http://arxiv.org/abs/1611.01717
Build-up of relatively young ($<\sim$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 $>$99% dry. The lake-forming climates’ trigger mechanism remains unknown. Here we show that these intermittency constraints, while inconsistent with many previously-proposed triggers for lake-forming climates, are consistent with a novel CH$_4$-burst mechanism. Chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize CH$_4$ clathrate. For past clathrate hydrate stability zone occupancy fractions $>\sim$0.2, we show that CH$_4$($\pm$C$_2$H$_6$) builds up to levels whose radiative forcing ($>$15 W/m$^2$, plus feedbacks) is sufficient to modulate lake-forming climates. Such occupancy fractions are consistent with CH$_4$+C$_2$H$_6$ production by $>$3 Ga water-rock reactions. Sub-lake CH$_4$ destabilization provides positive feedback. UV-limited CH$_4$ photolysis curtails individual lake-forming climates to $<$10$^6$ yr duration, consistent with data. Our results show how a warmer early Mars can undergo intermittent excursions to a warm, wet climate state.
E. Kite, C. Goldblatt, P. Gao, et. al.
Tue, 8 Nov 16
51/75
Comments: Submitted
You must be logged in to post a comment.