Jökull - 01.12.1969, Side 23

The present paper gives an account of
changes taking place in the North Icelandic
coastal area during the last 18 years. For evalu-
ating such changes three main sources of data
were used:
1) Records from near-surface thermographs
installed in coastal liners during the years
1949-1966.
2) Hydrographic data collected by the Mar-
ine Research Institute during cruises in
spring and summer 1950—1968.
3) Sea surface temperature measurements at
Grímsey during 1950—1968.
Locations of stations referred to in this paper
are shown in Fig. 1.
TRENDS OF SEA SURFACE
TEMPERATURE AT GRÍMSEY
Running means were used for studying tem-
perature trends at this station. These were
computed from data collected by the Danish
and Icelandic meteorological institutes for the
period up to and including 1958, and from
weekly measurements carried out for the Mar-
ine Research Institute, Reykjavík, during the
years 1960—1968. In view of the smallness of
Grímsey and its distance from land, it was as-
sumed tliat all sea temperature measurements
at this island are comparable.
In a few instances observations were missing,
e.g. throughout the year 1959. In sueh cases
calculated values were used, found by com-
parison witli observations at other localities
and/or the air temperature at Grímsey. Al-
though these calculated values may often be
questionable, they will not cause an appreci-
able error in the mean values based on many
years.
Running means of the annual temperature at
Grímsey for consecutive 5, 10 and 30 years are
shown in Fig. 2. The 30-year means illustrate
the temperature trencl over a long period,
wliereas the 5-year and the 10-year running
means indicate more clearly short-periodical
variations. It will be seen from the 30-year
running means that the annual surface tem-
perature decreased from the period 1876/1905
to 1881/1910. During this latter period it was
0.5° C below the 1901/1930 mean and 1.5° C
below the 1931/1960 mean. From then on the
temperature showed an upward trend until
1919/1948. In the following 14 years the 30-
year means remained alrnost constant, but seem
to be decreasing slightly during the last few
years. Thus the 1939/1968 mean is 0.2—0.3° C
lower than the 1931/1960 mean, but still 0.7—
0.8° C higher than the 1901/1930 mean.
The 5-year and the 10-year running means
also reveal a general lowering in sea surface
temperature during the 7th and 8tli decades
of the last century. A slight temperature max-
imum was indicated around 1891/1900, a tem-
perature minimum around 1902/1911, followecl
by an upward trend which became particularly
pronounced after 1911/1920. A temperature
maximum occurred between 1936 and 1941,
when the 5-year running mean was 1.5° C
above the 1901/1930 normal. Then the annual
means decreasecl again, reached a minimum in
the period 1948—1953, then rose again to reach
another maximum in the period 1957—1962,
but during the last few years the 5-year means
have shown a marked downward trend. The
1964/1968 mean rvas similar to the 1901/1930
normal.
Comparison between the 5-year means for
the months February, May, August and Nov-
ember (Fig. 3) shows that the variations were
greatest in May, but smallest in February. The
decline in sea temperature during recent years
is most pronounced in May, which is the time
of year when the drift ice normally has its
greatest eastwards extension. Referred to the
1931/1960 nornial, the 1964/1968 mean had
a negative temperature anomaly of 0.3° C in
February, about 2.0° C in May, 1.5° C in Au-
gust and 0.2° C in November.
SURFACE TEMPERATURE
IN INDIVIDUAL YEARS IN THE
WESTERN, MIDDLE AND EASTERN
PART OF THE COASTAL AREA
Temperature anomalies at three localities,
Húnaflói (H), Grímsey (G) and near Langanes
(L), for the months February, May, August ancl
November in the period 1949—1968 are shown
in Figs. 4—5.
It will be seen that year to year fluctuations
in winter temperatures are relatively small at
JÖKULL 19. ÁR 19