Title: Driven by Excess? Climatic Implications of New Global Mapping of Near-Surface Water-Equivalent Hydrogen on Mars,
Abstract: We present improved Mars Odyssey Neutron Spectrometer (MONS) maps of
near-surface Water-Equivalent Hydrogen (WEH) on Mars that have intriguing
implications for the global distribution of "excess" ice, which occurs when the
mass fraction of water ice exceeds the threshold amount needed to saturate the
pore volume in normal soils. We have refined the crossover technique of Feldman
et al. (2011) by using spatial deconvolution and Gaussian weighting to create
the first globally self-consistent map of WEH. At low latitudes, our new maps
indicate that WEH exceeds 15% in several near-equatorial regions, such as
Arabia Terra, which has important implications for the types of hydrated
minerals present at low latitudes. At high latitudes, we demonstrate that the
disparate MONS and Phoenix Robotic Arm (RA) observations of near surface WEH
can be reconciled by a three-layer model incorporating dry soil over fully
saturated pore ice over pure excess ice: such a three-layer model can also
potentially explain the strong anticorrelation of subsurface ice content and
ice table depth observed at high latitudes. At moderate latitudes, we show that
the distribution of recently formed impact craters is also consistent with our
latest MONS results, as both the shallowest ice-exposing crater and deepest
non-ice-exposing crater at each impact site are in good agreement with our
predictions of near-surface WEH. Overall, we find that our new mapping is
consistent with the widespread presence at mid-to-high Martian latitudes of
recently deposited shallow excess ice reservoirs that are not yet in
equilibrium with the atmosphere.