Retreat of Humboldt Gletscher, North Greenland, driven by undercutting from a warmer ocean

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 (CTD) 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 is caused by undercutting of grounded ice, which is a physical process not included in most ice sheet models.

洪堡冰川（Humboldt Gletscher）是格陵兰北部一座宽100千米、移动缓慢的冰川，其冰量变化相当于全球海平面上升19厘米。自1972年以来，洪堡冰川一直是海平面上升的第四大贡献源，但其物质亏损的原因尚未阐明。2019年采集的多波束测深（Multi-beam echo sounding）数据显示，其所在海域海床深度较此前认知深200米。温盐深（Conductivity Temperature Depth, CTD）数据显示，冰川前缘存在温度为0℃的大西洋源暖水，且自1962年以来海水升温0.9±0.1℃。本研究利用海洋模式重建了海洋对接地冰的底部侵蚀过程，并将其与冰体变薄至漂浮状态所引发的冰川退缩计算结果相结合，最终得以完全解释观测到的冰川退缩现象。其中三分之二的冰川退缩由接地冰的底部侵蚀所致，这一物理过程未被绝大多数冰盖模式纳入考量。