@article {4940, title = {McMurdo Dry Valley lake edge {\textquoteleft}moats{\textquoteright}: The ecological intersection between terrestrial and aquatic polar desert habitat}, journal = {Antarctic Science}, year = {2024}, month = {04/2024}, pages = {1 - 17}, abstract = {

Aquatic ecosystems - lakes, ponds and streams - are hotspots of biodiversity in the cold and arid environment of Continental Antarctica. Environmental change is expected to increasingly alter Antarctic aquatic ecosystems and modify the physical characteristics and interactions within the habitats that they support. Here, we describe physical and biological features of the peripheral \‘moat\’ of a closed-basin Antarctic lake. These moats mediate connectivity amongst streams, lake and soils. We highlight the cyclical moat transition from a frozen winter state to an active open-water summer system, through refreeze as winter returns. Summer melting begins at the lakebed, initially creating an ice-constrained lens of liquid water in November, which swiftly progresses upwards, creating open water in December. Conversely, freezing progresses slowly from the water surface downwards, with water at 1 m bottom depth remaining liquid until May. Moats support productive, diverse benthic communities that are taxonomically distinct from those under the adjacent permanent lake ice. We show how ion ratios suggest that summer exchange occurs amongst moats, streams, soils and sub-ice lake water, perhaps facilitated by within-moat density-driven convection. Moats occupy a small but dynamic area of lake habitat, are disproportionately affected by recent lake-level rises and may thus be particularly vulnerable to hydrological change.

}, keywords = {LTER-MCM, connectivity, ecosystem, ice, microbial mats, transition}, issn = {0954-1020}, doi = {10.1017/S0954102024000087}, url = {https://www.cambridge.org/core/journals/antarctic-science/article/mcmurdo-dry-valley-lake-edge-moats-the-ecological-intersection-between-terrestrial-and-aquatic-polar-desert-habitats/31D94DD51E651603482A3AE6E8A52A57}, author = {Stone, Michael S. and Devlin, Shawn and Ian Hawes and Kathleen A. Welch and Michael N. Gooseff and Cristina D. Takacs-Vesbach and Rachael M. Morgan-Kiss and Byron Adams and John E. Barrett and John C. Priscu and Peter T. Doran} } @article {4834, title = {Lipid biomarkers from microbial mats on the McMurdo Ice Shelf, Antarctica: Signatures for life in the cryosphere}, journal = {Frontiers in Microbiology}, volume = {13}, year = {2022}, month = {06/2022}, pages = {903621}, abstract = {

Persistent cold temperatures, a paucity of nutrients, freeze-thaw cycles, and the strongly seasonal light regime make Antarctica one of Earth\’s least hospitable surface environments for complex life. Cyanobacteria, however, are well-adapted to such conditions and are often the dominant primary producers in Antarctic inland water environments. In particular, the network of meltwater ponds on the \‘dirty ice\’ of the McMurdo Ice Shelf is an ecosystem with extensive cyanobacteria-dominated microbial mat accumulations. This study investigated intact polar lipids (IPLs), heterocyte glycolipids (HGs), and bacteriohopanepolyols (BHPs) in combination with 16S and 18S rRNA gene diversity in microbial mats of twelve ponds in this unique polar ecosystem. To constrain the effects of nutrient availability, temperature and freeze-thaw cycles on the lipid membrane composition, lipids were compared to stromatolite-forming cyanobacterial mats from ice-covered lakes in the McMurdo Dry Valleys as well as from (sub)tropical regions and hot springs. The 16S rRNA gene compositions of the McMurdo Ice Shelf mats confirm the dominance of Cyanobacteria and Proteobacteria while the 18S rRNA gene composition indicates the presence of Ochrophyta, Chlorophyta, Ciliophora, and other microfauna. IPL analyses revealed a predominantly bacterial community in the meltwater ponds, with archaeal lipids being barely detectable. IPLs are dominated by glycolipids and phospholipids, followed by aminolipids. The high abundance of sugar-bound lipids accords with a predominance of cyanobacterial primary producers. The phosphate-limited samples from the (sub)tropical, hot spring, and Lake Vanda sites revealed a higher abundance of aminolipids compared to those of the nitrogen-limited meltwater ponds, affirming the direct affects that N and P availability have on IPL compositions. The high abundance of polyunsaturated IPLs in the Antarctic microbial mats suggests that these lipids provide an important mechanism to maintain membrane fluidity in cold environments. High abundances of HG keto-ols and HG keto-diols, produced by heterocytous cyanobacteria, further support these findings and reveal a unique distribution compared to those from warmer climates.

