First, the ice is made of hydrogen and oxygen atoms, which together form the familiar water molecule of high school science class. 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 cores, 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. In short, the ice cores from Greenland and Antarctica have told us a lot about climate change going back hundreds of thousands of years.
As interesting as the ice core work in the polar regions has been, it’s been rather limited geographically. That is to say, we are interested in climate all over the Earth, and in particular where we live, more than we are interested in climate change just at the poles.
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 1800 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,” said Prof. Lonnie Thompson in a press release from Ohio State University. Thompson is the lead author of a study of the Peruvian ice core. “In fact, having drilled ice cores throughout the tropics for more than 30 years, we now know that this is the highest-resolution tropical ice core record that is likely to be retrieved,” he said.