Oceanographic Variations in Recent Decades and Their Impact on 
the Fertility of the Iceland Sea 
Unnsteinn Stefansson 
Marine Research Institute, P.O. Box 390, Skulagata 4, Reykjavik, ICELAND 
Due to its location at or near the oceanic polar front, the Iceland Sea (Fig. 1) is an area 
particularly sensitive to climatic changes. In warm years a strong influx of Atlantic water from 
the Irminger Sea can be traced all along the North Icelandic shelf area. This inflow is mainly 
determined by past meteorological conditions at the west and north coasts of Ireland 
(Steffansson, 1962; Stefansson and Gudmundsson, 1969). In periods when the ice belt along the 
east coast of Greenland is relatively narrow, the surface layers between Iceland and Jan Mayen 
consist of arctic water with practically no polar component. Conversely, in cold periods an 
appreciable proportion of cold, low-salinity polar water is found in this area, and large parts of 
the North Icelandic shelf area may be covered with drift ice. Sea surface temperatures north 
of Iceland, especially in spring, are closely correlated to the frequency and extension of drift 
ice (Stefansson, 1969; Malmberg, 1972). 
Changes during this century in North Icelandic waters have been characterized by i) a 
general warming up during the first decades (Stefansson, 1969) culminating in the thirties; ii) a 
slight downward trend in the forties and fifties, followed by a greatly increased extension of 
drift ice and a marked lowering of temperature and salinity in the period 1965-1971; and iii) in 
the last decade very cold years have alternated with relatively mild ones (Figs. 2-3). These 
variations can be traced down to a depth of 100-200 m, both in the North Icelandic shelf area 
and in the deep area between Iceland and Jan Mayen (Stefansson, 1969; Stefansson, 1968). At 
200-500 m in that region the temperatures have in general been slightly higher since 1965 than in 
the preceding period, presumably as the result of shallower winter convection due to lower 
salinities in the surface layers. There is no significant difference between the mean salinity 
(34.92) at 1000 m in the two periods 1949/1957 and 1973/1980. 
Since the overflow across the Iceland-Greenland Ridge probably consists largely of Arctic 
intermediate water including winter water from the Iceland Sea (Stefansson, 1968; Mann, 1969; 
Swift et al., 1980), changes in the salinity of that water may be reflected in the Overflow 
water. On the other hand, very rapid changes are known to exist in the Overflow, both with 
regard to T,S-characteristics and velocity. Hence the importance of monitoring both the short- 
period and long-period variations of the Overflow should be emphasized. At the same time the 
causes of short-periodic fluctuations need to be studied. 
bya 24° 16° Se 
J 
Fig. 1. The average residual surface currents of the Iceland Sea referred to 
the warm period before 1965 (Stefansson, 1961). 