}, keywords = {LTER-MCM, Antarctica, bacteriohopanepolyol, cyanobacteria, heterocyte glycolipids, homeoviscous adaptation, intact polar lipid, microbial mats}, doi = {10.3389/fmicb.2022.90362110.3389/fmicb.2022.903621.s001}, url = {https://www.frontiersin.org/articles/10.3389/fmicb.2022.903621/full}, author = {Evans, Thomas W. and Kalambokidis, Maria J. and Jungblut, Anne D. and Millar, Jasmin L. and Bauersachs, Thorsten and Grotheer, Hendrik and Mackey, Tyler J. and Ian Hawes and Summons, Roger E.} } @article {4578, title = {Antarctic ecosystems in transition {\textendash} life between stresses and opportunities}, journal = {Biological Reviews}, year = {2021}, month = {06/2021}, abstract = {

Important findings from the second decade of the 21st century on the impact of environmental change on biological processes in the Antarctic were synthesised by 26 international experts. Ten key messages emerged that have stakeholder-relevance and/or a high impact for the scientific community. They address (i) altered biogeochemical cycles, (ii) ocean acidification, (iii) climate change hotspots, (iv) unexpected dynamism in seabed-dwelling populations, (v) spatial range shifts, (vi) adaptation and thermal resilience, (vii) sea ice related biological fluctuations, (viii) pollution, (ix) endangered terrestrial endemism and (x) the discovery of unknown habitats. Most Antarctic biotas are exposed to multiple stresses and considered vulnerable to environmental change due to narrow tolerance ranges, rapid change, projected circumpolar impacts, low potential for timely genetic adaptation, and migration barriers. Important ecosystem functions, such as primary production and energy transfer between trophic levels, have already changed, and biodiversity patterns have shifted. A confidence assessment of the degree of \‘scientific understanding\’ revealed an intermediate level for most of the more detailed sub-messages, indicating that process-oriented research has been successful in the past decade. Additional efforts are necessary, however, to achieve the level of robustness in scientific knowledge that is required to inform protection measures of the unique Antarctic terrestrial and marine ecosystems, and their contributions to global biodiversity and ecosystem services.

}, keywords = {LTER-MCM, adaptation, benthic dynamism, biogeochemical cycles, climate change, invasion, new habitats, ocean acidification, Primary production, range shifts, sea ice}, doi = {10.1111/brv.12679}, url = {https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12679}, author = {Gutt, Julian and Isla, Enrique and Xavier, Jos{\'e} C. and Adams, Byron J. and Ahn, In-Young and Cheng, C.-H. Christina and Colesie, Claudia and Cummings, Vonda J. and di Prisco, Guido and Griffiths, Huw J. and Ian Hawes and Hogg, Ian D. and McIntyre, Trevor and Meiners, Klaus M. and Pearce, David A. and Lloyd S. Peck and Piepenburg, Dieter and Reisinger, Ryan R. and Saba, Grace and Schloss, Irene R. and Signori, Camila N. and Smith, Craig R. and Vacchi, Marino and Verde, Cinzia and Diana H. Wall} } @article {4732, title = {The magnitude and climate sensitivity of isotopic fractionation from ablation of Antarctic Dry Valley lakes}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {53}, year = {2021}, month = {12/2021}, pages = {352 - 371}, abstract = {

There has been extensive research on the effects of evaporation on the isotopic ratio of lacustrine and marine water bodies; however, there are limited data on how ablation or sublimation from lake or sea ice influences the isotopic ratio of the residual water body. This is a challenging problem because there remains uncertainty on the magnitude of fractionation during sublimation and because ablation can involve mixed-phase processes associated with simultaneous sublimation, melting, evaporation, and refreezing. This uncertainty limits the ability to draw quantitative inferences on changing hydrological budgets from stable isotope records in arctic, Antarctic, and alpine lakes. Here, we use in situ measurements of the isotopic ratio of water vapor along with the gradient diffusion method to constrain the isotopic ratio of the ablating ice from two lakes in the McMurdo Dry Valleys, Antarctica. We find that during austral summer, the isotopic fractionation of ablation was insignificant during periods of boundary layer instability that are typical during midday when latent heat is highest. This implies that the loss of mass during these periods did not yield any isotopic enrichment to the residual lake mass. However, fractionation increased after midday when the boundary layer stabilized and the latent heat flux was small. This diurnal pattern was mirrored on synoptic timescales, when following warm and stable conditions latent heat flux was low and dominated by higher fractionation for a few days. We hypothesize that the shifting from negligible to large isotopic fractionation reflects the development and subsequent exhaustion of liquid water on the surface. The results illustrate the complex and nonlinear controls on isotopic fractionation from icy lakes, which implies that the isotopic enrichment from ablation could vary significantly over timescales relevant for changing lake volumes. Future work using water isotope fluxes for longer periods of time and over additional perennial and seasonal ice-covered lake systems is critical for developing models of the isotopic mass balance of arctic and Antarctic lake systems.

