Timing and Paleoceanographic Impacts of the Onset of Arctic-Baffin Bay Throughflow

从北冰洋流向北大西洋的海冰和低盐度地表水（统称为淡水）数量的变化会对全球海洋环流和气候产生影响。这项研究包括分析最后一次冰期结束后冰川退缩后，北极淡水通量西线开放的时间和后果。北极的淡水流经西部的拉布拉多海，这是深海对流的关键区域。对巴芬湾北部沉积物岩心的多种分析和计算机建模将用于记录和探索过去11000年来海冰覆盖、北极淡水通量、海洋环流、海洋生产力和海洋酸化的巨大变化，这些变化与西部淡水路线的开放有关。这项研究的一个重要组成部分是研究北水盆（NOW）的历史，这是一个生产力高、海冰覆盖少的绿洲，在北极淡水进入巴芬湾北部的地方形成。现在的生产力归功于北极淡水的高营养含量和北极海冰浮冰被形成门户的狭窄通道阻塞。现在是生物生产力的热点，几千年来一直吸引着人类来到这个地区，并维持着今天的北极社区。通过西部淡水路线的淡水通量的历史和现在的历史都非常不为人所知，但这个系统的行为准备改变，以响应北极海冰覆盖的持续减少。了解北极淡水西线的开放和现在的开始如何随着时间的推移而变化，将为了解这些系统如何影响北极系统和未来的全球气候提供背景。该项目使用NOW多冰岩的现有沉积物岩心，以及该多冰岩的上游和下游地区，使用新型（电感耦合等离子质谱和藻类生物标志物的营养示踪剂）和传统（定量x射线矿物学、有孔虫组合、稳定的C和O同位素）代用物。利用群落地球系统模式（CESM）和冰川均衡调整模式和年代学发展（放射性碳和古地磁长期变化）验证了三个假设：假设1：北大西洋通流西部淡水通道的打开改变了淡水向北大西洋的流出，从而导致了大西洋经向翻转环流（AMOC）。假设2：冰川均衡隆起使CAA通道显著变浅，改变了北极流出物的组成，对碳酸盐保存和AMOC产生了影响。假设3：现在形成于全新世中后期，是北极海冰增加的结果。该项目是一项国际合作，涉及加拿大和欧盟的合作，以及外国研究生与科罗拉多大学教师和科学家的互动。该项目将为一名接受新型生物地球化学实验室技术培训的女性博士后提供支持和指导。一名博士生将研究CESM建模。几名本科生将接受培训并参与研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Changes in the amount of sea ice and low salinity surface water (together called freshwater) that flow from the Arctic Ocean to the North Atlantic have global ocean circulation and climate impacts. The research involves analysis of the timing and consequences of the opening of the western route for Arctic freshwater flux after the retreat of glacier ice at the end of the last glaciation. The Arctic freshwater flows through the western route to the Labrador Sea, which is a critical area of deep ocean convection. Diverse analyses of sediment cores from northern Baffin Bay and computer modeling will be used to document and explore the large changes in sea-ice cover, Arctic freshwater flux, ocean circulation, marine productivity, and ocean acidification over the last 11,000 years that are associated with opening of the western freshwater route. An important component of the research is to study the history of the North Water Polynya (NOW), an oasis of high productivity and low sea-ice cover that forms where the Arctic freshwater enters northern Baffin Bay. The productivity of the NOW owes to the high nutrient content of the Arctic freshwater and to the blockage of Arctic sea-ice floes by the constricted channels forming the gateway. The NOW is a hotspot of biological productivity that has attracted humans to the area for millennia and sustains Arctic communities today. Both the history of freshwater flux via the western freshwater route and the history of the NOW are very poorly known, yet the behavior of this system is poised to change in response to continuing reductions in Arctic sea-ice cover. The understanding of how the opening of the western route of Arctic freshwater and the initiation of the NOW have changed through time will provide context to understand how these systems will affect the Arctic systems and global climate in future.The project uses existing sediment cores from the NOW polynya, and areas upstream of and downstream from it using both novel (nutrient tracers from Inductively Coupled Plasma Mass Spectrometry and algal biomarkers) and traditional (quantitative X-ray mineralogy, foraminiferal assemblages, stable C and O isotopes) proxies, climate modeling with the Community Earth System Model (CESM) and Glacial Isostatic Adjustment modeling and chronology development (radiocarbon and paleomagnetic secular variation) to test three hypotheses: Hypothesis 1: The opening of the western freshwater route of the Arctic-Atlantic throughflow changed the freshwater outflow to the North Atlantic with consequences for the Atlantic Meridional Overturning Circulation (AMOC). Hypothesis 2: Significant shallowing of the CAA channels by glacial isostatic uplift has changed the composition of the Arctic outflow with consequences for carbonate preservation and the AMOC. Hypothesis 3: The NOW formed in the middle to late Holocene as a consequence of increased Arctic sea-ice. The project is an international effort involving Canadian and EU cooperation and foreign graduate student interaction with CU faculty and scientists. It will provide support and mentoring for a female post-doc who will receive training in novel biogeochemical laboratory techniques. A PhD student will work on the CESM modeling. Several undergraduate students will receive training and participate in the research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.