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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 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 detailThe utilization of polysaccharides by heterotrophic bacterioplankton in the Bay of Biscay (North Atlantic Ocean)
Piontek, Judith; Händel, Nicole; De Bodt, Caroline et al

in Journal of Plankton Research (2011), 33(11), 1719-1735

This study investigates the turnover of polysaccharides by heterotrophic bacterioplankton in the northern Bay of Biscay, a productive marine system on the shelf-break of the temperate Atlantic Ocean ... [more ▼]

This study investigates the turnover of polysaccharides by heterotrophic bacterioplankton in the northern Bay of Biscay, a productive marine system on the shelf-break of the temperate Atlantic Ocean. Field studies were conducted along the shelf-break south of Ireland and west of France (47° 07' 83'' N, 6° 92' 01'' E and 51° 34' 42'' N, 10° 49' 95'' E) during the development of phytoplankton blooms in late spring. Bacterial biomass production (BBP) near the surface ranged from 0.5 to 27.4 nmol C L-1 h-1 in both years. A direct relationship between BBP and the concentration of total polysaccharides strongly suggests the dependence of bacterial growth on the availability of semi-labile organic matter. Concentrations of combined glucose as well as rate constants of extracellular glucosidase activity and glucose uptake were determined to estimate the actual carbon fluxes from bacterial polysaccharide turnover. Results reveal that the degradation of polysaccharides n the upper 100 m of the water column sustained on average a glucose flux of 2.6 mmol C m-2 d-1 i that was available for bacterial uptake. The mean turnover time for polysaccharides was 170 and 165 days for alpha- and beta-glycosidic linked polymers, respectively. Free glucose, the labile hydrolysate of polysaccharides, had a mean turnover time of 4.5 days and supported 2.2 to 18.4% of BBP. The incorporation of glucose into bacterial biomass was stimulated by the availability of inorganic nitrogen. Overall, our results demonstrate that the bacterial recycling of polysaccharides in the Bay of Biscay generates a relevant flux of organic carbon in microbial food-webs and biogeochemical processes. [less ▲]

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See detailBenthic remineralization in the northwest European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

in Continental Shelf Research (2011), 31

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June ... [more ▼]

We report a dataset of sediment characteristics and biogeochemical fluxes at the watersediment interface at the northwest European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 18 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Water-sediment fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and lead-210 (210Pb) and thorium-234 (234Th) activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 μg g-1) contents comparable to previous investigations in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Water-sediment O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between water-sediment fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) seemed uncoupled from organic carbon degradation, as characterized by water-sediment O2 fluxes. The link between water-sediment fluxes of TA and O2 indicated the occurrence of metabolic driven dissolution of calcium carbonates (CaCO3) in the sediments (~ 0.33 ± 0.47 mmol m-2 d-1) which represented ~ 1 % of the pelagic calcification rates due to coccolithophores measured during the cruises. These CaCO3 dissolution rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation were low compared to water column rates of primary production and aphotic community respiration obtained during the cruises. [less ▲]

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See detailTowards a comprehensive C-budgeting approach of a cocoliothophorid bloom in the northern Bay of Biscay: results from PEACE project.
Harlay, Jérôme ULg; Borges, Alberto ULg; Delille, Bruno ULg et al

Conference (2010, May 03)

During coccolithophorid blooms, carbon (C) cycling in the photic zone is driven by the production and the degradation of organic matter (primary production and community respiration), as well as the ... [more ▼]

During coccolithophorid blooms, carbon (C) cycling in the photic zone is driven by the production and the degradation of organic matter (primary production and community respiration), as well as the production and the dissolution of biogenic calcium carbonate (CaCO3). Organic and inorganic metabolisms lead to a transfer of carbon to depth and both impact the flows of carbon dioxide (CO2) in the water column and the CO2 flux across the air-sea interface. Furthermore, due to complex dynamics of coccolithophores, the impact of metabolic C fluxes on CO2 fluxes is variable in time, depending on the stage of the bloom development, and mainly on the ratio of calcification to primary production (CAL:GPP). Understanding and quantifying C cycling of coccolithophorid blooms in natural conditions is a prerequisite to correctly validate biogeochemical models aiming at predicting feedbacks related to ocean acidification, which incorporate knowledge obtained from perturbation laboratory experiments. We carried out a trans-disciplinary cruise on board the R/V Belgica at the continental margin of the Bay of Biscay, in the midst of a coccolithophorid bloom, during which 14C primary production (GPPp), 14C calcification (CAL) and O2-based pelagic community respiration rates (PCR) were determined in the water column. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophorid blooms in the Northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

Poster (2010, May 03)

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate ... [more ▼]