}, keywords = {LTER-MCM, Dry Valley lakes, isotope fractionation, stable water isotopes}, issn = {1523-0430}, doi = {10.1080/15230430.2021.2001899}, url = {https://www.tandfonline.com/doi/full/10.1080/15230430.2021.2001899}, author = {Bellagamba, Anthony W. and Berkelhammer, Max and Winslow, Luke A. and Peter T. Doran and Myers, Krista F. and Devlin, Shawn and Ian Hawes} } @article {4395, title = {Energetic and environmental constraints on the community structure of benthic microbial mats in Lake Fryxell, Antarctica}, journal = {FEMS Microbiology Ecology}, volume = {96}, year = {2020}, month = {02/2020}, abstract = {

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 (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). 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 (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) 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 (O2) was saturated, PAR structured the community. In contrast, (O2) 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 (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

}, keywords = {LTER-MCM, Antarctica, energy, Lake Fryxell, microbial mat, Oxygen, Photosynthetically Active Radiation}, doi = {10.1093/femsec/fiz207}, url = {https://academic.oup.com/femsec/article/96/2/fiz207/5697196}, author = {Dillon, Megan L. and Ian Hawes and Jungblut, Anne D. and Mackey, Tyler J. and Eisen, Jonathan A. and Peter T. Doran and Sumner, Dawn Y.} } @inbook {4187, title = {Complex Structure but Simple Function in Microbial Mats from Antarctic Lakes}, booktitle = {The Structure and Function of Aquatic Microbial Communities}, year = {2019}, pages = {91 - 120}, publisher = {Springer International Publishing}, organization = {Springer International Publishing}, address = {Cham}, abstract = {

Microbial mats growing under the permanent ice cover of Antarctic lakes occupy an exceptionally low-disturbance regime. Constant temperature, the absence of bioturbation or physical disturbance from wind action or ice formation allow mats to accumulate, as annual growth layers, over many decades or even centuries. In so doing they often assume decimetre scale, three-dimensional morphologies such as elaborate pinnacle structures and conical mounds. Here we combine existing and new information to describe microbial structures in three Antarctic lakes\—simple prostrate mats in Lake Hoare, emergent cones in Lake Untersee and elaborate pinnacles in Lake Vanda. We attempt to determine whether structures emerge simply from uncoordinated organism-environment interactions or whether they represent an example of \“emergent complexity\”, within which some degree of self-organisation occurs to confer a holistic functional advantage to component organisms. While some holistic advantages were evident from the structures\—the increase in surface area allows greater biomass and overall productivity and nutrient exchange with overlying water\—the structures could also be understood in terms of potential interactions between individuals, their orientation and their environment. The data lack strong evidence of coordinated behaviour directed towards holistic advantages to the structure, though hints of coordinated behaviour are present as non-random distributions of structural elements. The great size of microbial structures in Antarctic lakes, and their relatively simple community composition, makes them excellent models for more focused research on microbial cooperation.

}, keywords = {LTER-MCM, biofilm, microbial ecology, microbial structures, self-organising structures, stromatolite}, isbn = {978-3-030-16775-2}, doi = {10.1007/978-3-030-16775-2_4}, url = {https://link.springer.com/chapter/10.1007/978-3-030-16775-2_4}, author = {Ian Hawes and Sumner, Dawn Y. and Jungblut, Anne D.}, editor = {Hurst, Christon J.} } @article {4294, title = {Environmental controls on bacteriohopanepolyol profiles of benthic microbial mats from Lake Fryxell, Antarctica}, journal = {Geobiology}, year = {2019}, month = {07/2019}, abstract = {

