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See detailBiogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Chou, Lei; De Bodt, Caroline et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2011), 58(2), 111-127

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 ... [more ▼]

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. [less ▲]

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See detailCarbon and nitrogen flows during a bloom of the coccolithophore Emiliania huxleyi: Modelling a mesocosm experiment
Joassin, Pascal ULg; Delille, Bruno ULg; Soetaert, Karline et al

in Journal of Marine Systems (2011), 85

A dynamic model has been developed to represent biogeochemical variables and processes observed during experimental blooms of the coccolithophore Emiliania huxleyi induced inmesocosms over a period of 23 ... [more ▼]

A dynamic model has been developed to represent biogeochemical variables and processes observed during experimental blooms of the coccolithophore Emiliania huxleyi induced inmesocosms over a period of 23 days. The model describes carbon (C), nitrogen (N), and phosphorus (P) cycling through E. huxleyi and the microbial loop, and computes pH and the partial pressure of carbon dioxide (pCO2) from dissolved inorganic carbon (DIC) and total alkalinity (TA). The main innovations are: 1) the representation of E. huxleyi dynamics using an unbalanced growthmodel in carbon and nitrogen, 2) the gathering of formulations describing typical processes involved in the export of carbon such as primary production, calcification, cellular dissolved organic carbon (DOC) excretion, transparent exopolymer (TEP) formation and viral lyses, and 3) an original and validated representation of the calcification process as a function of the net primary production with a modulation by the intra-cellular N:C ratio mimicking the effect of nutrients limitation on the onset of calcification. It is shown that this new mathematical formulation of calcification provides a better representation of the dynamics of TA, DIC and calcification rates derived from experimental data compared to classicaly used formulations (e.g. function of biomass or of net primary production without anymodulation term). In a first step, the model has been applied to the simulations of present pCO2 conditions. It adequately reproduces the observations for chemical and biological variables and provides an overall view of carbon and nitrogen dynamics. Carbon and nitrogen budgets are derived from the model for the different phases of the bloom, highlighting three distinct phases, reflecting the evolution of the cellular C:N ratio and the interaction between hosts and viruses. During the first phase, inorganic nutrients are massively consumed by E. huxleyi increasing its biomass. Uptakes of carbon and nitrogen are maintained at a constant ratio. The second phase is triggered by the exhaustion of phosphate (PO4 3−). Uptake of carbon and nitrogen being uncoupled, the cellular C:N ratio of E. huxleyi increases. This stimulates the active release of DOC, acting as precursors for TEP. The third phase is characterised by an enhancement of the phytoplankton mortality due to viral lysis. A huge amount of DOC has been accumulated in the mesocosm. [less ▲]

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See detailBenthic remineralization in the northwest European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

in Continental Shelf Research (2011), 31

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June ... [more ▼]

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 18 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Water-sediment fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and lead-210 (210Pb) and thorium-234 (234Th) activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 μg g-1) contents comparable to previous investigations in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Water-sediment O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between water-sediment fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) seemed uncoupled from organic carbon degradation, as characterized by water-sediment O2 fluxes. The link between water-sediment fluxes of TA and O2 indicated the occurrence of metabolic driven dissolution of calcium carbonates (CaCO3) in the sediments (~ 0.33 ± 0.47 mmol m-2 d-1) which represented ~ 1 % of the pelagic calcification rates due to coccolithophores measured during the cruises. These CaCO3 dissolution rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation were low compared to water column rates of primary production and aphotic community respiration obtained during the cruises. [less ▲]

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See detailTowards a comprehensive C-budgeting approach of a cocoliothophorid bloom in the northern Bay of Biscay: results from PEACE project.
Harlay, Jérôme ULg; Borges, Alberto ULg; Delille, Bruno ULg et al

Conference (2010, May 03)

During coccolithophorid blooms, carbon (C) cycling in the photic zone is driven by the production and the degradation of organic matter (primary production and community respiration), as well as the ... [more ▼]

