Dry Valleys Of Antarctica Research Articles

“Sarsen Stones” at German Hill, Central Otago, New Zealand, and Their Potential for In Situ Cosmogenic Isotope Dating of Landscape Evolution

Abstract 10Be concentrations measured in silica‐cemented Tertiary sandstones in Central Otago have yielded minimum exposure ages of up to 1400 ka, some of the oldest ever recorded outside the dry valleys of Antarctica and some arid deserts. The silica‐cemented sandstones outcrop as boulders in a region where their exposure is caused by the growth of anticlinal ridges above blind reverse faults. Initial studies using a combination of in situ cosmogenic isotope measurements and geomorphological observations on one range have demonstrated the potential of this technique to investigate Late Cenozoic fault growth and erosion rates. The best‐exposed and preserved occurrence of the quartz‐rich boulders is at German Hill on North Rough Ridge, where their stratigraphic context and their sedimentary and diagenetic origin, together with their method of emplacement and preservation on the modern land surface, can be studied in detail. These are all features that affect their suitability for cosmogenic isotope studies...

Early pliocene alpine glaciation in antarctica: terrestrial versus tidewater glaciers in wright valley

ABSTRACT. Alpine glacier deposits in the McMurdo Dry Valleys of Antarctica have been interpreted to indicate that early Pliocene climate in that region was not warmer than it is today. Correlation of these alpine‐glacier till sheets to marine deposits that contain evidence consistent with warmer‐than‐present climate has been used to constrain the age of both deposits, preclude the warm interpretation of the marine evidence, and constrain mountain uplift as determined from the marine deposit. We tested the interpretation that, in the early Pliocene, the alpine glaciers in Wright Valley terminated in a fjord and, thereby, constrain the age, temperature, and depth of the fjord. We did this by mapping the surficial geology in this region using the newly available microtopography based on the light detection and ranging (LIDAR) technique. Stratigraphic issues like these need to be resolved in order to quantify early Pliocene climate in Antarctica and contribute to understanding warm global‐climate dynamics.We found that the Pliocene Alpine‐IIIA (A‐IIIA), A‐IIIB and A‐IV drift sheets were more likely deposited from terrestrial alpine‐glacier lobes than glaciers terminating either at tidewater or with a floating appendage. The principal evidence is the occurrence of moraine fragments well below the minimum elevation of the early Pliocene fjord surface, and moraine arrangement in arcs indicative of arcuate glacier fronts without flairing near the proposed shoreline. Our A‐IIIA till is more widespread in the proglacial areas of the five alpine glaciers examined than previously proposed. We propose that the existing distribution of A‐IIIB till reflects glaciers even less extensive than today rather than truncation at a hypothetical fjord surface. Additionally, the A‐IV moraine remnants outline glaciers that were significantly larger than those associated with A‐III moraines.If we are correct, the age of the A‐III till, 3.4 ± 0.1 Ma at maximum, does not constrain the age of the Prospect fjord episode which can be closer to 5.5 ± 0.4 Ma as previously inferred. Moreover, if the alpine tills are not as old as the Prospect fjord episode, the polar paleoclimatic interpretation from those tills does not preclude the high temperature (0–3°C) and reduced salinity previously inferred for the Prospect fjord. However, if alpine glacier extent was not limited by Prospect fjord surface elevation, then paleoclimate during the A‐IIIA, A‐IIIB, and A‐IV glacial episodes can be quantitatively reconstructed. The Prospect fjord might have been deep, not shallow, and, hence, mountain uplift might be greater than currently thought which would explain minimal alpine‐glacier erosion into the valley sides.

Antarctic Dry Valleys and indigenous weathering in Mars meteorites: Implications for water and life on Mars

