ALBERT

Description: The Nordic Seas constitute the main ocean conveyor of heat between the North Atlantic Ocean and the Arctic Ocean. Although the decadal variability in the subpolar North Atlantic has been given significant attention lately, especially regarding the cooling trend since the mid-2000s, less is known about the potential connection downstream in the northern basins. Using sea surface heights from satellite altimetry over the past 25 years (1993–2017), we find significant variability on multiyear to decadal timescales in the Nordic Seas. In particular, the regional trends in sea surface height show signs of a weakening since the mid-2000s, as compared to the rapid increase in the preceding decade since the early 1990s. This change is most prominent in the Atlantic origin waters in the eastern Nordic Seas and is closely linked, as estimated from hydrography, to heat content. Furthermore, we formulate a simple heat budget for the eastern Nordic Seas to discuss the relative importance of local and remote sources of variability; advection of temperature anomalies in the Atlantic inflow is found to be the main mechanism. A conceptual model of ocean heat convergence, with only upstream temperature measurements at the inflow to the Nordic Seas as input, is able to reproduce key aspects of the decadal variability in the heat content of the Nordic Seas. Based on these results, we argue that there is a strong connection with the upstream subpolar North Atlantic. However, although the shift in trends in the mid-2000s is coincident in the Nordic Seas and the subpolar North Atlantic, the eastern Nordic Seas have not seen a reversal of trends but instead maintain elevated sea surface heights and heat content in the recent decade considered here.

Description: We present a binned product of sea surface temperature, sea surface salinity, and sea surface density data in the North Atlantic subpolar gyre from 1993 to 2017 that resolves seasonal variability along specific ship routes (https://doi.org/10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work were collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The data were binned along a selected usable transect. The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal timescales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the West Greenland Shelf. Variability in sea surface salinity increases towards Newfoundland south of 54∘ N, as well as in the western Iceland Basin along 59∘ N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.

Description: We present a binned product of sea surface temperature, sea surface salinity and sea surface density data in the North Atlantic subpolar gyre for the 1993–2017 that resolves seasonal variability along specific ship routes (doi:10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work was collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal time scales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the west Greenland shelf. Variability in sea surface salinity increases towards Newfoundland south of 54° N, as well as in the western Iceland Basin along 59° N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.