Exceptional accumulation and retention of dimethylsulfoniopropionate by molluscs

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of CSIRO Publishing for personal use, not for redistribution. The definitive version was published in Environmental Chemistry 13 (2016): 231-238, doi:10.1071/EN14267.Molluscs often play major roles in processing phytoplankton-synthesized dimethylsulfoniopropionate (DMSP) in local ecosystems. We find that some mollusc species retain tissue DMSP exceptionally tightly and exhibit unusually great and statistically nonnormal interindividual variation in DMSP accumulation and retention. Individual mussels (Mytilus, Geukensia) living within a single clump, for example, range 6- to 11-fold in tissue [DMSP] and are often nonnormal in statistical distribution. These properties cannot be explained by the elevation of the substrate on which the mussels are living or by mussel position in a clump. When mussels (M. edulis) are deprived of DMSP for up to 5 weeks in depuration experiments, some individuals retain high tissue [DMSP], whereas others exhibit reduced [DMSP]. Such interindividual divergence helps explain nonnormal distributions of tissue [DMSP] after depuration. We re-analyze published data from which the half-time for tissue DMSP loss during depuration can be calculated. In the only mollusc so studied (Haliotis), the half-time is 13-25 times longer than in similar-size fish. Besides posing a challenge for DMSP mass balance studies, retention and interindividual variation may point to as yet unknown properties of molluscs: Tight retention suggests functional roles for DMSP, and nonnormal statistical distributions suggest discontinuities among individuals in DMSP metabolism

The distribution of methylated sulfur compounds, DMS and DMSP, in Canadian subarctic and Arctic marine waters during summer 2015

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 15 (2018): 2449–2465, doi:10.5194/bg-15-2449-2018.We present seawater concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) measured across a transect from the Labrador Sea to the Canadian Arctic Archipelago during summer 2015. Using an automated ship-board gas chromatography system and a membrane-inlet mass spectrometer, we measured a wide range of DMS (∼ 1 to 18 nM) and DMSP (∼ 1 to 150 nM) concentrations. The highest DMS and DMSP concentrations occurred in a localized region of Baffin Bay, where surface waters were characterized by high chlorophyll a (chl a) fluorescence, indicative of elevated phytoplankton biomass. Across the full sampling transect, there were only weak relationships between DMS(P), chl a fluorescence and other measured variables, including positive relationships between DMSP : chl a ratios and several taxonomic marker pigments, and elevated DMS(P) concentrations in partially ice-covered areas. Our high spatial resolution measurements allowed us to examine DMS variability over small scales (< 1 km), documenting strong DMS concentration gradients across surface hydrographic frontal features. Our new observations fill in an important observational gap in the Arctic Ocean and provide additional information on sea–air DMS fluxes from this ocean region. In addition, this study constitutes a significant contribution to the existing Arctic DMS(P) dataset and provides a baseline for future measurements in the region.This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) through the Climate Change and Atmospheric Research program (Arctic-GEOTRACES)

Patterns and drivers of dimethylsulfide concentration in the northeast subarctic Pacific across multiple spatial and temporal scales.

