Collaborative Research: Arctic climate sensitivity to freshwater forcing: Improving model-data comparisons of the 8.2 ka event**

学术价值：主要研究人员将整合气候模型和古气候记录，以更好地了解北极气候系统对北大西洋变冷的敏感性。模式对大西洋经向翻转环流（MOC）未来变化的预估具有很大的数值分布。由于MOC在决定北大西洋周围气候方面起着核心作用，因此我们有必要知道这些模式中哪个（如果有的话）在预测MOC的响应方面具有技巧。对这些模式的一个有用的测试是模拟MOC过去的变化，有时强迫和响应是相当已知的。一个时间段，即8.2 ka事件，已被几个建模组选择为测试用例。这一事件在北大西洋周围的古气候记录中被观察到为一个突然的冷期。它的假设原因是冰川湖阿加西排入哈德逊湾，迄今为止完成的模拟主要集中在这种强迫上。然而，还有其他的同期强迫，以及用于模拟淡水通量的方法中的不确定性，还有待检验。pi将完成三组模拟，以量化这些额外强迫和强迫方法的重要性。这些模拟将使用NCAR社区气候系统模式第3版（CCSM3）完成。第一组模拟的目的是比较不同的淡水添加方法，或“软管”。没有公认的软管方法，他们的实验将允许他们提出一个共同的方法建议。第二组模拟将系统地研究模式对除冰湖排水外发生的另外三种淡水通量的响应。据推测，这些来源中的每一个都在产生海洋和气候反应方面发挥了特定的作用。在最后一组模拟中，他们将考虑额外的大气强迫的影响。这些额外的强迫在以前的模式实验中没有被考虑过，但可能对气候反应有所贡献。这项研究将是在8.2 ka事件模拟中以现实的方式纳入所有重要强迫的第一步。这对于了解北极气候敏感性和耦合气候模式准确反映这种敏感性的能力至关重要。更广泛的影响：大西洋MOC的变化可以在北大西洋周围及其他地区产生大而迅速的气候扰动。拟议的研究将通过评估我们预测未来与北大西洋淡水增加相关的快速变化的能力而造福社会。首席研究人员将与NSF支持的其他研究人员以及参与古hosing模型比对项目的世界各地的科学家进行协同合作。这项研究的成果之一将是他们生成的模型输出，存档于古气候模型比对项目。模式数据也将通过NCAR CCSM古气候工作组提供给科学界。该研究将通过在NCAR的SOARS项目中包括女科学家和一名学生来增加代表性不足的群体的参与。

ABSTRACTMorrillOPP-0713951Otto-BliesnerOPP-0713971Intellectual merit: The Principal Investigators will integrate climate modeling and paleoclimate records to better understand the sensitivity of the Arctic climate system to freshening of the North Atlantic. Model projections of future changes in the Atlantic meridional overturning circulation (MOC) have a large spread of values. Because the MOC plays a central role in determining the climate of the circum-North Atlantic, it is essential that we know which, if any, of these models has skill in predicting the response of the MOC. One useful test of the models is to simulate past changes in the MOC, at times when the forcing and response are reasonably well known. One time period, the 8.2 ka event, has been selected as a test case by several modeling groups. This event is observed as an abrupt cool period in circum-North Atlantic paleoclimate records. Its hypothesized cause is the drainage of glacial Lake Agassiz into Hudson Bay, and simulations completed to-date have focused mainly on this forcing. There are, however, other coeval forcings, as well as uncertainties in the methods used to model freshwater fluxes, that have yet to be examined. The PIs will complete three sets of simulations to quantify the importance of these additional forcings and the forcing methodology. These simulations will be completed using the NCAR Community Climate System Model Version 3 (CCSM3). The goal of the first set of simulations will be to compare different methods of freshwater addition, or "hosing." There is no accepted method of hosing and their experiments will allow them to make recommendations for a common methodology. The second set of simulations will systematically investigate the model response to three other freshwater fluxes that occurred in addition to the glacial lake drainage. It is hypothesized that each of these sources played a particular role in generating the ocean and climate response. In the last set of simulations, they will consider the effects of additional atmospheric forcings. These additional forcings have not been previously considered in model experiments, but could have contributed to the climate response. The research will be a first step toward incorporating all significant forcings in a realistic manner in simulations of the 8.2 ka event. This is essential for understanding Arctic climate sensitivity and the ability of coupled climate models to accurately reflect this sensitivity. Broader impacts: Changes in the Atlantic MOC can produce large and rapid climaticperturbations in the circum-North Atlantic and beyond. The proposed research willbenefit society by evaluating our ability to predict future rapid changes associated with freshwater increases in the North Atlantic. The Principal Investigators will participate in synergistic collaborations with other researchers supported by NSF and with scientists worldwide participating in the Paleohosing Model Intercomparison Project. A deliverable of this research will be the model output they generate, archived with the Paleoclimate Modeling Intercomparison Project. The model data will also be available to thescientific community through the NCAR CCSM Paleoclimate Working Group. Thresearch will increase the participation of under-represented groups by including women scientist and a student in the SOARS program at NCAR.