Jökull - 01.12.1969, Blaðsíða 34

Hydrographic Changes in the Waters Between
Iceland and Jan Mayen in the Last Decade
SVEN D-AAGE MALMBERG,
MARINE RESEARCH INSTITUTE, REYKJAVÍK, ICELAND
ABSTRACT
During the last few years a change has taken
place in the proportions of the different water
masses in the East-Icelandic Current northeast
of Iceland (Fig. 1). It is shown that the current
has changed from being an ice-free arctic cur-
rent in 1948—1958 to a polar current in 1964—
1968, transporting drift ice and preserving it,
especi.ally in the years 1965, 1967 and 1968. As
seen in Fig. 2 the salinity of 34.7%c is of special
interest in the area these last years. As demon-
strated in Fig. 11 this salinity is the critical one
for the area in question, should the surface
layer cool doiun to freezing point, —1.8° C.
At salinities of 34.7%c or lower the surface water
will not reach a density high enough to start
a deep vertical convection even at a tempera-
ture of —1.8° C, but at salinities of 34,8%c
or more this is possible. That means in the
latter case a deep vertical convection before
such a strong cooling is reached. The drift ice
conditions were extremely unfavourable in
North ancl East Icelandic waters in the spring
of 1965, 1967 and 1968. Thus a close relation-
ship between drift ice and hydrographic condi-
tions in the Easl-Icelandic Current is establish-
ecl, throwing light on the physical causes of
the situation.
A knoiuledge of the stratification, i. e. the
salinity in the surface layer, in late xuinter be-
tiueen Iceland and Jan Mayen, may, in con-
nection xuith knowledge of the atmospheric
circulation and air temperature, be a tool for
the precliction of ice in Icelandic luaters in
spring and summer.
INTRODUCTION
Between Langanes in northeast Iceland and
Jan Mayen we find the cold water of the East-
30 JÖKULL 19. ÁR
Icelandic Current, first described by the Dan-
ish oceanographer Martin Knudsen (1898). In
this area the current reaches depths of ca. 200
m. According to Stefánsson (1962, pp. 36—37)
this current consisted more or less of Arctic
water composed of a mixture of Polar water
(S < 34%c, t < 0° C) with water originallv
corning from the Norwegian Atlantic Current
(Helland-Hansen and Nansen, 1909, p. 319),
Atlantic water (S > 35%c) from the Irminger
current north of Iceland, and North Icelandic
Winter water (t = 1-2° C, S = 34.85-34.90%o).
In June 1965 it was noteworthy how much
farther south and east the cold tongue north-
east of Iceland reached than in previous
years. This stimulated a special study of the
hydrographic conditions in the area. In June
1967 the cold tongue had a similar extension
as in 1965, but in June 1968 it covered a far
greater area than ever observed before, even
filling a long stretch of the coast.
Not only has the cold tongue expanded, but
considerable changes have also taken place in
temperature and salinity in the uppermost
100—200 m in this area during the last 5 years
(1964—1968) compared to the period 1948—
1958.
This paper deals with changes in the pro-
portions of the different water masses in the
East-Icelandic Current, the effect of these
changes on the stratification ancl the vertical
stability, and the eff'ect of the stratification on
the drift ice conditions in North and East Ice-
lanclic waters.
Preliminary results of tliese studies have ap-
peared previously in the publications of the
International Council for the Exploration of
the Sea (Malmberg 1967 c, 1968 a, b, 1969) and
the Fisheries Association of Iceland (Malmberg
1967 a, b, Vilhjálmsson and Malmberg 1968).