The thermal structure of the anoxic trough in Lake Untersee, Antarctica

Bevington, James; McKay, Christopher P.; Dávila, Alfonso F.; Hawes, Ian; Tanabe, Yukiko; Andersen, Dale T.

doi:10.1017/s0954102018000354

Cited by 4 publications

(5 citation statements)

References 32 publications

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“…However, in the southern basin, the water below the sill (60–100 m) is stratified, with temperatures ranging between 3°C and 5°C, lower pH ( c. 7), higher specific conductivity (1100–1300 μS cm −1 ) and dissolved oxygen levels near 0%. This anoxic water does not mix with the overlying oxic water due to its higher density (Bevington et al 2018). The floor of the oxic sub-basin in Lake Untersee is covered by photosynthetic microbial mats, with the transparency of the lake ice to photosynthetically active radiation (PAR) being 4.9 ± 0.9% (Andersen et al 2011).…”

Section: Study Areamentioning

confidence: 99%

“…It has been suggested that Lake Untersee is recharged from melting of the Anuchin Glacier (Hermichen et al 1985, Wand et al 1997). Thus far, studies of Untersee have focused primarily on physical and chemical limnology (Hermichen et al 1985, Wand et al 1997, 2006, Steel et al 2015, Bevington et al 2018) and microbial ecology (Wand et al 2006, Andersen et al 2011, Koo et al 2017). Detailed studies have yet to investigate the thermodynamics of the ice cover and the hydrological balance of the lake.…”

Section: Introductionmentioning

confidence: 99%

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Energy and water mass balance of Lake Untersee and its perennial ice cover, East Antarctica

et al. 2019

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Lake Untersee is one of the largest perennially ice-covered lakes in Dronning Maud Land. We investigated the energy and water mass balance of Lake Untersee to understand its state of equilibrium. The thickness of the ice cover is strongly correlated with sublimation rates; variations in sublimation rates across the ice cover are largely determined by wind-driven turbulent heat fluxes and the number of snow-covered days. Lake extent and water level have remained stable for the past 20 years, indicating that the water mass balance is in equilibrium. The lake is damned by the Anuchin Glacier and mass balance calculation suggest that subaqueous melting of terminus ice contributes 40–45% of the annual water budget; since there is no evidence of streams flowing into the lake, the lake must be connected to a groundwater system that contributes 55–60% in order to maintain the lake budget in balance. The groundwater likely flows at a rate of ~8.8 × 10−2 m3 s−1, a reasonable estimate given the range of subglacial water flux in the region. The fate of its well-sealed ice cover is likely tied to changes in wind regime, whereas changes in water budget are more closely linked to the response of surrounding glaciers to climate change.

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Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energy and water mass balance of Lake Untersee and its perennial ice cover, East Antarctica

et al. 2019

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“…Lake Untersee is damned by a glacier so cooling of the water near the glacial wall induces a buoyancy-driven circulation that mixes the lake where the glacier reaches (Steel et al, 2015;Faucher et al, 2019). However, part of the lake is shielded from these currents and remains stratified (Bevington et al, 2018). It is worthwhile to reconsider the nature of the lake deposits observed in Gale crater in the context of an ice-covered lake.…”

Section: Proposed Geological Context and Implications For The Carbonamentioning

confidence: 99%

Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Kling

Haberle

McKay

et al. 2020

Icarus

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Sedimentary deposits characterized by the Mars Science Laboratory Curiosity rover provide evidence that Gale crater, Mars intermittently hosted a fluvio-lacustrine environment during the Hesperian. However, estimates of the CO 2 content of the atmosphere at the time the sediments in Gale crater were deposited are far less than needed by any climate model to maintain temperatures warm enough for sustained open water lake conditions due to the low solar energy input available at that time. To reconcile some of the in-situ sedimentological evidence for liquid water with climate modeling studies, we perform the water budget of evaporation against precipitation to estimate the minimum lifetimes and the rainfall requirements for open water and ice-covered lakes in Gale crater, for a wide range of pressures and temperatures. We found that both open water and ice-covered lakes are possible, and that ice-covered lakes provide better consistency in regards of the low erosion rates estimates for the Hesperian. We incrementally test the existence of open water conditions using energy balance calculations for the global, regional, and seasonal temperatures, and we assess if the preservation of liquid water was possible under perennial ice covers. We found scenarios where lacustrine conditions are preserved in a cold climate, where the resupply of water by the inflow of rivers and high precipitation rates are substituted by an abutting glacier. For equatorial temperatures as low as 240K-255K, the ice thickness ranges from 3-10 m, a value comparable to the range of those for the perennially ice-covered lakes in Antarctica (3-6 m). The ice-covered lake hypothesis is a compelling way to decouple the mineralogy and the climate by limiting the gas exchanges between the sediment and the CO 2 atmosphere, and it eliminates the requirement for global mean temperatures above the freezing point. Not only do ice-covered lakes provide a baseline for exploring the range of possible lake scenarios for Gale crater during the Hesperian that is fully consistent with climate studies, but also they might have been ideal environments to sustain life on Mars.

