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In this study, we investigated contributions of both local steric and remote baroclinic eects (i.e., steric variations external to the region of interest) to the inter-annual variability of winter sea level in the North Sea, with respect to the North Atlantic Oscillation (NAO), for the period of 1953−2010.On inter-annual time scales in this period, the NAO is signicantly correlated to sea level variations in the North Sea only in the winter months (December−March), while its correlation to sea temperature over much of the North Sea is only signicant in January and February. The discrepancy in sea level between observations and barotropic tide and surge models forced by tides and local atmospheric forcing, i.e., local atmospheric pressure eects and winds, in the present study are found to be consistent with pre- * Corresponding author. Tel. +49 40 42838 5753 Email address: xinping.chen@zmaw.de (Xinping Chen ) Preprint submitted to Elsevier September 11, 2014 vious studies. In the North Sea, local thermosteric eects caused by thermal expansion play a minor role on winter-mean NAO related sea level variability compared with NAO related atmospheric forcing. This is particularly true in the southeastern North Sea where water depths are mostly less than 25 m.Our calculations demonstrate that the discrepancy can be mostly explained by remote baroclinic eects, which appear as water mass exchanges on the continental shelf and are therefore only apparent in ocean bottom pressure.In the North Sea, NAO related sea level variations are a hybrid of barotropic and baroclinic processes. Hence, they can only be adequately modelled with three-dimensional baroclinic ocean models with more realistic open boundary conditions (than barotropic models) that allow the exchange of heat and salt.

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