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

in Biogeosciences Discussions (2008), 5

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 CO[SUB]2[/SUB] (pCO[SUB]2[/SUB]), dissolved oxygen (O[SUB]2[/SUB]), 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 detailBiocalcification by Emiliania huxleyi in batch culture experiments
De Bodt, Caroline; Harlay, Jérôme ULg; Chou, Lei

in Mineralogical Magazine (2008), 72(1), 251-256

Coccolithophores, among which Emiliania huxleyi is the most abundant and widespread species, are considered the most productive calcifying organism oil earth. The export of organic carbon and ... [more ▼]

Coccolithophores, among which Emiliania huxleyi is the most abundant and widespread species, are considered the most productive calcifying organism oil earth. The export of organic carbon and calcification are the main drivers of the biological CO2 pump and are expected to change with oceanic acidification. Coccolithophores are further known to produce transparent exopolymer particles (TEP) that promote particle aggregation. As a result, the TEP and biogenic calcium carbonate (CaCO3) contribute to the export of carbon from the surface ocean to deep waters. In this context, we followed the development and the decline of E. huxleyi using batch experiments with monospecific cultures. We studied the link between different processes Such as photosynthesis, calcification and the production of TEP. The onset of calcification was delayed in relation to photosynthesis. The timing and the general feature of the dynamics of calcification were closely related to the saturation state of seawater with respect to calcite, Omega(cal). The production of TEP was enhanced after the decline of phytoplankton growth. After nutrient exhaustion, particulate organic carbon (POC) concentration increased linearly with increasing TEP concentration, suggesting that TEP contributes to the POC increase. The production of CaCO3 is also strongly correlated with that of TEP, suggesting that calcification may be considered as a Source of TEP precursors. [less ▲]

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See detailA dynamic model of an experimental bloom of coccolithophores Emiliania huxleyi
Joassin, Pascal ULg; Borges, Alberto ULg; Chou, Lei et al

Conference (2007, November 27)

A dynamic model has been developed to represent biogeochemical events observed during an experimentally induced bloom of coccolithophores Emiliania huxleyi. This bloom occurred in a mesocosm experiment ... [more ▼]

A dynamic model has been developed to represent biogeochemical events observed during an experimentally induced bloom of coccolithophores Emiliania huxleyi. This bloom occurred in a mesocosm experiment (Bergen 2001 experiment) during which ecosystem development was followed over a 23-days period through changes of the stocks of inorganic nutrients (nitrate, ammonium and phosphate), dissolved inorganic carbon and pCO2, O2 concentration, pigments, particulate organic carbon and nitrogen, dissolved organic carbon, the production of Transparent Exopolymeric Particles (TEP), primary production, alkalinity, calcification and particulate inorganic carbon. The dynamic model is based on unbalanced algal growth and balanced growth for bacteria as described in Van den Meersche et al. (2004). In addition, in order to adequately reproduce the observations, the model has been extended by including an explicit description of calcification, T.E.P production and an enhanced mortality due to viruses. This last process, based on a critical promiscuity between cellular hosts and viral agents, successfully contributed to reproduce the bloom extinction as observed in the mesocosm experiment. This model will be implemented in a coupled physical-biogeochemical model of the Black Sea ecosystem in the framework of the EU Sesame project and in the Gulf of Biscay in the frame of the Belgian PEACE project. [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 detailCalcification and transparent exopolymer particles (TEP) production in batch cultures of Emiliania huxleyi exposed to different pCO2
De Bodt, Caroline; d'Hoop, Quentin; Harlay, Jérôme ULg et al

Poster (2007, April 15)

Ehux growth, calcification and related processes are sensitive to changes in initial pCO2. Our results show that the development of the Ehux cultures is delayed with increasing initial pCO2. TEP ... [more ▼]

