Tide gauge-based sea level variations since 1950 along the Norwegian and Russian coasts of the Arctic Ocean: Contribution of the steric and mass components

摘要

We investigate sea level change and variability in some areas of the Arctic region over the 1950-2009 period. Analysis of 62 long tide gauge records available during the studied period along the Norwegian and Russian coastlines shows that coastal mean sea level (corrected for Glacial Isostatic Adjustment and inverted barometer effects) in these two areas was almost stable until about 1980 but since then displayed a clear increasing trend. Until the mid-1990s, the mean coastal sea level closely follows the fluctuations of the Arctic Oscillation (AO) index, but after the mid-to-late 1990s the co-fluctuation with the AO disappears. Since 1995, the coastal mean sea level (average of the Norwegian and Russian tide gauge data) presents an increasing trend of ～4 mm/yr. Using in situ ocean temperature and salinity data down to 700 m from three different databases, we estimated the thermosteric, halosteric and steric (sum of thermosteric and halosteric) sea level since 1970 in the North Atlantic and Nordic Seas region (incomplete data coverage prevented us from analyzing steric data along the Russian coast). We note a strong anti-correlation between the thermosteric and halosteric components both in terms of spatial trends and regionally averaged time series. The latter show a strong change as of ～1995 that indicates simultaneous increase in temperature and salinity, a result confirmed by the Empirical Orthogonal Function decomposition over the studied region. Regionally distributed steric data are compared to altimetry-based sea level over 1993-2009. Spatial trend patterns of observed (altimetry-based) sea level over 1993-2009 are largely explained by steric patterns, but residual spatial trends suggest that other factors contribute, in particular regional ocean mass changes. Focusing again on Norwegian tide gauges, we then compare observed coastal mean sea level with the steric sea level and the ocean mass component estimated with GRACE space gravimetry data and conclude that the mass component has been increasing since 2003, possibly because of the recent acceleration in land ice melt.