Volatile organic compounds (VOCs) in the headspace of bubble chambers containing branches of live coral in filtered reef seawater were analysed using gas chromatography with mass spectrometry ...(GC-MS). When the coral released mucus it was a source of dimethyl sulfide (DMS) and isoprene; however, these VOCs were not emitted to the chamber headspace from mucus-free coral. This finding, which suggests that coral is an intermittent source of DMS and isoprene, was supported by the observation of occasional large pulses of atmospheric DMS (DMS
a
) over Heron Island reef on the southern Great Barrier Reef (GBR), Australia, in the austral winter. The highest DMS
a
pulse (320 ppt) was three orders of magnitude less than the DMS mixing ratio (460 ppb) measured in the headspace of a dynamically purged bubble chamber containing a mucus-coated branch of
Acropora aspera
indicating that coral reefs can be strong point sources of DMS
a
. Static headspace GC-MS analysis of coral fragments identified mainly DMS and seven other minor reduced sulfur compounds including dimethyl disulfide, methyl mercaptan, and carbon disulfide, while coral reef seawater was an indicated source of methylene chloride, acetone, and methyl ethyl ketone. The VOCs emitted by coral and reef seawater are capable of producing new atmospheric particles < 15 nm diameter as observed at Heron Island reef. DMS and isoprene are known to play a role in low-level cloud formation, so aerosol precursors such as these could influence regional climate through a sea surface temperature regulation mechanism hypothesized to operate over the GBR.
Atmospheric dimethylsulfide (DMSa), continually derived from the world's oceans, is a feed gas for the tropospheric production of new sulfate particles, leading to cloud condensation nuclei that ...influence the formation and properties of marine clouds and ultimately the Earth's radiation budget. Previous studies on the Great Barrier Reef (GBR), Australia, have indicated coral reefs are significant sessile sources of DMSa capable of enhancing the tropospheric DMSa burden mainly derived from phytoplankton in the surface ocean; however, specific environmental evidence of coral reef DMS emissions and their characteristics is lacking. By using on-site automated continuous analysis of DMSa and meteorological parameters at Heron Island in the southern GBR, we show that the coral reef was the source of occasional spikes of DMSa identified above the oceanic DMSa background signal. In most instances, these DMSa spikes were detected at low tide under low wind speeds, indicating they originated from the lagoonal platform reef surrounding the island, although evidence of longer-range transport of DMSa from a 70 km stretch of coral reefs in the southern GBR was also observed. The most intense DMSa spike occurred in the winter dry season at low tide when convective precipitation fell onto the aerially exposed platform reef. This co-occurrence of events appeared to biologically shock the coral resulting in a seasonally aberrant extreme DMSa spike concentration of 45.9 nmol m−3 (1122 ppt). Seasonal DMS emission fluxes for the 2012 wet season and 2013 dry season campaigns at Heron Island were 5.0 and 1.4 µmol m−2 day−1, respectively, of which the coral reef was estimated to contribute 4 % during the wet season and 14 % during the dry season to the dominant oceanic flux.
Dimethylsulfoniopropionate (DMSP) in scleractinian coral is usually analysed indirectly as dimethylsulfide (DMS) using gas chromatography (GC) with a sulfur-specific detector. We developed a ...headspace GC method for mass spectral analysis of DMSP in branching coral where hexa-deuterated DMSP (
d
6
-DMSP) was added to samples and standards to optimise the analytical precision and quantitative accuracy. Using this indirect HS-GC-MS method, we show that common coral sample handling techniques did not alter DMSP concentrations in
Acropora aspera
and that endogenous DMS was insignificant compared to the store of DMSP in
A. aspera
. Field application of the indirect HS-GC-MS method in all seasons over a 5-year period at Heron Island in the southern Great Barrier Reef indicated that healthy colonies of
A. aspera
ordinarily seasonally conserve their branch tip store of DMSP; however, this store increased to a higher concentration under extended thermal stress conditions driven by a strong El Niño Southern Oscillation event. A liquid chromatography mass spectral method (LC-MS) was subsequently developed for direct analysis of DMSP in branching coral, also utilising the
d
6
-DMSP internal standard. The quantitative comparison of DMSP in four species of
Acropora
coral by indirect HS-GC-MS and direct LC-MS analyses gave equivalent concentrations in
A. aspera
only; in the other three species, HS-GC-MS gave consistently higher concentrations, indicating that indirect analysis of DMSP may lead to artificially high values for some coral species.
