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1
Witherow, Rebecca A., W. Berry Lyons, Nancy A. N. Bertler, Kathleen A. Welch, Paul A. Mayewski, Sharon B. Sneed, Thomas Nylen, Michael J. Handley i Andrew Fountain. "The aeolian flux of calcium, chloride and nitrate to the McMurdo Dry Valleys landscape: evidence from snow pit analysis". Antarctic Science 18, nr 4 (14.11.2006): 497–505. http://dx.doi.org/10.1017/s095410200600054x.
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We have determined the flux of calcium, chloride and nitrate to the McMurdo Dry Valleys region by analysing snow pits for their chemical composition and their snow accumulation using multiple records spanning up to 48 years. The fluxes demonstrate patterns related to elevation and proximity to the ocean. In general, there is a strong relationship between the nitrate flux and snow accumulation, indicating that precipitation rates may have a great influence over the nitrogen concentrations in the soils of the valleys. Aeolian dust transport plays an important role in the deposition of some elements (e.g. Ca2+) into the McMurdo Dry Valleys' soils. Because of the antiquity of some of the soil surfaces in the McMurdo Dry Valleys regions, the accumulated atmospheric flux of salts to the soils has important ecological consequences. Although precipitation may be an important mechanism of salt deposition to the McMurdo Dry Valley surfaces, it is poorly understood because of difficulties in measurement and high losses from sublimation.
2
Smillie, Robert W. "Suite subdivision and petrological evolution of granitoids from the Taylor Valley and Ferrar Glacier region, south Victoria Land". Antarctic Science 4, nr 1 (marzec 1992): 71–87. http://dx.doi.org/10.1017/s0954102092000130.
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Detailed geological mapping and geochemical analysis of early Palaeozoic granitoid plutons and dykes from the Taylor Valley and Ferrar Glacier region in south Victoria Land reveal two distinct suites. This suite subdivision-approach is a departure from previous lithology-based schemes and can be applied elsewhere in south Victoria Land. The older calc-alkaline Dry Valleys 1 suite is dominated by the compositionally variable Bonney Pluton, a flow-foliated concordant pluton with an inferred length of over 100 km. Plutons of this suite are elongate in a NW-SE direction and appear to have been subjected to major structural control during their emplacement. The younger alkali-calcic Dry Valleys 2 suite comprises discordant plutons and numerous dyke swarms with complex age relationships. Field characteristics of this suite indicate that it was passively emplaced into fractures at higher levels in the crust than the Dry Valleys 1 suite. Whole-rock geochemistry confirms this suite subdivision based on field relationships and indicates that the two suites were derived from different parent magmas by fractional crystallization. The Dry Valleys 1 suite resembles Cordilleran I-type granitoids and is inferred to be derived from partial melting of the upper mantle and/or lower crust above an ancient subduction zone. The Dry Valleys 2 suite resembles Caledonian I-type granitoids and may have resulted from a later episode of crustal extension.
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Hall, B. L., G. H. Denton i B. Overturf. "Glacial Lake Wright, a high-level Antarctic lake during the LGM and early Holocene". Antarctic Science 13, nr 1 (marzec 2001): 53–60. http://dx.doi.org/10.1017/s0954102001000086.
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We report evidence of a large proglacial lake (Glacial Lake Wright) that existed in Wright Valley in the McMurdo Dry Valleys region of Antarctica at the last glacial maximum (LGM) and in the early Holocene. At its highstands, Glacial Lake Wright would have stretched 50 km and covered c. 210 km2. Chronology for lake-level changes comes from 30 AMS radiocarbon dates of lacustrine algae preserved in deltas, shorelines, and glaciolacustrine deposits that extend up to 480 m above present-day lakes. Emerging evidence suggests that Glacial Lake Wright was only one of a series of large lakes to occupy the McMurdo Dry Valleys and the valleys fronting the Royal Society Range at the LGM. Although the cause of such high lake levels is not well understood, it is believed to relate to cool, dry conditions which produced fewer clouds, less snowfall, and greater amounts of absorbed radiation, leading to increased meltwater production.
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Tang, Ya, Jiasui Xie i Hui Sun. "Revisiting sustainable development of dry valleys in Hengduan Mountains Region". Journal of Mountain Science 1, nr 1 (luty 2004): 38–45. http://dx.doi.org/10.1007/bf02919358.
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Esposito, R. M. M., S. A. Spaulding, D. M. McKnight, B. Van de Vijver, K. Kopalová, D. Lubinski, B. Hall i T. Whittaker. "Inland diatoms from the McMurdo Dry Valleys and James Ross Island, Antarctica". Botany 86, nr 12 (grudzień 2008): 1378–92. http://dx.doi.org/10.1139/b08-100.
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Diatom taxa present in the inland streams and lakes of the McMurdo Dry Valleys and James Ross Island, Antarctica, are presented in this paper. A total of nine taxa are illustrated, with descriptions of four new species ( Luticola austroatlantica sp. nov., Luticola dolia sp. nov., Luticola laeta sp. nov., Muelleria supra sp. nov.). In the perennially ice-covered lakes of the McMurdo Dry Valleys, diatoms are confined to benthic mats within the photic zone. In streams, diatoms are attached to benthic surfaces and within the microbial mat matrix. One species, L. austroatlantica, is found on James Ross Island, of the southern Atlantic archipelago, and the McMurdo Dry Valleys. The McMurdo Dry Valley populations are at the lower range of the size spectrum for the species. Streams flow for 6–10 weeks during the austral summer, when temperatures and solar radiation allow glacial ice to melt. The diatom flora of the region is characterized by species assemblages favored under harsh conditions, with naviculoid taxa as the dominant group and several major diatom groups conspicuously absent.
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Cox, Simon C., i Andrew H. Allibone. "Petrogenesis of orthogneisses in the Dry Valleys region, South Victoria Land". Antarctic Science 3, nr 4 (grudzień 1991): 405–17. http://dx.doi.org/10.1017/s0954102091000500.
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Granitoid gneisses intercalated with Koettlitz Group metasediments in the upper Ferrar, Taylor and Wright valleys of South Victoria Land comprise various hornblende+biotite orthogneisses and biotite orthogneisses, including the km-scale Dun and Calkin plutons. K-feldspar megacryst inclusion textures and discordant cross-cutting relationships with enclosing metasediments are interpreted as firm evidence of an intrusive origin for hornblende+biotite and biotite orthogneiss. The scale of several concordant orthogneiss bodies (including the Dun and Calkin plutons), the presence of mafic enclaves, and relict flow differentiation in hornblende+biotite orthogneiss are also compatible with a plutonic origin. Orthogneisses were emplaced prior to deformation that produced macroscopic upright, tight, folds about NW-trending axes. Petrography and geochemistry indicate I-type affinities for hornblende+biotite orthogneisses and the Dun Pluton. Hornblende+biotite and biotite orthogneisses (with the exception of the Dun Pluton) are part of a single petrogenetic suite, together with younger Bonney, Valhalla, and Hedley plutons. Emplacement of a continuum of I-type intrusives is envisaged which spanned Koettlitz Group deformation, and possibly caused much of the deformation. Hornblende+biotite and biotite orthogneisses are deformed precursors to the younger Bonney, Valhalla, and Hedley plutons. The Dun Pluton contains Fe-rich salitic clinopyroxene relicts and exhibits a unique geochemistry. It is rich in Sr, Al2O3, Na2O, and poor in FeO, K2O, Rb, Y, V. Chemical and petrographic features indicate an evolved body, possibly derived from a primitive source distinct from other orthogneisses and granitoids.
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Ukrainskiy, Pavel, Edgar Terekhin, Artyom Gusarov, Eugenia Zelenskaya i Fedor Lisetskii. "The Influence of Relief on the Density of Light-Forest Trees within the Small-Dry-Valley Network of Uplands in the Forest-Steppe Zone of Eastern Europe". Geosciences 10, nr 11 (24.10.2020): 420. http://dx.doi.org/10.3390/geosciences10110420.
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An active process of the invasion of woody vegetation, resulting in the formation of light forests, has been observed in predominantly herbaceous small dry valleys of the forest-steppe uplands of the East European Plain over the past two decades. This paper investigates the spatial features of the density of trees in such light forests and its relationship with relief parameters. The Belgorod Region, one of the administrative regions of European Russia, was chosen as a reference for the forest-steppe zone of the plain. The correlation between some relief characteristics (the height, slope, slope exposure cosine, topographic position index, morphometric protection index, terrain ruggedness index, and width and depth of small dry valleys) and the density of light-forest trees was estimated. The assessment was carried out at the local, subregional and regional levels of generalization. The relief influence on the density of trees in the small dry valley network is manifested both through the differentiation of moisture within the territory under study and the formation of various conditions for fixing tree seedlings in the soil. This influence on subregional and regional trends in the density is greater than on local trends. The results obtained are important for the management of herbaceous small-dry-valley ecosystems within the forest-steppe uplands in Eastern Europe.