During coccolithophorid blooms, carbon (C) cycling in the photic zone is driven by the production and the degradation of organic matter (primary production and community respiration), as well as the production and the dissolution of biogenic calcium carbonate (CaCO3). Organic and inorganic metabolisms lead to a transfer of carbon to depth and both impact the flows of carbon dioxide (CO2) in the water column and the CO2 flux across the air-sea interface. Furthermore, due to complex dynamics of coccolithophores, the impact of metabolic C fluxes on CO2 fluxes is variable in time, depending on the stage of the bloom development, and mainly on the ratio of calcification to primary production (CAL:GPP). Understanding and quantifying C cycling of coccolithophorid blooms in natural conditions is a prerequisite to correctly validate biogeochemical models aiming at predicting feedbacks related to ocean acidification, which incorporate knowledge obtained from perturbation laboratory experiments. We carried out a trans-disciplinary cruise on board the R/V Belgica at the continental margin of the Bay of Biscay, in the midst of a coccolithophorid bloom, during which 14C primary production (GPPp), 14C calcification (CAL) and O2-based pelagic community respiration rates (PCR) were determined in the water column. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophorid blooms in the Northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

Poster (2010, May 03)

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate ... [more ▼]

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate inorganic carbon). This would imply that coccolithophores would be the most important pelagic calcifier in the oceans, since other estimates of contemporary global pelagic calcification range between 0.7 Pg PIC yr-1 based on accumulation rates and sediment trap data (Milliman et al. 1999), and 1.4 Pg PIC yr-1, based on the seasonal cycle of total alkalinity (TA) in the euphotic zone (Lee 2001). The development of coccolithophorid blooms affects the seawater carbonate chemistry, and air-sea CO2 fluxes, through the organic carbon pump and the carbonate counter-pump. The ratio between calcification (carbonate counter-pump), and organic carbon production (organic carbon pump), the C:P ratio, depends on the life cycle (bloom development), and growth conditions of coccolithophores. At the onset of the coccolithophorid bloom, when nutrients are available for growth, organic carbon production dominates over calcification (C:P << 1, the so-called organic phase). At the end of the bloom, in nutrient depleted conditions, and high irradiances (due to stronger stratification), organic carbon production decreases and calcification increases (C:P ≤ 1, the so-called inorganic phase). Several manipulative experiments to test the effect of ocean acidification on coccolithophores have shown that while calcification would decrease, the export of organic carbon would increase mainly through increasing transparent exopolymer particles (TEP) production. For a credible implementation in mathematical models of such feed-back mechanisms to allow the projection of a future evolution of carbon biogeochemistry under global change, it is required to understand present day biogeochemistry and ecology of naturally occurring pelagic calcifying communities. In particular, the overall effect of phytoplankton communities on the C:P ratio, and the net effect on carbonate chemistry, and related air-sea CO2 fluxes. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophorid blooms in the Northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

Poster (2010, May 02)

We present a data-set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of ... [more ▼]

We present a data-set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of coccolithophores occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity (TA) showed a non-conservative behaviour as a function of salinity due to the cumulated effect of net community calcification (NCC) during bloom development on seawater carbonate chemistry. The cumulated impact of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO2) were evaluated. The decrease of DIC (and increase of pCO2) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO2) due to NCP (NCC:NCP « 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average -9.7 mmol C m-2 d-1 for the 3 cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average 12% of total air-sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the northern North Atlantic Ocean (where coccolithophorid blooms are the most intense and recurrent), and in the global ocean, then the potential feed-back on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 “production” from calcification is probably minor compared to feed-backs related to changes of NCP. [less ▲]

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See detailBenthic remineralization in the northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

Poster (2010, May 02)

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in ... [more ▼]

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 8 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Sediment-water fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and 234Th and 210Pb activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 µg g-1) contents comparable to previous publications in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Sediment-water O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content (apparently the main driver of total benthic organic carbon degradation) was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between sediment-water fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) was uncoupled from organic carbon degradation, characterized by sediment-water O2 fluxes. The link between sediment-water fluxes of TA and O2 indicated metabolic driven dissolution ( 0.33 +/- 0.47 mmol m-2 d-1) of calcium carbonates (CaCO3) in the sediments which represented ~1 % of the pelagic calcification rates due to coccolithophores. These rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation and CaCO3 dissolution were low compared to water column rates of primary production, aphotic community respiration and CaCO3 production obtained during the cruises. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

in Global Biogeochemical Cycles (2010), 24

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the ... [more ▼]

