RAPID CLIMATE CHANGE AND ARCTIC OCEAN FRESHNING

Abstract

18 O measured in the ice is a proxy for the temperature of the air from which Greenland precipitation is derived, the ice sheet itself acts as a "paleothermometer," one that may be accurately calibrated using gas isotope data and air thermal diffusion constants (e.g., Gatchev and Severinghaus, 2005). These records make it clear that extremely rapid excur- sions in the air temperature over Greenland have been characteristic of both Northern Hemi- sphere glacial conditions during oxygen isotope stage 3 (OIS3, 65- 25 ka) and of the last glacial- to-interglacial transition (ca. 21-10 ka). The variability during these intervals has been char- acterized by millennial-timescale excursions from warm to cold and cold to warm conditions in which the local temperature variations asso- ciated with the individual events have been on the order of 10 °C. Individual fl uctuations have been characterized by a "sawtooth" form, rather like the 100 k.y. Late Quaternary ice-age cycle itself, with the transition from cold to warm atmospheric conditions occurring on a time scale that is short compared to the time scale of cooling. This two-timescale characterization of the individual pulses suggests that they are the consequence of a physical process that involves what is referred to in the language of dynamical systems as a "relaxation oscillation."