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 License. The definitive version was published in Biogeosciences 16(8), (2019):1729-1754, doi:10.5194/bg-16-1729-2019.The northeast subarctic Pacific (NESAP) is a globally important source of the climate-active gas dimethylsulfide (DMS), yet the processes driving DMS variability across this region are poorly understood. Here we examine the spatial distribution of DMS at various spatial scales in contrasting oceanographic regimes of the NESAP. We present new high-spatial-resolution measurements of DMS across hydrographic frontal zones along the British Columbia continental shelf, together with key environmental variables and biological rate measurements. We combine these new data with existing observations to produce a revised summertime DMS climatology for the NESAP, yielding a broader context for our sub-mesoscale process studies. Our results demonstrate sharp DMS concentration gradients across hydrographic frontal zones and suggest the presence of two distinct DMS cycling regimes in the NESAP, corresponding to microphytoplankton-dominated waters along the continental shelf and nanoplankton-dominated waters in the cross-shelf transitional zone. DMS concentrations across the continental shelf transition (range < 1–10 nM, mean 3.9 nM) exhibited positive correlations to salinity (r=0.80), sea surface height anomaly (SSHA; r=0.51), and the relative abundance of prymnesiophyte and dinoflagellates (r=0.89). In contrast, DMS concentrations in nearshore coastal transects (range < 1–24 nM, mean 6.1 nM) showed a negative correlation with salinity (r=−0.69; r=−0.78) and SSHA (r=−0.81; r=−0.75) and a positive correlation to relative diatom abundance (r=0.88; r=0.86). These results highlight the importance of bloom-driven DMS production in continental shelf waters of this region and the role of prymnesiophytes and dinoflagellates in DMS cycling further offshore. In all areas, the rate of DMS consumption appeared to be an important control on observed concentration gradients, with higher DMS consumption rate constants associated with lower DMS concentrations. We compiled a data set of all available summertime DMS observations for the NESAP (including previously unpublished results) to examine the performance of several existing algorithms for predicting regional DMS concentrations. None of these existing algorithms was able to accurately reproduce observed DMS distributions across the NESAP, although performance was improved by the use of regionally tuned coefficients. Based on our compiled observations, we derived an average summertime distribution map for DMS concentrations and sea–air fluxes across the NESAP, estimating a mean regional flux of 0.30 Tg of DMS-derived sulfur to the atmosphere during the summer season.We dedicate this article to the memory of Ronald P. Kiene, a wonderful scientist, mentor and friend. His contributions to DMS and DMSP research have shaped our field over the past 3 decades, and he will be missed by many around the world. We also wish to thank many individuals involved in data collection and logistical aspects of the cruises presented here, including scientists from the Institute of Ocean Sciences, the captain and crew of the R/V Oceanus and the CCGS John P. Tully, and members of the Tortell, Kiene, Levine and Hatton laboratory groups. We also thank Theodore Ahlvin for GIS support and both reviewers for their insightful comments. Support for this work was provided from the US National Science Foundation (grant no. 1436344) and from the Natural Sciences and Engineering Research Council of Canada

Concentrations and cycling of DMS, DMSP, and DMSO in coastal and offshore waters of the Subarctic Pacific during summer, 2010-2011

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 3269–3286, doi:10.1002/2016JC012465.Concentrations of dimethylsulfide (DMS), measured in the Subarctic Pacific during summer 2010 and 2011, ranged from ∼1 to 40 nM, while dissolved dimethylsulfoxide (DMSO) concentrations (range 13-23 nM) exceeded those of dissolved dimethyl sulfoniopropionate (DMSP) (range 1.3–8.8 nM). Particulate DMSP dominated the reduced sulfur pool, reaching maximum concentrations of 100 nM. Coastal and off shore waters exhibited similar overall DMS concentration ranges, but sea-air DMS fluxes were lower in the oceanic waters due to lower wind speeds. Surface DMS concentrations showed statistically significant correlations with various hydrographic variables including the upwelling intensity (r2 = 0.52, p < 0.001) and the Chlorophyll a/mixed layer depth ratio (r2 = 0.52, p < 0.001), but these relationships provided little predictive power at small scales. Stable isotope tracer experiments indicated that the DMSP cleavage pathway always exceeded the DMSO reduction pathway as a DMS source, leading to at least 85% more DMS production in each experiment. Gross DMS production rates were positively correlated with the upwelling intensity, while net rates of DMS production were significantly correlated to surface water DMS concentrations. This latter result suggests that our measurements captured dominant processes driving surface DMS accumulation across a coastal-oceanic gradient.Natural Sciences and Engineering Research Council of Canada, from the Peter Wall Institute for Advanced Studies2017-10-2

Fluxes and gas transfer rates of the biogenic trace gas DMS derived from atmospheric gradients