Ehux growth, calcification and related processes are sensitive to changes in initial pCO2. Our results show that the development of the Ehux cultures is delayed with increasing initial pCO2. TEP accumulate until the end of the experiment and are enhanced after nutrient exhaustion. TEP contribute significantly to POC concentrations after the exponential growth phase. The very good correlation between TEP and calcite concentrations suggests that the calcification acts as a potential source of TEP in coccolithophore blooms. Finally, if calcite continues to decrease, calcification may be hampered in this species. [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 detailCalcification and transparent exopolymer particles (TEP) production in batch cultures of Emiliania huxleyi exposed to different pCO2
De Bodt, Caroline; d'Hoop, Quentin; Harlay, Jérôme ULg et al

Poster (2007, March 06)

Ehux growth, calcification and related processes are sensitive to changes in initial pCO2. Our results show that the development of the Ehux cultures is delayed with increasing initial pCO2. TEP ... [more ▼]

Ehux growth, calcification and related processes are sensitive to changes in initial pCO2. Our results show that the development of the Ehux cultures is delayed with increasing initial pCO2. TEP accumulate until the end of the experiment and are enhanced after nutrient exhaustion. TEP contribute significantly to POC concentrations after the exponential growth phase. The very good correlation between TEP and calcite concentrations suggests that the calcification acts as a potential source of TEP in coccolithophore blooms. Finally, an Ωcalcite of 3 seems to be necessary for Ehux to calcify. [less ▲]

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See detailCoccolithophorid calcium carbonate dissolution in surface waters
Harlay, Jérôme ULg; Koch, Craig; Young, Jeremy R et al

Poster (2007, March 06)

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 ... [more ▼]

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. [less ▲]

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See detailCalcification and transparent exopolymer particles (TEP) production in batch cultures of Emiliania huxleyi exposed to different pCO2
De Bodt, Caroline; d'Hoop, Quentin; Harlay, Jérôme ULg et al

Conference (2006, December 04)

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See detailBiogeocehmical study of a coccolithophore bloom at the continental margin in the Northeast Atlantic
Harlay, Jérôme ULg; van der Zee, Claar; Schiettecatte, Laure-Sophie et al

Conference (2005, June 14)

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. The continental ... [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. The continental margin in the Northern Bay of Biscay (North Atlantic Ocean) was visited in June 2004 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. Primary production and calcification were measured by 14C incubations and zooplankton grazing experiments were performed. Vertical distributions of transparent exopolymer (TEP) concentration and bacterial density, as well as the bacterial production in surface waters, were also determined to elucidate the fate of biogenic carbonate production. The organic and inorganic carbon fluxes are evaluated in terms of relevant processes and discussed in relation with the DIC and nutrient dynamics. [less ▲]

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See detailResponse of primary production and calcification to changes of pCO(2) during experimental blooms of the coccolithophorid Emiliania huxleyi
Delille, Bruno ULg; Harlay, Jérôme ULg; Zondervan, Ingrid et al

in Global Biogeochemical Cycles (2005), 19(2),

[1] Primary production and calcification in response to different partial pressures of CO2 (PCO2) ("glacial,'' "present,'' and "year 2100'' atmospheric CO2 concentrations) were investigated during a ... [more ▼]

[1] Primary production and calcification in response to different partial pressures of CO2 (PCO2) ("glacial,'' "present,'' and "year 2100'' atmospheric CO2 concentrations) were investigated during a mesocosm bloom dominated by the coccolithophorid Emiliania huxleyi. The day-to-day dynamics of net community production (NCP) and net community calcification (NCC) were assessed during the bloom development and decline by monitoring dissolved inorganic carbon (DIC) and total alkalinity ( TA), together with oxygen production and 14 C incorporation. When comparing year 2100 with glacial PCO2 conditions we observed: ( 1) no conspicuous change of net community productivity (NCPy); ( 2) a delay in the onset of calcification by 24 to 48 hours, reducing the duration of the calcifying phase in the course of the bloom; ( 3) a 40% decrease of NCC; and ( 4) enhanced loss of organic carbon from the water column. These results suggest a shift in the ratio of organic carbon to calcium carbonate production and vertical flux with rising atmospheric PCO2. [less ▲]

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See detailDissolved Inorganic Carbon dynamics in the northern Bay of Biscay during a Coccolithophore bloom
Harlay, Jérôme ULg; van der Zee, Claar; Schiettecatte, Laure-Sophie et al

Poster (2005, May 02)

