Bacterial production of humic-like fluorescent dissolved organic matter (FDOM H ) was examined in a 90 d culture experiment using a bacterial assemblage collected from coastal water with artificial seawater amended by glucose. A rapid decrease in dissolved organic carbon concentration was noticed during Days 1 to 5, and this coincided with an increase in bacterial numbers. The increase in FDOM H , which was determined by Excitation-Emission Matrix Spectroscopy (EEMS), was observed by Day 20, showing the production of FDOM H by bacteria. This increase lagged behind the increase in bacterial numbers, suggesting that the production of

No abstract

Concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS), and DMS flux are reported for the Great Barrier Reef (GBR), Great Barrier Reef Lagoon (GBRL), and Coral Sea. Generally higher concentrations of dimethylsulfoniopropionate and DMS occurred in coral reef waters, compared with GBRL concentrations. DMS flux from GBR coral reefs in summer ranged from nondetectable to 153 μmol m−2 d−1 (mean 6.4), while winter fluxes ranged from 0.02 to 15 μmol m−2 d−1 (mean 2.4). No significant seasonal difference in DMS flux occurred for the GBRL. High DMSw concentrations and DMS fluxes periodically occur at coral reefs during very low tides and elevated sea surface temperatures (SSTs). For the GBRL and GBR coral reefs there was a significant correlation between seawater DMSw concentrations and SST (p < 0.001), up to temperatures of 30 °C. During coral bleaching DMS flux from reefs almost completely shuts down when SSTs are >30 °C. The GBRL and associated coral reefs emit 439 and 32 MmolS per year, respectively. Cyclones on average produce 170 MmolS to the GBR atmosphere in summer. This amount can markedly increase during severe cyclones such as severe tropical Cyclone Debbie in March 2017. Overall, the annual DMS emission estimate from the GBRL and coral reefs in the GBR is 0.64 GmolS, with cyclones contributing 27% or greater of the annual emission estimate, depending on the cyclone intensity. Oxidation of atmospheric DMS can potentially affect solar radiation, SSTs, low‐level cloud cover, and rainfall causing cooling and warming of the climate in the GBR region as recent modeling predicts.

c Dimethylsulfoniopropionate (DMSP) is mainly produced by marine phytoplankton but is released into the microbial food web and degraded by marine bacteria to dimethyl sulfide (DMS) and other products. To reveal the abundance and distribution of bacterial DMSP degradation genes and the corresponding bacterial communities in relation to DMS and DMSP concentrations in seawater, we collected surface seawater samples from DMS hot spot sites during a cruise across the Pacific Ocean. We analyzed the genes encoding DMSP lyase (dddP) and DMSP demethylase (dmdA), which are responsible for the transformation of DMSP to DMS and DMSP assimilation, respectively. The averaged abundance (؎standard deviation) of these DMSP degradation genes relative to that of the 16S rRNA genes was 33% ؎ 12%. The abundances of these genes showed large spatial variations. dddP genes showed more variation in abundances than dmdA genes. Multidimensional analysis based on the abundances of DMSP degradation genes and environmental factors revealed that the distribution pattern of these genes was influenced by chlorophyll a concentrations and temperatures. dddP genes, dmdA subclade C/2 genes, and dmdA subclade D genes exhibited significant correlations with the marine Roseobacter clade, SAR11 subgroup Ib, and SAR11 subgroup Ia, respectively. SAR11 subgroups Ia and Ib, which possessed dmdA genes, were suggested to be the main potential DMSP consumers. The Roseobacter clade members possessing dddP genes in oligotrophic subtropical regions were possible DMS producers. These results suggest that DMSP degradation genes are abundant and widely distributed in the surface seawater and that the marine bacteria possessing these genes influence the degradation of DMSP and regulate the emissions of DMS in subtropical gyres of the Pacific Ocean. D imethylsulfoniopropionate (DMSP), the precursor of dimethylsulfide (DMS), is mainly produced by marine phytoplankton, marine macroalgae, and a few angiosperms in the ocean (1-3) and is an important carbon and sulfur source for marine bacteria (4). After DMSP has been released, it is mainly assimilated and degraded by marine bacteria (5, 6). Phytoplankton and their predators also degrade DMSP to a certain extent (7,8). Once incorporated into bacterial cells, DMSP is degraded via two major pathways: a demethylation pathway involving DMSP demethylase, encoded by dmdA (9), and a cleavage pathway involving several different ddd (DMSP-dependent DMS) (dddD, dddL, dddP, dddQ, dddY, and dddW) genes (10-15). dmdA, the first DMSP degradation gene identified, is the most widely distributed DMSP degradation gene. It was reported that approximately 60% of marine bacteria in the open ocean and coastal waters contain this gene (16). dmdA genes, which are found mainly in members of the SAR11, SAR116, Gammaproteobacteria, and Roseobacter clades (16-19), can be grouped into five clades and 14 subclades based on the genes' nucleotide sequences (16,20).In the cleavage pathway, bacteria transform DMSP to DMS. Aerosols formed from the oxidati...

We developed a new method for in situ measurement of air-sea fluxes of multiple volatile organic compounds (VOCs) by combining proton transfer reaction-mass spectrometry (PTR-MS) and gradient flux (GF) technique. The PTR-MS/GF system was first deployed to determine the air-sea flux of VOCs in the open ocean of the western Pacific, in addition to carbon dioxide and water vapor. Each profiling at seven heights from the ocean surface up to 14 m took 7 min. In total, 34 vertical profiles of VOCs in the marine atmosphere just above the ocean surface were obtained. The vertical gradient observed was significant for dimethyl sulfide (DMS) and acetone with the best-fit curves on quasi-logarithmic relationship. The mean fluxes of DMS and acetone were 5.5 ± 1.5 and 2.7 ± 1.3 μmol/m(2)/day, respectively. These fluxes are in general in accordance with those reported by previous expeditions.