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

The impact of bioaerosol trajectories on microbial community assembly and physicochemical dynamics in the atmosphere

This study explored the assembly mechanisms and physicochemical dynamics of microbial communities within atmospheric bioaerosols, focusing on the influence of different aerial trajectories. Over two years, samples near Seoul were classified into 'North', 'Southwest', and 'Others' categories based on their aerial trajectories. Physicochemical analysis of the PM2.5 particles revealed distinct ion compositions for each cluster, reflecting diverse environmental influences. Microbial community analysis revealed that shared dominant bacterial phyla were present in all clusters. However, distinct taxonomic profiles and biomarkers were also evident, such as coastal bacteria in the 'Southwest' cluster correlating with wind speed, and arid soil-originated bacteria in the 'North' cluster correlating with cations. These findings demonstrate that biomarkers in each cluster are representative of the distinct environments associated with their aerial trajectories. Notably, cluster 'Southwest' the highest microbial diversity and a strong alignment with the neutral community model, suggesting a large influence of passive dispersal from marine environments. Contrarily, 'North' and 'Others' were more influenced by niche-dependent factors. This study highlights the complex interplay between environmental factors and microbial dynamics in bioaerosols and provides important insights for environmental monitoring and public health risk assessment.

Procedures from samples to sulfur isotopic data: A review

RATIONALE

Sulfur isotopes have been widely used to solve some key scientific questions, especially in the last two decades with advanced instruments and analytical schemes. Different sulfur speciation and multiple isotopes analyzed in laboratories worldwide and in situ microanalysis have also been reported in many articles. However, methods of sampling to measurements are multifarious, and occasionally some inaccuracies are present in published papers. Vague methods may mislead newcomers to the field, puzzle readers, or lead to incorrect data-based correlations.

METHODS

We have reviewed multiple methods on sulfur isotopic analyses from the perspectives of sampling, laboratory work, and instrumental analysis in order to help reduce operational inhomogeneity and ensure the fidelity of sulfur isotopic data. We do not deem our proposed solutions as the ultimate standard methods but as a lead-in to the overall introduction and summary of the current methods used.

RESULTS

It has been shown that external contamination and transformation of different sulfur species should be avoided during the sampling, pretreatment, storage, and chemical treatment processes. Conversion rates and sulfur isotopic fractionations during sulfur extraction, purification, and conversion processes must be verified by researchers using standard or known samples. The unification of absence of isotopic fractionation is needed during all steps, and long-term monitoring of standard samples is recommended.

CONCLUSION

This review compiles more details on different methods in sampling, laboratory operation, and measurement of sulfur isotopes, which is beneficial for researchers' better practice in laboratories. Microanalyses and molecular studies are the frontier techniques that compare the bulk sample with the elemental analysis/continuous flow-gas source stable isotope ratio mass spectrometry method, but the latter is widely used. The development of sulfur isotopic measurements will lead to the innovation in scientific issues with sulfur proxies.

Novel sulfur isotope analyses constrain sulfurized porewater fluxes as a minor component of marine dissolved organic matter

Marine dissolved organic matter (DOM) is a major reservoir that links global carbon, nitrogen, and phosphorus. DOM is also important for marine sulfur biogeochemistry as the largest water column reservoir of organic sulfur. Dissolved organic sulfur (DOS) can originate from phytoplankton-derived biomolecules in the surface ocean or from abiotically "sulfurized" organic matter diffusing from sulfidic sediments. These sources differ in ³⁴S/³²S isotope ratios (δ³⁴S values), with phytoplankton-produced DOS tracking marine sulfate (21‰) and sulfurized DOS mirroring sedimentary porewater sulfide (∼0 to -10‰). We measured the δ³⁴S values of solid-phase extracted (SPE) DOM from marine water columns and porewater from sulfidic sediments. Marine DOM_SPE δ³⁴S values ranged from 14.9‰ to 19.9‰ and C:S ratios from 153 to 303, with lower δ³⁴S values corresponding to higher C:S ratios. Marine DOM_SPE samples showed consistent trends with depth: δ³⁴S values decreased, C:S ratios increased, and δ¹³C values were constant. Porewater DOM_SPE was ³⁴S-depleted (∼-0.6‰) and sulfur-rich (C:S ∼37) compared with water column samples. We interpret these trends as reflecting at most 20% (and on average ∼8%) contribution of abiotic sulfurized sources to marine DOS_SPE and conclude that sulfurized porewater is not a main component of oceanic DOS and DOM. We hypothesize that heterogeneity in δ³⁴S values and C:S ratios reflects the combination of sulfurized porewater inputs and preferential microbial scavenging of sulfur relative to carbon without isotope fractionation. Our findings strengthen links between oceanic sulfur and carbon cycling, supporting a realization that organic sulfur, not just sulfate, is important to marine biogeochemistry.

