Influence of Deep-Ocean Warming on Coastal Sea-Level Trends in the Gulf of Mexico 

<p class="p1"><span class="s1">Thirty years of satellite-altimeter data and longer tide-gauge records show that rates of coastal sea-level rise are increasing across parts of the global ocean. Such sea-level acceleration is particularly pronounced along the U.S. Gulf of Mexico coastline. Here, we use model output and observational data to investigate the mechanisms underlying these enhanced regional rates of change. Interrogating the Estimating the Circulation and Climate of the Ocean (ECCO) Version 5 ocean state estimate, we find that interannual-to-decadal coastal sea-level changes in the Gulf of Mexico largely reflect local changes in ocean mass. Based on model diagnostics, we determine that important contributions to coastal ocean-mass changes are made by: 1) net mass flux into the Gulf and 2) mass redistribution related to ocean warming within the Gulf. The redistribution of mass within the Gulf can be understood as an isostatic ocean response to warming of the Gulf of Mexico below the seasonal mixed layer. Observations of ocean bottom pressure from the Gravity Recovery and Climate Experiment (GRACE/GRACE-FO) similarly reveal trend patterns suggestive of redistribution of mass from deeper regions in the Gulf onto the shelf. This redistribution is driven by subsurface warming observed in Argo measurements of temperature. Since ~2008, rates of subsurface Gulf warming have increased, driving an increase in sea-level trends at the coast. Together, the mass flux into the Gulf and warming-driven redistribution of mass onto the shelf explain a dominant fraction of coastal sea level trends observed at tide gauge stations throughout the Gulf, particularly along the west Florida shelf. The mechanism identified here, relating offshore subsurface warming to coastal sea level, reveals the importance of open-ocean effects on the coast and also bathymetric geometry in shaping an observed response to warming. Results highlight the ability of ocean bottom pressure measurements from GRACE to capture the spatially varying redistribution of mass driven by oceanic uptake of heat.&#160;</span></p>