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the coccolithophore Emiliania huxleyi occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity showed a nonconservative behavior as a function of salinity due to the cumulative effect of net community calcification (NCC) on seawater carbonate chemistry during bloom development. The cumulative effect of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO(2)) were evaluated. The decrease of DIC (and increase of pCO(2)) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO(2)) due to NCP (NCC: NCP << 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average similar to-9.7 mmol C m(-2) d(-1) for the three cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average similar to 12% of total air-sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the North Atlantic Ocean (where blooms of coccolithophores are the most intense and recurrent), and in the global ocean, then the potential feedback on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 "production" from calcification is probably minor compared to potential feedbacks related to changes of NCP. [less ▲]

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See detailRole of pelagic calcification and export of carbonate production in climate change
Chou, Lei; Harlay, Jérôme ULg; De Bodt, Caroline et al

Poster (2009, November 16)

The marine carbon cycle constitutes a key component of the climate system. It has been shown that one-fourth of the anthropogenic CO2 emitted to the atmosphere is absorbed by the ocean, leading to the ... [more ▼]

The marine carbon cycle constitutes a key component of the climate system. It has been shown that one-fourth of the anthropogenic CO2 emitted to the atmosphere is absorbed by the ocean, leading to the acidification of the surface ocean and the modification of seawater carbonate chemistry. This could have major impacts on the ocean biogeochemical carbon cycling and ecosystem dynamics. Yet, the resulting feedbacks on climate change are still poorly understood. Interdisciplinary biogeochemical investigations, assisted by remote sensing, have been conducted during three consecutive years along the shelf break of the Northern Bay of Biscay where coccolithophorid blooms dominated by Emiliania huxleyi are frequently and recurrently observed. Rates of various processes governing the coccolithophore ecosystem dynamics have been determined and air-sea CO2 fluxes evaluated. The key results will be presented and discussed to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophorid blooms. [less ▲]

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See detailBiogeochemistry and carbon budget during a coccolithophorid bloom in the northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Borges, Alberto ULg; De Bodt, Caroline et al

Poster (2009, April 19)

Carbon cycling processes (primary production (PPp), calcification (CAL), bacterial production and pelagic community respiration (PCR)) and variables (partial pressure of CO2 (pCO2) and total alkalinity ... [more ▼]

Carbon cycling processes (primary production (PPp), calcification (CAL), bacterial production and pelagic community respiration (PCR)) and variables (partial pressure of CO2 (pCO2) and total alkalinity (TA)) were measured in early June 2006 at several stations in the northern Bay of Biscay. These measurements were characterized with respect to the coccolithophorid blooming (growth or decline) based on satellite remote sensing (high reflectance (HR)) and other biogeochemical measurements i.e. inorganic nutrients, chlorophyll-a (Chl-a), phaeopigments (Phaeo), particulate inorganic carbon (PIC), particulate organic carbon (POC) and particulate nitrogen (PN)). The major HR patch was located over the shelf, along the continental margin and corresponded to declining bloom conditions characterized by moderate Chl-a <1.0 µg L-1, dissolved phosphate (PO4) depletion, low (<2.0 µmol L-1) dissolved silicate (DSi), low potential primary production (<0.25 µmol C L-1 h-1) and calcification rates (0.02-0.10 µmol C L-1 h-1). Yet, surface waters were undersaturated in CO2 with respect to atmospheric equilibrium. We present a coherent scheme of the C dynamics of a coccolithophorid bloom along the continental margin of the Bay of Biscay, an active hydrodynamic area, based on standing stocks and processes including 14C-based particulate primary production, CAL and PCR. A carbon budget obtained by integrating PPp, CAL and PCR over the water column highlights the importance of C extracellular production to sustain the bacterial demand in the twilight zone, which has also several repercussions on the fate of organic and inorganic C production in the photic zone during the different stages of the bloom. [less ▲]

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See detailTowards a comprehensive C-budgeting approach of a coccolithophorid bloom in the Northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Borges, Alberto ULg; De Bodt, Caroline et al

Poster (2009, January 25)

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 ... [more ▼]

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. [less ▲]

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See detailBiogeochemical Investigations of Coccolithophore Blooms along the Continental Margin of the Northern Bay of Biscay: Highlights of the PEACE Project
Chou, Lei; Harlay, Jérôme ULg; De Bodt, Caroline et al

Poster (2008, October 06)

