02033nas a2200229   4500008004100000245011500041210006900156260001200225300001100237490000600248520129700254100002701551700001901578700002101597700002901618700002001647700002001667700002301687700001801710700002401728856005101752       2013                        eng d00aMicrobial growth under humic-free conditions in a supraglacial stream system on the Cotton Glacier, Antarctica0 aMicrobial growth under humicfree conditions in a supraglacial st  c09/2013  a0350220 v83 aDuring the austral summers of 2004 and 2009, we sampled a supraglacial stream on the Cotton Glacier, Antarctica. The stream dissolved organic matter (DOM) was low (44–48 μM C) and lacked detectable humic fluorescence signatures. Analysis of the excitation emissions matrices (EEMs) indicated that amino-acid fluorophores dominated, consistent with DOM of microbial origin, with little humic-like fluorescence. In most aquatic ecosystems, humic DOM attenuates harmful UV radiation and its absence may represent an additional stressor influencing the microbial community. Nonetheless, the stream contained an active microbial assemblage with bacterial cell abundances from 2.94 × 104 to 4.97 × 105 cells ml−1, and bacterial production ranging from 58.8 to 293.2 ng C l−1 d−1. Chlorophyll-a concentrations ranged from 0.3 to 0.53 μg l−1 indicating that algal phototrophs were the probable source of the DOM. Microbial isolates produced a rainbow of pigment colors, suggesting adaptation to stress, and were similar to those from other cryogenic systems (Proteobacteria and Bacteroidetes lineages). Supraglacial streams provide an example of contemporary microbial processes on the glacier surface and a natural laboratory for studying microbial adaptation to the absence of humics.1 aForeman, Christine, M.1 aCory, Rose, M.1 aMorris, Cindy, E1 aSanClements, Michael, D.1 aSmith, Heidi, J1 aLisle, John, T.1 aMiller, Penney, L.1 aChin, Yu-Ping1 aMcKnight, Diane, M.  uhttp://iopscience.iop.org/1748-9326/8/3/035022