Massive Ice Deposits Research Articles

Pollen as a potential indicator of the origin of massive ice in northwest Siberia

AbstractPollen and spores collected from massive ice bodies in northwest Siberia were studied with the aim to provide a cryogenic indication of their origin. We discuss perennial massive ice, which may occur as lenses, layers, or irregular masses in the frozen ground and may be buried or intrasedimental. Pollen assemblages in massive ice deposits of Holocene age indicated a nonglacial origin of the ice. Pollen assemblages from glacial snow cover and snow patches on tundra were analyzed to reveal signs of buried ice. This approach allowed us to assess the nature of several massive ice bodies as intrasedimental and buried, and demonstrated how pollen may be used as an indicator for the origin of massive ice in northwest Siberia.

Formation of metre-scale bladed roughness on Europa’s surface by ablation of ice

On Earth, the sublimation of massive ice deposits at equatorial latitudes under cold and dry conditions in the absence of any liquid melt leads to the formation of spiked and bladed textures eroded into the surface of the ice. These sublimation-sculpted blades are known as penitentes. For this process to take place on another planet, the ice must be sufficiently volatile to sublimate under surface conditions and diffusive processes that act to smooth the topography must operate more slowly. Here we calculate sublimation rates of water ice across the surface of Jupiter’s moon Europa. We find that surface sublimation rates exceed those of erosion by space weathering processes in Europa’s equatorial belt (latitudes below 23°), and that conditions would favour penitente growth. We estimate that penitentes on Europa could reach 15 m in depth with a spacing of 7.5 m near the equator, on average, if they were to have developed across the interval permitted by Europa’s mean surface age. Although available images of Europa have insufficient resolution to detect surface roughness at the multi-metre scale, radar and thermal data are consistent with our interpretation. We suggest that penitentes could pose a hazard to a future lander on Europa.

New slope-normalized global gully density and orientation maps for Mars

Abstract We reanalyse the global distribution of gullies in order to provide a set of observational constraints that models of gully formation must explain. We validate our results derived from the global data with four detailed case studies. We show that the availability of steep slopes is an essential factor to consider when assessing the spatial distribution and abundance of gullies. When the availability of steep slopes is taken into account, it reveals, with a few exceptions, that gullies are found almost uniformly across the whole 30°–90° latitude band. Our analysis also reveals that massive ice deposits are anti-correlated with gullies, and that the undulations in the equatorwards limits of the gully distribution could be explained by longitudinal variations in maximum surface temperatures (controlled by variations in surface properties, including thermal inertia and albedo). We find a sharp transition in both hemispheres between pole-facing gullies, which extend from 30° to 40°, to a more mixed, but dominantly equator-facing orientation of gullies polewards of 40°. We have no definitive explanation for this transition but, based on previous studies, we suggest it could be linked to the availability of near-surface ice deposits.

Sounding the subsurface of Athabasca Valles using MARSIS radar data: Exploring the volcanic and fluvial hypotheses for the origin of the rafted plate terrain

To test the volcanic and fluvial hypotheses for the origin of the rafted plate terrain observed in the vicinity of Athabasca Valles (5°N, 150°E, Central Elysium Planitia), we investigated the subsurface radar echo from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) 5‐MHz band data over this area. The backscattered signal losses were compared to finite difference time domain (FDTD) simulations of those arising from three hypothetical geoelectrical subsurface models, which differed in their assumed composition (percentage basalt versus ice) and assumed mode of origin (fluvial discharge/“frozen sea,” mudflow, and low‐viscosity lavas). The dielectric values used in these models are derived from laboratory measurements of Mars analog materials under Mars‐like conditions. FDTD simulations suggest that if the near‐surface environment is ice‐rich, it will result in an average loss rate of 0.053 dB/m for massive ice (having less than 1% of suspended particulates) and 0.065 dB/m for a mudflow (consisting of a 50/50 mixture of ice and basaltic dust). Whereas the losses associated with a lava flow model increase to 0.19 dB/m. In comparison, the actual signal losses experienced by MARSIS within this region were on the order of 0.18 dB/m within the first 160 m beneath the surface. This suggests that propagation characteristics of Athabasca's near‐subsurface are more consistent with a volcanic rather than a fluvial or mudflow origin of the rafted plate terrain, although limitations on radar sounding depth in this region cannot rule out the possibility of more deeply buried massive ice deposits.

