http://www.dri.edu
	Spring 2007

Innovation—Layers in Ice Cores Revealed by New Method

Graduate student Rhonda Zager extracts a core from Siple Dome Antarctica.
photo by Dr. Ken Tayler

When researchers are examining cores made of layers of ice—layers laid down thousands, even hundreds of thousands of years ago that preserve records of ancient climate—how do they know where one layer of ice ends and another begins? Ice is not an easy substance on which to conduct research, and one of the issues that ice-core researchers have is how to distinguish—repeatedly and reliably—annual layers of ancient ice in cores. Before samples are taken these cores for analysis, the researchers must have an accurate way of determining from what layer their samples are taken and how that layer correlates to layers in other cores. At DRI, Drs. Ken McGwire and Ken Taylor have developed a new method to aid in ice-core research that helps to address this problem of figuring out where individual layers are in ice cores.

Ice cores are taken from numerous locations for analysis of different records preserved in the layers of ice. Analysis of certain isotopes in ice can help determine what ancient temperatures have been. Dust and ash layers in ice cores show evidence of times when volcanoes erupted, forest fires raged or deserts spread. All of these indicators of ancient climate conditions are found in the ice layers and are used to build a picture of the climate and history of Earth when conditions were quite different from today. To determine when climate changes occurred, researchers need an accurate count of the ice layers to match climate indicators from one place to another.

When researchers have examined ice cores, layers in the ice have been counted by hand, sketched and logged, or estimated from photographs. The problem with all of these methods is that these records are all somewhat subjective. McGwire and Taylor, together with collaborators at the U.S. National Ice Core Laboratory in Denver and Pennsylvania State University, have developed a method using an optical-scanning technique that promises to improve upon how layers in an ice core may be counted. This imaging technique creates an archival image of the characteristics of the core, which is important because the core is destructively sampled by many analysis methods and it degrades over time even if it is kept cold and sealed from air, since it is no longer under pressure.

The optical scanning setup is in a special cold room where the ice cores are processed. In this room, ice cores are loaded into a carriage, which then passes under a scanner, taking images at a scale of less than 1/20th of a millimeter! The scanning process was designed to eliminate many possible sources of image distortion and has the added benefit of minimizing handling. After the images are taken, they are saved for subsequent analysis in the warmth of an office, rather than in the cold room.

~ story by Sara Marcus