Balch et al. (2007) evaluated global pelagic contemporary calcification from remote sensing data (mainly associated to coccolithophores) to 1.6 ± 0.3 Pg PIC yr-1 (1 Pg = 1015 g; PIC = particulate inorganic carbon). This would imply that coccolithophores would be the most important pelagic calcifier in the oceans, since other estimates of contemporary global pelagic calcification range between 0.7 Pg PIC yr-1 based on accumulation rates and sediment trap data (Milliman et al. 1999), and 1.4 Pg PIC yr-1, based on the seasonal cycle of total alkalinity (TA) in the euphotic zone (Lee 2001). The development of coccolithophorid blooms affects the seawater carbonate chemistry, and air-sea CO2 fluxes, through the organic carbon pump and the carbonate counter-pump. The ratio between calcification (carbonate counter-pump), and organic carbon production (organic carbon pump), the C:P ratio, depends on the life cycle (bloom development), and growth conditions of coccolithophores. At the onset of the coccolithophorid bloom, when nutrients are available for growth, organic carbon production dominates over calcification (C:P << 1, the so-called organic phase). At the end of the bloom, in nutrient depleted conditions, and high irradiances (due to stronger stratification), organic carbon production decreases and calcification increases (C:P ≤ 1, the so-called inorganic phase). Several manipulative experiments to test the effect of ocean acidification on coccolithophores have shown that while calcification would decrease, the export of organic carbon would increase mainly through increasing transparent exopolymer particles (TEP) production. For a credible implementation in mathematical models of such feed-back mechanisms to allow the projection of a future evolution of carbon biogeochemistry under global change, it is required to understand present day biogeochemistry and ecology of naturally occurring pelagic calcifying communities. In particular, the overall effect of phytoplankton communities on the C:P ratio, and the net effect on carbonate chemistry, and related air-sea CO2 fluxes. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophorid blooms in the Northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

Poster (2010, May 02)

We present a data-set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of ... [more ▼]

We present a data-set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of coccolithophores occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity (TA) showed a non-conservative behaviour as a function of salinity due to the cumulated effect of net community calcification (NCC) during bloom development on seawater carbonate chemistry. The cumulated impact of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO2) were evaluated. The decrease of DIC (and increase of pCO2) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO2) due to NCP (NCC:NCP « 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average -9.7 mmol C m-2 d-1 for the 3 cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average 12% of total air-sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the northern North Atlantic Ocean (where coccolithophorid blooms are the most intense and recurrent), and in the global ocean, then the potential feed-back on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 “production” from calcification is probably minor compared to feed-backs related to changes of NCP. [less ▲]

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See detailBenthic remineralization in the northeast European continental margin (northern Bay of Biscay)
Suykens, Kim; Schmidt, Sabine; Delille, Bruno ULg et al

Poster (2010, May 02)

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in ... [more ▼]

We report a data-set of sediment characteristics and biogeochemical fluxes at the water-sediment interface at the northeast European continental margin (northern Bay of Biscay). Cores were obtained in June 2006, May 2007 and 2008, at 8 stations on the shelf break (120 to 180 m), and at 2 stations on the continental slope (520 m and 680 m). Sediment-water fluxes of dissolved oxygen (O2), total alkalinity (TA), nitrate (NO3-), and dissolved silicate (DSi) were measured at a total of 20 stations. Sediment characteristics include: grain size, chlorophyll-a (Chl-a) and phaeopigment (Phaeo) content, particulate organic (POC) and inorganic (PIC) carbon content, and 234Th and 210Pb activities. Sediments were sandy (fine to coarse) with organic matter (OM) (1.0 - 4.0 %) and Chl-a (0.01 - 0.95 µg g-1) contents comparable to previous publications in the same region, and a relatively high PIC fraction (0.8 - 10.2 %). Sediment-water O2 fluxes (-2.4 to -8.4 mmol O2 m-2 d-1) were low compared to other coastal environments and correlated well with OM and Chl-a content. 234Th activity profiles indicated that Chl-a sediment content (apparently the main driver of total benthic organic carbon degradation) was mainly controlled by physical mixing processes related to local hydrodynamics. The correlation between sediment-water fluxes of O2 and NO3- indicated a close coupling of nitrification/denitrification and total benthic organic carbon degradation. Dissolution of biogenic silica (0.05 to 0.95 mmol m-2 d-1) was uncoupled from organic carbon degradation, characterized by sediment-water O2 fluxes. The link between sediment-water fluxes of TA and O2 indicated metabolic driven dissolution ( 0.33 +/- 0.47 mmol m-2 d-1) of calcium carbonates (CaCO3) in the sediments which represented ~1 % of the pelagic calcification rates due to coccolithophores. These rates were below those reported in sediments of continental slopes and of the deep ocean, probably due to the high over-saturation with respect to CaCO3 of the water column overlying the continental shelf sediments of the northern Bay of Biscay. Rates of total benthic organic carbon degradation and CaCO3 dissolution were low compared to water column rates of primary production, aphotic community respiration and CaCO3 production obtained during the cruises. [less ▲]

