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Airborne electromagnetic surveys collected in December 2011 and November 2018 and three soil sampling transects were used to analyze the spatial heterogeneity of shallow (<4 m) soil properties in lower Taylor Valley (TV), East Antarctica. Soil resistivities from 2011 to 2018 ranged from ∼33 Ωm to ∼3,500 Ωm with 200 Ωm assigned as an upper boundary for brine‐saturated sediments. Elevations below ∼50 m above sea level (masl) typically exhibit the lowest resistivities with resistivity increasing at high elevations on steeper slopes. Soil water content was empirically estimated from electrical resistivities using Archie's Law and range from ∼<1% to ∼68% by volume. An increase in silt‐ and clay‐sized particles at low elevations increases soil porosity but decreases hydraulic conductivity, promoting greater residence times of soil water at low elevations near Lake Fryxell. Soil resistivity variability between 2011 and 2018 shows soils at different stages of soil freeze‐thaw cycles, which are caused predominantly by solar warming of soils as opposed to air temperature. This study furthers the understanding of the hydrogeologic structure of the shallow subsurface in TV and identifies locations of soils that are potentially prone to greater rates of thaw and resulting ecosystem homogenization of soil properties from projected increases in hydrological connectivity across the region over the coming decades. Plain Language Summary: Liquid water is vital to all life on Earth; however, it is only available to life on land in Taylor Valley (TV), East Antarctica, during the brief Antarctic summer due to extremely cold and dry climate conditions. Water is released November‐February each year, providing nutrients to microbial and algal communities in the region. We used specialized instruments to locate liquid water in the subsurface and map soil water distributions to describe soil properties within TV in December 2011 and November 2018. Soil samples were collected to analyze how soil properties varied at different elevations and to determine how this variance affected soil water levels at different locations. Weather data were examined to study how climate variables affect soil water levels, and satellite imagery was used to examine snow conditions on the surface. We find that 2011 soils were typically wetter than 2018 soils, likely due to warmer climate conditions in 2011. Additionally, we found that low elevation soils were typically composed of finer‐grained sediments, which keep soil water in place for longer time periods. This research identifies areas more prone to thawing within the TV, which is important for understanding how soil organisms will be affected in a warming world. Key Points: McMurdo Dry Valleys soil properties are characterized using resistivity data from two airborne electromagnetic surveys from 2011 to 2018Soil water content in the shallow subsurface largely controls resistivity variabilityHigher percentages of silt‐ and clay‐sized particles at low elevations promote greater residence times of soil water [ABSTRACT FROM AUTHOR]

Environments where geothermal waters and glacier meltwater mix are common on Earth yet little is known about the biogeochemical processes that occur when hot, reduced geothermal water mixes with cold, oxidized glacial meltwater in natural systems. Mount St. Helens provides an ideal location to study the interaction between geothermal and glacier waters since the water sources, and their mixing environment in Step Creek, are exposed in the volcanic crater. We find that the two water sources contain distinct major ion, trace element, dissolved organic matter (DOM), and biological signatures. The hot spring contains high concentrations of biogeochemically reactive components (e.g., siderophile and chalcophile trace elements and DOM) compared to the glacier discharge but a large fraction of these solutes do not remain in solution after the waters mix. In contrast, glacier discharge contains fewer solutes but most of these solutes remain in solution after the waters mix. The mixing of glacier and hot spring water in Step Creek supports seston and benthic ecosystems that have higher phototrophic and microbial biomass than those in the source waters, suggesting that the mixing environment in this high‐gradient stream provide a more comprehensive suite of soluble and essential nutrients that promote primary production and DOM cycling. Plain Language Summary: Most of the waters that drain from the crater of Mount St. Helens originate from hot spring seeps or the glacier within the crater. We found these two water sources have distinct chemical fingerprints. When the two water types mix in Step Creek, many of the chemical species from the hot spring either precipitate out of solution or are consumed by the aquatic ecosystem, while most of the chemical species from the glacier flow downstream. The chemical energy and the combination of essential nutrients supplied by the two water sources appear to stimulate a more productive downstream aquatic ecosystem. Key Points: Glacier and hot spring discharges contained distinct major ion, trace element, dissolved organic matter, and biological signaturesMany of the chemical species from the glacier remained in solution after the waters mixed but many of those from the hot spring did notMixed waters supported seston and benthic ecosystems that had higher phototrophic and microbial biomass than either of the water sources [ABSTRACT FROM AUTHOR]

