Sea level changes in the North Atlantic by solar forcing and internal variability

Abstract

Sea level change due to variations in the thermohaline structure of the North Atlantic has been calculated using a coupled ocean-atmosphere model of intermediate complexity (ECBilt). Two 1000-year simulations are made, one using a constant solar forcing and one using an estimate of historic variations in solar activity. In the solar forced simulation sea level variations are a proxy for climate variations. Anomalies in sea surface temperature (SST) of the northern North Atlantic are generated by the solar radiation changes. These SST anomalies modulate the ocean thermohaline circulation (THC), affecting surface salinities in the northern North Atlantic which are subsequently advected to the deep ocean. The associated deep ocean geopotential thickness anomalies dominate sea level in the North Atlantic and are advected southwards with the overturning circulation. Sea level change in the solar forced simulation is primarily an indirect response to solar radiation changes, which modulate the THC. In the unforced run, changes in the THC affect sea level in a similar way. However, in this simulation THC variability is no longer generated by sea surface temperature variations but by sea surface salinity variations, resulting from internal climate dynamics. The present results will aid in analyses of reconstructed low-frequency sea-level variations based on proxy data.