Researchers from the University of California, Irvine (UCI) and NASA's Jet Propulsion Laboratory have made a groundbreaking discovery regarding the rapid ice melting in Greenland. While studying the Petermann Glacier in northwest Greenland, the team identified a previously unknown interaction between the ice and the ocean, which could have significant implications for future sea level rise predictions.
Using satellite radar data from European missions, the UCI/NASA team observed that the grounding line of the Petermann Glacier, where the ice detaches from the land bed and floats in the ocean, experiences substantial shifts during tidal cycles. This movement allows warm seawater to intrude and accelerate the melting of ice. The findings, published in the Proceedings of the National Academy of Sciences, suggest that the magnitude of future sea level rise caused by polar ice deterioration may have been significantly underestimated by the scientific community. Lead author Enrico Ciraci, UCI assistant specialist in Earth system science and NASA postdoctoral fellow, highlighted the unexpected migration of Petermann Glacier's grounding line during tidal cycles. This migration, ranging from 2 to 6 kilometers, is an order of magnitude larger than what was previously believed for grounding lines on a rigid bed.
The traditional understanding was that grounding lines beneath ocean-reaching glaciers were stationary during tidal cycles and did not experience ice melt. However, the study challenges this notion by revealing that warm ocean water infiltrates beneath the ice through preexisting subglacial channels, resulting in the highest melt rates occurring at the grounding zone. The researchers observed that the grounding line of Petermann Glacier retreated nearly 4 kilometers between 2016 and 2022. As a consequence, warm water carved a massive cavity, approximately 670 feet tall, in the underside of the glacier, and this cavity persisted throughout 2022.
Senior co-author Eric Rignot, UCI professor of Earth system science and NASA JPL research scientist, emphasized that these ice-ocean interactions make the glaciers more vulnerable to ocean warming. Importantly, these dynamics have not been included in models used for sea level rise projections. If incorporated, they could increase the estimates of sea level rise by up to 200 percent, not just for Petermann Glacier but also for other glaciers ending in the ocean, including northern Greenland and Antarctica.
The PNAS paper highlights that the Greenland ice sheet has already lost billions of tons of ice to the ocean in recent decades, predominantly due to the warming of subsurface ocean waters driven by climate change. Exposure to ocean water intensifies the melting of ice at the glacier front and weakens the resistance to glacier movement, causing accelerated sliding of the ice toward the sea.
The research conducted by Ciraci was supported by the NASA Postdoctoral Program at the Jet Propulsion Laboratory. The study involved collaboration with scientists from various institutions including UCI, Finland's Iceye mission, China's Tongji University, the University of Houston, the German Aerospace Center, and the Italian Space Agency.
In conclusion, this pioneering study reveals the previously unknown impact of tidal cycles on ice melting in Greenland. The findings highlight the vulnerability of glaciers to warm ocean water intrusion and call for the inclusion of these dynamics in future sea level rise projections. The implications extend beyond Petermann Glacier to other glaciers in Greenland and Antarctica, emphasizing the urgent need to reassess predictions of sea level rise in the face of climate change.
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