Contrasting Community Composition and Co-Occurrence Relationships of the Active Pico-Sized Haptophytes in the Surface and Subsurface Chlorophyll Maximum Layers of the Arctic Ocean in Summer

Haptophytes (Hacrobia: Haptophyta), which can perform phototrophic, phagotrophic, or mixotrophic nutritional modes, are critical for element cycling in a variety of aquatic ecosystems. However, their diversity, particularly in the changing Arctic Ocean (AO), remains largely unknown. In the present study, the biodiversity, community composition, and co-occurrence networks of pico-sized haptophytes in the surface water and subsurface chlorophyll maximum (SCM) layer of the AO were explored. Our results found higher alpha diversity estimates in the surface water compared with in the SCM based on high-throughput sequencing of haptophyte specific 18S rRNA. The community composition of the surface water was significantly different from that of the SCM, and water temperature was identified as the primary factor shaping the community compositions. Prymnesiales (mostly Chrysochromulina), uncultured Prymnesiophyceae, and Phaeocystis dominated the surface water communities, whereas Phaeocystis dominated the SCM communities, followed by Chrysochromulina, uncultured Prymnesiophyceae, and the remaining taxa. The communities of the surface water and SCM layer developed relatively independent modules in the metacommunity network. Nodes in the surface water were more closely connected to one another than those in the SCM. Network stability analysis revealed that surface water networks were more stable than SCM networks. These findings suggest that SCM communities are more susceptible to environmental fluctuations than those in surface water and that future global changes (e.g., global warming) may profoundly influence the development, persistence, and service of SCM in the AO.

Multi isotope systematics of precipitation to trace the sources of air pollutants in Seoul, Korea

Multiple sulfur (δ³⁴S_sulfate, Δ³³S_sulfate, & Δ³⁶S_sulfate), nitrogen and oxygen (δ¹⁵N_nitrate & δ¹⁸O_nitrate) and strontium (⁸⁷Sr/⁸⁶Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia. The δ³⁴S_sulfate values (from 1.9 to 14.6‰ with a median of 4.7‰) and the δ¹⁵N_nitrate values (from -2.0 to 13.3‰ with a median of 1.0‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is a predominant source for sulfur and nitrogen, but other natural sources including biogenic contributions of DMS also add to their total budget. The seasonal variations are observed in δ³⁴S_sulfate and δ¹⁵N_nitrate values (both higher in winter season), which is likely to result from the increase of coal use for domestic heating in China. The δ¹⁸O_nitrate values also varied seasonally depending on the NO_x oxidation pathway, being about 20‰ higher in winter than in summer season. The Δ³³S_sulfate and Δ³⁶S_sulfate values are not anomalous, showing the absence of MIF signals in precipitation of Seoul. The ⁸⁷Sr/⁸⁶Sr ratio of the precipitation samples range from 0.70988 to 0.71487 with a median of 0.71073, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K⁺+NH₄⁺)/(Ca²⁺+Mg²⁺) and Cl^-/Na⁺ suggest the overwhelming effect of anthropogenic input rather than carbonate dust on the end-member with lower ⁸⁷Sr/⁸⁶Sr ratios.

Sulfur isotope analysis of cysteine and methionine via preparatory liquid chromatography and elemental analyzer isotope ratio mass spectrometry

RATIONALE

Sulfur isotope analysis of organic sulfur-containing molecules has previously been hindered by challenging preparatory chemistry and analytical requirements for large sample sizes. The natural-abundance sulfur isotopic compositions of the sulfur-containing amino acids, cysteine and methionine, have therefore not yet been investigated despite potential utility in biomedicine, ecology, oceanography, biogeochemistry, and other fields.

METHODS

Cysteine and methionine were subjected to hot acid hydrolysis followed by quantitative oxidation in performic acid to yield cysteic acid and methionine sulfone. These stable, oxidized products were then separated by reversed-phase high-performance liquid chromatography (HPLC) and verified via offline liquid chromatography/mass spectrometry (LC/MS). The sulfur isotope ratios (δ³⁴ S values) of purified analytes were then measured via combustion elemental analyzer coupled to isotope ratio mass spectrometry (EA/IRMS). The EA was equipped with a temperature-ramped chromatographic column and programmable helium carrier flow rates.

RESULTS

On-column focusing of SO₂ in the EA/IRMS system, combined with reduced He carrier flow during elution, greatly improved sensitivity, allowing precise (0.1-0.3‰ 1 s.d.) δ³⁴ S measurements of 1 to 10 μg sulfur. We validated that our method for purification of cysteine and methionine was negligibly fractionating using amino acid and protein standards. Proof-of-concept measurements of fish muscle tissue and bacteria demonstrated differences up to 4‰ between the δ³⁴ S values of cysteine and methionine that can be connected to biosynthetic pathways.