Graphical Abstract
Dimethylsulfoniopropionate (DMSP) was quantified in
Acropora
spp. of branching coral using deuterated stable isotope dilution mass spectrometry
Dimethylsulfoniopropionate (DMSP) and eleven other target zwitterions were quantified in the branch tips of six
Acropora
species and
Stylophora pistillata
hard coral growing on the reef flat ...surrounding Heron Island in the southern Great Barrier Reef (GBR), Australia. Hydrophilic interaction liquid chromatography mass spectrometry (HILIC-MS) was used for sample analysis with isotope dilution MS applied to quantify DMSP. The concentration of DMSP was ten times greater in
A. aspera
than
A. valida
, with this difference being maintained throughout the spring, summer and winter seasons. In contrast, glycine betaine was present in significantly higher concentrations in these species during the summer than the winter. Exposure of branch tips of
A. aspera
to air and hypo-saline seawater for up to 1 h did not alter the concentrations of DMSP present in the coral when compared with control samples. DMSP was the most abundant target zwitterion in the six
Acropora
species examined, ranging from 44-78% of all target zwitterions in
A. millepora
and
A. aspera
, respectively. In contrast, DMSP only accounted for 7% in
S. pistillata
, with glycine betaine and stachydrine collectively accounting for 88% of all target zwitterions in this species. The abundance of DMSP in the six
Acropora
species examined points to
Acropora
coral being an important source for the biogeochemical cycling of sulfur throughout the GBR, since this reef-building branching coral dominates the coral cover of the GBR.
Graphical Abstract
HILIC-MS extracted ion chromatogram showing zwitterionic metabolites from the branching coral
Acropora isopora
Measurements of DMSP production from Acropora intermedia collected from Heron Island, in the southern Great Barrier Reef (GBR) from 2001 to 2003, show a distinct seasonal cycle of increased ...production in summer, and lower production in winter, despite severe coral bleaching in 2002. Increasing seawater temperatures by +2°C in summer and winter increased DMSP production from A. intermedia by approximately 45%. Compared with winter 2001 and summer 2002, marked increases in cellular DMSP occurred in A. intermedia in the winter of 2002 and summer 2003, five to six months after coral bleaching, and seemed to be related to high seawater temperatures and high rainfall. In contrast to these results cellular Chl a concentrations in A. intermedia decreased from 2001 to 2002 and then increased in summer 2003 as the coral slowly recovered. A parallel study conducted on Pocillopera damicornis from a fringing reef off Magnetic Island in the central GBR, highlighted marked variation in cellular concentrations of Chl a, DMSP, and algal symbionts, in colonies that were collected five months after a severe bleaching event. The increases in cellular DMSP at both low and high symbiont concentrations, and the highly significant correlation between cellular DMSP and Chl a, could reflect an adaptive response to enhanced levels of reduced oxygen species produced during the bleaching event, and may have aided the coral's recovery. The increases in cellular DMSP could also be explained by a change in the symbiont community. Comparison with measurements made mainly on Acropora coral from different locations in the GBR over different years, suggests that changes in the cellular or tissue concentration of DMSP are a sensitive indicator of coral stress.
•Cellular concentrations of DMSP in Acropora are a sensitive indicator of coral stress.•Cumulative stress events cause changes in coral DMSP.•Cellular DMSP is significantly correlated with Chl a and zooxanthellae.
