Subsurface warming as a trigger for Heinrich events

很少有发现比海因里希事件更能激发古气候界的兴趣，这些事件代表了在晚更新世冰川期间，冰山从劳伦蒂冰盖的哈德逊海峡冰流向北大西洋的周期性排放。虽然通常被认为是内部冰盖不稳定，但它们出现在大西洋子午线翻转环流(AMOC)大幅减少的顶峰时，表明气候可能是触发因素。模型表明，海洋对AMOC减少的反应可能会通过中等深度(地下)水域变暖、不稳定的接地线和冰架以及伴随着冰流涌动而触发海因里希事件。然而，地下变暖的证据仍然存在广泛的争论，另一个涉及卤水形成的假说解释了在中等水深记录的地球化学信号。在这个项目中，来自俄勒冈州立大学的一个由地质学家、古海洋学家和地球化学家组成的团队将评估海因里希事件是由海因里希事件由海因里希事件触发的假设，该假设是在AMOC大幅下降后引发的。利用从北大西洋中西部和中部的几个中等深度地点测量的海底有孔虫的各种或地球化学指标，他们将确定相对于海因里希事件的变暖的时间和幅度，特别是海因里希事件1。这项研究的结果将是解决海因里希事件的其他神秘的气候背景。这项工作还超越了对地质记录的解释，展示了陆地冰未来对海洋环流和温度变化做出反应的可能性，这是预测未来海平面上升的一个非常令人关切的问题。因此，这项工作具有直接的社会意义，因为它增进了对冰盖对海洋环流和温度当前和未来可能发生的变化的反应的理解，而海洋环流和温度的变化是预测陆冰消失和海平面上升的最大原因之一。该项目还将为指导和培训青年科学家提供一个独特的环境。该提案将通过增加地球科学多样性计划，培养一名博士生，并从代表性较低的群体中招收一名本科生。

Few discoveries have galvanized the interest of the paleoclimate community more than Heinrich events, which represent the episodic discharge of icebergs from the Hudson Strait Ice Stream of the Laurentide Ice Sheet to the North Atlantic Ocean during late-Pleistocene glaciations. Although commonly attributed to internal ice-sheet instabilities, their occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) suggests a possible trigger by climate. Models suggest that ocean responses to an AMOC reduction might trigger Heinrich events through warming of intermediate-depth (subsurface) waters, destabilizing grounding lines and ice shelves with attendant ice-stream surging. Evidence for subsurface warming remains widely debated, however, with an alternative hypothesis involving brine formation to explain geochemical signals recorded at intermediate water depths. In this project, a team of geologists, paleoceanographers, and geochemists from Oregon State University will evaluate the hypothesis that Heinrich events were triggered by subsurface warming following a strong reduction in the AMOC. Using a variety or geochemical proxies measured on benthic foraminifera from several intermediate-depth sites in the western and central subpolar North Atlantic, they will establish the timing and amplitude of warming relative to Heinrich events, with particular emphasis on Heinrich event 1. The outcome of this study will be resolution of the otherwise enigmatic climatic context of Heinrich events. This work also extends beyond an explanation of the geologic record by providing a demonstration of the potential for a future response of land ice to changing ocean circulation and temperature, an issue of great concern in projections of future sea-level rise. This work thus has direct societal relevance by developing an improved understanding of the response of ice sheets to current and possible future changes in ocean circulation and temperature, which are among the greatest causes for concern in projections of land-ice loss and consequent sea-level rise. This project will also provide a unique environment for mentoring and training young scientists. The proposal will train a Ph.D. student and recruit an undergraduate student from an underrepresented group through the Increasing Diversity in Earth Science program.