Dacey John W. H.

No Thumbnail Available
Last Name
First Name
John W. H.

Search Results

Now showing 1 - 20 of 25
  • Article
    Metabolism of dimethylsulfoniopropionate (DMSP) by juvenile Atlantic menhaden Brevoortia tyrannus
    (Inter-Research, 2006-09-30) Hill, Richard W. ; Dacey, John W. H.
    Dimethylsulfoniopropionate (DMSP) synthesized by marine phytoplankton is the principal source of dimethylsulfide (DMS), an important climate-affecting gas. Prior research has demonstrated that grazing by invertebrate phytoplanktivores often affects the dynamics of DMS production from algal DMSP, but the effects of grazing by phytoplanktivorous fish have not previously been investigated. We studied the fate of algal DMSP following grazing by juvenile Atlantic menhaden Brevoortia tyrannus (13 cm fork length), which are generally viewed as the most specialized for phytoplanktivory of all postlarval fish. The menhaden were fed the dinoflagellate Prorocentrum micans, containing 1 to 2 pmol DMSP cell–1. During the first 24 h following ingestion of algal DMSP, almost none of the DMSP (ca. 1%) appeared as DMS. About 21% of ingested DMSP appeared in the water column as dissolved DMSP, peaking in concentration 9 to 11 h after feeding; in natural settings, this fraction would be poised for microbial metabolism, including potential conversion to DMS in surface waters from which outgassing to the atmosphere could occur. About 10% of ingested DMSP appeared in fecal pellets that tended to sink rapidly toward the bottom of the tanks. About 33% of ingested DMSP was deposited in the tissues of the menhaden, in particular in the red and white swimming muscles, in which we observed concentrations exceeding 0.7 µmol g–1. This final fraction could ultimately be metabolized to DMS, or it could be passed up food chains and possibly act as a taste factor in commercially important piscivores such as striped bass and bluefish. In total, our research demonstrated that at least two-thirds of the ingested DMSP ends up in tissues or feces or in solution in the ambient water in the first 24 h after feeding, and virtually none is converted to ambient DMS during that time period.
  • Article
    Dimethylsulfoniopropionate in six species of giant clams and the evolution of dimethylsulfide after death
    (National Research Council Canada, 2004-06-23) Hill, Richard W. ; Dacey, John W. H. ; Hill, Susan D. ; Edward, Ahser ; Hicks, Wayne A.
    Substantial accumulation of dimethylsulfoniopropionate (DMSP) is documented in tissues of all six of the common species of giant clams (Tridacnidae). Results include measures of DMSP concentrations in siphonal mantle, byssal mantle, adductor muscle, and gill tissues obtained by gas chromatography of alkalized extracts plus evidence of DMSP from mass spectrometry. Formation of dimethylsulfide (DMS) by tissues after death is documented. The tridacnid clams maintain symbiotic associations with populations of dinoflagellates, which live within the enlarged siphonal mantle. We postulated that because of their association with dinoflagellates, the clams would chronically accumulate DMSP to high concentrations. Our results show that DMSP occurs at over 30 mmol·kg–1 in many tissues of tridacnid clams (sometimes 50–60 mmol·kg–1), meaning that these clams accumulate DMSP to the highest documented tissue concentrations in the animal kingdom. DMSP at such concentrations could affect multiple properties and functions. Our particular interest for this research was to assess whether postmortem breakdown of DMSP is responsible for the rapid development of potent off-odors and off-tastes that have blocked the commercial success of giant clam aquaculture. High concentrations of DMS produced in the day after death probably account for the peculiar perishability of giant clam tissues.
  • Article
    The distribution of methylated sulfur compounds, DMS and DMSP, in Canadian subarctic and Arctic marine waters during summer 2015
    (Copernicus Publications on behalf of the European Geosciences Union, 2018-04-23) Jarníková, Tereza ; Dacey, John W. H. ; Lizotte, Martine ; Levasseur, Maurice ; Tortell, Philippe D.
    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.
