Influence of Deep-Ocean Warming on Coastal Sea-Level Trends in the Gulf
of Mexico
Abstract
Rates of sea-level rise are increasing across the global ocean. Since
$\sim 2008$, sea-level acceleration is particularly
pronounced along the US Gulf of Mexico coastline. Here we use model
solutions and observational data to identify the physical mechanisms
responsible for enhanced rates of recent coastal sea-level rise in this
region. Specifically, we quantify the effect of offshore subsurface
ocean warming on coastal sea-level rise and its relationship to regional
hypsometry. Using the Estimating the Circulation and Climate of the
Ocean (ECCO) Version 5 ocean state estimate, we establish that coastal
sea-level changes are largely the result of changes in regional ocean
mass, reflected in ocean bottom pressure, on interannual to decadal
timescales. These coastal ocean bottom pressure changes reflect both net
mass flux into and out of the Gulf, as well as internal mass
redistribution within the Gulf, which can be understood as an isostatic
ocean response to subsurface offshore warming. We test the relationships
among coastal sea-level, ocean bottom pressure, and subsurface ocean
warming predicted by the model using data from satellite gravimetry,
satellite altimetery, tide gauges, and Argo floats. Our 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 accounts for $>$
50\% of the coastal sea-level trend observed over the
2008-2017 decade. This study elucidates a physical mechanism whereby
coastal sea-level responds to open-ocean subsurface warming and
motivates future studies of this linkage in other regions.