In the framework of the Belgian global change programme, we have developed a project devoted to the study of the inorganic carbon cycle in the Bay of Biscay where coccolithophore blooms occur frequently ... [more ▼]

In the framework of the Belgian global change programme, we have developed a project devoted to the study of the inorganic carbon cycle in the Bay of Biscay where coccolithophore blooms occur frequently. The study focuses on processes associated with the oceanic production and dissolution of calcium carbonate and related CO2 fluxes. Real time remote sensing allowed to localize the coccolithophore bloom that the R.V. Belgica visited in June 2004 during a multidisciplinary scientific cruise. We will present vertical profiles of pH, Talk, along with other parameters (salinity, temperature, chlorophyll a and phaeopigments) and 14C incorporation experiments. Inorganic carbon fluxes will be discussed in the photic zone, in correlation with the biological activity of phytoplankton (biological and carbonate pumps). [less ▲]

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See detailTesting the direct effect of CO2 concentration on a bloom of the coccolithophorid Emiliania huxleyi in mesocosm experiments
Engel, Anja; Zondervan, Ingrid; Aerts, Katrien et al

in Limnology and Oceanography (2005), 50(2), 493-507

We studied the direct effects of CO, and related changes in seawater carbonate chemistry on marine planktonic organisms in a mesocosm experiment. In nine outdoor enclosures (similar to 11 m(3) each), the ... [more ▼]

We studied the direct effects of CO, and related changes in seawater carbonate chemistry on marine planktonic organisms in a mesocosm experiment. In nine outdoor enclosures (similar to 11 m(3) each), the partial pressure of CO2 (pCO(2)) in the seawater was modified by an aeration system. The triplicate mesocosm treatments represented low (similar to 190 parts per million by volume (ppmV) CO2), present (similar to 410 ppmV CO2), and high (similar to 710 ppmV CO2) pCO(2) conditions. After initial fertilization with nitrate and phosphate a bloom dominated by the coccolithophorid Emiliania huxleyi occurred simultaneously in all of the nine mesocosms; it was monitored over a 19-day period, The three CO2 treatments assimilated nitrate and phosphate similarly. The concentration of particulate constituents was highly variable among the replicate mesocosms, disguising direct CO2-related effects. Normalization of production rates within each treatment, however, indicated that the net specific growth rate of E. huxleyi, the rate of calcification per cell, and the elemental stoichiometry of uptake and production processes were sensitive to changes in pCO(2). This broad influence of CO2 on the E huxleyi bloom suggests that changes in CO2 concentration directly affect cell physiology with likely effects on the marine biogeochemistry. [less ▲]

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See detailAlkenone carbon isotopes during a bloom of Emiliania huxleyi: Effects of CO2 concentration and production
Benthien, Albert; Riebesell, Ulf; Engel, Anja et al

Poster (2004, September 05)

The carbon isotopic composition of the C37-alkenones has been used in various paleoceanographic studies to estimate the ancient surface water CO2 concentration [CO2aq]. A number of recent culture, field ... [more ▼]

The carbon isotopic composition of the C37-alkenones has been used in various paleoceanographic studies to estimate the ancient surface water CO2 concentration [CO2aq]. A number of recent culture, field and sediment studies, however, indicate that the carbon isotopic fractionation in haptophyte algae is predominantly controlled by physiological processes and environmental factors other than the ambient [CO2aq]. The most prominent factors are algal growth rate, nutrient availability, light intensity, the carbon uptake mechanism, and the carbon source. To what extent these different factors might affect the carbon isotopic signal of alkenones ultimately preserved in the sediment is still under debate. Causes of uncertainty are the individual strenghts and weaknesses of the different methodological approaches. Culture experiments, for example, cannot perfectly recreate the sum of natural growth conditions and physical processes affecting the carbon isotopic signal in the field and its preservation in the sediment. On the other hand, core-top data represent several hundred to a couple of thousand years and therefore only reflect an average. Here, we present the first study testing the effects of [CO2aq] on the alkenone isotopic signal under natural bloom conditions in a semi-closed system. In a series of 9 floating mesocosms in a Norwegian fjord a bloom of Emiliania huxleyi was followed over a three week period. The mesocosms were covered by gas tight tents. The atmospheric and seawater pCO2 were manipulated to achieve different CO2 levels in the tent atmosphere ranging from pre-industrial (190 ppmv) to year 2100 levels (680 ppmv) as predicted by the IPCC’s report. We found that during the exponential growth phase the isotopic fractionation of alkenones decreased by 5 to 7 per mill and reached a plateau during the stationary phase. During the stationary phase the alkenone content per cell increased from 1-2 pg/cell to 6-8 pg/cell. Between the [CO2aq] treatments we observed an alkenone isotopic difference of only 2 per mill. These results indicate that changes in algal physiology and/or environmental conditions occuring during the course of an algal bloom strongly affect alkenone isotope fractionation. This effect overrides a comparatively small variation in the alkenone isotopic signal due to [CO2aq]. Implications for alkenone isotopic fractionation as a paleo-production or paleo-nutrient proxy will be discussed. [less ▲]