  • Article
    CO2 deposition over the multi-year ice of the western Weddell Sea
    (American Geophysical Union, 2006-07-13) Zemmelink, Hendrik J. ; Delille, Bruno ; Tison, Jean-Louis ; Hintsa, Eric J. ; Houghton, Leah A. ; Dacey, John W. H.
    Field measurements by eddy correlation (EC) indicate an average uptake of 0.6 g CO2 m−2 d−1 by the ice-covered western Weddell Sea in December 2004. At the same time, snow that covers ice floes of the western Weddell Sea becomes undersaturated with CO2 relative to the atmosphere during early summer. Gradients of CO2 from the ice to the atmosphere do not support significant diffusive fluxes and are not strong enough to explain the observed CO2 deposition. We hypothesize that the transport of air through the snow pack is controlled by turbulence and that undersaturation of CO2 is caused by biological productivity at the ice-snow and snow-atmosphere interface. The total carbon uptake by the multi-year ice zone of the western Weddell Sea in December could have been as high as 6.6 Tg C y−1.
  • Article
    Relaxed eddy accumulation measurements of the sea-to-air transfer of dimethylsulfide over the northeastern Pacific
    (American Geophysical Union, 2004-01-30) Zemmelink, Hendrik J. ; Gieskes, Winfried W. C. ; Klaassen, Wim ; Beukema, Wim J. ; de Groot, Henk W. ; Baar, Hein J. W. de ; Hintsa, Eric J. ; McGillis, Wade R. ; Dacey, John W. H.
    Gas transfer rates were determined from relaxed eddy accumulation (REA) measurements of the flux of dimethylsulfide (DMS) over the northeastern Pacific Ocean. This first application of the REA technique for the measurement of DMS fluxes over the open ocean produced estimates of the gas transfer rate that are on average higher than those calculated from commonly used parameterizations. The relationship between the total gas transfer rate and wind speed was found to be gas kgas = 0.53 (±0.05) U102. Because of the effect of the airside resistance, the waterside transfer rate was up to 16% higher than kgas. Removal of the airside transfer component from the total transfer rate resulted in a relation between wind speed and waterside transfer of k660 = 0.61 (±0.06) U102. However, DMS fluxes showed a high degree of scatter that could not readily be accounted for by wind speed and atmospheric stability. It has to be concluded that these measurements do not permit an accurate parameterization of gas transfer as a function of wind speed.
  • Article
    Sea-to-air fluxes from measurements of the atmospheric gradient of dimethylsulfide and comparison with simultaneous relaxed eddy accumulation measurements
    (American Geophysical Union, 2004-01-30) Hintsa, Eric J. ; Dacey, John W. H. ; McGillis, Wade R. ; Edson, James B. ; Zappa, Christopher J. ; Zemmelink, Hendrik J.
    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.
  • Article
    Direct measurements of biogenic dimethylsulphide fluxes from the oceans : a synthesis
    (National Research Council Canada, 2004-06-24) Zemmelink, Hendrik J. ; Dacey, John W. H. ; Hintsa, Eric J.
    This paper provides a brief overview of the state-of-the-art of techniques that are currently used for field measurements of trace gas fluxes and the subsequent derivation of gas transfer rates over the oceans. Special attention is given to the relaxed eddy accumulation (REA) and gradient flux (GF) techniques, which rely on empirical functions thus far mainly validated over land. The universality of these functions and their application at sea have not yet been fully evaluated. New experiments have shown that the emission of dimethylsulphide (DMS) can be measured by the REA and GF techniques. Moreover, these measurements have provided parameterizations of gas exchange rates that are within the range of relationships between wind speed and gas transfer that have recently been derived from eddy correlation (EC) and deliberate tracer measurements. Using DMS as a model, gas is potentially a powerful approach to intercalibrate the REA, GF, and EC techniques, test their applicability in the marine environment, and investigate processes that determine trace gas exchange across the ocean surface.
  • Article
    Processing of ingested dimethylsulfoniopropionate by mussels Mytilus edulis and scallops Argopecten irradians
    (Inter-Research, 2007-08-07) Hill, Richard W. ; Dacey, John W. H.
