Over the past two decades, ice loss from Greenland's shrinking ice sheet has contributed one quarter of the global rise in sea level. Retreating outlet glaciers were responsible for about half the ice lost. But understanding the dynamics of the calving front — a glacier's terminus, where icebergs split off — remains limited and "poorly understood for several reasons," said NYU Abu Dhabi Postdoctoral Associate and Visiting Assistant Professor Carl Gladish.
For one, access to the environment poses a challenge. For the past five summers, Gladish, who works with the Center for Global Sea-level Change, led by Professor of Mathematics David Holland, has collected observations at Jakobshavn Glacier, through which 8 percent of the Greenland Ice Sheet ultimately flows into the ocean. Jakobshavn terminates at the head of the long, narrow Ilulissat Icefjord. Icebergs as big as skyscrapers, unable to pass the shallow sill where fjord meets ocean, clutter the way. "But, more intrinsically," Gladish continued, "the glacier-ocean interface is simply very complex," involving different systems operating on disparate timescales by little-understood rules.
With temperature and salinity measurements from Ilulissat, Gladish, who received his Ph.D. in atmospheric and ocean science and mathematics, runs numerical models to better understand the interactions between glacier, fjord, and ocean. "It's a hypothetical world," he explained. By varying conditions at the fjord boundaries, he can test different "what-if scenarios." "Modeling cannot substitute for observations," he said. "However, a numerical model allows us to work out the consequences of our hypotheses about what governs the physical behavior" of the environment.
The team is trying to discover how the retreat of a glacier is being driven by melting at the interface of glacier and ocean, an interaction that should have a relatively small impact on a glacier as a whole. "It is kind of like trying to explain why a person can become ill after eating something small that upsets their system," he said. "But there is strong evidence that temperature changes of one or two degrees Celsius are indeed responsible for quite large changes at major glaciers around Greenland."
This article originally appeared in NYUAD's 2013-14 Research Report (13MB PDF).