Sea level rise is one of the most threatening aspects of the present-day climate change, especially for low-lying and flood-vulnerable coastal regions

The National Oceanic and Atmospheric Administration (NOAA) awarded a $431,197 Cooperative Agreement under the Cooperative Institute (Inter-Agency Funded Activities) program (CFDA 11.405) to the University of Miami's Rosenstiel School of Marine and Atmospheric Science (RSMAS) to investigate the mechanisms of interannual-to-decadal dynamic sea-level variability along the U.S. East Coast. The research aims to understand how changes in the North Atlantic Western Boundary Current system, including the Loop Current in the Gulf of Mexico and the Florida Current, relate to coastal sea level and the frequency of nuisance flooding. The award will leverage high-resolution ocean models to estimate potential future increases in coastal sea level along the North Atlantic Western Boundary and their relationship to the projected decline of the Atlantic Meridional Overturning Circulation. The project builds on previously funded research and will run from January 1, 2025, to December 31, 2027.

The east coast of the united states (U. S.), including the gulf of mexico (GOM), has already been subject to higher-than-average rates of sea level rise, which is a superposition of the global mean sea level rise and dynamic sea level changes. While coastal flooding is mainly caused by synoptic storm surges, lower-amplitude, longer-term, and larger-scale dynamic sea-level changes along with the global mean sea level rise provide background conditions for tidal and synoptic fluctuations and significantly affect the frequency of coastal inundations. Due to geostrophy, sea level along the U. S. East coast is strongly linked to the north atlantic western boundary currents, consisting of the loop current in the GOM, the florida current in the florida straits, and the gulf stream further north. These currents contribute most of the northward volume and heat transport in the upper limb of the atlantic meridional overturning circulation (AMOC). Theoretical considerations along with the analyses of observational and model-simulated data suggest an antiphase relationship between the AMOC and the U.S. East coast dynamic sea-level. However, the actual relationships are more complex and can differ from one region to another. This proposal is a continuation of the previously funded research aimed to carry out the accurate attribution of the dynamic sea level variability along the U.S. East coast. Here, we propose to continue investigating the mechanisms of the interannual-to-decadal dynamic sea-level variability along the U. S. East coast using available observations and ocean models, with a particular focus on how changes in the large-scale ocean circulation are related to coastal sea level and the frequency of nuisance floods. Specifically, we will investigate how changes in the north atlantic western boundary current system is related to the gyre-scale interannual sea level variability in the north atlantic, known as the north atlantic tripole mode. Both are strongly linked with the north atlantic oscillation and with the AMOC-induced ocean heat and freshwater divergence/convergence. We will explore where and how the large-scale sea level signals generated in the ocean interior break through the western boundary current geostrophic barrier, HIT the U. S. East coast, and propagate into the GOM. We will evaluate how these processes affect the subseasonal-to-seasonal coastal sea level changes and how they modulate the frequency and amplitude of nuisance flooding. Most climate models contributing to the coupled model intercomparison project phase 6 (CMIP6) project a decline of the AMOC by 3445% of its present-day strength towards the end of the 21ST century. In climate models, a long-term decline in the AMOC is generally associated with a dynamic sea-level rise along the north atlantic western boundary. However, on interannual time scales, a weaker AMOC is associated with heat divergence in the subtropical gyre and thus a decreased sea-level in the subtropical band of the north atlantic tripole. We propose to reconcile this contrasting influence of the AMOC at the two different time scales. In addition, because coarse resolution CMIP models fail to realistically simulate the western boundary currents and coastal sea level variability, we propose to leverage the efforts of regional high-resolution dynamic downscaling of CMIP6 models carried out at aoml to estimate the potential future increases in coastal sea level along the north atlantic western boundary and investigate how these changes are related to the projected AMOC decline.