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See detailDissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay)
Suykens, Kim; Delille, Bruno ULg; Chou, Lei et al

in Global Biogeochemical Cycles (2010), 24

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the ... [more ▼]

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the coccolithophore Emiliania huxleyi occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity showed a nonconservative behavior as a function of salinity due to the cumulative effect of net community calcification (NCC) on seawater carbonate chemistry during bloom development. The cumulative effect of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO(2)) were evaluated. The decrease of DIC (and increase of pCO(2)) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO(2)) due to NCP (NCC: NCP << 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average similar to-9.7 mmol C m(-2) d(-1) for the three cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average similar to 12% of total air-sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the North Atlantic Ocean (where blooms of coccolithophores are the most intense and recurrent), and in the global ocean, then the potential feedback on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 "production" from calcification is probably minor compared to potential feedbacks related to changes of NCP. [less ▲]

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See detailIndividual and interacting effects of pCO2 and temperature on Emiliania huxleyi calcification: Study of the calcite production, the coccolith morphology and the coccosphere size
De Bodt, Caroline; Van Oostende, Nicolas; Harlay, Jérôme ULg et al

in Biogeosciences (2010), 7

The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and ... [more ▼]

The impact of ocean acidification and increased water temperature on marine ecosystems, in particular those involving calcifying organisms, has been gradually recognised. We examined the individual and combined effects of increased pCO2 (180 ppm V CO2, 380 ppm V CO2 and 750 ppm V CO2 corresponding to past, present and future CO2 conditions, respectively) and temperature (13°C and 18°C) during the calcification phase of the coccolithophore E. huxleyi using batch culture experiments. We showed that the cell abundance-normalized particulate organic carbon concentration (POC) increased from the present to the future CO2 treatments. A significant effect of pCO2 and of temperature on calcification was found, manifesting itself in a lower cell abundance-normalized particulate inorganic carbon (PIC) content as well as a lower PIC:POC ratio at future CO2 levels and at 18°C. Coccosphere-sized particles showed a size reduction trend with both increasing temperature and CO2 concentration. The influence of the different treatments on coccolith morphology was studied by categorizing SEM coccolith micrographs. The number of well-formed coccoliths decreased with increasing pCO2 while temperature did not have a significant impact on coccolith morphology. No interacting effect of pCO2 and temperature was observed on calcite production, coccolith morphology or on coccosphere size. Finally, our results suggest that ocean acidification might have a larger adverse impact on coccolithophorid calcification than surface water warming. [less ▲]

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See detailRole of pelagic calcification and export of carbonate production in climate change
Chou, Lei; Harlay, Jérôme ULg; De Bodt, Caroline et al

Poster (2009, November 16)

The marine carbon cycle constitutes a key component of the climate system. It has been shown that one-fourth of the anthropogenic CO2 emitted to the atmosphere is absorbed by the ocean, leading to the ... [more ▼]

The marine carbon cycle constitutes a key component of the climate system. It has been shown that one-fourth of the anthropogenic CO2 emitted to the atmosphere is absorbed by the ocean, leading to the acidification of the surface ocean and the modification of seawater carbonate chemistry. This could have major impacts on the ocean biogeochemical carbon cycling and ecosystem dynamics. Yet, the resulting feedbacks on climate change are still poorly understood. Interdisciplinary biogeochemical investigations, assisted by remote sensing, have been conducted during three consecutive years along the shelf break of the Northern Bay of Biscay where coccolithophorid blooms dominated by Emiliania huxleyi are frequently and recurrently observed. Rates of various processes governing the coccolithophore ecosystem dynamics have been determined and air-sea CO2 fluxes evaluated. The key results will be presented and discussed to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophorid blooms. [less ▲]

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See detailBiogeochemistry and carbon budget during a coccolithophorid bloom in the northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Borges, Alberto ULg; De Bodt, Caroline et al

Poster (2009, April 19)

Carbon cycling processes (primary production (PPp), calcification (CAL), bacterial production and pelagic community respiration (PCR)) and variables (partial pressure of CO2 (pCO2) and total alkalinity ... [more ▼]

