Tuesday, November 13, 2007

Snow Day from 11/08/07

Snow Day- 11/8

The weather wasn’t very good for doing science yesterday. The crew went out for a bit, but had to come back to came when snow started to fall making visibility a problem. Dr. Marv Speece entertained us in the afternoon with a lecture on geophysics. We went to bed last night with fluffy snowflakes falling through still air. Sometime around three this morning the wind started howling so that the tents were all flapping frantically. Needless to say, no data collection again today. It’s hard to tell if it’s currently snowing or are the 20+ mph winds just blowing the fluff that fell yesterday. Current temperature is around 17F, positive numbers thank goodness. Anyway, it’s hard to see much except shades of white and gray, and even more difficult to function outside for very long.

Our chief, Dr. Ross Powell, Glacial Sedimentologist from Northern Illinois University, continued our lecture series on glaciers in the science tent. Ross first visited Antarctica in the 70’s as a graduate student and has been here numerous times since then. He’s been particularly interested in the Mackay glacier over the last ten years and is very keen to get some good sediment records showing up on our seismic survey. On days that we’re working at the survey site, his primary responsibility is supervising the data collection process and pondering the great complexities of glacier behavior.

Today’s lecture focused on different types of glaciers, their behaviors and sediment records based on climatic differences, and how that all relates to future climate changes. I asked Ross to explain what we’re all doing here in Granite Harbor and gave him a two paragraph maximum.

Ross says, “On the continental shelf around Antarctica are some very deep troughs and basins that were scoured and eroded out when the ice sheet was much larger and expanded over those areas. Since the ice sheet last started to shrink and retreat, some of those troughs and basins, which can reach over 900 meters below sea level, have been special repositories for marine sediment. Ocean currents have carried and concentrated sediment in the basins so that it accumulates very rapidly, at a rate of several millimeters every decade. Because these basins have been exposed and have been receiving this sediment over the past 20,000 to 7,000 years as the ice sheet retreated and opened-up the continental shelf, thick accumulations of these geologically very young sediments has been stored in the basins, some now reaching up to 200 meters thick. These thick piles of sediments are made mainly of the remains of marine plants or algae named diatoms that form the basis of the food web in the highly productive Southern Ocean. These marine plants need sunlight and a good supply of nutrients from the water to flourish; some even like living in sea ice that forms every winter around Antarctica by sea water freezing. Nutrients are best provided by strong winds blowing across the water surface causing deep waters that carry the nutrients to rise up to the surface where the diatoms live.

What we want to do is core one of these types of sediment records that now lie at the bottom of the Mackay Sea Valley, and look for periods of time in the core when diatoms were flourishing and when they weren’t, going back over the last 7,000 years. Other types of sediment accumulate when diatoms are not abundant, because waters are either less nutritious or perhaps were covered with very thick sea ice cutting down on the sunlight reaching the upper seawater layer. These types of records can tell us a great deal about the ocean circulation changes over time, which we want to understand, and compare those changes in Antarctica with what has happened in lower latitudes such as around New Zealand and even in tropical waters closer to the equator. We need to understand how these ocean waters in different areas of the world are linked to each other, so we can better predict how they may change as global warming continues. It is especially important for Antarctica because of the possibility of all of its ice melting as Earth continues to warm.”

Thank you very much, Ross!

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