Recent rapid grounding line retreat at Ryder Glacier focused around a sub-ice shelf melt channel: first indications from airborne radio-echo sounding

During the GEOEO North of Greenland expedition with Swedish Icebreaker Oden in the summer of 2024, radio-echo sounding (RES) campaigns were undertaken at CH Ostenfeld, Ryder and Petermann glaciers. The CH Ostenfeld RES survey focused on the ice trunk upstream of the current calving front, which has been the glacier’s terminus since the collapse of CH Ostenfeld’s floating tongue in 2002/2003. At Ryder and Petermann glaciers, less extensive RES surveys were focused on the grounding zones areas, covering both the grounded ice and the floating ice tongues. Ryder Glacier’s grounding line has recently retreated across the fjord unevenly, with observed retreat of c. 8 km in the north-eastern part and less than 2 km in the south-western section (Millan et al., 2023). Millan et al. (2023) also report cumulative mass loss at Ryder Glacier during 2000-2021 as c. 55 Gt, dominated by basal melt (c. 46 Gt) likely driven by the presence of warm Atlantic water, followed by surface melt, runoff and calving (Box et al., 2022; Slater and Straneo, 2022).

Here, we present an overview of the data acquisition campaign at Ryder Glacier, as well as radargrams from the survey lines. The radargrams show evidence of a sub-ice shelf structure interpreted to represent a sub-ice shelf melt channel. Evidence for it is visible in the radargrams at four instances (across various survey lines) along a 22 km quasi-flowline of Ryder Glacier’s tongue. Between the farthest upstream and farthest downstream location, the channel width increases from c. 500 m to c. 2 km, while channel depth ranges between c. 100 and 400 m. At the farthest downstream location, the sub-ice shelf melt channel seems moreover to be co-located with a supraglacial melt channel clearly identifiable from satellite imagery.  The suspected sub-ice shelf melt channel is also coincident with the region of largest grounding line retreat. At present, the most recent mapped grounding line of Ryder Glacier is from 2020, but work is ongoing to retrieve the 2024 grounding line to enable evaluation of the significance of the new RES observations. Better understanding of the spatio-temporality of basal melt and its implications for grounding line retreat and ice dynamics is important for assessing the future behaviour of Ryder Glacier.

References:

Box, J. E., Hubbard, A., Bahr, D. B., Colgan, W. T., Fettweis, X., Mankoff, K. D., Wehrlé, A., Noël, B., van den Broeke, M. R., Wouters, B., Bjørk, A. A., and Fausto, R. S. 2022.  Greenland ice sheet climate disequilibrium and committed sea-level rise, Nature Climate Change, 12, doi.org/10.1038/s41558-022-01441-2;

Millan, R., Jager, E., Mouginot, J. et al. 2023.  Rapid disintegration and weakening of ice shelves in North Greenland. Nat Commun 14, 6914. doi.org/10.1038/s41467-023-42198-2

Slater, D. A. and Straneo, F. 2022. Submarine melting of glaciers in Greenland amplified by atmospheric warming, Nature Geoscience, 15, doi.org/10.1038/s41561-022-01035-9