On the relationship between the meridional overturning circulation, alongshore wind stress, and United States East Coast sea level in the Community Earth System Model Large Ensemble

By the late twenty-first century, climate models project enhanced dynamic sea level (DSL) rise along the western boundary of the North Atlantic associated with a decline in the Atlantic meridional overturning circulation (AMOC). In contrast, coastal DSL variability over the last few decades has been driven largely by local winds, with limited evidence for coupling to AMOC strength. The unclear forcing-dependence and timescale-dependence of relationships between local winds, AMOC strength, and DSL obscures: (1) the validity of tide gauge-derived DSL gradients as a proxy of AMOC strength and (2) the assessment of climate model reliability. Here we analyze these relationships in the Community Earth System Model Large Ensemble (CESM-LE) over the 1920-2100 period. In CESM-LE, the amplitude of interannual to multidecadal DSL variability and its along-coast correlation are comparable to detrended annual mean tide gauge records. A crossover timescale'' of approximately 5-15 years partitions a local wind-driven coastal DSL regime from an overturning-related regime. Processes unrelated to either AMOC strength or local winds are important at interannual to decadal timescales. As external forcing increases in strength over the twenty-first century, DSL variability associated with the overturning circulation becomes dominant. While the largely externally forced, AMOC-associated, component explains only 29 +/- 12% of DSL variance over the 1920-2010 period, it explains 89 +/- 3% of the variance in the 2011-2100 period. We discuss the implications of these results on the reliability of climate model projections of regional DSL, the use of coastal DSL as a proxy for AMOC, and the origins of multidecadal DSL variability.