    Dimethylsulfoniopropionate (DMSP) synthesized by marine phytoplankton is the principal source of dimethylsulfide (DMS), an important climate-affecting gas. Grazing by small zooplankton on phytoplankton often accelerates DMS production from algal DMSP. The effects of grazing by benthic suspension feeders, such as bivalve molluscs, however, have not been studied, even though their populations sometimes process a sizable fraction of local phytoplankton production. We fed Tetraselmis sp. Strain UW474 (27 to 42 fmol DMSP cell–1) to adult mussels Mytilus edulis and scallops Argopecten irradians and studied the fate of the algal DMSP during the 24 h following ingestion. Almost none of the ingested DMSP reappeared in the environment as DMS or DMSP; the amount that appeared in the ambient water as DMS was <1% of that ingested, and the sum total that appeared either as fecal DMSP (which microbes might convert to DMS) or in the water as DMS or DMSP was ≤3 to 4% of that ingested. In the short term, therefore, thriving bivalve populations probably strongly reduce the rate of DMS formation (direct or indirect) from local algal DMSP, in contrast to zooplankton populations. Ingested DMSP is likely accumulated in the bodies of mussels and scallops. However, although we have weak evidence of partial accumulation in scallop gastrointestinal tissue, we were unable to document accumulation in mussels because of high variability and statistical nonnormality in their naturally occurring DMSP content. In total, we showed that in the 24 h following feeding, mussels and scallops do not facilitate ambient DMS formation from algal DMSP and evidently sequester most of the algal DMSP they ingest.
  • Article
    Supplement to physical exchanges at the air–sea interface : UK–SOLAS field measurements
    (American Meteorological Society, 2009-05) Brooks, Ian M. ; Yelland, Margaret J. ; Upstill-Goddard, Robert C. ; Nightingale, Philip D. ; Archer, Stephen D. ; D'Asaro, Eric A. ; Beale, Rachael ; Beatty, Cory ; Blomquist, Byron ; Bloom, A. Anthony ; Brooks, Barbara J. ; Cluderay, John ; Coles, David ; Dacey, John W. H. ; DeGrandpre, Michael D. ; Dixon, Jo ; Drennan, William M. ; Gabriele, Joseph ; Goldson, Laura E. ; Hardman-Mountford, Nick ; Hill, Martin K. ; Horn, Matt ; Hsueh, Ping-Chang ; Huebert, Barry ; De Leeuw, Gerrit ; Leighton, Timothy G. ; Liddicoat, Malcolm ; Lingard, Justin J. N. ; McNeil, Craig L. ; McQuaid, James B. ; Moat, Bengamin I. ; Moore, Gerald ; Neill, Craig L. ; Norris, Sarah J. ; O'Doherty, Simon ; Pascal, Robin W. ; Prytherch, John ; Rebozo, Mike ; Sahlee, Erik ; Salter, Matt ; Schuster, Ute ; Skjelvan, Ingunn ; Slagter, Hans ; Smith, Michael H. ; Smith, Paul D. ; Srokosz, Meric ; Stephens, John A. ; Taylor, Peter K. ; Telszewski, Maciej ; Walsh, Roisin ; Ward, Brian ; Woolf, David K. ; Young, Dickon ; Zemmelink, Hendrik J.
  • Article
    Rain-induced turbulence and air-sea gas transfer
    (American Geophysical Union, 2009-07-09) Zappa, Christopher J. ; Ho, David T. ; McGillis, Wade R. ; Banner, Michael L. ; Dacey, John W. H. ; Bliven, Larry F. ; Ma, Barry ; Nystuen, Jeffrey A.
    Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate ɛ are strongly influenced by near-surface stratification. The gas transfer rate scales with ɛ inline equation for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of ɛ beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10−2 W kg−1. Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, ɛ is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of ɛ fundamental to gas transfer.
