부산대학교 도서관

Jakobshavn Isbræ, a major outlet glacier in Greenland, lost its protective ice shelf in 2002 and has been speeding up and retreating since. We image its grounding line for the first time with a terrestrial radar interferometer deployed in 2016 and detect its migration at tidal frequencies. The southern half of the glacier develops a floating section (3 km × 3 km) that migrates in phase with the tidal difference, up to a distance of 2.8 km, far more than previously expected. We attribute the migration to kilometer‐scale seawater intrusions, 10–20 cm in height, with the tide. The intrusions reveal that the glacier bed may be up to 800 m deeper than expected on the south side, which illustrates that our knowledge of bed topography remains limited for this glacier. We expect seawater intrusions to cause rapid melt of basal ice and play a major role in the glacier evolution. Plain Language Summary: The transition boundary between grounded glacier ice and floating glacier ice, or grounding line, has never been mapped in much detail on the largest, fastest outlet glaciers of Greenland because available satellite radar imagery does not provide short enough repeat pass data. Here, we use a terrestrial radar interferometer which images the glacier every 2 min to map the grounding line repeatedly with differential interferometry. Surprisingly the glacier develops a small floating section on the south side where the grounding line migrates over considerable distances—0.5 to 2.8 km—during the tidal cycle, which is 10 times farther than previously expected from flotation. We attribute the migration to seawater intrusions over a bed 100–800 m deeper than previously known. Seawater intrusions will carry sufficient ocean heat to melt basal ice vigorously, a factor that has not been incorporated in modeling studies of this glacier. Key Points: We present the first mapping of the grounding line of Jakobshavn Isbr$\ae$, Greenland at ocean tidal frequenciesThe grounding line migrates over kilometers, far more than expected from flotation, which we attribute to kilometer‐size seawater intrusionsSeawater intrusions along a bed several hundred meters deeper than expected must be included in future glacier modeling studies [ABSTRACT FROM AUTHOR]