Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p34a..03f&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P34A-03
Mathematics
Logic
0720 Glaciers, 0722 Rock Glaciers, 0726 Ice Sheets, 6225 Mars
Scientific paper
Spacecraft data have confirmed the presence of lobate deposits, up to 180,000 km2 in area, formed by cold-based glaciers on the northwest flanks of the Tharsis Montes volcanos in the tropics of Mars. We use the fundamental differences between the atmospheric snow accumulation environments on Earth and Mars, geological observations, and ice sheet models to show that Mars should be characterized by two equilibrium lines and that glacial accumulation should be favored on the flanks of large volcanos, not their summits as seen on Earth. Atmospheric general circulation models show that upwelling and adiabatic cooling of moist polar air will favor deposition of snow on the northwest flanks of the Tharsis Montes. Predicted accumulation rates, together with sample spin-axis obliquity histories are used to show that mean obliquity in excess of 45o and multiple 120,000 year obliquity cycles are necessary to produce the observed deposits. These results indicate that the formation of these deposits required multiple successive stages of advance and retreat before their full extent could be reached, and thus imply that spin axis obliquity remained at these high values for millions of years during the Late Amazonian. Calculations of spin-axis geometry histories prior to about 20 Ma ago are not possible, but these results provide insight into the nature of the obliquity history of Mars in the Amazonian, and begin to establish data points for the geologically based reconstruction of the orbital history of Mars. We present reconstruction of Tharsis Montes glaciations based on our climate parameterization which allows for the changing ice sheet configuration to modify its own climate. One scenario involves a long-term growth to steady state in a constant climate, while the other uses a transient climate that varies with a 100 Ka cycle within a longer period 2.5 Ma envelope. The climate certainly varies with the obliquity on Mars, so that the climate in fact would never remain constant for such a long period. Both volume and area of the transient ice sheet show considerable waxing and waning of the ice sheet, with areas that are often much larger that the 2.6 Ma steady ice sheet, but with much smaller total volumes. After the same 2.6 Ma, the transient ice sheet attains only about 35% of the equivalent steady ice sheet. We conclude that: 1) The properties of the Martian atmosphere make the formation, accumulation, and behavior of snow and ice different from those on the Earth in significant ways; 2) Models of mass balance and spatial distribution on the western flanks of Tharsis Montes lead to patterns that are strikingly similar to the geological evidence for ice accumulation and glacial flow; 3) Volumes are comparable to about half the volume of the current North Polar Cap, implying that during periods of very high obliquity, a significant percentage of the polar cap is transported to the tropics.
Fastook James L.
Head James W.
Marchant David R.
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