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。这项研究涉及分析在上一次冰川末期冰川消退后，开通西线对北极淡水流量的时间和后果。北极的淡水通过西线流入拉布拉多海，拉布拉多海是深海对流的关键区域。将使用对巴芬湾北部沉积物岩心的各种分析和计算机模拟来记录和探索过去11,000年来与西部淡水路线开通有关的海冰覆盖、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。这项研究的一个重要组成部分是研究北水波利尼亚(NOW)的历史，这是一个生产力高、海冰覆盖率低的绿洲，北极淡水进入巴芬湾北部的地方形成了这一绿洲。现在的生产力归功于北极淡水的高营养含量，以及形成门户的狭窄水道对北冰洋浮冰的堵塞。现在是生物生产力的热点，数千年来一直吸引着人类来到该地区，并维持着今天的北极社区。通过西部淡水路线的淡水流量的历史和现在的历史都非常鲜为人知，但这个系统的行为准备改变，以应对北冰洋海冰覆盖的持续减少。了解北极淡水西线的开放和NOW的启动是如何随着时间的推移而发生变化的，将为理解这些系统将如何影响未来的北极系统和全球气候提供背景。该项目使用来自NOW Polynya及其上下游地区的现有沉积物岩芯，使用新的(来自电感耦合等离子体质谱仪和藻类生物标记物的营养示踪剂)和传统的(定量X射线矿物学、有孔虫组合、稳定的碳和氧同位素)代理，用共同体地球系统模型(CESM)和冰川均衡调整模型和年表发展(放射性碳和古地磁的长期变化)进行气候模拟，以检验三个假设：假设1：北极-大西洋贯通流的西部淡水路线的开通改变了向北大西洋的淡水外流，从而导致大西洋子午线翻转环流(AMOC)。假设2：冰川均衡抬升使CAA航道显着变浅，改变了北极外流的组成，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晚期，是北极海冰增加的结果。该项目是一项国际努力，涉及加拿大和欧盟的合作以及外国研究生与加州大学教职员工和科学家的互动。它将为一名女性博士后提供支持和指导，她将接受新的生物地球化学实验室技术培训。一名博士生将致力于CESM建模。几名本科生将接受培训并参与研究。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.