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

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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.