What’s the first thing that comes to mind when you hear Antarctica or Greenland? If you’re like most people, the answer is probably ice and lots of it. And, it is ice that draws paleoclimatologists literally to the ends of the Earth in the quest for knowledge about where our planet has been, where it is, and where it might be going.
A Bubbly Record of Climate Conditions
Ice provides a unique contribution to our view of past climate because the bubbles within ice cores capture the gas concentration of our well-mixed atmosphere while the ice itself records other properties. At Earth’s highest latitudes and altitudes, ice is typically the only environmental data available for scientists to reconstruct the climate hundreds to thousands of years ago.
Scientists obtain this information by traveling to ice sheets, like Antarctica or Greenland, and using a special drill that bores down into the ice and removes a cylindrical tube called an ice core. Drilling thousands of meters into ice is a feat of technology, endurance, and persistence in extreme environments, exemplified by the joint Russian, U.S., and French team that worked together to recover the iconic record of atmospheric carbon dioxide from the ice at the Russian Vostok Station in Antarctica in 1987. In 2012, Russian scientists extended the ice core to an incredible 3,768 meters, reaching Lake Vostok underneath the East Antarctic Ice Sheet.
After scientists procure ice cores, they slice them up into various portions each allotted to a specific analytical or archival purpose. As the scientists divide the cores for analysis, they don special clean suits to prevent the core samples from becoming contaminated. Once they've prepared the samples, the scientists run a variety of physical and chemical analyses on the cores. Some of these ice procedures are consumptive, meaning their analysis requires destruction of the ice, while others have no effect on the ice. Scientists study the gas composition of the bubbles in the ice by crushing a sample of the core in a vacuum. Overall, most of the core is reserved for archival purposes, preserving a long record of Earth's history for future research.
The Layers of Information in Ice Cores
Ice cores have distinct layers in them that form throughout the years. With each passing year, snow falls over the ice sheets and each layer of snow has a different texture and a different chemistry, with winter snow differing from summer snow as well. During the summer, when the sun is up for 24 hours many days, the top layer of the snow changes in texture. As winter arrives and it turns cold and dark again, new snow falls on top of the summer snow forming distinct layers. Each of these layers provides scientists with a vast amount of information about the climate each year.
Ice cores can tell scientists about temperature, precipitation, atmospheric composition, volcanic activity, and even wind patterns. The thickness of each layer allows scientists to determine how much snow fell in the area during a particular year. When several cores are taken from nearby locations, scientists can also determine wind patterns based on where the snow drifted, which can be interpolated from the thickness of the layers in the cores. And, the chemical composition of the snow itself can tell scientists about the temperatures in the area as colder temperatures lead to a higher concentration of a particular oxygen isotope in the snow.
Depending on atmospheric conditions, dust from nearby locations can also accumulate in the layers of ice cores. In addition to seasonal dust, gigantic volcanic eruptions anywhere on the globe can spew enormous quantities of dust into the atmosphere that can accumulate in ice. All of the dust layers, combined with the chemical composition of the ice and a flow model that assesses how the ice accumulates over time allow scientists to date the age of ice cores.
Weaving a Continuous Picture of Past Climate
Scientists tie all of these different threads of information provided by the ice cores together and weave them into a single continuous picture of Earth’s past climate. Visit the Ice Core page to access these data from NCEI’s Paleoclimatology Program.