  • Article
    Influence of rain on air-sea gas exchange : lessons from a model ocean
    (American Geophysical Union, 2004-07-01) Ho, David T. ; Zappa, Christopher J. ; McGillis, Wade R. ; Bliven, Larry F. ; Ward, Brian ; Dacey, John W. H. ; Schlosser, Peter ; Hendricks, Melissa B.
    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.
  • Article
    Metabolic balance of coastal Antarctic waters revealed by autonomous pCO2 and ΔO2/Ar measurements
    (John Wiley & Sons, 2014-10-03) Tortell, Philippe D. ; Asher, Elizabeth C. ; Ducklow, Hugh W. ; Goldman, Johanna A. L. ; Dacey, John W. H. ; Grzymski, Joseph J. ; Young, Jodi N. ; Kranz, Sven A. ; Bernard, Kim S. ; Morel, Francois M. M.
    We use autonomous gas measurements to examine the metabolic balance (photosynthesis minus respiration) of coastal Antarctic waters during the spring/summer growth season. Our observations capture the development of a massive phytoplankton bloom and reveal striking variability in pCO2 and biological oxygen saturation (ΔO2/Ar) resulting from large shifts in community metabolism on time scales ranging from hours to weeks. Diel oscillations in surface gases are used to derive a high-resolution time series of net community production (NCP) that is consistent with 14C-based primary productivity estimates and with the observed seasonal evolution of phytoplankton biomass. A combination of physical mixing, grazing, and light availability appears to drive variability in coastal Antarctic NCP, leading to strong shifts between net autotrophy and heterotrophy on various time scales. Our approach provides insight into the metabolic responses of polar ocean ecosystems to environmental forcing and could be employed to autonomously detect climate-dependent changes in marine primary productivity.
  • Preprint
    Exceptional accumulation and retention of dimethylsulfoniopropionate by molluscs
    ( 2015-05) Hill, Richard W. ; Dacey, John W. H.
    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.
  • Article
    Dimethylsulfide emissions over the multi-year ice of the western Weddell Sea
    (American Geophysical Union, 2008-03-20) Zemmelink, Hendrik J. ; Dacey, John W. H. ; Houghton, Leah A. ; Hintsa, Eric J. ; Liss, P. S.
    This study, conducted in December 2004, is the first to present observations of DMS in a snow pack covering the multi-year sea ice of the western Weddell Sea. The snow layer is important because it is the interface through which DMS needs to be transported in order to be emitted directly from the ice to the overlying atmosphere. High concentrations of DMS, up to 6000 nmol m−3, were found during the first weeks of December but concentrations sharply decline as late spring-early summer progresses. This implies that DMS contained in sea ice is efficiently vented through the snow into the atmosphere. Indeed, field measurements by relaxed eddy accumulation indicate an average release of 11 μmol DMS m−2 d−1 from the ice and snow throughout December.
  • Article
    Fluxes and gas transfer rates of the biogenic trace gas DMS derived from atmospheric gradients
    (American Geophysical Union, 2004-06-30) Zemmelink, Hendrik J. ; Dacey, John W. H. ; Hintsa, Eric J. ; McGillis, Wade R. ; Gieskes, Winfried W. C. ; Klaassen, Wim ; de Groot, Henk W. ; Baar, Hein J. W. de
    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.
  • Article
    Environmental turbulent mixing controls on air-water gas exchange in marine and aquatic systems
    (American Geophysical Union, 2007-05-17) Zappa, Christopher J. ; McGillis, Wade R. ; Raymond, Peter A. ; Edson, James B. ; Hintsa, Eric J. ; Zemmelink, Hendrik J. ; Dacey, John W. H. ; Ho, David T.
    Air-water gas transfer influences CO2 and other climatically important trace gas fluxes on regional and global scales, yet the magnitude of the transfer is not well known. Widely used models of gas exchange rates are based on empirical relationships linked to wind speed, even though physical processes other than wind are known to play important roles. Here the first field investigations are described supporting a new mechanistic model based on surface water turbulence that predicts gas exchange for a range of aquatic and marine processes. Findings indicate that the gas transfer rate varies linearly with the turbulent dissipation rate to the inline equation power in a range of systems with different types of forcing - in the coastal ocean, in a macro-tidal river estuary, in a large tidal freshwater river, and in a model (i.e., artificial) ocean. These results have important implications for understanding carbon cycling.