Meridiani Planum sediments on Mars formed through weathering in massive ice deposits

Although a number of hypotheses have been put forward to explain the sulphate deposits discovered by the Opportunity rover at Meridiani Planum, Mars, the sedimentary layers remain enigmatic. A re-analysis of the chemistry, sedimentology and geology of the deposits suggests they formed through a reworking of the sublimation residue from a large-scale deposit of ice and dust.

Geophysical mapping of ground ice using a combination of capacitive coupled resistivity and ground‐penetrating radar, Northwest Territories, Canada

The nature and distribution of ground ice are two of the most unpredictable geological variables in near‐surface deposits characterized by continuous permafrost. Subsurface information about ground ice distribution and structure can be obtained either by invasive and environmentally destructive techniques like drilling and excavation or by noninvasive low‐impact geophysical methods. In this study, coordinated measurements by two complementary geophysical tools, capacitive‐coupled resistivity (CCR) and ground‐penetrating radar (GPR) were used to map ground ice in a variety of locations in the Mackenzie Delta region of the western Canadian Arctic. Both CCR and GPR systems are highly portable (especially on snow covered surfaces) and very effective in collecting data under winter conditions when cold ground temperatures ensure that nearly all liquid water is frozen and signal penetration is enhanced. CCR and GPR readily detect stratigraphic differences including the contacts between massive ice deposits and enclosing sediments. GPR is widely used in permafrost research, but CCR has been used in only a few studies. This is the first study to combine results from both systems by collecting complementary data sets along coincident transects. We demonstrate that when combined, these data increase the quality and interpretation of subsurface information beyond what could be determined by either of the instruments alone. The complementary nature of these two geophysical tools facilitated the detection and mapping of massive ground ice, ice‐rich sediments, ice wedges, thermokarst, and basic stratigraphic relationships. This study breaks new ground by documenting the benefits of using these techniques together in permafrost investigations.

Introduction to special section on the Phoenix Mission: Landing Site Characterization Experiments, Mission Overviews, and Expected Science

Phoenix, the first Mars Scout mission, capitalizes on the large NASA investments in the Mars Polar Lander and the Mars Surveyor 2001 missions. On 4 August 2007, Phoenix was launched to Mars from Cape Canaveral, Florida, on a Delta 2 launch vehicle. The heritage derived from the canceled 2001 lander with a science payload inherited from MPL and 2001 instruments gives significant advantages. To manage, build, and test the spacecraft and its instruments, a partnership has been forged between the Jet Propulsion Laboratory, the University of Arizona (home institution of principal investigator P. H. Smith), and Lockheed Martin in Denver; instrument and scientific contributions from Canada and Europe have augmented the mission. The science mission focuses on providing the ground truth for the 2002 Odyssey discovery of massive ice deposits hidden under surface soils in the circumpolar regions. The science objectives, the instrument suite, and the measurements needed to meet the objectives are briefly described here with reference made to more complete instrument papers included in this special section. The choice of a landing site in the vicinity of 68°N and 233°E balances scientific value and landing safety. Phoenix will land on 25 May 2008 during a complex entry, descent, and landing sequence using pulsed thrusters as the final braking strategy. After a safe landing, twin fan‐like solar panels are unfurled and provide the energy needed for the mission. Throughout the 90‐sol primary mission, activities are planned on a tactical basis by the science team; their requests are passed to an uplink team of sequencing engineers for translation to spacecraft commands. Commands are transmitted each Martian morning through the Deep Space Network by way of a Mars orbiter to the spacecraft. Data are returned at the end of the Martian day by the same path. Satisfying the mission's goals requires digging and providing samples of interesting layers to three on‐deck instruments. By verifying that massive water ice is found near the surface and determining the history of the icy soil by studying the mineralogical, chemical, and microscopic properties of the soil grains, Phoenix will address questions concerning the effects of climate change in the northern plains. A conclusion that unfrozen water has modified the soil naturally leads to speculation as to the biological potential of the soil, another scientific objective of the mission.

