Sulfur isotope homogeneity of oceanic DMSP and DMS

Abstract

Oceanic emissions of volatile dimethyl sulfide (DMS) represent the largest natural source of biogenic sulfur to the global atmosphere, where it mediates aerosol dynamics. To constrain the contribution of oceanic DMS to aerosols we established the sulfur isotope ratios ( 34 S/ 32 S ratio, δ 34 S) of DMS and its precursor, dimethylsulfoniopropionate (DMSP), in a range of marine environments. In view of the low oceanic concentrations of DMS/P, we applied a unique method for the analysis of δ 34 S at the picomole level in individual compounds. Surface water DMSP collected from six different ocean provinces revealed a remarkable consistency in δ 34 S values ranging between +18.9 and +20.3‰. Sulfur isotope composition of DMS analyzed in freshly collected seawater was similar to δ 34 S of DMSP, showing that the in situ fractionation between these species is small (<+1‰). Based on volatilization experiments, emission of DMS to the atmosphere results in a relatively small fractionation (−0.5 ± 0.2‰) compared with the seawater DMS pool. Because δ 34 S values of oceanic DMS closely reflect that of DMSP, we conclude that the homogenous δ 34 S of DMSP at the ocean surface represents the δ 34 S of DMS emitted to the atmosphere, within +1‰. The δ 34 S of oceanic DMS flux to the atmosphere is thus relatively constant and distinct from anthropogenic sources of atmospheric sulfate, thereby enabling estimation of the DMS contribution to aerosols., a metabolite of marine phytoplankton, is one of the major organosulfur compounds produced in the oceans (1). One of its degradation products, dimethylsulfide (DMS), is volatile and supersaturated in all marine surface waters. Large amounts of DMS (0.55-1.1 Tmol S·y −1 ) are released from the ocean to the atmosphere (2), where it contributes to the formation and growth of aerosol particles (3). Over remote oceans, distant from anthropogenic sulfur inputs, DMS is the major source of nonsea-salt sulfate aerosol (4, 5). The oxidation of DMS to submicron sulfate aerosols was suggested to increase cloud-condensation nuclei and the albedo of clouds, leading to a potential climate feedback loop operating through the DMS-producing biota in the surface ocean (6). Although evidence for the direct, local climate feedback via DMS is limited (7), DMS likely contributes, together with organic and sea-spray aerosol sources, to the complex dynamics of climate-active aerosols in the lower atmosphere (3, 7).Sulfur isotope measurements ( 34 S/ 32 S ratio, δ 34 S) may offer a way to constrain the contribution of ocean-derived DMS to global sulfur cycling and aerosol budgets. 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 ...

Sulfur isotopic composition of surface snow along a latitudinal transect in East Antarctica

“…Indeed, the existing data sets include one from the South Pole covering approximately the past 50 years [ Patris et al ., ], the Camp Maudheimvidda (CM) and Camp Victoria (CV) ice cores from Dronning Maud Land (spanning the present to 1100 years ago) [ Jonsell et al ., ], and the Dome C shallow core [ Baroni et al ., ] (Figure ). These East Antarctic sites have δ 34 S values ranging from 13.9 to 18.1‰, similar to biogenic sulfur [ Amrani et al ., ; Calhoun et al ., ; Oduro et al ., ], suggesting that marine biogenic activity has a strong influence in East Antarctica. The contributions of other sources to the total sulfate are estimated to be minor: Volcanic degassing is estimated to contribute 10–20% based on a δ 34 S value from CV [ Jonsell et al ., ], and stratospheric sulfate is estimated to contribute approximately 5% based on aerosol chemistry observations at Neumayer Station [ Minikin et al ., ].…”

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.…”

“…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. Earlier δ 34 S values of SO 4 -2 have been reported between +15 and +19‰; marine biogenic ~+17.5‰ and sea salt SO 4 -2 as +21‰ (Normal et al, 1999;Fig.…”

Background atmospheric sulfate deposition at a remote alpine site in the Southern Canadian Rocky Mountains

“…Increased continental biogenic emissions would tend to decrease the δ 34 S‐SO 4 2− values of summer rain, which is opposite to the trend observed in this study. However, sulfate derived from marine biogenic emissions (mainly dimethyl sulfide (DMS)) are substantial (~19% of annual global S emissions), with more positive δ 34 S‐SO 4 2− values (+18.9 to +20.3‰) [ Amrani et al, ; Seguin et al, ] relative to this study. Primary productivity from phytoplankton and algae that produce DMS is elevated in the summer [e.g., Li et al, ; Norman et al, ].…”