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Mellon, Michael T., Christopher P. Mckay i Jennifer L. Heldmann. "Polygonal ground in the McMurdo Dry Valleys of Antarctica and its relationship to ice-table depth and the recent Antarctic climate history". Antarctic Science 26, nr 4 (26.11.2013): 413–26. http://dx.doi.org/10.1017/s0954102013000710.
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AbstractThe occurrence of dry permafrost overlying ice-rich permafrost is unique to the Antarctic Dry Valleys on Earth and to the high latitudes of Mars. The stability and distribution of this ice are poorly understood and fundamental to understanding the Antarctic climate as far back as a few million years. Polygonal patterned ground is nearly ubiquitous in these regions and is integrally linked to the history of the icy permafrost and climate. We examined the morphology of polygonal ground in Beacon Valley and the Beacon Heights region of the Antarctic Dry Valleys, and show that polygon size is correlated with ice-table depth (the boundary between dry and ice-rich permafrost). A numerical model of seasonal stress in permafrost shows that the ice-table depth is a dominant factor. Remote sensing and field observations of polygon size are therefore important tools for investigating subsurface ice. Polygons are long-lived landforms and observed characteristics indicate no major fluctuations in the ice-table depth during their development. We conclude that the Beacon Valley and Beacon Heights polygons have developed for at least 104 years to achieve their present mature-stage morphology and that the ice-table depth has been stable for a similar length of time.
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Clausen, Eric. "Origin of the Redwater River Drainage Basin Determined by Topographic Map Interpretation: Eastern Montana, USA". Journal of Geography and Geology 11, nr 1 (26.02.2019): 42. http://dx.doi.org/10.5539/jgg.v11n1p42.
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Topographic and geologic map interpretation strongly suggests the eastern Montana Redwater River valley eroded headward across large southeast-oriented ice-marginal melt water floods. The north-oriented Redwater River heads in an area to the south of recognized continental glaciation and flows into the recognized glaciated region before joining the east-oriented Missouri River. Detailed topographic maps show the eastern drainage divide is asymmetric with steeper slopes on the Redwater River side and is crossed by shallow dry valleys linking northwest-oriented Redwater River tributaries with southeast-oriented streams that flow as barbed tributaries to the northeast-oriented Yellowstone River. The western drainage divide is also crossed by shallow dry valleys linking northwest-oriented drainage routes to north-oriented Missouri River tributaries with southeast-oriented and barbed tributaries to the northeast- and north-oriented Redwater River. Alluvium from upstream Yellowstone River source areas found within the Redwater River drainage basin suggests the Redwater River and much longer Yellowstone River valleys eroded headward from a continental ice sheet margin as headward erosion of the larger Yellowstone River valley across the southeast-oriented flood flow was supplemented by northeast- and north-oriented flow moving at the present day Redwater-Yellowstone River drainage divide elevation.
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Lyons, W. B., S. W. Tyler, R. A. Wharton, D. M. McKnight i B. H. Vaughn. "A Late Holocene desiccation of Lake Hoare and Lake Fryxell, McMurdo Dry Valleys, Antarctica". Antarctic Science 10, nr 3 (wrzesień 1998): 247–56. http://dx.doi.org/10.1017/s0954102098000340.
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Stable isotope data from waters of lakes in the McMurdo Dry Valleys (MDV) of southern Victoria Land, Antarctica are presented in order to establish the climatic history of this region over the past two millennia. New data from Lake Fryxell and Lake Hoare in Toylor Valley, along with previously published data from Lake Vanda, Wright Valley and Lake Bonney, Taylor Valley are used to infer the recent climatic history of MDV. Lakes Vanda, Fryxell and Bonney appear to have lost their ice covers and evaporated to small, hypersaline ponds by 1000 to ~1200 yr BP. Lake Hoare either desiccated or did not exist prior to 1200 yr BP. These data indicate a major lowering of lake level prior to ~1000 yr BP, followed by a warmer and/or more humid climate since then.
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Hubbard, Alun, Wendy Lawson, Brian Anderson, Bryn Hubbard i Heinz Blatter. "Evidence for subglacial ponding across Taylor Glacier, Dry Valleys, Antarctica". Annals of Glaciology 39 (2004): 79–84. http://dx.doi.org/10.3189/172756404781813970.
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AbstractIce-penetrating radar and modelling data are presented suggesting the presence of a zone of temperate ice, water ponding or saturated sediment beneath the tongue of Taylor Glacier, Dry Valleys, Antarctica. The proposed subglacial zone lies 3–6 km up-glacier of the terminus and is 400– 1000m across. The zone coincides with an extensive topographic overdeepening to 80m below sea level. High values of residual bed reflective power across this zone compared to other regions and the margins of the glacier require a high dielectric contrast between the ice and the bed and are strongly indicative of the presence of basal water or saturated sediment. Analysis of the hydraulic equipotential surface also indicates strong convergence into this zone of subglacial water flow paths. However, thermodynamic modelling reveals that basal temperatures in this region could not exceed –7˚C relative to the pressure-melting point. Such a result is at odds with the radar observations unless the subglacial water is a hypersaline brine.
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Krusic, A. G., M. L. Prentice i J. M. Licciardi. "Climatic implications of reconstructed early–mid Pliocene equilibrium-line altitudes in the McMurdo Dry Valleys, Antarctica". Annals of Glaciology 50, nr 50 (2009): 31–36. http://dx.doi.org/10.3189/172756409787769564.
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AbstractEarly–mid Pliocene moraines in the McMurdo Dry Valleys, Antarctica, are more extensive than the present alpine glaciers in this region, indicating substantial climatic differences between the early–mid Pliocene and the present. To quantify this difference in the glacier–climate regime, we estimated the equilibrium-line altitude (ELA) change since the early–mid Pliocene by calculating the modern ELA and reconstructing the ELAs of four alpine glaciers in Wright and Taylor Valleys at their early–mid Pliocene maxima. The area–altitude balance ratio method was used on modern and reconstructed early–mid Pliocene hypsometry. In Wright and Victoria Valleys, mass-balance data identify present-day ELAs of 800–1600ma.s.l. and an average balance ratio of 1.1. The estimated ELAs of the much larger early–mid Pliocene glaciers in Wright and Taylor Valleys range from 600 to 950±170ma.s.l., and thus are 250–600±170m lower than modern ELAs in these valleys. The depressed ELAs during the early–mid-Pliocene most likely indicate a wetter and therefore warmer climate in the Dry Valleys during this period than previous studies have recognized.
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Konfal, Stephanie A., T. J. Wilson i B. L. Hall. "Palaeoshoreline records of glacial isostatic adjustment in the Dry Valleys region, Antarctica". Geological Society, London, Special Publications 381, nr 1 (2013): 455–67. http://dx.doi.org/10.1144/sp381.26.
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Obryk, M. K., P. T. Doran, E. D. Waddington i C. P. Mckay. "The influence of föhn winds on Glacial Lake Washburn and palaeotemperatures in the McMurdo Dry Valleys, Antarctica, during the Last Glacial Maximum". Antarctic Science 29, nr 5 (17.03.2017): 457–67. http://dx.doi.org/10.1017/s0954102017000062.
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AbstractLarge glacial lakes, including Glacial Lake Washburn, were present in the McMurdo Dry Valleys, Antarctica, during the Last Glacial Maximum (LGM) despite a colder and drier climate. To address the mechanism capable of generating enough meltwater to sustain these large lakes, a conceptual model was developed based on the warming potential of infrequent contemporary föhn winds. The model suggests that föhn winds were capable of generating enough meltwater to sustain large glacial lakes during the LGM by increasing degree days above freezing (DDAF) and prolonging the melt season. A present-day relationship between infrequent summer föhn winds and DDAF was established. It is assumed that the Taylor Dome ice core record represents large-scale palaeoclimatic variations for the McMurdo Dry Valleys region. This analysis suggests that because of the warming influence of the more frequent föhn winds, summer DDAF in the McMurdo Dry Valleys during the LGM were equivalent to present-day values, but this enhanced summer signal is not preserved in the annually averaged ice core temperature record.
