References of "Harlay, Jérôme"
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See detailAlkenone carbon isotopes during a bloom of Emiliania huxleyi: Effects of CO2 concentration and production
Benthien, Albert; Zondervan, Ingrid; Riebesell, Ulf et al

Poster (2003, April 07)

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 (passive/active), and the carbon source (CO2aq/bicarbonate). To what extent these different factors might affect the carbon isotopic signal of alkenones ultimately preserved in the sediment is still under debate. A cause 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 domes to adjust and maintain 3 different CO2 partial pressures 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 detailImpact of elevated pCO2 on optical properties of the coccolithophorid Emiliania huxleyi grown under nitrate limitation
Denis, Michel; Sciandra, Antoine; Harlay, Jérôme ULg et al

Conference (2003, April 06)

Side scatter and red fluorescence properties of the coccolithophore Emiliania huxleyi were investigated when NO3-limited continuous cultures were submitted to a CO2 partial pressure (pCO2) increase from ... [more ▼]

Side scatter and red fluorescence properties of the coccolithophore Emiliania huxleyi were investigated 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. Side scatter of a single cell is considered to reflect not only its overall shape but mainly its inner structure and content through a complex combination of optical properties including absorption, diffusion, refractive index and refraction. Consequently, the cultures of Emiliania huxleyi were monitored by flow cytometry to detect possible changes in its optical properties at the single cell level under the effect of CO2 doubling in the atmospheric phase. The average SD for counting 5 replicates was less than 1.6% over the period of the study. It was 0.1 and 0.2% for 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 as expected and had no detectable effect on the red fluorescence. To validate the assignment of this change on coccolith dissolution, the same experiment was repeated with a culture of a non-calcifying species, Dunaliella tertiolecta. The acidification of D. tertiolecta suspension induced no detectable change, both on fluorescence and side scatter. During the time of the experiment, the decline of side scatter 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 2.8% of the initial signal. The average SD of red fluorescence being 0.1%, this increase must be considered as significant. 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 coccoliths 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 like those observed on published electron micrographs. 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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See detailBiological responses to CO2-related changes in seawater carbonate chemistry during a bloom of Emiliania huxleyi
Zondervan, Ingrid; Aerts, Katrien; Bellerby, Richard et al

Conference (2003, April 06)

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See detailOn the coupling of primary production and calcification during a field experiment in the northeastern Atlantic
Chou, Lei; Harlay, Jérôme ULg; Roevros, Nathalie et al

Poster (2003, April 06)

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of ... [more ▼]

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of biogenic calcium carbonate and associated organic matter in the photic zone and of their fate during settling is essential for a better assessment of the oceanic carbon cycle. In the framework of the Belgian global change programme, we conducted a field experiment on board the R/V Belgica in Spring 2002 along the Northern Bay of Biscay margin during successive coccolithophorid Emiliania huxleyi (Ehux) blooms. We aim, in particular, at quantifying the role of calcifying phytoplanktonic organisms in sequestering carbon. With near real-time transmission of remote sensing data during the survey, we were able to track the position and evolution of the various coccolithophore blooms along the shelf break. Bio-optical measurements were performed for modelling purpose and for calibration of the recently launched MERIS Sensor. During the field campaign, special attention was paid to the precise determination of the dissolved inorganic carbon chemistry. Primary production and rate of calcification were measured using C14 incorporation experiments and the organic to inorganic particulate carbon ratio quantified. Phytoplankton speciation was determined by microscopic examination, flow cytometry and HPLC pigment analyses. Zooplankton grazing experiments on phytoplankton were also performed. Suspended particles were characterised by their chemical composition and morphology. Th234 was used to quantify particle residence times and particulate organic carbon fluxes in surface waters. The results indicate significant particle export during the sampling period, with particle residence times in the upper 80 m ranging from 15 to 45 days. In this presentation, we will integrate the results obtained from remote sensing, biooptical investigation, water chemistry and process studies to elucidate the coupling of primary production and calcification during Ehux blooms and its importance in the marine biogeochemical cycle of carbon. [less ▲]

