干旱区生态环境知识资源中心

To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800 m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20-40 cm of loose cryotic sediments and sandstone boulders, This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O-H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting delta O-18 profiles and regression slope values between the uppermost 6 cm of the buried massive ice (upward convex delta O-18 profile and SD-18O = 5.1) and that below it (progressive increase in delta O-18 and SD-18O = 6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex delta O-18 profile in the uppermost 6 cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured delta O-18 profile is 0.2 . 10(-3) mm yr(-1), a value that is more similar to net ice removal rates derived from He-3 data from cobbles in Beacon Valley till (7.0 . 10(-3) mm yr(-1)) than sublimation rates computed based on current climate (0.1-0.2 mm yr(-1)). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size). (C) 2010 Elsevier B.V. All rights reserved.