Distribution and variability of dissolved hydrogen in the Mediterranean Sea

Hydrogen is one of the most interesting of the oceanic reduced gases because of its important role in both microbial nitrogen fixation and the anaerobic microbial food chain. A recent investigation in the Mediterranean Sea and Gulf of Cadiz on the USNS Bartlett has confirmed previous studies showing warm ocean waters to be supersaturated relative to atmospheric equilibrium in the mixed layer and undersaturated at depth...

The diversity of sulfide oxidation and sulfate reduction genes expressed by the bacterial communities of the Cariaco Basin, Venezuela

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Open Microbiology Journal 10 (2016): 140-149, doi:10.2174/1874285801610010140.Qualitative expression of dissimilative sulfite reductase (dsrA), a key gene in sulfate reduction, and sulfide:quinone oxidoreductase (sqr), a key gene in sulfide oxidation was investigated. Neither of the two could be amplified from mRNA retrieved with Niskin bottles but were amplified from mRNA retrieved by the Deep SID. The sqr and sqr-like genes retrieved from the Cariaco Basin were related to the sqr genes from a Bradyrhizobium sp., Methylomicrobium alcaliphilum, Sulfurovum sp. NBC37-1, Sulfurimonas autotrophica, Thiorhodospira sibirica and Chlorobium tepidum. The dsrA gene sequences obtained from the redoxcline of the Cariaco Basin belonged to chemoorganotrophic and chemoautotrophic sulfate and sulfur reducers belonging to the class Deltaproteobacteria (phylum Proteobacteria) and the order Clostridiales (phylum Firmicutes).Support for this work came from NSF grant MCB03-47811 to AYC, MIS, and GTT and NSF grant OCE-1061774 to VPE and CT

Interannual and Subdecadal Variability in the Nutrient Geochemistry of the Cariaco Basin

The CARIACO Ocean Time Series program has made monthly measurements of oxygen, nutrients, and carbon system parameters (∑CO2, alkalinity, pH) in the Cariaco Basin since 1996. At the same time, sediment traps have collected settling particles at four to five depths ranging from 150 to 1,200 m. The depth of the transition from oxic to anoxic conditions has fluctuated dramatically over the time series due to changes in the occurrence of Caribbean water intrusions into the deep basin. Nutrient concentrations in the deep basin have increased steadily with time in a proportion reflective of the elemental ratios in the settling organic matter, although N:P ratios in the water column (approximately 16:1) differ from ratios in the accumulating nutrients (11:1) and the settling flux (ranging between 5:1 and 12.5:1). This difference is likely due to changes in the source material for remineralization, either because of sizeable ecosystem changes or changes in the relative importance of the terrestrial input of inorganic P or scavenging of P by mineral precipitation near the oxic/anoxic interface. Alternatively, there may have been changes in the degree of preferential remineralization of P

Determining the flux of methane into Hudson Canyon at the edge of methane clathrate hydrate stability

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 3882–3892, doi:10.1002/2016GC006421.Methane seeps were investigated in Hudson Canyon, the largest shelf-break canyon on the northern U.S. Atlantic Margin. The seeps investigated are located at or updip of the nominal limit of methane clathrate hydrate stability. The acoustic identification of bubble streams was used to guide water column sampling in a 32 km2 region within the canyon's thalweg. By incorporating measurements of dissolved methane concentration with methane oxidation rates and current velocity into a steady state box model, the total emission of methane to the water column in this region was estimated to be 12 kmol methane per day (range: 6–24 kmol methane per day). These analyses suggest that the emitted methane is largely retained inside the canyon walls below 300 m water depth, and that it is aerobically oxidized to near completion within the larger extent of Hudson Canyon. Based on estimated methane emissions and measured oxidation rates, the oxidation of this methane to dissolved CO2 is expected to have minimal influences on seawater pH.National Science Foundation Grant Number: OCE-1318102; U.S. Department of Energy award Grant Numbers: DE-FE0013999 and NSF OCE-1352301, DOE-USGS, DE-FE0002911 and DE-FE00058062017-04-1