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See detailCoccolithophorid Emiliania huxleyi to elevated pCO2 under nitrate limitation
Sciandra, Antoine; Harlay, Jérôme ULg; Lefèvre, Dominique et al

Conference (2003, April 06)

The effects of a partial pressure of CO2 (pCO2) increased from 400 to 700 ppm on nitrogen-limited growing cells of the coccolithophore Emiliania huxleyi were studied. Nitrogen limitation was obtained ... [more ▼]

The effects of a partial pressure of CO2 (pCO2) increased from 400 to 700 ppm on nitrogen-limited growing cells of the coccolithophore Emiliania huxleyi were studied. Nitrogen limitation was obtained within NO3-limited continuous cultures renewed at the rate of 0.5 d−1 and submitted to saturating light level. pCO2 was controlled by bubbling CO2-rich or CO2-free air in the cultures. It is shown that the increase of pCO2 has a rapid effect on cell physiology taking place within the 2 cell divisions occurring after the perturbation. Net calcification rate (C) was depressed from approximately 25%, and, as opposed to what has been reported by previous studies on N-replete cultures, net community production (NCP) was depressed in the same proportion. These results therefore suggest that the increase of pCO2 had not noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited. [less ▲]

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See detailQuantification of the Carbonate Pump: Case study of an Emiliania huxleyi bloom in the Bay of Biscay
Harlay, Jérôme ULg; Chou, Lei; Roevros, Nathalie et al

Poster (2003, April 03)

Little attention has been paid until now 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 ▼]

Little attention has been paid until now 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 in 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 detailAssessment of the importance of the carbonate pump in surface waters of the Bay of Biscay
Harlay, Jérôme ULg; Chou, Lei; Dedonder, Virginie et al

Poster (2003, January 07)

Marine carbon research in the past decade has been mainly devoted to the understanding and quantification of processes controlling the fluxes of organic matter in the ocean. Little attention has been paid ... [more ▼]

Marine carbon research in the past decade has been mainly devoted to the understanding and quantification of processes controlling the fluxes of organic matter in the ocean. Little attention has been paid until now to the particulate inorganic carbon whose net fluxes to the sediments are comparable to those of the organic matter. There remains still a large uncertainty in the production and the fate of biogenic calcium carbonate in the oceanic carbon cycle. 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. The rate of primary production and of calcification by phytoplankton is evaluated by 14C incubation experiments during a coccolithophorid bloom-forming period in the area of investigation. The relative production of organic matter and calcium carbonate in the photic zone along a transect from the continental shelf across the slope to deep waters will be presented. A tentative mass balance of the carbon fluxes for this area will be constructed. These preliminary results confirm the importance that the calcium carbonate pump may play in open ocean. [less ▲]

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See detailCalcification and organic production of coccolithophorids Emiliania huxleyi under different atmospheric pCO2 in a mesocosm experiment
Delille, Bruno ULg; Harlay, Jérôme ULg; Chou, Lei et al

Poster (2003, January 07)

The response of primary production and calcification of the coccolithophorid Emiliania huxleyi to different partial pressures of CO2 (p CO2) have been investigated during a mesocosm bloom experiment in a ... [more ▼]

The response of primary production and calcification of the coccolithophorid Emiliania huxleyi to different partial pressures of CO2 (p CO2) have been investigated during a mesocosm bloom experiment in a Norwegian fjord. Glacial, present and next century atmospheric p CO2 conditions (respectively 180, 370 and 700 ppmV) have been simulated above the surface of large sea-water enclosures. If production of organic matter remains constant under elevated p CO2, the production of inorganic carbon appears to be affected in two ways. First, the beginning of calcification is delayed. Second, the production rate of inorganic carbon appears to be lowered by 40% in the future conditions, decreasing subsequently the calcification/photosynthesis ratio from 1 to 0.6. During the experiment a strong viral growth have been experienced, which have seriously depressed calcification as well. We propose the threshold of 5.10 6 cell/ml for E huxleyi virus abundance above which the production and calcification of the population of E. huxleyi are severely affected. [less ▲]

