Antarctic paleolake sediments and the search for extinct life on Mars

Evidence of lakes in Mars history is substantial. The proposed similarities between the ancient Martian environment and certain modern environments on Earth have led exobiologists to study antarctic lakes as analogs to those purported to have existed on Mars. We have investigated modern sedimentation processes (especially with respect to delta(13)C of carbonate and organic matter) in lakes in the McMurdo Dry Valleys region df east Antarctica and assessed various paleolake deposits with respect to their utility as Martian analogs and targets for future Mars exobiology missions. Three main types of paleolake deposit were identified and assessed: strand lines, perched deltas, and lacustrine sand mounds. Deltas are usually identified as good targets, but our research shows that authigenic carbonates are not readily identifiable in the sediments. Large deltas, although most likely to attract attention through remote sensing, generally are difficult sites for discovery of paleobiological matter, and delta(13)C signals follow no coherent pattern. Lacustrine sand mounds, on the other hand, contain abundant authigenic carbonate and freeze-dried organic matter and appear to be excellent records of paleolimnological conditions. The advantage of studying lake bottom deposits versus lake edge deposits is retrieval of a stable lake-wide signal. Deltas are therefore most useful in that they are generally large-scale features capable of drawing attention to a region of potential for the discovery of smaller lacustrine sand mounds.