Melting, not calving, may be driving Antarctica’s ice loss

Nature : Nearly half of Antarctica’s ice shelvesâmdash;the portions of the ice sheet that extend over the oceanâmdash;are thinning due to warming ocean currents, according to new monitoring data and computer modeling. In fact, some ice sheets are losing more ice from such basal melting than from the calvingâmdash;or breaking offâmdash;of icebergs, once thought to be the primary factor in ice-shelf dynamics. Eric Rignot of the University of California, Irvine, and colleagues, whose paper has been published in Science, also found that about half of the total meltwater comes from just 10 small ice shelves along the southeast Pacific coastline. Despite those losses, other ice shelves are thickening or maintaining equilibrium. Rignot and coworkers’ findings point up the difficulty of projecting long-term ice-sheet evolution because of the many factors involved, including sea-floor topography and ocean circulation, which change over time.