Ice logging with light and sound

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.