The Arctic has been undergoing rapid climate changes for several decades, including dramatic warming with the surface temperature increasing at a rate of 2 times larger than the global mean which is usually called the Arctic amplification. In this paper, we will use a set of processed altimeter sea level data by Armitage et al. (2016, 2018) from CPOM (Centre for Polar Observation and Modelling, University College London) to validate the sea surface height (SSH) data from the new published reanalysis dataset, ORAS5, by the European Centre for Medium-Range Weather Forecasts (ECMWF). And then we will use the ORAS5 sea surface height data to analyze the sea level variation of the Arctic Ocean since 1979 (since when sea ice is observed by remote sensing).

We use the monthly SSH data of ORAS5 from 1979 to 2018 to analyze the features of the seasonal and inter-annual Arctic sea level variability. The climatological SSH in the Arctic Ocean shows a prominent contrast between the high SSH in the Canadian Basin, associated with the anticyclonic Beaufort Gyre, and the low SSH in the Greenland Sea related to the cyclonic Greenland Sea gyre, and the significant gradients of SSH between them is associated with the transpolar drift. EOF analysis shows the most important sea level variability in the Arctic Ocean is seasonal. The largest amplitude of seasonal cycle occurs in the East Siberian Sea. The seasonal sea level variability is associated with the seasonal cycle of atmospheric circulation and sea ice. The second important EOF mode of sea level variability is the inter-annual variability related to AO, which shows an obvious sea level oscillation between deep basins (> 500 m) and coastal seas (< 500 m). The temporal evolution of the second mode is in good correlation to the accumulative AO index. We also find the influence of Arctic Dipole Anomaly (DA) to the low-frequency Arctic sea level variation in the EOF analysis.

During the time period of this study, the sea level in most areas of the Arctic Ocean shows rising trend. A contrast sea level trend can be found in the deep basin, with the Canadian basin having the fastest sea level rise with the rate up to 8mm/a. The coastal seas also have obvious sea level rise, with an average rate of about 3 mm/yr. The mean sea level of the Arctic Ocean has a rate of about 2.7 mm/yr. Obviously, the decadal sea level trend of the Arctic Ocean is consistent with Arctic amplification, and due to the shallow water effect, the Arctic sea level may continue to rise at a rate larger than the global mean sea level.