HR: 16:00h
AN: C12C-01    [PDF]
TI: Formation of Obliquity-Driven Subsurface Ice Deposits on Mars: Study With a General Circulation Model
AU: * Richardson, M I
EM: mir@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Mischna, M A
EM: mischna@ucla.edu
AF: California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Mischna, M A
EM: mischna@ucla.edu
AF: University of California, Los Angeles, Department of Earth and Space Sciences 595 Charles Young Drive East, Los Angeles, CA 90025 United States
AU: McCleese, D J
EM: daniel.j.mccleese@jpl.nasa.gov
AF: California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125 United States
AU: Wilson, R J
EM: rjw@gfdl.noaa.gov
AF: Geophysical Fluid Dynamics Laboratory, PO Box 308, Princeton, NJ 08542 United States
AU: Vasavada, A R
EM: ashwin@ess.ucla.edu
AF: University of California, Los Angeles, Department of Earth and Space Sciences 595 Charles Young Drive East, Los Angeles, CA 90025 United States
AB: The discovery by Mars Odyssey of large deposits of subsurface ice in regions where surface ice is no longer stable has raised questions about putative past climatic conditions under different orbital states. We have used the GFDL Mars General Circulation Model (MGCM) as a tool for examining these questions, and suggest that these deposits may be quasi-stable permafrost remnants from an earlier period of high obliquity, covered by a sublimation lag deposit formed when the mean annual temperature exceeded the local frost point temperature. We have incorporated a thermal and vapor diffusion code into our GCM to simulate the behavior of water in the regolith and the processes that move water from the atmosphere to the surface and back. Water in the regolith may exist as vapor, ice or adsorbate, in relative abundances dependent upon the soil temperature and ambient pressure. The model results show the effectiveness of ice as a means to reduce the local thermal inertia, thereby reducing annual maximum temperatures and increasing the probability that surface ice deposits of a given thickness will survive throughout the warmer summer, and hence build, essentially, a permafrost layer over obliquity timescales. The development of an ice sheet beneath a sublimation lag appears similar to glacial remnants found in the Antarctic Dry Valleys beneath tens of centimeters of sublimation till. On Earth, these deposits have existed, largely unchanged, for millions of years. On Mars, we suggest that these mid-latitude deposits are several hundred thousand years old, at most-the remnant deposits of the past few martian obliquity cycles. The development of a sublimation lag of a few tens of centimeters seems to be enough to retain ice in these regions until the next high obliquity period.
DE: 0343 Planetary atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
DE: 1655 Water cycles (1836)
DE: 3344 Paleoclimatology
DE: 5416 Glaciation
DE: 6225 Mars
SC: Cryosphere [C]
MN: 2003 Fall Meeting