INVENTORY OF NON-POLAR ICE-RELATED DEPOSITS ON MARS: IMPLICATIONS FOR THE HISTORY OF CLIMATE CHANGE

Comprehensive analyses of non-polar ice-related deposits have shown that Mars has been a glacially active planet with remnant ice-related deposits at all latitudes. We combine perspectives from geological, geophysical, radar remote sensing, glacial flow modeling, astronomical parameter, general circulation model, and terrestrial analog studies to trace these phases and assess their causes, consequences, water vapor transport paths and spin-axis/orbital histories. Deposits identified to date include: 1) A latitude-dependent mantle interpreted to represent an ice age in the last few million years; 2) Mid-latitude debris covered glacial deposits including lineated valley fill, lobate debris aprons, and concentric crater fill; evidence for glacial highstands (e.g., perched lobes, trimlines, moraines) suggesting that these deposits represent the last remnants of more extensive plateau glaciation; 3) Fan-shaped tropical mountain glacier deposits formed in the Late Amazonian during periods of high obliquity on the NW flanks of Tharsis Montes and Olympus Mons; 4) Pedestal and excess-ejecta craters indicating Amazonian regional mid-high latitude ice cover; thicknesses several tens to over a hundred meters; 5) The Dorsa Argentea Formation, interpreted to represent a remnant Hesperian south circumpolar ice cap, a volumetrically very significant sequestered ice deposit representing a step-function in climate evolution. Climate simulations support the interpretation that the current polar caps become unstable at obliquities >30°, that latitude-dependent mantles form at obliquities between the current mean and ~35°, that mid-latitude glaciers form at ~35° obliquity with appropriate dust opacity, and that tropical mountain glaciers form at obliquities of ~45°. On the basis of the inventory of water-related deposits to date, the DAF appears to represent the sequestered record of a significantly different climate that characterized the early history of Mars. This was followed in the Amazonian by a hyperarid cold climate with a lower-volume water cycle dominated by mobilization and lateral migration of surface snow and ice in response to variations in spin-axis/orbital parameters; the active water inventory decreased with time due to progressive sequestration of snow and ice beneath sublimation lags.