ICESat team flies over thinning Arctic sea ice
Posted by Tim Creyts
Finally a break in the weather and we are back in the air monitoring sea ice. Our mission is at latitude 86N. We fly straight out and then a zig-zag pattern back at a low-altitude (1,500 ft. above ground) to survey sea ice in the Arctic Ocean north of Greenland, flying along earlier ICESat tracks. The first segment of the flight is along a former ICESat track. Many of our flights are based on re-flying the ICESat tracks in order to collect continuous data for areas where we have baseline information.
Our goal is to sample the thick multiyear ice where it collects near the Greenland coast, and follow the gradient to thinner ice towards the North Pole. We use the laser, radar and gravity to collect ice thickness data. The multiyear sea ice is an important part of the Arctic cooling system. Collecting against Greenland and Canada, it provides a continual ice cover over portions of the Arctic Circle. The multiyear ice is also a key habitat to Arctic wildlife, including the emblematic Polar Bears.
The weather over the Arctic Ocean has been highly variable as the far north transitions from “winter” mode to “summer” mode. This transition means that there are high thermal gradients, sea ice begins to break up changing the overall albedo of the ocean surface, and the reducing ice cover allows a water to air exchange. Ultimately all these shifts in the system changes the weather. We have not flown to Fairbanks yet because of this variability—there hasn’t been a clear day to do the flying.
The team did get in a second day of flying in a sequence of 4 low-altitude missions that are designed to map two ice streams in the North East section of Greenland. We are focused on the Zachariae Isstrøm (Ice Stream) and lower Northeast (NE) Greenland Ice Stream, flying the area on a 10 km grid pattern to get a clear ‘picture’ of the conditions. The NE Ice Stream is the largest drainage basin in this sector of the ice sheet and satellite data suggests this area of the ice cap is just beginning to thin. This flight will be combined with the other three flights this season to give an impression of how this major outlet is changing as well as set a baseline for assessing future changes.
As I noted we have been fighting the weather to get flights in this week, both over the ocean and Greenland. One of the difficulties of airborne data collection is the instruments need visibility in order to record ice surface conditions. Fortunately we are able to be flexible with planning so that if it is clear in one area we rearrange the flights to take advantage of the weather window. However we have had several no fly days leaving the ground and flight crew time to learn the surroundings and enjoy the sledding around Thule. Greenland is made up of one very large ice sheet surrounded by rough topography: small plateaus with fjords cut into them and mountain ranges with incised valleys. Near Thule, recession of the ice sheet over the past several millenia has “stranded” a smaller ice cap on a small plateau surrounded by frozen outwash plains from the outlet glaciers. This small icecap offers a fairly steep hill for sledding which many of us will attempt, but only one or two will descend with any grace gliding on our red or blue plastic “tubs” and “saucers”.
Tim Creyts is a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory specializing in how water flows beneath glaciers and ice sheets. Tim has spent several seasons in the field in Alaska, the Yukon, and Greenland, and most recently as leader of a team investigating how water flows at the base of Blackfoot Glacier, MT. Tim will be working as part of the ICE Bridge project.