References of "Grégoire, Marilaure"
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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 detail3D Modelling of the Black Sea northwestern shelf ecosystem : Benthic Fluxes
Capet, Arthur ULg; Grégoire, Marilaure ULg

Scientific conference (2010, October)

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See detailOnboard implementation of the GHER model for the Black Sea, with SST and CTD data assimilation
Vandenbulcke, Luc ULg; Capet, Arthur ULg; Beckers, Jean-Marie ULg et al

in Journal of Operational Oceanography (2010), 3(2), 47-54

The first operational implementation of the GHER hydrodynamic model is described. It took place onboard the research vessel Alliance with all computation and sharing of forecasts being realised from the ... [more ▼]

The first operational implementation of the GHER hydrodynamic model is described. It took place onboard the research vessel Alliance with all computation and sharing of forecasts being realised from the vessel in near-real time. The forecasts were realised in the context of the Turkish Straits System 2008 campaign, which aimed at the real-time characterisation of the Marmara Sea and (south-western) Black Sea. The model performed badly at first, mainly because of poor initial conditions. Hence, as the model includes a reduced-rank extended Kalman filter assimilation scheme, after a hindcast where sea surface temperature and temperature and salinity profiles were assimilated, the model yielded realistic forecasts. Furthermore, the time required to run a one-day simulation (about 300 seconds of simulation, or 500 with pre-processing and data transfers included) was very limited and thus operational use of the model is possible. [less ▲]

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See detailCarbon, nitrogen, oxygen and sulfide budgets in the Black Sea: A biogeochemical model of the whole water column coupling the oxic and anoxic parts
Grégoire, Marilaure ULg; Soetaert, Karline

in Ecological Modelling (2010)

Carbon, nitrogen, oxygen and sulfide budgets are derived for the Black Sea water column from a coupled physical-biogeochemical model. The model is applied in the deep part of the sea and simulates ... [more ▼]

Carbon, nitrogen, oxygen and sulfide budgets are derived for the Black Sea water column from a coupled physical-biogeochemical model. The model is applied in the deep part of the sea and simulates processes over the whole water column including the anoxic layer that extends from ~ 115 m to the bottom (~ 2000 m). The biogeochemical model involves a refined representation of the Black Sea foodweb from bacteria to gelatinous carnivores. It includes notably a series of biogeochemical processes typical for oxygen deficient conditions with, for instance, bacterial respiration using different types of oxidants (i.e denitrification, sulfate reduction), the lower efficiency of detritus degradation, the ANAMMOX (ANaerobic AMMonium OXidation) process and the occurrence of particular redox reactions. The model has been calibrated and validated against all available data gathered in the Black Sea TU Ocean Base and this exercise is described in Gregoire et al., (2008). In the present paper, we focus on the biogeochemical flows produced by the model and we compare model estimations with the measurements performed during the R.V. KNORR expedition conducted in the Black Sea from April to July 1988 (Murray and the Black Sea Knorr Expedition, 1991). Model estimations of hydrogen sulfide oxidation, metal sulfide precipitation, hydrogen sulfide formation in the sediments and water column, export flux to the anoxic layer and to the sediments, denitrification, primary and bacterial production are in the range of field observations. With a simulated Gross Primary Production (GPP) of 7.9 molC m-2 yr-1 and a Community Respiration (CR) of 6.3 molC m-2 yr-1, the system is net autotrophic with a Net Community Production (NCP) of 1.6 molC m-2 yr-1. This NCP corresponds to 20 % of the GPP and is exported to the anoxic layer. In order to model Particulate Organic Matter (POM) fluxes to the bottom and hydrogen sulfide profiles in agreement with in-situ observations, we have to consider that the degradation of POM in anoxic conditions is less efficient that in oxygenated waters as it has often been observed (see discussion in Hedges et al., 1999). The vertical POM profile produced by the model can be fitted to the classic power function describing the oceanic carbon rate (CR=Z-) using an attenuation coefficient  of 0.36 which is the value proposed for another anoxic environment (i.e. the Mexico Margin) by Devol and Hartnett, (2001). Due to the lower efficiency of detritus degradation in anoxic conditions and to the aggregation of particles that enhanced the sinking, an important part of the export to the anoxic layer (i.e. 33 %, 0.52 molC m-2 yr-1) escapes remineralization in the water column and reaches the sediments. Therefore, sediments are active sites of sulfide production contributing to 26 % of the total sulfide production. In the upper layer, the oxygen dynamics is mainly governed by photosynthesis and respiration processes as well as by air-sea exchanges. ~ 71 % of the oxygen produced by phytoplankton (photosynthesis + nitrate reduction) is lost through respiration, ~ 21 % by outgasing to the atmosphere, ~ 5 % through nitrification and only ~ 2 % in the oxidation of reduced components (e.g. Mn2+, Fe2+, H2S). The model estimates the amount of nitrogen lost through denitrification at 307 mmolN m-2 yr-1 that can be partitioned into a loss of ~ 55 % through the use of nitrate for the oxidation of detritus in low oxygen conditions, ~ 40 % in the ANAMMOX process and the remaining ~ 5% in the oxidation of reduced substances by nitrate. In agreement with data analysis performed on long time series collected since the 1960's (Konovalov and Murray, 2001), the sulfide and nitrogen budgets established for the anoxic layer are not balanced in response to the enhanced particle fluxes induced by eutrophication: the NH4 and H2S concentrations increase. [less ▲]

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See detail3D Modelling of the Black Sea northwestern Shelf Ecosystem
Capet, Arthur ULg; Grégoire, Marilaure ULg

Conference (2010, May 14)

Some validation procedures are presented concerning the physicis and the biology, as well as the decomposition of the oxygen cycle in its different components. The role of the Sevastopol eddy of retaining ... [more ▼]

Some validation procedures are presented concerning the physicis and the biology, as well as the decomposition of the oxygen cycle in its different components. The role of the Sevastopol eddy of retaining POM in the Crimea peninsula causing intense bacterial oxygen consumption is evidenced. [less ▲]

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See detailThe assessment of the past decades based on modelling and data analysis: some examples
Grégoire, Marilaure ULg; Gorsky, G.; Sesame participants, .

Conference (2010, May)

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See detailA recipe for biogeochemical modelling using 3D pelagic models
Grégoire, Marilaure ULg

Conference (2010, March)

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See detailAssessing ecosystem changes in the North Western shelf of the Black Sea using 3D coupled models
Capet, Arthur ULg; Beckers, Jean-Marie ULg; Joassin, Pascal et al

Conference (2009, November 11)

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See detailModeling the hydrodynamics and the ecosystem dynamics of the Bay of Calvi
Lenartz, F.; Alvera Azcarate, Aïda ULg; Beckers, Jean-Marie ULg et al

Poster (2009, November)

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See detailAssessment of the long term changes of the SES ecosystem
Grégoire, Marilaure ULg

Conference (2009, November)

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See detail3D modelling of the Black Sea ecosystem
Capet, Arthur ULg; Beckers, Jean-Marie ULg; Joassin, Pascal et al

Poster (2009, April 24)

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