Bacteriohopanepolyols (BHPs) are pentacyclic triterpenoid lipids that contribute to the structural integrity and physiology of some bacteria. Because some BHPs originate from specific classes of bacteria, BHPs have potential as taxonomically and environmentally diagnostic biomarkers. For example, a stereoisomer of bacteriohopanetetrol (informally BHT II) has been associated with anaerobic ammonium oxidation (anammox) bacteria and suboxic to anoxic marine environments where anammox is active. As a result, the detection of BHT II in the sedimentary record and fluctuations in the relative abundance of BHT II may inform reconstructions of nitrogen cycling and ocean redox changes through the geological record. However, there are uncertainties concerning the sources of BHT II and whether or not BHT II is produced in abundance in non-marine environments, both of which are pertinent to interpretations of BHT II signatures in sediments. To address these questions, we investigate the BHP composition of benthic microbial mats from Lake Fryxell, Antarctica. Lake Fryxell is a perennially ice-covered lake with a sharp oxycline in a density-stabilized water column. We describe the diversity and abundance of BHPs in benthic microbial mats across a transect from oxic to anoxic conditions. Generally, BHP abundances and diversity vary with the morphologies of microbial mats, which were previously shown to reflect local environmental conditions, such as irradiance and oxygen and sulfide concentrations. BHT II was identified in mats that exist within oxic to anoxic portions of the lake. However, anammox bacteria have yet to be identified in Lake Fryxell. We examine our results in the context of BHPs as biomarkers in modern and ancient environments.

}, keywords = {LTER-MCM, anammox, bacteriohopanepolyol, bacteriohopanetetrol isomer, biomarker, McMurdo Dry Valleys}, doi = {10.1111/gbi.12353}, url = {https://onlinelibrary.wiley.com/doi/full/10.1111/gbi.12353}, author = {Matys, Emily D. and Mackey, Tyler J. and Grettenberger, Christen and Mueller, Elliott and Jungblut, Anne D. and Sumner, Dawn Y. and Ian Hawes and Summons, Roger E.} } @article {4140, title = {In a PICL: The sedimentary deposits and facies of perennially ice-covered lakes}, journal = {Sedimentology}, volume = {66}, year = {2019}, month = {04/2019}, abstract = {

Perennially ice-covered lakes can have significantly different facies than open-water lakes because sediment is transported onto the ice, where it accumulates, and sand grains preferentially melt through to be deposited on the lake floor. To characterize the facies in these lakes, sedimentary deposits from five Antarctic perennially ice-covered lakes were described using lake-bottom observations, underwater video and images, and sediment cores. One lake was dominated by laminated microbial mats and mud (derived from an abutting glacier), with disseminated sand and rare gravel. The other four lakes were dominated by laminated microbial mats and moderately well to moderately sorted medium to very coarse sand with sparse granules and pebbles; they contained minor interstitial or laminated mud (derived from streams and abutting glaciers). The sand was disseminated or localized in mounds and 1 m to more than 10 m long elongate ridges. Mounds were centimetres to metres in diameter; conical, elongate or round in shape; and isolated or deposited near or on top of one another. Sand layers in the mounds had normal, inverse, or no grading. Nine mixed mud and sand facies were defined for perennially ice-covered lakes based on the relative proportion of mud to sand and the style of sand deposition. While perennially ice-covered lake facies overlap with other ice-influenced lakes and glaciomarine facies, they are characterized by a paucity of grains coarser than granules, a narrow range in sand grain sizes, and inverse grading in the sand mounds. These facies can be used to infer changes in ice cover through time and to identify perennially ice-covered lakes in the rock record. Ancient perennially ice-covered lakes are expected on Earth and Mars, and their characterization will provide new insights into past climatic conditions and habitability.

}, keywords = {LTER-MCM}, doi = {10.1111/sed.12522}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.12522}, author = {Rivera-Hernandez, Frances and Sumner, Dawn Y. and Mackey, Tyler J. and Ian Hawes and Dale T. Andersen} } @article {4837, title = {Meteorological connectivity from regions of high biodiversity within the McMurdo Dry Valleys of Antarctica}, journal = {Journal of Applied Meteorology and Climatology}, volume = {58}, year = {2019}, month = {11/2019}, pages = {2437 - 2452}, abstract = {

Meteorological connectivity between biological hot spots of the McMurdo Dry Valleys (MDVs) of Antarctica is thought to play a role in species distribution and abundance through the aeolian transport of bioaerosols. Understanding the potential role of such meteorological connectivity requires an understanding of near-surface wind flow within and between valley airsheds. To address this, we applied Lagrangian wind trajectory modeling to mesoscale (spatial resolution of ~1 km) weather model output to predict connectivity pathways, focusing on regions of high biodiversity. Our models produce maps of a likelihood metric of wind connectivity that demonstrate the synoptic and mesoscale dependence of connections between local, near-local, and nonlocal areas on wind transport, modulated by synoptic weather and topographic forcing. These connectivity areas can have spatial trends modulated by the synoptic weather patterns and locally induced topographically forced winds. This method is transferrable to other regions of Antarctica for broader terrestrial, coastal, and offshore ecological connectivity research. Also, our analysis and methods can inform better placement of aeolian dust and bioaerosol samplers in the McMurdo Dry Valleys, provide preliminary guidelines behind the meteorological controls of sediment transport and smaller particle distribution, and present quantifiable knowledge informing new hypotheses around the potential of wind acting as a physical driver for biological connectivity in the MDVs.

