Discrete Climatic Events on Timescales of Decades to Centuries: Clues from Polar Landforms

Details Discrete Climatic Events on Timescales of Decades to Centuries: Clues from Polar Landforms Discrete Climatic Events on Timescales of Decades to Centuries: Clues from Polar Landforms

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p52a0365b&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P52A-0365

Mathematics

Logic

5407 Atmospheres: Evolution, 5415 Erosion And Weathering, 5462 Polar Regions, 6225 Mars

Scientific paper

Recent observations indicate fast (meters per year) evolution of features, named Swiss-cheese for their morphologic appearance, on the surface of the southern residual frost cap [Malin et al., Science, 2001]. The onset of growth of these features may be responding in a sensitive way to changes in Martian climatic conditions on the timescales of decades to centuries. We have developed a model to examine the growth and development of the Swiss-cheese depressions. Swiss-cheese features were first identified by Thomas et al. [Science, 2000] using Mars Orbiter Camera imagery. They have flat floors and steep sided walls. Their lateral sizes are of the order of a few hundred meters. They are quite shallow with shadow and MOLA measurements indicating a depth of about 8 meters. Although the depressions are fairly circular the smaller ones do display a slight but consistent asymmetry in the form of a small cusp which points poleward indicating that the origin of these features is connected with insolation. As the seasonal frost disappears their walls appear to darken considerably relative to the surrounding terrain. The flat interior of the depression however does not appear to change in this way. There is a clear size division between smaller and larger depressions. Our modeling indicates that the growth timescales of the small-size population are on the order of a few Martian decades to centuries. This populations has a narrow size distribution with most of the depressions in any one area being roughly the same size. The similar size of adjacent depressions argues for some discrete climatic event which triggered this form of erosion of the cap. Larger depressions in other parts of the cap display an interior moat which indicates their walls have begun to be eroded outward after a period of inactivity or perhaps deposition. The width of these moats along with the observed expansion rates of the depressions [Malin et al., Science, 2001] indicates that these larger depressions were reactivated close to the same time as the smaller ones began forming. It is possible therefore that the same climatic event is responsible in both cases. Modeling these quickly evolving polar landforms can offer clues to Martian climatic events on timescales of decades to centuries. Changes in orbital parameters on these timescales are negligible, implying that Mars' climate has some intrinsically variability. It seems unlikely that we happen to be observing Mars during a single short-lived episode of Swiss-cheese growth. A more likely possibility is that this is part of a longer term cyclic process containing many of these climatic events. We report on these possible events and develop some scenarios of the recent history of Mars' climate and southern residual cap.

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