The timeliness and necessity of the programme is emphasized by the fact that since the establishment of PROMICE, we have experienced several years of record-high tempera-tures in Greenland. As a consequence, record high mass loss of the Greenland ice sheet has occurred through melt and calving of icebergs. The high temperatures and melt rates were measured by the automatic weather stations (AWS) in PROMICE, as unique in-situ measurements in the ice marginal areas where the melt is taking place. In southern Greenland we measured record-high melt of -9.3 m and -8.1 metres in 2010 and 2012, respectively. Although 2012 had the highest air temperatures, more melt was recorded in 2010 in most locations. Analysis of the AWS data from the PROMICE network shows that this was due to low amounts of snow accumulation in the winter/spring of 2010.
For some regions the distributed melt has been calculated. For the record-warm year of 2010 we calculated surface melt water to run off from the Kangerlussuaq catchment, exceeding ‘normal’ values by about 150%. Results from the Nuuk region show that over the past 20 years ice sheet melt here has increased by roughly 50%. In the Kangerlussuaq area melt was heavily amplified by the melt-albedo feedback, because melt darkens the snow and ice surface, further increasing melt. The effect of darkened ice surface will linger for several years or more, and already had implications for record runoff year 2012, during which the Kangerlussuaq bridge was washed away. These results not only confirm large-scale mass balance modelling results from other groups, but also reveal the physical explanation behind the recorded increase in mass loss.
Presently we are developing a model that can calculate surface melt across the entire ice sheet based fully on observations from AWSs and satellites.
Airborne campaigns were carried out successfully in 2007 and 2011 yielding ice elevation and thickness along a flux gate around the Greenland ice sheet margin. Software for calculating ice surface velocities from satellite (SAR) has been developed and ice surface velocity maps have been produced. Additionally, the seasonal velocity variation at a number of outlet glaciers has been retrieved from GPS-instruments. Thus we now have data needed to estimate the mass loss from calving, bringing us closer to the PROMICE goal of estimating the full mass loss of the Greenland Ice sheet. Additionally the retreat of the Greenland ice sheet has been assessed by mapping. We have recently completed the PROMICE map of Greenland ice masses based on aero-photogrammetric maps. It shows that in the mid-1980’s, the ice sheet covered 1,716 x 103 km2, and ice caps and glaciers covered 88 x 103 km2. Based on satellite imagery, we updated our 1980’s ice margins to 2011, and we found a net combined area loss of 2,560 km2 from the 128 sites of larger detected change, excluding known glacier surges. The mapping effort of PROMICE was pivotal in the timely correction of the Times Atlas by the global scientific community, when they erroneously claimed a large retreat of the Greenland ice sheet based on a flawed analysis of available data.
|Status||Udgivet - 29 okt. 2013|
|Navn||Danmarks og Grønlands Geologiske Undersøgelse Rapport|
- Programområde 5: Natur og klima