Jökull - 01.12.1969, Qupperneq 45

TABLE3
Temperature, salinity and density of the water tnasses in the Iceland Sea.
(Stefánsson 1962).
North Icelandic Winter water Arctic Int. water Arctic Bottom water
Temperature, °C 1-2 0-2 -0.9
Salinity, %c 34.85-34.90 34.80-35.00 34.92
Density 27.95-27.92 27.97-28.00 28.10
Density 27.95 reacl 1.02795 gr cm~3.
The effect of increased stability in the sur-
face layer seems to have been in progress dur-
ing the last few years northeast of Iceland.
The uppermost 100—200 m have been occupi-
ed by water of relatively low density or low
cnough to prevent a vertical convection, al-
though the water mass cools down to freezing
point, — 1.8° C.
We will now take a look at the density of
the various water masses in the region in rela-
bon to the temperature and salinity values.
Stefánsson (1962, pp. 36—37) has defined the
water masses of the Iceland Sea as shown in
Table 3.
According to the temperature ancl salinitv
values given in Table 1 the temperature of
0° C and the salinity of 34.85%c are approxi-
mately the values observecl at 100—200 m depth
m the area in question during the years 1964—
1968. These values correspond to the density
28.01. The density of a watermass with salinitv
^4.7%oc or lower (as observed in June 1965, 1967
and 1968 in the uppermost 100—200 m) cannot
be higher than 27.96, even thougli the water
mass reaches freezing point, at ca. — 1.8° C.
With surface salinities of 34.8%0 or higher (as
observed in (une 1950—1958) the density will
at least 28.05 at — 1.8° C, i.e. a deep
vertical convection will start before freezing
point is reached. A density of 28.01 is alreadv
reached at — 0.8° C. This temperature value
fairly agrees with observations in 1950—1958,
but cluring that period temperatures below
— 1° C were not observed in the area, except
in June 1953 when the temperature was about
— 1° C in a limited area at 100 m depth (Ste-
fánsson 1962, p. 105). It should also be men-
tioned that according to the scarce data from
the area in the first halí of this century, the
observations in the years 1901, 1902 and 1903
were similar to those of the last few years, but
the 1930, 1933 and 1935 observations were
similar to tliose of 1950—1958.*
In short (see Fig. 11), when the surface lay-
ers northeast of Iceland have a salinity of
34.7%0 or lower, as observed in the extremely
unlavourable ice years in Icelandic waters in
1965, 1967 and 1968, the water will not reach
a high enough density to start a deep vertical
convection even at a temperature of — 1.8° C,
but at salinities of 34.8%c or more this is pos-
sible. Tliat means in the latter case a cleep
vertical convection before such a strong cool-
ing is reached. This explains the trencl which
appears in the t-S diagrams shown in Fig. 2.
The changed hydrographic conditions in the
waters northeast of Iceland in the last few
years have contributed to the preservation
and formation of sea ice ancl the ice has of
course intensified the changed situation, pro-
ducing a decrease in salinity and an increase
in stability and subsequent cooling the follow-
ing winter and spring. The situation is then
*) Recently available data frorn June 1962
in the area in question also reveal the situa-
tion of the period 1948—1958 (Malmherg
1969 b).
JÖKULL 19. ÁR 41