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De Los Ríos, Asunción, Jacek Wierzchos i Carmen Ascaso. "The lithic microbial ecosystems of Antarctica’s McMurdo Dry Valleys". Antarctic Science 26, nr 5 (7.07.2014): 459–77. http://dx.doi.org/10.1017/s0954102014000194.
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AbstractWe review the lithic microbial ecosystems of the McMurdo Dry Valleys as the main form of terrestrial colonization in this region, and assess the role of environmental controls such as temperature, solar radiation, water availability, wind, nutrient availability, salinity and the physicochemical properties of the colonized rock. Epilithic communities, especially those dominated by lichens, are able to withstand extreme environmental conditions but subsurface endolithic microhabitats provide more tolerant conditions. Endolithic microbial communities can be grouped into two main classes: eukaryotic communities (dominated by lichenized fungi and algae) and prokaryotic communities (dominated by cyanobacteria). Heterotrophic bacteria and non-lichenized algae and fungi (mainly black fungi) are also components of these communities. These lithobiontic microorganisms generally have effective mechanisms against freezing temperatures and desiccation. Extracellular polymeric substances play an important role not only in protecting microbial cells but also in community organization and in mitigating microenvironmental conditions. Antarctic lithobiontic communities are comprised of microbial consortia within which multiple interactions between the different biological and abiotic components are essential for microbial survival, whilst fossils and biomarkers provide evidence of earlier successful microbial life in Antarctic deserts. Finally, the uniqueness of the present lithobiont assemblages suggests they are the outcome of geographical isolation during the evolution of the continent and not merely the descendants of a subset of globally distributed taxa that have adapted to the extreme environmental conditions.
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Doran, Peter T., Christopher P. McKay, Andrew G. Fountain, Thomas Nylen, Diane M. McKnight, Chris Jaros i John E. Barrett. "Hydrologic response to extreme warm and cold summers in the McMurdo Dry Valleys, East Antarctica". Antarctic Science 20, nr 5 (16.05.2008): 499–509. http://dx.doi.org/10.1017/s0954102008001272.
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AbstractThe meteorological characteristics and hydrological response of an extreme warm, and cold summer in the McMurdo Dry Valleys are compared. The driver behind the warmer summer conditions was the occurrence of down-valley winds, which were not present during the colder summer. Occurrence of the summer down-valley winds coincided with lower than typical mean sea level pressure in the Ross Sea region. There was no significant difference in the amount of solar radiation received during the two summers. Compared to the cold summer, glaciological and hydrological response to the warm summer in Taylor Valley included significant glacier mass loss, and 3- to nearly 6000-fold increase in annual streamflow. Lake levels decreased slightly during the cold summer, and increased between 0.54 and 1.01 m during the warm summer, effectively erasing the prior 14 years of lake level lowering in a period of three months. Lake level rise during the warm summer was shown to be strongly associated with and increase in degree days above freezing at higher elevations. We suggest that strong summer down-valley winds may have been responsible for the generation of large glacial lakes during the Last Glacial Maximum when ice core records recorded annual temperatures significantly colder than present.
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Shean, David E., James W. Head i David R. Marchant. "Shallow seismic surveys and ice thickness estimates of the Mullins Valley debris-covered glacier, McMurdo Dry Valleys, Antarctica". Antarctic Science 19, nr 4 (16.08.2007): 485–96. http://dx.doi.org/10.1017/s0954102007000624.
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AbstractSeveral debris-covered glaciers occupy tributaries of upper Beacon Valley, Antarctica. Understanding their flow dynamics and ice thickness is important for palaeoclimate studies and for understanding the origins of ancient ice elsewhere in the McMurdo Dry Valleys region. We present the results of several shallow seismic surveys in Mullins Valley, where the largest of these debris-covered glaciers is located. Our results suggest that beneath a thin sublimation till and near-surface horizon of dirty glacier ice, lies relatively pure glacier ice (P-wave velocity ~3700–3800 m s-1), with total thickness estimates of ~90–95 m towards the valley head, and ~40–65 m near the entrance to Beacon Valley, ~2.5 km downglacier. P-wave velocities decrease downvalley, suggesting that the material properties of the ice change with increasing distance from the ice-accumulation zone. These new data are used to calibrate an ice thickness profile for the active portion of the Mullins Valley debris-covered glacier (upper ~3.5 km) and to shed light on the origin and spatial distribution of enclosed debris.
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Schmidt, S. K., R. C. Lynch, A. J. King, D. Karki, M. S. Robeson, L. Nagy, M. W. Williams, M. S. Mitter i K. R. Freeman. "Phylogeography of microbial phototrophs in the dry valleys of the high Himalayas and Antarctica". Proceedings of the Royal Society B: Biological Sciences 278, nr 1706 (8.09.2010): 702–8. http://dx.doi.org/10.1098/rspb.2010.1254.
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High-elevation valleys in dry areas of the Himalayas are among the most extreme, yet least explored environments on Earth. These barren, rocky valleys are subjected to year-round temperature fluctuations across the freezing point and very low availability of water and nutrients, causing previous workers to hypothesize that no photoautotrophic life (primary producers) exists in these locations. However, there has been no work using modern biogeochemical or culture-independent molecular methods to test the hypothesis that photoautotrophs are absent from high Himalayan soil systems. Here, we show that although microbial biomass levels are as low as those of the Dry Valleys of Antarctica, there are abundant microbial photoautotrophs, displaying unexpected phylogenetic diversity, in barren soils from just below the permanent ice line of the central Himalayas. Furthermore, we discovered that one of the dominant algal clades from the high Himalayas also contains the dominant algae in culture-independent surveys of both soil and ice samples from the Dry Valleys of Antarctica, revealing an unexpected link between these environmentally similar but geographically very distant systems. Phylogenetic and biogeographic analyses demonstrated that although this algal clade is globally distributed to other high-altitude and high-latitude soils, it shows significant genetic isolation by geographical distance patterns, indicating local adaptation and perhaps speciation in each region. Our results are the first to demonstrate the remarkable similarities of microbial life of arid soils of Antarctica and the high Himalayas. Our findings are a starting point for future comparative studies of the dry valleys of the Himalayas and Antarctica that will yield new insights into the cold and dry limits to life on Earth.
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Heindel, Ruth C., Angela M. Spickard i Ross A. Virginia. "Landscape-scale soil phosphorus variability in the McMurdo Dry Valleys". Antarctic Science 29, nr 3 (6.02.2017): 252–63. http://dx.doi.org/10.1017/s0954102016000742.
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AbstractThe predicted increase in liquid water availability in the McMurdo Dry Valleys (MDV), Antarctica, may have profound consequences for nutrient cycling in soil and aquatic ecosystems. Our ability to predict future changes relies on our understanding of current nutrient cycling processes. Multiple hypotheses exist to explain the variability in soil phosphorus content and availability found throughout the MDV region. We analysed 146 surface soil samples from the MDV to determine the relative importance of parent material, landscape age, soil chemistry and texture, and topography on two biologically relevant phosphorus pools, HCl- and NaHCO3-extractable phosphorus. While HCl-extractable phosphorus is highly predicted by parent material, NaHCO3-extractable phosphorus is unrelated to parent material but is significantly correlated with soil conductivity, soil texture and topography. Neither measure of soil phosphorus was related to landscape age across a gradient of ~20 000 to 1 500 000 years. Glacial history has played an important role in the availability of soil phosphorus by shaping patterns of soil texture and parent material. With a predicted increase in water availability, the rate of mineral weathering may increase, releasing more HCl-extractable phosphorus into soil and aquatic ecosystems.
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Eveland, J. W., M. N. Gooseff, D. J. Lampkin, J. E. Barrett i C. D. Takacs-Vesbach. "Seasonal controls on snow distribution and aerial ablation at the snow-patch and landscape scales, McMurdo Dry Valleys, Antarctica". Cryosphere Discussions 6, nr 5 (12.09.2012): 3823–62. http://dx.doi.org/10.5194/tcd-6-3823-2012.
