The Petermann ice shelf breaks up - ice calving of 28 km from the Petermann floating ice shelf on Greenland, which was 70 km long

Background: The Petermann Glacier (81° N-61° W) extends out in the Petermann Fjord as a 70 km floating ice shelf. Petermann Glacier has a thickness of 900 m when it moves into the fjord thinning along its way out in the fjord with an average speed of 1 km per year to 40 m at the end of the ice shelf (ice front) of which 4 m is above the sea level. Petermann ice shelf is the longest floating ice shelf on the Northern hemisphere. Previous research (A. Higgins, Polarforschung 60 (1), 1990) has established that the position of the outer end of the ice shelf (ice front) has been relative stable, within 15 km from 1870 up to 1950 with some significant calving events each 5-10 years. Airplane photographs between 1958 and 1961 showed that 17 km of the ice shelf broke off.

Nansen Center: The Nansen Center in Bergen, Norway with Professor Ola M. Johannessen and Dr. Mohamed Babiker have over the last few years studied and monitored the calving from Petermann ice shelf by use of satellite images from the radar instrument (ASAR) onboard ESA ENVISAT and the US LANDSAT ETM.

Gigantic calving 5. August, 2010: By use of satellite images we are able to monitor the Petermann Glacier and its floating ice shelf in “real time”. The LANDSAT image from 22 of July this year (2010) indicated crack patterns across the ice shelf 25-30 km from the ice front (see attached figure). On the radar image the 3 of August these crack patterns are not clearly visible, but from the radar image the day after, the 4th of August, a dramatic change has taken place. A crack in the ice shelf 28 km in from the ice front all across the ice shelf is clearly seen (dark feature in the image) with a width varying between 300-900 m. The radar image the day after, 5th of August, shows very clearly that 28 km of the outer part of the floating ice shelf has broken off and is drifting out of the Petermann Fjord. On the 7th. of August the outer part of the ice shelf, now a huge ice island, has drifted further 10 km out in the fjord (see enclosed figure). In “recent time” this is the largest calving event recorded and at present the 70 km floating ice shelf is reduced with 1/3 to 42 km. The area of the calving ice shelf was as large as 270 km2. We have also studied other recent calving events from the Petermanns ice shelf, for example in 1991 168 km2 calved off, in 2001-71 km2 and in 2008 -31 km2 before the present gigantic calving of 270 km2.

Scientific causes: What are the scientific reasons for this last huge calving? Potential it can be:

1. Inflow of warmer “ocean” water into the Petermann Fjord under the ice shelf
2. Very strong wind from south out of the fjord which causes “crack” patterns across the ice shelf
3. Increasing air temperature, which caused increased melting during the few summer months or a combination of these three.

Earlier research of the Petermann Glacier and ice shelf has shown that melting from the bottom of the floating ice shelf by the fjord water was 20 times than that of surface melting during the summer (E. Rignot and K. Steffen, Geophysical Research Letters Vol. 35 - 2008). If warmer water flows in under the ice shelf it will become thinner and potentially break up and calve. The other reason may be caused by strong wind events blowing out of the Petermann Fjord and thereby caused detachment of the outer part of the ice shelf. This in combination with potential increased melting from below could be the major causes for the gigantic present calving of 270 km2.

Unfortunately we do not have available observations of either the fjord temperature or the air temperature for this last calving 4-5 of August, but we have studied available meteorological maps from Danish Meteorological Institute from 27th of July to 6th of August. During the first part of this period there was weak wind in the Petermann area, but from the beginning of August a strong low pressure system developed over the North-Eastern part of Canada causing wind from the south in the Petermann Fjord area. Retrieval of wind from ENVISAT radar over open water on the 3rd. of August indicates a wind speed of 15 m/s out of the fjord. This could be an important contribution to the gigantic calving event.

However in order to understand these calving events and other events in many of the Greenland fjords we need more in situ data from glaciological, meteorological and oceanographically variables combined with modelling in addition to satellite data, in order to access what will happen with calving events and loss of mass from Greenland, which affect both global sea level and ocean circulation in the future, a great challenge for the scientific community.

Further information: Prof. Ola M. Johannessen, Phone +47 901 35 336.

The full press release including additional satellite images are found at;

ftp://ftp.nersc.no/Press/PM-NERSC-Petermann-100810.pdf

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