Sediments show bipolar melting cycle

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.

Many factors can affect the rate of sedimentation at high-latitude sites, including the temperature and speed of ocean currents and the debris content of the icebergs. St. John contends that the matching patterns and rates of sedimentation at sites near the two poles suggest a worldwide phenomenon, such as a large-scale climate change.

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