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Abstract. Accumulated snow in the McMurdo Dry Valleys, while limited, has great ecological significance to subnivian soil environments. Though sublimation dominates the ablation process in this region, measurable increases in soil moisture and insulation from temperature extremes provide more favorable conditions with respect to subnivian soil communities. While precipitation is not substantial, significant amounts of snow can accumulate, via aeolian redistribution, in topographic lees along the valley bottoms, forming thousands of discontinuous snow patches. These patches have the potential to act as significant sources of local melt water, controlling biogeochemical cycling and the landscape distribution of microbial communities. Therefore, determining the spatial and temporal dynamics of snow at multiple scales is imperative to understanding the broader ecological role of snow in this region. High-resolution satellite imagery acquired during the 2009–2010 and 2010–2011 austral summers was used to quantify the distribution of snow across Taylor and Wright Valleys. Extracted snow-covered area from the imagery was used as the basis for assessing seasonal variability and seasonal controls on accumulation and ablation of snow at multiple scales. In addition, fifteen 1 km2 plots (3 in each of 5 study regions) were selected to assess the prevalence of snow cover at finer spatial scales. Results confirm that snow patches tend to form in the same locations each year with some minor deviations observed. At the snow-patch scale, neighboring patches often exhibit considerable differences in aerial ablation rates, and particular snow patches do not reflect trends for snow-covered area observed at the landscape scale. These differences are presumably related to microtopographic influences over snow depth and exposure. This highlights the importance of both the landscape and snow-patch scales in assessing the effects of snow cover on biogeochemical cycling and microbial communities.
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Arcone, Steven A., i Karl Kreutz. "GPR reflection profiles of Clark and Commonwealth Glaciers, Dry Valleys, Antarctica". Annals of Glaciology 50, nr 51 (2009): 121–29. http://dx.doi.org/10.3189/172756409789097531.
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AbstractEnglacial horizons deeper than 100m are absent within 100MHz ground-penetrating radar (GPR) surface profiles we recorded on Clark and Commonwealth Glaciers in the Antarctic Dry Valleys region. Both glaciers show continuous bottom horizons to 280 m, with bottom signal-to-noise ratios near 30 dB. Density horizons should fade below 50 m depth because impermeable ice occurred by 36 m. Folding within Commonwealth Glacier could preclude radar strata beneath about 80 m depth, but there is no significant folding within Clark Glacier. Strong sulfate concentrations and contrasts exist in our shallow ice core. However, it appears that high background concentration levels, and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of, or below, our system sensitivity by about 77m depth. Further verification of this conclusion awaits processing of our deep-core chemistry profiles.
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Marchant, David R., i George H. Denton. "Miocene and Pliocene paleoclimate of the Dry Valleys region, Southern Victoria land: a geomorphological approach". Marine Micropaleontology 27, nr 1-4 (kwiecień 1996): 253–71. http://dx.doi.org/10.1016/0377-8398(95)00065-8.
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Bertler, Nancy A. N., Paul A. Mayewski, Peter J. Barrett, Sharon B. Sneed, Michael J. Handley i Karl J. Kreutz. "Monsoonal circulation of the McMurdo Dry Valleys, Ross Sea region, Antarctica: signal from the snow chemistry". Annals of Glaciology 39 (2004): 139–45. http://dx.doi.org/10.3189/172756404781814087.
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AbstractMcMurdo Dry Valleys (MDV; Ross Sea region, Antarctica) precipitation exhibits extreme seasonality in ion concentration, 3–5 orders of magnitude between summer and winter precipitation. To identify aerosol sources and investigate causes for the observed amplitude in concentration variability, four snow pits were sampled along a coast–Polar Plateau transect across the MDV. The elevation of the sites ranges from 50 to 2400 m and the distance from the coast from 8 to 93 km. Average chemistry gradients along the transect indicate that most species have either a predominant marine or terrestrial source in the MDV. Empirical orthogonal function analysis on the snow-chemistry time series shows that at least 57% of aerosol deposition occurs concurrently. A conceptual climate model, based on meteorological observations, is used to explain the strong seasonality in the MDV. Our results suggest that radiative forcing of the ice-free valleys creates a surface low-pressure cell during summer which promotes air-mass flow from the Ross Sea. The associated precipitating air mass is relatively warm, humid and contains a high concentration of aerosols. During winter, the MDV are dominated by air masses draining off the East Antarctic ice sheet, that are characterized by cold, dry and low concentrations of aerosols. The strong differences between these two air-mass sources create in the MDV a polar version of the monsoonal flow, with humid, warm summers and dry, cold winters.
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Hector, Basile, Jean-Martial Cohard, Luc Séguis, Sylvie Galle i Christophe Peugeot. "Hydrological functioning of western African inland valleys explored with a critical zone model". Hydrology and Earth System Sciences 22, nr 11 (14.11.2018): 5867–88. http://dx.doi.org/10.5194/hess-22-5867-2018.
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Abstract. Inland valleys are seasonally waterlogged headwater wetlands, widespread across western Africa. Their role in the hydrological cycle in the humid, hard-rock-dominated Sudanian savanna is not yet well understood. Thus, while in the region recurrent floods are a major issue, and hydropower has been recognized as an important development pathway, the scientific community lacks precise knowledge of streamflow (Q) generation processes and how they could be affected by the presence of inland valleys. Furthermore, inland valleys carry an important agronomic potential, and with the strong demographic rates of the region, they are highly subject to undergoing land cover changes. We address both the questions of the hydrological functioning of inland valleys in the Sudanian savanna of western Africa and the impact of land cover changes on these systems through deterministic sensitivity experiments using a physically based critical zone model (ParFlow-CLM) applied to a virtual generic catchment which comprises an inland valley. Model forcings are based on 20 years of data from the AMMA-CATCH observation service and parameters are evaluated against multiple field data (Q, evapotranspiration – ET –, soil moisture, water table levels, and water storage) acquired on a pilot elementary catchment. The hydrological model applied to the conceptual lithological/pedological model proposed in this study reproduces the main behaviours observed, which allowed those virtual experiments to be conducted. We found that yearly water budgets were highly sensitive to the vegetation distribution: average yearly ET for a tree-covered catchment (944 mm) exceeds that of herbaceous cover (791 mm). ET differences between the two covers vary between 12 % and 24 % of the precipitation of the year for the wettest and driest years, respectively. Consequently, the tree-covered catchment produces a yearly Q amount of 28 % lower on average as compared to a herbaceous-covered catchment, ranging from 20 % for the wettest year to 47 % for a dry year. Trees also buffer interannual variability in ET by 26 % (with respect to herbaceous). On the other hand, pedological features (presence – or absence – of the low-permeability layer commonly found below inland valleys, upstream and lateral contributive areas) had limited impact on yearly water budgets but marked consequences for intraseasonal hydrological processes (sustained/non-sustained baseflow in the dry season, catchment water storage redistribution). Therefore, subsurface features and vegetation cover of inland valleys have potentially significant impacts on downstream water-dependent ecosystems and water uses as hydropower generation, and should focus our attention.
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Eveland, J. W., M. N. Gooseff, D. J. Lampkin, J. E. Barrett i C. D. Takacs-Vesbach. "Seasonal controls on snow distribution and aerial ablation at the snow-patch and landscape scales, McMurdo Dry Valleys, Antarctica". Cryosphere 7, nr 3 (11.06.2013): 917–31. http://dx.doi.org/10.5194/tc-7-917-2013.
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Abstract. Accumulated snow in the McMurdo Dry Valleys, while limited, has great ecological significance to subnivian soil environments. Though sublimation dominates the ablation process in this region, measurable increases in soil moisture and insulation from temperature extremes provide more favorable conditions with respect to subnivian soil communities. While precipitation is not substantial, significant amounts of snow can accumulate, via wind transport, in topographic lees along the valley bottoms, forming thousands of discontinuous snow patches. These patches have the potential to act as significant sources of local meltwater, controlling biogeochemical cycling and the landscape distribution of microbial communities. Therefore, determining the spatial and temporal dynamics of snow at multiple scales is imperative to understanding the broader ecological role of snow in this region. High-resolution satellite imagery acquired during the 2009–2010 and 2010–2011 austral summers was used to quantify the distribution of snow across Taylor and Wright valleys. Extracted snow-covered area from the imagery was used as the basis for assessing inter-annual variability and seasonal controls on accumulation and ablation of snow at multiple scales. In addition to landscape analyses, fifteen 1 km2 plots (3 in each of 5 study regions) were selected to assess the prevalence of snow cover at finer spatial scales, referred to herein as the snow-patch scale. Results confirm that snow patches tend to form in the same locations each year with some minor deviations observed. At the snow-patch scale, neighboring patches often exhibit considerable differences in aerial ablation rates, and particular snow patches do not reflect trends for snow-covered area observed at the landscape scale. These differences are presumably related to microtopographic influences acting on individual snow patches, such as wind sheltering and differences in snow depth due to the underlying topography. This highlights the importance of both the landscape and snow-patch scales in assessing the effects of snow cover on biogeochemical cycling and microbial communities.