A dimethyl sulfide (DMS) vertical concentration profile and DMS surface emission flux were quantified in undisturbed acid sulfate soils (ASS) at Cudgen Lake on the north coast of New South Wales, ...Australia. A deuterated internal standard was used to account for soil adsorption characteristics. The DMS vertical concentration profile increased exponentially from 0.6 m depth to the surface layer. This profile reflected the adsorption properties of the ASS horizons present and the experimentally determined octanol/water partition coefficient for DMS of 1.36, suggesting that DMS would be mobilised in the soil water medium for upward translocation in time due to surface evaporation. The organic material in the oxidised ASS crustal layer had a chemically strong adsorption affinity for DMS, which appeared to restrain its emission from surface soil particles to the atmosphere. The seasonally averaged DMS surface flux estimate from the Cudgen Lake ASS was 9 ng S m−2 min−1, which is relatively low by comparison to DMS fluxes reported from other wetland soils such as salt-marshes and acidic peat bogs. The worldwide annual average DMS emission from ASS was estimated to be 1.14 × 10−3 Tg S, which is globally insignificant by comparison to DMS emission from the world's oceans.
Display omitted
•Dimethyl sulfide is most abundant in the oxidised organic crustal soil layer.•Soil-air surface flux of dimethyl sulfide is restrained by crustal adsorption.•Acid sulfate soils appear to be a globally insignificant source of dimethyl sulfide.
In order to accurately measure the antioxidant capacity in corals, it is essential to optimally extract antioxidants from coral tissue. Here, we compared the two most commonly used methods for coral ...tissue extraction, air blasting (similar to Water-Pik method) and grinding, with or without sonication, to optimally extract antioxidants in corals. By air blasting, the coral tissue was stripped off the skeleton with a stream of compressed air into a polyethylene bag containing a known volume of buffer, whereas by grinding, both the coral tissue and skeleton were crushed using a mortar and pestle into a powder and homogenised in buffer. We found that air blasting was the most appropriate sample preparation method to use as it allowed for a more efficient and complete extraction of antioxidants from coral tissue, without the need for a second extraction step.
•Air blasting is the appropriate method for antioxidant extraction from coral tissue.•Grinding generated too much skeletal debris that could have trapped antioxidants.•Sonication time did not influence the extraction of antioxidants from coral tissue.
Dimethylsulfoniopropionate (DMSP) is an important source of dissolved organic matter for the marine food web and its cycling is a key step in ocean-atmosphere fluxes involved in the global sulfur ...cycle. To date, the abundance and biogeography of the genes encoding bacterial DMSP cycling in the eastern Indian Ocean (EIO) is virtually unknown. Moreover, DMSP measurements from the IO are sparse compared to other major oceans. In May–June 2019, we characterized dissolved DMSP (DMSPd) concentrations and the abundance of representative bacterial DMSP cycling genes along the 110 °E transect line as part of a voyage that contributed to Australia's involvement in the second International Indian Ocean Expedition. During the multidisciplinary voyage, surface water samples were collected from 19 stations spanning temperate to tropical waters of the EIO (39.5 °S to 11.5 °S, 110 °E). Somewhat surprisingly, a trend of greater DMSPd was measured in ultraoligotrophic (<0.02 μmol L−1 of nitrate/nitrite), low latitude waters compared to relatively nutrient-rich high latitudes, which contradicts global DMSPd patterns of high concentrations at high latitudes. Additionally, the average DMSPd concentration in EIO samples (17.2 ± 18.64 nM) was an order of magnitude greater than concentrations previously reported at similar latitudes in the Pacific and Atlantic Oceans, which suggests DMSPd is a readily available food source for microbes in a region that is often considered an ocean desert. The abundances of the bacterial DMSP production gene (dsyB), the DMSP lyase gene (dddP) and phylogenetically diverse DMSP demethylation genes (dmdA subclade A/1, D/all and E/2) were reported for the first time in the EIO region, demonstrating significant shifts in all genes with latitude. The SAR11 dmdA (D/all) gene was the dominant DMSP degradation gene across the transect (3.4 ± 0.94% of bacteria) and was notably positively correlated to DMSPd, demonstrating a tight coupling between the variables across the 30° transect. Our results also showed greater DMSPd and relative abundance of genes encoding both DMSP degradation pathways (dddP, dmdA A/1 and D/all) within a Leeuwin Current meander when compared to adjacent stations outside of the meander, providing evidence that mesoscale perturbations from the Leeuwin Current can greatly influence the EIO sulfur cycle. Overall, our data indicates that reduced sulfur in the form of DMSP is an abundant and readily available food source for some microbial metabolisms within the ultraoligotrophic surface waters of the EIO.
