9 February, 1998
Hello from the Nathaniel B. Palmer! Things are going well here in Antarctica. We worked on the Multibeam survey all day today and the night crew should be finishing it up. After that, we have some deep tow planned as well as some coring (probably kasten cores, due to our little problem with the piston core two days ago). The waves were higher today than they have been in the past. The wind was blowing a lot harder than it has been, and our required path for the survey was sliding us up and down out of the troughs of the waves. It sure made walking in a straight line difficult! There are handrails along all the hallways . . . and they are there to help you out during rough seas. The seas weren't extraordinarily rough, but the handrails still helped! Today was Ashley Lowe's birthday. After we ate chocolate cake (yummmmm!), we played some silly party games. One of the games that we made up was to see who could walk the furthest in a straight line. Julia Smith won . . . but she was only able to walk about 5 feet!
Yesterday, we talked about what an ice SHELF was and how it was formed. That brings us to our question: "How do you suppose the ice SHEET forms." The ice sheet is the large mass of ice and snow that covers most of the Antarctic continent. Many sources describe Antarctica as being 98% covered by ice. Newer satellite images, however, show that ice covers 99.6% of the continent. Antarctica's ice sheets contain 90% of the world's ice and are said to contain between 70-85% of the world's fresh water.
Because Antarctica is the driest continent on Earth, the amount of snow deposited in any one year is relatively low. But Antarctica is also very cold, so the snow has accumulated over many years without melting. As snow is deposited year after year in the interior of the ice sheet, it consolidates to form ice. The ice sheet averages over a mile thick, and it is almost 3 miles thick in some places. You can imagine that the weight of that much ice is very great. As a result of pressure created by the weight of the ice sheet, the ice flows from the high interior of the continent towards the lower Antarctic coast. At the coast, large slabs break off the ice sheet to form icebergs. In some areas, the ice sheet slides off the land and floats on the water . . . which is an ice shelf (like we talked about yesterday). In slightly warmer climates, ice is removed from ice sheets primarily by melting. It is only in a polar setting such as Antarctica where calving of icebergs is the major way that ice is removed from the ice sheet.
The Antarctic ice sheet has two parts -- the East Antarctic Ice Sheet and the West Antarctic Ice Sheet. The East Antarctic Ice Sheet is more stable than the West Antarctic Ice Sheet. This is because the land below the East Antarctic Ice Sheet is almost entirely above sea level. This is called a "land-based" ice sheet. Land-based ice sheets are believed to be very stable and react very slowly to changes in the environment. The West Antarctic Ice Sheet, however, is considered a "marine-based" ice sheet. This means that the base of the ice sheet sits on rocks that are mostly below sea level. In some locations, the West Antarctic Ice Sheet rests on rock over one mile below sea level. Greenland is also covered by a marine-based ice sheet.
Polar ice sheets are considered stable as long as the amount of ice that is added to an ice sheet by precipitation equals the amount of ice that is removed by making icebergs. In marine-based ice sheets, it is easier to upset that balance and lose more material than is gained -- which causes the ice sheet to break down. Marine-based ice sheets can be affected by many different factors, including the flow speed of the ice and the temperature of the ocean. Ice shelves form a direct connection to the ocean and they are an easy way for the ice to thin and break apart on a marine-based ice sheet. Yesterday, we discussed the disintegration of some ice shelves near the Antarctic Peninsula. Researchers are currently studying the West Antarctic Ice Sheet to predict its future stability. In fact, our research here in Antarctica is a small part of the WAIS Initiative (West Antarctic Ice Sheet). The WAIS Initiative is a collaborative study by researchers from many fields of discipline and from many different universities. There are some estimates that the West Antarctic Ice Sheet could collapse within the next 1000 years and cause sea levels to rise as much as 20 feet. Scientists want to have a clear understanding of ice sheets in order to understand what is happening today and predict what will happen in the future.
By now, you should have a pretty good understanding of ice shelves and ice sheets. Tomorrow we will return to our discussion about the ASA staff on board the Nathaniel B. Palmer. Please continue sending your questions to me. I really enjoy reading and answering them! If, for some reason, you don't receive an answer within 48 hours, please resend the question. It seems as though some of the mail has not been getting through. I'm sorry for the inconvenience, but I continue to be amazed at how well things have been working -- especially considering the fact that we are very far away . . . in Antarctica! Looking forward to hearing from you soon! You know I'll be back tomorrow . . .
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