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Colesie, Claudia, Maxime Gommeaux, T. G. Allan Green i Burkhard Büdel. "Biological soil crusts in continental Antarctica: Garwood Valley, southern Victoria Land, and Diamond Hill, Darwin Mountains region". Antarctic Science 26, nr 2 (23.05.2013): 115–23. http://dx.doi.org/10.1017/s0954102013000291.
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AbstractBiological soil crusts are associations of lichens, mosses, algae, cyanobacteria, microfungi and bacteria in different proportions forming a thin veneer within the top centimetres of soil surfaces. They occur in all biomes, but particularly in arid and semi-arid regions, even in the most extreme climates. They carry out crucial ecosystem functions, such as soil stabilization, influencing water and nutrient cycles, and contribute to the formation of microniches for heterotrophic life. In continental Antarctica especially, these roles are essential because no higher plants provide such ecosystem services. We provide a detailed description of biological soil crusts from Garwood Valley, McMurdo Dry Valleys region (78°S) and Diamond Hill (80°S) in the Darwin Mountains region. The coverage was low at 3.3% and 0.8% of the soil surface. At Garwood Valley the crusts were composed of green algal lichens, cyanobacteria, several species of green algae and the mossHennediella heimii(Hedw.) R.H. Zander. Diamond Hill crusts appear to be unique in not having any species of cyanobacteria. Major parts are embedded in the soil, and their thickness correlates with higher chlorophyll contents, higher soil organic carbon and nitrogen, which are fundamental components of this species poor cold desert zone.
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Speirs, Johanna C., Daniel F. Steinhoff, Hamish A. McGowan, David H. Bromwich i Andrew J. Monaghan. "Foehn Winds in the McMurdo Dry Valleys, Antarctica: The Origin of Extreme Warming Events*". Journal of Climate 23, nr 13 (1.07.2010): 3577–98. http://dx.doi.org/10.1175/2010jcli3382.1.
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Abstract Foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the McMurdo Dry Valleys (MDVs) of Antarctica. Strong foehn winds in the MDVs cause dramatic warming at onset and have significant effects on landscape forming processes; however, no detailed scientific investigation of foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau. Herein observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during foehn events in the MDVs are presented. Results show that foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow, which is channeled into the valleys from higher levels. Modeling of a winter foehn event identifies mountain wave activity similar to that associated with midlatitude foehn winds. These events are found to be caused by strong pressure gradients over the mountain ranges of the MDVs related to synoptic-scale cyclones positioned off the coast of Marie Byrd Land. Analysis of meteorological records for 2006 and 2007 finds an increase of 10% in the frequency of foehn events in 2007 compared to 2006, which corresponds to stronger pressure gradients in the Ross Sea region. It is postulated that the intra- and interannual frequency and intensity of foehn events in the MDVs may therefore vary in response to the position and frequency of cyclones in the Ross Sea region.
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Lyons, W. Berry, Kathleen A. Welch, Christopher B. Gardner, Chris Jaros, Daryl L. Moorhead, Jennifer L. Knoepfle i Peter T. Doran. "The geochemistry of upland ponds, Taylor Valley, Antarctica". Antarctic Science 24, nr 1 (23.09.2011): 3–14. http://dx.doi.org/10.1017/s0954102011000617.
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AbstractThe McMurdo Dry Valleys of Antarctica are the largest ice-free region on the continent. These valleys contain numerous water bodies that receive seasonal melt from glaciers. For forty years, research emphasis has been placed on the larger water bodies, the permanent ice-covered lakes. We present results from the first study describing the geochemistry of ponds in the higher elevations of Taylor Valley. Unlike the lakes at lower elevations, the landscape on which these ponds lie is among the oldest in Taylor Valley. These upland ponds wax and wane in size depending on the local climatic conditions, and their ionic concentrations and isotopic composition vary annually depending on the amount of meltwater generated and their hydrologic connectivity. This study evaluates the impact of changes in summer climate on the chemistry of these ponds. Although pond chemistry reflects the initial meltwater chemistry, dissolution and chemical weathering within the stream channels, and possibly permafrost fluid input, the primary control is the dilution effect of glacier melt during warmer summers. These processes lead to differences in solute concentrations and ionic ratios between ponds, despite their nearby proximity. The change in size of these ponds over time has important consequences on their geochemical behaviour and potential to provide water and solutes to the subsurface.
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Xue, Dong Jian, Zheng Wei He i Xiang Dong Zheng. "The Distribution Regularity of Geohazard in the Dry-Hot Valley of Jinsha River: Case Study in Derong County". Advanced Materials Research 518-523 (maj 2012): 5754–59. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.5754.
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Derong County is located in Ganzi Tibetan Autonomous Prefecture in southern part of Sichuan Province, in the upper of the Jinsha River, where there is a subtropical plateau monsoon climate, abundant sunshine, and large amount of evaporation, so it is a typical dry-hot valleys region. Derong County is the area of more ups and downs in the terrain, deep valleys, steep mountains, complex geological conditions, intense tectonic activity, various climate types, and has obvious vertical zone effect by temperature, serious physical weathering of rock, and landslide, debris flow, collapse and other geohazards are easily induced under the influence of rainfall and human engineering activities. These geohazards have brought serious harm to the people's lives and property, and have a great impact on the socio-economic development. Through the analysis of geohazards in the study area to investigate its distribution and development trends, this paper provide a basis for geohazard prevention and economic development.
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Coleine, Claudia, Nuttapon Pombubpa, Laura Zucconi, Silvano Onofri, Jason E. Stajich i Laura Selbmann. "Endolithic Fungal Species Markers for Harshest Conditions in the McMurdo Dry Valleys, Antarctica". Life 10, nr 2 (6.02.2020): 13. http://dx.doi.org/10.3390/life10020013.
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The microbial communities that inhabit lithic niches inside sandstone in the Antarctic McMurdo Dry Valleys of life’s limits on Earth. The cryptoendolithic communities survive in these ice-free areas that have the lowest temperatures on Earth coupled with strong thermal fluctuations, extreme aridity, oligotrophy and high levels of solar and UV radiation. In this study, based on DNA metabarcoding, targeting the fungal Internal Transcribed Spacer region 1 (ITS1) and multivariate statistical analyses, we supply the first comprehensive overview onto the fungal diversity and composition of these communities sampled over a broad geographic area of the Antarctic hyper-arid cold desert. Six locations with surfaces that experience variable sun exposure were sampled to compare communities from a common area across a gradient of environmental pressure. The Operational Taxonomic Units (OTUs) identified were primarily members of the Ascomycota phylum, comprised mostly of the Lecanoromycetes and Dothideomycetes classes. The fungal species Friedmanniomyces endolithicus, endemic to Antarctica, was found to be a marker species to the harshest conditions occurring in the shady, south exposed rock surfaces. Analysis of community composition showed that sun exposure was an environmental property that explained community diversity and structured endolithic colonization.
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Marchant, David R., George H. Denton, Carl C. Swisher i Noel Potter. "Late Cenozoic Antarctic paleoclimate reconstructed from volcanic ashes in the Dry Valleys region of southern Victoria Land". Geological Society of America Bulletin 108, nr 2 (luty 1996): 181–94. http://dx.doi.org/10.1130/0016-7606(1996)108<0181:lcaprf>2.3.co;2.
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Grombacher, Denys, Esben Auken, Nikolaj Foged, Thue Bording, Neil Foley, Peter T. Doran, Jill Mikucki i in. "Induced polarization effects in airborne transient electromagnetic data collected in the McMurdo Dry Valleys, Antarctica". Geophysical Journal International 226, nr 3 (5.05.2021): 1574–83. http://dx.doi.org/10.1093/gji/ggab148.
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SUMMARY Airborne electromagnetics (EM) is a geophysical tool well suited to mapping glacial and hydrogeological structures in polar environments. This non-invasive method offers significant spatial coverage without requiring access to the ground surface, enabling the mapping of geological units to hundreds of metres depth over highly varied terrain. This method shows great potential for large-scale surveys in polar environments, as common targets such as permafrost, ice and brine-rich groundwater systems in these settings can be easily differentiated because of their significant contrasts in electrical properties. This potential was highlighted in a 2011 airborne EM survey in the McMurdo Dry Valleys that mapped the existence of a large-scale regional groundwater system in Taylor Valley. A more comprehensive airborne EM survey was flown in November 2018 to broadly map potential groundwater systems throughout the region. Data collected in this survey displayed significant perturbations from a process called induced polarization (IP), an effect that can greatly limit or prevent traditional EM workflows from producing reliable geological interpretations. Here, we present several examples of observed IP signatures over a range of conditions and detail how workflows explicitly designed to handle IP effects can produce reliable geological interpretations and data fits in these situations. Future polar EM surveys can be expected to encounter strong IP effects given the likely presence of geological materials (e.g. ice and permafrost) that can accentuate the influence of IP.
