Destabilization of marine-based Zachariæ Isstrøm, northeast Greenland since 2012 from a combination of interferometry data and Operation IceBridge observations.
Tuesday, 16 December 2014: 5:00 PM
We study the 79north (Nioghalvfjerdsbræ) and Zachariæ Isstrøm sector of the Greenland Ice Sheet using a combination of satellite and Operation IceBridge (OIB) remote sensing data and numerical ocean modeling. Around 2004, the southern portion of the floating ice tongue of Zachariæ Isstrøm began to break up, presumably due to changes in sea-ice/ocean conditions in the northeast. While the floating portion of the glacier started to speed up in response to the reduction in ice shelf buttressing, it was not until 2012 that the velocity of the grounded portion increased significantly. In 2014, the glacier is calving at its grounding line, which retreated 5 km in 1996-2011. The southern ice tongue is gone, and the northern ice tongue is detached from the glacier. We use satellite-derived ice velocity and refined ice thickness based on mass conservation to estimate discharge of these glaciers. We compare the results with RACMO surface mass balance and reconstruct the mass balance of this sector for the period 1992-2014 to show that most mass loss picked up after 2012, not in the earlier 2000's as stated in a recent study. We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates. The grounding line of 79north also retreated in 1996-2011, but its flow speed has remained constant. We attribute this contrasting evolution of the two glaciers to a difference in sea floor bathymetry, which allows an intrusion of larger amounts of warm subsurface waters for Zachariæ since the early 2000s, but limits access of such currents for 79north. The latter will likely undergo a fast recession until its grounding reaches a topographic barrier about 30 km upstream, where ice retreat will temporarily slow down. We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland.