22 January, 2003
Glaciers in Antarctica
Antarctica is a desert and the driest place on earth, but the Antarctic ice sheet has an area of about 13.3 million square miles. This enormous amount of ice has accumulated over millions of years with very little melt. It provides a natural laboratory for scientists to study evidence of past climates and environments.
In the Dry Valleys, scientists are studying glaciers in an attempt to measure the mass balance of the glaciers and to relate these data sets with the other hydrological processes including the lakes and streams. The mass of the glacier is balanced when the amount of ice accumulating is equal to the ice that is ablating. (Ablation means the loss of ice through melting or sublimating. Sublimation is the process where the ice changes state from a solid to a gas without melting first.) Understanding the glacier-climate connection today may help unravel mysteries of the past, including ancient Lake Washburn that used to fill Taylor Valley.
To calculate the mass balance of a glacier, or how much ice and snow is lost or gained, scientists place bamboo poles, or ablation stakes, on top of the glacier and then measure from the top of the stake to the surface of the ice twice a season in November and January. They are able to calculate the loss of ice and the gain of snow accumulation.
Andrew Fountain is the PI (principal investigator) from Portland State University who heads the glacier team. This year Thomas Nylen, also from PSU, is leading the studies and data collection in the field and is assisted by Amy Ebnet, a graduate student from PSU.
Thomas told me that Antarctic glaciers are different from others in the world in a several ways. Moraines of Antarctic glaciers are not usually as big as other alpine glaciers in the mid latitudes. Lateral and terminal moraines are where the glacier has dropped rocks from its surface down its sides. Glaciers act as a conveyor belt, transporting rocks down from higher locations. Rocks dropped on top of the glacier slowly move along with the ice as it travels. Eventually they are dropped in front of the glacier. If the glacier retreats, you may see several different terminal moraines.
Another way they are different is in their ablation rates. Antarctic glaciers ablate about 30 cm a year, while other places in the world ablate that much in a day! Last year, the glaciers ablated about one meter because of the warm temperatures AND the amount of solar radiation. Solar radiation is an important variable. For example, yesterday the temperature was above freezing, but there was a heavy cloud cover and little solar radiation. The streams stopped flowing because the melt from the glaciers was low.
An additional difference between Antarctic glaciers and other glaciers in the world is the ratio of ablation. Antarctic glaciers generally ablate in a ratio of 30% melt and 70% sublimation, whereas other glaciers have almost the exact opposite ratio. Along the face of the glacier there is a higher percentage of melt.
An interesting feature on the dry valley glaciers, which also occurs in other parts of the world, is cryoconite holes. When sediment falls on the top of the glacier, it is a darker color than the ice so it absorbs more solar radiation. As it heats up, the sediment melts down 10s of centimeters below the ice surface. Often algae, rotifers, and tardigrades exist in the cryoconite holes. This is just another testament to water bringing forth life, sometimes in amazingly remote and harsh places. Nematodes have not been found in these holes, mainly because there is too much water.
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