HR: 11:35h
AN: C12C-06    [Abstracts]
TI: Distribution and Stability of Accretion in Lake Vostok
AU: * Bell, R E
EM: robinb@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Studinger, M
EM: mstuding@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Clarke, G
EM: gclarke@eos.ubc.ca
AF: University of British Columbia, 2329 West Mall, Vancouver, BC V6T 1Z4 Canada
AU: Tikku, A
EM: tikkua@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 8th St., Troy, NY 12180 United States
AB: The flux of water through Lake Vostok is controlled by the distribution of melting and freezing at the base of the East Antarctic ice sheet as it traverses the Lake. The freezing or accretion is dominant in the southern half of the lake. Understanding the distribution of active accretion through the analysis of accretion ice profiles along flowlines provides insights into the stability of the lake processes through time and the origin of the accretion ice samples. The distribution of accretion ice along flow in Lake Vostok will be a function of the location of accretion zones, accretion rates, ice sheet velocities and any temporal changes in the accretion rates and ice sheet velocity. We consider the impact of spatial variation in the accretion processes. Four models were developed (1) accretion across the entire lake at a fixed accretion rate, (2) a narrow region of accretion along the western shoreline, (3) localized accretion along both the eastern and western shorelines and finally (4) localized shoreline accretion with background accretion at lower rates over the entire lake. These models produce distinct accretion ice profiles along flow. We have examined several accretion profiles constructed along flowlines in Lake Vostok. The northern two profiles are the longest (70 km) and best constrained. Both profiles indicate formation of a thick interval of accretion ice (50-100m) within the first 10km of the western shoreline and both profiles are characterized by an increase in the slope of the accretion ice for the last 10-20 km before the ice sheet regrounds along the eastern shoreline. In the center of the lake both profiles are characterized by a gradual ramp up to the east. The northern accretion ice profile is characterized by a continuous steep slope of 4.3 m/km; the southerly profile is characterized by a lower slope over the center of the lake (1.5 m/km). The form of these accretion ice profiles requires accretion at both shorelines and accretion over much of the lake. The shoreline accretion rates are 1.6-1.8 cm/yr based on an ice sheet velocity of 2 m/year while lower rates are required in center of the lake. The interpretation of the accretion ice profiles, particularly the presence of the steep ramps at the shoreline provides insights into the present processes of accretion over the lake. The samples of accretion ice recovered in the Vostok core represent spatial and temporal samples of Lake Vostok and its shorelines along the Vostok trajectory. The variation in the accretion ice has been attributed both to the changing environments along the flowline and temporal events. No thickness change in the accretion profiles can be attributed to the change in ice sheet velocity from ~1m/yr during the Last Glacial Maximum to the present ~2m/yr. The absence of a thickness change in the accreted ice profiles associated with this velocity change requires that the accretion rates have also changed in Lake Vostok since the Last Glacial Maximum.
DE: 0724 Ice cores (4932)
DE: 0726 Ice sheets
DE: 0746 Lakes (9345)
DE: 0774 Dynamics
DE: 0798 Modeling
SC: Cryosphere [C]
MN: Fall Meeting 2005