The two “problem children” of West Antarctica – the Thwaites Glacier and the Pine Island Glacier – have lost great amounts of ice in recent decades and continue to melt extremely rapidly. According to a new study, the loss of ice from these two glaciers could contribute to sea level rise of up to 3.4 meters in the coming centuries. The study, published in the journal Nature Geoscience, involved scientists from the University of Maine, the British Antarctic Survey and Imperial College London, among others.
Thwaites Glacier and Pine Island Glacier are particularly susceptible to rapid melting because the bedrock topography slopes inland and warm ocean water can flow under floating portions of the glacier tongues, causing uncontrolled ice loss. The research team, led by the University of Maine, wanted to understand how relative (local) sea level has changed since the mid-Holocene about 5,500 years ago – a time when the climate was warmer, sea level was higher and glaciers were smaller than today.
To do this, they collected shells and penguin bones from remote islands in Pine Island Bay on former beaches that are now above modern sea level. Using radiocarbon dating, the team examined shells and bones to determine when the beaches were formed. Using the data they obtained, they found that relative sea level in the region has steadily declined over the past 5,000 years, suggesting that glaciers have been relatively stable during this time without large-scale increase or retreat.
Large glaciers load the earth’s crust with their weight and push it down. When large areas of ice melt, the earth’s crust rises again, so that former beaches are now higher than sea level.
“Relative sea-level change allows you to see large-scale crustal loading and unloading by ice. For example, glacier readvance, which would result in crustal loading, would slow the rate of relative sea-level fall or potentially even cause submergence of the land below sea level,” said Brenda Hall, a professor in the University of Maine’s School of Earth and Climate Sciences and Climate Change Institute and co-author of the study.
Examination of the shells also revealed that the relative sea level drop at that time was almost five times lower than today, for which the current rapid loss of ice in the region is most likely responsible.
Dr. Joanne Johnson, a geologist with the British Antarctic Survey and lead researcher with the Geological History Constraints team, which is part of the international Thwaites Glacier Collaboration that conducted the research, explains, “Looking back in time allows us to understand how these massive glaciers react to changes in climate. Our results show that even when climate was warmer 5,000 years ago, the glaciers were not substantially smaller than they are today. However, the much slower rate of relative sea level fall we measured implies that the dramatic ice loss we are now seeing is unprecedented in the recent geological past. We urgently need to understand more about these glaciers to determine whether their current retreat could be reversed, and under what conditions that could happen. This is crucial if we are to plan effectively for future sea level rise.”
Julia Hager, PolarJournal
Contributed image: David Vaughan
Link to the study: Scott Braddock, Brenda L. Hall, Joanne S. Johnson et al. Relative sea-level data preclude major late Holocene ice-mass change in Pine Island Bay. Nature Geoscience, 2022; DOI: 10.1038/s41561-022-00961-y.
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