Discovery of large conical stromatolites in Lake Untersee, A

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TitleDiscovery of large conical stromatolites in Lake Untersee, AntarcticaAbstractLake Untersee is one of the largest (11.4km2) and deepest (>160m) freshwater lakes in East Antarctica. Located at 71^circS the lake has a perennial ice cover, a water column that, with the exception of a small anoxic basin in the southwest of the lake, is well mixed, supersaturated with dissolved oxygen, alkaline (pH 10.4) and exceedingly clear. The floor of the lake is covered with photosynthetic microbial mats to depths of at least 100m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures, one of which - cm-scale cuspate pinnacles dominated by Leptolyngbya spp. - is common in Antarctica, but the second - laminated, conical stromatolites that rise up to 0.5m above the lake floor, dominated by Phormidium spp. - has not previously been reported in any modern environment. The laminae that form the conical stromatolites are 0.2-0.8mm in thickness consisting of fine clays and organic material; carbon dating implies that laminations may occur on near decadal timescales. The uniformly steep sides (59.6Â±2.5^circ) and the regular laminar structure of the cones suggest that they may provide a modern analog for growth of some of the oldest well-described Archean stromatolites. Mechanisms underlying the formation of these stromatolites are as yet unclear, but their growth is distinct from that of the cuspate pinnacles. The sympatric occurrence of pinnacles and cones related to microbial communities with distinct cyanobacterial compositions suggest that specific microbial behaviors underpin the morphological differences in the structures. Copyright 2011 Blackwell Publishing Ltd.AcknowledgementsWe would like to thank the Tawani Foundation of Chicago; NASAÅ› Exobiology and Astrobiology Programs and the Arctic and Antarctic Research Institute/Russian Antarctic Expedition for supporting the Tawani 2008 International Antarctic Scientific Expedition. We are grateful to Colonel (IL) JN Pritzker IL ARNG (Retired) for his leadership and support for the expedition; NIWA, New Zealand, and the Facility for Electron Microscopy Research (HojatollahVali), McGill University, Canada provided analytical facilities; We would like to acknowledge Brad Herried and the Antarctic Geospatial Information Center (AGIC) for help with Antarctic mapping. Logistics support was provided by Antarctic Logistics Centre International, Cape Town, SA; Von Braun Center for Science Innovation; National Space Science Technology, NASA; We also thank Ed Tracy of the Tawani Foundation, Marty Kress of VCSI, Inc., and special thanks to Art Mortvedt and other team members for their support during the expedition.

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1st AuthorAndersen, D.AuthorAndersen, D.Sumner, D.Hawes, I.Webster-Brown, J.Mckay, C.Year2011JournalGeobiologyVolume9Number3Pages280-293DOI10.1111/j.1472-4669.2011.00279.xURLhttps://www.scopus.com/inward/recor.....f34d650d8f699a9f86574331eKeywordscarbonwater, anoxic sedimentcyanobacteriumdissolved oxygenice covermicrobial communitymicrobial matmorphologyradiocarbon datingstromatolitetemperature gradienttimescalewater column, Antarcticaarticlechemical modelchemistrycyanobacteriumecosystemphotosynthesisradiometric datingsediment, Antarctic RegionsCarbonCyanobacteriaEcosystemGeologic SedimentsModels, ChemicalPhotosynthesisRadiometric DatingWater, AntarcticaEast AntarcticaLake Untersee, CyanobacteriaLeptolyngbyaPhormidium, rank3

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TypeArticleCitationAndersen, D., Sumner, D., Hawes, I., Webster-Brown, J. and Mckay, C. (2011). Discovery of large conical stromatolites in Lake Untersee, Antarctica. Geobiology, 9(3): 280-293