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See detailBiogeochemical implications of calcification and secondary production of a population of the brittle star Acrocnida brachiata in a temperate coastal ecosystem
Harlay, Jérôme ULg; Gentil, Franck; Davoult, Dominique

Poster (2004, May 10)

The production of organic matter and calcium carbonate by a population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, and relations ... [more ▼]

The production of organic matter and calcium carbonate by a population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, and relations between the size and the ash-free dry weight (AFDW) or the calcimass. During a two-year survey in the Bay of Seine (English Channel, France), one of the four major estuaries affecting the biogeochemical cycling of elements in the southern bight of the North Sea, benthic production of this species amounted to 40.3 g.m-2.yr-1 for AFDW and 80.0 g.m-2.yr-1 for CaCO3. Respiration, based on secondary production, was estimated to be 736 mmol CO2.m-2.yr-1. Using the molar ratio () of CO2 released to CaCO3 precipitated, this biogenic precipitation of calcium carbonate would result in an additional release of 617 mmol CO2.m-2.yr-1. The results of the present study demonstrate that marine calcification should be considered as a significant source of CO2 to seawater and thus a potential source of CO2 to the atmosphere, emphasizing the important role of the biomineralization and dissolution in the carbon budget of temperate coastal ecosystems. This additional biogenic source of CO2 could increase in the future in two ways: firstly, as a positive feedback of  to the rising pCO2 and, secondly, as a positive response to the availability of nutrients due to eutrophication. [less ▲]

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See detailDelayed and reduced coccolithophorid calcification under elevated PCO2
Delille, Bruno ULg; Harlay, Jérôme ULg; Zondervan, Ingrid et al

Poster (2004, May 10)

Numerous experiments to date have demonstrated that elevated PCO2 is detrimental to biogenic calcification rates. However, most of these experiments have been realized in batch or continuous cultures and ... [more ▼]

Numerous experiments to date have demonstrated that elevated PCO2 is detrimental to biogenic calcification rates. However, most of these experiments have been realized in batch or continuous cultures and give little information on the dynamics of calcification in natural conditions. The present work describes the development and decay of a nutrient-induced bloom of the coccolithophorid Emiliania huxleyi in a mesocosm experiment. The monitoring of Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TAlk) within the seawater enclosures allowed us to describe comprehensively day to day dynamics of both calcification and organic carbon production. Three atmospheric PCO2 conditions (glacial, present and next century) were simulated by bubbling CO2 mixtures, while total alkalinity was left to evolve from its present value. No conspicuous change of Net Community Production under elevated PCO2 was recorded while the production of inorganic carbon appeared to be affected in two ways. Firstly, the production rate of inorganic carbon appeared to be lowered by 40% in the next century PCO2 conditions, decreasing concomitantly the calcification to photosynthesis ratio from 0.75 (glacial conditions) to 0.45 (next century conditions). Secondly, the onset of calcification was delayed by 24~48h under elevated PCO2 conditions, reducing the overall length of calcification in the course of the bloom. These two effects would act to reduce the amount of precipitated CaCO3 by coccolithophorids in a High CO2 world [less ▲]

