02314nas a2200265   4500008004100000245012500041210006900166260001200235490000700247520147000254653001501724653001101739653001701750653001801767653001101785653004001796100002201836700001501858700002301873700002201896700002401918700002101942700002101963856006401984       2020                        eng d00aEnergetic and environmental constraints on the community structure of benthic microbial mats in Lake Fryxell, Antarctica0 aEnergetic and environmental constraints on the community structu  c02/20200 v963 a<p>Ecological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O<sub>2</sub>). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O<sub>2</sub>). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O<sub>2</sub>) and PAR conditions: high (O<sub>2</sub>) and maximum PAR, variable (O<sub>2</sub>) with lower maximum PAR, and low (O<sub>2</sub>) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O<sub>2</sub>) was saturated, PAR structured the community. In contrast, (O<sub>2</sub>) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O<sub>2</sub>). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.</p>10aAntarctica10aenergy10aLake Fryxell10amicrobial mat10aOxygen10aPhotosynthetically Active Radiation1 aDillon, Megan, L.1 aHawes, Ian1 aJungblut, Anne, D.1 aMackey, Tyler, J.1 aEisen, Jonathan, A.1 aDoran, Peter, T.1 aSumner, Dawn, Y.  uhttps://academic.oup.com/femsec/article/96/2/fiz207/569719601330nas a2200193   4500008004100000245009800041210006900139260004000208490000900248520071900257653001500976653001400991653001501005653001701020653001901037100002101056700002101077856003801098       2016                        eng d00aNoble Gas Radioisotope Constraints on Water Residence Time and Solvent Sources in Lake Bonney0 aNoble Gas Radioisotope Constraints on Water Residence Time and S  aChicago, ILbUniversity of Illinois0 vM.S.3 a<p>A noble gas radionuclide analysis of perennially ice covered West Lake Bonney was performed in order to determine water residence time and ice cover timing. Bulk gas samples were collected at four depths in the lake. Krypton and argon gases were selectively isolated from the bulk gas and measurements of 81Kr, 85Kr and 39Ar were made. Radiokrypton and radioargon analyses yielded lower limit ages of 78 to 285 years, significantly younger than expected based on previous dating efforts. It was determined that these new data do not invalidate previous work, but instead offer new insight into the timing of the most recent episode of direct communication between the atmosphere and West Lake Bonney waters.</p>10aAntarctica10anoble gas10aradioargon10aradiokrypton10aresidence time1 aCronin, Kyle, D.1 aDoran, Peter, T.  uhttp://hdl.handle.net/10027/2157002215nas a2200205   4500008004100000245009200041210006900133260004000202490001000242520158200252653001501834653001001849653001301859653002401872653001601896653001601912100002201928700002101950856003801971       2014                        eng d00aGeophysics, Water Balance, and History of Thick Perennial Ice Covers on Antarctic Lakes0 aGeophysics Water Balance and History of Thick Perennial Ice Cove  aChicago, ILbUniversity of Illinois0 vPh.D.3 a<p>Antarctic lakes are studied as sentinels of future change, for paleolimnological records contained in the sediments, and as habitats for the simple food webs that can exist in inhospitable environments. Understanding how lakes are formed and are sustained in response to landscape and climate conditions is critical in addressing the aforementioned research themes. This thesis is governed by the overarching hypothesis that an understanding of hydrologic and sediment transport processes associated with lake ice formation and preservation can be used to reveal past climatic changes, and further our awareness of current changes in climate and water balance in the McMurdo Dry Valleys of Antarctica. The first chapter focuses on water loss from closed basin lakes in Taylor Valley, Antarctica, and presents updated estimates of sublimation and ablation rates from long-term empirical measurements. The second and third chapters address the formation of Lake Vida, Antarctica. The former investigates the accretion of a 27 m ice cover, and considers the origin of thick sediment layers in the ice cover, and the latter uses two geophysical methods to quantify the extent and volume of the brine network in the subsurface beneath the lake. The results presented herein advance the study of hydrogeology in continuous permafrost, provide additional evidence for fluctuating climate states in the McMurdo Dry Valleys throughout the mid to late Holocene, and provide a case study for the preservation of water in a cold, desert environment analogous to neighboring planets.</p>10aAntarctica10abrine10alake ice10aMcMurdo Dry Valleys10apolar lakes10asublimation1 aDugan, Hilary, A.1 aDoran, Peter, T.  uhttp://hdl.handle.net/10027/19407