Glaciers around the globe are shrinking, and they’re disappearing fastest at glacial fronts—locations where the ice meets water. Over the last 20 years, roughly half of the ice loss from Greenland’s ice sheet has occurred at glacial fronts. In order to predict how the world’s glaciers will respond as bodies of water around the world warm and sea levels rise, scientists must first uncover the processes driving ice loss. Both melting and calving—when chunks of ice break off from glaciers—whittle away at glaciers’ mass: Tidewater calving has consumed entire ice fields in Alaska, for example. But forecasting glacial behavior is complicated by the fact that similar climatological conditions can produce varying behaviors: Some glaciers are observed to advance even while their neighbors melt away.
Ice loss via calving has been well studied, but the thermodynamic processes driving melting of glaciers submerged in water is less well understood, despite the fact that much of Antarctica’s ice loss has been attributed to melt beneath floating ice shelves. To fill in this gap, Truffer and Motyka sought to find out how subaqueous melt would affect glacial stability in varied environments around the world. The authors made use of data collected by many teams using multiple methods on subaqueous melt rates, including radar, direct measurements of melt, and measures of water temperature and salinity.
Melting rates are influenced by the temperature of the water, heat transfer across the boundary between the water and the ice, and even the shape of the fjord, which affects the flow of currents over the ice and thus the transport of heat. At the same time, the thermodynamics of the water body into which glaciers are submerged can affect their shape. According to the authors, this two-way relationship, together with variations in water temperature and salinity, can account for much of the confusingly varied behavior of glaciers that end in water.
By analyzing glacier behavior in different settings around the world, the team found that subaqueous melt has a profound influence on glacier behavior—up to a point. Melting may trigger a glacier to rapidly retreat, but once that retreat is well underway, the process of melting may take a backseat to mechanical processes such as calving as the ice becomes increasingly unstable. The study provides new insights into the feedback systems at play in rapidly changing glacial fronts. (Reviews of Geophysics, doi:10.1002/2015RG000494, 2016)
—Kate Wheeling, Freelance Writer
Citation: Wheeling, K. (2016), At the intersection of ice and water, Eos, 97, doi:10.1029/2016EO047627. Published on 9 March 2016.