Subinertial variability across and around the Greenland-Scotland Ridge and its impacts on the ocean circulation

本项目将研究格陵兰-苏格兰海脊(GSR)环流，其中北向流动的暖流和咸水表面流与南向流动的密集溢流和北极外流相遇，以在一系列高分辨率现实数值模式模拟中量化次惯性变化(周期为几天到几十天)与时间平均流相比的相对重要性。这项工作将量化亚惯性变化对以下方面的影响：(1)进出GSR两侧深海盆地的跨脊体积输送；(2)跨锋面水团交换；(3)浅层大陆架上下跨陆架突破体积输送。将首次在GSR范围内估计沿海脊的大陆架(格陵兰、冰岛、法罗和苏格兰大陆架)上的体积、热量和盐通量，包括它们的空间和时间变异性。项目成果将提供对GSR变异性的性质和重要性的基本了解，GSR变异性在全球气候系统中发挥着关键作用，并为潜在的观测战略提供信息。更广泛的影响包括支持职业生涯早期的女性个人投资和培训本科生以获得实际研究经验。亚惯性变率超过海峡、GSR沿线以及冰岛和法罗群岛周围(靠近沿海边缘的潮汐除外)的季节和超惯性变率，以及它可能主导GSR上某些地方的时间平均气流的假设，将通过几个目标进行测试。这些活动包括：确定次惯性流、海面高度和等高度位移变率的特征；量化这种变率如何影响跨脊线体积输送；描述与高输送事件有关的空间结构和尺度，以及由于跨锋面热和盐通量而改变水团性质；以及量化次惯性变率如何影响跨脊线体积输送。基于这些发现，将推荐一种观测策略来捕捉对平均气流重要的亚惯性变率。将使用的工具包括麻省理工学院大气环流模式(MITgCM)区域海洋-海冰配置的三个现有的为期一年的流体静力模拟，它们已被证明真实地代表了区域海洋的性质和动态。将使用用于拉格朗日分析的离线粒子跟踪工具(由PI开发)，该工具使用具有预测-校正方案的梯形求解器，并使用完整的四维速度场来计算粒子轨迹。公开可用的数据集将用于模型与数据的比较。目标是量化数值模拟的真实性和估计偏差，并阐明稀疏、间歇观测和不准确模拟中的补充信息。将使用的产品包括水文剖面、系泊时间序列、滑翔机数据集以及网格和沿轨测高数据产品。如果计划中的地表水和海洋地形(SWOT)任务的质量控制高分辨率卫星测高在本项目持续时间内发布，它们也将得到利用。这一奖励反映了NSF的法定任务，并已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。

This project will examine Greenland-Scotland Ridge (GSR) circulation, where northward-flowing warm and saline surface currents meet southward-flowing dense overflows and Arctic outflows, to quantify the relative importance of subinertial variability (with periods of days to tens of days) compared to the time-average flow in a series of high-resolution realistic numerical model simulations. The work will quantify the impact of subinertial variability on (1) cross-ridge volume transports to and from the deep ocean basins on either side of the GSR; (2) cross-frontal water mass exchange; and (3) cross-shelfbreak volume transport on and off the shallow continental shelves. The first GSR-wide estimates of volume, heat, and salt fluxes across continental shelfbreaks along the ridge (the Greenland, Iceland, Faroe, and Scottish shelves) will be provided, including their spatial and temporal variability. Project outcomes will provide fundamental understanding of the nature and importance of GSR variability, which plays a key role in the global climate system and inform potential observing strategies. Further broader impacts include support of an early-career female PI and train an undergraduate student to gain practical research experience. Hypotheses that subinertial variability exceeds seasonal and superinertial variability in channels, along the GSR, and around the Iceland and the Faroes (excepting tides close to coastal margins) and that it may dominate the time-mean flow in some places on the GSR will be tested by addressing several objectives. These include characterizing subinertial current, sea surface height and isopycnal displacement variability; quantifying how such variability impacts the cross-ridge volume transport; characterizing the spatial structures and scales associated with high-transport events, and how water mass properties are modified due to cross-frontal heat and salt fluxes; and quantifying how subinertial variability impacts the cross-shelfbreak volume transport. Based on these findings, an observational strategy will be recommended to capture the subinertial variability where it is important to the mean flow. Tools to be used include three existing one-year-long hydrostatic simulations from regional ocean-sea ice configurations of the Massachusetts Institute of Technology general circulation model (MITgcm), which have been shown to realistically represent the regional ocean properties and dynamics. An offline particle tracking tool for Lagrangian analyses (developed by the PIs) will be used, which employs a trapezoidal solver with a predictor-corrector scheme, and uses the full four-dimensional velocity fields to calculate particle trajectories. Publicly-available data sets will be used for a model-data comparison. Goals are to quantify the realism of the numerical simulations and estimate bias, and to elucidate the complementary information in sparse, intermittent observations and inaccurate simulations. Products to be used include hydrographic profiles, mooring timeseries, glider datasets , and gridded and along-track altimetry data products. If quality-controlled high resolution satellite altimetry from the planned Surface Water and Ocean Topography (SWOT) mission are released within the duration of this project, they will also be utilized.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.