The bubbles visible in this piece from an Antarctic ice core sample contain carbon dioxide and other gases that were trapped in the ice when formed thousands of years ago

About Ice Cores

Introduction

Glaciers form as layers of snow accumulate on top of each other. Each layer of snow is different in chemistry and texture, summer snow differing from winter snow. Over time, the buried snow compresses under the weight of the snow above it, forming ice. Particulates and dissolved chemicals that were captured by the falling snow become a part of the ice, as do bubbles of trapped air. Layers of ice accumulate over seasons and years, creating a record of the climate conditions at the time of formation, including snow accumulation, local temperature, the chemical composition of the atmosphere including greenhouse gas concentrations, volcanic activity, and solar activity.

The dark band in this ice core from the West Antarctic Ice Sheet Divide (WAIS Divide) is a layer of volcanic ash that settled on the ice sheet approximately 21,000 years ago

The dark band in this ice core from the West Antarctic Ice Sheet Divide (WAIS Divide) is a layer of volcanic ash that settled on the ice sheet approximately 21,000 years ago.
—Credit: Heidi Roop, NSF

Ice cores are cylinders of ice drilled from ice sheets and glaciers. They are essentially frozen time capsules that allow scientists to reconstruct climate far into the past. Layers in ice cores correspond to years and seasons, with the youngest ice at the top and the oldest ice at the bottom of the core. By drilling down into the ice sheet or glacier and recovering ice from ancient times, scientists are able to determine the past composition and behavior of the atmosphere, what the climate was like when the snow fell, and how the size of ice sheets and glaciers have changed in the past in response to different climate conditions. Ice cores have provided climate and ice dynamics information over many hundred thousand years in very high, sometimes seasonal, resolution. This information allows scientists to determine how and why climate changed in the past. By understanding how and why climate changed in the past, scientists are able to improve predictions of how climate will change in the future.

Because of their high time-resolution, the physical nature of their proxy records, and their ability to archive actual greenhouse (and non-greenhouse) gas concentrations from the past, ice cores have become one of the golden standards in paleoclimate research.

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