GPS Measurements of Crustal Uplift near Jakobshavn Isbrae due to Glacial Ice Mass Loss

We analyze 2006–2009 data from four continuous Global Positioning System (GPS)
receivers located between 5 and 150 km from the glacier Jakobshavn Isbræ, West
Greenland. The GPS stations were established on bedrock to determine the vertical crustal
motion due to the unloading of ice from Jakobshavn Isbræ. All stations experienced
uplift, but the uplift rate at Kangia North, only 5 km from the glacier front, was about
10 mm yr−1 larger than the rate at Ilulissat, located only "45 km further away. This
suggests that most of the uplift is due to the unloading of the Earth’s surface as Jakobshavn
thins and loses mass. Our estimate of Jakobshavn’s contribution to uplift rates at Kangia
North and Ilulissat are 14.6 ± 1.7 mm yr−1 and 4.9 ± 1.1 mm yr−1, respectively. The
observed rates are consistent with a glacier thinning model based on repeat altimeter
surveys from NASA’s Airborne Topographic Mapper (ATM), which shows that
Jakobshavn lost mass at an average rate of 22 ± 2 km3 yr−1 between 2006 and 2009. At
Kangia North and Ilulissat, the predicted uplift rates computed using thinning estimates
from the ATM laser altimetry are 12.1 ± 0.9 mm yr−1 and 3.2 ± 0.3 mm yr−1,
respectively. The observed rates are slightly larger than the predicted rates. The fact that
the GPS uplift rates are much larger closer to Jakobshavn than further away, and are
consistent with rates inferred using the ATM!based glacier thinning model, shows
that GPS measurements of crustal motion are a potentially useful method for assessing
ice!mass change models.