Meltwater Discharge in the Arctic During the Deglacial Period

首席研究员将根据d18o、沉积物岩性和过去15000年的地球化学，建立一个厚皮乳象（N. pachyderma）的ms年表，记录低d18o水从劳伦泰德冰盖（Laurentide Ice Sheet）北部融化的入侵，从而构建最近一次冰川消退期间通过麦肯齐河系统（Mackenzie River system）流入北冰洋的融水历史。先前的稳定同位素重建表明，融水排放对北极中部盆地的影响很大，沉积学研究发现，在冰期，从加拿大北部到弗拉姆海峡发生了两次浮冰碎片事件。这些结果表明，北极盐度的变化可能在北大西洋翻转环流的变异性中发挥了主要作用。这些融水事件应该在厚皮N. d18o中显示为最小值，并且异常的幅度应该与融水事件的大小成正比。这些岩心于1989年收集，并保存在伍兹霍尔海洋研究所的岩心库中。它们完好无损，未取样。根据颜色变化，岩心沉积速率（~1 ~ 3cm / r-1）允许开发一个相对高分辨率的冰川融水排放记录。知识价值。这项研究将为一个非常重要的气候问题提供见解：大西洋翻转环流对北冰洋和北大西洋亚极地盐度降低有多敏感？对未来气候的准确预测需要这些知识，然而，过去大西洋翻转的最好例子是在地质记录中。大西洋盐度的变化可能会影响环流和向北大西洋的热量输送：高纬度地区在过去40年里以前所未有的方式变新鲜，格陵兰海对流可能已经在减少。然而，很难知道需要多大的盐度变化才能显著改变环流。物理海洋学家并不确定，而且对未来温室气候的大量数值模拟预测了从大西洋海平面没有变化到减少15 Sv的一系列结果。要充分了解环流对盐度变化的敏感程度，需要研究地质记录和北冰洋在这些变化中所起作用的具体知识。更广泛的影响。研究生培训是本项目的重要组成部分。莎伦·霍夫曼（研究生二年级）将为这些核心提供钍的数据。额外的培训将包括高中参与者获得的研究经验，他们将参与本项目的样品制备和分析程序。首席研究员定期在各种场所向公众发表演讲，包括公共图书馆，本科课程，以及海洋科学新闻研究员的年度WHOI媒体聚会。最近对杂志（《发现》、《新闻周刊》）、报纸（《波士顿环球报》、《华尔街日报》）和广播（当地NPR电台）的采访证明了这项研究结果可能被讨论的地方。首席研究员在华盛顿特区和伍兹霍尔向参众两院议员及其工作人员作了气候简报和正式证词。

ABSTRACTCurryOPP-0520073The Principal Investigator will construct a history of meltwater discharge into the Arctic Ocean through the Mackenzie River system during the most recent deglaciation by developing an AMS-dated chronology of N. pachyderma by d18 O and sediment lithology, and geochemistry for the last 15,000 years which will record the incursion of low- d18 O water melting from the northern Laurentide Ice Sheet. Previous stable isotopic reconstructions show that the effects of meltwater discharge in the central Arctic basin were large and sedimentological studies trace two ice rafted debris events from northern Canada to the Fram Strait during the deglacial period. These results imply that changes in Arctic salinity likely played a major role in the variability of North Atlantic overturning circulation. These meltwater events should show up as minima in N. pachyderma d18 O and the magnitude of the anomalies should be proportional to the size of the meltwater event. The cores were collected in 1989 and archived in the Woods Hole Oceanographic Institution core repository. They are in excellent condition and remain unsampled. Based on color changes, core sedimentation rates (~1 to 3 cm kyr-1) permit the development of a relatively high-resolution record of deglacial meltwater discharge. Intellectual Merit. This research will provide insight into a very important climate question: how sensitive is the Atlantic overturning circulation to reduced salinity in the Arctic Ocean and subpolar North Atlantic? Accurate future projections of climate require this knowledge, yet the best examples of past changes in Atlantic overturning are in the geological record. Atlantic salinity is changing in ways that may affect circulation and heat transport to the North Atlantic: high latitude locations have been freshening for the last forty years in ways never before documented and reduced Greenland Sea convection may already be underway. However, it is difficult to know how much of a salinity change is needed to alter the circulation significantly. Physical oceanographers are unsure and the numerous numerical simulations of future greenhouse climate predict a full range of outcomes from no change in the overturning to a 15 Sv reduction in the Atlantic. To fully understand how sensitive the circulation is to changing salinity requires study of the geological record and specific knowledge of the Arctic Ocean's role in these changes. Broader Impacts. Graduate student training is a significant part of this project. Sharon Hoffman, (a second year graduate student) will produce the thorium data for the cores. Additional training will include the research experiences gained by the high school participants who will be involved with sample preparation and analytical procedures for this project. The Principal Investigator regularly speaks before the public in a variety of venues, including public libraries, undergraduate classes, and at annual WHOI gathering of media for Ocean Science Journalism Fellows. Recent interviews with magazines (Discover, Newsweek), newspapers (Boston Globe, Wall Street Journal) and radio (local NPR station) attest to the places where the results of this research are likely to be discussed. The Principal Investigator has presented climate briefings and formal testimony to members of the House of Representatives, the Senate, and their staffs in Washington, DC and at Woods Hole.