Michael Scarratt

Production of methyl bromide and methyl chloride in laboratory cultures of marine phytoplankton II

Methyl halides (monohalomethanes), especially methyl bromide, are known to contribute significantly to ozone destruction in the stratosphere. Budgets of natural and anthropogenic methyl bromide suggest that marine organisms may be the source of a significant proportion of the total global production. Since phytoplankton are abundant in surface waters, they are obvious candidates. Cultures of nine phytoplankton species were grown in CO2-enriched, nitrate-limited medium in sealed glass vessels. Species tested include Chaetoceros calcitrans, Isochrysis sp., Porphyridium sp., Synechococcus sp., Phaeodactylum tricornutum, Tetraselmis sp., Prorocentrum sp., Emiliania huxleyi and Phaeocystis sp. Methyl bromide (CH3Br) and methyl chloride (CH3Cl) concentrations were determined by bubbling the cultures with high-purity air, cryotrapping the effluent and analyzing it on a gas chromatograph with an electron capture detector. The Phaeocystis sp. samples were monitored with GCMS. Cell population, bacterial population, Chl a, pH, and nitrate concentration were monitored for periods of at least two weeks. CH3Cl was produced by all cultures. CH3Br was absent in Tetraselmis sp. and Isochrysis sp. cultures, but present in all the others. Methyl iodide (CH3I) was present in most cultures but could not be quantified due to analytical limitations. CH3I and CH3Br production was fastest in stationary phase and continued long after cell division had ceased. Axeic cultures of Phaeocystis sp. achieved almost identical production rates of CH3Cl and CH3Br as xenic cultures of the same species. Species from tropical waters had faster CH3Cl and CH3Br production rates than temperate species. Scaling the observed production rates using global standing stock estimates for Chl a and particulate nitrogen indicate that phytoplankton can account for only a fraction of the CH3Cl and CH3Br believed to be produced in the ocean. Calculations based on the estimated global biomass of Phaeocystis sp. and E. huxleyi blooms show that their contribution is insignificantly small.

Production of methyl chloride and methyl bromide in laboratory cultures of marine phytoplankton

Abstract Laboratory cultures of three phytoplankton species ( Phaeodactylum tricornutum, Phaeocystis sp., Thalassiosira weissflogii ) were tested for methyl halide (monohalomethane) production by sparging and cryotrapping coupled with GC-ECD detection. Both axenic and xenic cultures were tested under various nutrient regimens. Production of methyl bromide (CH 3 Br) and methyl chloride (CH 3 Cl) was observed in all cultures. Methyl iodide (CH 3 I) production was also observed but could not be quantified due to Chromatographic interference. No consistent differences in production rates were observed between axenic and xenic cultures or between nutrient regimens. Methyl halide production was not directly dependent on photosynthesis. Within each species, total methyl halide production was most closely correlated with biomass, measured as utilized nitrate (ΔDIN) or Chl a . Among the three species, Phaeocystis sp. had the highest production rates and T. weissflogii the lowest. In all cases, the biomass-normalized production rates were only a fraction of the levels needed for the ocean to constitute a significant global source of either CH 3 Cl or CH 3 Br. However, it must be noted that these data comprise results from a limited number of species and a limited range of conditions.

Biological and physical processes influencing sea ice, under‐ice algae, and dimethylsulfoniopropionate during spring in the Canadian Arctic Archipelago

This study presents temporal variations in concentrations of chlorophyll a (Chl a), particulate and dissolved dimethylsulfoniopropionate (DMSPp and DMSPd) in the sea ice and underlying water column in the Canadian Arctic Archipelago during the spring of 2010 and 2011. During both years, bottom ice Chl a, DMSPp and DMSPd concentrations were high (up to 1328 µg L−1, 15,082 nmol L−1, and 6110 nmol L−1, respectively) in May and decreased thereafter. The release of bottom ice algae and DMSPp in the water column was gradual in 2010 and rapid (8 days) in 2011. Bottom brine drainage during the presnowmelt period in 2010 and a rapid loss of the snow cover in 2011 coinciding with rain events explain most of the difference between the 2 years. During both years, less than 13% of the DMSPd lost from the ice was detected in the water column, suggesting a rapid microbial consumption. An under-ice diatom bloom developed in both years. In 2010, the bloom was dominated by centric diatoms while in 2011 pennates dominated, likely reflecting seeding by ice algae following the faster snowmelt progression induced by rainfall events in 2011. Both under-ice blooms were associated with high DMSPp concentrations (up to 185 nmol L−1), but pennate diatoms showed DMSPp/Chl a ratios twice higher than centrics. These results highlight the key role of snowmelt and precipitation on the temporal pattern of ice-DMSP release to the water column and on the timing, taxonomic composition, and DMSP content of phytoplankton under-ice blooms in the Arctic.

