Methane production induced by dimethylsulfide in surface water of an upwelling ecosystem

Abstract

a b s t r a c tCoastal upwelling ecosystems are areas of high productivity and strong outgassing, where most gases, such as N 2 O and CH 4 , are produced in subsurface waters by anaerobic metabolisms. We describe seasonal CH 4 variation as well as potential mechanisms producing CH 4 in surface waters of the central Chile upwelling ecosystem (36°S). Surface waters were always supersaturated in CH 4 (from 125% up to 550%), showing a clear seasonal signal triggered by wind driven upwelling processes (austral springsummer period), that matched with the periods of high chlorophyll-a and dimethylsulfoniopropionate (DMSP) levels. Methane cycling experiments, with/without the addition of dimethylsulfide (including 13 C-DMS) and acetylene (a nonspecific inhibitor of CH 4 oxidation) along with monthly measurements of CH 4 , DMSP and other oceanographic variables revealed that DMS can be a CH 4 precursor. Net CH 4 cycling rates (control) fluctuated between À0.64 and 1.44 nmol L À1 d À1 . After the addition of acetylene, CH 4 cycling rates almost duplicated relative to the control, suggesting a strong methanotrophic activity. With a spike of DMS, the net CH 4 cycling rate significantly increased relative to the acetylene and control treatment. Additionally, the d 13 C values of CH 4 at the end of the incubations (after addition of 13 C enriched-DMS) were changed, reaching À32‰ PDB compared to natural values between À44‰ and À46‰ PDB. These findings indicate that, in spite of the strong CH 4 consumption by methanotrophs, this upwelling area is an important source of CH 4 to the atmosphere. The effluxes are derived partially from in situ surface production and seem to be related to DMSP/DMS metabolism.

Methane distribution and oxidation around the Lena Delta in summer 2013

“…For lakes and oceans, a link is reported between photosynthesis and methane production (Tang et al, 2014), or even evidence of methane production by marine algae (Lenhart et al, 2016), and this activity results in oversaturated methane concentrations in surface waters. Dimethylsulfoniopropionate (DMSP), which is formed as an osmoprotectant and antioxidant in microalgae, could also be a source of in situ methane production (Florez-Leiva et al, 2013). However, the contributions of photosynthesis and DMSP production to in situ methane concentrations remain to be established.…”

Climate relevant trace gases (N2O and CH4) in the Eurasian Basin (Arctic Ocean)

“…Although it remains unclear at present how CH 4 is formed in sea ice, it is possible that CH 4 could be produced via the methylotrophic pathway mediated by methylated compounds (Schäfer, 2007;Sun et al, 2011). One candidate for methylated compounds is DMSP and/or DMS, as indicated in the surface water by Damm et al (2010) and Florez-Leiva et al (2013). This assumption is supported by the extensive production of DMSP, a precursor for CH 4 production, which is produced as an osmolyte, or cryoprotectant by sea ice algae during primary production in the sea ice (Kirst et al, 1991;Levasseur et al, 1994).…”

“…Karl and Tilbrook (1994) found that methanogens living in association with zooplankton and fish fecal pellets, as well as other particulate matter, may resolve this paradox. More recently, CH 4 formation was reported to proceed the metabolism of organic methyl-compounds of methylotrophs, such as methylphosphonate (MPn) (Karl et al, 2008), dimethylsulfoniopropionate (DMSP) (Damm et al, 2010), and dimethylsulphide (DMS) (Florez-Leiva et al, 2013). Other geological/thermogenic production processes, such as CH 4 hydrates in continental margin sediments, mud volcanoes, and cold seeps, could also be responsible for CH 4 release, as is the case in the Arctic Ocean, which has been the focus of scientific interest in previous decades (Westbrook et al, 2009;Shakhova et al, 2010;Smith et al, 2014).…”

Dissolved Methane Distribution in the Reloncaví Fjord and Adjacent Marine System During Austral Winter (41°–43° S)

“…In addition, methylotrophic methanogens that use the products generated from the degradation of methylated amine in microalgae could be responsible for the production of CH 4 (Oremland et al 1982;King et al 1983;King 1984). Recently, this mechanism has been described using substrates as DMSP (Damm et al 2010) and also DMS (Florez-Leiva et al 2013). CH 4 content and emissions in aquatic systems reflect the characteristics of the surrounding catchment area, such as topography, soil type, and texture, as well as land use and other anthropogenic activities (Jones and Mulholland 1998), and also the features of the adjacent marine system, such as tidal and wave movements and geomorphology (US EPA 2010).…”

“…CH 4 is generally formed by methanogens during anaerobic organic matter degradation (Reeburgh 2007), or by methylotrophs (Sowers and Ferry 1983;Sun et al 2011). CH 4 formation via methylotrophy occurs by transformations and cycling of methyl compounds, mediated by bacterioplankton, such as methylphosphonate (MPn) (Karl et al 2008), dimethylsulphoniopropionate (DMSP) (Damm et al 2010), and dimethyl sulfide (DMS) (Florez-Leiva et al 2013). In addition, CH 4 can be consumed (oxidized) via aerobic methanothophy (Hanson and Hanson 1996), or when O 2 is exhausted, NO 3 − and SO 4 2− act as electron acceptors (Valentine 2011).…”