The Dry Valleys of Antarctica are an excellent analog of the environment at the surface of Mars. Soil formation histories involving slow processes of sublimation and migration of water-soluble ions in polar desert environments are characteristic of both Mars and the Dry Valleys. At the present time, the environment in the Dry Valleys is probably the most similar to that in the mid-latitudes on Mars although similar conditions may be found in areas of the polar regions during their respective Mars summers. It is thought that Mars is currently in an interglacial period, and that subsurface water ice is sublimating poleward. Because the Mars sublimation zones seem to be the most similar to the Antarctic Dry Valleys, the Dry Valleys-type Mars climate is migrating towards the poles. Mars has likely undergone drastic obliquity changes, which means that the Dry Valleys analog to Mars may be valid for large parts of Mars, including the polar regions, at different times in geologic history. Dry Valleys soils contain traces of silicate alteration products and secondary salts much like those found in Mars meteorites. A martian origin for some of the meteorite secondary phases has been verified previously; it can be based on the presence of shock effects and other features which could not have formed after the rocks were ejected from Mars, or demonstrable modification of a feature by the passage of the meteorite through Earth's atmosphere (proving the feature to be pre-terrestrial). The martian weathering products provide critical information for deciphering the near-surface history of Mars. Definite martian secondary phases include Ca-carbonate, Ca-sulfate, and Mg-sulfate. These salts are also found in soils from the Dry Valleys of Antarctica. Results of earlier Wright Valley work are consistent with what is now known about Mars based on meteorite and orbital data. Results from recent and current Mars missions support this inference. Aqueous processes are active even in permanently frozen Antarctic Dry Valleys soils, and similar processes are probably also occurring on Mars today, especially at the mid-latitudes. Both weathering products and life in Dry Valleys soils are distributed heterogeneously. Such variations should be taken into account in future studies of martian soils and also in the search for possible life on Mars.

Wet and cold thick atmosphere on early Mars

The evidence of past fluvial activity on the surface of Mars indicates that since the end of the intense period of crater formation liquid water has flowed on the surface. There is also evidence that indicates that Mars has maintained a cold dry climate over this same time. This apparent contradiction can be resolved if the early martian atmosphere is thick (>100 hPa) but cold (less then -20°C). Snow based hydrological cycles such as found in the dry valleys of Antarctica can then explain both the fluvial features and the cold arid climate. Life could flourish under such conditions.

Biologically–induced elemental variations in Antarctic sandstones: a potential test for Martian micro-organisms

Lichen-dominated cryptoendolithic communities from the Dry Valleys of Antarctica have been the subject of much research over recent years owing to their potential as analogues of Martian life forms. Their ability to mobilize iron compounds and organize themselves into distinct coloured biotic zones suggests that they may alter the chemistry of their host rock. By conducting a major, minor and trace element study utilizing inductively coupled plasma atomic emission spectroscopy (ICP-AES) and mass spectrometry (ICP-MS) techniques, we have been investigating the relationship between the microbes and the chemistry of the sandstones. Different layers within a suite of sandstones collected from six localities in the Dry Valleys have been analysed to establish if or how the microbes influence or directly affect the chemical composition of the rocks. Background petrographic studies have shown significant differences in mineralogical maturity between rocks colonized by the communities and those that are not, and the chemistry results have shown significant elemental disparity between colonized and uncolonized rocks. By obtaining accurate percentages of the minerals present in each sample the differences in elemental concentrations could be construed to be caused by the differences in mineralogy between samples. The nature and extent of the concentration differences has led to the conclusion that either the cryptoendolith communities are able to alter their host rock by the solubilization and mobilization of elements that are then subsequently removed or that the organisms are simple opportunists that can only successfully colonize rocks that provide the ideal substrate, being mineralogically mature with ample pore space and less concentrated in the elements tested for.

Effects of temperature and humidity upon the transport of sedimentary particles by wind

AbstractWind tunnel simulations of aeolian transport carried out over a range in mean temperature between 32 °C and −9 °C suggest that cold airflows support higher mass transport rates (Q) than very warm air. The magnitude of this increase is larger than expected, so that analytical and semi‐empirical models underestimate Q. Extrapolation of the results suggests that, at −40 °C, as for example in the dry valleys of Antarctica in winter, Q may be as much as 70% higher than for the equivalent wind speed in hot deserts at air temperatures of 40 °C. Temperature‐dependent changes in air density and turbulence contribute to this result. The decreased tension of water adsorbed onto particle surfaces at low temperatures is postulated to reduce interparticle cohesion and, thus, to increase the elasticity of particle impacts on cold beds. Definition of the roles that temperature and humidity play in aeolian transport is relevant to studies of palaeoenvironmental reconstruction and extraterrestrial (or planetary) geology. Investigation of present‐day, cold climate features and of climate change effects also requires knowledge of these fundamental relations.

