Processes Driving Interannual Variability of Deep Convection in the Nordic Seas from an Ensemble of Earth System Model Historical Simulations
Journal Article
Overview
abstract
Abstract; The Nordic seas play an important role in the polar and global climate system, connecting the subpolar North Atlantic to the Arctic Ocean, while also being the primary region for the formation of lower North Atlantic Deep Water, a key contributor to the Atlantic meridional overturning circulation. Oceanic deep convection in the Nordic seas undergoes considerable interannual variability, as indicated by local observational and reanalysis studies and by the variability of the observed transport of the Denmark Strait overflow. In this paper, we investigate the oceanic and atmospheric processes associated with this variability using results from a global, fully coupled Earth system model configuration with regional refinement of the horizontal resolution in the Arctic and subarctic in all model components (ocean, sea ice, atmosphere, and land models). We consider an ensemble of five simulations with historical variations of greenhouse gases over the period 1950–2014. In these experiments, Nordic seas convection features strong interannual variability. We find that high convection winters are accompanied by two separate scenarios with active drivers in the ocean and the atmosphere, respectively, occurring partly independently and partly at the same time: enhanced salinity advection via the Atlantic Water inflow into the Nordic seas and an increased frequency of synoptic cyclonic circulation patterns over Scandinavia and the Norwegian Sea with associated northerly winds across the Nordic seas. Both scenarios lead to similar conditions that enhance oceanic deep convection: sea ice reduction (in the Greenland–Iceland Seas) and increased heat flux exchanges in the ocean interior.; ; Significance Statement; The purpose of this work is to study processes in the ocean and atmosphere that affect the intensity of deep convection in the Nordic seas. This is important because deep convection is associated with the formation of water masses that feed into the Atlantic meridional overturning circulation, which, in turn, helps redistribute heat within Earth system. We find that the primary trigger for deep convection in the Nordic seas is enhanced advection of warm and saline Atlantic Water, which, combined with more frequent cold northerly winds, leads to enhanced heat fluxes between the warm upper ocean and the colder atmosphere on top. On the Greenland side of the Nordic seas, this process is also modulated by sea ice.;
