References of "Harlay, Jérôme"
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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 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 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 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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