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.

海洋环流与冰盖动力学之间的相互作用在第四纪气候中发挥着关键作用。相较于大西洋经向翻转环流（Atlantic Meridional Overturning Circulation, AMOC）的表层与深层分支，针对海因里希冷期（Heinrich Stadials, HSs）等关键时期的中层水域研究仍较为匮乏，尤以东北大西洋海域为甚。本研究利用比斯开湾约1000米水深处的底栖有孔虫组合（benthic foraminiferal assemblage）数据，重建了距今约32至14 ka cal BP的古环境变化。研究结果凸显了底栖有孔虫的高敏感性：其物种特异性响应可有效追踪末次三次HS事件期间受大陆（欧洲冰盖动力学）与海洋（AMOC）驱动因子调控的环境变化。总体而言，HS事件的典型特征为中寡营养型物种与缺氧指示种同时出现，且高能环境指示种丰度较低。这证实了东北大西洋三次HS事件期间中层环流整体处于迟缓状态。HS1的独特之处在于其早期阶段高有机通量指示种的大量富集，这与HS1是研究时段内冰盖退缩与海洋融水释放规模最大的时期这一事实高度一致。最后，有孔虫记录揭示了受区域冰川不稳定性驱动的HS2中期再通风事件。