On the synoptic hydrography of intermediate and deep water masses in the Iceland Basin

Abstract

The hydrography of intermediate deep water masses in the Iceland Basin is studied from quasi-synoptic surveys carried out in 1990 and 1991. The general water mass structure was identical for both years. The interaction and mixing of the different water types present in the basin is reviewed by means of property-property plots, vertical tracer sections and isopycnal analyses. It appears that overflow waters from the Norwegian Sea are modified in successive stages during their descent into the deep Iceland Basin. They mix with Sub-Polar Mode Water at short distances from the sills in the Faroe Bank Channel and on the Iceland-Faroe Ridge, thereby forming Iceland-Scotland Overflow Water. This water type entrains Labrador Sea water during the descent into the deep Iceland Basin, where Iceland-Scotland Overflow Water is further modified mainly by diapycnal mixing with overlying Lower Deep Water, which contains a large fraction of Antarctic Bottom Water. At intermediate levels Labrador Sea Water and Intermediate Water appear to mix laterally with a slope water mass flowing along the Icelandic and Reykjanes slopes. This slope water is formed by the direct mixing of Iceland-Scotland Overflow Water with Sub-Polar Mode Water and differs from the water mass, encountered in the central Iceland Basin. The intermediate and deep circulation in the Iceland Basin has a cyclonic character with smaller-scale variations due to topographic steering along ridges on the Icelandic slope.