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Yang, Jie, Yousry A. El-Kassaby i Wenbin Guan. "Multiple Ecological Drivers Determining Vegetation Attributes across Scales in a Mountainous Dry Valley, Southwest China". Forests 11, nr 11 (28.10.2020): 1140. http://dx.doi.org/10.3390/f11111140.
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Identifying the ecological processes determining spatial variation in community composition and structure is a central issue in arid areas, especially in the face of climate change. This study aims to estimate how environmental and spatial processes jointly determine vegetation attributes across scales in the Min dry valley, one of the dry valleys in Hengduan Mountainous region suffering severe ecological degradation. A total of 48 plots along slope transects were investigated at three sites along the dry valley, with vegetation and environmental information gathered. Distance-based Moran’s eigenvector maps (dbMEM) was used to extract local spatial variables, while geographic coordinates were used as regional spatial variables. We used redundancy analysis (RDA) and variation partitioning to detect the relative importance of environmental and spatial processes in influencing community composition and vegetation structure (including biomass, coverage, height, density, α and β diversity), and to identify the most determinant environmental variables at different spatial scales. Results showed that both environmental and spatial processes accounted for significant and comparable variations in both vegetation composition and structure. Local spatial variables provided significant and comparable contribution as regional spatial variables to vegetation composition, while provided more contribution than regional spatial variables to vegetation structure. Topography had an overriding effect relative to soil on both vegetation composition and structure. Multi-scale analyses showed elevation was the most important variable (associated with soil moisture and nutrient) at the regional scale; while microtopography, especially slope aspect and shape, dominated at the local scale. We also demonstrated how vegetation composition and structure varied along environmental gradients. The study revealed the overriding role of topography in determining vegetation attributes in this mountainous dry valley, highlighting the advantage of multi-scale spatial analysis for better understanding spatial variation in vegetation pattern and with their important implications for biodiversity conservation and ecological management in the arid mountain areas.
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MONTAÑO-ARIAS, GENARO, ISOLDA LUNA-VEGA, JUAN J. MORRONE i DAVID ESPINOSA. "Biogeographical identity of the Mesoamerican dominion with emphasis on seasonally dry tropical forests". Phytotaxa 376, nr 6 (22.11.2018): 277. http://dx.doi.org/10.11646/phytotaxa.376.6.3.
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Several studies on the geographical limits and regionalization of the Neotropics have recognized this region as a biogeographical unit. Recent regionalization proposals recognize the existence of a Mesoamerican dominion within the Neotropics, extending from the northern portion of the Mexican Pacific coast into the lowlands of south-central Mexico and most of northern Central America (Guatemala, Belize, Honduras, El Salvador and Nicaragua). In this study, we assessed the biogeographical identity of the Mesoamerican dominion through the analysis of the geographical patterns of diversity of 356 species included in 28 genera and 16 families of plants, with a preferential distribution in the seasonally dry tropical forests of Mexico and Central America. Occurrence data were obtained from online databases (e.g., GBIF, SNIB, MEXU and TROPICOS) and refined using taxonomic and geographical information. We used the Biodiverse 2.0 program to obtain maps of species richness, centres of endemism and conducted analyses of similarity among areas. The analyses led to corroborate the geographical limits of the Mesoamerican dominion. With respect to the species with distributions that extend to America arid, the Brazilian sub-region and Florida and the Greater Antilles. From these analyses, we could identify for the Mesoamerican dominion two highly diverse areas in southern Mexico: the Balsas Basin (more than 60 species) and the Central Valleys of Oaxaca (28). We also identified seven areas of higher dissimilarity corresponding to river basins throughout the study area: Grande de Santiago, Armería-Coahuayana, Tepalcatepec (western Balsas), Eastern Balsas, Papagayo, Verde, higth Papaloapan (Tehuacán-Cuicatlán Valley) and Tehuantepec. The high values of dissimilarity in the Pacific watershed of southern Mexico are responsible for the high species turnover observed for the seasonally dry tropical forests in the Mesoamerican dominion.
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Gardner, Christopher B., i W. Berry Lyons. "Modelled composition of cryogenically produced subglacial brines, Antarctica". Antarctic Science 31, nr 3 (29.03.2019): 165–66. http://dx.doi.org/10.1017/s095410201900004x.
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Polar subglacial hydrologic systems have garnered much interest since the recognition of Lake Vostok in 1996. In Antarctica, these environments are hydrologically diverse, including isolated lakes of different sizes, river–lake flow-through systems, “swamps” and groundwater (Siegert 2016). The refreezing of subglacial meltwater is also an important process beneath a large portion of the East Antarctic Ice Sheet (Bell et al. 2011). As subglacial water refreezes it exsolves salts, potentially leaving behind saline and hypersaline brines. Brines thought to derive from this cryoconcentration process have been observed in the northern polar permafrost regions and in the McMurdo Dry Valleys (MDVs) region of Antarctica. Additionally, sediments in the Victoria Land Basin have diagenetic signatures produced by brine movement dating from 3–11 m.y.a, suggesting hypersaline brines have existed in the McMurdo region since at least this time (Staudigel et al. 2018).
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Vandenberghe, J. "Paleoenvironment and Stratigraphy during the Last Glacial in the Belgian-Dutch Border Region". Quaternary Research 24, nr 1 (lipiec 1985): 23–38. http://dx.doi.org/10.1016/0033-5894(85)90081-x.
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The Weichselian deposits of the flat Dutch-Belgian coversand area are characterized by highly varying facies types. The geomorphological location and the role of water during the deposition and the transportation of the original eolian sediments may fully explain the texture and sedimentary structures of the lithostratigraphic units. Directly deposited eolian loams and sands on the dry interfluves contrast with the same, but reworked, sediments in wet valleys and depressions. The formation of periglacial phenomena is also dependent on the geomorphologic, lithologic, and hydrologic conditions. The occurrence of peaty beds is restricted to wet environments without precise climatic significance. The Pleniglacial sequence is subdivided into early and late Pleniglacial stades, both characterized by (partial) permafrost conditions, interrupted by a middle Pleniglacial interstadial complex with clearly milder conditions.
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Howkins, Adrian, Stephen Chignell i Andrew Fountain. "Vanda Station, Antarctica: a biography of the Anthropocene". Journal of the British Academy 9s6 (2021): 61–89. http://dx.doi.org/10.5871/jba/009s6.061.
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This article uses the history of New Zealand�s Vanda Station in Antarctica as a case study of the inseparability of human history and environmental change in the age of the Anthropocene. Vanda Station was built in the late 1960s to promote New Zealand�s sovereignty claims to Antarctica and to promote scientific research in the predominantly ice-free McMurdo Dry Valleys region. Over the course of the 1970s and 1980s, the levels of the nearby Lake Vanda rose dramatically, and in the early 1990s the decision was taken to close the station. Rather than seeing the closure of Vanda simply as a consequence of the rising lake levels, this article suggests instead that it was the result of a number of interconnected social, political, scientific, and environmental factors. Although the concept of the Anthropocene is not unproblematic, a biographical approach to the history of Vanda Station can add depth and nuance to our understanding of the geological age of humans. In the McMurdo Dry Valleys, the �birth�, �life� and �death� of Vanda Station helps to demonstrate how the political status quo maintained itself through a partial adaptation to the new realities of the Anthropocene. This political adaptation, however, relies on maintaining human-nature dichotomies and resisting the full implications of viewing the region as an eco-social system.
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Vanham, D., E. Fleischhacker i W. Rauch. "Impact of an extreme dry and hot summer on water supply security in an alpine region". Water Science and Technology 59, nr 3 (1.02.2009): 469–77. http://dx.doi.org/10.2166/wst.2009.887.
