Hydrographic variability of Denmark Strait Overflow Water near Cape Farewell with multi-decadal to weekly time scales

Abstract

Data in temperature and salinity from near-bottom layer of Denmark Strait Overflow Water in the Irminger Sea near 60°N are presented. These are hydrographic section data from data archives, literature, and CTD observations along the former WOCE AR7E line, as well as data from continuous measurements at two locations. For both salinity and temperature, hydrographic variability was present at all time scales that could be analysed, from multi-decadal to weekly. A mechanistic explanation for the primal cause of the hydrographic variability is still lacking. The direct cause of the observed variability has to be sought in variations of the properties of the source water types involved in the overflow across the sill in Denmark Strait, variations in the mutual ratios of these source water types, and in inhomogeneities in the DSOW layer. The strongest changes occurred at the longest time scales, as is often found for ultimately randomly forced geophysical time series. However, a significant annual cycle of the DSOW, not reported before, was observed at the foot of the East Greenland continental slope, likely a deterministic contribution to the hydrographic variability signal.