Friday, December 02, 2016

Martian Lakes Forming Climates Were Caused by Methane Outbursts and Short Term


Kite et al


Build-up of relatively young (<∼3.6 Ga) deltas and alluvial fans on Mars required lakes to persist for >3 Kyr (assuming dilute flow), but the watersheds' little-weathered soils indicate a climate history that was >99% dry. The lake-forming climates' trigger mechanism remains unknown. Here we show that these intermittency constraints, while inconsistent with many previously-proposed triggers for lake-forming climates, are consistent with a novel CH4-burst mechanism. Chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize CH4 clathrate. For past clathrate hydrate stability zone occupancy fractions >∼0.2, we show that CH4(±C2H6) builds up to levels whose radiative forcing (>15 W/m2, plus feedbacks) is sufficient to modulate lake-forming climates. Such occupancy fractions are consistent with CH4+C2H6 production by >3 Ga water-rock reactions. Sub-lake CH4 destabilization provides positive feedback. UV-limited CH4 photolysis curtails individual lake-forming climates to

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