Coccolithophorid calcium carbonate dissolution in surface waters

The role of calcifying organisms in the ocean biogeochemistry has been receiving increasing attention since CO2-related global change issues such as ocean acidification were pointed out by the scientific community. The implications of changing oceanic pH in modifying ecosystems dominated by planktonic calcifiers have been shown by mesocosm and laboratory experiments based on CO2 manipulations. The major concern of such experiments focussed on variations in the rates of ecosystem primary production and calcification due to changes in algal physiology or specific composition. Our results, from an interdisciplinary survey of coccolithophore-dominated blooms in the northern Bay of Biscay (NE Atlantic), suggest that biogenic calcite dissolution is occurring in the photic zone where surface waters are oversaturated with respect to calcite. The dissolution of CaCO3 in surface waters, evidenced by scanning electron microscopy observations, has an impact on the preservation and export of carbon in coccolithophore-dominated ecosystems and on the exchange of CO2 across the ocean-atmosphere interface. Both aspects of suspended calcite concentration reduction in natural environments (lower rates of production or dissolution) could be considered as a perturbation of the oceanic carbon cycle. We aim at presenting here a biogeochemical description of processes, including integrated primary production, calcification, and parameters such as transparent exopolymer particles concentration and particulate inorganic carbon profiles, during field studies. A mechanism for calcite dissolution, based on biological activity in microenvironments (including grazing, bacterial respiration and DMS production) is presented as a conceptual model in coccolithophore blooms

Outbreak of West Nile virus infection in humans, Romania, July to October 2010

A total of 57 cases of West Nile virus infection (54 with neuroinvasive infection and three with fever) were identified in Romania between July and October 2010. The median age of the cases was 53.4 years, with the highest incidence in the age group 60–69 years. The case fatality rate was 8.8%. Cases were distributed in 19 districts in the southern, western, central and eastern parts of the country. Molecular investigation revealed lineage 2 West Nile virus, related to the Volgograd 2007 strain

Coccolithophorid calcium carbonate dissolution in surface waters

info:eu-repo/semantics/publishe

Silica retention in the Scheldt continuum and its impact on coastal eutrophication (SISCO): Final report EV/17

SISCO (Silica retention in the Scheldt continuum and its impact on coastal eutrophication) was an interdisciplinary consortium consisting of biologists, (bio)geochemists and hydrodynamic-biogeochemical modellers. The overall objective was to elucidate the biogeochemical cycling of silicon (Si) and its anthropogenic perturbation in the Scheldt continuum river-estuary-coastal zone. We aimed specifically at 1) identifying the sources and sinks of Si in the aquatic continuum, 2) quantifying the major processes controlling the biogeochemical behaviour of Si in the water column, 3) evaluating the early diagenesis of Si in order to determine the burial fluxes and internal recycling rates within the sediments, and 4) developing a Si module within an existing transport-reaction model to assess the Si fluxes carried by the Scheldt to the Southern Bight of the North Sea. To achieve the aims, we applied an integrated approach combining 1) analyses of historical data, 2) field surveys and laboratory investigations, and 3) model development. Analysis of historical chlorophyll a data (1995-2006) in the upper Scheldt estuary exhibited a high inter-annual variability of the phytoplankton biomass in summer, which could be attributed primarily to the flushing rates of the freshwater in the upper estuary. This points towards a strong hydrodynamic control on phytoplankton development in the upper estuary. The intensive phytoplankton monitoring survey in 2003 showed that phytoplankton biomass not only differed between the tidal Rupel and Scheldt branches but also in their tributaries. The difference was ascribed to the smaller cross-section of the rivers in the Rupel basin, resulting in a higher water velocity and lower retention time of the water, which would limit phytoplankton development. Study of the phytoplankton community composition along the river-estuarine-coastal zone continuum of the Scheldt revealed a succession from a riverine to a marine phytoplankton community. There is no single estuarine phytoplankton community but rather a succession of estuarine species along the salinity gradient. Monthly monitoring survey of phytoplankton in 2003 in the Belgian coastal zone exhibited a pronounced spatio-temporal variability in the timing and magnitude of the spring bloom. The spring bloom started earlier in the western part of the Belgian coastal zone probably due to a more favourable mixing depth to photic depth ratio. The magnitude of the spring bloom was higher in the eastern part of the coastal zone, probably because of higher nitrogen (N) and phosphorus (P) inputs from the Scheldt. Temporal evolution of dissolved and biogenic silica concentrations along the Scheldt freshwater estuary and in its tributaries was investigated during one year in 2003. In the tributaries, dissolved silica (DSi) concentrations remained high and biogenic silica (BSi) concentrations were low throughout the year. In the freshwater estuary during summer however, DSi was completely consumed and BSi concentration increased. Mass balance calculations showed that silica consumption and retention in the freshwater estuary were important at a seasonal time-scale: from May to September, one third of the total amount of riverine silica was retained. The consumption and retention were high when discharge was low (and inversely), suggesting that silica retention would be of much less significance when annual fluxes were considered. The longitudinal distribution of DSi and BSi along the salinity gradient in the Scheldt estuary was determined. The 1D-CONTRAST model was used to simulate the conservative mixing in the brackish estuary of DSi from the freshwater and the seawater end-members; existing datasets of DSi and salinity was used as inputs for boundary conditions. Comparison of the observed DSi profiles with the model outputs indicated a consumption of DSi in the brackish estuary in spring-summer and a conservative transport in winter. BSi were found to be closely link

