The Earth’s gravity field is not uniform. Instead, it mounds in some spots due to the density of rock or ice below, the flow of groundwater or ocean currents and other factors. To measure those variations, the European Space Agency launched the Gravity field and steady-state Ocean Circulation Explorer (GOCE) in 2009.
During its four-year run, GOCE was able to make a number of observations that showed gravity changes over time — including the gravity scar left by the 2011 Japanese earthquake. And, with the help of an older satellite called GRACE, GOCE's observations showed that melting glaciers in West Antarctica have lost so much mass that there's been a dip in gravity over the region. (GOCE provided detail about individual glacial systems.)
An animation from the European Space Agency shows how combined measurements from the two satellites reveal ice mass changes and gravity fluctuations over a section of West Antarctica:
The detailed map of the gravity loss gives researchers another way to analyze how the southernmost continent’s complex ice melt dynamics are driven by global climate change.
News from the past two years that Antartica has reached record high winter sea ice coverage might seem to contradict the new findings, but sea ice and land ice are different. Overall, the Antarctic continent is losing ice — and quickly — when land ice is thrown into the calculation. According to the ESA press release, "Antarctica as a whole has been shrinking in volume by 125 cubic kilometers a year."