Ninth International Conference on Permafrost ... - IARC Research

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Thermal Conditions in Martian Permafrost: Past and PresentMikhail A. KreslavskyUniversity of California – Santa CruzPresent ConditionsGlobal cryosphereThe temperature of the Martian surface has beenmonitored by several orbital thermal infrared sensors.These measurements, accompanied by careful and cautiousmodeling, give rather accurate knowledge of the thermalregime of the uppermost meters of the surface in the presentepoch.The year-average surface temperature on Mars is wellbelow 0°C everywhere on the planet, meaning a thick globalcryosphere. The day-average temperature also never exceedsthe ice melting point, meaning the absence of the active layerof Martian permafrost in the present epoch.Observations with orbital gamma-ray and neutron sensorssensitive to the presence of hydrogen in the uppermost meterof the surface have indicated that high latitudes (above ~60° in both hemispheres) contain much hydrogen, whichobviously means the presence of water ice. This ice isabundant, and its amount in the soil noticeably exceeds 50%by volume. At mid and low latitudes, ice in the upper meter isless abundant or absent. The hydrogen content in equatorialregions is spatially variable and in some regions exceeds 10wt% water-equivalent by weight. Deeper in the ground, icemay be present virtually everywhere.Calculations of the ground ice stability against diffusionof water vapor to the atmosphere (e.g., Mellon & Jakosky1995, Schorghofer & Aharonson 2005) show that the groundice is stable at high latitudes and unstable at low latitudes;in addition to latitude, surface albedo and thermal propertiesinfluence stability.Patterned groundHigh-resolution images reveal a great variety of polygonalpatterns (e.g., Mangold et al. 2004), totally coveringmore than one-quarter of the planet (predominantly athigh latitudes). The extent of massive polygonal patternoccurrence somewhat exceeds the limits of the observedhigh hydrogen content. Polygonal patterns are often forminghierarchical systems of different scales (Fig. 1). Thesepatterns were probably initiated by thermal cracking of icerichpermafrost. On Earth, thermal cracking of permafrostusually leads to formation of ice-wedge polygons due toseasonal thaw of the active layer. On Mars, seasonal thawdoes not occur, and the cracks evolve into sand-wedgepolygons and/or sublimation polygons, features, observed inextremely cold and dry terrestrial environments (Marchantet al. 2002).Thermal cracking of ice-rich frozen soils occurs due to ananomalously high bulk thermal expansion coefficient of theice-soil mixtures. However, the thermal expansion coefficientdecreases with the temperature decrease. Very high seasonalFigure 1. Two scales of polygonal pattern on Mars. HiRISE imagePSP_001404_2490, 69°N, 106°W.temperature amplitude at high latitudes on Mars favorsthermal cracking, while generally low temperatures are notfavorable.The absence of polygons in the low-latitude hydrogen-richregions has been interpreted as evidence for the absence ofwater ice in the soil (the hydrogen being bound in hydratedminerals). However, in these regions, the seasonal temperatureamplitudes are modest (typically, 20–30 K;
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s trecords the most recent climate variations and can be used toconstrain timing of other recent geological events (e.g., themost recent gully activity).Stresses causing thermal cracking are proportional tothe seasonal amplitude of the surface temperature. At highlatitudes on Mars the winter temperature is buffered bycondensation of the atmospheric carbon dioxide at ~140K. Thus, the amplitude of seasonal surface temperaturevariations is solely defined by the year-maximum day-averagetemperature. On Mars, weak atmosphere is mostly thermallydecoupled from the surface, and the surface temperature iscontrolled mostly by direct insolation, other contributionsbeing minor. The year-maximum day-average temperatureis an increasing function of the year-maximum day-averageinsolation. Since the winter temperature is the same, the yearaveragesurface temperature is also an increasing functionof the year-maximum day-average temperature, and hence,of the insolation. Thus, the year-maximum day-averageinsolation is a good proxy of the climate signal with regardto cryoturbation and formation of the polygonal patterns.The insolation regime is controlled by evolution of spinand orbit parameters of Mars. For the recent epoch, theseparameters were accurately calculated by Laskar et al. 2004.Figure 2 presents evolution of the year-maximum dayaverageinsolation at high latitudes (70°) in both hemispheresFigure 2. Evolution of the year-maximum day-average insolation(in parts of the martian solar constant) over the last 200 ka forhorizontal surfaces at 70° latitude in the Northern (top) and Southern(bottom) Hemispheres. Bold segments show probable most recentperiods of intensive polygon formationover the last 200 ka. Formation of new cracks is expected tobe on increasing insolation branches close to the insolationmaxima, as marked on the plots (Fig. 2).In the Southern Hemisphere, the polygon formation canbe active at the present time. Older crack systems can havebeen formed 100 ka ago. If even older polygonal cracksare observed in the southern high latitudes, they may dateback to 400 ka ago (not shown in Fig. 2). In the NorthernHemisphere, the most recent insolation peak occurred 20 kaago, but it was lower than the present-day insolation at thesouth. The more probable period of activity is 75 ka ago, andit is most close to the age estimates by Kostama et al. 2006.An earlier high insolation peak occurred 275 ka ago.Applying these results to the geologic studies, we need tokeep in mind that the other factors, such as surface albedo(which can change due to painting of the surface with thinlayers of fine dust) and thickness of dry layer above theground ice (which depends on atmospheric water vaporcontent) can strongly influence the formation of polygonalpatterns.ReferencesKostama, V.-P., Kreslavsky, M.A. & Head, J.W. 2006.Recent high-latitude icy mantle in the northern plainsof Mars: Characteristics and ages of emplacement.Geophys. Res. Lett. 33: L11201.Kreslavsky, M.A. 2007. Statistical Characterization ofSpatial Distribution of Impact Craters: Implicationsto Present-Day Cratering Rate on Mars. 7th Conf. onMars, LPI Contribution No. 1353: 3325.Laskar, J. et al. 2004. Long term evolution and chaoticdiffusion of the insolation quantities of Mars. Icarus170: 343-364.Levy, J.S., Head, J.W. & Marchant, D.R. 2008. Marsthermal contraction crack polygon classificationand distribution: Morphological characterization atHiRISE resolution. Lunar Planetary Sci. XXXIX:#1171.Malin, M.C. et al. 2006. Present-day impact cratering rateand contemporary gully activity on Mars. Science314: 1573-1577.Mangold, N. et al. 2004. Spatial relationships betweenpatterned ground and ground ice detected by theNeutron Spectrometer on Mars. J. Geophys. Res. 109:E08001.Marchant, D.R. et al. 2002. Formation of patterned-groundand sublimation till over Miocene glacier ice inBeacon Valley, Antarctica. Geol. Soc. Am. Bull.114(6): 718-730.Mellon, M.T. & Jakosky, B.M. 1995. The distribution andbehavior of Martian ground ice during past andpresent epochs. J. Geophys. Res. 100: 11781-11799.Schorghofer, N. & Aharonson, O. 2005. Stability andexchange of subsurface ice on Mars. J. Geophys. Res.110: E05003.152
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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Ni n t h In t e r n at i o n a l Co
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