Deep-Sea Exploration of the US Gulf of Mexico with NOAA Ship Okeanos Explorer

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Paleolimnology in the High Arctic - implications for the exploration of Mars

Paleolimnology provides information on the past chemical, physical and biological nature of water bodies. In polar regions, where global climatic changes can be exacerbated compared with lower latitudes, the science has become important for reconstructing past changes and in so doing, predicting possible effects of future changes. Owing to the association of life with water bodies, particularly stable water bodies sustained over many millennia, paleolake regions on the surface of Mars are of exobiological importance. In this mini-review, we use experience gathered in the High Arctic to describe the importance of paleolimnology in the Earth's polar regions as it pertains to the future application of this science to robotic and human exploration missions to the planet Mar

Biosignatures associated with freshwater microbialites

Freshwater microbialites (i.e., lithifying microbial mats) are quite rare in northern latitudes of the North American continent, with two lakes (Pavilion and Kelly Lakes) of southeastern BC containing a morphological variety of such structures. We investigated Kelly Lake microbialites using carbon isotope systematics, phospholipid fatty acids (PLFAs) and quantitative PCR to obtain biosignatures associated with microbial metabolism. δC values (mean δC -4.9 ± 1.1‱, = 8) were not in isotopic equilibrium with the atmosphere; however, they do indicate C-depleted inorganic carbon into Kelly Lake. The values of carbonates on microbialite surfaces (δC) fell within the range predicted for equilibrium precipitation from ambient lake water δC (-2.2 to -5.3‱). Deep microbialites (26 m) had an enriched δC value of -0.3 ± 0.5‱, which is a signature of photoautotrophy. The deeper microbialites (>20 m) had higher biomass estimates (via PLFAs), and a greater relative abundance of cyanobacteria (measured by 16S copies via qPCR). The majority of PLFAs constituted monounsaturated and saturated PLFAs, which is consistent with gram-negative bacteria, including cyanobacteria. The central PLFA δC values were highly depleted (-9.3 to -15.7‱) relative to δC values of bulk organic matter, suggesting a predominance of photoautotrophy. A heterotrophic signature was also detected via the depleted and 15:0 lipids (-3.2 to -5.2‱). Based on our carbonate isotopic biosignatures, PLFA, and qPCR measurements, photoautotrophy is enriched in the microbialites of Kelly Lake. This photoautotrophy enrichment is consistent with the microbialites of neighboring Pavilion Lake. This indication of photoautotrophy within Kelly Lake at its deepest depths raises new insights into the limits of measurable carbonate isotopic biosignatures under light and nutrient limitations

Multiple parameters enable deconvolution of water-rock reaction paths in low-temperature vent fluids of the Kamaʻehuakanaloa (Lōʻihi) seamount

International audienceNew data for vent-fluid compositions at Kamaʻehuakanaloa including CO2 and CH4 concentrations Persistent vent-fluid composition for three decades Geochemical modeling of water-rock-gas reactions that produce the 20-50 ºC vent fluids Low-temperature basalt alteration results in high Fe/low H2S vent fluids Key role of active intraplate volcanoes on ocean Fe-cycle Abstract The contribution of venting fluids at mid-ocean ridges to global ocean biogeochemical cycles is well recognized. Less is known about the role of magmatically-active intra-plate volcanoes. In this study, new compositional fluid data were acquired from 20-50 ºC vent fluids at Kamaʻehuakanaloa (previously known as Lōʻihi) seamount (Hawai'ian archipelago) and used to model the wide diversity of reaction conditions capable of producing the Fe-, Si-and CO2-rich vent fluids observed. Our conceptual model includes a first step where seawater reacts with increasing proportions of basalt and gas as the temperature increases, and a second step where the resulting hydrothermal fluid mixes with unaltered seawater while continuing to react with basalt until the fluid mixture reaches 20 ºC. A series of reaction paths were chosen to vary: the maximum temperature during Step 1 (50 to 400 ºC) and the proportions of basalt and gas reacting; the degree, F, of low-temperature basalt alteration during Step 2, which corresponds to the extent to which the hot fluid generated during Step 1 continues to react with more basalt as it ascends to the seafloor. Our model shows that the 20-50 ºC vent fluids are greatly dependent on the degree of low-temperature basalt alteration during fluid upwelling. Indeed, the compositions of Kamaʻehuakanaloa vent fluids cannot be reconciled with a general model of subsurface mechanical mixing of high-temperature end-member vent fluid and seawater alone. Instead, they require both subsurface equilibrium mixing between a ≥350 ºC hydrothermal fluid end-member and seawater and further basalt alteration that must occur as the fluid mixture rises to the seafloor. Although it involves only ~4% of the amount of basalt having reacted during Step 1, this lowtemperature basalt alteration during Step 2 leads to the characteristic enrichments in Fe observed in the Kamaʻehuakanaloa vent fluids and a concomitant depletion in H2S. We hypothesize that low-temperature basalt alteration during an extended path of fluid upwelling through the subseafloor might arise as a direct consequence of the height and steep-sloped topography of Kamaʻehuakanaloa seamount. If correct, this suggests a more general case -that input from magmatically-active intraplate volcanoes, which have been relatively overlooked throughout the history of submarine vent investigations to date, could differ significantly from global mid-ocean ridge fluxes and contribute more substantially than previously recognized to the global ocean Fe cycle