiferal communities (Figure 4a), despite a velocity increase of the GEBC along the entire French Atlantic margin at the end of HS1b (Toucanne et al., 2021). As such, the benthic foraminiferal community change noticed in the South between 15.8 and 15.2 ka BP is possibly a relatively local phenomenon and may not represent a widespread oceanographic event.

## 5.3. Benefits of ETA for Micropaleontological Studies

The ETA framework allows to satisfyingly pinpoint benthic foraminiferal community shifts in time and to compare these along the French Atlantic margin. Throughout the studied time interval, the ETA metrics obtained on fossil benthic foraminiferal assemblages clearly mirror changes observed in other proxies, such as *N. pachyderma* percentages (Depuydt et al., 2022a, 2024; Fersi et al., 2021; Mojtahid et al., 2017; Zaragosi et al., 2001), palynological (Fersi et al., 2021; Penaud et al., 2024) and geochemical records (Ménot et al., 2006), and turbidite flux reconstructions (Toucanne et al., 2010, 2012). This observation validates ETA as a valuable tool to investigate records of fossil faunal assemblages, since the approach successfully identifies previously recognized environmental tipping points. Moreover, the ETA metrics quantify the dynamics of communities both temporally and spatially within the same space of trajectory resemblance. This cannot be done with univariate and multivariate methods traditionally applied in the field of micropaleontology. The ETA metrics also identified a twofold departing/recovering trend in the Central and South areas during HS1a, which did not stand out in previous investigations carried out on the same data (Depuydt et al., 2022a, 2024; Mojtahid et al., 2017).

The strengths of ETA also lie in the possibility of cross comparing records obtained from different localities and from an array of fossil organisms (e.g., ostracods, dinocysts, pollen, foraminifera ...). In this case, the absence of one group of fossil organisms could possibly be compensated by the presence of another and the construction of a composite faunal record. Although we produced for this study a synchronous linearly interpolated data set, ETA may also be used to compare asynchronous records, that is when trajectories differ in the number of surveys or when survey times do not match (De Cáceres et al., 2019). This is of particular interest since it is often the scenario faced when working with fossil records and is a widespread caveat when comparing records with commonly used analytical methods. ETA may also be applied to recent fossil macrofaunal and microfaunal assemblages to constrain the dynamics of communities having faced an anthropogenic impact. In this instance, the application of the recently developed ecological quality assessment within the framework of ETA (Sturbois et al., 2023) could provide valuable insights into recent community dynamics, for example between pre- and post-industrial times. This is especially relevant for benthic foraminiferal assemblages, which are regularly utilized in biomonitoring and reconstructions of prehistoric times (e.g., Bouchet et al., 2021; Charrieau et al., 2019; Durand et al., 2018). Lastly, the advent of online curation has provided scientists with vast amounts of readily available data. This, together with the rapid improvement of analytical methods and computational speed, offers new prospects for researchers. Combining and refreshing the analysis of previously acquired micropalaeontological assemblage data with the ETA framework could offer a novel view on the response of communities to keystone events, such as sapropels or global climatic tipping points (e.g., Paleocene-Eocene Thermal Maximum or the Cretaceous-Paleogene boundary).
## 6. Conclusions

The application of Ecological Trajectory Analysis (ETA) to fossil benthic foraminiferal assemblages from the French Atlantic margin satisfyingly pinpoints major environmental shifts of the last deglaciation. The identification of previously documented benthic foraminiferal changes with ETA validates it as a sturdy analytical method when considering downcore fossil communities. Moreover, ETA clearly highlights temporal and spatial differences amongst benthic foraminiferal communities along the French Atlantic margin and allows to concisely quantify these changes, which cannot be performed with commonly used methods in the field of micropaleontology. The instability of fossil benthic foraminiferal communities in the North during the preHS1 period stands out from the more central and southern areas. A clear twofold departing/recovering trend characterizes the response of benthic foraminiferal communities to the melting of the Eurasian Ice Sheet Complex and resulting freshwater discharges of HS1a. This departing/recovering pattern is not as dramatic in the North, where communities were destabilized prior to the onset of HS1a, possibly because of early phases of ice calving and freshwater runoff originating from the Channel River and Irish Ice Stream. The response to the events of the later HS1b period also differs latitudinally, with a departing trend of communities in the South at approximately 15.4 ka BP which is not matched in the Central area. Looking at the wider picture, the application of ETA to fossil benthic foraminiferal assemblages stresses that such novel multivariate analytical methods can provide an improved assessment of changes in fossil communities and their relationship to environmental shifts.

## Conflict of Interest

The authors declare no conflicts of interest relevant to this study.

## Data Availability Statement

The benthic foraminiferal counts from the three cores used for this study are archived and freely available at Mojtahid et al. (2017; core MD99-2328), Depuydt et al. (2022b; core BOBGEO-CS05), and Depuydt et al. (2022c; core SU81-44).

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