Improbable Eden: The Dry Valleys of Antarctica, essay by Bill Green; photography by Craig Potton

Improbable Eden: The Dry Valleys of Antarctica, essay by Bill Green; photography by Craig Potton

Resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground

To help interpret the polygonal patterned ground on Mars, we present recent findings about a similar form of patterned ground in a particularly cold and arid region on Earth, the Dry Valleys of Antarctica. In this region, distinct arrays of interconnected polygons, which we refer to herein simply as patterned ground, characterize many surfaces, reflecting a subsurface network of interconnected, subvertical wedges of sand that grow incrementally as sand progressively fills soil fractures. The fractures form initially as thermoelastic stresses arise during periods of rapid cooling of frozen ground, and they continue to open and close in response to thermal cycles. We describe the initiation and maturation of the patterned ground using data for the growth of sand wedges and for the evolution of crack patterns and microrelief over time scales ranging up to 106 years.

Stratigraphic profiling with ground‐penetrating radar in permafrost: A review of possible analogs for Mars

We review our past and ongoing use of ground‐penetrating radar to investigate permafrost in Alaska and in the Dry Valleys of Antarctica. The results may be relevant to radar efforts on Mars because of arid conditions and the presence of ice. The pulses were centered at 50, 100, and 400 MHz. We interpret profiles from two sites in the eastern Taylor Valley to show glaciolacustrine and glaciofluvial stratigraphy. The maximum depth of stratigraphy profiled there was about 33 m. Near Fairbanks, Alaska, the depth of penetration at 50 MHz was near 80 m in marginally frozen and stratified alluvial sands. At the Fairbanks sites, supplementary drilling was required to differentiate between reflections from conductive bedrock, a graphitic schist, and those from the water table at depths of 20–25 m. At a site on the North Slope of Alaska, we profiled present and remnant freezing fronts in an alluvial floodplain. The relative permittivity at most sites ranged between about 4 and 5.5, which is consistent with dry conditions, the mineralogy, and low ice content. Weak interface reflectivity or the lack of further interfaces may have limited the interpretation of maximum penetration where no water table was present because signal absorption should have been low and scarce diffractions imply that scattering was weak. The interface reflectivities beneath Taylor Valley may be a function of only density contrasts, since free water, and possibly ice, is absent.

Polar endoliths – an anti-correlation of climatic extremes and microbial biodiversity

We examined the environmental stresses experienced by cyanobacteria living in endolithic gneissic habitats in the Haughton impact structure, Devon Island, Canadian High Arctic (75° N) and compared them with the endolithic habitat at the opposite latitude in the Dry Valleys of Antarctica (76° S). In the Arctic during the summer, there is a period for growth of approximately 2.5 months when temperatures rise above freezing. During this period, freeze–thaw can occur during the diurnal cycle, but freeze–thaw excursions are rare within higher-frequency temperature changes on the scale of minutes, in contrast with the Antarctic Dry Valleys. In the Arctic location rainfall of approximately 3 mm can occur in a single day and provides moisture for endolithic organisms for several days afterwards. This rainfall is an order of magnitude higher than that received in the Dry Valleys over 1 year. In the Dry Valleys, endolithic communities may potentially receive higher levels of ultraviolet radiation than the Arctic location because ozone depletion is more extreme. The less extreme environmental stresses experienced in the Arctic are confirmed by the presence of substantial epilithic growth, in contrast to the Dry Valleys. Despite the more extreme conditions experienced in the Antarctic location, the diversity of organisms within the endolithic habitat, which includes lichen and eukaryotic algal components, is higher than observed at the Arctic location, where genera of cyanobacteria dominate. The lower biodiversity in the Arctic may reflect the higher water flow through the rocks caused by precipitation and the more heterogeneous physical structure of the substrate. The data illustrate an instance in which extreme climate is anti-correlated with microbial biological diversity.

Microbial activity discovered in previously ice‐entombed Arctic ecosystems

One of the more intriguing discoveries in the biogeochemical sciences in recent years is the tremendous capacity of microbial populations to occupy and flourish in extreme habitats [Rothschild and Mancinelli 2001]. Microbial populations survive and multiply under a diversity of harsh conditions, including the hot springs of Yellowstone National Park, Wyoming, and on the ocean floor around thermal vents. At the other extreme, active microbial communities occupy some of the coldest and driest habitats on Earth. For instance, a variety of bacterial and fungal species have been found in the Dry Valleys of Antarctica, and there is evidence that microbes are also present beneath the Antarctic Ice Sheet in Lake Vostok, a system that has not been exposed to the atmosphere for thousands of years.

