Towards a comprehensive C-budgeting approach of a coccolithophorid bloom in the Northern Bay of Biscay (June 2006)

A biogeochemical multidisciplinary survey was carried out in the northern Bay of Biscay, in early June 2006, during which 14C-based primary production and calcification were determined as well as O2-based community respiration. Contemporary remote sensing images showed several patches of high reflectance (HR) in the investigated area. Based on remote sensing and in situ measured biogeochemical parameters, the area exhibited varying coccolithophorid bloom stages from its early development to the post-bloom stages. The major HR patch, characterizing a post-stationary stage of the bloom, was located between 48°N and 49°N over the shelf along the continental margin. It was associated with moderate chlorophyll-a levels, never exceeding 1.0 µg L-1, dissolved phosphorus and silica depletion, and undersaturation of CO2 with respect to atmospheric equilibrium. Considered as the main drivers of the C cycle in this area, the CO2 fluxes associated with primary production, calcification and respiration were integrated in order to provide a comprehensive C budget in the area

Dynamics of bacteria, phytoplankton and extracellular carbohydrates during blooms of the coccolithophore Emiliania huxleyi

The composition of bacterial and phytoplankton communities during phytoplankton blooms, and their interactions, are important properties of the microbial food web, which can potentially have a strong impact on the fate of organic matter and hence carbon cycling in the world’s oceans. During late spring (May-June 2006-2008) we investigated the relationship between the community structures of phytoplankton (pigment-based) and free-living and particle-associated bacterioplankton (denaturant gradient gel electrophoresis), and environmental constraints during natural coccolithophore blooms along the North East Atlantic continental margin (Bay of Biscay). The alternation between diatom and coccolithophore blooms (mainly Emiliania huxleyi) of similar biomass was partly driven by changes in nutrient stoichiometry (N:P and dSi:N). High concentrations of transparent exopolymer particles (TEP) were associated with stratified, coccolithophore-rich water masses. Free-living and particle-associated bacterial communities had different typical representatives but showed a considerable overlap in composition. Furthermore, the structure of the bacterial communities was significantly correlated to the abundance of phytoplankton groups and water column stratification. At selected stations, we assessed the relationship of dimethyl sulphide (DMS) and dimethylsulphonioproprionate (DMSP) concentrations and the fate of phytoplankton in terms of cell lysis rates and microzooplankton grazing. Coccolithophores constituted an important source of particulate DMSP, and cell lysis enhanced the release of dissolved DMSP. Finally, we assessed the role of bacterial activity and life cycle stage of the coccolithophore E. huxleyi on the dynamics of dissolved carbohydrates and TEP by measuring their production and composition during the stationary growth phase of batch cultures, and by tracing the fate of photosynthetically fixed carbon by stable isotope probing in non-axenic calcifying E. huxleyi cultures using liquid chromatographic separation of high molecular weight neutral aldoses (HMW NAld) combined with isotope ratio mass spectrometry. Bacteria favoured the accumulation of polysaccharides and the formation of TEP, and enhanced their aggregation in calcifying E. huxleyi cultures. The production of coccoliths was probably the main source of HMW NAld in our non-axenic calcifying E. huxleyi cultures. Extracellular release of carbon in the dissolved and the particulate pools reached up to 76% of total primary production during the stationary growth phase of E. huxleyi

Individual and interacting effects of pCO2 and temperature on Emiliania huxleyi calcification: Study of the calcite production, the coccolith morphology and the coccosphere size

The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppm V CO2, 380 ppm V CO2 and 750 ppm V CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13°C and 18°C) during the calcification phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that the cell abundance-normalized particulate organic carbon concentration (POC) increased from the present to the future CO2 treatments. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cell abundance-normalized particulate inorganic carbon (PIC) content as well as a lower PIC:POC ratio at future CO2 levels and at 18°C. Coccosphere-sized particles showed a size reduction trend with both increasing temperature and CO2 concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effect of pCO2 and temperature was observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming

Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)

Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO2 fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers

Seawater carbonate chemistry, growth rate and Emiliania huxleyi (strain AC481) biological processes during experiments, 2010

The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppmV CO2, 380 ppmV CO2 and 750 ppmV CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13 °C and 18 °C) during the exponential growth phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that cellular production rate of Particulate Organic Carbon (POC) increased from the present to the future CO2 treatments at 13 °C. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cellular production rate of Particulate Inorganic Carbon (PIC) as well as a lower PIC:POC ratio at future CO2 levels and at 18 °C. Coccosphere-sized particles showed a size reduction with both increasing temperature and CO2concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effects of pCO2 and temperature were observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006-2008)

info:eu-repo/semantics/publishe

Study of the individual and combined effect of pCO2 and temperature on the coccolithophore E. huxleyi

info:eu-repo/semantics/publishe

Low-nutrient organic matter in the Sargasso Sea thermocline: A hypothesis for its role, identity, and carbon cycle implications

Despite slow nutrient supply to the subtropical surface ocean, its rates of annual inorganic carbon drawdown and net oxygen production are similar to those of nutrient-rich high latitude waters. This surprisingly rapid carbon drawdown, if due to the production and export of marine biomass, cannot be explained in terms of known nutrient supply mechanisms. Moreover, carbon budgets have failed to detect the export of this organic matter. One possible explanation is the export of nutrient-poor organic matter with a composition that avoids detection as sinking particles. We describe three signs of the decomposition of such organic matter in the shallow Sargasso Sea subsurface. First, summertime oxygen consumption at 80–400 m occurs without the rate of nitrate and phosphate production expected from the remineralization of marine biomass, matching the observed summertime mixed layer inorganic carbon drawdown. Second, a seasonal change in the 18O/16O of subsurface nitrate suggests summertime heterotrophic bacterial nitrate assimilation down to ~400 m, as may be required for the remineralization of nutrient-poor organic matter. Third, incubation of subsurface seawater leads to nitrate drawdown and heterotrophic bacterial growth, supporting the thermocline nitrate 18O/16O evidence for heterotrophic nitrate assimilation. These three pieces of evidence suggest the export of nutrient-poor organic matter from the surface at a rate adequate to explain net community production in the Sargasso Sea. We propose that transparent exopolymer particles or related compounds, generated by a nutrient-limited upper ocean ecosystem, comprise this nutrient-poor export, and that its properties cause its flux out of the euphotic zone to be underestimated by sediment traps. Such nutrient-poor organic matter would contribute little to fisheries, deep ocean carbon dioxide storage, or organic carbon burial, so that it may change our view of the significance of net community production in the subtropical ocea

Coccolithophore blooms in the Bay of Biscay: Results from the PEACE project

Pelagic and benthic processes were determined in the nothern Bay of Biscay when coccolithophores blooms occured between 2006 and 2008. Here we present a synthesis of pelagic primary production, calcification and respiration and benthic respiration and dissolution of CaCO3. Or results suggest that CaCO3 dissolution in the surface sediments is small (~1%) compared to integrated pelagic calcification. Benthic respiration increases with the organic load of the sediment and represents ~8% of the integrated pelagic respiration. The relationship between dissolution and respiration rates suggests a metabolic driven dissolution in waters supersaturated with respect to calcite (omega>3.5). We address a mass balance of the described processes and associated CO2 fluxes in the water column