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See detailCharacterization of marine CaCO3 particles in the context of Global Change
Aerts, Katrien; Godoi, Ricardo; Harlay, Jérôme ULg et al

Poster (2003, January 07)

The expected increase in greenhouse gasses concentrations as a result of human activity is leading to significant climate change in the coming years. The fate of the anthropogenic CO2 has been intensively ... [more ▼]

The expected increase in greenhouse gasses concentrations as a result of human activity is leading to significant climate change in the coming years. The fate of the anthropogenic CO2 has been intensively studied. Being the largest reservoir of reactive carbon, the ocean acts as an important sink for anthropogenic CO2 and plays a significant role on the global biogeochemical cycle of carbon and its perturbations. There remain, however, large uncertainties concerning the uptake of carbon by the ocean, mainly due to insufficient knowledge of processes controlling the carbonate chemistry in surface waters. The effects of precipitation of calcium carbonate by calcifying organisms in the euphotic zone and redissolution of their skeletons have not been fully taken into account. This precipitation-dissolution process affects both the concentration of dissolved inorganic carbon and of total alkalinity and plays thus a significant role in the buffering capacity of seawater and its potential to act as a sink or a source of CO2 for the atmosphere. We aim to study the processes associated with the oceanic production and dissolution of CaCO3 in order to quantify the role of calcifying phytoplanktonic organisms in sequestering CO2. The calcareous skeletons of Coccolithophores, which comprise one of the main groups of calcifying organisms in the photic zone of the ocean, are analysed. The gut content of copepods, which grazes on coccolithophores is examined by different methods like Electron Probe Micro-Analysis (EPMA) and Micro X-Ray Fluorescence (M-XRF) in order to detect the possible dissolution features at the calcite surface. Automatic EPMA is used for the characterization of individual particles from ocean samples for their composition, morphology and size. Subsequent statistical processing techniques classifies the particles into specific particle clusters. [less ▲]

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See detailResponse of coccolithophorid Emiliania huxleyi to elevated partial pressure of CO2 under nitrogen limitation
Sciandra, A.; Harlay, Jérôme ULg; Lefevre, D. et al

in Marine Ecology. Progress Series (2003), 261

Precipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange Of CO2 at the ocean-atmosphere interface. Previous ... [more ▼]

Precipitation of calcium carbonate by phytoplankton in the photic oceanic layer is an important process regulating the carbon cycling and the exchange Of CO2 at the ocean-atmosphere interface. Previous experiments have demonstrated that, under nutrient-sufficient conditions, doubling the partial pressure Of CO2 (pCO(2)) in seawater-a likely scenario for the end of the century-can significantly decrease both the rate of calcification by coccolithophorids and the ratio of inorganic to organic carbon production. The present work investigates the effects of high pCO(2) on calcification by the coccolithophore Emiliania huxleyi (Strain TW1) grown under nitrogen-limiting conditions, a situation that can also prevail in the ocean. Nitrogen limitation was achieved in NO3-limited continuous cultures renewed at the rate of 0.5 d(-1) and exposed to a saturating light level. pCO(2) was increased from 400 to 700 ppm and controlled by bubbling CO2-rich or CO2-free air into the cultures. The pCO(2) shift has a rapid effect on cell physiology that occurs within 2 cell divisions subsequent to the perturbation. Net calcification rate (C) decreased by 25% and, in contrast to previous studies with N-replete cultures, gross community production (GCP) and dark community respiration (DCR) also decreased. These results suggest that increasing pCO(2) has no noticeable effect on the calcification/photosynthesis ratio (C/P) when cells of E. huxleyi are NO3-limited. [less ▲]

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