Nitrogen isotopic composition of pore water ammonium, Blake Ridge, Site 997, ODP Leg 164

Ammonium (NH4 +) concentration profiles in piston-core sediments of the Carolina Rise and Blake Ridge generally have linear concentration profiles within the sulfate reduction zone (Borowski, 1998). Deep Sea Drilling Project (DSDP) Site 533, located on the Blake Ridge, also displayed a linear ammonium concentration profile through the sulfate reduction zone and the profile linearity continues into the upper methanogenic zone to a depth of ~200 meters below seafloor (mbsf), where the first methane gas hydrates probably occur (Jenden and Gieskes, 1983; Kvenvolden and Barnard, 1983). Sediments from the Ocean Drilling Program (ODP) Leg 164 deep holes (Sites 994, 995, and 997) also exhibit linear ammonium profiles above the top of the gas hydrate zone (~200 mbsf) (Paull, Matsumoto, Wallace, et al., 1996)

Sulfide mineralization within modern, deep-sea marine sediments and oxygenation of the early Earth

The Earth’s atmosphere and oceans have not always been oxygenated. The exact pathway and timing of the oxygenation of the Earth’s early oceans is poorly constrained, although it appears that oxygenation was essentially complete by the beginning of the Cambrian (545 million years ago). Indeed, the appearance and diversification of the first animals may have been dependent on threshold levels of oxygen. Eventually we intend to use the sulfur isotopic composition of sulfide minerals (iron monosulfides and pyrite) present in sedimentary rocks to reconstruct the oxygenation of Proterozoic oceans, but first must strive to understand sulfide mineral formation in the modern ocean – specifically with reference to certain deep-sea environments. We examine the sediments of two piston cores collected over the Blake Ridge gas hydrate deposits (offshore southeastern North America) by extracting total sedimentary sulfide using chromium reduction. We use an improved titration procedure to assay for sulfide sulfur concentration that involves addition of an excess amount of potassium iodate/potassium iodide (KIO3/KI) solution in order to completely oxidize dissolved sulfide to elemental sulfur. Our results show that authigenic sulfide sulfur generally increases in concentration downcore from ~0.05 to peak concentrations approaching 0.4 weight per cent sulfur. These results are consistent with localized sulfide production at about 13 meters and rapid sulfide mineral formation there. We will further test the hypothesis by examining d34S values of authigenic sulfide minerals, expecting to see enrichments in d34S where peak sulfide concentrations occur

Nuclear thermal propulsion transportation systems for lunar/Mars exploration

Nuclear thermal propulsion technology development is underway at NASA and DoE for Space Exploration Initiative (SEI) missions to Mars, with initial near-earth flights to validate flight readiness. Several reactor concepts are being considered for these missions, and important selection criteria will be evaluated before final selection of a system. These criteria include: safety and reliability, technical risk, cost, and performance, in that order. Of the concepts evaluated to date, the Nuclear Engine for Rocket Vehicle Applications (NERVA) derivative (NDR) is the only concept that has demonstrated full power, life, and performance in actual reactor tests. Other concepts will require significant design work and must demonstrate proof-of-concept. Technical risk, and hence, development cost should therefore be lowest for the concept, and the NDR concept is currently being considered for the initial SEI missions. As lighter weight, higher performance systems are developed and validated, including appropriate safety and astronaut-rating requirements, they will be considered to support future SEI application. A space transportation system using a modular nuclear thermal rocket (NTR) system for lunar and Mars missions is expected to result in significant life cycle cost savings. Finally, several key issues remain for NTR's, including public acceptance and operational issues. Nonetheless, NTR's are believed to be the 'next generation' of space propulsion systems - the key to space exploration

New technique detects gas hydrates

As exploration and development moves into deep waters, the possibility of encountering gas hydrates within seafloor sediments becomes increasingly likely. The ability to accurately detect gas hydrates is key to producing deepwater fields, allowing operators to safely design and place offshore drilling and production platforms, subsea production equipment and flow lines, as well as pipelines

A Geologic Record of Competing Sulfate-depletion Processes Within Continental-rise Sediments Overlying Methane Gas Hydrates of the Blake Ridge Region (Continental Rise, Offshore Southeastern United States)

Geochemical signals locked within sediments and sedimentary rocks record geochemical processes through geologic time. Sulfide minerals (elemental sulfur, iron monosulfides, and pyrite) are formed within marine sediments as dissolved sulfide is produced by various geochemical processes, which include sulfate reduction and anaerobic methane oxidation (AMO). The concentration and sulfur isotopic composition (d34S) of sulfide minerals gives clues about the relative importance of these competing geochemical processes, and consequently about sedimentation rates and upward methane transport. Marine sediments of the Blake Ridge(offshore South Carolina and Georgia) contain sulfide minerals that point to AMO as an important diagenetic process both today and in the recent geological past. At the present-day methane-sulfate interface, upward-diffusing methane is consumed by reaction with downward-diffusing sulfate, producing a geochemical environment that promotes the authigenic precipitation of sulfide minerals. These sulfide minerals, mainly pyrite, are enriched in the heavy isotope of sulfur (34S), whereas solid-phase sulfide higher in the sulfate reduction zone contains more 32S. This result is consistent with larger fluxes of methane in the region derived from underlying methane gas hydrate deposits. The sedimentary record of a portion of the Blake Ridge (ODP Site 995) back to the Late Miocene (~6.2 Ma) shows that changing depositional conditions seem to emphasize sulfate reduction over AMO in progressively older sediments. Sulfide mineral concentration changes from low baseline values (0.2 weight percent) in youthful sediments to higher values (0.4 to 0.6 wt %) in older sediments. Baseline values of d34S also increase from -45‰ to -30‰ with increasing depth and sediment age. Geochemical conditions today favor more sulfide mineralization in association with AMO, whereas conditions in the past likely responded to higher delivery rates of sedimentary organic matter – conditions necessary to ultimately produce the amount of methane gas hydrates occurring within the Blake Ridge region