}, keywords = {LTER-MCM, Antarctica, atmosphere, biosphere-atmosphere interaction, mesoscale models, mesoscale processes, numerical analysis/modeling}, issn = {1558-8424}, doi = {10.1175/JAMC-D-18-0336.1}, url = {https://journals.ametsoc.org/view/journals/apme/58/11/jamc-d-18-0336.1.xml}, author = {Katurji, Marwan and Khan, Basit and Sprenger, Michael A. and Datta, Rajasweta and Joy, Kurt and Zawar-Reza, Peyman and Ian Hawes} } @article {3708, title = {Growth dynamics of a laminated microbial mat in response to variable irradiance in an Antarctic lake}, journal = {Freshwater Biology}, volume = {61}, year = {2016}, month = {02/2016}, pages = {396 - 410}, abstract = {
  1. Laminated microbial mats are important ecosystem components of perennially ice-covered Antarctic dry valley lakes. In order to understand better their response to changing environment, we made observations and carried out a manipulation experiment to determine their response to variations in irradiance in Lake Hoare (77\°38\′ S, 162\°53\′ E).
  2. Ice transparency was the most variable parameter that affected benthic light dose, both spatially and between years. Patterns of lamina accrual corresponded to irradiance history, with laminae that were initiated in high transmission years thicker than those from low transmission years.
  3. A shading experiment confirmed that accrual of lamina thickness, calcite precipitation and ash-free dry mass were determined by irradiance, but photosynthetic biomass and phototrophic species composition were less affected.
  4. Buried laminae decomposed only slowly over time, with potentially viable phototrophs many laminae down into the microbial mat. Decay rate increased only slightly with shading.
  5. We conclude that the microbial mats in Lake Hoare are characterised by remarkable stability, with slow accumulation rates and turnover of biomass over time. Photosynthetic biomass and species composition appeared to be stable across long time periods, with interannual variation in lamination pattern due to differential accumulation of extracellular polysaccharide and representing the visible expression of annual growth conditions.
}, keywords = {LTER-MCM}, doi = {10.1111/fwb.2016.61.issue-410.1111/fwb.12715}, url = {http://doi.wiley.com/10.1111/fwb.12715}, author = {Ian Hawes and Jungblut, Anne D. and Maciek K. Obryk and Peter T. Doran} } @article {3961, title = {Lake Vanda: A sentinel for climate change in the McMurdo Sound Region of Antarctica}, journal = {Global and Planetary Change}, volume = {144}, year = {2016}, month = {Jan-09-2016}, pages = {213 - 227}, abstract = {

Lake Vanda is a perennially ice-covered, meromictic, endorheic lake located in the McMurdo Dry Valleys of Antarctica, and an exceptional sentinel of climate change within the region. Lake levels rose 15 m over the past 68 years in response to climate-driven variability in ice-cover sublimation, meltwater production, and annual discharge of the Onyx River, the main source of water to the lake. Evidence from a new bathymetric map and water balance model combined with annual growth laminations in benthic mats suggest that the most recent filling trend began abruptly 80 years ago, in the early 1930s. This change increased lake volume by \> 50\%, triggered the formation of a new, upper, thermohaline convection cell, and cooled the lower convection cell by at least 2 \°C and the bottom-most waters by at \> 4 \°C. Additionally, the depth of the deep chlorophyll a maximum rose by \> 2 m, and deep-growing benthic algal mats declined while shallow benthic mats colonized freshly inundated areas. We attribute changes in hydrology to regional variations in air flow related to the strength and position of the Amundsen Sea Low (ASL) pressure system which have increased the frequency of down-valley, f{\"o}hn winds associated with surface air temperature warming in the McMurdo Dry Valleys. The ASL has also been implicated in the recent warming of the Antarctic Peninsula, and provides a common link for climate-related change on opposite sides of the continent. If this trend persists, Lake Vanda should continue to rise and cool over the next 200 years until a new equilibrium lake level is achieved. Most likely, future lake rise will lead to isothermal conditions not conducive to thermohaline convection, resulting in a drastically different physical, biogeochemical, and biological structure than observed today.

