11 June, 1998

Could the East Antarctic Ice Sheet have collapsed as recently as 3 MA? When did the ice sheet form? Is the East Antarctic Ice sheet stable? Unlike the ice in Western Antarctica, this ice is grounded well above sea level. Some groups posit it is stable, others claim that it is dynamic. This field season, we will be gathering evidence that may help to resolve these questions.

When we are in Beacon Valley this austral summer, we will be sampling and mapping.

There is evidence that there is ice that is as old as 12 million years. The age is constrained (bracketed) by a layer of ash above the ice, and a layer below. The ash is in place - that means that it has not been rained on, moved around by glaciers or anything else. Volcanic ash can be absolutely dated by radiometric methods. We will use Ar39/Ar40. This analysis will be done in the lab over the northern summer.

The evidence for a stable ice sheet are:

The buried ice" is a key piece of evidence for the claim of a stable East Antarctic Ice Sheet.

Cores from the ocean floor around Antarctic show no interuption of sediment from melting icebergs which would be expected if the continent wa ice free during the Pliocene (the geologic time period that includes 3 ma).

The condition of the ash incdicates that it has remained undisturbed since it fell.

TheSirius deposit found in the Transantarctic Mountains contains lake beds with twigs and leaves of Nothofagus trees. The age of this deposit is controversial, and this deposit is one piece of evidence for a "dynamic" East Antarctic Ice Sheet. The Sirius formation is dated by diatoms. Marchant, Denton and Sugden believe that the diatoms were windborne. (Indeed, there are windborne diatoms found at the South Pole)

There is an outcrop of Sirius formation on Mt. Feather, near one end of Beacon Valley.

Hope to hear from you in December and January!!

Cheers and Penguins!

Hillary