Geological evidence for climate change during the Amazonian period of Mars: Polar layer stratigraphy and tropical glacier formation.

摘要

The martian north polar cap contains spiraling troughs cutting hundreds of meters into the cap. The polar layered deposits (PLD), layers of varying ice to dust ratios, exposed on the walls of these troughs extend throughout the cap and contain the record of recent climate change. Early analysis produced models with obliquity cycles causing layer formation, similar to terrestrial models in which orbital Milankovitch cycles drive ice ages and climate change. Recent, higher-resolution datasets allow us to study the layers in new ways and at a new level of detail in order to better understand the climate record they contain.; Quantitative analysis of the PLD provides insight into layer formation and its relation to climate change. Paleoceanographic techniques for analyzing terrestrial climate records are adapted for use on martian "ice cores" constructed from images and topography data. Curve-shape matching algorithms examine the lateral continuity of the PLD and Fast Fourier Transforms look for vertical patterns within the PLD stratigraphy. This analysis reveals that layers are continuous across the cap. There are 30-meter layer packets linked to insolation cycles in the upper 300 m of the cap; there is evidence for a lag deposit within the cap formed during the last martian ice age.; Analysis of layer orientations in three dimensions using images and digital elevation models finds that the internal structure of the PLD is more complicated than a dome, implying that troughs existed during the accumulation of the visible PLD. Review of terrestrial ice sheet characteristics provides insights into ways in which the observable PLD surface textures formed and suggests measurements for future spacecraft.; There is evidence for the removal of ice from the polar caps at various stages in polar history. Equatorial lobate features found on the flank of Olympus Mons variously interpreted as landslides or rock glaciers are examined with the new data available. The lobate deposits are debris-covered glaciers that formed episodically throughout recent Mars history.; Collectively, this work outlines several lines of evidence in the geological record for recent climate change on Mars and brings new approaches to the study of this record.