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S10, doi:10.1029/2003JC001795.Gas transfer rates were determined from vertical profile measurements of atmospheric dimethylsulfide (DMS) gradients over the equatorial Pacific Ocean obtained during the GasEx-2001 cruise. A quadratic relationship between gas transfer velocity and wind speed was derived from the DMS flux measurements; this relationship was in close agreement with a parameterization derived from relaxed eddy accumulation measurements of DMS over the northeastern Pacific Ocean. However, the GasEx-2001 relationship results in gas transfer rates that are a factor 2 higher than gas transfer rates calculated from a parameterization that is based on coincident eddy correlation measurements of CO2 flux. The measurement precision of both the profiling and eddy correlation techniques applied during GasEx-2001 is comparable; the two gas transfer data sets are in agreement within their uncertainty. Differences in the number of samples and the wind speed range over which CO2 and DMS fluxes were measured are likely causes for the observed discrepancy.Funding for this work came from the Netherlands Organization for Scientific Research (NWO) and from the NOP project 951203: ‘‘Micrometeorology of air/sea fluxes of carbon dioxide. This work was supported by the Global Carbon Cycle project of the NOAA Office of Global Programs grant NA17RJ1223, National Science Foundation grant OCE-9986724, and NSF grant ATM-0120569

Revising upper-ocean sulfur dynamics near Bermuda : new lessons from 3 years of concentration and rate measurements

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Chemistry 13 (2016): 302-313, doi:10.1071/EN15045.Oceanic biogeochemical cycling of dimethylsulfide (DMS), and its precursor dimethylsulfoniopropionate (DMSP), has gained considerable attention over the past three decades because of the potential role of DMS in climate mediation. Here we report 3 years of monthly vertical profiles of organic sulfur cycle concentrations (DMS, particulate DMSP (DMSPp) and dissolved DMSP (DMSPd)) and rates (DMSPd consumption, biological DMS consumption and DMS photolysis) from the Bermuda Atlantic Time-series Study (BATS) site taken between 2005 and 2008. Concentrations confirm the summer paradox with mixed layer DMS peaking ~90 days after peak DMSPp and ~50 days after peak DMSPp : Chl. A small decline in mixed layer DMS was observed relative to those measured during a previous study at BATS (1992–1994), potentially driven by long-term climate shifts at the site. On average, DMS cycling occurred on longer timescales than DMSPd (0.43 ± 0.35 v. 1.39 ± 0.76 day–1) with DMSPd consumption rates remaining elevated throughout the year despite significant seasonal variability in the bacterial DMSP degrader community. DMSPp was estimated to account for 4–5 % of mixed layer primary production and turned over at a significantly slower rate (~0.2 day–1). Photolysis drove DMS loss in the mixed layer during the summer, whereas biological consumption of DMS was the dominant loss process in the winter and at depth. These findings offer new insight into the underlying mechanisms driving DMS(P) cycling in the oligotrophic ocean, provide an extended dataset for future model evaluation and hypothesis testing and highlight the need for a reexamination of past modelling results and conclusions drawn from data collected with old methodologies.The authors acknowledge funding from the National Science Foundation (NSF) (OCE-0425166) and the Center for Microbial Oceanography Research and Education (CMORE) a NSF Science and Technology Center (EF-0424599)

Sea-to-air fluxes from measurements of the atmospheric gradient of dimethylsulfide and comparison with simultaneous relaxed eddy accumulation measurements

We measured vertical profiles of dimethylsulfide (DMS) in the atmospheric marine boundary layer from R/P FLIP during the 2000 FAIRS cruise. Applying Monin-Obukhov similarity theory to the DMS gradients and simultaneous micrometeorological data, we calculated sea-to-air DMS fluxes for 34 profiles. From the fluxes and measured seawater DMS concentrations, we calculated the waterside gas transfer velocity, kw. Gas transfer velocities from the gradient flux approach are within the range of previous commonly used parameterizations of kw as a function of wind speed but are a factor of 2 smaller than simultaneous determinations of transfer velocity using the relaxed eddy accumulation technique. This is the first field comparison of these different techniques for measuring DMS flux from the ocean; the accuracy of the techniques and possible reasons for the discrepancy are discussed

Environmental, biochemical and genetic drivers of DMSP degradation and DMS production in the Sargasso Sea

