Browsing by Author "Psenner, Roland"

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Carbon fluxes through bacterial communities on glacier surfaces
(2010-12) Anesio, Alexandre M.; Sattler, Birgit; Foreman, Christine M.; Telling, Jon; Hodson, Andy; Tranter, Martyn; Psenner, Roland
There is very little information about the activity of microbial communities on the surfaceof glaciers, though there is an increasing body of evidence to show that they strongly influence the biogeochemistry of these habitats. We measured bacterial abundance and production in cryoconite holes on Arctic, Antarctic and Alpine glaciers in order to estimate the role of heterotrophic bacteria within the carbon budget of glacial ecosystems. Our results demonstrate an active bacterial community on the surface of glaciers with doubling times that vary from a few hours to hundreds of days depending on the glacier and position (water or sediments) within the cryoconite hole. However, bacterial production is only ~2â€“3% of the published literature values of community respiration from similar habitats, indicating that other types of microbes (e.g. eukaryotic organisms) may also play a role in the C cycle of glaciers. We estimate that only up to 7% of the organic C in cryoconite sediments is utilized by the heterotrophic bacterial community annually, suggesting that the surface of glaciers can accumulate organic carbon, and that this C may be important for biogeochemical activity downstream to adjacent ecosystems.
Laser-induced fluorescence emission (LIFE) from Lake Fryxell (Antarctica) cryoconites
(2010-12) Sattler, Birgit; Storrie-Lombardi, Michael C.; Foreman, Christine M.; Tilg, Markus; Psenner, Roland
Laser-induced fluorescence emission (LIFE) images were obtained in situ from a 27 cm longice core at Lake Fryxell, Antarctica. The excitation was accomplished with a simple 532nm green laser pen light, and the fluorescence images were captured with a small compact digital camera. The targets for the experiment were mm-scale cryoconite assemblages found in the ice covers of this perennially frozen Antarctic lake. The fluorescence response originates from photo-pigments in cyanobacteriadominated cryoconite assemblages with phycoerythrin (PE) exhibiting the optimal target cross section. This inexpensive, low-mass, low-energy method avoids manipulation of the in situ habitat and individual target organisms and does not disturb the microbial community or the surrounding ice matrix. We establish the correlation between fluorescence intensity and PE concentration.We show that cryoconite fluorescence response does not appear to decrease with depth in the ice cover, in agreement with similar findings at Lake Untersee, a perennially ice-covered lake in Dronning Maud Land, Antarctica. Optical reflection and refraction events at the air/ice interface can complicate quantitative estimates of total pigment concentrations. Laser targeting of a single mm-scale cryoconite can result in multiple neighboring excitation events secondary to reflection and refraction phenomena in the multiple air/ice interface of the bubbles surrounding the primary target.