Macroscale patterns of the biological cycling of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the Northwest Atlantic

The influence of the seasonal development of microplankton communities on the cycling of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) was investigated along a South–North gradient (36–59°N) in the Northwest (NW) Atlantic Ocean. Three surveys allowed the sampling of surface mixed layer (SML) waters at stations extending from the subtropical gyre to the Greenland Current during May, July and October 2003. Pools and transformation rates of DMSP and DMS were quantified and related to prevailing physical and biochemical conditions, phytoplankton abundance and taxonomic composition, as well as bacterioplankton abundance and leucine uptake. The South–North progression of the diatom bloom, a prominent feature in the NW Atlantic, did not influence the production of DMS whereas conditions in the N Atlantic Drift lead to a persistent bloom of DMSP-rich flagellate-dominated phytoplankton community and high net DMS production rates. Macroscale patterns of the observed variables were further explored using principal component analysis (PCA). The first axis of the PCA showed a strong association between the spatio-temporal distribution of DMSP and the abundance of several phytoplankton groups including dinoflagellates and prymnesiophytes, as well as with microbial-mediated DMSPd consumption and yields and rates of the conversion of DMSP into DMS. The second axis revealed a strong association between concentrations of DMS and SML depth and photosynthetically active radiation, a result supporting the prominent role of solar radiation as a driver of DMS dynamics.

Modeling analysis of the effect of iron enrichment on dimethyl sulfide dynamics in the NE Pacific (SERIES experiment)

The large-scale iron enrichment conducted in the NE Pacific during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) triggered a phytoplankton bloom dominated successively by nanophytoplankton and large diatoms. During the first 14 days, surface dimethyl sulfide (DMS) levels increased both inside (up to 22 nmol L-1) and outside (up to 19 nmol L-1) the patch, with no consistent Fe effect. Later, DMS concentrations became sixfold lower inside the patch than outside. In this study, we used a DMS budget module embedded in a one-dimensional ocean turbulence model to investigate the contribution of the interacting physical, photochemical, and biological processes to this particular DMS response. Temporal variations in biological net DMS production were reconstructed using an inverse modeling approach. Our results show that short-term (days) variations in both the physical processes (i.e., turbulent mixing and ventilation) and the biological cycling of DMS are needed to explain the time evolution of DMS concentrations both outside and inside the Fe-enriched patch. The biological net DMS production was generally high (up to 0.35 nmol L-1 h-1) and comparable outside and inside the patch during the first 10 days, corresponding to the observed accumulation of DMS inside and outside the patch. Later, it became negative (net DMS biological consumption) inside the patch, suggesting a change in dimethylsulfoniopropionate bacterial metabolism. This study stresses the importance of short-term variations in biological processes and their sensitivity to the physical environment in shaping the DMS response to iron enrichment.