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“…Lake Untersee has two sub-basins; the largest, 160 m deep, lies adjacent to the Anuchin Glacier and is separated by a sill at 50 m depth from a smaller, 100 m deep basin to the south. The northern deep basin is well-mixed due to buoyancy-driven convection caused by melting of the ice-wall at the glacier-lake interface 11 , 23 ; however, the smaller southern basin is chemically stratified below the sill depth (c. 50 m) and its higher density prevents mixing with the overlying oxic water column 24 , 25 . Lake Untersee loses c. 1% of its water annually from the sublimation of the 2–4 m thick ice cover.…”

Section: Introductionmentioning

confidence: 99%

Sources of solutes and carbon cycling in perennially ice-covered Lake Untersee, Antarctica

Marsh

Lacelle

Faucher

et al. 2020

Sci Rep

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perennially ice-covered lakes that host benthic microbial ecosystems are present in many regions of Antarctica. Lake Untersee is an ultra-oligotrophic lake that is substantially different from any other lakes on the continent as it does not develop a seasonal moat and therefore shares similarities to sub-glacial lakes where they are sealed to the atmosphere. Here, we determine the source of major solutes and carbon to Lake Untersee, evaluate the carbon cycling and assess the metabolic functioning of microbial mats using an isotope geochemistry approach. The findings suggest that the glacial meltwater recharging the closed-basin and well-sealed Lake Untersee largely determines the major solute chemistry of the oxic water column with plagioclase and alumino-silicate weathering contributing < 5% of the Ca 2+-na + solutes to the lake. the tic concentration in the lake is very low and is sourced from melting of glacial ice and direct release of occluded co 2 gases into the water column. The comparison of δ 13 c tic of the oxic lake waters with the δ 13 c in the top microbial mat layer show no fractionation due to non-discriminating photosynthetic fixation of HCO 3 in the high pH and carbon-starved water. the 14 C results indicate that phototrophs are also fixing respired CO 2 from heterotrophic metabolism of the underlying microbial mats layers. The findings provide insights into the development of collaboration in carbon partitioning within the microbial mats to support their growth in a carbon-starved ecosystem. Numerous perennially ice-covered lakes have been inventoried in Antarctica, including in the McMurdo Dry Valleys (MDV), Bunger Hills, Vestfold Hills, Schirmacher Oasis, and Soya Coast 1,2. These lakes have varied chemistries as a result of source water and Holocene history of the lakes, but many are oligotrophic and support benthic cyanobacterial mats and heterotrophic bacterial communities 3-5. Primary productivity is often limited by light attenuation through the ice-cover and nutrient availability (e.g., C and P), however, summer moating and streams provide seasonal recharge of nutrients to the lakes 4,6. Analysis of carbon isotopes (e.g., δ 13 C, 14 C) can provide insights about the source of carbon and transformations of organic matter as photosynthesis and remineralization control the isotopic composition of most organic matter. For example, carbon isotope geochemistry of dissolved inorganic carbon (δ 13 C DIC) and organic carbon (δ 13 C DOC) have been used to trace carbon sources and cycling in the MDV lake ecosystem 3,7-9. Lake Untersee is a 169-m deep ultra-oligotrophic lake that is substantially different from other lakes in Antarctica 10,11. It is recharged by subaqueous melting of glacial ice and subglacial meltwater, and the lake remains ice-covered with no open water along the margin (summer moating) that would provide access to nutrients, CO 2 and enhanced sunlight 12-14. In the absence of large metazoans, photosynthetic microbial mats cover the floor of the lake from just below the ice cover ...

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The thermal structure of the anoxic trough in Lake Untersee, Antarctica

Cited by 4 publications

References 32 publications

Energy and water mass balance of Lake Untersee and its perennial ice cover, East Antarctica

Energy and water mass balance of Lake Untersee and its perennial ice cover, East Antarctica

Subsistence of ice-covered lakes during the Hesperian at Gale crater, Mars

Sources of solutes and carbon cycling in perennially ice-covered Lake Untersee, Antarctica

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