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Environmental Microbiology 14 (2012): 1210-1223, doi:10.1111/j.1462-2920.2012.02700.x.Dimethylsulfide (DMS) is a climatically relevant trace gas produced and cycled by the surface ocean food web. Mechanisms driving intraannual variability in DMS production and dimethylsulfoniopropionate (DMSP) degradation in open-ocean, oligotrophic regions were investigated during a 10 month time-series at the Bermuda Atlantic Time-series Study site in the Sargasso Sea. Abundance and transcription of bacterial DMSP degradation genes, DMSP lyase enzyme activity, and DMS and DMSP concentrations, consumption rates, and production rates were quantified over time and depth. This interdisciplinary dataset was used to test current hypotheses of the role of light and carbon supply in regulating upper-ocean sulfur cycling. Findings supported UV-A dependent phytoplankton DMS production. Bacterial DMSP degraders may also contribute significantly to DMS production when temperatures are elevated and UV-A dose is moderate, but may favor DMSP demethylation under low UV-A doses. Three groups of bacterial DMSP degraders with distinct intraannual variability were identified and niche differentiation was indicated. The combination of genetic and biochemical data suggest a modified ‘bacterial switch’ hypothesis where the prevalence of different bacterial DMSP degradation pathways is regulated by a complex set of factors including carbon supply, temperature, and UV-A dose.This research was funded by National Science Foundation (NSF) grants OCE- 0525928, OCE-072417, and OCE-042516. Additional funding was provided by the NSF Center for Microbial Oceanography Research and Education (CMORE), the Gordon and Betty Moore Foundation, the Scurlock Fund, the Ocean Ventures Fund, a National Defense Science and Engineering Graduate Fellowship, and an Environmental Protection Agency STAR Graduate Fellowship

Influence of rain on air-sea gas exchange : lessons from a model ocean

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S18, doi:10.1029/2003JC001806.Rain has been shown to significantly enhance the rate of air-water gas exchange in fresh water environments, and the mechanism behind this enhancement has been studied in laboratory experiments. In the ocean, the effects of rain are complicated by the potential influence of density stratification at the water surface. Since it is difficult to perform controlled rain-induced gas exchange experiments in the open ocean, an SF6 evasion experiment was conducted in the artificial ocean at Biosphere 2. The measurements show a rapid depletion of SF6 in the surface layer due to rain enhancement of air-sea gas exchange, and the gas transfer velocity was similar to that predicted from the relationship established from freshwater laboratory experiments. However, because vertical mixing is reduced by stratification, the overall gas flux is lower than that found during freshwater experiments. Physical measurements of various properties of the ocean during the rain events further elucidate the mechanisms behind the observed response. The findings suggest that short, intense rain events accelerate gas exchange in oceanic environments.Funding was provided by a generous grant from the David and Lucile Packard Foundation

The effect of age on outcomes of coronary artery bypass surgery compared with balloon angioplasty or bare-metal stent implantation among patients with multivessel coronary disease. A collaborative analysis of individual patient data from 10 randomized trials.

OBJECTIVES: This study sought to assess whether patient age modifies the comparative effectiveness of coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI). BACKGROUND: Increasingly, CABG and PCI are performed in older patients to treat multivessel disease, but their comparative effectiveness is uncertain. METHODS: Individual data from 7,812 patients randomized in 1 of 10 clinical trials of CABG or PCI were pooled. Age was analyzed as a continuous variable in the primary analysis and was divided into tertiles for descriptive purposes (≤56.2 years, 56.3 to 65.1 years, ≥65.2 years). The outcomes assessed were death, myocardial infarction and repeat revascularization over complete follow-up, and angina at 1 year. RESULTS: Older patients were more likely to have hypertension, diabetes, and 3-vessel disease compared with younger patients (p < 0.001 for trend). Over a median follow-up of 5.9 years, the effect of CABG versus PCI on mortality varied according to age (interaction p < 0.01), with adjusted CABG-to-PCI hazard ratios and 95% confidence intervals (CI) of 1.23 (95% CI: 0.95 to 1.59) in the youngest tertile; 0.89 (95% CI: 0.73 to 1.10) in the middle tertile; and 0.79 (95% CI: 0.67 to 0.94) in the oldest tertile. The CABG-to-PCI hazard ratio of less than 1 for patients 59 years of age and older. A similar interaction of age with treatment was present for the composite outcome of death or myocardial infarction. In contrast, patient age did not alter the comparative effectiveness of CABG and PCI on the outcomes of repeat revascularization or angina. CONCLUSIONS: Patient age modifies the comparative effectiveness of CABG and PCI on hard cardiac events, with CABG favored at older ages and PCI favored at younger ages