Life on the Edge: The Science of Glaciers that Meet Oceans

Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)
Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)

In an October 2015 article in Earth & Space Science News, David Holland and Denise Holland suggest steps to increase the understanding of glacier melt to improve projections of sea level rise.

IPCC (Intergovernmental Panel on Climate Change) reports have concluded that anthropogenic causes are to blame for glacier retreat in the last century. They predict that increased melt in the present century will rise global sea levels. The authors report that the contribution of the West Antarctic Ice Sheet, alone will change low-lying coastal and communities worldwide and threaten marine ecosystems.

They note that the rate of sea level rise will be influenced by a number of factors, including the local shifts in the gravitational pull of land masses, along with changes in water currents, wind patterns, and water temperature and salinity. The rebound of land masses, once the weight of glaciers and ice sheets is removed, will also influence sea levels.

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Map of Antarctica (source: Maximilian Dörrbecker [Chumwa])
The complex nature of the interface between ice sheets and the ocean also creates uncertainty about the future of many of the West Antarctic glaciers, as it is difficult to make predictions of how the ice will react in the future. In one possible scenario, the circulation of warm ocean waters that is currently held off by continued cold meltwater runoff from Antarctica could grow larger, and the cold water barrier would no longer block it from teaching the continent. The warm water would thus be able to make direct contact with the underside of the glacier and warm it from below, greatly increasing the glacier melt.

Holland and Holland note that many problems with predicting the effects of West Antarctic glacier melt stem from a deficit of data. Though satellites are able to measure glacier volume, they are unable to observe the water resting underneath glaciers or the land mass upon which some glaciers rest. Another area of difficulty in predicting the melting of the West Antarctic glacier involves a shortfall in scientific understanding of calving—the process in which the section of a glacier front breaks and falls into the ocean. Scientists compare the difficulties of constructing models of calving to the challenges of predicting earthquakes. They remain unable to make long-term predictions about when they will occur.

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Sketch of the Antarctic coast showing interactions of ice sheet, glaciers and oceans. (Source: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany )

Holland and Holland state that in order to create accurate predictions for the contributions of the West Antarctic Ice Sheet to sea level rise, scientists need to couple glacier and ocean models. Currently there is little cooperation between glaciologists and oceanographers, even though both work on sea level rise since each uses separate models specific to their disciplines. To address this problem Holland and Holland report, the World Climate Research Programme (WCRP) has established a project, Climate and Cryosphere (CliC). This project held a meeting in October 2014, in which the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) was established. The project seeks to draw on the efforts glaciological and oceanographic modelers. The participants in the project work together to create coupled and interactive glacier-ocean models. The goal is to follow this suite of glacier-ocean models with regional simulations of specific outlet glaciers such as those found in West Antarctica.

Holland and Holland say that scientists, by coupling glacier and ocean models, can greatly improve the accuracy of future sea level rise projections attributed to the West Antarctic Ice Sheet and its outlet glaciers. Because of the increasing threat of sea level rise to communities around the world, the accuracy of such projections is of great value. It is to be hoped that this importance will support efforts to produce these projections, which require increased cooperative effort between nations and between disciplines.

 

 

 

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