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Ice at the end of the Earth
By Christopher Darvill - Durham University
The westerly winds batter the tent, signalling that it’s time to get up. At this latitude, they pass unhindered around the world save for a small piece of land jutting into the Southern Ocean. This is Tierra del Fuego, southernmost South America, written into science and legend by Darwin and Chatwin. It is a sensational landscape, from the jagged mountains of the Cordillera down to the low pampas plains where we are camped. Such a place invites a mixture of weird and wonderful people – scientists and travellers alike. We met a Canadian the other day, battling the winds on a unicycle.
Occasionally a vehicle rumbles past but no-one stops; we just get odd looks. Yesterday’s task was mapping the hummocks that pockmark the surrounding fields. Thousands of years ago, during a period called the Last Glacial Maximum, global climate was much cooler and this caused huge lobes of ice to flow down from the mountains, splaying out over these vast plains and eroding and dumping great volumes of debris in moraines. The most obvious signs of this former ice are the enormous blocks of granite, as big as houses, dumped on the valley side. Darwin thought the rocks were moved by icebergs, but only because he could not conceive that such a glacier could have travelled so far.
I am here to establish exactly when ice advanced and retreated. That can tell us about climate change in the past; but working out a chronology is difficult. Today we are digging down into layers of gravel moved by glacial meltwater and sampling at different depths. When the ice deposited these materials, they became exposed to the atmosphere for the first time and started accumulating rare isotopes like 10Be and 26Al, triggered by cosmic rays from outer space. Back in the UK we can measure the isotopes to work out how long ago the ice advanced to expose the rocks. Advancing ice can mean a changing climate and the timing of that change can tell us about how the southern hemisphere climate system works.
In the evening, we find another place to pitch the tent for the night. After six o’clock, the sun drops to the horizon beneath a thick layer of grey cloud and the grass blazes a bright golden-orange. The colours are magical, but the winds are picking-up again; it’s time for bed.
Field notes in the wind, Tierra del Fuego, southernmost South America. My Ph.D. research is into the timing of advance and retreat of huge ice lobes in the region, and using this to infer changes in past climate. These winds have a dramatic effect on both precipitation and note-making!