CoAuthors

Kate Zhang (JIFRESSE, University of California Los Angeles, United States); William Johns (University of Miami, United States); Joshua Willis (Jet Propulsion Laboratory, United States); Will Hobbs (University of Tasmania, Australia); Marlos Goes (CIMAS/University of Miami/NOAA-AOML, United States); Hong Zhang (Jet Propulsion Laboratory, United States); Dimitris Menemenlis (Jet Propulsion Laboratory, United States)

The system of ocean currents in the Atlantic Ocean, characterized by a northward flow of warm and salty water in the upper layers and a southward flow of colder and fresher water at depth, is called the Atlantic Meridional Overturning Circulation (AMOC). By redistributing heat and other properties, the AMOC influences the global and regional climate, weather, sea level, and ecosystems. Climate models suggest that the AMOC may slow down towards the end of this century in response to the emission of greenhouse gases. A simple dynamic mechanism implies that an AMOC slowdown will accelerate sea level rise and increase the frequency of floods along the North America east coast. Here, we explore an alternative mechanism, according to which the AMOC-induced redistribution of heat causes large-scale warming and cooling, with the associated sea level increase and decrease, respectively. Specifically, when the subtropical North Atlantic warms and its sea level increases, the subpolar North Atlantic and the tropics cool and their sea levels decrease, and vice versa. This gyre-scale variability pattern is known as the North Atlantic sea surface temperature and sea surface height tripole. The tripole exerts its influence on sea level along the U.S. East coast. It is most influential south of Cape Hatteras and in the Gulf of Mexico, where the tripole-related coastal sea level changes can reach amplitudes of about 10 cm, which is close to the magnitude of the global mean sea level rise over the last 30 years. It is shown that the AMOC-induced heat transport led to a substantial warming in the subtropical North Atlantic in 2010-2015, accelerated coastal sea level rise along the South Atlantic Bight and Gulf of Mexico coasts, and dramatically increasing the risk of floods. The study finds that 30-50% of local flood days in 2015-2020, when the subtropical North Atlantic was exceptionally warm, can be attributed to the AMOC-induced redistribution of heat in the North Atlantic.