A study by a team of researchers from the Rosenstiel School of Marine and Atmospheric Science, University of Miami found that the acceleration of upward vertical motion of the rocky margins of Greenland indicates that accelerated ice loss in western Greenland started in the late 1990s. A paper on their findings was published online 16 May in the journal Nature Geoscience.
The vertical motions of the rocky margins of Greenland and Antarctica respond to the mass changes of the ice sheets that cover them—up to 2 km thick in Greenland’s case.
However, these motions can be obscured by episodes of glacial advance or retreat that occurred hundreds to thousands of years ago, which trigger a delayed response because of viscous flow in the underlying mantle. Here we present high-precision global positioning system (GPS) data that describe the vertical motion of the rocky margins of Greenland, Iceland and Svalbard. We focus on vertical accelerations rather than velocities to avoid the confounding effects of past events.
Our data show an acceleration of uplift over the past decade that represents an essentially instantaneous, elastic response to the recent accelerated melting of ice throughout the North Atlantic region. Our comparison of the GPS data to models for glacial isostatic adjustment suggests that some parts of western coastal Greenland were experiencing accelerated melting of coastal ice by the late 1990s. Using a simple elastic model, we estimate that western Greenland’s ice loss is accelerating at an average rate of 8.7±3.5 Gt yr-2, whereas the rate for southeastern Greenland—based on limited data—falls at 12.5±5.5 Gt yr-2.
—Jiang et al.
According to the study, some coastal areas are going up by nearly one inch per year and if current trends continue, that number could accelerate to as much as two inches per year by 2025, explains Tim Dixon, professor of geophysics at the University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS) and principal investigator of the study.
It’s been known for several years that climate change is contributing to the melting of Greenland’s ice sheet. What’s surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response. Even more surprising, the rise seems to be accelerating, implying that melting is accelerating.
The same process is affecting the islands of Iceland and Svalbard, which also have ice caps, explains Shimon Wdowinski, research associate professor in the University of Miami RSMAS, and co-author of the study.
Using specialized global positioning system (GPS) receivers stationed on the rocky shores of Greenland, the scientists looked at data from 1995 onward. The raw GPS data were analyzed for high accuracy position information, as well as the vertical velocity and acceleration of each GPS site.
The measurements are restricted to places where rock is exposed, limiting the study to coastal areas. However, previous data indicate that ice in Greenland’s interior is in approximate balance: yearly losses from ice melting and flowing toward the coast are balanced by new snow accumulation, which gradually turns to ice. Most ice loss occurs at the warmer coast, by melting and iceberg calving and where the GPS data are most sensitive to changes. In western Greenland, the uplift seems to have started in the late 1990s.
Melting of Greenland’s land-based ice contributes to global sea level rise. If the acceleration of uplift and the implied acceleration of melting continue, Greenland could soon become the largest contributor to global sea level rise, says Yan Jiang, Ph.D. candidate at the University of Miami RSMAS and co-author of the study.
This work was supported by the National Science Foundation and NASA. The team plans to continue its studies, looking at additional GPS stations in sensitive coastal areas, where ice loss is believed to be highest.
Yan Jiang, Timothy H. Dixon & Shimon Wdowinski (2010) Accelerating uplift in the North Atlantic region as an indicator of ice loss. Nature Geoscience doi: 10.1038/ngeo845