In 1998, ODP scientists extracted a 150-foot-long sediment core from the muddy bottom of the Palmer Deep - a submerged section of the continental shelf along the west Antarctic Peninsula about 3,000 feet below sea level. The sediment sample was loaded with the shells of microscopic creatures called diatoms dating back some 10,000 years to the beginning of the Holocene - the most recent geologic epoch.

"The Antarctic Peninsula is an ideal region to investigate climate change at decadal to millennial time scales due to its location in one of the Earth`s most dynamic climate systems," notes Dunbar. "The ODP sample gives us the first continuous, high-resolution Holocene sediment record from the Antarctic continental margin."

The sediment sample revealed higher concentrations of diatom shells during the mid-Holocene, roughly 5,500 to 7,000 years ago, which indicates that the waters surrounding the Antarctic Peninsula were more biologically productive then.

According to Dunbar, higher productivity suggests that sea ice was less abundant during the mid-Holocene - a further indication that temperatures were higher.

"We think it was quite a bit warmer then," he observes, noting that geochemical analysis of the sediment also revealed higher levels of nitrogen during the mid-Holocene.

"Warmer temperatures may have produced freshwater streams that fed nitrogen and other nutrients into coastal waters," he explains.

Climate surprises

Further analysis revealed other surprises. According to the researchers, Western Antarctica appears to have undergone periods of warming and cooling during the mid-Holocene - regular cycles lasting 400, 200, 140 and 70 years.

"We believe these cycles of warming and cooling may have been caused by variations in the amount of energy emitted by the Sun," says Dunbar, noting that solar activity routinely increases and decreases on a predi
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
14-Dec-2001