Stable isotope ratios and sea surface temperatures of sediment core GIK23414-8@en

Investigating past interglacial climates not only help to understand how the climate system operates in general, it also forms a vital basis for climate predictions. We reconstructed vertical stratification changes in temperature and salinity in the North Atlantic for a period some 400 ka ago (MIS11), an interglacial time analogue of a future climate. As inferred from a unique set of biogeochemical, geochemical, and faunal data, the internal upper ocean stratification across MIS 11 shows distinct depth-dependent dynamical changes related to vertical as well as lateral shifts in the upper Atlantic meridional circulation system. Importantly, transient cold events are recognized near the end of the long phase of postglacial warming at surface, subsurface, mid, and deeper water layers. These data demonstrate that MIS 11 coolings over the North Atlantic were initially triggered by freshwater input at the surface and expansion of cold polar waters into the Subpolar Gyre. The cooling signal was then transmitted downwards into mid-water depths. Since the cold events occurred after the main deglacial phase we suggest that their cause might be related to continuous melting of the Greenland ice sheet, a mechanism that might also be relevant for the present and upcoming climate.对过去冰间期气候的研究，不仅有助于从整体上解析气候系统的运作机制，同时也是气候预测研究的重要基石。本研究重建了约40万年前（对应深海氧同位素11期（Marine Isotope Stage 11, MIS11））北大西洋海域的温度与盐度垂直层结变化——该冰间期是未来气候的优质地质类比对象。基于一套独特的生物地球化学、地球化学及动物群实测数据，MIS11时期的上层海洋内部层结呈现出显著的深度依赖性动力变化，这类变化与大西洋经向环流上层系统的垂直与侧向迁移紧密相关。尤为关键的是，在表层、次表层、中层及深层水体的长期冰后升温阶段末期，均识别出了瞬态寒冷事件。实测数据表明，北大西洋海域MIS11时期的降温事件最初由表层淡水输入以及寒冷极水向副极地环流（Subpolar Gyre）的扩张所触发，随后降温信号向下传递至中层水体深度。由于此类寒冷事件发生于主冰消期之后，我们推测其成因可能与格陵兰冰盖的持续消融有关——这一机制或许同样适用于当前及未来的气候系统。