Collaborative Research: Investigating the Role of Coastal Polynya Variability in Modulating Antarctic Marine-Terminating Glacier Drawdown

南极冰盖是海平面上升的主要原因，其大部分质量损失发生在冰层与海洋交汇的边缘。冰川和冰流流向海岸，可以漂浮在水面上，形成冰架。冰架几乎占整个南极海岸线的一半，并阻挡着南极大陆内陆冰的流动；因此，它们对南极冰盖的整体稳定是不可或缺的。冰架的质量损失主要有两个过程：冰山崩解和底部融化。两者的时间和空间波动由不同的过程驱动；冰架融化的一个主要驱动因素是邻近的南大洋提供的热量。反过来，海洋热是由冰架环境的各个方面驱动的。海洋热含量变化的最重要因素之一是海冰的存在。这项研究将集中在沿海冰川(海冰中的开阔水域)的影响，它们如何调节当地的海洋环境，以及该环境如何推动冰架底部融化。迄今为止，冰川和冰架融化之间的关系还没有在整个南极范围内得到描述。了解波利尼亚冰架的大小和持续时间、海洋分层和冰架融化之间的反馈以及这些反馈的强度，将提高表征对冰架长期稳定性的影响，进而对整个南极冰盖的影响的能力。这项研究的一个关键方面是，它将为理解不同地理环境中的冰架-海洋相互作用提供一个框架。这一点，加上各种模型的改进，将有助于解释未来气候变化对这些系统的影响，因为它们的反应可能非常不同，总体上不同于冰盖的大范围反应。该项目还将提供更广泛的背景，以便更好地设计未来对特定沿海冰架和冰架过程的观测研究。这项研究侧重于四个主要假设：1)沿海冰架范围的变化与冰架融化速率的变化相关，这种相关性在南极洲各地各不相同；2)通过当地水域的层化，冰架融化和沉积制度之间的反馈调节；3)冰架范围与海底水深测量一起调节到达冰缘的温暖近海水域的体积；以及4)冰架与冰川之间反馈的强度因地理环境而异，并影响冰川系统的长期稳定性。观测数据，包括穿冰雷达、雷达和激光测高，以及现场水文数据，以及从南大洋状况估计项目和南极洲BedMachine项目获得的数据集，将与海洋(麻省理工学院全球环流模型，MITgcm)和冰盖(冰盖和海平面系统模型，ISSM)模型结合使用，以揭示潜在的动力学。通过对观测数据的联合分析，能够在一系列环境中调查波利尼亚、海洋和冰架信号及其随时间的相互作用。该数据分析的结果还为建模任务提供了输入和验证数据，这将允许我们在观察中描述反馈的特征。耦合模拟将使我们能够研究不同动力机制下波尼亚环流和冰架之间的相互作用，并了解冰和海洋随时间的反馈。诊断和解释冰盖-冰架相互作用的泛南极空间变异性是本研究的主要目的，它有别于针对特定区域相互作用过程的其他项目。因此，这项研究集中在南极海岸周围的七个初步目标地点，以建立一个框架来解释不同地理环境下的冰架-海洋耦合变异性。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。

Most of the mass loss from the Antarctic Ice Sheet, a major contributor to sea level rise, occurs at its margins, where ice meets the ocean. Glaciers and ice streams flow towards the coast and can go afloat over the water, forming ice shelves. Ice shelves make up almost half of the entire Antarctic coastline, and hold back the flow of inland ice in Antarctica continent; thus they are integral to the overall stability of the Antarctic Ice Sheet. Ice shelves lose mass by two main processes: iceberg calving and basal melting. Temporal and spatial fluctuations in both are driven by various processes; a major driver of ice shelf melt is the heat provided by the neighboring Southern Ocean. Ocean heat, in turn, is driven by various aspects of the ice shelf environment. One of the most significant contributors to changes in the ocean’s heat content is the presence of sea ice. This research will focus on the effects of coastal polynyas (areas of open water amidst sea ice), how they modulate the local ocean environment, and how that environment drives ice shelf basal melting. To date, the relationship between polynyas and ice shelf melt has not been characterized on an Antarctic-wide scale. Understanding the feedbacks between polynya size and duration, ocean stratification, and ice shelf melt, and the strength of those feedbacks, will improve the ability to characterize influences on the long-term stability of ice shelves, and in turn, the Antarctic Ice Sheet as a whole. A critical aspect of this study is that it will provide a framework for understanding ice shelf-ocean interaction across a diverse range of geographic settings. This, together with improvements of various models, will help interpret the impacts of future climate change on these systems, as their responses are likely quite variable and, overall, different from the large-scale response of the ice sheet. This project will also provide a broader context to better design future observational studies of specific coastal polynya and ice shelf processes.This study focuses on four main hypotheses: 1) Variations of coastal polynya extent are correlated with those of the ice shelf melt rates, and this correlation varies around Antarctica; 2) Polynya extent modulates a feedback between ice shelf melt and accretion regimes through stratification of local waters; 3) Polynya extent together with seafloor bathymetry regulate the volume of warm offshore waters that reach ice margins; and 4) The strength of the feedback between polynya and glacier ice varies with geographic setting and influences the long-term stability of the glacial system. Observational data, including ice-penetrating radar, radar and laser altimetry, and in situ hydrographic data, and derived data sets from the Southern Ocean State Estimate (SOSE) project and BedMachine Antarctica, will be used in conjunction with ocean (MIT global circulation model, MITgcm) and ice sheet (Ice sheet and Sea-level System Model, ISSM) models to reveal underlying dynamics. The joint analysis of the observational data enables an investigation of polynya, ocean, and ice shelf signals and their interplay over time across a range of settings. The results of this data analysis also provide inputs and validation data for the modeling tasks, which will allow for characterization of the feedbacks in our observations. The coupled modeling will enable us to examine the interaction between polynya circulation and ice shelves in different dynamical regimes and to understand ice and ocean feedback over time. Diagnosing and interpreting the pan-Antarctic spatial variability of the polynya-ice shelf interaction are the main objectives of this research and separates this study from other projects targeted at the interactive processes in specific regions. As such, this research focuses on seven preliminary target sites around the Antarctic coast to establish a framework for interpreting coupled ice shelf-ocean variability across a diverse range of geographic settings.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.