  • Article
    Behaviour of the ocean DMS(P) pools in the Sargasso Sea viewed in a coupled physical-biogeochemical ocean model
    (National Research Council Canada, 2004-06-23) Le Clainche, Yvonnick ; Levasseur, Maurice ; Vezina, Alain ; Dacey, John W. H. ; Saucier, Francois J.
    The dimethylsulfide (DMS) production model NODEM (Northern Oceans DMS Emission Model) was coupled with the water column ocean model GOTM (General Ocean Turbulence Model) that includes a two-equation k&150;ε turbulence scheme. This coupled physical-biogeochemical ocean model represents a significant improvement over the previous uncoupled version of NODEM that was driven by a diagnostic vertical mixing scheme. Using the same set of biogeochemical parameters, the coupled model is used to simulate the annual cycles of 1992 and 1993 at Hydrostation S in the Sargasso Sea. The better reproduction of the turbulent mixing environment corrects some deficiencies in nitrogen cycling, especially in the seasonal evolution of the nutrient concentrations. Hence, the coupled model captures the late-winter chlorophyll- and DMS(P)-rich blooms. It is also more adept at reproducing the vertical distribution of chlorophyll and DMS(P) in summer. Moreover, the DMS pool becomes less dependent on parameters controlling the nitrogen cycle and relatively more sensitive to parameters related to the sulfur cycle. Finally, the coupled model reproduces some of the observed differences in DMS(P) pools between 1992 and 1993, the latter being an independent data set not used in calibrating the initial version of NODEM.
  • Article
    Patterns and drivers of dimethylsulfide concentration in the northeast subarctic Pacific across multiple spatial and temporal scales.
    (European Geosciences Union, 2019-04-25) Herr, Alysia E. ; Kiene, Ronald P. ; Dacey, John W. H. ; Tortell, Philippe D.
    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.
  • Article
    Emission of dimethylsulfide from Weddell Sea leads
    (American Geophysical Union, 2005-12-10) Zemmelink, Hendrik J. ; Houghton, Leah A. ; Dacey, John W. H. ; Worby, A. P. ; Liss, P. S.
    The distribution of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was examined in lead water in pack ice of the Weddell Sea. Samples were taken by pulling water into a syringe from a series of depths from 0.002 m to 4 m and deeper. Concentrations of DMS, DMSP and DMSO remained low throughout the water column relative to surface water, which was highly enriched. Concentrations of the major sulfur compounds increased by over an order of magnitude during periods with smooth surface water conditions. This increase coincided with a profound stratification of the water column, caused by a decrease in salinity of near surface water. We estimate that the DMS emission from leads and open water in Antarctic sea ice could contribute significantly to the yearly DMS flux from the Southern Ocean.
  • Article
    High concentrations and turnover rates of DMS, DMSP and DMSO in Antarctic sea ice
    (American Geophysical Union, 2011-12-14) Asher, Elizabeth C. ; Dacey, John W. H. ; Mills, Matthew M. ; Arrigo, Kevin R. ; Tortell, Philippe D.
    The vast Antarctic sea-ice zone (SIZ) is a potentially significant source of the climate-active gas dimethylsulfide (DMS), yet few data are available on the concentrations and turnover rates of DMS and the related compounds dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) in sea ice environments. Here we present new measurements characterizing the spatial variability of DMS, DMSP, and DMSO concentrations across the Antarctic SIZ, and results from tracer experiments quantifying the production rates of DMS from various sources. We observed extremely high concentrations (>200 nM) and turnover rates (>100 nM d−1) of DMS in sea-ice brines, indicating intense cycling of DMS/P/O. Our results demonstrate a previously unrecognized role for DMSO reduction as a major pathway of DMS production in Antarctic sea ice.