Ice Voyage into Antarctic Past
Icy voyage into Antarctic past
Protected by a Danish support ship that nudged aside threatening icebergs, scientists on the most recent leg of the Ocean Drilling Project spent two months in the waters off Antarctica pulling up sediment cores from the ocean bottom. Their cores are leading researchers to revamp scientific theories about the Antarctic's prehistoric shift from a temperate region laced with rivers and forests to its present state as the icebox of the world.
Results from previous drilling projects have suggested that ice sheets started to spread over the eastern end of the Antarctic continent in the early part of the Oligocene period, 35 million years ago. But the sediments from Leg 119 indicate that extensive ice sheets were already covering East Antarctica by 37 million years ago and must have started growing before that time. Moreover, the scientists found evidence that tentatively suggests the ice may date back as far as 42 million years ago.
Part of the evidence comes in the form of glacial till, or sand and pebbles ground up by the action of glaciers. When this till appears in the sedimentary record, it alerts scientists to the presence of ice on the continent, says John Barron, of the U.S. Geological Survey in Menlo Park, Calif., who was co-chief scientist of Leg 119, which ended in February. As well, scientists are examining sections from more northern drill sites that document changes in currents at the ocean bottom. …