CONCLUSIONS

We have developed a sensitive, precise method for measuring the natural-abundance sulfur isotopic compositions of cysteine and methionine isolated from biological samples. This capability opens up diverse applications of sulfur isotopes in amino acids and proteins, from use as a tracer in organisms and the environment, to fundamental aspects of metabolism and biosynthesis.

Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle

Sulfate aerosol (SO₄^2-) preserved in Antarctic ice cores is discussed in the light of interactions between marine biological activity and climate since it is mainly sourced from biogenic emissions from the surface ocean and scatters solar radiation during traveling in the atmosphere. However, there has been a paradox between the ice core record and the marine sediment record; the former shows constant non-sea-salt (nss-) SO₄^2- flux throughout the glacial-interglacial changes, and the latter shows a decrease in biogenic productivity during glacial periods compared to interglacial periods. Here, by ensuring the homogeneity of sulfur isotopic compositions of atmospheric nss-SO₄^2- (δ³⁴S_nss) over East Antarctica, we established the applicability of the signature as a robust tool for distinguishing marine biogenic and nonmarine biogenic SO₄^2-. Our findings, in conjunction with existing records of nss-SO₄^2- flux and δ³⁴S_nss in Antarctic ice cores, provide an estimate of the relative importance of marine biogenic SO₄^2- during the last glacial period to be 48 ± 10% of nss-SO₄^2-, slightly lower than 59 ± 11% during the interglacial periods. Thus, our results tend to reconcile the ice core and sediment records, with both suggesting the decrease in marine productivity around Southern Ocean under the cold climate.

Sulfur isotopes ratio of atmospheric carbonyl sulfide constrains its sources

Carbonyl sulfide (COS) is the major long-lived sulfur bearing gas in the atmosphere, and is used to estimate the rates of regional and global (both past and current) photosynthesis. Sulfur isotope measurements (³⁴S/³²S ratio, δ³⁴S) of COS may offer a way for improved determinations of atmospheric COS sources. However, measuring the COS δ³⁴S at the atmospheric concentrations of ~0.5 ppb is challenging. Here we present high-accuracy δ³⁴S measurements of atmospheric COS done by gas chromatograph (GC) connected to a multicollector inductively coupled plasma mass spectrometer (MC-ICPMS), after pre-concentrating from 2-liters of air. We showed that the precision of COS δ³⁴S measurement for gas standards is ≤0.2‰, and that N₂ and CO₂ in the gas standard mixture had no effect on the measured δ³⁴S. Natural air samples were collected in Israel and in the Canary Islands. The COS δ³⁴S values in both locations were found to be 13.2 ± 0.6‰, and are believed to represent the background tropospheric value. This δ³⁴S value is markedly different from the previously reported value of 4.9‰. We estimate the expected isotopic signature of COS sources and sinks, and use the δ³⁴S value of atmospheric COS we measured to estimate that ~48% of it originates from the ocean.

Variability in sulfur isotope composition suggests unique dimethylsulfoniopropionate cycling and microalgae metabolism in Antarctic sea ice

Sea ice microbial communities produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), a precursor of the climate cooling gas dimethylsulfide. Despite their importance to the polar sulfur cycle, drivers and metabolic pathways of sea ice DMSP are uncertain. Here we report the first measurements of sea ice DMSP sulfur isotopic composition (³⁴S/³²S ratio, δ³⁴S). δ³⁴S values in ice cores from the Ross Sea and Weddell Sea reveal considerable variability across seasons and between ice horizons (from +10.6 to +23.6‰). We discuss how the most extreme δ³⁴S values observed could be related to unique DMSP cycling in the seasonally extreme physiochemical conditions of isolated brine inclusions in winter-spring. Using cell cultures, we show that part of the DMSP δ³⁴S variability could be explained by distinct DMSP metabolism in sea ice microalgae. These findings advance our understanding of the sea ice sulfur cycle and metabolic adaptations of microbes in extreme environments.

