Jökull - 01.01.2012, Blaðsíða 94

F. Pálsson et al.
Table 2. Volume (km3) and area (km2) estimated from available maps. All the numbers correspond to the
autumn. The ∼1890 LIAmax volume is predicted (see Figure 14).– Vensl flatarmáls og rúmmáls jökulíss í
Langjökli. Gögn frá tímabilinu 1937–2004 eru notuð til að áætla rúmmál um 1890 eftir að flatarmál var metið
út frá ystu stöðu jökulsins við lok litlu ísaldar.
Year LIAmax 1937 1945 1986 1997 2004
V (km3 ice) 248 229 ± 3.5 215 ± 2.5 202 ± 2.5 198 ± 1 188 ± 1
A (km2) 1093 ± 20 1029 ± 15 991 ± 5 937 ± 15 924 ± 15 906 ± 2
volume change the equation results in an approximate
linear segment (Figure 14), yielding a LIA maximum
volume of Langjökull of 248 km3 (Table 2).
880 920 960 1000 1040 1080
Area (km2)
180
200
220
240
V
ol
um
e
(k
m
3 )
1937
1945
1986
1997
2004
1890
Figure 14. Scatter plot of volume and area (from
Table 2). The volume for 1890 is predicted from
LIAmax area. – Vensl flatarmáls og rúmmáls jökulíss
í Langjökli. Gögn frá tímabilinu 1937–2004 eru not-
uð til að áætla rúmmál um 1890 eftir að flatarmál var
metið út frá ystu stöðu jökulsins við lok litlu ísaldar.
Relationship with climate fluctuations
The observed volume reduction of Langjökull and
the average mass balance deduced from the volume
change are compared to the annual mean tempera-
ture and precipitation at Stykkishólmur and Hvera-
vellir (Figure 15; Table 3). The mass balance esti-
mates are in accord with the annual mean temperature
at Stykkishólmur averaged over the same time inter-
vals (Table 3a, c; correlation r = 0.90). The relation-
ship obtained between the average mass balance and
the total precipitation is much less (r = 0.36). The first
40 years (from LIAmax to 1937) can be roughly di-
vided into three climatic intervals: 1890–1920 slightly
warmer (∼0.3◦C at Stykkishólmur) than the latter half
of the 19th century (1860–1890), warming up from
1920 to 1925 (by ∼1.5◦C at Stykkishólmur), staying
there to 1937 (in fact to ∼1960). Hence from inspec-
tion of Figure 14b and c, we suggest that the mass bal-
ance was close to zero from 1890 to the first years of
the 1920s. The mass balance estimate between 1937
and 1945 is most likely representative for most of the
time up to ∼1960 (however, little less negative than
the 1937 to 1945 average). It is known that during the
cold period of the mid-1960s, the fronts of many out-
lets of the ice caps in Iceland were at a standstill or ad-
vanced slightly (measurements of the Iceland Glacio-
logical Society since the 1930s, semi-annual reports
in the society journal, Jökull). In the 1980s and into
the 1990s the mass balance was close to zero for the
major ice caps in Iceland (e.g. Gudmundsson et al.,
2009a, 2011; Adalgeirsdóttir et al., 2006, 2011). Cur-
rently Langjökull is losing mass at a fast rate (Table 1;
Figures 8, 9 and 15). This is consistent with the warm-
ing in Iceland that has taken place since mid 1990s
(Figure 15; Björnsson et al., 2005; Jóhannesson et al.,
2007).
The mass balance sensitivity to temperature is cal-
culated for different time intervals (Table 4), using
both annual averages as well as summer averages of
temperature from Stykkishólmur and Hveravellir. Al-
though the estimates are quite variable, the general
conclusion is that the sensitivity is close to -2 mwe
yr−1K−1 for the coastal station and -1 mwe yr−1 K−1
for the inland station in both cases, slightly higher for
92 JÖKULL No. 62, 2012