Oceanographic context. (a) Annual mean climatological (1955–2012 mean) temperature (colours) and salinity (contours) from a vertical section across 75°N (highlighted by the yellow bar), highlighting the different water-masses22. 75°N is chosen because it most clearly illustrated the water-mass structure. This water-mass structure is present throughout the open water of the GIN seas, but with the volume of Arctic-sources waters decreasing to the south. (b) Greenland-Iceland-Norway Seas schematic with bivalve site location (yellow circle), at 66°31.59′N, 18°11.74′W, 80 m water depth). c and d: Zonally averaged annual mean climatological (1955–2012 mean) temperature (contour colours, °C) and density (contour lines, kg.m−3) from the (c) West (averaged from 15.75–13.75°W) of Iceland and (d) East (averaged from 23.75–21.75°W) of Iceland22 as illustrated by the grey regions on the outline map of Iceland.