Lake Bonney (McMurdo Dry Valleys, east Antarctica) represents a year‐round refugium for life adapted to permanent extreme conditions. Despite intensive research since the 1960s, due to the logistical constraints posed by 4‐months of 24‐h darkness, knowledge of how the resident photosynthetic microorganisms respond to the polar winter is limited. In addition, the lake level has risen by more than 3 m since 2004: impacts of rapid lake level rise on phytoplankton community structure is also poorly understood. From 2004 to 2015 an in situ submersible spectrofluorometer (bbe FluoroProbe) was deployed in Lake Bonney during the austral summer to quantify the vertical structure of four functional algal groups (green algae, mixed algae, and cryptophytes, cyanobacteria). During the 2013–2014 field season the Fluoroprobe was mounted on autonomous cable‐crawling profilers deployed in both the east and west lobes of Lake Bonney, obtaining the first daily phytoplankton profiles through the polar night. Our findings showed that phytoplankton communities were differentially impacted by physical and chemical factors over long‐term versus seasonal time scales. Following a summer of rapid lake level rise (2010–2011), an increase in depth integrated chlorophyll a (chl‐a) occurred in Lake Bonney caused by stimulation of photoautotrophic green algae. Conversely, peaks in chl‐a during the polar night were associated with an increase in mixotrophic haptophytes and cryptophytes. Collectively our data reveal that phytoplankton groups possessing variable trophic abilities are differentially competitive during seasonal and long‐term time scales owing to periods of higher nutrients (photoautotrophs) versus light/energy limitation (mixotrophs). Key Points: A profiling fluorometer collected the first over‐winter daily phytoplankton profilesPhytoplankton communities were differentially impacted by physical and chemical factors over long‐term versus seasonal time scalesPhyoplankton groups are differentially competitive due to periods of higher nutrients versus light/energy limitation [ABSTRACT FROM AUTHOR]

The weather of the McMurdo Dry Valleys, Antarctica, the largest ice‐free region of the Antarctica, has been continuously monitored since 1985 with currently 14 operational meteorological stations distributed throughout the valleys. Because climate is based on a 30‐year record of weather, this is the first study to truly define the contemporary climate of the McMurdo Dry Valleys. Mean air temperature and solar radiation based on all stations were −20°C and 102 W m−2, respectively. Depending on the site location, the mean annual air temperatures on the valleys floors ranged between −15°C and −30°C, and mean annual solar radiation varied between 72 and 122 W m−2. Surface air temperature decreased by 0.7°C per decade from 1986 to 2006 at Lake Hoare station (longest continuous record), after which the record is highly variable with no trend. All stations with sufficiently long records showed similar trend shifts in 2005 ±1 year. Summer is defined as November through February, using a physically based process: up‐valley warming from the coast associated with a change in atmospheric stability. Key Points: Thirty years of meteorological observations between 1986 and 2017 from McMurdo Dry Valleys, Antarctica, are summarizedSurface air temperatures decreased from 1986 to 2005 ±1Summer season is redefined using physically based processes and is applicable to other ice‐free regions around Antarctica [ABSTRACT FROM AUTHOR]

Although perennially ice‐covered Antarctic lakes have experienced variable ice thicknesses over the past several decades, future ice thickness trends and associated aquatic biological responses under projected global warming remain unknown. Heat stored in the water column in chemically stratified Antarctic lakes that have middepth temperature maxima can significantly influence the ice thickness trends via upward heat flux to the ice/water interface. We modeled the ice thickness of the west lobe of Lake Bonney, Antarctica, based on possible future climate scenarios utilizing a 1D thermodynamic model that accounts for surface radiative fluxes as well as the heat flux associated with the temperature evolution of the water column. Model results predict that the ice cover of Lake Bonney will shift from perennial to seasonal within one to four decades, a change that will drastically influence ecosystem processes within the lake. Key Point: Future loss of permanent ice cover is predicted [ABSTRACT FROM AUTHOR]

A discrete warming event (December 21, 2001–January 12, 2002) in the McMurdo Dry Valleys, Antarctica, enhanced glacier melt, stream flow, and melting of permafrost. Effects of this warming included a rapid rise in lake levels and widespread increases in soil water availability resulting from melting of subsurface ice. These increases in liquid water offset hydrologic responses to a cooling trend experienced over the previous decade and altered ecosystem properties in both aquatic and terrestrial ecosystems. Here, we present hydrological and meteorological data from the McMurdo Dry Valleys Long Term Ecological Research project to examine the influence of a discrete climate event (warming of >2 °C) on terrestrial environments and soil biotic communities. Increases in soil moisture following this event stimulated populations of a subordinate soil invertebrate species ( Eudorylaimus antarcticus, Nematoda). The pulse of melt-water had significant influences on Taylor Valley ecosystems that persisted for several years, and illustrates that the importance of discrete climate events, long recognized in hot deserts, are also significant drivers of soil and aquatic ecosystems in polar deserts. Thus, predictions of Antarctic ecosystem responses to climate change which focus on linear temperature trends may miss the potentially significant influence of infrequent climate events on hydrology and linked ecological processes. [ABSTRACT FROM AUTHOR]