Population Age Structure of Nematodes in the Antarctic Dry Valleys: Perspectives on Time, Space, and Habitat Suitability

Patterns of nematode population dynamics in an extreme environment were studies in the McMurdo Dry Valleys of Antarctica. Nematode populations are sensitive to soil disturbance and are useful indicators of environmental change. We hypothesized that the pristine soil environments of Antarctica that are suitable for life would support stable both spatially and temporally nematode populations. We established three sampling sites across an elevation gradient in Taylor Valley and sampled each site at larger and smaller spatial scales three-times over a 6-yr period (1993, 1995, and 1999). Nematode variables and soil moisture were significantly different among years. Soil moisture, nematode abundance, and life cycle parameters varied also with elevation, but not spatial scale at the grid size over the 6 yr. Generally, soil moisture declined during the time of the study and was greatest at the lowest elevation. Throughout the 6 yr, Scottnema lindsayae was most abundant at the highest elevation and dominated all sites, while Eudorylaimus antarcticus was most abundant at the lowest elevation. Plectus antarcticus was present only at the lowest elevation. While Scottnema was negatively correlated with soil moisture, Eudorylaimus and Plectus showed a positive relationship. Similarities among nematode species in life cycle characteristics (e.g., long life cycles and low reproductive rates) may indicate adaptive strategy for survival in the Dry Valleys soil environments. The differences, however, may indicate species specific sensitivity to changes in the soil characteristics such as moisture. Temporal variation of variables describing nematode populations in Antarctic soil suggests the nematode species respond to short-term climate variation and, thus, may be affected by long-term climate change.

Zeolites in Soil Environments

Research Article| January 01, 2001 Zeolites in Soil Environments Douglas W. Ming; Douglas W. Ming Mail Code SN2, NASA Johnson Space Center, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar Janis L. Boettinger Janis L. Boettinger Department of Plants, Soils, and Biometeorology, Utah State University, Logan, Utah 84322 Search for other works by this author on: GSW Google Scholar Author and Article Information Douglas W. Ming Mail Code SN2, NASA Johnson Space Center, Houston, Texas 77058 Janis L. Boettinger Department of Plants, Soils, and Biometeorology, Utah State University, Logan, Utah 84322 Publisher: Mineralogical Society of America First Online: 09 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2001) 45 (1): 323–345. https://doi.org/10.2138/rmg.2001.45.11 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Douglas W. Ming, Janis L. Boettinger; Zeolites in Soil Environments. Reviews in Mineralogy and Geochemistry 2001;; 45 (1): 323–345. doi: https://doi.org/10.2138/rmg.2001.45.11 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search “The limited occurrence of these minerals has resulted in a scant knowledge about their properties in the soils.” Zelazny and Calhoun (1977) As pointed out by the above authors, the occurrence of natural zeolites in soils is rare and not well known, and only about 75 papers have been published describing the occurrence of zeolites in soils. These occurrences range from hot, humid soils in India to cold, arid soils in the Dry Valleys of Antarctica. Most of these reports describe residual zeolite phases that have persisted from the parent material during soil formation; however, there are reports... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Origins of sulphate in Antarctic dry-valley soils as deduced from anomalous 17O compositions.

The dry valleys of Antarctica are some of the oldest terrestrial surfaces on the Earth. Despite much study of soil weathering and development, ecosystem dynamics and the occurrence of life in these extreme environments, the reasons behind the exceptionally high salt content of the dry-valley soils have remained uncertain. In particular, the origins of sulphate are still controversial; proposed sources include wind-blown sea salt, chemical weatherings, marine incursion, hydrothermal processes and oxidation of biogenic sulphur in the atmosphere. Here we report measurements of delta18O and delta17O values of sulphates from a range of dry-valley soils. These sulphates all have a large positive anomaly of 17O, of up to 3.4/1000. This suggests that Antarctic sulphate comes not just from sea salt (which has no anomaly of 17O) but also from the atmospheric oxidation of reduced gaseous sulphur compounds, the only known process that can generate the observed 17O anomaly. This source is more prominent in high inland soils, suggesting that the distributions of sulphate are largely explained by differences in particle size and transport mode which exist between sea-salt aerosols and aerosols formed from biogenic sulphur emission.

