UVB radiation modifies protein and photosynthetic pigment content, volume and ultrastructure of marine diatoms

Three marine diatom species (Cyclotella sp., Nitzschia closterium and Thalassiosira nordenskioldii) were exposed to a range of daily doses of ultraviolet B radiation (UVBR: 280-320 nm). The lowest UVBR treatments (<2000 J m-2 d-1, DNA weighted biologically effective dose, normalised at 300 nm: daily BEDDNA 300 nm) resulted in decreased division rates, volume enlargement and elevated cellular protein and pigment content levels. The highest UVBR treatments (between 2000 and 3800 J m-2 d-1 daily BEDDNA 300 nm) resulted in complete growth inhibition, accompanied by only minor changes in protein, pigments and cell volume. Recovery of cell division after UVBR exposure was decreasingly successful with increasing UVBR dose rates. Ultrastructural examination of exposed Cyclotella cells indicated that high UVBR levels induced plasmolysis and disorientation of cell organelles. Lower levels (<2000 J m-2 d-1 daily BEDDNA 300 nm) seemed to cause an increase in volume and the amount of chloroplasts. The results support the notion conceived earlier that UVBR causes DNA damage, an arrest in the S or G2 phase of the cell cycle, and consequently growth without cell division

Micrometeorologie van lucht/zee fluxen van CO2 en dimethylsulfide

Abstract niet beschikbaarThe sea to air flux of CO2 and the biogenic volatile sulfur compound dimethylsulphide were assessed with the Relaxed Eddy Accumulation (REA) and the Gradient Flux techniques from stationary and moving platforms in the Atlantic and Pacific Oceans during the FAIRS and GasEx cruise. The correlation between the techniques was good, with REA on average higher than GF. Fluxes derived from micrometeorological measurements agreed within error bars with those obtained by the conventional equations as proposed by Liss and Merlivat (1986), Wanninkhof (1992), and Jacobs (1999). The relationships between the transfer velocity and wind speed based on the micrometeorological measurements agreed within 10% and were on average higher than the equation proposed by Wanninkhof (1992). The effect of temperature on the computed sea to air flux of CO2 were investigated on a micrometeorological scale as well as on a small scale (top few metres of the watercolumn). The definition of skin temperature relies on a known bulk temperature of the water, which is shown to be not only highly stratified in the thermal structure but also very resilient versus disturbances, being wind speed. The skin temperature models, which were derived from open ocean work, are not directly applicable to coastal seas. As the skin temperature and the thermal structure is so rigid under the various wind conditions the gas exchange coefficients, derived from windtunnel experiments under the assumption of a well mixed layer are now under scrutiny.SG-NO

CO2 deposition over the multi-year ice of the western Weddell Sea

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

Spatial and temporal analysis of estuarine bacterioneuston and bacterioplankton using culture-dependent and culture-independent methodologies

Bacterioneuston may play a key role in water–air exchange of gases and in processing organic matter and pollutants that accumulate at the sea-surface microlayer (SML). However, the phylogenetic diversity of bacterioneuston has been poorly characterized. We analyzed 24 samples each from the SML and underlying water (UW) at three sites in the Ria de Aveiro estuary, Portugal. Cultivation and culture-independent techniques were used to compare bacterioneuston and bacterioplankton. Culturable heterotrophic bacteria were enriched in the SML. The culturable community was dominated by Psychrobacter and Acinetobacter. The presence of high numbers of Psychrobacter was a notable result. Differences were confined to a few genera overrepresented in UW samples (Kocuria, Agrococcus and Vibrio). 16S rDNA DGGE profiles were highly stable in terms of number and position of bands between sampling sites and dates but cluster analysis revealed a slight tendency for grouping according to sampled layer. SML-specific DGGE bands affiliated with Actinobacteria, Cyanobacteria, Gammaproteobacteria and Bacteroidetes. Low similarity between nucleotide sequences of DGGE-bands and previously reported sequences suggest the occurrence of SML-specific populations. Enrichment of SML for Pseudomonas and Aeromonas was questioned and the diversity of both communities was analyzed. Consistent differences between SML and UW aeromonads communities were not identified. In terms of Pseudomonas, a culturable operational taxonomic unit was consistently overrepresented within SML samples. Taken together, our results indicate that the similarity between SML and UW communities depends on spatial and temporal factors

Global oceanic DMS data inter-comparability

The global surface seawater dimethylsulphide (DMS) database (http://saga. pmel. noaa. gov/dms/) contains >50,000 data points and is the second largest trace gas database after carbon dioxide. However, there has been relatively little quality control on the data that have been collated to date. Furthermore, the recent development of technologies capable of high frequency (>1 Hz) DMS measurements will have a disproportionate effect on the database in future years. At this juncture, the comparability of analytical techniques, sample handling methodologies and standards are pressing issues that the DMS community needs to address. In October 2010, during the Fifth International Symposium on Biological and Environmental Chemistry of DMS(P) and Related Compounds held in Goa, India, attendees participated in a discussion concerning the current DMS database and its future development. We develop some of the ideas from that session and combine them with available data. From the few inter-comparison exercises that have been conducted we show that variability between existing measurements within the DMS database is likely to be ≤25%. Tests comparing different DMSP·HCl standards demonstrate that a reference calibration standard would be beneficial for the DMS community. Confidence in future data collation would be substantially improved with a comprehensive inter-comparison experiment between new analytical techniques and sampling methodologies (e. g., mass spectrometers with equilibrators attached to a continuous flow of seawater) and more established methods (i. e., filtered samples analysed with purge and trap gas chromatography). We conclude with recommendations for the future expansion of the DMS database and its data quality control. © 2011 Springer Science+Business Media B.V