A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica

We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96-99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (,0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42,000 years to approach steady state beginning from a completely dry initial condition

Extreme hydrochemical conditions in natural microcosms entombed within Antarctic ice

Cryoconite holes are near-vertical tubes that form in the surface of glaciers when solar-heated debris melts into the ice. Those that form in the McMurdo Dry Valleys of Antarctica are distinctive, in that they have ice lids and are closed to the atmosphere for periods of years to decades. Photoautotrophs and heterotrophs grow within this closed environment, perturbing the poorly buffered water chemistry, yet maintaining the potential for photosynthesis. Microbial excretion and decomposition of organic matter produces dissolved organic carbon (DOC): dissolved inorganic carbon ratios of ?1 : 2. Much of the dissolved nitrogen pool (80–100%) exists as dissolved organic nitrogen (DON). The DON:DOC ratio is ?1 : 11 (mol/mol), typical of organic particulate material at the Earth’s surface. The combination of photoautotrophy, heterotrophy and weak chemical buffering within these microcosms promotes values of pH, pCO2, O2 saturation and percentage total dissolved nitrogen as DON that reach 10·99, 10?7·6 atm, 160% and 100% respectively, which are a unique combination among the surface waters on Earth. These ice-sealed cryoconite holes could be important analogues of refugia on Snowball Earth and other icy planets

Determination of Dissolved Oxygen in the Cryosphere: A Comprehensive Laboratory and Field Evaluation of Fiber Optic Sensors

Recent advances in the Cryospheric Sciences have shown that icy environments are host to consortia of microbial communities, whose function and dynamics are often controlled by the concentrations of dissolved oxygen (DO) in solution. To date, only limited spot determinations of DO have been possible in these environments. They reveal the potential for rates of change that exceed realistic manual sampling rates, highlighting the need to explore methods for the continuous measurement of DO concentrations. We report the first comprehensive field and laboratory performance tests of fiber-optic sensors (PreSens, Regensburg, Germany) for measuring DO in icy ecosystems. A series of laboratory tests performed at low and standard temperatures (-5 to 20 °C) demonstrates high precision (0.3% at 50 µmol/kg and 1.3% at 300 µmol/kg), rapid response times (<20 s), and minimal drift (<0.4%). Survival of freeze thaw was problematic, unless the sensor film was mechanically fixed to the fiber and protected by a stainless steel sheath. Results of two field deployments of sensors to the Swiss Alps and Antarctica largely demonstrate a performance consistent with laboratory tests and superior to traditional methods

Evolution of cryoconite holes and their contribution to meltwater runoff from glaciers in the McMurdo Dry Valleys, Antarctica

Cryoconite holes are water-filled holes in the surface of a glacier caused by enhanced ice melt around trapped sediment. Measurements on the ablation zones of four glaciers in Taylor Valley, Antarctica, show that cryoconite holes cover about 4-6% of the ice surface. They typically vary in diameter from 5 to 145 cm, with depths ranging from 4 to 56 cm. In some cases, huge holes form with 5 m depths and 30 m diameters. Unlike cryoconite holes elsewhere, these have ice lids up to 36 cm thick and melt from within each spring. About one-half of the holes are connected to the near-surface hydrologic system and the remainder are isolated. The duration of isolation, estimated from the chloride accumulation in hole waters, commonly shows ages of several years, with one hole of 10 years. The cryoconite holes in the McMurdo Dry Valleys create a near-surface hydrologic system tens of cm below the ice surface. The glacier surface itself is generally frozen and dry. Comparison of water levels between holes a few meters apart shows independent cycles of water storage and release. Most likely, local freeze-thaw effects control water pas