Recent studies have demonstrated that changing ocean chemistry due to ocean acidification poses a growing threat for marine organisms such as corals, coccolithophores and many others that form calcareous ... [more ▼]

Recent studies have demonstrated that changing ocean chemistry due to ocean acidification poses a growing threat for marine organisms such as corals, coccolithophores and many others that form calcareous skeletons. Its biogeochemical feedbacks and impact on the oceanic carbon cycle are yet to be quantified. Coccolithophores are the major calcifying phytoplankton in the sub-polar and temperate regions of the world’s ocean. They produce furthermore transparent exopolymer particles (TEP), which are known to promote aggregate formation. Combined with the CaCO3 ballast effect, large-scale coccolithophore blooms could thus contribute to the export of organic carbon to deep waters on relatively short time scales. During the Belgian PEACE project, we have conducted yearly interdisciplinary biogeochemical surveys, assisted by remote sensing, along the continental margin of the northern Bay of Biscay where coccolithophore blooms dominated by Emiliania huxleyi are frequently and recurrently observed (Figure 1). Rates of various processes governing the coccolithophore ecosystem dynamics have been determined and associated biogeochemical parameters analysed. The overall objective is to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophore blooms. Here we report the principal results obtained during the 2006 campaign. [less ▲]

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See detailCoccolithophore bloom dynamics shape bacterioplankton communities in the northern Bay of Biscay
Van Oostende, Nicolas; Vyverman, Wim; Harlay, Jérôme ULg et al

Poster (2008, August 17)

Coccolithophores (Prymnesiophyceae) such as Emiliania huxleyi belong to the most productive calcifying organisms in the oceans. During two consecutive years we assessed bacterial diversity and dynamics ... [more ▼]

Coccolithophores (Prymnesiophyceae) such as Emiliania huxleyi belong to the most productive calcifying organisms in the oceans. During two consecutive years we assessed bacterial diversity and dynamics during the course of spring phytoplankton blooms dominated by coccolithophores in the northern part of the Bay of Biscay. Bacterioplankton community composition was assessed by means of denaturing gradient gel electrophoresis (DGGE) in combination with 16S rRNA gene clone libraries. We used ordination analysis to relate bacterioplankton community dynamics to phytoplankton pigment data and environmental parameters (nutrient concentrations, total alkalinity, concentration of transparent exopolymeric particles (TEP), pCO2). We found a clear difference in composition between the free-living and the particle-associated bacterial assemblage, with the identified Flavobacteria and Sphingobacteria phylotypes being characteristic for the particle-associated bacterial assemblage and Alfaproteobacteria and members of the SAR86 cluster dominating the free-living bacterial assemblage. Stations along the continental margin, at different stages in the coccolithophore bloom, were characterized by distinct bacterial assemblages which correlated well with changes in phytoplankton community composition and TEP abundance. We hypothesize that coccolithophore bloom dynamics shape both the free-living and the particle associated bacterial assemblages through phytoplankton group-specific associations and TEP production [less ▲]

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See detailA mathematical modelling of bloom of the coccolithophore Emiliania huxleyi in a mesocosm experiment
Joassin, Pascal ULg; Delille, Bruno ULg; Soetaert, Karline et al

Poster (2008, July 23)

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during ... [more ▼]

A dynamic model has been developed to represent biogeochemical variables and processes observed during a bloom of Emiliania huxleyi coccolithophore. This bloom was induced in a mesocosm experiment during which the ecosystem development was followed over a period of 23-days through changes in various biogeochemical parameters such as inorganic nutrients (nitrate, ammonium and phosphate), total alkalinity (TA), dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), dissolved oxygen (O2), photosynthetic pigments, particulate organic carbon (POC), dissolved organic carbon (DOC), Transparent Exopolymer Particles (TEP), primary production, and calcification. This dynamic model is based on unbalanced algal growth and balanced bacterial growth. In order to adequately reproduce the observations, the model includes an explicit description of phosphorus cycling, calcification, TEP production and an enhanced mortality due to viral lysis. The model represented carbon, nitrogen and phosphorus fluxes observed in the mesocosms. Modelled profiles of algal biomass and final concentrations of DIC and nutrients are in agreement with the experimental observations. [less ▲]

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See detailBiogeochemistry of a late coccolithophorid bloom at the continental margin of the Bay of Biscay
Harlay, Jérôme ULg; De Bodt, Caroline; d'Hoop, Quentin et al

