PHYSICAL PROPERTIES OF THE DEEP ICE CORE FROM CAMP CENTURY, GREENLAND.

摘要

The analyses of crystal sizes, ice fabrics, and air volumes on the surface to bedrock ice core from Camp Century, Greenland were undertaken in order to characterize the large scale physical features of a continental ice sheet. Each of these parameters displays significant variations with depth, and most of these variations are related in some manner to ice flow or climatic change.; The evolution of crystalline textures and fabrics in the Camp Century core is divided according to depth into five zones of development. Through the first three zones crystal sizes increase and fabrics strengthen in a manner similar to that observed in other deep ice cores and predicted in ice sheet models. However, the transition into the fourth zone is marked by a drastic decrease in crystal size and a sudden transformation to strong single pole fabrics. These textural changes constitute a discontinuity which coincides in depth with the transition from Holocene to Wisconsin ice. The similarity between this development in the Camp Century ice core and other deep cores indicates that the climatic boundary also represents a rheological boundary which must be considered in future flow models.; The fabric development in the Camp Century ice was closely monitored by several statistical methods. It is concluded that ice fabric interpretation can be greatly enhanced by the calculation of eigenvalue statistics which should be used in conjunction with stereographic scatter plots.; The long-term variations of air volume in the Camp Century core include a gradual decrease of about 8.5% in air content following the Wisconsin glaciation. The magnitude of the air volume decrease indicates that the maximum change in ice sheet elevation of northwest Greenland during the late Wisconsin was of the order of four to five hundred meters. The rate of the decrease suggests that the ice sheet elevation changed gradually over a period of several thousand years.; In the bottom 50 meters of the Camp Century ice core, the total air volume decreases rapidly to about half the normal value. Evidence from total air content and gas composition analyses indicates that the basal portion of the ice sheet was subjected to partial melting at some time in the past. Such an occurrence could significantly affect the interpretation of the climatic history at Camp Century derived from the stable oxygen isotope composition.