OPP-PRF: Submesoscale Fjord Variability and Its Influence on Glacial Melt

了解冰与海洋交界处的过程，特别是在冰川融化的表面，仍然是我们预测这些冰川融化和退缩及其对海平面上升影响的一项关键挑战。这些冰川的融水对快速变化的极地海洋也有着深远的影响。最近的观测和数值模拟发现，在水下冰川的表面出现了出乎意料的高度融化，最近的理论表明，一种可能的解释是，在冰川峡湾（连接冰川和开阔海洋的狭窄、深和水下山谷）内存在相对小尺度（亚中尺度）的洋流。本研究将把亚中尺度洋流与冰-海边界层的物理现象联系起来，开发出考虑冰-海边界附近海洋环流多尺度效应的改进物理模型。这项研究对社会至关重要，因为它将提高我们对峡湾海洋环流如何促进冰川融化和退缩的理解，这将有助于改善这些地区海平面上升和海洋生物变化的预测。本项目将培养一名博士后研究员（作为主要研究人员），并提供资金指导两名暑期本科生。目前，观测到的冰川融化速率与预测的冰川融化速率之间存在数量级差异。最近的模式表明，冰-海边界层的能量动力学和峡湾内的亚中尺度变化可能导致这些融化速率的升高。假设这些差异是由多尺度冰-海相互作用引起的，这些尺度上的重要过程和融化循环反馈共同导致了融化速率的放大。峡湾的高分辨率亚中尺度解析模拟和冰川冰-海洋边界的大涡模拟（LES）将用于验证峡湾亚中尺度变化是峡湾内涡流动能的主要来源的假设，并且可能被整个冰川前缘融化驱动的剪切、对流和离心不稳定的组合所激发。这些结果将用于测试和开发改进的冰-海洋边界层参数化，这些参数化与之前和正在进行的阿拉斯加LeConte冰川海底表面的观测相一致。这些改进的参数化将减少冰川融化速率估算（以及海平面上升预测）的不确定性，并提高我们对峡湾环流及其对极地沿海生物地球化学影响的理解。这些改进也可能有利于我们对其他类型的冰-海边界的理解。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。

Understanding the processes at the boundary where ice and ocean meet, specifically at the faces of melting glaciers, remains a key challenge in our ability to predict the melting and retreat of these glaciers and their influence on sea level rise. The meltwater from these glaciers also has far-reaching implications for the rapidly-changing polar oceans. Recent observations and numerical simulations find unexpectedly high melting at the faces of submerged glaciers, and recent theory suggests that one possible explanation is the existence of relatively small-scale (submesoscale) ocean currents within glacial fjords (which are narrow, deep, and submerged valleys connecting glaciers to the open ocean). This research will connect the submesoscale ocean currents with the physics at the ice-ocean boundary layer to develop improved physical models that take into account the multiscale effects of ocean circulation near ice-ocean boundaries. The research is of critical importance to society since it will improve our understanding of how ocean circulation in fjords contributes to glacial melt and retreat, which will help improve projections of sea level rise and changes in marine life in these regions. This project will enable the training of a postdoctoral researcher (as the primary investigator) and provide funds to mentor two summer undergraduate students. Currently, there are order-of-magnitude discrepancies between observed and predicted melt rates at marine-terminating glaciers. Recent models suggest that the energetic dynamics at the ice-ocean boundary layer and submesoscale variability within fjords potentially contribute to these elevated melt rates. These discrepancies are hypothesized to arise from multi-scale ice-ocean interactions, with important processes and melt-circulation feedbacks across these scales that together contribute to an amplified melt rate. High-resolution submesoscale-resolving simulations of fjords and Large Eddy Simulations (LES) of the glacial ice-ocean boundary will be used to test the hypothesis that fjord submesoscale variability is a primary source of eddy kinetic energy within fjords and is potentially excited by a combination of shear, convective, and centrifugal instabilities driven by melt over the entire glacial front. These results will be used to test and develop improved parameterizations for the ice-ocean boundary layer that are consistent with previous and ongoing observations at the submarine face of LeConte Glacier, Alaska. These improved parameterizations will reduce uncertainty in glacial melt rate estimates (and thus, sea level rise projections) and improve our understanding of fjord circulation and its influence on polar coastal biogeochemistry. These improvements also likely to benefit our understanding of other types of ice-ocean boundaries.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.