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See detailOn the coupling of primary production and calcification at the continental margin
Harlay, Jérôme ULg; Chou, Lei; Roevros, Nathalie et al

Poster (2004, March 05)

Until now, little attention has been paid to the processes controlling the production, dissolution and fate of biogenic calcium carbonate in the oceans. It is however well known that net deposition rates ... [more ▼]

Until now, little attention has been paid to the processes controlling the production, dissolution and fate of biogenic calcium carbonate in the oceans. It is however well known that net deposition rates of inorganic carbon to the sediments are comparable to those of organic matter. There remains still large uncertainties concerning the production and redissolution of biogenic carbonate in the marine system and thus about the role of the carbonate pump in response to anthropogenic CO2 perturbations. The understanding of these processes is also a prerequisite to predict the response of marine organisms to global environmental changes. In the framework of the Belgian global change programme, we have developed a project devoted to the study of the inorganic carbon cycle in the Bay of Biscay where coccolithophorid blooms occur frequently. The study focuses on processes associated with the oceanic production and dissolution of calcium carbonate, by combining field investigations, laboratory experiments and modelling efforts. Remote sensing demonstrates a close relationship between vertical mixing along the continental margin and the development of the phytoplankton bloom. We will present here, results of 14C incorporation experiments used to evaluate the rate of production of organic and inorganic particulate carbon, obtained during a coccolithophorid spring bloom in the investigated area. A tentative mass balance of the carbon fluxes for this area will be presented, confirming the importance that the calcium carbonate pump may play in the oceanic system. [less ▲]

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See detailEffect of elevated PCO2 on optical properties of the coccolithophorid Emiliania huxleyi grown under nitrate limitation
Denis, M.; Sciandra; Harlay, Jérôme ULg et al

in Cytometry. Part A : The Journal of the International Society for Analytical Cytology (2004), 59A(1), 105

Side scatter and red fluorescence properties of the coccolithophore Emiliania huxleyi were investigated by flow cytometry when NO3-limited continuous cultures were submitted to a CO2 partial pressure ... [more ▼]

Side scatter and red fluorescence properties of the coccolithophore Emiliania huxleyi were investigated by flow cytometry when NO3-limited continuous cultures were submitted to a CO2 partial pressure (pCO2) increase from 400 to 700 ppm. Cultures renewed at the rate of 0.5 d-1 and were submitted to saturating light level. pCO2 was controlled by bubbling CO2-rich or CO2- free air in the cultures. Most of the analyses were repeated 5 times and the average SD were < 1.6%, 0.1 and 0.2% for counting, fluorescence and side scatter respectively. Considering the possible decalcification induced by the increase of CO2 in the chemostat atmosphere, the maximum variation that can be expected for side scatter is that provided by the coccolith depletion upon acidification of the cell suspension. The acidification induced a large (36%) decrease of the side scatter signal but had no detectable effect on the red fluorescence. A control was run with a non-calcifying species, Dunaliella tertiolecta, where acidification induced no detectable change, both on fluorescence and side scatter. During the time of the experiment, the decline of side scatter in chemostat 1 never approached the potential 36% change observed when coccoliths are fully dissolved. Interestingly, the specific chl a fluorescence of E. huxleyi slightly increased during the period of high CO2 level. At the end of the experiment this increase amounted to a significant 2.8% of the initial signal. Furthermore, it progressed linearly with time over the period of observation. However, the experiment did not last enough to know if the fluorescence increase had already reached its maximum value. The acidification experiment supported the use of side scatter as a relevant parameter to trace potential changes in calcification. Since the estimated 25% decrease in calcification induced by the rise in CO2 atmosphere did not result in dramatic changes in side scatter values, we can conclude that the number of cocoliths and the overall shape and granulosity of cells was not significantly affected by this decrease. Changes must have only affected tiny structure details of the coccoliths which is supported by scanning electron microscopy observations. The small but significant increase of the fluorescence signal can be considered as a physiological response to the CO2 rise. This suggests a more dynamic photosynthetic process that would result in a higher rate of organic matter production providing that the system is not nutrient limited as in the present situation. [less ▲]

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