Jökull - 01.01.2012, Blaðsíða 83

Reviewed research article
Mass and volume changes of Langjökull ice cap, Iceland,
∼1890 to 2009, deduced from old maps, satellite images and
in situ mass balance measurements
Finnur Pálsson1, Sverrir Guðmundsson1, Helgi Björnsson1, Etienne Berthier 2,
Eyjólfur Magnússon1, Snævarr Guðmundsson1 and Hannes H. Haraldsson3
1Institute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík, Iceland
2LEGOS-CNRS, University of Toulouse, Toulouse, France
3Landsvirkjun, Háaleitisbraut 68, 103 Reykjavík, Iceland
Corresponding author: fp@hi.is
Abstract – We describe the mass balance of Langjökull ice cap, Iceland, (∼920 km2, ∼190 km3) during several
time intervals of different climate conditions that span the 20th century until present. The elevation range of
Langjökull is 460–1440 m a.s.l. with a zero mass balance equilibrium line altitude (ELA) of 1000 m (southern
outlets). The mass balance of the ice cap has been observed in situ every year since 1996–1997 and also
assessed from estimation of glacier volume changes by comparing series of elevation maps from: 1937, 1945–
1946, 1986, 1997 and 2004. The glacier margin of the Little Ice Age maximum (LIA; ∼1890) was estimated from
the location of end moraines. The difference between the 1997–2004 annnual specific net balance estimated by
volume change and in situ measurements is negligible (∼5 cmwe). During the two warm periods 1936–1946
and 1997–2009 the mean mass balance was similar; -1.6 and -1.3 mwe yr−1, respectively. The colder climate
during 1946–1986 and cooler yet in 1986–1997 resulted in specific mass balance close to zero; -0.3 and -0.2
mwe yr−1, respectively.
INTRODUCTION
At present about 11% of Iceland (103,000 km2) is
covered by glaciers (Figure 1; Björnsson and Páls-
son, 2008). Icelandic ice caps are temperate, charac-
terized by high annual mass turnover rate (1.5–3 mwe
yr−1). They are highly sensitive to climate fluctua-
tions and currently melting at a fast rate (e.g. Björns-
son and Pálsson, 2008; Gudmundsson et al., 2011).
Iceland, an island in the North Atlantic Ocean, close
to the Arctic Circle, enjoys a relatively mild and wet
oceanic climate and small seasonal variations in air
temperature due to the warm Irminger ocean current.
Average winter temperatures hover around 0◦C near
the southern coast, where the average temperature of
the warmest month is only 11◦C and the mean annual
temperature is about 5◦C (Einarsson, 1984; Björnsson
and Pálsson, 2008). Along the northern coast, the cli-
mate is affected by the polar East Greenland Current,
which occasionally brings sea ice. Heavy snowfall is
frequently induced by cyclones crossing the North At-
lantic, where air and water masses of tropical and arc-
tic origins meet.
Langjökull (∼920 km2, ∼190 km3) is the sec-
ond largest ice cap in Iceland, located in the mid
west of the island (Figure 1). The two largest outlets
of Langjökull surge at an interval of ∼10–20 years
(Björnsson et al., 2003a), and there are indications
JÖKULL No. 62, 2012 81