A geologic record of methane consumption associated with methane gas hydrates at Blake Ridge region (continental rise, offshore southeastern United States)

Geochemical signals locked within sedimentary rocks are a record of earth processes. Sulfide minerals (elemental sulfur, iron monosulfides, and pyrite) are formed within marine sediments by several different geochemical processes mediated by microbes. Investigating the concentration and sulfur isotopic composition (d34S) of sulfide minerals gives clues about the relative importance of these competing geochemical processes. Marine sediments of the Blake Ridge(offshore South Carolina and Georgia) contain sulfide minerals that point to anaerobic methane oxidation (AMO) as an important diagenetic process both today and in the recent geological past (Miocene). At the present-day methane-sulfate interface, upward-diffusing methane is consumed by reaction with downward-diffusing sulfate, producing a geochemical environment that promotes the authigenic precipitation of sulfide minerals. These sulfide minerals, mainly pyrite, are enriched in the heavy isotope of sulfur (34S), whereas sulfides higher in the sulfate reduction zone contain more 32S. This result is consistent with larger fluxes of methane in the region being produced by methane gas hydrate deposits. The sedimentary record back to the Late Miocene (~6.2 Ma) shows that changing depositional conditions seems to progressively favor sulfate reduction over AMO. Sulfide mineral amounts change from baseline values of 0.2 weight percent to 0.4 to 0.6 wt %. Baseline values of d34S also increase from -45o/oo to -30o/oo. Geochemical conditions today favor AMO whereas conditions in the past responded to loading of sedimentary organic matter – conditions necessary to produce the amount of methane gas hydrates within the Blake Ridge region

Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA

We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and sub‐fractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a Km of 41.9 µM and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution

Sulfide mineralization in deep-water marine sediments related to methane transport, methane consumption, and methane gas hydrates

Patterns of sulfide sulfur concentration and sulfur isotopic composition (d34S) are perhaps related to upward methane transport, especially in sediments underlain by methane gas hydrate deposits. Increased methane delivery augments the affect of anaerobic methane oxidation (AMO) occurring at the sulfate-methane interface (SMI). Sulfate and methane co-consumption results in production of dissolved sulfide at the interface that is eventually sequestered within sulfide minerals (elemental sulfur, iron monosulfide, pyrite). We examine the sediments of two piston cores collected over the Blake Ridge gas hydrate deposits (offshore southeastern North America) by extracting total sedimentary sulfide using chromium reduction. We use an improved titration procedure to assay for sulfide sulfur concentration that involves addition of an excess amount of potassium iodate/potassium iodide (KIO3/KI) solution in order to completely oxidize dissolved sulfide to elemental sulfur. The remaining iodine ions are then back-titrated with sodium thiosulfate solution, avoiding leakage of hydrogen sulfide gas, thus increasing measurement accuracy. Our results show that authigenic sulfide sulfur generally increases in concentration downcore from ~0.05 to peak concentrations approaching 0.4 weight per cent sulfur. These results are consistent with localized sulfide production at the SMI and rapid sulfide mineral formation there. We will further test the hypothesis by examining d34S values of authigenic sulfide minerals, expecting to see enrichments in d34S near the interface. Discrete horizons showing sulfide mineralization with 34S enrichments potentially record periods of increased methane flux, highlighting an increased role for AMO as a biogeochemical process and perhaps identifying existence of underlying gas hydrates

Data report: Carbon isotopic composition of dissolved CO2, CO2 gas, and methane, Blake-Bahama Ridge and northeast Bermuda Rise, ODP Leg 172

Carbon isotopic data of interstitial dissolved CO2 (ΣCO2), CO2 gas, and methane show that a variety of microbial diagenetic processes produce the observed isotopic trends. Anaerobic methane oxidation (AMO) is an important process near the sulfate-methane interface (SMI) that strongly influences the isotopic composition of ΣCO2 in the sulfate reduction and upper methanogenic zones, which in turn impacts methane isotopic composition. Dissolved CO2 and methane are maximally depleted in 3C near the SMI, where C values are as light as –31.8‰ and –101‰ PDB for ΣCO2 and methane, respectively. CO2 reduction links the CO2 and methane pools in the methanogenic zone so that the carbon isotopic composition of both pools evolves in concert, generally showing increasing enrichments of C with increasing depth. These isotopic trends mirror those within other methane-rich continental rise sediments worldwide