Angela D. Hatton

Influence of photochemistry on the marine biogeochemical cycle of dimethylsulphide in the northern North sea

Shipboard experiments were conducted in the northern North Sea to assess the rate of removal of dimethylsulphide (DMS) and the rate of production of DMSO due to both UVB and UVA/visible light. Experiments were conducted using 0.2-μm filtered seawater and natural light conditions. The DMS photolysis rate constant was determined to be between 0.03 and 0.07 h−1, and initial photolysis rates were between 1.3 and 2.5 nmol dm−3 d−1. Using these rates, the in situ profiles for downward irradiance, and the DMS concentration in the water column, a photochemical turnover rate constant of between 0.1 and 0.37 d−1 was determined for the upper 20 m of the water column, with a photochemical turnover time of between 2.5 and 9.5 days. DMSO photoproduction rates were up to 1.20 nmol dm−3 d−1. Furthermore, results indicate that under UVA/visible light most of the DMS is photo-oxidised to form DMSO, whereas under UVB radiation DMS may be removed via a second photolysis pathway.

Biological production of methyl bromide in the coastal waters of the North Sea and open ocean of the northeast Atlantic

Two separate studies in different oceanic regions provide evidence for the production of methyl bromide (CH3Br) by the prymnesiophyte Phaeocystis. A sampling program to study the seasonal cycle of CH3Br in a coastal area demonstrated that the seawater was supersaturated with respect to CH3Br for over 3 months of the year. The greatest saturation was observed during a bloom of Phaeocystis. Also, in situ field measurements demonstrated that CH3Br was supersaturated over a large region of the northeast Atlantic. A positive correlation was observed between CH3Br and dimethylsulphoniopropionate (DMSP), indicating that there was a source common to both compounds. An accessory pigment, hexanoyloxyfucoxanthin, which indicates the presence of prymnesiophytes, also correlated positively with CH3Br.

The effect of chronic and acute low pH on the intracellular DMSP production and epithelial cell morphology of red coralline algae

Abstract The release of dimethylsulphoniopropionate (DMSP) by marine algae has major impacts on the global sulphur cycle and may influence local climate through the formation of dimethylsulphide (DMS). However, the effect of global change on DMSP/DMS (DMS(P)) production by algae is not well understood. This study examined the effect of low pH on DMS(P) production and epithelial cell morphology of the free-living red coralline alga Lithothamnion glaciale. Three pH treatments were used in the 80-day experiment: (1) current pH level (8.18, control), (2) low, chronic pH representing a 2100 ocean acidification (OA) scenario (7.70) and (3) low, acute pH (7.75, with a 3-day spike to 6.47), representing acute variable conditions that might be associated with leaks from carbon capture and storage infrastructure, at CO2 vent sites or in areas of upwelling. DMS(P) production was not significantly enhanced under low, stable pH conditions, indicating that red coralline algae may have some resilience to OA. However, intracellular and water column DMS(P) concentrations were significantly higher than the control when pH was acutely spiked. Cracks were observed between the cell walls of the algal skeleton in both low pH treatments. It is proposed that this structural change may cause membrane damage that allows DMS(P) to leak from the cells into the water column, with subsequent implications for the cycling of DMS(P) in coralline algae habitats.

Particulate dimethylsulphoxide and dimethylsulphoniopropionate in phytoplankton cultures and Scottish coastal waters

Abstract.Dimethylsulphoniopropionate (DMSP), an algal compatible solute, has for many years been considered to play a key role in dimethylsulphide (DMS) production, influencing the concentrations of DMS in sea water available to be transferred to the atmosphere. However, in recent years it has been shown that dimethylsulphoxide (DMSO) can also be produced directly within the cells of marine phytoplankton. The exact role DMSO plays in cells is still subject to debate, but it is thought that it may act as an antioxidant or cryoprotectant. Whatever the reason, it has been suggested that release through algal mortality and permeative loss of DMSO from cells may contribute to dissolved DMSO concentrations and as such this pathway must also be considered an important component of DMS biogeochemistry. Experiments were conducted to investigate the intracellular concentrations of DMSO and the ratio of DMSP:DMSO in a range of phytoplankton species and in natural samples. Results indicate that prymnesiophytes and dinoflagellates are the main producers, generating relatively higher concentrations of particulate DMSO than diatoms. Results from both laboratory and field experiments show that there is a strong relationship between DMSOp and DMSPp, with DMSO generally representing between 10 and 20% of the intracellular sulphur pool. Field data also indicates that dissolved DMSO concentrations in surface waters were not significantly correlated with those for particulate DMSO, but were significantly correlated with DMS concentrations.

The role of dimethylsulphoxide in the marine biogeochemical cycle of dimethylsulphide

Dimethylsulphoxide ((CH 3 ) 2 SO; DMSO) occurs naturally in marine and freshwater environments, rainwater, and the atmosphere. It is thought to be an environmentally significant compound due to the potential role it plays in the biogeochemical cycle of the climatically active trace gas, dimethylsulphide (DMS). Generally it has been assumed that the photochemical and bacterial oxidations of DMS to DMSO represent major sources of this compound and significant sinks for DMS in the marine environment. Conversely, it has also been suggested that DMSO may be a potential source for oceanic DMS. Recent research has improved understanding of the origin and fate of DMSO in sea water, although it seems likely that the full role this compound may play in the marine sulphur cycle has still to be elucidated. The methods available for determining DMSO in aqueous samples and current knowledge of the distribution of DMSO in marine waters are reviewed. Mechanisms for DMSO production and loss pathways are also considered, as well as the possible role this compound may play in the cycling of DMS and global climate.

