The water mass characteristics of the Northeast Water Polynya: Polar Sea data 1992–1993

Hydrographic cruises in the summers of 1992 and 1993 were carried out in the North-East Water (NEW) Polynya. For both years, CTD casts on the NEW Polynya shelf area yielded a signature of a highly homogeneous, cold (θ = −1.74°C) and relatively fresh (S = 32.40 ppt) water just below the surface pycnocline, which we refer to as the Northeast Water Polynya Intermediate Water (PyIW). Its homogeneity, its location and the fact that its core temperature is very close to the freezing point all suggest that this water is formed convectively through a loss of buoyancy to the atmosphere over the open portions of the Polynya. The source waters are the low salinity surface waters found in the northern sector of the Polynya area. The thickness of the PyIW varied from 10 to 60 m throughout the northern (Norske-Westwind through system) and central (Belgica Bank) portion of shelf region. It was not found over the slope nor in Belgica Trough immediately to the south. A volumetric θ-S analysis of the PyIW demonstrated that it suffered a small loss between the two years and that its areal distribution and core water type remained virtually constant. Some qualitative assessments are made concerning its formation and loss. The small interannual variability of the PyIW layer implies a high residence time that has important physical and biological repercussions. The summer modification of the Polynya surface waters is also discussed; and by relating the water-type change with the summer heat budget, estimates of 47 and 75 cm were made for the amount of ice thinning occurring over the area for the two years, respectively. The water found below the sills (at 265 m) of the Norske-Westwind Trough system has a warmer (θ = 0.78°C) and saltier (S = 34.83 ppt) water type, than that of the PyIW, which characterizes it as a species of return Atlantic Intermediate Water.