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See detailSeasonal and interannual variations of community metabolism rates of a Posidonia oceanica seagrass meadow
Champenois, Willy ULg; Borges, Alberto ULg

in Limnology & Oceanography (2012), 57(1), 347-361

We report gross primary production (GPP), community respiration (CR), and net community production (NCP) over a Posidonia oceanica meadow at 10 m in Corsica (Bay of Revellata) based on the open water O2 ... [more ▼]

We report gross primary production (GPP), community respiration (CR), and net community production (NCP) over a Posidonia oceanica meadow at 10 m in Corsica (Bay of Revellata) based on the open water O2 mass balance from a data set of hourly measurements with an array of three O2 optodes deployed from August 2006 to October 2009. The method was checked by comparison with discrete measurements of metabolic rates derived from benthic chamber incubations also based on the diel change of O2. This comparison was satisfactory and actually highlights the potential caveats of benthic incubation measurements related to O2 accumulation in small chambers leading to photorespiration and an underestimation of GPP. Our data confirmed previous P. oceanica meadows GPP and CR values, strong seasonal variations, and net autotrophy. High-resolution data revealed strong interannual variability, with a decrease of GPP by 35% and NCP by 87% during 2006-2007 characterized by a mild and less stormy winter compared with 2007-2008 and 2008-2009. P. oceanica meadows are then expected to decrease export of organic carbon to adjacent communities (decrease of NCP), since a decrease in frequency and intensity of marine storms is expected in the future in the Mediterranean Sea as a result of a northward shift of the Atlantic storm track. [less ▲]

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See detailFirst assessment of the biogeochemistry of the Congo River and its tributaries
Darchambeau, François ULg; Borges, Alberto ULg; Wabakanghanzi, José Nlandu et al

Scientific conference (2011, November 29)

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See detailVariability of methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Abril, Gwenael; Delille, Bruno ULg et al

Poster (2011, July 11)

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See detailBiogeochemistry of the Congo river: Preliminary data
Darchambeau, François ULg; Borges, Alberto ULg; Wabakanghanzi, José Nlandu et al

Conference (2011, June 03)

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See detailVariability of methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Abril, G.; Delille, Bruno ULg et al

Poster (2011, April 08)

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See detailFirst assessment of the biogeochemistry of the Congo River and tributaries
Darchambeau, François ULg; Bouillon, S.; Wabakanghanzi, J. N. et al

Poster (2011, April 08)

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See detailEvaluation of sinks and sources of CO2 in the global coastal ocean using a spatially-explicit typology of estuaries and continental shelves
Laruelle, G. G.; Dürr, H. H.; Slomp, C. P. et al

Conference (2011, April 08)

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See detailSeasonal and inter-annual variability of air-sea CO2 fluxes and seawater carbonate chemistry in the Southern North Sea
Gypens, N.; Lacroix, G.; Lancelot, C. et al

Poster (2011, April 08)

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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

Poster (2011, April 03)

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 detailParticulate carbon export during a bloom of Emiliania huxleyi in the Northwest European continental margin (northern Bay of Biscay)
Schmidt, Sabine; Harlay, Jérôme ULg; Borges, Alberto ULg et al

Poster (2011, April 03)

Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological ... [more ▼]

Coccolithophores, the dominant pelagic calcifiers in the oceans, play a key role in the marine carbon cycle through calcification, primary production and carbon export, the main drivers of the biological CO2 pump. Massive blooms of Emiliania huxleyi are observed each year at the continental margin of the Bay of Biscay. The BG02/11 cruise (RV Belgica), supported by near-real time remote sensing data, was conducted in early May 2002, along a transect on the outer shelf of the Northern Bay of Biscay between the La Chapelle Bank (southern region of the transect) and Goban Spur (northern region of the transect) (47.0°-50.5°N, 5.0°-11.0°W). Biogeochemical variables including primary production, calcification, partial pressure of CO2 (pCO2), chlorophyll-a (Chl-a), particle load, particulate organic and inorganic carbon (POC, PIC), Th-234 were measured in surface waters to assess particle dynamics, and carbon export in relation to the development of a coccolithophore bloom. We observed a marked northward decrease in water irradiance, Chl-a concentration and calcification rates: the bloom exhibited lower values and may have been less well developed in the Goban Spur area. There was also a large northward decrease in particulate 234Th settling fluxes along the transect from La Chapelle Bank to Goban Spur. The export fluxes of POC and PIC from the top 80 m, determined using the ratios of POC and PIC to Th-234 of particles, ranged from 81 to 323 mgC m-2 d-1 and from 30 to 128 mgC m-2 d-1, respectively. The highest fluxes were observed in waters presenting a well-developed coccolithophore bloom, as shown by high reflectance of surface waters. Despite the high calcification rates at the southernmost stations, surface waters were a net sink of atmospheric CO2 during this cruise. These results tend to demonstrate the enhancement of coccolithophore blooms on the efficiency of the surface community to export carbon to deep ocean. However, improvements in the estimation of POC and PIC export during coccolithophore blooms are needed to not only understand the present calcification to primary production (C:P) ratio, but also to help understand future sequestration of organic and inorganic carbon to the deep ocean. [less ▲]

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See detailDistribution and composition of organic carbon in the Tana River Basin, (Kenya)
Tamooh, F.; van den Meersche, K.; Borges, Alberto ULg et al

