Evidence harvested from ocean sediments suggests that the North and South Poles have experienced regular periods of significant melting simultaneously.
A 600-meter core drilled from a site off Greenland's eastern coast and a 200-m core from off Antarctica reveal several episodes of particularly high sediment accumulation in the past 3 million years, says Kristen E. St. John, a geologist at Appalachian State University in Boone, N.C.
These spates of high sedimentation occurred about 0.9 million, 1.9 million, and 2.8 million years ago and match periods of increased sea level. During these times, about twice the average amount of coarse sand fell onto the ocean floor at the drilling sites. St. John says the increased sandfall probably occurred when sand-riddled ice sheets disintegrated into flotillas of icebergs. As these melted and drifted toward lower latitudes, they dropped the sand to the ocean bottom, she contends.