Biogeochemical study of a coccolithophore bloom in the northern Bay of Biscay (NE Atlantic Ocean) in June 2004

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the different stages of a coccolithophore bloom dominated by Emiliania huxleyi. The cruise was carried out after the main spring phytoplankton bloom that started in mid-April and peaked in mid-May. Consequently, low phosphate (PO4<0.2 μM) and silicate (DSi<2.0 μM) concentrations, low partial pressure of carbon dioxide (pCO2) and high calcite saturation degree in surface waters combined with thermal stratification, probably favoured the blooming of coccolithophores. During the period of the year our cruise was carried out, internal tides induce enhanced vertical mixing at the continental shelf break leading to the injection of inorganic nutrients to surface waters that probably trigger the bloom. The bloom developed as the water-column stratified and as the water mass was advected over the continental shelf, following the general residual circulation in the area. The most developed phase of the bloom was sampled in a remote sensed high reflectance (HR) patch over the continental shelf that was characterized by low chlorophyll-a (Chl-a) concentration in surface waters (<1.0 μg L-1), high particulate inorganic carbon (PIC) concentration (~8 μmol L-1) and coccolithophore abundance up to 57×106 cells L-1. Transparent exopolymer particles (TEP) concentrations ranged between 15 and 120 μg Xeq L-1 and carbon content of TEP represented up to 26% of the particulate organic carbon (POC; maximum concentration of 15.5 μmol L-1 in the upper 40 m). Integrated primary production (PP) ranged between 210 mg C m-2 d-1 and 680 mg C m-2 d-1 and integrated calcification (CAL) ranged between 14 and 140 mg C m-2 d-1, within the range of PP and CAL values previously reported during coccolithophore blooms in open and shelf waters of the North Atlantic Ocean. Bacterial protein production (BPP) measurements in surface waters (0.3 to 0.7 μg C L-1 h-1) were much higher than those reported during early phases of coccolithophore blooms in natural conditions, but similar to those during peak and declining coocolithophorid blooms reported in mesocosms. Total alkalinity anomalies with respect to conservative mixing (ΔTA) down to -49 μmol kg-1 are consistent with the occurrence of biogenic precipitation of calcite, while pCO2 remained 15 to 107 μatm lower than atmospheric equilibrium (372 μatm). The correlation between ΔTA and pCO2 suggested that pCO2 increased in part due to calcification, but this increase was insufficient to overcome the background under-saturation of CO2. This is related to the biogeochemical history of the water masses due to net carbon fixation by the successive phytoplankton 2CCC