New results acquired in south-Brittany (MD08-3204 CQ core: Bay of Quiberon and VK03-58bis core: south Glénan islands) allow depicting Holocene paleoenvironmental changes from 8.5 ka BP to present through a multi-proxy dataset including sedimentological and palynological data. First, grain-size analyses and AMS-14C dates highlight a common sedimentary history for both study cores. The relative sea level (RSL) slowdown was accompanied by a significant drop of the sedimentation rates between ca. 8.3 and 5.7 ka BP, after being relatively higher at the onset of the Holocene. This interval led to the establishment of a shell-condensed level, identified in core VK03-58bis by the “Turritella layer” and interpreted as a marker for the maximum flooding surface. Palynological data (pollen grains and dinoflagellate cyst assemblages) acquired in core MD08-3204 CQ argue for an amplification of the fluvial influence since 5.7 ka BP; the establishment of the highstand system tract (i.e., mixed marine and fluviatile influences on the platform) then accompanying the slowdown of the RSL rise-rates. On the shelf, the amplification of Anthropogenic Pollen Indicators (API) is then better detected since 4.2 ka BP, not only due to human impact increase but also due to a stronger fluvial influence on the shelf during the Late Holocene. Palynological data, recorded on the 8.5–8.3 ka BP interval along an inshore-offshore gradient, also demonstrate the complexity of the palynological signal such as i) the fluvial influence that promotes some pollinic taxa (i.e., Corylus, Alnus) from proximal areas and ii) the macro-regionalization of palynomorph sources in distal cores. In addition, the comparison of palynological tracers, including API, over the last 7 kyrs, with south-Brittany coastal and mid-shelf sites subjected to northern vs. southern Loire catchment areas, allowed discussing a major hydro-climatic effect on the reconstructed palynological signals. Strengthened subpolar gyre dynamics (SPG), combined with recurrent positive North Atlantic Oscillation (NAO) configurations, appear responsible for increased winter precipitations and fluvial discharges over northern Europe, such as in Brittany. Conversely, weakened SPG intervals, associated with negative NAO-like modes, are characterized by intensified winter fluvial discharges over southern Europe. Interestingly, we record, at an infra-orbital timescale, major peaks of API during periods of strengthened (/weakened) SPG dynamics in sites subjects to Brittany watersheds (/Loire watersheds) inputs. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

We discuss vegetation and climate changes across western Europe over the last deglaciation, especially zooming on the Heinrich Stadial 1 (HS1) interval in the northern Bay of Biscay. Our study focuses on the marine palynological investigation of core MD13-3438, with new pollen analyses, here compared to a set of paleohydrographical marine proxies (including dinoflagellate cysts / dinocysts) obtained on the same core. We show that the recorded pollen signature is, at that time, tightly related to the fluvial dynamics of the ‘Fleuve Manche’ paleoriver, the latter being coupled with European Ice Sheet fluctuations, as well as influenced by fluvial deliveries from closer French rivers of the Atlantic coast. The onset of HS1 (18.2–16.7 ka BP), marked by enhanced ‘Fleuve Manche’ paleoriver seasonal runoff, is characterized by: i) two episodes of substantial fluvio-glacial input, concomitant with warmer summers and marked by increases of temperate forest pollen grain percentages; ii) and three episodes of moderate runoff, concomitant with extended colder winters and corresponding to increases of boreal forest pollen grain percentages. We suggest an important role of the variability of the North Atlantic atmospheric circulation in explaining those multidecadal changes in pollen sources recorded in the marine realm. When westerlies are deflected southward (respectively northward), they would bring higher humidity to the southern-western and closer (respectively northern-eastern and more distal) distributaries/rivers of the ‘Fleuve Manche’ paleoriver system, associated to moderate (respectively intense) runoff. Then, extreme cold and dry climate conditions are recorded at the onset of Heinrich Event 1 (16.7–15.6 ka BP) with marked occurrences of steppic pollen grains, followed by more humid conditions at the end of HS1, with mixed signatures of open-vegetation and temperate forest taxa. The wettest conditions are recorded during the Bølling-Allerød, concomitantly with the sea level rise and the advection of warm and salty waters by the North Atlantic Current to the study site. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

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 benthic 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 meso-oligotrophic 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. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.