Forcing of Subannual‐to‐Decadal Sea Level Variability and the Recent Rapid Rise Along the U.S. Gulf Coast

Abstract From the mid‐late 2000s through at least the mid‐2010s, dynamic sea level (DSL) along the U.S. Gulf Coast rose at a rate of ∼5–6 mm , almost twice the rate of global mean steric plus barystatic sea level rise. Previous statistical and numerical modeling studies have suggested a number of hypotheses for this enhanced rise. However, the contributions from various atmospheric and hydrologic forcings had not yet been quantified in a physical model. This study quantifies forcing contributions to DSL using adjoint sensitivities from the observationally‐constrained Estimating the Circulation and Climate of the Ocean (ECCO) state estimation framework. DSL reconstructions with air‐sea fluxes from the ECCO state estimate and JRA55‐do river discharge show that winds along the Gulf and U.S. Atlantic coasts generate ∼80%–90% of subannual and 55%–70% of interannual variability of Gulf Coast DSL, indicating the dominant influence of coastal Kelvin and topographic Rossby waves at these shorter timescales. In contrast, only 1.0–1.6 mm (20%–30%) of the 2006–2017 DSL rise is associated with winds along the coastal waveguide. The remainder of the 2006–2017 DSL rise is associated with winds and heat fluxes in the tropical Caribbean and Atlantic (2.0–2.2 mm ), and winds and heat/freshwater fluxes in the subtropical‐to‐subpolar North Atlantic (1.7–1.9 mm ). A decline in Mississippi river discharge during this same period produced a decrease in Gulf Coast DSL that was most impactful along the western Gulf Coast (−1.0 mm ), reducing the rapid rise slightly.