The marine geochemistry of methane

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August, 1977In the highly productive coastal surface waters near Walvis Bay, methane is present in concentrations considerably above those which would be predicted from solubility equilibrium with the atmosphere. A one dimensional diffusive model and a one dimensional horizontal advection diffusion model were used to describe the methane distribution. Evaluation of the model fits to the data suggests that both advective supply of methane-rich coastal waters and in situ biological methane production are important sources for the mixed layer methane excess. The complexity of the hydrographic regime near Walvis Bay makes it impossible to make a quantitative estimate of the rate of methane production. In the less productive Murray-Wilkinson Basin in the Gulf of Maine, a mixed layer methane excess is also observed. Methane concentrations are closely correlated with hydrographic parameters and the source of methane at a middepth maximum appears to be the highly anoxic sediments in the adjoining Franklin Basin. Diffusion of methane from the middepth maximum is probably adequate to maintain the surface methane excess against loss across the air-sea interface. Coastal waters are frequently enriched in methane, and it has been shown that advective supply of these methane-rich waters may be a significant source of methane for the mixed layer near the coast. Thus the widespread occurrence of a methane maximum at the base of the mixed layer in the open ocean, coupled with surface waters typically 30-70% supersaturated with respect to solubility equilbrium, suggests that advective supply of methane might be an important methane source for the open ocean as well. However, a study of the western subtropical Atlantic shows that advective transport can probably supply only a fraction of the methane present in the maximum. Also the loss of methane across the air-sea interface was observed to be twenty times greater than the flux from the maximum. Thus in situ methane production must be very important to the open ocean methane distribution. A series of phytoplankton culture experiments demonstrated that cultures of both Coccolithus huxleyi and Thalassiosira pseudonana produce trace amounts of methane during logarithmic growth. (Because the cultures are highly oxygenated, anaerobic methane bacteria can be neglected as methane sources. However heterotrophic bacteria cannot be excluded as possible sources of methane to the cultures.) After three algal generations, the rate of methane increase closely parallels the growth curve suggesting that the methane is in fact coming from the algae. A methane production rate of 2 x 10-10 nmole methane/viable cell/hr was calculated from the data. This rate is three to four orders of magnitude slower than the rates of oxygen consumption and glutamate and glucose uptake measured by other workers. for algae and bacteria. The methane production rate calculated from the culture experiments is the correct order of magnitude to account for the methane production occurring in the open ocean. Methane is present in quite low concentrations in the deep ocean. By calculating water mass ages from GEOSECS and other data, it is possible to estimate methane consumption rates in the deep sea. Methane consumption is rapid at first (probably greater than 0.06 nmole/l/yr). At depth consumption appears extremely slow. This may be due to the fact that the methane concentrations in the deep sea are so low that methane oxidizing bacteria cannot use methane as a substrate, or due to reduced metabolic activity in the bacteria at the high pressures and low temperatures of the sea floor. Methane is present in very high concentrations in anoxic basins, indicating that methanogenic bacteria are active. However, near the anoxic-oxic interface in both the Black Sea and the Cariaco Trench a one dimensional advection diffusion model predicts that methane consumption is occurring in the anoxic zone. In the Black Sea the methane depletion may be indicative of the presence of rapid methane oxidation near the Bosporus overflow. However in the Cariaco Trench the validity of such an explanation is difficult to evaluate since the overflow process is so poorly understood. A box model for the Trench has been developed which incorporates time dependence and supply of chemical species to the water from the sediments at all depths in the Trench. This model can explain the silica and sulfide data quite well, but methane depletion near the interface, relative to the model predictions, still occurs. Thus either anaerobic methane oxidation or decreased methane production in the sediments must be hypothesized.Financial support was provided by an NSF Graduate Student Fellowship and a research fellowship from Woods Hole Oceanographic Institution. Field and laboratory work were supported by NSF Doctoral Dissertation Support Grant DES75-0273l, ONR Contract NOOOl4-74-C0262, NR 083-004. and the Woods Hole Oceanographic Institution Education Office

Methane production in the waters off Walvis Bay

Also published as: Journal of Geophysical Research, Vol. 82, No. 31, October 20, 1977, pp. 4947-4953Nine stations were occupied in the vicinity of Walvis Bay, Namibia, during a detailed study of the distribution of methane in this highly productive coastal environment. The principal features of the observed coastal methane distribution included ( I) excess methane in the mixed layer of from 2 times to greater than 300 times solubility equilibrium with the atmosphere, (2) a subsurface maximum, located in the top of the pycnocline, at which concentrations ranged from 2.6 to 440 times solubility equilibrium. (3) an intermediate depth minimum, where concentrations were comparable to those offshore at similar depths and which we attribute to the influence of onshore movement of subsurface offshore water, and (4) a bottom maximum, which we attribute to input of methane to the water column from the anoxic sediments in the Walvis Bay area. An attempt was made to identify the relative importance for methane supply to the coastal mixed layer of in situ biological production and of eddy diffusive and advective transport of methane-rich water which has been in contact with the bottom at the coast. Calculations suggest that both in situ production and physical processes are major sources of excess methane for the highly productive coastal surface waters. However, the complicated circulation patterns make quantification extremely difficult.Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004 and for the National Science Foundation under Grant DES 75-02?31