Labrador Sea convection blows life towards the northeastern Atlantic

Deep convection in the Labrador and Irminger Seas inflates the cold and low-saline subpolar gyre, which is a rich nutrient and zooplankton source for the surrounding warmer waters of subtropical origin. Based on zooplankton observations and an ocean model simulation forced with atmospheric reanalysis fields, we show that northeastward shifts of the subpolar gyre limb in the Irminger Sea result in biologically productive periods in the waters southwest of Iceland – both oceanic and on the shelf. The on-shelf zooplankton abundances show characteristic sub-decadal variability, which closely reflects the oceanic abundances of the ecologically most important zooplankton species – Calanus finmarchicus. The abundance of this species is furthermore related to the winter mixed layer depth (MLD) in the northern Irminger Sea. The MLD variability is regulated by remote heat losses and convection in the Labrador Sea, through northward advection of unstable Labrador Waters, together with regional atmospheric forcing. Lateral shifts of the biologically productive subarctic front southwest of Iceland might also influence on-shelf zooplankton abundance. The sub-decadal oceanic and on-shelf biological production peaks are possibly predictable by half a year (local winter convection to subsequent summer production), and the advective time-lag from the Labrador Sea might induce an even longer predictability horizon (up to 1.5 years).