Two types of thermobaric deep convection possible in the Greenland Sea

Abstract

[1] A numerical experiment has been executed with a fine-resolution (grid size of 1 m), two-dimensional model to investigate detailed features of open ocean deep convection related to the nonlinearity of the equation of state for seawater and to interpret recent summer observations in the Greenland Sea, suggesting two types of winter convection. When cold, fresh waters (Arctic origin) occupy the surface mixed layer, convective overturning of the water column occurs abruptly. Thermobaric convective plumes branch into small-scale (∼O(10 ∼ 100 m)) eddies and engulf ambient deep water on the way down. They induce significant fluctuations in profiles of water properties but do not homogenize the overturned layer completely. As a result, stable stratification remains at depths where temperature, salinity, and potential density decrease. When warm, saline waters (Atlantic origin) exist in the surface mixed layer, it deepens by surface cooling, entraining the underlying water vigorously. Water properties are nearly homogenized in the deepening mixed layer and have opposite features to the first case. These results support a deduction that two different profiles of water properties observed in the Greenland Sea are signatures of two types of deep convection.