Protodolomite was detected in sediments from Great Salt Lake (GSL), Utah, United States, that have no history of elevated temperature or pressure, conditions that are thought to promote dolomitization of sedimentary carbonates. Protodolomite was abundant in a non-oolitic sediment core from the South Arm (SA) of GSL at < 17% salinity but was rare in an oolitic sediment core collected from the North Arm (NA) of GSL at > 26% salinity. Protodolomite was also abundant in a non-oolitic NA sediment hand sample yet was absent in a nearby oolitic sediment hand sample in locations that likely receive allochthonous nutrients. Protodolomite was not detected in benthic photosynthetic mats from the SA. However, the mats comprised aragonite with halite and minimal calcite; benthic photosynthetic mats do not form in the NA. To begin to identify potential controls on the formation of protodolomite in the SA and NA of GSL, the composition and abundance of 16S rRNA gene transcripts, carbon cycling activities, and porewater geochemistry of the sediment cores were characterized. Transcripts affiliated with a dominant halophilic, heterotrophic sulfate-reducing bacterium were detected in the uppermost sections of the SA core and their abundance was positively correlated with rates of acetate oxidation/assimilation and concentrations of sulfide. Differences in the quality of organic matter between the SA and NA cores, as indicated by carbon to nitrogen ratios, indicate fresh deposition of photosynthetic biomass at the SA sediment core site but not in the NA sediment core site. Sediment grains from the SA core exhibit micrometer-sized euhedral protodolomite crystals that were not detected in the NA core. Collectively, these observations suggest that deposition of photosynthetic biomass drives the development of a sharp, anoxic lens of heterotrophic sulfate reduction. Sulfide, in turn, may promote dehydration of Mg 2+-water complexes and primary protodolomite nucleation and growth. The scarcity of dolomite in the NA sediment core may result from constraints imposed by a combination of extreme hypersalinity and depositional environment on phototrophs and sulfate reducers, their activities, and the thermodynamics of protodolomite formation.

Terrestrial icy environments have been found to preserve organic material and contain habitable niches for microbial life. The cryosphere of other planetary bodies may therefore also serve as an accessible location to search for signs of life. The Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets (WATSON) is a compact deep-UV fluorescence spectrometer for nondestructive ice borehole analysis and spatial mapping of organics and microbes, intended to address the heterogeneity and low bulk densities of organics and microbial cells in ice. WATSON can be either operated standalone or integrated into a wireline drilling system. We present an overview of the WATSON instrument and results from laboratory experiments intended to determine (i) the sensitivity of WATSON to organic material in a water ice matrix and (ii) the ability to detect organic material under various thicknesses of ice. The results of these experiments show that in bubbled ice the instrument has a depth of penetration of 10 mm and a detection limit of fewer than 300 cells. WATSON incorporates a scanning system that can map the distribution of organics and microbes over a 75 by 25 mm area. WATSON demonstrates a sensitive fluorescence mapping technique for organic and microbial detection in icy environments including terrestrial glaciers and ice sheets, and planetary surfaces including Europa, Enceladus, or the martian polar caps.ADC ¼ analog to digital converter DUV ¼ deep-UV LOD ¼ limit of detection LOQ ¼ limit of quantitation LPS ¼ laser power supply PBS ¼ phosphate-buffered saline WATSON ¼ Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets 784 ESHELMAN ET AL.

Monthly sediment trap samples collected from a deep water station (42 m) in Windermere for a period of 1 year were analyzed for 0.5 M HCl extractable and total Fe, Mn, Al, Pb, Cu, Zn, total C, N, and total solids. Concomitant algal counts showed the year to be fairly typical in terms of the known sequence of phytoplankton.The annual depositional fluxes are compared with previously determined values based on sediment studies. The ratio of the annual trap to sediment flux for Al (5 1) indicates the absence of local sediment resuspension. The ratios for Fe, Pb, and Zn (1.1, 1.4, and 1.5, but not significantly > 1) suggest some possible biogeochemical cycling at the sediment-water interface. The deposition of Fe, Al, and Pb is predominantly associated with detrital material and occurs mainly during winter. The behavior of Zn is largely independent of other variables examined. The ratios for C (1.8), total solids (2.2), N (3.2), Mn (8.6), and Cu (9.5) are all significantly > 1. The C and N values are thought to reflect the microbial breakdown of organic matter at the sediment surface and more particularly the preferential degradation of proteinaceous (i.e. N rich) material. The major influence on the deposition and recycling of Mn is its well known redox cycle involving oxidative precipitation and reductive remobilization.Cu undergoes an independent deposition-remobilization cycle, probably related to uptake by diatoms and their rapid microbial decomposition after sedimentation.

Dissolved (qO.45 pm) and particulate concentrations of Fe, Mn, Al, Cu, Pb, and Zn were measured at intervals of 2-6 weeks in rivers, sewage effluents, atmospheric deposition, and surface lake waters within the Windermere (U.K.) catchment over a 2-yr period. Factor analysis revealed a number of geochemical associations: a large proportion of the particulate Fe, Al, Pb, and Cu appears to be associated with detrital mineral and organic material in the rivers, sewage effluents, and atmospheric deposition; redox processes, probably occurring higher in the catchment, have an appreciable influence on the riverine concentrations of dissolved Fe and Mn, particulate Mn, and to a lesser extent particulate Fe and Zn; pollution terms account for most of the variance of dissolved Fe, Cu, Pb, and Zn, and particulate Cu, Pb, and Zn in the sewage effluent and atmospheric deposition data sets, respectively; and an association in the rivers of dissolved Al and Zn concentrations with discharge is probably related to catchment soil processes.Mass balances were determined for the metals, including a detailed assessment of the errors involved. An inbalance was apparent between the inputs and outputs (flushing and sedimentation), probably due to underestimation of particulate loads in the rivers. Fe, Mn, and Al were predominantly (> 90%) supplied by rivers, while Cu, Pb, and Zn received significant inputs from direct atmospheric deposition and sewage discharges. The residence times of the dissolved metals in Windermere were in the order: Cu > Zn > Pb * Fe, a sequence consistent with observations in various alpine lakes. More than 50% of the dissolved inputs of each metal was retained in the lake, except for Cu, which appeared to show a small net loss from the lake.