•Unexpected trend of south to north increase in DMSPd concentration along the 110 °E meridian.•High DMSPd concentrations in ultraoligotrophic regions indicates this compound is an abundant food source for some microbes.•Clear positive relationship between the SAR11 DMSP demethylation gene (dmdA D/all) and DMSPd across the entire transect.•Intrusions from the Leeuwin Current enhanced DMSPd concentration and DMSP degradation gene abundance on the 110 °E line.
Earth’s Radiation Budget is partly dictated by the fragile and complex balance between biogenic volatile organic compounds (BVOCs) and greenhouse gases (GHGs), which have the potential to impose ...cooling or warming once emitted to the atmosphere. Whilst methane (CH
4
) is strictly associated with global warming due to its solar-radiation absorbing properties, dimethyl sulfide (DMS) is generally considered a cooling gas through the light scattering properties of its atmospheric oxidation products. However, DMS may also partially contribute to the Earth’s warming through a small portion of it being degraded to CH
4
in the water column. Coral reefs emit both DMS and CH
4
but they have not previously been simultaneously measured. Here, we report DMS and CH
4
fluxes as well as aerosol particle counts at Heron Island, southern Great Barrier Reef, during the austral summer of 2016. Sea-to-air DMS and CH
4
fluxes were on average 24.9 ± 1.81 and 1.36 ± 0.11 µmol m
-2
d
-1
, whilst intermediate (< 0.5-2.5 um) and large (> 2.5 um) particle number concentrations averaged 5.51 x 10
6
± 1.73 x 10
5
m
-3
and 1.15 x 10
6
± 4.63 x 10
4
m
-3
, respectively. Positive correlations were found between DMS emissions and the abundance of intermediate (R
2
= 0.1669,
p
< 0.001,
n
= 93) and large (R
2
= 0.0869,
p
= 0.004,
n
= 93) aerosol particles, suggesting that DMS sea-to-air emissions significantly contribute to the growth of existing particles to the measured size ranges at the Heron Island lagoon. Additionally, a strong positive correlation was found between DMS and CH
4
fluxes (R
2
= 0.7526,
p
< 0.00001,
n
= 93), suggesting that the emission of these volatile compounds from coral reefs is closely linked. The slope of the regression between DMS and CH
4
suggests that CH
4
emissions at the Heron Island lagoon represent 5% of that of DMS, which is consistent with the average sea-to-air fluxes reported in this study (i.e. 24.9 ± 1.81 µmol m
-2
d
-1
for DMS and 1.36 ± 0.11 for CH
4
). These findings provide new insights on the complexity of BVOC and GHG emissions in coral reef systems and their potential role in climate regulation.
Marine dimethylsulfide (DMS) is an important source of natural sulfur to the atmosphere, with potential implications for the Earth’s radiative balance. Coral reefs are important regional sources of ...DMS, yet their contribution is not accounted for in global DMS climatologies or in model simulations. This study accounts for coral-reef-derived DMS and investigates its influence on the atmosphere of the Great Barrier Reef (GBR), Australia, using the Australian Community Climate and Earth System Simulator Atmospheric Model version 2 (ACCESS-AM2). A climatology of seawater surface DMS (DMS
w
) concentration in the GBR and an estimate of direct coral-to-air DMS flux during coral exposure to air at low tide are incorporated into the model, increasing DMS emissions from the GBR region by 0.02 Tg yr
-1
. Inclusion of coral-reef-derived DMS increased annual mean atmospheric DMS concentration over north-eastern Australia by 29%, contributing to an increase in gas-phase sulfate aerosol precursors of up to 18% over the GBR. The findings suggest that the GBR is an important regional source of atmospheric sulfur, with the potential to influence local-scale aerosol-cloud processes. However, no influence on sulfate aerosol mass or number concentration was detected, even with a reduction in anthropogenic sulfur dioxide emissions, indicating that DMS may not significantly influence the regional atmosphere at monthly, annual or large spatial scales. Further research is needed to improve the representation of coral-reef-derived DMS in climate models and determine its influence on local, sub-daily aerosol-cloud processes, for which observational studies suggest that DMS may play a more important role.
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