PROFILE
Measuring the fever of
the glaciers’ firn and ice
The firn and ice of glaciers can be at temperatures far below freezing point,
writes Professor Martin Hoelzle
G
lacial ice acts as a natural
mental and climate history. They allow
(about 0°C). In the Alps, for example,
where there are no direct instrumental
that is at the pressure melting point
serve important information about
most glaciers are temperate and there
archive and is able to pre-
the past atmosphere. Measurements
are no glaciers which are entirely cold.
analysis of climate evolution in areas
observations. Cold thermal conditions
ensure that practically no meltwater
of firn and ice temperatures, however,
Often, one finds cold and temperate
1990s, even for high-altitude and
tion areas of the same glacier. Such
information stored in the snow/ice
continued climate change raises
The largest polythermal glacier in the
air bubbles cannot be displaced or
become erased.
in the Monte Rosa area. Large parts of
show substantial warming since the
latitude locations. The expected
concerns that this natural archive will
The firn and ice of high alpine glaciers
in different mountain regions or from
ice caps and ice sheets at high latitudes is mostly cold. The term “cold”
has a very specific meaning among
glaciologists: Cold means that the gla-
cier has a temperature below freezing
over the entire year, as opposed to
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“temperate” ice which refers to ice
climate and environmental
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ice coexisting in accumulation or abla-
glaciers are then called polythermal.
can arise and percolate through
the porous firn layers, so that the
crystals, and in the trace gases within
European Alps is the Grenzgletscher
washed out.
the Greenland ice sheet, virtually the
The first ice temperature profiles were
glaciers and smaller ice caps of high
tury in north-west Greenland and they
entire Antarctic ice sheet, and many
mountain Asia consist of cold or poly-
thermal ice.
Cold accumulation areas are very
important for ice core research focus-
ing on the reconstruction of environ-
measured in the 1950s at Camp Cen-
revealed temperatures of -24°C at the
surface and -13°C at 1,400m depth at
the interface between ice and bedrock.
In recent years, firn and ice tempera-
tures have been measured in the
Alps within several tens of boreholes.
PROFILE
According to these studies, cold firn
have shown that short but sometimes
sea level. The measured average
factor in quickly increasing englacial
can occur between 3800-4800m above
firn temperature in the Mont Blanc
summit area reaches down to about
-15°C and down to around -12°C on
the Monte Rosa. What is surprising is
intense snowmelt events are a major
temperatures.
The
latent
heat
released by refreezing of percolating
meltwater causes a rapid increase in
temperature within the firn/ice body
the large spatial variability of temper-
and creates ice layers several centime-
Actual ‘cold spots’ on shady slopes or
great importance, because it could
tion alternate with almost temperate
ments like Greenland and the high
atures observed on the glaciers:
flat saddles with little snow accumulaparts in exposed southern slopes with
high amounts of solar radiation.
Measured englacial temperature profiles
also reflect the surface temperature
history and can thus be interpreted
as a climate archive. However, this
applies only if the conditions on the
surface (snow accumulation, melt
energy input, etc.) have not changed
too dramatically over the reconstruction
tres to metres thick. This effect is of
warm large firn areas in cold environmountains of Asia.
“The first ice temperature profiles
were measured in the 1950s at Camp
Century in north-west Greenland
and they revealed temperatures of
-24°C at the surface and -13°C at
1,400m depth at the interface
between ice and bedrock.”
However, recent studies from Green-
period. In Greenland, for instance, a
land show that the production of ice
ature over a period of several thou-
acting the direct warming of deeper
reconstruction of the surface temper-
sands of years back in time was
perature decrease of around -23°C,
lenses so thick that they now act as an
to 5,000 BP) showed an increase of
force meltwater to run off along the
colation of further meltwater and
surface. Therefore, the deeper firn
layers cannot be warmed by percolat-
temperatures today is very fast, we
ing meltwater through the effect of
climatic influences on the formation
more. The increased meltwater pro-
latent heat release by refreezing any
of cold firn and ice. Therefore, the
duction has serious implications,
phere and cold snow and firn were
of glaciers, ice caps and ice sheets
energy fluxes between the atmos-
investigated in detail. Measurements
these unique archives.
Furthermore, stability of steep hang-
ing glaciers frozen to bedrock can be
weakened due to increased meltwater
running along the bedrock, resulting
in large ice avalanches endangering
the valleys below. For these reasons,
it would be considered a strong asset
to install a world-wide firn and ice
temperature
monitoring
system
embedded in the already existing
international monitoring strategies of
glaciers, ice caps and ice sheets of the
Global Terrestrial Network on Glaciers
(GTN-G) within the Global Climate
Observing System (GCOS).
water). These ice layers of several
-1°C in comparison of today.
have to better understand the micro-
losing the climate records stored in
aquiclude (an impermeable layer of
metres in thickness prevent the per-
However, as the increase in air
therefore need to be drilled soon in
sensitive warming areas to avoid
years has refrozen in near-surface ice
about +2.5°C and the Little Ice Age
(around 15th to 19th century) about
stored in cold firn and ice. Ice cores
layers in the firn. The meltwater cre-
ated during the recent series of warm
the Climatic Optimum (around 9,000
ical and environmental information
layers can also have impacts counter-
possible. The Last Ice Age (around
110,000 to 12,000 BP) showed a tem-
and the erasure of the valuable histor-
among which is the increased runoff
leading to an enhanced sea level rise
Martin Hoelzle
Full Professor, Physical Geography
Department of Geosciences
University of Fribourg, Switzerland
Tel: +41 26 300 90 22
[email protected]
http://www.unifr.ch/geoscience/
geographie/en/staff/physical-geographygroup/prof.-m.-hoelzle
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