}, keywords = {LTER-MCM}, issn = {09218181}, doi = {10.1016/j.gloplacha.2016.06.007}, url = {http://www.sciencedirect.com/science/article/pii/S092181811530014X}, author = {Castendyk, Devin and Maciek K. Obryk and Leidman, Sasha Z. and Michael N. Gooseff and Ian Hawes} } @article {3710, title = {Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake}, journal = {Applied and Environmental Microbiology}, volume = {82}, year = {2016}, month = {01/2016}, pages = {620 - 630}, keywords = {LTER-MCM}, issn = {0099-2240}, doi = {10.1128/AEM.02699-15}, url = {http://aem.asm.org/lookup/doi/10.1128/AEM.02699-15}, author = {Jungblut, Anne D. and Ian Hawes and Mackey, Tyler J. and Krusor, Megan and Peter T. Doran and Sumner, Dawn Y. and Eisen, Jonathan A. and Hillman, Colin and Goroncy, Alexander K.}, editor = {Stams, A. J.} } @article {3248, title = {Antarctic microbial mats: A modern analog for Archean lacustrine oxygen oases}, journal = {Geology}, year = {2015}, month = {10/2015}, pages = {G36966.1}, abstract = {

The evolution of oxygenic photosynthesis was the most important geochemical event in

Earth history, causing the Great Oxidation Event (GOE) ~2.4 b.y. ago. However, evidence is mixed as to whether O2 production occurred locally as much as 2.8 b.y. ago, creating O2 oases, or initiated just prior to the GOE. The biogeochemical dynamics of possible O2 oases have been poorly constrained due to the absence of modern analogs. However, cyanobacteria in microbial mats in a perennially anoxic region of Lake Fryxell, Antarctica, create a 1\–2 mm O2-containing layer in the upper mat during summer, providing the first known modern analog for formation of benthic O2 oases. In Lake Fryxell, benthic cyanobacteria are present below the oxycline in the lake. Mat photosynthesis rates were slow due to low photon flux rate (1\–2 μmol m-2 s-1) under thick ice cover, but photosynthetic O2 production was sufficient to sustain up to 50 μmol O2 L-1, sandwiched between anoxic overlying water and anoxic sedi- ments. We hypothesize that Archean cyanobacteria could have similarly created O2 oases in benthic mats prior to the GOE. Analogous mats may have been at least partly responsible for geological evidence of oxidative weathering prior to the GOE, and habitats such as Lake Fryxell provide natural laboratories where the impact of benthic O2 oases on biogeochemical signatures can be investigated.\ 

