May 13, 2000

No Icebergs

Waves breaking over the back deck of the Nathaniel B. Palmer.

Larsen Ice Shelf research

Prior to beginning to report on our research it is important to understand why we are in the Antarctic and the Larsen Ice Shelf area in particular. Mounting evidence suggest that the earth is experiencing a period of rapid climatic change. Throughout the Antarctic Peninsula changes in ice cover, the extent of ice sheets and sea ice development along with changes in nesting habits of various penguin species reflect what historical temperature records tell us, the average temperature is rising. Understanding whether this temperature increase is due to "global warming" or is simply part of a cyclic trend in global temperatures is the goal of this Antarctic research.

The Antarctic Peninsula is the focus of this research because it is the refrigerator of the Antarctic. Small changes in temperature have a much more dramatic effect here than in the colder parts of the continent. Just as the effect of leaving the refrigerator door open has much more effect on the foods inside than leaving the freezer door open does. Over a short period of time, the foods in the 'fridge will warm to a critical temperature faster than those in the freezer.

On this cruise we will be collecting samples and data that, when processed, will help us to understand the history of the northern Larsen Ice Shelf during the Holocene, the past 10,000 years of earth history. Currently the northern Larsen Ice Shelf is undergoing catastrophic retreat as evidenced by the breakup of the ice sheet over the past 5 years. This breakup has been monitored by satellite imagery. This breakup is clearly related to the pronounced warming trend that has occurred in the Antarctic Peninsula over the past 40 years but whether this warming trend is related to global warming or is part of a cyclic temperature regime is far from clear. Research on this cruise will hopefully provide some insight into this question.

Sediments accumulating on the ocean floor can be used to infer a climatic history. With a fixed core length, the rate of sediment accumulation governs how far back in time you can look. The slower the sedimentation rate the longer the period of time recorded in a core. Cores taken in areas of high sedimentation show finer detail and hence allow for more detailed records, but span a shorter period of time. Past work along the western side of the Antarctic Peninsula in areas of both high and low sedimentation rates has generated climatic history curves that correspond well for the sections that overlap, approximately the past 3700 years. In the west Antarctic Peninsula temperature oscillations between warm and cold appear to have occurred in 50 to 70 year, 200 to 300 year and 2500-year cycles over the past 8000 years.

This research which involves US, Canadian and Italian researchers plans to collect cores that will allow for similar climatic constructions to be created for the east side of the Antarctic Peninsula. The Larsen Ice Shelf area is unique because the breakup of the ice sheet over the past few years has made the underlying sediments accessible for the first time.

Bottom sampling is accomplished with a number of different instruments that I will highlight in upcoming postings.

It's just after noon on Saturday, the sky has cleared, seas are still running around 12-14 feet and although the sun is out it is dramatically cooler, around 32 F with a strong wind out of the west. We have not sighted any icebergs yet, but certainly could at any time. Current position is 60 45 south, 58 19 west. Assuming we keep up our current speed we should be off the coast of King George Island around 9 tonight and in the Antarctic sound by dawn on Sunday.

Cheers from the south,

Dave Tewksbury
tewksbda@nbp.polar.org

<< May 13 * May 14>>