PROMICE airborne snapshots of ice flow volume and iceberg production in 2007 to 2011
PROMICE Newsletter No. 6 2014
By using airborne ice thickness measurements, the volume of ice flowing to the ocean is calculated.
In the PROMICE project two airborne surveys of the Greenland ice sheet’s thickness were carried out, one in 2007 and one in 2011. The surveys followed a route tracing the perimeter of the ice sheet (Figure 1). In addition to advanced GPS equipment for high-precision position observations, the aircraft carried a radar for measuring the bed of the ice sheet and a laser for measuring the surface elevation. Together these two measurements provide ice thickness along the flight path. A single flight campaign takes approximately 10 days using the Dash-6 Twin Otter aircraft (Figure 2).
Using ice flow speed data from satellite measurements, thickness data allow us to calculate the amount of ice that flows out from the interior of the ice sheet. On its way to the coast some of the ice melts at the surface and runs off as melt water. What is left becomes icebergs that calve into the ocean from the large outlet glaciers, like Jakobshavn Isbræ on the west coast; the so-called dynamic mass loss. Flow speed is calculated from satellite images taken 46 days apart (Figure 3). By identifying the same features in the two images it is possible to calculate how fast, and in which direction the ice is flowing. The amount of ice that is melted at the surface can be estimated from ground data and computer models simulating the climate over longer periods. The difference between these two numbers is then the ice mass that leaves the ice sheet as icebergs.
When working with the mass balance of the Inland ice, it is typically divided into a number of independent basins. In a paper published in Geological Survey of Denmark and Greenland Bulletin later this year, we use this method to compute the volume of ice flowing out of the basin that is home to Jakobshavn Isbræ – one of the fastest glaciers in Greenland. The average ice mass flowing out from this catchment in 2007 and 2011 was approximately 70 Gigatonnes per year, equivalent with nearly 10 tons per person on Earth, per year! Not all ice that flows into the ocean contributes to seal level rise, though. Just like some ice is melting along the margin of the ice sheet, some ice is also added by precipitation in the interior, thereby removing water from the oceans. Therefore, when discussing sea level rise, one must consider the total mass budget, where only the net deficit contributes to increasing sea levels.
How the dynamic mass loss is coupled to climate change is not well understood. Therefore it is valuable to investigate further.
Data from the airborne surveys are available by firstname.lastname@example.org
PROMICE is financed by the Ministry of Climate, Energy and Building through the climate support programme DANCEA (Danish Cooperation for Environment in the Arctic), which is managed by the Danish Energy Agency.
· The purpose of PROMICE is to monitor the mass loss of the Greenland ice sheet, both the melting on the surface and the volume of icebergs discharged into the sea
· PROMICE is headed in Denmark by GEUS in cooperation with DTU Space and Asiaq in Greenland. Furthermore the programme collaborates with the Danish Meteorological Institute and foreign universities and authorities.
· Read more about PROMICE on promice.org, where you can find photos and videos, get direct access to measuring data from the ice sheet and the PROMICE outreach material. On the website you can also subscribe to our newsletter.
 1 Gigatonne = 1,000,000,000 tonnes, or one billion tonnes.