The melting of ice has emerged as a pressing concern in recent years due to the visible impacts of climate change. While the focus has largely been on the images of polar bears stranded on melting ice floes, the consequences extend far beyond that. The freshening of seawater, alteration of marine ecosystems, sea-level rise contributing to flooding, and changes in ice-albedo feedbacks all play a role in modifying Earth’s temperature. Recent research published in Geophysical Research Letters sheds light on the impact of late-season melting of the Greenland Ice Sheet and its effect on ice flow.

The Study’s Findings

The study, conducted by Ryan Ing and his colleagues from the University of Edinburgh, focused on the melt events that took place during 2022. This year witnessed seasonal air temperatures that were higher than what had been previously recorded for the Greenland Ice Sheet during the late melt season. The team aimed to analyze the relationship between intense melting events and the annual movement of the ice sheet. While they observed a significant acceleration in ice motion during these events, it was short-lived and did not have a substantial impact on the overall annual motion of the ice sheet.

Using satellite imagery spanning five years, the researchers studied seven glaciers in west Greenland that terminated on both land and in the ocean. They combined ice velocities obtained from GPS and the Sentinel-1 space satellite with meteorological data from weather stations. In 2022, west Greenland witnessed the largest daily run-off in the late-melt season since 1950, with a series of melt events covering around 37% of the ice sheet’s area. The prevalence of warm air over the ice sheet led to surface melting, peaking at 9.6 cm water equivalent per day.

During these melt events, one weather station recorded a rapid increase in air temperature from -17.7°C to 2.7°C within 24 hours. The surge in surface meltwater overwhelmed the subglacial drainage system, lubricating the base of the glacier and reducing basal friction. As a result, the velocity of the ice sheet’s motion increased by up to 240%, reaching a maximum of 236 m per year. However, as the summer progresses and larger subglacial channels develop, the ice motion slows down.

Understanding Subglacial Drainage System

The study highlighted the role of the subglacial drainage system in moderating the impact of seasonal melting on the Greenland Ice Sheet. During the late melt season, the contracting channels beneath the ice become overwhelmed when there is a substantial surge in surface melt. In contrast, during the peak melt season in summer, the larger channels can easily accommodate the extra meltwater, resulting in less pronounced increases in basal water pressure and ice motion.

While the study found that changes in ice motion did not significantly impact the annual ice discharge of the ice sheet, there was a notable increase in total annual runoff due to late-season melt events. This increase in meltwater runoff is critical considering that 50% of the Greenland Ice Sheet’s annual mass loss is attributed to it. The study emphasizes that the increase in annual ice discharge from late-season melt events may not be a primary factor in ice sheet mass loss, but the rise in meltwater runoff is a significant concern that could become more critical as Earth’s climate warms in the future.

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