Sulfur isotope variability of oceanic DMSP generation and its contributions to marine biogenic sulfur emissions

Abstract

Oceanic dimethylsulfoniopropionate (DMSP) is the precursor to dimethylsulfide (DMS), which plays a role in climate regulation through transformation to methanesulfonic acid (MSA) and nonseasalt sulfate (NSS-SO 4 2− ) aerosols. Here, we report measurements of the abundance and sulfur isotope compositions of DMSP from one phytoplankton species (Prorocentrum minimum) and five intertidal macroalgal species (Ulva lactuca, Ulva linza, Ulvaria obscura, Ulva prolifera, and Polysiphonia hendryi) in marine waters. We show that the sulfur isotope compositions (δ 34 S) of DMSP are depleted in 34 S relative to the source seawater sulfate by ∼1-3‰ and are correlated with the observed intracellular content of methionine, suggesting a link to metabolic pathways of methionine production. We suggest that this variability of δ 34 S is transferred to atmospheric geochemical products of DMSP degradation (DMS, MSA, and NSS-SO 4 2− ), carrying implications for the interpretation of variability in δ 34 S of MSA and NSS-SO 4 2− that links them to changes in growth conditions and populations of DMSP producers rather than to the contributions of DMS and non-DMS sources. COO − ] is a secondary metabolite that is produced and stored in large amounts by marine macroalgae (1) and microalgae (2). This β-sulfonium compound is widespread among marine taxa but is particularly abundant within specific groups of phytoplankton, zooplankton, macroalgae, halophytic plants, macroinvertebrates, and fishes (3-5). DMSP plays important ecophysiological functions in marine algae by acting as an antioxidant (6), a cryoprotectant, an osmolyte, and a precursor to an activated defense system (3). It is also an important carbon and sulfur source for marine bacterioplankton (7).The synthesis of DMSP by algae has been reviewed previously (3,8). It starts with the assimilation of seawater sulfate into the cytoplasm. The sulfate is subsequently transported into the chloroplasts, where it is reduced to sulfide in the presence of glutathionine and then transformed into cysteine. Cysteine is used to synthesize methionine, which is then transformed into DMSP via one of three pathways that differ among taxonomic groups of plants and algae (9-12). Thus, the biosynthesis of DMSP ultimately depends on the activity of the sulfate assimilation pathway; however, little is known about how DMSP synthesis differs among algae from diverse origins, except that the whole molecule is derived from sulfur amino acids.DMSP and its cleavage product dimethylsulfide [DMS; (CH 3 ) 2 S] have attracted much research interest because of their possible role in climate regulation (13,14). Since the introduction of the Charlson, Lovelock, Andreae, Warren (CLAW) hypothesis, which argues for feedback between biological DMS production, Earth's solar radiation, and the regulation of global climate (15), there has been an increasing emphasis by environmental scientists on determining the strength of the sea-to-air biogeochemical sources of DMS. This sea-to-air exchange of DMS is mediated through turbu...

Sulfur isotope homogeneity of oceanic DMSP and DMS

“…Even lower δ 34 S of DMSP (+11.3‰) was recorded in a salt marsh on Dauphin Island (SI Appendix, S8). These results demonstrate that there can be a larger variability of δ 34 S in DMSP in estuarine and coastal waters, depending on location and local conditions, as has been shown previously for bulk S isotope analysis of different algae species (15,16) and DMSP of estuarine environments (8). Nevertheless, from a global perspective, the δ 34 S values of DMSP and its volatile breakdown product DMS are likely overwhelmingly dominated by the open ocean DMSP/DMS signature.…”

“…Recently, Oduro et al (8) used a multistep extraction of large seawater volumes (e.g., 50 L) coupled with Raney nickel dehydrosulfurization and subsequent fluorination for the S isotope analysis of DMSP in intertidal macroalgae (+17.3 to +19.3‰) and estuarine phytoplankton blooms (+19 to +20‰). However, there are still no direct DMS and DMSP δ 34 S data in oligotrophic oceans owing to their typically low concentrations of 0.5-5 and 5-80 nM, respectively (9).…”

Observational evidence for the formation of DMS-derived aerosols during Arctic phytoplankton blooms

“…(Norman et al, 1999) and Concordia station (75.1 • S, 123.3 • E; 3233 m a.s.l) . We estimated the amount of biogenic SO Another method for estimating biogenic SO 2− 4 is to use S-isotope ratios (δ 34 S) of SO 2− 4 aerosols, because the δ 34 S values of biogenic DMS (18 ± 2 ‰) are greater than those of anthropogenic SO 2− 4 (5 ± 1 ‰) but less than that of sea salt (21.0 ± 0.1 ‰) (e.g., Wadleigh, 2004;Lin et al, 2012;Oduro et al, 2012). A wide range in δ 34 S (0-8 ‰) has been reported for anthropogenic SO 2 compared with values reported for other sources (Krouse and Grinenko, 1991).…”

Stable Isotopic and Chemical Characteristics of Bulk Aerosols during Winter and Summer Seasons at a Station in Western Coast of India (Goa)

“…To the best of our knowledge, this is the first report containing S isotopic information on Indian aerosols. Nonetheless, from available literature containing S isotopic composition data from other regions and oceanic realms (Norman et al, 1999;Oduro et al, 2012;Amrani et al, 2013), we showed typical end member values in the Fig. 6 and attempted to provide interpretation for observed δ 34 S values of bulk aerosols over Goa.…”

“…As Goa is a typical costal locale experiencing strong biogeochemical in the coastal waters just before arrival of monsoon, enhancement of δ 34 S shows most likely tracks changes in the sulfur inventory. Recently Amrani et al (2013) and Oduro et al (2012) have shown oceanic emissions of volatile dimethyl sulfide (DMS) and its precursor, dimethylsulfoniopropionate (DMSP) represent the largest natural source of biogenic sulfur to the global atmosphere, where it mediates aerosol dynamics and may, in turn, affect climate. Amrani et al (2013) reported δ 34 S of DMS and DMSP ranging between +18.9 and +20.3‰, remarkable consistent across the globe.…”