The distribution and relative abundance of ammonia-oxidizing bacteria in lakes of the McMurdo Dry Valley, Antarctica

Marked differences in the concentrations of major ions and cations, macronutrient chemistry and general trophic status exist among the lakes of the McMurdo dry valleys in Antarctica. These differences have been attributed to both variations in stream inputs and in situ lake processes (Priscu, 1995; Lizotte et al., 1996, Spigel and Priscu, 1996). This study examines the role of nitrifying bacteria in nitrogen transformations in these lakes. Applying two polymerase chain reaction (PCR) assays targeting the 16S rRNA genes of ammonia-oxidizing bacteria and the active site of the ammonia monooxygenase gene (amoA), the distribution of ammonia-oxidizers was examined in six Antarctic lakes: Lake Bonney, Lake Hoare, Lake Fryxell and Lake Joyce in the Taylor Valley, Lake Miers in the the Miers Valley and Lake Vanda in the Wright Valley. Using a two stage amplification procedure, ammonia-oxidizers from both the beta and gamma- subclasses of the Proteobacteria were detected and their relative abundances were determined in samples collected from all sites. Ammonia-oxidizers were detected in all lakes sampled. Members of the gamma subclass were only present in the saline lakes. In general, nitrifiers were most abundant at depths above the pycnocline and were usually associated with lower concentrations of NH4 and elevated concentrations of NO3 or NO2. The distribution of nitrifiers suggests that the primary N2O peak observed in most of the lakes was produced via nitrification. Preliminary data on the rate of nitrification (Priscu et al., 1996) support the occurrence of nitrification and the presence of nitrifiers at the depth intervals where nitrifiers were detected. In all lakes, except Lake Miers, the data indicate that nitrifying bacteria have an important role in the vertical distribution of nitrogen compounds in these systems.

Meet the superbug: Radiation‐resistant bacteria may clean up the nation's worst waste sites

If a massive nuclear war ever blanketed the planet with radioactive fallout, cockroaches, despite all the jokes, would be goners. A bacterium known as Deinococcus radiodurans might survive, however. Its name, which means strange berry that withstands radiation, indicates the reason that the microbe fascinates scientists. Labeled the world's toughest bacterium by The Guinness Book of World Records, D. radiodurans shrugs off doses of radiation many thousands of times stronger than those that would kill a person. I had difficulty believing anything like this could exist, says John R. Battista of Louisiana State University in Baton Rouge, recalling his introduction to the microbe in 1988. Believe it or not, D. radiodurans does exist-and in some unusual places. Pinkish in color and giving off the smell of rotten cabbages, the bacteria were originally isolated in the 1950s from tins of meat that had spoiled despite supposedly sterilizing irradiation. Since then, they've showed up in elephant and llama feces, in irradiated haddock and duck, and in granite from Antarctica's Dry Valleys, the place on Earth thought to most closely resemble the surface of Mars. Reviving the idea that comets seeded planets with the precursors of life, or even life itself, scientists have had fun speculating that only a radiation-tolerant bacterium such as D. radiodurans could survive interstellar journeys. This is the kind of organism that could do something like that, muses Marvin Frazier, director of the Department of Energy's (DOE) Microbial Genome Program in Germantown, Md., which funded the just-completed effort to sequence all of D. radiodurans' genes. In more earthly matters, investigators have crafted an explanation for why the bacterium evolved its immunity to radiation. They propose that it's the byproduct of skills needed to survive a lack of water. Scientists have also established that the microbe doesn't simply shield its DNA from the radiation. It instead has an unprecedented ability to repair genetic damage. While the basic biology of D. radiodurans has proved fascinating, DOE's interest in the bacterium stems from a very practical issue. The agency hopes that the microbe, after appropriate genetic manipulation, might help detoxify the thousands of toxicwaste sites nationwide that include radioactive materials. Using microbes as a cleanup crew is a strategy known as bioremediation. A recent study, in which D. radiodurans was engineered to degrade an organic toxin common to such waste sites, offers encouraging results, says Frazier.

