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

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.