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Climate change will induce an increasing drought risk in western and southern Europe and a resulting increase in water stress. This paper investigates the impact of both the extreme hot and dry summer of 2003 and the PRUDENCE CHRM climate change scenario summer for 2071–2100 on the monthly water balance (available water resources versus water demand) within the Kitzbueheler Region in the Austrian Alps. As a baseline period the climate normal period from 1961 to 1990 was chosen. In both summer scenarios total flow and ground water recharge decrease substantially, due to the decrease in precipitation and increase in evapotranspiration However, regional water availability is still sufficient to serve all water demand stakeholders. As a result of decreased snow cover duration, flow seasonality changes within the CHRM scenario. Especially springs are very vulnerable to these climatological conditions; average local groundwater recharge is reduced by 20% up to 70% within both scenarios. Due to the hydrogeological characteristics of the case study area and the typical small structured alpine water supply infrastructure, local deficits can occur. But also groundwater aquifers in the valleys show a decrease in water availability. These results are supported by observations made in 2003 throughout Austria and Switzerland.
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Wyłupek, Teresa Grażyna, Marta Ziemińska-Smyk i Zbigniew Czarnecki. "Floristic diversity and agricultural value of Phalaridetum arundinaceae (Koch 1926 n.n.) Lib. 1931 in the selected river valleys of the Zamość region". Acta Agrobotanica 32, nr 2 (2015): 109–13. http://dx.doi.org/10.5586/aa.2015.017.
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<p>The study presents the results of a floristic survey conducted using the Braun-Blanquet method (50 phytosociological relevés) in permanent grasslands in three river valleys of the Zamość region (Por, Huczwa, Wieprz). The goal of the survey was to determine the floristic diversity and fodder value of the <em>Phalaridetum arundinaceae</em> association (Koch 1926 n.n.) Lib. 1931. </p><p>A total of 93 plant species from 25 botanical families were identified in the areas under study. The species richness of the <em>Phalaridetum arundinaceae</em> differed among river valleys. It was observed that these are often transitional forms similar to the association of the <em>Molinio-Arrhenatheretea</em> class, <em>Molinietalia</em> order. Predominance of hemicryptophytes and a relatively large share of geophytes was recorded. Based on the fodder value score calculated for the dry matter of the association, the community under study can be classified as having a medium or poor nutritional value.</p>
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PRADO, D. E. "SEASONALLY DRY FORESTS OF TROPICAL SOUTH AMERICA: FROM FORGOTTEN ECOSYSTEMS TO A NEW PHYTOGEOGRAPHIC UNIT". Edinburgh Journal of Botany 57, nr 3 (listopad 2000): 437–61. http://dx.doi.org/10.1017/s096042860000041x.
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The Pleistocenic Arc, which must have originated from the climatic shifts in South America during the late Pleistocene, ranges from the Caatingas of north-eastern Brazil through south-eastern Brazil to the Paraguay and Paraná rivers confluence, into south-western Bolivia and north-western Argentina, and extends sporadically into dry Andean valleys of Peru or coastal western Ecuador. It is regarded as a new phytogeographic unit for South America, here named the Tropical Seasonal Forests Region, as it is characterized by a considerable number of endemic plant taxa at both generic and species level. The paradigm of the arc is the distribution pattern of Anadenanthera colubrina (Fabaceae), which, when superimposed on those of other woody species of seasonal forests, permits a reasonably accurate mapping of the new region, which might also have biogeographic implications for endemic bird taxa. The plant communities of this newly recognized unit are unique in their nature and floristic composition, when compared with other floristic areas of the continent by means of classic phytosociological and numerical analyses (PCA). These ecosystems have remained submerged within other vegetation units in South American phytogeography (such as the Chaquenian or Amazonian regions), and have been particularly neglected in conservation policies. An urgent call is made for these areas to be preserved before they disappear, because they are located in areas with some of the best agricultural soils of tropical South America, and therefore subject to clearing for farming.
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Foley, Neil, Slawek M. Tulaczyk, Denys Grombacher, Peter T. Doran, Jill Mikucki, Krista F. Myers, Nikolaj Foged, Hilary Dugan, Esben Auken i Ross Virginia. "Evidence for Pathways of Concentrated Submarine Groundwater Discharge in East Antarctica from Helicopter-Borne Electrical Resistivity Measurements". Hydrology 6, nr 2 (20.06.2019): 54. http://dx.doi.org/10.3390/hydrology6020054.
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The Southern Ocean receives limited liquid surface water input from the Antarctic continent. It has been speculated, however, that significant liquid water may flow from beneath the Antarctic Ice Sheet, and that this subglacial flow carries that water along with dissolved nutrients to the coast. The delivery of solutes, particularly limiting nutrients like bioavailable iron, to the Southern Ocean may contribute to ecosystem processes including primary productivity. Using a helicopter-borne time domain electromagnetic survey along the coastal margins of the McMurdo Dry Valleys region of Southern Victoria Land, Antarctica, we detected subsurface connections between inland lakes, aquifers, and subglacial waters. These waters, which appear as electrically conductive anomalies, are saline and may contain high concentrations of biologically important ions, including iron and silica. Local hydraulic gradients may drive these waters to the coast, where we postulate they emerge as submarine groundwater discharge. This high latitude groundwater system, imaged regionally in the McMurdo Dry Valleys, may be representative of a broader system of Antarctic submarine groundwater discharge that fertilizes the Southern Ocean. In total, it has the potential to deliver tens of gigagrams of bioavailable Fe and Si to the coastal zone.
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Chwala, C., A. Gmeiner, W. Qiu, S. Hipp, D. Nienaber, U. Siart, T. Eibert i in. "Precipitation observation using microwave backhaul links in the alpine and pre-alpine region of Southern Germany". Hydrology and Earth System Sciences 16, nr 8 (13.08.2012): 2647–61. http://dx.doi.org/10.5194/hess-16-2647-2012.
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Abstract. Measuring rain rates over complex terrain is afflicted with large uncertainties, because rain gauges are influenced by orography and weather radars are mostly not able to look into mountain valleys. We apply a new method to estimate near surface rain rates exploiting attenuation data from commercial microwave links in the alpine region of Southern Germany. Received signal level (RSL) data are recorded minutely with small data loggers at the towers and then sent to a database server via GSM (Global System for Mobile Communications). Due to the large RSL fluctuations in periods without rain, the determination of attenuation caused by precipitation is not straightforward. To be able to continuously process the RSL data from July 2010 to October 2010, we introduce a new method to detect wet and dry periods using spectral time series analysis. Its performance and limitations are presented, showing that the mean detection error rates of wet and dry periods can be reduced to 10% for all five links. After, the wet/dry classification rain rates are derived from the RSL and compared to rain gauge and weather radar measurements. The resulting correlations differ for different links and reach values of R2 = 0.81 for the link-gauge comparison and R2 = 0.85 for the link-radar comparison.
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Arenz, B. E., i R. A. Blanchette. "Distribution and abundance of soil fungi in Antarctica at sites on the Peninsula, Ross Sea Region and McMurdo Dry Valleys". Soil Biology and Biochemistry 43, nr 2 (luty 2011): 308–15. http://dx.doi.org/10.1016/j.soilbio.2010.10.016.
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Wang, Yanjun, Lei Wang, Xu Liu, Yashan Li, Xueqiu Wang i Yulin Fang. "Climatic regionalization of wine grapes in the Hengduan Mountain region of China". Spanish Journal of Agricultural Research 16, nr 2 (11.07.2018): e0303. http://dx.doi.org/10.5424/sjar/2018162-12457.
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The Hengduan Mountain region of China is one of the world's highest altitude and lowest latitude wine grape cultivation areas. This study screened the existing regional indexes; the active accumulated temperature (AAT) for grapes in the growing season was chosen as the heat index, and the dryness index (DI) in the growing season was chosen as the water index for climatic regionalization. An analysis of 90-meter resolution digital elevation model (DEM) data and the corresponding slope degree and direction for the Hengduan Mountain region in the range of 97°E-103°E, 27°N-33°N, as well as daily meteorological data over 30 years (1981-2010) from 53 stations in the study region, were used to establish the AAT and DI models for the northern area of the Hengduan Mountains. According to the multiple stepwise regression method, the interaction terms among different geographical and topographic factors were considered. In addition, the residual errors were interpolated and corrected based on the modeling, and this approach further improved the simulation accuracy of meteorological factors. A regional climatic map of wine grapes was produced according to these results. The model was used to calculate the suitable altitude range for wine grape cultivation in different regions of the Hengduan Mountains. The study shows that the distribution of suitable wine grape cultivation areas in the northern part of the mountain range generally mimics distribution of dry warm and dry hot valleys. The accuracy of the results was confirmed based on the existing locations of vineyards in the Hengduan Mountain region.