A morphological view on potential niches for exobiology on Mars

The discovery of microbiota in the Dry Valleys of Antarctica has encouraged the construction of new models of Martian ecosystems in order to determine if life could have once existed on Mars. The Antarctic cyanobacteria reside just below the surface of sandstone rocks where they are protected from the extreme cold and dry environment. Analogy with the Antarctic Dry Valleys supports speculation that hypothetical micro-organisms existed on Mars in the early history of the planet and could have migrated into suitable rocks as the availability of liquid water decreased. Although evidence for sandstone layers on Mars has not been substantiated, the palaeohydrology of Martian fluvial valleys (MFVs) reveals the evidence of lake bed sediment depositions which have formed consolidated sediments. As the MFVs formation may result from underground drainage processes, the sediment material would be expected to contain debris such as pumice washload, and pumilith of volcanic and meteoritic origin. These materials may have formed consolidated porous terrains similar to the Antarctic sandstone. Therefore, the endolithic model is consistent with the Martian liquid water habitat model of perenially ice-covered lakes.

Mars after the viking missions: Is life still possible?

The results of the biology and organic chemistry experiments carried aboard the Viking landers seem to rule out the possibility of life on Mars. However, we present a possible model of Martian ecology which is based on the premise that Martian life could be endolithic, and thus missed by the Viking biology experiments. This model is based, in part, on the endolithic microbiota found in the dry valleys of Antarctica. In addition, we combine our model with a previously described model which suggests that Mars may go through ice ages and periods of relatively mild climate.

Lake Hoare, Antarctica: sedimentation through a thick perennial ice cover.

Lake Hoare in the Dry Valleys of Antarctica is covered with a perennial ice cover more than 3 m thick, yet there is a complex record of sedimentation and of growth of microbial mats on the lake bottom. Rough topography on the ice covering the lake surface traps sand that is transported by the wind. In late summer, vertical conduits form by melting and fracturing, making the ice permeable to both liquid water and gases. Cross-sections of the ice cover show that sand is able to penetrate into and apparently through it by descending through these conduits. This is the primary sedimentation mechanism in the lake. Sediment traps retrieved from the lake bottom indicate that rates of deposition can vary by large amounts over lateral scales as small as 1 m. This conclusion is supported by cores taken in a 3 x 3 grid with a spacing of 1.5 m. Despite the close spacing of the cores, the poor stratigraphic correlation that is observed indicates substantial lateral variability in sedimentation rate. Apparently, sand descends into the lake from discrete, highly localized sources in the ice that may in some cases deposit a large amount of sand into the lake in a very short time. In some locations on the lake bottom, distinctive sand mounds have been formed by this process. They are primary sedimentary structures and appear unique to the perennially ice-covered lacustrine environment. In some locations they are tens of centimetres high and gently rounded with stable slopes; in others they reach approximately 1 m in height and have a conical shape with slopes at angle of repose. A simple formation model suggests that these differences can be explained by local variations in water depth and sedimentation rate. Rapid colonization of fresh sand surfaces by microbial mats composed of cyanobacteria, eukaryotic algae, and heterotrophic bacteria produces a complex intercalation of organic and sandy layers that are a distinctive form of modern stromatolites.

Winter Frost Injury to Lichens: Colorado Front Range

Saxicolous lichens in exposed habitats on the East Slope of the Colorado Front Range were damaged by an unusual sequence of weather events in late January and early February 1989. Rapid cooling of hydrated, metabolically active thalli caused spalling of upper cortices and algal layers, exposing white medullary tissue. Foliose and umbilicate species were damaged more severely than crustose species; young tissue was particularly frost tender. Frost injury, though uncommon in the southern Rocky Mountains, probably occurs frequently enough to influence patterns of lichen distribution in winter-snowfree microenvironments. Lichens are renowned for their ability to withstand severe cold (Hale 1983). Their reputation derives partly from experiments in which desiccated thalli survived chilling to temperatures as low as 1960C (Kappen & Lange 1972), and partly from the occurrence of lichens in low-temperature environments such as the dry valleys of Antarctica (Friedmann 1982). Thresholds of cold tolerance vary with moisture content, rate of cooling, rate of rewarming, time of year, photobiont, and species (Kappen 1973; Kappen & Lange 1970, 1972; Larson 1982; Nash et al. 1987; Riedmiiller-Schblm 1974). Reports of cold injury under natural conditions (Brodo 1965; Laundon 1966; Showman 1979) are