Conference (2011, February 13)

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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 detailOverview of CO2 dynamics within sea ice
Delille, Bruno ULg; Geilfus, N.; Vancoppenolle, M. et al

Conference (2011)

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See detail5.04 - Carbon Dioxide and Methane Dynamics in Estuaries
Borges, Alberto ULg; Abril, Gwenaël

in Wolanski, Eric; McLusky, Donald (Eds.) Treatise on Estuarine and Coastal Science, Volume 5: Biogeochemistry (2011)

Estuaries profoundly transform the large amounts of carbon delivered from rivers before their transfer to the adjacent coastal zone. As a consequence of the complex biogeochemical reworking of ... [more ▼]

Estuaries profoundly transform the large amounts of carbon delivered from rivers before their transfer to the adjacent coastal zone. As a consequence of the complex biogeochemical reworking of allochthonous carbon in the sediments and the water column, CO2 and CH4 are emitted into the atmosphere. We attempt to synthesize available knowledge on biogeochemical cycling of CO2 and CH4 in estuarine environments, with a particular emphasis on the exchange with the atmosphere. Unlike CH4, the global emission of CO2 to the atmosphere from estuaries is significant compared to other components of the global carbon cycle [less ▲]

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See detailBiogeochemical response of Emiliania huxleyi (PML B92/11) to elevated CO2 and temperature under phosphorous limitation: A chemostat study
Borchard; Borges, Alberto ULg; Händel, Nicole et al

in Journal of Experimental Marine Biology & Ecology (2011), 410

The present study investigates the combined effect of phosphorous limitation, elevated partial pressure of CO2 (pCO2) and temperature on a calcifying strain of Emiliania huxleyi (PML B92/11) by means of a ... [more ▼]

The present study investigates the combined effect of phosphorous limitation, elevated partial pressure of CO2 (pCO2) and temperature on a calcifying strain of Emiliania huxleyi (PML B92/11) by means of a fully controlled continuous culture facility. Two levels of phosphorous limitation were consecutively applied by renewal of culture media (N:P = 26) at dilution rates (D) of 0.3 d− 1 and 0.1 d− 1. CO2 and temperature conditions were 300, 550 and 900 μatm pCO2 at 14 °C and 900 μatm pCO2 at 18 °C. In general, the steady state cell density and particulate organic carbon (POC) production increased with pCO2, yielding significantly higher concentrations in cultures grown at 900 μatm pCO2 compared to 300 and 550 μatm pCO2. At 900 μatm pCO2, elevation of temperature as expected for a greenhouse ocean, further increased cell densities and POC concentrations. In contrast to POC concentration, C-quotas (pmol C cell− 1) were similar at D = 0.3 d− 1 in all cultures. At D = 0.1 d− 1, a reduction of C-quotas by up to 15% was observed in the 900 μatm pCO2 at 18 °C culture. As a result of growth rate reduction, POC:PON:POP ratios deviated strongly from the Redfield ratio, primarily due to an increase in POC. Ratios of particulate inorganic and organic carbon (PIC:POC) ranged from 0.14 to 0.18 at D = 0.3 d− 1, and from 0.11 to 0.17 at D = 0.1 d− 1, with variations primarily induced by the changes in POC. At D = 0.1 d− 1, cell volume was reduced by up to 22% in cultures grown at 900 μatm pCO2. Our results indicate that changes in pCO2, temperature and phosphorus supply affect cell density, POC concentration and size of E. huxleyi (PML B92/11) to varying degrees, and will likely impact bloom development as well as biogeochemical cycling in a greenhouse ocean. [less ▲]

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See detailDiffusive methane emissions to the atmosphere from Lake Kivu (Eastern Africa)
Borges, Alberto ULg; Abril, Gwenaël; Delille, Bruno ULg et al

in Journal of Geophysical Research. Biogeosciences (2011), 116(G03032),

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons ... [more ▼]

We report a data-set of methane (CH4) concentrations in the surface waters of Lake Kivu obtained during four cruises (March 2007, September 2007, June 2008, April 2009) covering the two main seasons, rainy (October to May) and dry (June to September). Spatial gradients of CH4 concentrations were modest in the surface waters of the main basin. In Kabuno Bay (a small sub-basin), CH4 concentrations in surface waters were significantly higher than in the main basin. Seasonal variations of CH4 in the main basin were strongly driven by deepening of the mixolimnion and mixing of surface waters with deeper waters rich in CH4. On an annual basis, both Kabuno Bay and the main basin of Lake Kivu were over-saturated in CH4 with respect to atmospheric equilibrium (7330% and 2510%, respectively), and emitted CH4 to the atmosphere (39 mmol m-2 yr-1 and 13 mmol m-2 yr-1, respectively). The source of CH4 to atmosphere was two orders of magnitude lower than the CH4 upward flux. The source of CH4 to the atmosphere from Lake Kivu corresponded to ~60% of the terrestrial sink of atmospheric CH4 over the lake’s catchment. A global cross-system comparison of CH4 in surface waters of lakes shows that both Kabuno Bay and the main basin are at the lower end of values in lakes globally, despite the huge amounts of CH4 in the deeper layers of the lake. This is related to the strongly meromictic nature of the lake that promotes an intense removal of CH4 by bacterial oxidation. [less ▲]

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