The Greenland Sea in Water 1993 and 1994: preconditioning for deep convection

Abstract

We present here a detailed analysis of the time-dependent large-scale and mesoscale features observed in the Greenland Sea during winter and spring 1993 and 1994. Based on a comprehensive data set, this study gives particular emphasis to the data from hydrology and RAFOS-VCM floats. In both years, the basin underwent an overturning to 1000 and 800 m depth, respectively, with extensive horizontal variability. These inhomogeneities are shown to be closely linked with mesoscale eddies identified at a late stage during the preconditioning phase to deep convection. It is suggested that these eddies are remnants of previous convective events. One of them, found at 500 m depth in 1994, was thoroughly studied. The dynamical coupling between the eddy and the modified Atlantic Water (mAW), advected over it from the northwest, led to the deepest convected water column found within the basin during this particular year. Sea ice, absent in the gyre in winter 1994, but partly present in the colder 1993 winter, does not appear to be a strong prerequisite for deep convection. Heat loss at the surface, combined with salt input by the mAW, and remnant subsurface mesoscale eddies of past convective events, are the most likely agents that determine the depth reached by convection and the characteristics of the new Greenland Arctic Intermediate Water formed in the Greenland Gyre in 1993 and 1994.