}, keywords = {LTER-MCM}, issn = {0091-7613}, doi = {10.1130/G36966.1}, url = {http://geology.gsapubs.org/lookup/doi/10.1130/G36966.1}, author = {Sumner, Dawn Y. and Ian Hawes and Mackey, Tyler J. and Jungblut, Anne D. and Peter T. Doran} } @article {3254, title = {Cyanobacterial diversity in benthic mats of the McMurdo Dry Valley lakes, Antarctica}, journal = {Polar Biology}, volume = {38}, year = {2015}, month = {01/2015}, pages = {1097 - 1110}, abstract = {
Perennially ice-covered, meromictic lakes in\ the McMurdo Dry Valleys, Antarctica, are useful models to\ study the relationship between cyanobacterial and environmental\ variables. They have rich benthic cyanobacterial\ mat accumulations and stable stratification of physical and\ chemical conditions. Here, we evaluated cyanobacteria\ from benthic mats from multiple depths in three geographically\ separated ice-covered lakes, Lakes Vanda,\ Hoare and Joyce, using 16S rRNA gene clone libraries. We\ identified 19 ribotypes, mostly Oscillatoriales and several
Chroococcales, as well as potentially novel cyanobacterial\ ribotypes. The majority of ribotype diversity was shared\ between lakes, and only a weak relationship between ribotype\ community structure and environmental variables\ was evident. Multivariate analysis of all lake\–depth combinations\ implied that photosynthetically active radiation,\ dissolved reactive phosphorus and conductivity were\ potentially important for shaping benthic communities in\ McMurdo Dry Valley lakes. Cyanobacterial-specific pigment\ signature analysis by high-performance liquid chromatography
showed that the cyanobacterial communities\ responded to light conditions similarly, irrespective of\ community composition. The results imply a capability\ within a suite of cyanobacteria to colonise, adapt and grow\ across broad environmental ranges and geographic space,\ and such adaptability may provide a high degree of community\ resistance and resilience to future climate-driven\ environmental change in Antarctic terrestrial aquatic
ecosystems.
}, keywords = {LTER-MCM}, issn = {0722-4060}, doi = {10.1007/s00300-015-1669-0}, url = {http://link.springer.com/10.1007/s00300-015-1669-0http://link.springer.com/content/pdf/10.1007/s00300-015-1669-0}, author = {Zhang, L. and Jungblut, Anne D. and Ian Hawes and Dale T. Andersen and Sumner, Dawn Y. and Mackey, Tyler J.} } @article {1059, title = {Estimating photosynthetic activity in microbial mats in an ice-covered Antarctic lake using automated oxygen microelectode profiling and variable chlorophyll fluorescence}, journal = {Limnology and Oceanography}, volume = {59}, year = {2014}, month = {08/2014}, pages = {674-688}, chapter = {674}, abstract = { An automated oxygen microprofiler measured a positive flux of oxygen from microbial mats in ice-covered Lake Hoare, Antarctica, from noon, at a photon flux of 20 {\textmu}mol m-2 s-1, through to midnight (< 2 {\textmu}mol photons m-2 s-1). Daily average oxygen flux was 200 {\textmu}mol m-2 h-1; and, whereas it was maximal at noon, when a 10 mm broad concentration peak was observed 5 mm below the mat surface, flux correlated only weakly with irradiance. In contrast, relative electron transfer rate, estimated from variable chlorophyll fluorescence, suggested a linear relationship between photosystem activity and irradiance. This contradiction arose because of the conjunction of photosynthetic production of oxygen deep into these transparent, gelatinous mats (diel oxygen change was observed to 17 mm depth) and oxygen diffusion rates too slow to allow equilibration of oxygen concentration profiles with instantaneous production and consumption of oxygen. To confirm this, we developed a mathematical simulation of oxygen dynamics that included diffusion, photosynthesis, and respiration. The simulation further indicated that (1) net oxygen evolution is light limited is and confined to the upper few millimeters of the mat, (2) below 5{\textendash}7 mm, respiration balanced photosynthesis, (3) below 17 mm, respiration and photosynthesis approached zero, even though organic carbon and dissolved oxygen were present, and (4) photosynthesis deep into the mat was dependent on high light transmission through the gelatinous matrix. These conclusions are consistent with current understanding of mat growth dynamics and point to approaches for long-term analysis of microbial mat productivity.}, keywords = {LTER-MCM}, doi = {10.4319/lo.2014.59.3.0674}, author = {Ian Hawes and H. Giles and Peter T. Doran} } @inbook {1175, title = {Saline lakes and ponds in the McMurdo Dry Valleys: ecological analogs to martian paleolake environments}, booktitle = {Life in Antarctic Deserts and other Cold Dry Environments}, year = {2010}, pages = {160 - 194}, publisher = {Cambridge University Press}, organization = {Cambridge University Press}, address = {Cambridge}, keywords = {LTER-MCM}, isbn = {9780521889193}, doi = {10.1017/CBO9780511712258.006}, url = {http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511712258\&cid=CBO9780511712258A013}, author = {Jill A. Mikucki and W. Berry Lyons and Ian Hawes and Brian D. Lanoil and Peter T. Doran} } @inbook {1215, title = {Ice-based freshwater ecosystems}, booktitle = {Polar Lakes and Rivers: Limnology of Arctic and Antarctic Aquatic Ecosystems}, year = {2008}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {Oxford}, keywords = {LTER-MCM}, doi = {LTER}, author = {Ian Hawes and Clive Howard-Williams and Andrew G Fountain}, editor = {Warwick F. Vincent and Johanna Laybourn-Parry} } @article {1201, title = {Reply to comment by K. Gajewski on {\textquotedblleft}Abrupt environmental change in Canada{\textquoteright}s northernmost lake{\textquotedblright}}, journal = {Geophysical Research Letters}, volume = {35}, year = {2008}, month = {2008}, keywords = {LTER-MCM}, doi = {10.1029/2007GL032889}, url = {http://www.agu.org/pubs/crossref/2008/2007GL032889.shtml}, author = {Dermot Antoniades and Catherine Crawley and Douglas, Marianne S. V. and Pienitz, R and Dale T. Andersen and Peter T. Doran and Ian Hawes and Pollard, W and Warwick F. Vincent} } @article {1266, title = {Environmental factors associated with deep chlorophyll maxima in dry valley lakes, South Victoria Land, Antarctica}, journal = {Arctic, Antarctic, and Alpine Research}, volume = {38}, year = {2006}, pages = {179-189}, keywords = {LTER-MCM}, doi = {LTER}, author = {Burnett, L and Daryl L. Moorhead and Ian Hawes and Clive Howard-Williams} } @article {1310, title = {Contributions of Benthic Microbial Mats to Net Primary Production in Lake Hoare, Antarctica}, journal = {Antarctic Science}, volume = {17}, year = {2005}, keywords = {LTER-MCM}, author = {Daryl L. Moorhead and Schmeling, S and Ian Hawes} } @article {1410, title = {Absorption and utilization of low irradiance by cyanobacterial mats in two ice-covered Antarctic lakes}, journal = {Journal of Phycology}, volume = {37}, year = {2001}, pages = {5-15}, keywords = {LTER-MCM}, author = {Ian Hawes and Schwartz, A-M} } @article {1412, title = {Benthic primary production in two perennially ice-covered Antarctic lakes: comparisons of annual accumulation predicted from photosynthesis models with estimates from internal growth markers}, journal = {Antarctic Science}, volume = {13}, year = {2001}, pages = {18-27}, keywords = {LTER-MCM}, author = {Ian Hawes and Daryl L. Moorhead and Sutherland, J and Schmeling, J and Schwartz, A} } @article {1466, title = {McMurdo LTER: Photosynthesis in an extreme shade habitat: benthic microbial mats from Lake Hoare, Antarctica}, journal = {Journal of Phycology}, volume = {35}, year = {1999}, pages = {448-459}, keywords = {LTER-MCM}, author = {Ian Hawes and Anne-Maree Schwarz} } @inbook {1520, title = {Optical Properties of the McMurdo Dry Valley Lakes, Antarctica}, booktitle = {Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, series = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {189-203}, keywords = {LTER-MCM}, author = {Clive Howard-Williams and Anne-Maree Schwarz and Ian Hawes and John C. Priscu} } @inbook {1526, title = {Primary Production Processes in Streams of the McMurdo Dry Valleys, Antarctica}, booktitle = {Ecosystem Processes in a Polar Desert: The McMurdo Dry Valleys, Antarctica}, series = {Antarctic Research Series}, volume = {72}, year = {1998}, pages = {129-140}, keywords = {LTER-MCM}, author = {Ian Hawes and Clive Howard-Williams} } @inbook {1544, title = {The abundance of planktonic virus-like particles in Antarctic lakes}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {241-250}, publisher = {Balkema Press}, organization = {Balkema Press}, address = {Rotterdam}, keywords = {LTER-MCM}, author = {Kepner, R.L. and Robert A. Wharton Jr. and Galchenko, V} } @inbook {1548, title = {Carbon dynamics of aquatic microbial mats in the Antarctic dry valleys: A modelling synthesis}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {181-196}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {Daryl L. Moorhead and W. Shane Davis and Robert A. Wharton Jr.} } @inbook {1549, title = {Chemical weathering rates and reactions in the Lake Fryxell Basin, Taylor Valley : Comparison to temperate river basins}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {147-154}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Kathleen A. Welch and C. A. Nezat and K. Crick and Jeffrey K. Toxey and J.A. Mastrine and Diane M. McKnight} } @inbook {1550, title = {Climate history of the McMurdo Dry Valleys since the last glacial maximum: A synthesis}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {155-162}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {W. Berry Lyons and Louis R. Bartek and Paul A. Mayewski and Peter T. Doran} } @inbook {1559, title = {The microbial loop in Antarctic lakes}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {231-240}, publisher = {Balkema Press}, organization = {Balkema Press}, address = {Rotterdam}, keywords = {LTER-MCM}, author = {Johanna Laybourn-Parry} } @inbook {1563, title = {Sources and sinks of nutrients in a polar desert stream, the Onyx River, Antarctica}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {155-170}, publisher = {Balkema Press}, organization = {Balkema Press}, address = {Rotterdam}, keywords = {LTER-MCM}, author = {Clive Howard-Williams and Ian Hawes and Anne-Maree Schwarz and Julie A. Hall} } @inbook {1564, title = {Species composition and primary production of algal communities in Dry Valley streams in Antarctica: Examination of the functional role of biodiversity}, booktitle = {Ecosystem Processes in Antarctic Ice-free Landscapes}, year = {1997}, pages = {171-179}, publisher = {Balkema Press, Rotterdam}, organization = {Balkema Press, Rotterdam}, keywords = {LTER-MCM}, author = {Dev K. Niyogi and Cathy M. Tate and Diane M. McKnight and John H. Duff and Alexander S. Alger} } @article {1591, title = {McMurdo LTER: Photosynthesis in benthic cyanobacterial mats from Lake Hoare, Antarctica}, journal = {Antarctic Journal of the U.S.}, volume = {30}, year = {1995}, pages = {296-297}, keywords = {LTER-MCM}, author = {Ian Hawes and Anne-Maree Schwarz} }