After more than a decade of shallow or non-existent convection currents in the Labrador Sea — with only a brief return to deep-water convection at the turn of the century — the carbon-dioxide-sequestering subpolar gyre in the North Atlantic Ocean seems to have bounced back.
Kjetil Våge of the Woods Hole Oceanographic Institution in Massachusetts and his colleagues report data from the system of floats known as the Argo programme. These show a return last winter to mixing as deep as 1,800 metres in the Labrador Sea, 1,000 metres in the Irminger Sea and 1,600 metres south of Greenland. Triangles in the image (above) indicate these depths (in metres).
The change happened surprisingly quickly. The reasons for it include unusually low air temperatures, an increased flux of fresh water and pack-ice from the Arctic and changes in the North Atlantic storm track.