Abstract
Abstract. Here we present results of the first comprehensive study of sulphur compounds and methane in the oligotrophic tropical western Pacific Ocean. The concentrations of dimethylsuphide (DMS), dimethylsulphoniopropionate (DMSP), dimethylsulphoxide (DMSO), and methane (CH4), as well as various phytoplankton marker pigments in the surface ocean were measured along a north–south transit from Japan to Australia in October 2009. DMS (0.9 nmol L−1), dissolved DMSP (DMSPd, 1.6 nmol L−1) and particulate DMSP (DMSPp, 2 nmol L−1) concentrations were generally low, while dissolved DMSO (DMSOd, 4.4 nmol L−1) and particulate DMSO (DMSOp, 11.5 nmol L−1) concentrations were comparably enhanced. Positive correlations were found between DMSO and DMSP as well as DMSP and DMSO with chlorophyll a, which suggests a similar source for both compounds. Similar phytoplankton groups were identified as being important for the DMSO and DMSP pool, thus, the same algae taxa might produce both DMSP and DMSO. In contrast, phytoplankton seemed to play only a minor role for the DMS distribution in the western Pacific Ocean. The observed DMSPp : DMSOp ratios were very low and seem to be characteristic of oligotrophic tropical waters representing the extreme endpoint of the global DMSPp : DMSOp ratio vs SST relationship. It is most likely that nutrient limitation and oxidative stress in the tropical western Pacific Ocean triggered enhanced DMSO production leading to an accumulation of DMSO in the sea surface. Positive correlations between DMSPd and CH4, as well as between DMSO (particulate and total) and CH4, were found along the transit. We conclude that DMSP and DMSO and/or their degradation products might serve as potential substrates for CH4 production in the oxic surface layer of the western Pacific Ocean.
Highlights
IntroductionSciencesOceanic dimethylsulphide (DMS) is the most important source of biogenic sulphur to the atmosphere and, the oceanic DMS fluxOcconestaitnuteSs aciseignnicfiecant component of the global sulphur cycle, see e.g. Vogt and Liss (2009).The oceanic distributions of DMS and its major precursor dimethylsulphoniopropionate (DMSP) result from a complex interplay of biological and non-biological pathways, such as formation by phytoplankton and microbial cleavage of DMSP to DMS on the one haSndo, alindd mEiacrrotbhial consumption as well as photochemical oxidation of DMS and its loss to the atmosphere on the other hand (Simo, 2004; Stefels et al., 2007; Vogt and Liss, 2009; Schafer et al, 2010)
Phytoplankton biomass given as total chlorophyll a (TChl a concentration in mg m−3) was very low (0.05–0.25 mg m−3), except for north of 36◦ N (TChl a > 1 mg m−3) where colder waters (16–20 ◦C) of the Oyashio Current were observed, in the vicinity of islands and in the region of the Great Barrier Reef (Fig. 1b)
Measured concentrations of marker pigments and chlorophyll a (Chl a) along the transit were used to calculate the biomass of the major phytoplankton groups (Fig. 2)
Summary
SciencesOceanic dimethylsulphide (DMS) is the most important source of biogenic sulphur to the atmosphere and, the oceanic DMS fluxOcconestaitnuteSs aciseignnicfiecant component of the global sulphur cycle, see e.g. Vogt and Liss (2009).The oceanic distributions of DMS and its major precursor dimethylsulphoniopropionate (DMSP) result from a complex interplay of biological and non-biological pathways, such as formation by phytoplankton and microbial cleavage of DMSP to DMS on the one haSndo, alindd mEiacrrotbhial consumption as well as photochemical oxidation of DMS and its loss to the atmosphere on the other hand (Simo, 2004; Stefels et al., 2007; Vogt and Liss, 2009; Schafer et al, 2010). C. Zindler et al.: Interactions along a north–south transit in the western Pacific Ocean and DMSO play important roles in the oceanic nutrient cycle. Zindler et al.: Interactions along a north–south transit in the western Pacific Ocean and DMSO play important roles in the oceanic nutrient cycle They are ubiquitous in the ocean and are responsible for the transfer and cycling of sulphur and carbon between different trophic levels in plankton (Kiene et al, 2000; Simo, 2004; Simoet al., 2002; Yoch, 2002). DMSP can supply between 8 and 15 % of carbon for bacteria and can serve as an energy source, which makes it the most important single substrate for marine bacterioplankton (Kiene et al, 2000; Simoet al., 2002). DMSO seems to be an important substrate for specialized bacteria that use DMSO as carbon or electron source (Lee et al, 1999a; Simoet al., 2000)
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