Geodetic Science Snapshots - Cryosphere

A novel combination of ground penetrating radar and terrestrial LiDAR scanning provides details about the state of seasonal snowpack in Colorado without destroying the snow layers. Testing shows high variability in volumetric liquid water contents. The rapid changes in the amount of liquid water occurred in small areas over short time periods. Understanding the state of a snowpack is important for managing water resources.

The freeze-thaw dynamics of permafrost on the north slope of Alaska was measured over 12 years using a Global Navigation Satellite System (GNSS) site permanently embedded in the permafrost near Barrow, Alaska. The data reveal subsidence due to thawing each summer plus interannual variations. The technique provides a new spatial and temporal approach to quantify permafrost changes and it can be applied at more than 200 GNSS sites in cold regions.

GPS measurements in the Amundsen Sea Embayment show a rapid rise of as much as 41 millimeters per year. One reason for the rapid rise is a softer, more pliant mantle beneath the land surface. This may have implications for global sea level change forecasts.

Ground-based GNSS sites can measure the extent of sea ice. The method relies on measuring the signal to noise ratio of the satellite signal that reflects off of the ice. A single GNSS site, GTGU, situated on the coast of a bay at the Onsala Space Observatory, Sweden, measured sea ice extent over a three-year period.

Snow accumulation along the Mercer and Whillans ice streams in West Antarctica was measured between 2007 and 2017 with an array of Global Positioning System (GPS) stations. The snow was measured using the signals from GPS satellites that reflect off of the snow surface into the bottom of the station antenna; an innovative and cost-effective method called GPS interferometric reflectometry (GPS-IR).

Greenland’s ice and snow mass has been melting at an accelerated rate for many years. A network of GNSS sites, set-up on coastal bedrock, has been utilized to measure a huge outflow of ice and water in 2012 and 2010 from the Rink Glacier. The horizontal motion at the GNSS site captures a solitary mass transport wave traveling coastward down the glacier in the summers of those two melt years.

Global Positioning System (GPS) measurements of the uplift of the ground surface beneath the Greenland ice sheet is critical to determining the amount of ice mass that has been lost since the Last Glacial Maximum (LGM). The GPS data show larger uplift rates than previously recognized and suggest that satellite studies have underestimated the ice mass loss by about 20 gigatons per year or about 1.5 meters of sea level rise since the LGM.

In Palmer Land, in the southern Antarctic Peninsula, the pattern of deformation measured by a dense network of GPS receivers cannot be explained by our current understanding of ice sheet change across the region. In particular, the GPS measurements indicate that either there was more ice in this region in the past, or ice retreat in the southwestern Weddell Sea region continued until much more recently than previously thought.

GPS sensors record the motion of the Helheim Glacier in Greenland as ice calving occurs at its terminus. As the iceberg rotates and rolls off sideways, the glacier springs backwards and moves downwards. This action produces an earthquake and the GPS sensors record all the motion and help to explain how glacial earthquakes occur.

The North Antarctic Peninsula (NAP) has lost significant ice over decades and the amount and rate of land rebound as the ice is removed can be used to decipher the structure of the crust and upper mantle. Using vertical motion of the land recorded at the Palmer GPS site since 1995, augmented with other GPS data and a simple four-layer model yields a thicker crust and a more fluid upper mantle than expected.

The ice stream in northeast Greenland shows rapid ice loss because of rising air surface temperatures and the loss of sea ice, which is associated with rising sea surface temperatures. The thinning glaciers are detected by a combination of satellite and aerial imagery plus GPS measurements of ground surface rebound.

Imaging and other measurements over two years shows that an ice cliff in coastal Antarctica is eroding much faster than in the past 10,000 years due to recent climate changes. The Antarctic landscape is being transformed much faster than natural processes, even though the continent has a relatively small human footprint.

Snow and ice melts in Greenland every summer, but the summer of 2010 melting season was so much longer and hotter than in previous years that an extra 100 billion tons of ice melted from the ice sheet and flowed out to sea. GPS measurements captured the extra or anomalous uplift of the bedrock in response to the greater than normal summer loss in ice mass.

Researchers have been monitoring melting ice for years in an attempt to understand how ice sheets will affect our changing climate. One way to watch the melting is by using networks of scientific GPS stations such as POLENET. POLENET covers much of the coast of Greenland and Antarctica, as well as a few tall mountains that rise above the ice sheet in the interior of Antarctica. John Wahr of the University of Colorado Boulder works on refining the method of using GPS data to determine melting rates.

Melting continental glaciers, such as the Stikine icefield in Alaska and Canada contribute to rising sea-level, and therefore it is important to monitor how quickly individual glaciers are losing mass.