A process to make massive ice in the martian regolith using long-term diffusion and thermal cracking

This paper describes a “simple standard” model of water transport through regolith that includes diffusive migration and phase changes driven by damped seasonal temperature waves. A hitherto unused first-order process is then added, that can produce ice densities much greater than those allowed by the initial dry porosity. Voids are produced in cooling icy regolith when tensile stresses exceed the cracking threshold ( ∼ 2 MPa ) . These stresses build up through an interaction of thermal contraction and elastic–plastic response. When the cracks open up after tensile failure there is purely thermal void enhancement and subsequent reduction as the regolith warms again. When the cracks are open the porosity is increased and they partially fill with ice crystals. Thus the void reduction on warming cannot go back to the original zero point and the bulk density of ice is increased with each temperature cycle. The cracking and thermal adjustment happen at scales of meters to millimeters. The large cracks can occur in pure ice and/or homogeneous icy material and the smaller cracks are produced by rock cobbles, pebbles, and grains having a much smaller coefficient of thermal expansion than ice. Thus a hierarchy of cracks and voids forms each temperature cycle and augments the ice content. The process can take the upper few meters of a pore-saturated icy soil from 28% by mass ice content to 70% in 10 Ma. This mechanism and the seasonal temperature cycle can plausibly produce massive ice deposits in the upper few meters of Mars' high-latitude regolith by diffusion and also keep the massive-ice regolith effectively porous to water vapor transport. The obliquity cycle can produce tensile stresses nearing 2 MPa down to ∼ 100 m depth so even deeper cracking could be happening.

The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains

In this paper we consider the hydraulic and thermal conditions that gave rise to the elevated source regions of the Late Hesperian outflow channels and explore their implications for the evolution of the Martian hydrosphere. We find that if the outflow channel floodwaters were derived from a subpermafrost aquifer, then it implies that, throughout the planet's first billion years of evolution, as much as one third of its surface was covered by standing bodies of water and ice. Following the development of the global dichotomy, the bulk of this water would have existed as an ice-covered ocean in the northern plains. We demonstrate that the progressive crustal assimilation of this early surface reservoir of H 2O (punctuated by possible episodes of less extensive flooding) was a natural consequence of the planet's subsequent climatic and geothermal evolution—potentially cycling the equivalent of a km-deep global ocean of water through the atmosphere and subsurface every ∼10 9 years. In response to the long-term decline in planetary heat flow, the progressive cold-trapping of H 2O into the growing cryosphere is expected to have significantly depleted the original inventory of groundwater—a development that could well explain the apparent decline in outflow channel activity observed during the Amazonian. Although primarily a theoretical analysis, our findings appear remarkably consistent with the geomorphic and topographic evidence that Mars once possessed a primordial ocean and that a substantial relic of that body continues to survive as massive ice deposits within the northern plains. Confirmation of the presence of such deposits, combined with the potential detection of a global-scale groundwater system, would provide persuasive support for the validity of this analysis.

Les formes de glaces des grottes de la Nahanni, Territoires du Nord-Ouest, Canada

Exploration has been continuing on the karst system developed within the cliffs of the First Canyon (300–1050 m deep) of the South Nahanni River(61°18′ N, 124°10′ W). Probably the most northerly on the North American continent, this karst region is within the discontinuous permafrost zone, at the southern limit of the tundra. The caves contain ice of the type which depends on the present subarctic climate (two-dimensional hexagonal ice crystals, ice like calcite speleothem and 'secondary' ice), or on a long-term climatic change of ± 2400 years (massive ice deposits and sponge-like ice deposits).

Ice-Blocked Tubes in the Aiyansh Flow, British Columbia

The Aiyansh lava flow (55 7'N, 128?54'W) is the only flow in Canada known to contain lava tubes, resulting from piping of fluid lava. A corrected radiocarbon date of samples from involuted trees on the edge of the flow indicates an age of 250 ? 130 BP (GSC-1124), and suggests that the Aiyansh flow is one of the youngest volcanic features in western Canada. While the main tube area is in the snout of the flow, some 22.5 to 32 km from the cone (SutherlandBrown, 1969), a series of tubes some of which contain massive ice deposits, are situated adjacent to and extend under the cinder cone. The ice formations, having been assigned an accurate date, are unique in the speleological literature because they indicate that massive ice deposits can form under present climatic conditions. Studies of ice deposits in lava tubes or caves almost uniformly lack chronological frameworks. Some writers suggest that the ice in selected caves may be fossil glacial ice from the Pleistocene (Casteret, 1954; Halliday, 1970). Others conclude that massive formations in Europe date from a warm period approximately 8,000 to 4,000 years ago, and their basis of judgment rests on observations that cave temperatures are only several tenths of a degree below freezing (Trombe, 1952; Abel, 1953). Recently, I used standard petrographic techniques to determine the method of ice formation in a high altitude cave; however, as with other