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

Abstract

Based on latest estimates (e.g., https://sealevel.nasa.gov), global mean sea level has risen nearly 100 mm since 1993. However, the rate of rise has not been constant in space or time and recent observations (since ∼ 2008) reveal pronounced regional acceleration in the Gulf of Mexico (GoM). Here we use model solutions and observational data to identify the physical mechanisms responsible for enhanced rates of coastal sea-level rise in this region. We quantify the effect of offshore subsurface ocean warming on coastal sea-level rise and its relationship to regional hypsometry, the distribution of ocean area with depth. Using an Estimating the Circulation and Climate of the Ocean (ECCO) state estimate, we establish that coastal sea-level changes at the 10-year timescale are largely the result of changes in regional ocean mass, reflected in ocean bottom pressure. These coastal bottom pressure changes reflect both net mass flux into the Gulf, as well as internal mass redistribution within the Gulf, which can be understood as an isostatic ocean response to subsurface warming. We test the relationships among coastal sea-level, bottom pressure, and subsurface warming identified in ECCO using observations from satellite gravimetry, altimetry, tide gauges, and Argo floats. Estimates of mass redistribution explain a significant fraction of coastal sea-level trends observed by tide gauges. For instance, at St. Petersburg, Florida, this mass redistribution mechanism accounts for >50% of the coastal sea-level trend observed between 2008 and 2017. This study thus elucidates a physical mechanism whereby coastal sea-level responds to open-ocean subsurface density change.