Poster (2007, July 02)

Recent findings have led to growing concern regarding the impact of ocean acidification on marine calcifyers, but little is known about their biogeochemistry in natural (field) conditions (a major but ... [more ▼]

Recent findings have led to growing concern regarding the impact of ocean acidification on marine calcifyers, but little is known about their biogeochemistry in natural (field) conditions (a major but overlooked pre-requisite for realistic modelling of the future evolution of marine C cycling in a high CO2 world). The changes that will undergo these species in the near future and the biological feedback to decreasing oceanic pH are still open to debate. Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the subpolar and temperate zones of the worlds oceans. Within the framework of the Climate and Atmosphere Belgian Federal Science Policy Office programme, the continental margin of the Northern Bay of Biscay (North Atlantic Ocean) was visited in June 2006 during a transdisciplinary investigation of a late-spring bloom dominated by Ehux. Remote sensing images, transmitted onboard on a daily basis, were of valuable significance to pinpoint the coccolithophorid bloom along the margin, and to sample stations with contrasted biogeochemical properties.We determined 14C-based primary production and calcification rates, as well as pelagic respiration rates (O2 incubations). The magnitude of the biological and carbonate carbon fluxes will be synthesized and discussed in the light of biogeochemical parameters, such as Transparent Exopolymer Particles (TEP), chlorophyll-a, particulate carbon concentrations, particle dynamics and particulate organic carbon export (deduced from 234Th fluxes). Additional information on the bloom biogeochemistry will be presented (activity of dissolved esterase enzymes and bacterial community structure) to emphasize the importance of coccolithophorid blooms in the contemporary carbon cycle. [less ▲]

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See detailBiogeochemistry of a late marginal coccolithophorid bloom in the Bay of Biscay
Harlay, Jérôme ULg; de Bodt, Caroline; d'Hoop, Quentin et al

Conference (2007, April 15)

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s oceans. Within the ... [more ▼]

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s oceans. Within the framework of the “Climate and Atmosphere” Belgian Federal Science Policy Office programme, the continental margin of the Northern Bay of Biscay (North Atlantic Ocean) was visited in June 2006 during a multidisciplinary investigation of a late-spring bloom dominated by Ehux. Field sampling was assisted by daily transmission to the RV Belgica of remote sensing images, indicating the bloom development in the area. Various stations on the shelf and the shelf-break were sampled for the vertical distributions of nutrients, Transparent Exopolymer Particles (TEP), chlorophyll-a and particulate carbon concentrations. These data will be presented, here, in relation with 14C based integrated primary production, dissolved esterase activity and the bacterial community structure to emphasize the importance of coccolithophorid blooms in the biogeochemistry of the Northern Atlantic’s continental shelf. [less ▲]

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See detailRapid decline of the CO2 buffering capacity in the North Sea and implications for the North Atlantic Ocean
Thomas, Helmuth; Prowe, A. E. Friederike; van Heuven, Steven et al

in Global Biogeochemical Cycles (2007), 21(GB4001),

New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO2 partial pressure (pCO2) in surface waters rose by 22 matm, thus faster than atmospheric pCO2, which in ... [more ▼]

New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO2 partial pressure (pCO2) in surface waters rose by 22 matm, thus faster than atmospheric pCO2, which in the same period rose approximately 11 matm. The surprisingly rapid decline in air-sea partial pressure difference (DpCO2) is primarily a response to an elevated water column inventory of dissolved inorganic carbon (DIC), which, in turn, reflects mostly anthropogenic CO2 input rather than natural interannual variability. The resulting decline in the buffering capacity of the inorganic carbonate system (increasing Revelle factor) sets up a theoretically predicted feedback loop whereby the invasion of anthropogenic CO2 reduces the ocean’s ability to uptake additional CO2. Model simulations for the North Atlantic Ocean and thermodynamic principles reveal that this feedback should be stronger, at present, in colder midlatitude and subpolar waters because of the lower present-day buffer capacity and elevated DIC levels driven either by northward advected surface water and/or excess local air-sea CO2 uptake. This buffer capacity feedback mechanism helps to explain at least part of the observed trend of decreasing air-sea DpCO2 over time as reported in several other recent North Atlantic studies. [less ▲]

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