mirrored file at http://SaturnianCosmology.Org/ For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== ------------------------------------------------------------------------ next up previous * Next:* GISP2 and GRIP *Up:* The GISP2 ice core * Previous:* The Younger Dryas ------------------------------------------------------------------------ The Last 110 kyr and the Dansgaard/Oeschger Events The isotopic temperature records show 23 interstadial (or Dansgaard/Oeschger) events first recognized in the GRIP record [/ Dansgaard et al/., 1993] and verified in the GISP2 record [/ Grootes et al/., 1993], between 110 and 15 kyr BP. Intensified formation of North Atlantic Deep Water (NADW) has been invoked to explain some of these events. NADW forms when waters from the oceanic thermocline upwell to the surface, cool, and sink in the seas around Greenland. Heat is transferred from ocean to atmosphere in the process. Partly because these seas were ice covered, NADW formation was generally slow during glacial times. Intensification of NADW formation would cause rapid warmings in Greenland and other land masses adjacent to the North Atlantic, which can explain the impressive magnitude of the climate changes as well as their rapidity. These dramatic climate changes were not restricted to Greenland and nearby boreal areas, as evidenced by the GRIP CH record [/ Chappellaz et al/., 1993]. Most of the 23 Greenland interstadial events observed at GISP2 are not yet associated with major changes in Antarctic climate. However, at least eight of the nine Greenland events lasting longer than 2 kyr are linked to periods of warmer climates in East Antarctica [/ Bender et al/., 1994] as inferred from the Vostok isotopic temperature record [/ Jouzel et al/., 1987]. They are also associated with diminished ice volume, as inferred from variations in the O of CaCO in deep sea sediments [/ Shackleton and Pisias/, 1985]. / Bender et al/. [1994] suggested that intensification of NADW formation resulted in some melting of ice sheets and an increased heat flux from the Southern Ocean to the atmosphere, both of which caused Antarctica to warm. Diminution of NADW formation would eventually reverse the climate amelioration and return Greenland and Antarctica to cold, glacial conditions. The GISP2 glaciochemical series provide a sensitive record (see calcium example from / Mayewski et al/. [1994b], and / Bender et al/. [1994], Figure 3) of change in the atmospheric circulation systems affecting Greenland [/ Mayewski et al/., 1994b]. Modeling common temporal behavior of these chemical series reveals a record of change in the relative size and intensity of the circulation system that transports well-mixed air masses to Greenland (the measure of relative size and intensity is defined as the polar circulation index (PCI)). The large-scale atmospheric circulation patterns capable of transporting the seasalt and dust captured in the GISP2 record are dominated by westerly or meridional patterns in the circumpolar vortex; therefore, the periods of increased PCI which mark stadial (cold) intervals indicate stronger and larger-scale circulation [/ Mayewski et al/., 1994b]. Massive iceberg discharge events (previously defined from the marine record and correlated with certain stadials in the ice core record [/ Bond et al/., 1993] can also be interpreted from the glaciochemical record as being accompanied by notable expansions of ocean ice cover (sea ice and icebergs) and the PCI [/ Mayewski et al/., 1994b]. ------------------------------------------------------------------------ next up previous * Next:* GISP2 and GRIP *Up:* The GISP2 ice core * Previous:* The Younger Dryas ------------------------------------------------------------------------ ------------------------------------------------------------------------ /U.S. National Report to IUGG, 1991-1994 Rev. Geophys. Vol. 33 Suppl., © 1995 American Geophysical Union/