Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice

Abstract

Ground ice in the crust and soil may be one of the largest reservoirs of water on Mars. Near-surface ground ice is predicted to be stable at latitudes higher than 40 degrees (ref. 4), where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed. Mid-latitude soils have also been implicated as a water-ice reservoir, the capacity of which is predicted to vary on a 100,000-year timescale owing to orbitally driven variations in climate. It is uncertain, however, whether near-surface ground ice currently exists at these latitudes, and how it is changing with time. Here we report observational evidence for a mid-latitude reservoir of near-surface water ice occupying the pore space of soils. The thickness of the ice-occupied soil reservoir (1-10 m) and its distribution in the 30 degrees to 60 degrees latitude bands indicate a reservoir of (1.5-6.0) x 104 km3, equivalent to a global layer of water 10-40 cm thick. We infer that the reservoir was created during the last phase of high orbital obliquity less than 100,000 years ago, and is now being diminished.

Polygon pattern geomorphometry on Svalbard (Norway) and western Utopia Planitia (Mars) using high-resolution stereo remote-sensing data

“…14). The large upland polygons (UP1) are probably very old and were formed after the deposition of the mantling material during conditions of high obliquity Head, 2000, 2002;Mustard et al, 2001;Head et al, 2003). An old age is also indicated by the fact that these polygons are truncated by the scalloped depressions (Fig.…”

“…Geologically, the region is characterized by two main units: the Vastitas Borealis interior unit (ABv i ), which underlies the Astapus Colles unit (ABa) (Tanaka et al, 2005). The ABa unit is interpreted as a fine-grained volatile-rich (i.e., ice-rich) mantling layer tens of meters thick which was deposited during recent variations in Mars' orbital parameters (i.e., higher obliquity) (e.g., Head, 2000, 2002;Mustard et al, 2001;Head et al, 2003). The older ABv i unit consists mainly of outflow channel sediments and subsequently reworked ice-rich deposits (Tanaka et al, 2005).…”

Transverse Aeolian Ridges (TARs) on Mars

“…Another hypothesis that is also related to the near-surface of the martian regolith is that sand-grade material might be buried by centimeteror meter-scale deposits of a dust -and ice-rich mantling material. This mantle, almost pervasive at N60°latitudes in both hemispheres but transitioning to a dissected, discontinuous mantle at 30-60°l atitude (Mustard et al, 2001;Kreslavsky and Head, 2002;Head et al, 2003) is partly responsible for topographic smoothing at subkilometer scale at latitudes N30°in both hemispheres (Kreslavsky and Head, 2000). It is interpreted to be composed of water ice condensed from the atmosphere that includes and is overlain by fine air fall dust.…”

Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE

“…Mustard et al, 2001;Kreslavsky and Head, 2002;Head et al, 2003). They may have formed by transport of ice from polar reservoirs, followed by airfall deposition in mid to high latitudes during periods of high obliquity less than 5 Ma ago; after a return to lower obliquity (including the present), the ice-rich mantle would progressively become eroded from lower to higher latitudes (e.g., Mustard et al, 2001;Head et al, 2003;, much as the Earth's annual orbital progression affects seasonal snow cover on Earth. Alternatively, more recent GCM results of Levrard et al (2004) and Madeleine et al (2007) predict that as obliquity decreases from high values (P45°), low-latitude ice deposits become unstable and are redeposited in the mid-latitudes as an ice-dust mantle.…”

“…These mantling deposits are postulated to be made of ground ice-cemented dust with unknown relative proportions of dust and ice (e.g. Mustard et al, 2001;Kreslavsky and Head, 2002;Head et al, 2003). They may have formed by transport of ice from polar reservoirs, followed by airfall deposition in mid to high latitudes during periods of high obliquity less than 5 Ma ago; after a return to lower obliquity (including the present), the ice-rich mantle would progressively become eroded from lower to higher latitudes (e.g., Mustard et al, 2001;Head et al, 2003;, much as the Earth's annual orbital progression affects seasonal snow cover on Earth.…”