Headspace-Solid Phase Microextraction Approach for Dimethylsulfoniopropionate Quantification in Solanum lycopersicum Plants Subjected to Water Stress

Dimethylsulfoniopropionate (DMSP) and dimethyl sulphide (DMS) are compounds found mainly in marine phytoplankton and in some halophytic plants. DMS is a globally important biogenic volatile in regulating of global sulfur cycle and planetary albedo, whereas DMSP is involved in the maintenance of plant-environment homeostasis. Plants emit minute amounts of DMS compared to marine phytoplankton and there is a need for hypersensitive analytic techniques to enable its quantification in plants. Solid Phase Micro Extraction from Head Space (HS-SPME) is a simple, rapid, solvent-free and cost-effective extraction mode, which can be easily hyphenated with GC-MS for the analysis of volatile organic compounds. Using tomato (Solanum lycopersicum) plants subjected to water stress as a model system, we standardized a sensitive and accurate protocol for detecting and quantifying DMSP pool sizes, and potential DMS emissions, in cryoextracted leaves. The method relies on the determination of DMS free and from DMSP pools before and after the alkaline hydrolysis via Headspace-Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS). We found a significant (2.5 time) increase of DMSP content in water-stressed leaves reflecting clear stress to the photosynthetic apparatus. We hypothesize that increased DMSP, and in turn DMS, in water-stressed leaves are produced by carbon sources other than direct photosynthesis, and function to protect plants either osmotically or as antioxidants. Finally, our results suggest that SPME is a powerful and suitable technique for the detection and quantification of biogenic gasses in trace amounts.

Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets

Achondrite meteorites have anomalous enrichments in (33)S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying (33)S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the (33)S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous (33)S depletions in IIIF iron meteorites (<-0.02 per mil), and (33)S enrichments in other magmatic iron meteorite groups. The (33)S depletions support the idea that differentiated planetesimals inherited sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.

Development and Initial Biogeochemical Applications of Compound-Specific Sulfur Isotope Analysis

Compound-specific isotope analysis (CSIA) has been extended to the 32S and 34S stable isotopes of sulfur (δ34S) through the combination of gas chromatography (GC) and multi-collector inductively coupled mass spectrometry (ICPMS). The molecular level resolution of sulfur-CSIA is greatly expanding the biogeochemical applications ofexisting sulfur isotope methods, particularly with respect to organic sulfur compounds. Sulfur participates in a variety of important biogeochemical and redox processes, with distinctive isotopic fractionations accompanying many of these. For example, hydrogen sulfideproduced duringmicrobial sulfate reduction can be strongly depleted in 34S (up to 66‰ in δ34S) compared to the source sulfate. An improved understanding of sulfur biogeochemistry at the molecular level will assist in the interpretation of studies of sulfur cycling associated with the modern and paleo-environments. A comparison of δ34S values between organic and inorganic sulfurspecies mayhelp to illuminate the complex role of sulfur in sedimentary organic diagenesis and the pathways of organic sulfurformation. The δ34S values of individual organic sulfur compounds from natural settings can be currently measured by GC-ICPMS with impressive accuracy, precision (&lt;0.5‰) and sensitivity (≥20 pmol S) over a broad range of analyte volatility. The new sulfur-CSIA capability has already been used to study pathways of early diagenetic organic sulfurisation, volatile sulfur emission from the oceans, oil correlations, thermochemical sulfate reduction of petroleum hydrocarbons, and the relationship between OSCs and mineralising sulfides of large metal deposits.

A sensitive method for the sulfur isotope analysis of dimethyl sulfide and dimethylsulfoniopropionate in seawater

RATIONALE

Dimethyl sulfide (DMS) is the major volatile sulfur species emitted to the atmosphere from the oceans. The sulfur isotope ratio ((34)S/(32)S) of DMS may offer a way to calculate the contribution of marine DMS to global sulfur cycling. The S-isotopic analysis of DMS is difficult due to its low concentrations in natural seawater and high chemical reactivity. Here we present a sensitive, precise and accurate method for determining the S-isotopic composition of natural DMS and its precursor, dimethylsulfoniopropionate (DMSP), in seawater.

METHODS

The method was based on a purge of DMS from aqueous solutions or natural seawater to a cryogenic trap and subsequent separation of DMS by gas chromatography. The separated DMS was then transferred from the gas chromatograph to a multicollector inductively coupled plasma mass spectrometer (GC/MC-ICPMS system) for measurement of (34)S/(32)S ratios. Correction for mass bias was accomplished using standard-sample bracketing with peaks of SF6 as a reference gas.

RESULTS

Results obtained from synthetic DMS and DMSP dissolved in artificial seawater show >98% recovery of DMS and very good precision (0.1 to 0.3‰), accuracy and linearity (0.2‰) for the 26-179 picomoles (pmol) of DMS or DMSP injected. The system was tested with natural seawater from Eilat (Red Sea, Israel) and similar precision and accuracy for both DMS and DMSP were obtained. The δ(34)S values of DMS and DMSP from Eilat seawater were 19.2 ± 0.2‰ and 19.7 ± 0.2‰, respectively.

CONCLUSIONS

The coupling of a purge-and-trap system with a GC/MC-ICPMS system was shown to be a sensitive, accurate and robust approach for the S-isotope analysis of nanomolar (nM) concentrations of DMS and DMSP from aqueous solutions and natural seawater.

Sulfur isotope homogeneity of oceanic DMSP and DMS

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.