Antarctica
© DGFI/Planetary VisionsChanges in Earth's gravity field caused by West Antarctica ice loss.
West Antarctica's incredible weight loss can be felt from space, a new study reports.

So much ice has disappeared from West Antarctica in recent years that Earth's gravity is now weaker there, researchers reported in the Aug. 28 issue of the journal Geophysical Research Letters.

Earth's gravity fluctuates in small ways that are caused by changes in mass. When hefty ice sheets melt, there is less ice and thus less gravitational force pulling in that area.

The new results come partly from the European Space Agency's GOCE satellites, a four-year endeavor to finely map Earth's gravity. The GOCE gravity map was combined with gravity measurements recorded from the GRACE satellites, an ongoing NASA-Germany mission that tracks changes in Earth's ice sheets via gravity. Merging the information from both satellites allowed researchers to sharply illuminate West Antarctica's ice loss.

The satellites measured a dip in Earth's gravity field due to extensive ice loss in West Antarctica, the new study reports. The shrinking glaciers and ice shelves, whittled by warm ocean currents, tugged more gently when the satellites sped by overhead.

Each space mission consists of two satellites orbiting near each other. Slight distance changes occur between the satellites as they dip or rise over gravity highs and lows. Computers translate those shifts, sometimes smaller than a hair's width, into an estimate of Earth's gravity field.

The precise measurements suggest West Antarctica shed some 209 billion metric tons (230 billion tons) of ice each year between 2009 and 2012. This region of Antarctica may have passed a tipping point into unstoppable collapse, according to earlier studies published this year.

Three of West Antarctica's retreating glaciers account for most of the ice loss, in agreement with past studies. Between 2009 and 2012, Pine Island Glacier lost 67 billion metric tons (74 billion tons) of ice per year; Thwaites Glacier lost 63 billion metric tons (69 billion tons) of ice per year; and Getz Ice Shelf lost 55 billion metric tons (61 billion tons) of ice per year.

The research team, led by Johannes Bouman from the German Geodetic Research Institute, now plans to analyze ice loss from all of Antarctica, according to a statement from ESA. The GOCE satellite mission ended in 2013, when the machines ran out of fuel (as planned) and broke up in Earth's atmosphere.