Antarctica

Source: JPL

Nancy Atkinson at Universe Today wrote a fabulous post on what it’s like to hunt for meteorites at the bottom of the world. In her article, she writes about Dr. Lucy McFadden’s research and focus of looking for potential meteorites from the asteroids Ceres and Vesta that may have landed in Antarctica.

Why does one go to Antarctica to look for meteorites?

Although meteorites fall uniformly all over the Earth –estimates are between 30-80 tons a year, — most are in the form of dust. For the bigger rock-sized pieces, many fall in the ocean and those that fall on land can be buried by shifting terrain, broken down by chemical weathering, or are easily confused with Earth rocks. But Antarctica’s blue ice sheets are clear and barren, making it easy to spy a dark rock that’s likely a sample from space.

However, there’s another reason Antarctica is such a great place to look for meteorites. “There’s something special about Antarctica. Meteorites collect in certain areas there,” McFadden said. “The ice sheets are always moving, and the meteorites move with them. But the rocks get trapped by the barriers of the mountains, and that’s where the meteorites are found. Once you get a meteorite up against a barrier, the constant blowing of the polar winds ablates the ice, and rocks effectively come to the surface.” Over periods of tens or hundreds of thousands of years, very significant concentrations can build up in these areas.

There have been many previous finds of meteorites in Antarctica as well. This site lists some of the more famous finds and their locations.

I’m going to summarize two global warming and climate change studies that were published today.

Ice cores reveal fluctuations in the Earth’s greenhouse gases
A core drilled through 3 kilometers of ice in the middle of Antarctica has returned CO₂ (carbon dioxide), CH₄ (methane) and O₂ (oxygen) stretching back 800,000 years. Temperature curves (implied based on the ratio of O₂ isotopes) mostly show a close correlation between the amount of CO₂ in the atmosphere and the relative temperature.

“The temperature curve over the past 800,000 years matches the CO2 curve beautifully – during glacial periods in which the climate is cold, there is less CO2 in the atmosphere,” says Professor Thomas Blunier from the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen. He explains that when it is cold there is less plant growth, and so there are fewer plants to absorb the CO2 from the air, while more CO2 is absorbed in the oceans, so the final calculation is a low CO2 content in the atmosphere during glacial periods. This produces a lower greenhouse effect, and leads to an even colder climate.

However, the new results show that during the glacial period that occurred between 650,000 and 750,000 years ago, the CO2 level was extremely low – lower than any previous measurements have indicated. It happened twice in this period, while the temperature was not lower than during other glacial periods.

Warming climate is changing life on global scale
A NASA study suggests that human induced climate change is impacting ecosystems and habitats at a large scale. The study looked at physical and biological impacts going back to 1970 and compared them to rising temperatures over that time frame.

Observed impacts included changes to physical systems, such as glaciers shrinking, permafrost melting, and lakes and rivers warming. Biological systems also were impacted in a variety of ways, such as leaves unfolding and flowers blooming earlier in the spring, birds arriving earlier during migration periods, and plant and animal species moving toward Earth’s poles and higher in elevation. In aquatic environments such as oceans, lakes, and rivers, plankton and fish are shifting from cold-adapted to warm-adapted communities.

The team conducted a “joint attribution” study. They showed that at the global scale, about 90 percent of observed changes in diverse physical and biological systems are consistent with warming. Other driving forces, such as land use change from forest to agriculture, were ruled out as having significant influence on the observed impacts.

Rocks and boulders collected from glaciers in Antarctica could help scientists determine glacial behavior and impacts of climate change along the West Antarctic Ice Sheet.

Scientists from the British Antarctic Survey, Durham University and the Alfred Wegener Institute for Polar and Marine Research collected football (soccer one can assume?) sized boulders. It sounds like the researchers used a form of cosmogenic dating to determine how long the boulders had been exposed to sunlight.

Image credit: NASA

Initial results show that Pine Island Glacier has ‘thinned’ by around 4 centimetres per year over the past 5,000 years, while Smith and Pope Glaciers thinned by just over 2 cm per year during the past 14,500 years. These rates are more than 20 times slower than recent changes: satellite, airborne and ground based observations made since the 1990s show that Pine Island Glacier has thinned by around 1.6 metres per year in recent years.

[...]

Co-author Dr Mike Bentley from the University of Durham said, “When rocks are left high and dry by thinning glaciers they are exposed to high energy cosmic rays which bombard the rock. This creates atoms of particular elements that we can extract and measure in the laboratory - the longer they have been exposed the greater the build-up of these elements. The discovery that we can place a fix on when rocks were left behind by the ice has revolutionised our understanding of how the Antarctic ice sheet has behaved in the past.”

British scientists are reporting in the latest journal of Geology that the retreat of the Antarctic ice shelves is not a new phenomenon. From the article:

Writing in the latest issue of the journal “Geology,” British scientists said a survey had shown that ice shelves had retreated thousands of years ago as a result of rising air and ocean temperatures. “What this tells us is that ice shelves don’t just break up because they get too big as the global warning skeptics argue,” said Dominic Hodgson, a scientist with the British Antarctic Survey and one of the leading investigators.