DMSP removal and DMSO production in sedimenting particulate matter in the northern North Sea

Work was conducted to establish if the downward flux of sedimenting material represents a sink for particulate dimethylsulphoniopropionate (DMSP) and to investigate the fate of this DMSP within the sedimenting material. Four sediment traps were successfully deployed for a maximum of 24 h in the northern North Sea between the 5th June and the 1st July 1999. After recovery, samples were taken immediately and analysed for levels of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and DMSP. Any remaining trap material was incubated in the dark at in situ seawater temperature for a maximum of 120 h. Results from the sediment traps showed that only 1% of the DMSP standing stock was lost daily due to sedimentation. However, results from the incubation experiment demonstrated not only that the downward flux of DMSP is underestimated due to its degradation within the trap material, with between 30% and 47% of the DMSP being lost over 48 h, but also that up to 21% of the DMSP lost may be converted to DMSO. These results clearly demonstrate that DMSO is generated within sedimenting material.

Distribution of biogenic sulphur compounds during and just after the southwest monsoon in the Arabian Sea

The Arabian Sea is characterised by strong seasonal oscillations of biological productivity generated by its monsoonal climate. The southwest monsoon causes reversal in the surface circulation of the Arabian Sea, which generates a seasonal upwelling of nutrient-rich waters along the coast of Oman. Concentrations of biogenic sulphur compounds were measured on a transect from the eutrophic waters off the coast of Oman to the oligotrophic waters of the open Arabian Sea, during the UK NERC Arabesque cruise 27 August–4 October 1994. The concentrations of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphoniopropionate (DMSP) were found to be elevated in the eutrophic area due to enhanced biological production. However, this increase in DMS, DMSO and DMSP concentration was not observed until after the southwest monsoon had relaxed, and appeared to correspond to increased concentrations of hexanoyloxyfucoxanthin, an indicator of prymnesiophytes. DMSO concentrations were correlated with those of DMS and DMSP in the near surface waters of the Arabian Sea. Additionally, DMSO appeared to be ubiquitous throughout the water column, being easily detectable in deep waters, which suggests that DMSO may act as a sink for DMS in the world’s oceans.

Dimethylsulphoxide and other biogenic sulphur compounds in the Galapagos Plume

Concentrations of biogenic sulphur compounds were measured at a series of stations inside and outside the high productivity plume to the west of the Galapagos Islands, during the PlumEx study in November 1993. This is the first field data set generated using a new specific enzyme technique for the determination of dimethylsulphoxide (DMSO). DMSO in seawater arises from the photochemical and bacterial oxidation of dimethylsulphide (DMS) and is thought to be a key compound in the marine biogeochemical sulphur cycle. The distribution of DMSO is discussed relative to DMS and dimethylsulphoniopropionate (DMSP) levels, together with data for chlorophyll and hydrography. Clearly elevated concentrations of DMSO, DMSPp and DMS were seen within the high productivity plume, and the significance of DMSO in deep waters is discussed.

Dynamic photoinhibition exhibited by red coralline algae in the red sea

BackgroundRed coralline algae are critical components of tropical reef systems, and their success and development is, at least in part, dependent on photosynthesis. However, natural variability in the photosynthetic characteristics of red coralline algae is poorly understood. This study investigated diurnal variability in encrusting Porolithon sp. and free-living Lithophyllum kotschyanum. Measured parameters included: photosynthetic characteristics, pigment composition, thallus reflectance and intracellular concentrations of dimethylsulphoniopropionate (DMSP), an algal antioxidant that is derived from methionine, an indirect product of photosynthesis. L. kotschyanum thalli were characterised by a bleached topside and a pigmented underside.ResultsMinimum saturation intensity and intracellular DMSP concentrations in Porolithon sp. were characterised by significant diurnal patterns in response to the high-light regime. A smaller diurnal pattern in minimum saturation intensity in the topside of L. kotschyanum was also evident. The overall reflectance of the topside of L. kotschyanum also exhibited a diurnal pattern, becoming increasingly reflective with increasing ambient irradiance. The underside of L. kotschyanum, which is shaded from ambient light exposure, exhibited a much smaller diurnal variability.ConclusionsThis study highlights a number of dynamic photoinhibition strategies adopted by coralline algae, enabling them to tolerate, rather than be inhibited by, the naturally high irradiance of tropical reef systems; a factor that may become more important in the future under global change projections. In this context, this research has significant implications for tropical reef management planning and conservation monitoring, which, if natural variability is not taken into account, may become flawed. The information provided by this research may be used to inform future investigations into the contribution of coralline algae to reef accretion, ecosystem service provision and palaeoenvironmental reconstruction.

Coupling of dimethylsulfide oxidation to biomass production by a marine flavobacterium

ABSTRACT Dimethylsulfide (DMS) is an important climatically active gas. In the sea, DMS is produced primarily by microbial metabolism of the compatible solute dimethylsulfoniopropionate. Laboratory growth of Bacteroidetes with DMS resulted in its oxidation to dimethyl sulfoxide but only in the presence of glucose. We hypothesized that electrons liberated from sulfur oxidation were used to augment biomass production.