Production of Dibromomethane and Changes in the Bacterial Community in Bromoform-Enriched Seawater.

The responses of bacterial communities to halocarbon were examined using a 28-d incubation of bromoform- and methanol-enriched subarctic surface seawater. Significant increases were observed in dibromomethane concentrations and bacterial 16S rRNA gene copy numbers in the treated substrates incubated for 13 d. The accumulated bacterial community was investigated by denaturing gradient gel electrophoresis and amplicon analyses. The dominant genotypes corresponded to the genera Roseobacter, Lentibacter, and Amylibacter; the family Flavobacteriaceae; and the phylum Planctomycetes, including methylotrophs of the genus Methylophaga and the family Methylophilaceae. Therefore, various phylotypes responded along with the dehalogenation processes in subarctic seawater.

The conservative behavior of dissolved organic carbon in surface waters of the southern Chukchi Sea, Arctic Ocean, during early summer.

The spatial distribution of dissolved organic carbon (DOC) concentrations and the optical properties of dissolved organic matter (DOM) determined by ultraviolet-visible absorbance and fluorescence spectroscopy were measured in surface waters of the southern Chukchi Sea, western Arctic Ocean, during the early summer of 2013. Neither the DOC concentration nor the optical parameters of the DOM correlated with salinity. Principal component analysis using the DOM optical parameters clearly separated the DOM sources. A significant linear relationship was evident between the DOC and the principal component score for specific water masses, indicating that a high DOC level was related to a terrigenous source, whereas a low DOC level was related to a marine source. Relationships between the DOC and the principal component scores of the surface waters of the southern Chukchi Sea implied that the major factor controlling the distribution of DOC concentrations was the mixing of plural water masses rather than local production and degradation.

Laterally spreading iron, humic-like dissolved organic matter and nutrients in cold, dense subsurface water of the Arctic Ocean.

The location and magnitude of oceanic iron sources remain uncertain owing to a scarcity of data, particularly in the Arctic Ocean. The formation of cold, dense water in the subsurface layer of the western Arctic Ocean is a key process in the lateral transport of iron, macronutrients, and other chemical constituents. Here, we present iron, humic-like fluorescent dissolved organic matter, and nutrient concentration data in waters above the continental slope and shelf and along two transects across the shelf-basin interface in the western Arctic Ocean. We detected high concentrations in shelf bottom waters and in a plume that extended in the subsurface cold dense water of the halocline layer in slope and basin regions. At σθ = 26.5, dissolved Fe, humic-like fluorescence intensity, and nutrient maxima coincided with N* minima (large negative values of N* indicate significant denitrification within shelf sediments). These results suggest that these constituents are supplied from the shelf sediments and then transported laterally to basin regions. Humic dissolved organic matter probably plays the most important role in the subsurface maxima and lateral transport of dissolved Fe in the halocline layer as natural Fe-binding organic ligand.

Equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) for sensitive, high-resolution measurement of dimethyl sulfide dissolved in seawater.

We developed an equilibrator inlet-proton transfer reaction-mass spectrometry (EI-PTR-MS) method for fast detection of dimethyl sulfide (DMS) dissolved in seawater. Dissolved DMS extracted by bubbling pure nitrogen through the sample was continuously directed to the PTR-MS instrument. The equilibration of DMS between seawater and the carrier gas, and the response time of the system, were evaluated in the laboratory. DMS reached equilibrium with an overall response time of 1 min. The detection limit (50 pmol L(-1) at 5 s integration) was sufficient for detection of DMS concentrations in the open ocean. The EI-PTR-MS instrument was deployed during a research cruise in the western North Pacific Ocean. Comparison of the EI-PTR-MS results with results obtained by means of membrane tube equilibrator-gas chromatography/mass spectrometry agreed reasonably well on average (R(2) = 0.99). EI-PTR-MS captured temporal variations of dissolved DMS concentrations, including elevated peaks associated with patches of high biogenic activity. These results demonstrate that the EI-PTR-MS technique was effective for highly time-resolved measurements of DMS in the open ocean. Further measurements will improve our understanding of the biogeochemical mechanisms of the production, consumption, and distribution of DMS on the ocean surface and, hence, the air-sea flux of DMS, which is a climatically important species.

Development of a silicone membrane tube equilibrator for measuring partial pressures of volatile organic compounds in natural water.

Methods for determining volatile organic compounds (VOCs) in water and air are required so that the VOCs' fluxes in water environments can be estimated. We developed a silicone membrane tube equilibrator for collecting gas-phase samples containing VOCs at equilibrium with natural water. The equilibrator consists of six silicone tubes housed in a polyvinyl chloride pipe. Equilibrated air samples collected from the equilibrator were analyzed with an automated preconcentration gas chromatography-mass spectrometry system for hourly measurements of VOC partial pressures. The partial pressures of all the target VOCs reached equilibrium within 1 h in the equilibrator. The system was used to determine VOC partial pressures in Lake Kasumigaura, a shallow eutrophic lake with a high concentration of suspended particulate matter (SPM). Compressed air was used daily to remove SPM deposited on the inner wall of the equilibrator and to maintain the equilibrium conditions for more than a week without the need to shut the system down. CH2Br2, CHCl3, CHBrCl2, CH2BrCl, C2H5I, C2Cl4, CH3I, and CH3Br in the lake were supersaturated with respect to the air, whereas CH3CI was undersaturated. CHCl3 had the highest flux (6.2 nmol m(-2) hr(-1)) during the observation period.