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Estimates of biogenic methane production rates in deep marine sediments at Hydrate Ridge, Cascadia Margin
Methane hydrate found in marine sediments is thought to contain gigaton quantities of methane and is
considered an important potential fuel source and climate-forcing agent. Much of the methane in hydrates is
biogenic, so models that predict the presence and distribution of hydrates require accurate rates of in situ
methanogenesis. We estimated the in situ methanogenesis rates in Hydrate Ridge (HR) sediments by coupling
experimentally derived minimal rates of methanogenesis to methanogen biomass determinations for discrete
locations in the sediment column. When starved in a biomass recycle reactor, Methanoculleus submarinus
produced ca. 0.017 fmol methane/cell/day. Quantitative PCR (QPCR) directed at the methyl coenzyme M
reductase subunit A gene (mcrA) indicated that 75% of the HR sediments analyzed contained <1,000 methanogens/
g. The highest numbers of methanogens were found mostly from sediments <10 m below seafloor. By
considering methanogenesis rates for starved methanogens (adjusted to account for in situ temperatures) and
the numbers of methanogens at selected depths, we derived an upper estimate of <4.25 fmol methane
produced/g sediment/day for the samples with fewer methanogens than the QPCR method could detect. The
actual rates could vary depending on the real number of methanogens and various seafloor parameters that
influence microbial activity. However, our calculated rate is lower than rates previously reported for such
sediments and close to the rate derived using geochemical modeling of the sediments. These data will help to
improve models that predict microbial gas generation in marine sediments and determine the potential
influence of this source of methane on the global carbon cycle
Paying to Save: Tax Withholding and Asset Allocation among Low- and Moderate-Income Taxpayers
Local Embeddedness and Economic and Social Upgrading in Madagascar's Export Apparel Industry
Intertemporal Efficiency and Equity Under Hyperbolic Preferences. Ex Ante Versus Ex Post Procrastination
Search of the Orion spur for continuous gravitational waves using a loosely coherent algorithm on data from LIGO interferometers
We report results of a wideband search for periodic gravitational waves from isolated neutron stars within the Orion spur towards both the inner and outer regions of our Galaxy. As gravitational waves interact very weakly with matter, the search is unimpeded by dust and concentrations of stars. One search disk (A) is 6.87° in diameter and centered on 20h10m54.71s+33°33′25.29′′, and the other (B) is 7.45° in diameter and centered on 8h35m20.61s-46°49′25.151′′. We explored the frequency range of 50-1500 Hz and frequency derivative from 0 to -5×10-9 Hz/s. A multistage, loosely coherent search program allowed probing more deeply than before in these two regions, while increasing coherence length with every stage. Rigorous follow-up parameters have winnowed the initial coincidence set to only 70 candidates, to be examined manually. None of those 70 candidates proved to be consistent with an isolated gravitational-wave emitter, and 95% confidence level upper limits were placed on continuous-wave strain amplitudes. Near 169 Hz we achieve our lowest 95% C.L. upper limit on the worst-case linearly polarized strain amplitude h0 of 6.3×10-25, while at the high end of our frequency range we achieve a worst-case upper limit of 3.4×10-24 for all polarizations and sky locations. © 2016 American Physical Society
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