Mechanisms of decadal sea level variability in the Eastern North Atlantic and the Mediterranean Sea

Abstract

[eng] Decadal sea level variations from tide gauge records along the Western European coast and in the Mediterranean Sea commencing in the late 19th and early 20th centuries are examined relative to large-scale atmospheric forcing. Recent studies have provided evidence for a link between sea level in the Eastern North Atlantic and atmospheric forcing, however the nature of this relationship is still unclear. Here the outputs of a regional barotropic model and a nearly global baroclinic model are used in conjunction with wind stress and heat flux data to explore the physical mechanisms responsible for the observed sea level variability. All tide gauge records show significant decadal variability (up to 15 cm) and are highly correlated with the NAO and among themselves at decadal periods. There is a coherent sea level signal that affects the eastern boundary of the North Atlantic northward of 25ºN and is limited to a narrow band of the order of a few hundred kilometers along the coast. This band tends to become narrower towards higher latitudes. We find that longshore wind and wave propagation along the boundary are the major contributors to coastal sea level variability but no significant contribution from mass redistribution linked to changes in the strength of the subtropical gyre is observed. The mass component dominates sea level in the Mediterranean and is mainly driven by mass exchanges with the Atlantic, which explains the correlation between both regions. Southward of 25ºN, sea level changes are mainly driven by heat advection through Ekman fluxes.