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This article is part of the Fall 2021 issue of the Earth Science Matters Newsletter.

Global sea level is rising at increasingly faster rates threatening coastal cities and ecosystems. A growing portion of sea-level rise is due to melting – decreasing mass balance – of the Greenland Ice Sheet. The northern sector of the Greenland Ice Sheet is one region that is susceptible to ice mass loss from increased future outlet glacier melting and discharge. As the ice sheet melts, it loses ice mass through outlet glaciers that connect the ice sheet to the sea. However, the extent and dynamics of outlet glaciers in this region, and their vulnerability to climate change, has been poorly documented.

Research Vessel Oden near Ryder Glacier, Greenland
Research Vessel Oden near the ice tongue of the Ryder Glacier, northwest Greenland. During summer 2019, USGS scientists participated in the Ryder Expedition to investigate the cryosphere’s dynamic history and response to climate change. 

In the summer of 2019, the Swedish icebreaker Oden, sponsored by the Swedish Polar Secretariat and an international group of researchers, entered unchartered waters of Sherard Osborn Fjord, where the Ryder Glacier drains about 2% of Greenland’s ice sheet into the adjacent Lincoln Sea, a sector of the Arctic Ocean. One result of this expedition was a new study by USGS, Stockholm University and other scientists that reconstructs the Holocene (the last 11,700 years) dynamics of Ryder Glacier and its floating ice tongue. The Holocene interglacial period provides critical baseline climate and glacier variability data against which recent anthropogenic climate factors and current trends can be compared. USGS participants conducted radiocarbon dating on marine microfossils they collected from a transect of marine sediment cores located between the modern Ryder Glacier floating ice tongue margin and the mouth of Sherard Osborn Fjord and then combined these results with sediment analyses used to reconstruct glacier history.  

The sediment records show that Ryder Glacier retreated from its maximum grounded position on the seafloor at the fjord mouth during the Early Holocene between about 11,000 and 8,000 years ago and receded more than 120 km to the end of Sherard Osborn Fjord during the Middle Holocene (3,900 to 6,300 years ago), a period known for relatively warm regional climate. This ice retreat was followed by a re-advance of Ryder Glacier thereafter in the Late Holocene.

piston coring on the deck of icebreaker
Piston coring on the deck of icebreaker Oden, September 2019. Sediment recovered in piston cores provides a nearly complete record of Holocene interglacial history of the Ryder Glacier and the Sherard Osborn Fjord paleoceanography.

Today, Ryder Glacier is grounded more than 40 km seaward of its position during the Middle Holocene, highlighting the potential for substantial glacial retreat and melting in response to ongoing climate change and Arctic Ocean warming temperatures. When these findings are combined with studies of other Greenland and Antarctic Ice Sheet outlet glaciers, results will improve model predictions of the contributions that melting land ice has on sea-level rise. The importance of understanding climate change and glacial response during the Holocene will provide valuable insight on future scenarios that will help inform decision making and future climate policy.

The paper, “The Holocene dynamics of Ryder Glacier and ice tongue in north Greenland” was recently published in The Cryosphere.

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