Polar ice may well be the purest solid substance on Earth, and yet the impurities it contains—gases, dust, and micro-organisms—provide a rich record of Earth's past climate, volcanism, and one-celled life going back ˜400,000 years. Until recently detailed records had been deciphered mostly in chemical and biological laboratories from meter-long ice cores removed by drills capable of coring to bedrock thousands of meters down. Now, borehole instruments are adding a new dimension to the study of ice sheets. They can rapidly log records of past climate, volcanism, c-axis ice fabric, and soon, even microbial life and grain size.
Gary Clow, a pioneer in borehole logging, has been measuring temperature profiles that provide information on climate and ice flow [Dahl-Jensen et al., 1998]. From sonic velocity profiles, Kendrick Taylor and Gregg Lamorey are able to infer c-axis fabrics, which record the history of ice flow Robert Hawley and Ed Waddington have developed a video logger that detects annual layers in firn ice.