Retreat of Humboldt Gletscher, North Greenland, Driven by Undercutting From a Warmer Ocean

• Published in: Geophysical research letters 2021-03, Vol.48 (6), p.e2020GL091342-n/a
• Main Authors: Rignot, Eric, An, Lu, Chauche, Nolwenn, Morlighem, Mathieu, Jeong, Seongsu, Wood, Michael, Mouginot, Jeremie, Willis, Josh K., Klaucke, Ingo, Weinrebe, Wilhelm, Muenchow, Andreas
• Format: Article
• Language: English
• Subjects: Abrupt/Rapid Climate Change; Air/Sea Constituent Fluxes; Air/Sea Interactions; Atmospheric; Atmospheric Composition and Structure; Atmospheric Effects; Atmospheric Processes; Avalanches; bathymetry; Benefit‐cost Analysis; Biogeosciences; Climate and Interannual Variability; Climate Change and Variability; Climate Dynamics; Climate Impact; Climate Impacts; Climate Variability; Climatology; Computational Geophysics; Cryosphere; Decadal Ocean Variability; Disaster Risk Analysis and Assessment; Earth System Modeling; Earthquake Ground Motions and Engineering Seismology; Echo sounding; Echoes; Effusive Volcanism; Environmental Sciences; Equivalence; Explosive Volcanism; Flotation; General Circulation; Geodesy and Gravity; Geological; Glaciation; Glacier fronts; Glacier retreat; Glaciers; glaciology; Global Change; Global Change from Geodesy; Global sea level; Gravity and Isostasy; Greenland; Hydrological Cycles and Budgets; Hydrology; Ice; Ice Cores; Ice sheet models; Ice sheets; Ice volume; Impacts of Global Change; Informatics; Land/Atmosphere Interactions; Marine Geology and Geophysics; Mass Balance; Modeling; Mud Volcanism; Natural Hazards; Numerical Modeling; Numerical Solutions; Ocean floor; Ocean influence of Earth rotation; Ocean models; Ocean Monitoring with Geodetic Techniques; Ocean temperature; Ocean warming; Ocean/Atmosphere Interactions; Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions; Oceanic; Oceanography: General; Oceanography: Physical; Oceans; Paleoceanography; Physical Modeling; physical ocean; Policy Sciences; Radio Oceanography; Radio Science; Regional Climate Change; Regional Modeling; Remote Sensing; Remote Sensing and Disasters; Remote Sensing of Volcanoes; Research Letter; Risk; Sciences of the Universe; Sea level; Sea Level Change; Sea level changes; Sea level rise; Sea Level: Variations and Mean; Seismology; Shallow water; Solid Earth; Space Geodetic Surveys; Submarine troughs; Surface Waves and Tides; Theoretical Modeling; Thinning; Tsunamis and Storm Surges; Volcanic Effects; Volcanic Hazards and Risks; Volcano Monitoring; Volcano Seismology; Volcano/Climate Interactions; Volcanology; Warm water; Water Cycles; Water depth; Water temperature
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL091342

Humboldt Gletscher is a 100‐km wide, slow‐moving glacier in north Greenland which holds a 19‐cm global sea level equivalent. Humboldt has been the fourth largest contributor to sea level rise since 1972 but the cause of its mass loss has not been elucidated. Multi‐beam echo sounding data collected in 2019 indicate a seabed 200 m deeper than previously known. Conductivity temperature depth data reveal the presence of warm water of Atlantic origin at 0°C at the glacier front and a warming of the ocean waters by 0.9 ± 0.1°C since 1962. Using an ocean model, we reconstruct grounded ice undercutting by the ocean, combine it with calculated retreat caused by ice thinning to floatation, and are able to fully explain the observed retreat. Two thirds of the retreat are caused by undercutting of grounded ice, which is a physical process not included in most ice sheet models. Plain Language Summary Humboldt Gletscher is the widest glacier in Greenland, slow moving, and terminating in shallow waters in its southern half, but grounded 200 m deeper than previously known in its northern half, with a submarine trough extending more than 100 km inland. The glacier has been retreating at 0.6 km/year and contributing significantly to sea level rise. We attribute the retreat to undercutting of grounded ice by warmer ocean waters combined with a retreat caused by ice thinning to floatation sooner due to glacier speed up. The glacier, which hosts an ice volume equivalent to a 19‐cm global sea level, will remain a major contributor to sea level rise this Century. Key Points The 100‐km wide Humboldt Gletscher holds a 19‐cm sea level rise equivalent, lost 161 billion tons of mass, and retreated 13 km since 1972 Warm waters at 0°C flood a 350–400 m deep trough on its northern flank that remains below sea level more than 100 km inland We explain the glacier retreat as 70% from ocean‐induced undercutting and 30% from thinning‐induced retreat