June 24, 2013 in City

Rock Doc: Ice studies lead science to core of climatology

E. Kirsten Peters
 

Late in the last century, scientists published reams of data about Earth’s climate derived from ice cores taken from Greenland and the Antarctic. By drilling down into the polar ice with hollow bits, workers were able to pull columns of ice up to the surface. The material brought to light was special for several reasons.

First, the ice cores show annual layers going back in time. That means scientists can count backward through time from the surface downward, a bit like school kids counting the rings of a tree.

The ice has tiny air bubbles in it, air that was trapped in surface snow layers in times gone by. This means that scientists can analyze the small air samples that are sealed in the ice and determine the composition of the air that was blowing around the Earth in past millennia.

Chemical analyses of the air in the glacial ice show that our planet’s atmosphere has gone through cycles of change over thousands of years. In particular, the concentrations of greenhouse gases such as carbon dioxide and methane (the main ingredient in natural gas) have varied over time. The specific dates of the changes can be determined by counting up the layers in the ice core – a pretty nifty trick.

But wait, there’s more!

First, the ice is made of hydrogen and oxygen atoms. But atoms are not all created equal. Some oxygen atoms weigh more than other oxygen atoms – we say that oxygen has different isotopes. The great thing about that fact is that using the ratios of the isotopes of oxygen found in the ice, scientists can calculate past temperatures. Again, by counting up the annual layers in the ice core, we can quite precisely date when temperature changes occurred. Beyond that, some other information about weather and climate can be deduced by things like how much dust is in a particular layer of ice.

As interesting as the ice core work in the polar regions has been, it’s been rather limited geographically. But now new information about climate is starting to be unearthed from two ice cores taken from Peru’s Quelccaya Ice Cap. These two cores have nearly 1,800 annual layers in them. That means they are not anywhere near as long as the polar ice cores, but they are in an interesting place – at a low latitude rather than at high latitudes.

“These ice cores provide the longest and highest-resolution tropical ice core record to date,” Ohio State University professor Lonnie Thompson said in a news release. Thompson is the lead author of a study of the Peruvian ice core.

The Peruvian ice core appears to show the influence of El Nino changes at sea. This gives us a new way to study temperature fluctuations in part of the Pacific Ocean over nearly two millennia.

Climate is complex, and a great deal of effort is required to learn how it has varied in Earth’s past. But step by step we are learning a great deal more than we knew when this Rock Doc read about the Ice Age in elementary school.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard universities. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.


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