In situ microbial metabolism as a cause of gas anomalies in ice

Abstract

Isolated spikes of anomalously high concentrations of N2O have been reported at depths in Greenland and Antarctic ice cores corresponding to narrow time intervals over the past Ϸ10 5 years. Now, using a calibrated spectrofluorimeter to map protein-bound Trp, a proxy for microbes, versus depth in the 3,053-m GISP2 ice core, we find six depths at which localized spikes of high cell concentrations coincide with N2O spikes. We show that the excess gases are consistent with accumulation of in situ metabolic wastes during residence times of the excess microbes in the ice. Because of sparseness of N2O measurements and our spectrofluorimetry versus depth, the total number of microbially produced N2O spikes in GISP2 is probably much larger than six. Spikes of excess methanogens coincident with CH4 spikes are found at three depths in the bottom 3% of GISP2, most likely because of methanogenic metabolism in the underlying silty ice, followed by turbulent flow of the lowest Ϸ90 m of ice. The apparent rates of in situ production of N2O and CH4 spikes by metabolism are observed to be consistent with a single activation energy, U, and maintain proportionality to exp(؊U/RT) over the entire temperature range down to ؊40°C. Fluorescence of nonmicrobial aerosols in GISP2 ice is distinguishable from microbial fluorescence by its different emission spectra. Our spectrofluorimetric scans throughout the GISP2 ice core lead us to conclude that both microbes and nonmicrobial aerosols are deposited in discontinuous bursts, which may provide a tool for studying wind storms in the distant past.climate ͉ ice cores ͉ proxy for dust storms ͉ scanning fluorimetry ͉ N2O

Fluxes of microbes, organic aerosols, dust, sea-salt Na ions, non-sea-salt Ca ions, and methanesulfonate onto Greenland and Antarctic ice

“…climate proxy (Rohde and Price, 2007;Rohde et al, 2008). We also showed that microbes and non-Trp aerosols are deposited in discrete bursts with peak values that fluctuate on seasonal to decadal scales.…”

“…Essentially all of those spectra are consistent with the spectral shape of protein-bound Trp. See Rohde et al (2008) for experimental details, including a discussion of how we used ground-truth measurements of cells to relate cell size and concentration to fluorescence intensity. The curves in the upper right panel are color-coded to indicate the different spectral shapes for E. coli cells, bacillus spores, kaolinite clay grains, and volcanic ash.…”

“…We have recently discussed our method of determining concentrations of microbes and non-microbial aerosols based on the spectral shapes in six channels of emission wavelength resulting from fluorescence excited by our 224-nm laser (Rohde and Price, 2007;Rohde et al, 2008). We calibrated the instrument by relating the intensity of protein-bound tryptophan (Trp) autofluorescence in microbial cells to direct counts of stained cells in the GISP2 ice core from Greenland (Tung et al, 2005).…”

Microbial characterization of a subzero, hypersaline methane seep in the Canadian High Arctic

“…The origin of these plumes is under extensive debate (Lefèvre and Forget, 2009) and could be attributable to either geological or biological sources, the latter including methanogenesis by microbial communities inhabiting the Martian subsurface. For example, terrestrial methanogens and associated evidence of in situ methanogenic activity have been detected in similar Earth analogue cryo-environments such as Greenland deep subsurface glacial ice cores (Tung et al, 2005;Rohde et al, 2008) and permafrost (Rivkina et al, 2007). Laboratory microcosm analyses also indicate biological methane formation can occur at subzero temperatures in permafrost (Rivkina et al, 2007).…”

Abundance, viability and diversity of the indigenous microbial populations at different depths of the NEEM Greenland ice core

“…In addition, the microbial diversity and abundance in selected GISP2 samples differed depending on deposition climate (Miteva et al 2009). In the light of possible metabolic activity of glacial microbial populations, Price (2007) suggested that the excessively high CO 2 , N 2 O and CH 4 values measured at some GISP2 depths were due to in situ production by microorganisms (Rohde et al 2008). Systematic measurements of chlorophyll autofluorescence along the GISP2 and D4 Greenland ice cores suggested an opportunity to study the evolution of archived marine cyanobacteria back in time (Price & Bay 2012).…”