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Whitlock, Cathy, i Rosemary Sherriff. "A 14,000-Yr Fire History From the Mixed Conifer Forest of Southern Yellowstone National Park". UW National Parks Service Research Station Annual Reports 20 (1.01.1996): 123–31. http://dx.doi.org/10.13001/uwnpsrc.1996.3305.
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The Yellowstone region has been divided into geovegetation regions based on characteristics of the vegetation, climate, and geology (Despain, 1990). The Northern Range or Yellowstone-Lamar valleys features open Douglas-fir parkland, summerÂwet conditions, and substrates composed of glacial debris and sedimentary and granitic material. The Central Plateau is an area of lodgepole forest, relatively dry summers, and infertile rhyolite soils. The Absaroka region consists of mixed conifer forest, relatively dry summers, and andesitic and sedimentary rock types. The environmental history of the geovegetation regions, as revealed from a network of pollen and charcoal records, has been equally distinctive (Whitlock, 1993; Whitlock and Bartlein, 1993; Whitlock et al., 1994, 1995). The Northern Range experienced wetter-than-present summers in the early Holocene between 10 and 7 ka (ka = 1000 14C years before present) as a result of intensified monsoonal circulation. The development of Douglas-fir parkland there has occurred with drying in the late Holocene. The paleoecologic record shows few fires in the early Holocene and increased burning in the last 7000 years as the climate became drier (Millspaugh, in prep.). In the Central Plateau, areas of rhyolite supported lodgepole-pine forest for the last 10,000 years with little change. Charcoal data from this region indicate that fires were most frequent in the early Holocene between 10 and 7 ka, when southern and central Yellowstone National Park (YNP) and Grand Teton National Park (GTNP) were warmer and drier than at present. Fire frequency has decreased in the last few millennia with the onset of present-day cool conditions (Millspaugh, in prep.; Whitlock and Millspaugh, in press). Despite these changes in Holocene climate and fire regime the vegetation of the Central Plateau remained a lodgepole pine forest, presumably because of the infertile soils.
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Bishop, Janice L., Brandy L. Anglen, Lisa M. Pratt, Howell G. M. Edwards, David J. Des Marais i Peter T. Doran. "A spectroscopy and isotope study of sediments from the Antarctic Dry Valleys as analogues for potential paleolakes on Mars". International Journal of Astrobiology 2, nr 4 (październik 2003): 273–87. http://dx.doi.org/10.1017/s1473550403001654.
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A spectroscopy and isotope study has been performed on igneous sediments from Lake Hoare, a nearly isolated ecosystem in the Dry Valleys region of Antarctica. The mineralogy and chemistry of these sediments were studied in order to gain insights into the biogeochemical processes occurring in a permanently ice-covered lake and to assist in characterizing potential habitats for life in paleolakes on Mars. Obtaining visible/near-infrared, mid-infrared and Raman spectra of such sediments provides the ground truth needed for using reflectance, emittance and Raman spectroscopy for exploration of geology, and perhaps biology, on Mars. Samples measured in this study include a sediment from the ice surface, lake bottom sediment cores from oxic and anoxic zones of the lake and the magnetic fractions of two samples.These sediments are dominated by quartz, pyroxene, plagioclase and K-feldspar, but also contain calcite, organics, clays, sulphides and iron oxides/hydroxides that resulted from chemical and biological alteration processes. Chlorophyll-like bands are observed in the spectra of the sediment-mat layers on the surface of the lake bottom, especially in the deep anoxic region. Layers of high calcite concentration in the oxic sediments and layers of high pyrite concentration in the anoxic sediments are indicators of periods of active biogeochemical processing in the lake. Micro-Raman spectra revealed the presence of ~5 μm-sized pyrite deposits on the surface of quartz grains in the anoxic sediments. C, N and S isotope trends are compared with the chemistry and spectral properties. The δ13C and δ15N trends highlight the differences in the balance of microbial processes in the anoxic sediments versus the oxic sediments. The biogenic pyrite found in the sediments from the anoxic zone is associated with depleted δ34S values, high organic C levels and chlorophyll spectral bands and could be used as a potential biomarker mineral for paleolakes on Mars.
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Summerfield, M. A., D. E. Sugden, G. H. Denton, D. R. Marchant, H. A. P. Cockburn i F. M. Stuart. "Cosmogenic isotope data support previous evidence of extremely low rates of denudation in the Dry Valleys region, southern Victoria Land, Antarctica". Geological Society, London, Special Publications 162, nr 1 (1999): 255–67. http://dx.doi.org/10.1144/gsl.sp.1999.162.01.20.
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McKay, Christopher P., Edward Balaban, Simon Abrahams i Nick Lewis. "Dry permafrost over ice-cemented ground at Elephant Head, Ellsworth Land, Antarctica". Antarctic Science 31, nr 05 (30.07.2019): 263–70. http://dx.doi.org/10.1017/s0954102019000269.
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AbstractDry permafrost - ground with temperature always below 0°C and containing negligible ice - overlying ice-cemented ground has been reported in the Dry Valleys of Antarctica and on Mars. Here we report on a new site (79°49.213'S, 83°18.860'W, 718 m elevation) located on the side of Mount Dolence in Ellsworth Land, Antarctica. Year-round temperature and humidity measurements indicate that dry permafrost is present between depths of 13.5 and 49.0 cm - the location of ice-cemented ground. The mean annual frost point of the ice-cemented ground is -17.0 ± 0.2°C and the mean annual frost point of the atmosphere is -22.7 ± 1°C. The corresponding mean annual temperatures are -19.2°C and -20.3°C. Neither the temperature of the ice-cemented ground nor the air rise above freezing. Both the dry permafrost and the ice table may be habitable. In the dry soil at 3 cm depth there are 80 hours in the summer when temperature exceeds -5°C and water activity exceeds 0.8. At the ice table, temperature exceeds -10°C and water activity exceeds 0.8 for 35 hours in the year. The ice table and the dry permafrost above it would be considered a ‘Special Region’ on Mars. Further microbial investigation of this site is indicated.
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WINANT, GABRIEL. "“Green Pastures of Plenty from Dry Desert Ground”: Nature, Labor, and the Growth and Structure of a California Grape Company". Enterprise & Society 16, nr 1 (16.01.2015): 109–40. http://dx.doi.org/10.1017/eso.2014.13.
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This article examines the growth and change of a southern California table grape firm, the George F. Johnston Company. Combining business, labor, and environmental history, it traces the company’s expansion from a semi-arid region just east of Los Angeles to the fully arid deserts of the Coachella and Imperial Valleys of California. The Johnston Company moved south and east into this more hostile environment to produce grapes out of the traditional season, beating the competition to market. In the process, it produced a racially stratified workforce and contributed to an ecological catastrophe. The Johnston case suggests that agricultural production pits capitalists in a triangular struggle over the moment of the harvest with nature and labor. This struggle is intensified by competitive dynamics that drive firms to expand or shift the timing of the productive process.
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Dugan, H. A., P. T. Doran, B. Wagner, F. Kenig, C. H. Fritsen, S. Arcone, E. Kuhn, N. E. Ostrom, J. Warnock i A. E. Murray. "27 m of lake ice on an Antarctic lake reveals past hydrologic variability". Cryosphere Discussions 8, nr 4 (23.07.2014): 4127–58. http://dx.doi.org/10.5194/tcd-8-4127-2014.
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Abstract. Lake Vida, located in Victoria Valley, is one of the largest lakes in the McMurdo Dry Valleys. Unlike other lakes in the region, the surface ice extends at least 27 m, which has created an extreme and unique habitat by isolating a liquid-brine with salinity of 195 g L−1. Below 21 m, the ice is marked by well-sorted sand layers up to 20 cm thick, within a matrix of salty ice. From ice chemistry, isotopic abundances of 18O and 2H, ground penetrating radar profiles, and mineralogy, we conclude that the entire 27 m of ice formed from surface runoff, and the sediment layers represent the accumulation of fluvial and aeolian deposits. Radiocarbon and optically stimulated luminescence dating limit the maximum age of the lower ice to 6300 14C yr BP. As the ice cover ablated downwards during periods of low surface inflow, progressive accumulation of sediment layers insulated and preserved the ice and brine beneath; analogous to the processes that preserve shallow ground ice. The repetition of these sediment layers reveals climatic variability in Victoria Valley during the mid- to late Holocene. Lake Vida is an excellent Mars analog for understanding the preservation of subsurface brine, ice and sediment in a cold desert environment.