Dense water formation in the Greenland Sea between 1999 and 2009

A 10-year continuous hydrographic data record from moored profilers located in the central Greenland Sea between 1999 and 2009 were used to examine the mixed-layer depth evolution through winter as well as interannual variability in water column properties and convection depth. The water column has become significantly warmer and more saline through the decade. The depth of convection each winter was a result of heat loss to the atmosphere, the water column stratification, and lateral fluxes of heat and salt. Even though the mixed-layer depth differed from year to year the evolution through each winter showed a similar pattern which could be separated into three distinct phases. Most of the mixed-layer cooling took place during the first phase. In the second phase the mixed layer deepened rapidly before it stabilized and restratified in the third phase at the end of the winter. The high temporal resolution of the data set allowed for a detailed investigation of the mixed layer and its direct response to atmospheric forcing on short time scales. The effect of short, intense atmospheric events, called cold air outbreaks, on the mixed layer depended strongly on which phase they occurred within. While strong atmospheric forcing in the first phase of the convection process mainly cooled the mixed layer, it led to a significant mixed-layer deepening during the second phase. Experiments done with a one-dimensional mixed-layer model suggested that intense events of heat loss early in winter are more favorable for deep convection to occur