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，海因里希事件代表了晚更新世冰期期间从劳伦泰德冰盖的哈德逊海峡冰流到北大西洋的冰山的间歇性排放。虽然通常归因于内部冰盖的不稳定，但它们发生在大西洋经向翻转环流（AMOC）大幅减少的高潮，这表明气候可能是一个触发因素。模型表明，海洋对AMOC减少的反应可能会引发海因里希事件，原因是中深度（地下）水域变暖，使接地线和冰架不稳定，并伴随冰流激增。然而，地下变暖的证据仍然存在广泛的争议，另一种涉及卤水形成的假设可以解释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AMOC强烈减少后的地下变暖引发的假设。利用在北大西洋西部和中部亚极地几个中深度地点测量的底栖有孔虫的各种地球化学代用物，他们将确定相对于海因里希事件的变暖时间和幅度，特别强调海因里希事件1。这项研究的结果将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，它展示了陆地冰对海洋环流和温度变化的未来反应的潜力，海洋环流和温度变化是预测未来海平面上升时非常关注的问题。因此，这项工作通过提高对冰盖对当前和未来可能发生的海洋环流和温度变化的反应的理解，具有直接的社会意义，而海洋环流和温度变化是陆地冰损失和随之而来的海平面上升预测中最令人关注的原因之一。该项目还将为指导和培训年轻科学家提供一个独特的环境。该提案将培养一名博士生，并通过增加地球科学项目的多样性从一个代表性不足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.