Researchers studying Petermann Glacier in northwest Greenland have identified an unexpected interaction between ice and ocean, causing unexpected glacier melt. The interactions could point to accelerated levels of future sea level rise beyond what was previously projected by experts.
The study’s authors, from the University of California, Irvine and NASA's Jet Propulsion Laboratory, examined Petermann Glacier’s grounding line — the transition boundary where grounded ice meets ocean waters, at which point ice begins to float and melt in the ocean. This boundary has been described as “crucial for measuring and understanding ice sheet mass balance, glacier dynamics, and their contributions to sea level rise.” The grounding line is a point within the larger grounding zone, which encompasses a broader transition “from fully grounded ice to freely floating ice.”
The grounding line is a critical metric, as glaciers around the globe are melting quickly and ice loss contributes to sea level rise. Glacier melt is accountable for 21% of global sea level rise over the past two decades. In Greenland alone, billions of tons of ice have been melted into the ocean, accounting for 14 mm of global sea level rise over the past five decades.
Prior to the study, grounding lines were believed to be relatively stable, not subject to ice melt or any migration during tidal cycles.
However, the authors discovered that the warming ocean in fact melts the underside of Petermann Glacier as well as moving the grounding line. During the study period of six years, from 2016 and 2022, the grounding line of Petermann Glacier retreated almost 4 kilometers and was subject to a 670-foot-tall cavity beneath the glacier due to the warm ocean waters. The cavity remained open during the entire tidal cycle in 2022.
This previously unaccounted-for interaction between ice and ocean changes preexisting projections of sea level rise. "These ice-ocean interactions make the glaciers more sensitive to ocean warming," said co-author Eric Rignot, UCI professor of Earth System Science and NASA JPL research scientist.
"These dynamics are not included in models, and if we were to include them, it would increase projections of sea level rise by up to 200 percent — not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica," Rignot continued.
Sources: PNAS, Nature, Earth-Science Reviews, Nature, PNAS, ScienceDaily