DMSP and DMS in the Northwest Atlantic : Late-summer distributions, production rates and sea-air fluxes

Abstract.DMSP and DMS were measured along a set of transects in the Northwest Atlantic during September, 1999. Six 24 h Lagrangian stations were occupied between 36° and 61° N latitude, covering subtropical to polar water types. Profiles of total DMSP (DMSPt), DMS, chl a, and oceanographic variables were determined at each station. Phytoplankton abundance and species assemblage were determined in surface waters and at the depth of the Chl a maximum in all profiles. Between profile stations, DMSPt and DMS samples were collected by a pump while the vessel was moving. Chl a and DMSPt were most abundant in the northern regions, with very low levels in subtropical waters. There was no direct correlation between DMSPt and Chl a. Maximum DMSPt concentrations reached 203 nM in coastal waters and 112 nM in the open ocean. A strong correlation was observed between DMSPt and the abundance of dinoflagellates (Spearman r=0.91; p <0.0001; n=13) and prymnesiophytes (Spearman r=0.91; p<0.0001; n=13). Cryptophytes also showed a weak but significant correlation (Spearman r=0.58; p=0.039; n=13). The waters around Greenland were the only site dominated by diatoms and their abundance was not correlated with DMSPt concentrations. DMS concentrations were low and fairly uniform, with maximum levels of 4.7 nM in coastal waters and 2.2 nM in the open ocean. DMS fluxes from surface waters were calculated based on observed sea-surface concentrations and wind speeds and showed a strong peak associated with a storm event, although no depletion of DMS resulting from the storm was observed. In situ incubation experiments showed DMSP consumption and DMS production rates to be relatively high, notwithstanding the generally low phytoplankton biomass.

Carbon disulphide production in laboratory cultures of marine phytoplankton

Abstract Carbon disulphide (CS 2 ) data were collected from axenic monocultures of six species of marine phytoplankton. The tested species included Chaetoceros calcitrans , Phaeodactylum tricornutum , Phaeocystis sp., Porphyridium purpureum , Synechococcus sp. and Isochrysis sp. For a period of between two weeks and forty days, substantial accumulation of CS 2 was found in the cultures of C . calcitrans , P . tricornutum and Phaeocystis sp ., whereas the change of CS 2 concentration in the remaining cultures was insignificant. C . calcitrans had a potential for CS 2 production about 10 times higher than P . tricornutum or Phaeocystis sp. The formation of the compound was strongly dependent on the physiological state of the cultured species. More investigation is needed to elucidate the mechanisms responsible for the formation of this sulphur compound in these cultures.

Multispecies mass mortality of marine fauna linked to a toxic dinoflagellate bloom

Following heavy precipitation, we observed an intense algal bloom in the St. Lawrence Estuary (SLE) that coincided with an unusually high mortality of several species of marine fish, birds and mammals, including species designated at risk. The algal species was identified as Alexandrium tamarense and was determined to contain a potent mixture of paralytic shellfish toxins (PST). Significant levels of PST were found in the liver and/or gastrointestinal contents of several carcasses tested as well as in live planktivorous fish, molluscs and plankton samples collected during the bloom. This provided strong evidence for the trophic transfer of PST resulting in mortalities of multiple wildlife species. This conclusion was strengthened by the sequence of mortalities, which followed the drift of the bloom along the coast of the St. Lawrence Estuary. No other cause of mortality was identified in the majority of animals examined at necropsy. Reports of marine fauna presenting signs of neurological dysfunction were also supportive of exposure to these neurotoxins. The event reported here represents the first well-documented case of multispecies mass mortality of marine fish, birds and mammals linked to a PST-producing algal bloom.

Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and 15 dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the 16 fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, 17 corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 μatm, at two temperatures (in situ and +5 °C; 10 °C 18 and 15 °C) was monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom 19 dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the 20 acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, 21 warming the water by 5 °C resulted in a significant increase of the average bacterial production (BP) in all 15 °C mesocosms 22 as compared to 10 °C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt = particulate + dissolved 23 DMSP) concentrations tracked the development of the bloom although the rise in DMSPt persisted for a few days after the 24 peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low 25 concentrations of DMS (< 1 nmol L) increased to reach peak values ranging from 30 to 130 nmol L towards the end of the 26 experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66 % and 69 % at 10 °C and 15 °C, 27 respectively, over the duration of the experiment. On the other hand, a 5 °C warming increased DMS concentrations by an 28 average of 240 % as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant 29 positive correlations found between bacterial production rates and concentrations of DMS throughout our experiment point 30 towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver for the mitigating effect of 31 warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean. 32 Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-338 Manuscript under review for journal Biogeosciences Discussion started: 22 August 2018 c