Combined satellite observation for current mass balance and decadal changes of the Antarctic Ice Shelves

The mass balance of the Antarctic Ice Sheet has a direct impact on the global sea level and thus its assessment is crucial to predict near-future changes of the global environment in response to a warming world. Ice shelves are freshwater ice already discharged from the grounded ice sheet and currently floating on the ocean. So, they have already contributed to increase the sea level. However, their behaviors must be better understood because the ice shelves give buttressing effects on the ice sheet and partly control ice discharge from the ice sheet. This project used a range of satellite remote sensing data to examine current status and decadal changes of ice shelves in Dronning Maud Land (DML), in the Atlantic and Indian Sea sectors of Antarctica. We focused on this region because knowledge in this area is more limited than other areas. We have four main findings in this project; scientific results and technical details are briefly presented below. (1) Seismometers at Troll Station recorded a range of signals that were neither earthquake nor icequake. We found using ESA's Envisat satellite images that these signals have been originated from drifting tabular icebergs. These iceberg-origin signals are presumably caused by collides with elevated seabed, other icebergs, and ice shelves, as well as by seawater moving around the icebergs. Combination of seismic data and microwave satellite remote sensing may enable more comprehensive year-around monitoring of drifting icebergs, than using either of them alone. Such monitoring is crucial to estimate offshore inputs of freshwater, evaluate impacts of icebergs on sea ice growth in the winter time, and map approximate positions of undocumented seamounts and banks as the locations where large icebergs linger for an extended period. (2) We analyzed the subset of the Radasat-2 satellite data, which were collected since 2011 to monitor the DML coast, to examine iceberg calving location and frequency, motion of the calving front, and a range of surface features of the ice shelves. We compared Radasat2 scenes collected in different seasons and ESA?s Sentinel-1 and -2 images, and found that these show very similar capacities to study these issues, and images collected in winter work better than those collected in summer (despite denser sea ice near the calving front during the winter time). Comparing our datasets collected six times in 2012-13 to other datasets in 2004 and 2009, we identified handful small calving events, which amount to 5% of the front. The remaining 95% of the calving front advanced in accordance with the local flow. (3) Radarsat2 imagery was further analyzed using feature tracking techniques to derive maps of ice motion. We identified three undocumented locations in the frontal zone of the Fimbul Ice Shelf where ice is mostly stagnated and elevated by ~10 m. These so-called ice rumples play important roles in the stability of the ice shelf. (4) We compared our ice motion dataset to other datasets covering earlier years, and concluded that the vicinity of the grounding line of the Fimbul Ice Shelf, where grounded ice gets afloat, has been slowed down by a few meters per year over the past decade. This feature may be relevant to the ice rumples in the frontal area, but the mechanisms of this slow down remain unknown.

This project hosted a new collaboration with NORSAR scientists who have seismic expertise which we don't have at NPI. Also, together with this project and other more field-oriented projects, we generated a more comprehensive knwoledge on dynamics of Dronning Maud Land coast, East Antarctica.

This project will use remote sensing techniques to develop comprehensive knowledge of the current status and decadal changes of the Dronning Maud Land (DML) Ice Shelves in East Antarctica where Norway makes a terrestrial claim. The knowledge involves dete rmining the temporal variations in the 1) ice-flow fields, 2) surface elevation, and 3) ice thickness. These parameters will be used to assess the mass balance and basal melting rates of the ice shelves. The variations in these parameters reflect the dynamics of the interconnected system that is composed of ocean, shelf ice, and outlet glacier, a system that also heavily affects the mass balance of the upstream ice sheet. Moreover, algorithms developed in this project will contribute to ESA's program. A P h.D. student supported by this project will analyze the satellite data and interpret these results in the context of glaciology. To initiate the thesis work at the beginning of the 2014-15 academic year, we request the project start date of 1st of August, 2014. All parameters derived in this project will be full y released through NPI's data center.