Doctoral Dissertation Research: The Geographic Extent of Late Pleistocene Subsurface Ocean Warming in the Northern Atlantic Ocean Basin and the Origin of Heinrich Events

这项博士论文研究项目将探讨海因里希事件的触发机制，海因里希事件是全球气候突然变化的一种广为人知的表现。海因里希事件被解释为大量冰山从劳伦蒂冰盖崩解出来，劳伦蒂冰盖在上一个冰河时代覆盖了北美大陆的大部分地区。海因里希事件的气候背景是全球性的。因此，确定这些事件是千禧年规模的全球气候变化的组成部分。然而，引发这些事件的物理过程仍然知之甚少。这项博士论文研究项目将利用海底生物中的镁钙比，开发北大西洋次表层水温对已知海因里希事件的高分辨率记录，以评估可归因于海洋环流变化的海因里希事件的外部触发机制。该方法将为海底生物的镁钙古测温提供一种新的分析方法。对从外部拉布拉多海盆地抬升的一个海洋沉积物岩心的分析表明，在该岩心位置的海因里希事件的地层特征出现之前，底层水温变暖。有必要复制和进一步评估这种模式的地理分布，以确立其作为海因里希事件强迫机制的作用。来自雷克雅内斯海脊和拉布拉多海的勘探数据表明，该项目在感兴趣的深度和地点的海洋沉积物岩心含有海因里希事件特征和实现该项目研究目标所需的材料。对突然的冰盖不稳定和海洋变化的研究对未来气候具有重要意义。确认中深度海洋变暖在触发过去的冰盖不稳定性方面发挥了重要作用，这将为类似配置的南极冰盖区段未来的潜在行为提供关键的洞察。该项目可以为目前正在开发的冰盖模型提供验证，这些模型用于预测陆地冰的减少和随之而来的海平面上升。该项目还将产生新的数据，以测试博士生开发的用于等离子质谱仪的新附件的准确性，以便更有效地测量海洋沉积物中的镁钙古温度计。该项目应增进对冰盖对海洋环流和温度目前和未来可能变化的反应的了解，这些因素是海平面上升预测中最令人关切和不确定的因素之一。作为博士论文研究改进奖，该项目将为有前途的学生建立独立的研究生涯提供支持。

This doctoral dissertation research project will examine the triggering mechanisms of Heinrich events, which are a widely recognized expression of abrupt global climate change. Heinrich events are interpreted as massive discharges of icebergs calved from the Laurentide Ice Sheet, the ice mass that covered a large share of the North American continent during the last ice age. The climatic context of Heinrich events was global in scale. Identifying these events therefore is an integral part of millennial-scale global climate change. The physical processes that triggered these events remain poorly understood, however. This doctoral dissertation research project will develop high-resolution records of North Atlantic Ocean subsurface water temperature bracketing known Heinrich events using magnesium-to-calcium ratios in seafloor-dwelling organisms in order to evaluate an external triggering mechanism for Heinrich events attributed to changes in oceanic circulation. This approach will employ a new analytical method for Mg-Ca paleothermometry on seafloor-dwelling organisms. Analysis of one ocean sediment core raised from the outer Labrador Sea basin suggested that bottom-water temperatures warmed before stratigraphic signatures of Heinrich events at that core location. Replication and further assessment of the geographic distribution of this pattern is necessary in order to establish its role as a forcing mechanism of Heinrich events. Exploratory data from the Reykjanes Ridge and the Labrador Sea have shown that the ocean sediment cores targeted for this project at the depths and locations of interest contain Heinrich event signatures and material necessary in order to carry out this project's research goals.The study of abrupt ice sheet destabilization and oceanic change has significant implications for future climate. Confirmation that intermediate-depth ocean warming played a significant role in triggering past ice-sheet instabilities will provide critical insights into potential future behavior of similarly configured Antarctic ice-sheet sectors. The project could provide validation for ice-sheet models currently being developed for projections of land-ice loss and attendant sea level rise. The project also will yield new data to test the accuracy of a new accessory developed by the doctoral student for use with plasma mass spectrometers in order to more effectively measure Mg-Ca paleothermometry in marine sediments. The project should improve understanding of the response of ice sheets to current and possible future changes in ocean circulation and temperature, factors which are among the greatest causes for concern and uncertainty in projections of sea-level rise. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising student to establish an independent research career.