Carbon cycling processes (primary production (PPp), calcification (CAL), bacterial production and pelagic community respiration (PCR)) and variables (partial pressure of CO2 (pCO2) and total alkalinity (TA)) were measured in early June 2006 at several stations in the northern Bay of Biscay. These measurements were characterized with respect to the coccolithophorid blooming (growth or decline) based on satellite remote sensing (high reflectance (HR)) and other biogeochemical measurements i.e. inorganic nutrients, chlorophyll-a (Chl-a), phaeopigments (Phaeo), particulate inorganic carbon (PIC), particulate organic carbon (POC) and particulate nitrogen (PN)). The major HR patch was located over the shelf, along the continental margin and corresponded to declining bloom conditions characterized by moderate Chl-a <1.0 µg L-1, dissolved phosphate (PO4) depletion, low (<2.0 µmol L-1) dissolved silicate (DSi), low potential primary production (<0.25 µmol C L-1 h-1) and calcification rates (0.02-0.10 µmol C L-1 h-1). Yet, surface waters were undersaturated in CO2 with respect to atmospheric equilibrium. We present a coherent scheme of the C dynamics of a coccolithophorid bloom along the continental margin of the Bay of Biscay, an active hydrodynamic area, based on standing stocks and processes including 14C-based particulate primary production, CAL and PCR. A carbon budget obtained by integrating PPp, CAL and PCR over the water column highlights the importance of C extracellular production to sustain the bacterial demand in the twilight zone, which has also several repercussions on the fate of organic and inorganic C production in the photic zone during the different stages of the bloom. [less ▲]

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See detailCell lysis during coccolithophorid blooms in the Northern Bay of Biscay
De Bodt, Caroline; Harlay, Jérôme ULg; Roevros, Nathalie et al

Poster (2009, January 25)

Phytoplankton cell lysis occurs in natural populations and is often associated with viral activity and zooplankton grazing. Cell lysis rates are expected to increase towards the decaying phase of the ... [more ▼]

Phytoplankton cell lysis occurs in natural populations and is often associated with viral activity and zooplankton grazing. Cell lysis rates are expected to increase towards the decaying phase of the bloom and may be associated with enhanced microbial activity and export of particulate matter to the seafloor. Their estimation was based on the measurement of esterase (a cytoplasmic enzyme) activity expected to appear in the water only after cell breakage. Field investigations, supported by remote sensing data, were conducted in recent years during late spring in the Northern Bay of Biscay, where frequent and recurrent coccolithophorid blooms are observed. Results on cell lysis rates determined in surface waters will be presented with relevant biogeochemical parameters (temperature, particulate organic and inorganic carbon, transparent exopolymer particles, nutrients, chlorophyll a) in order to investigate phytoplankton dynamics in relation to coccolithophorid development. The use of this parameter to characterize bloom termination, especially during coccolithophorid blooms will be discussed. [less ▲]

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See detailTowards a comprehensive C-budgeting approach of a coccolithophorid bloom in the Northern Bay of Biscay (June 2006)
Harlay, Jérôme ULg; Borges, Alberto ULg; De Bodt, Caroline et al

Poster (2009, January 25)

A biogeochemical multidisciplinary survey was carried out in the northern Bay of Biscay, in early June 2006, during which 14C-based primary production and calcification were determined as well as O2-based ... [more ▼]

A biogeochemical multidisciplinary survey was carried out in the northern Bay of Biscay, in early June 2006, during which 14C-based primary production and calcification were determined as well as O2-based community respiration. Contemporary remote sensing images showed several patches of high reflectance (HR) in the investigated area. Based on remote sensing and in situ measured biogeochemical parameters, the area exhibited varying coccolithophorid bloom stages from its early development to the post-bloom stages. The major HR patch, characterizing a post-stationary stage of the bloom, was located between 48°N and 49°N over the shelf along the continental margin. It was associated with moderate chlorophyll-a levels, never exceeding 1.0 µg L-1, dissolved phosphorus and silica depletion, and undersaturation of CO2 with respect to atmospheric equilibrium. Considered as the main drivers of the C cycle in this area, the CO2 fluxes associated with primary production, calcification and respiration were integrated in order to provide a comprehensive C budget in the area. [less ▲]

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See detailDynamics of polysaccharides and transparent exopolymer particles during a coccolithophorid bloom in the Bay of Biscay
Händel, Nicole; Piontek, Judith; Harlay, Jérôme ULg et al

Poster (2009, January 25)

Carbohydrates comprise a large fraction (~30 %) of organic matter in the ocean (Pakulski and Benner, 1994). The production of polysaccarides (CCHO) in seawater is mainly linked to autotrophic processes ... [more ▼]

Carbohydrates comprise a large fraction (~30 %) of organic matter in the ocean (Pakulski and Benner, 1994). The production of polysaccarides (CCHO) in seawater is mainly linked to autotrophic processes. CCHO serve as structural and storage compounds, or are released by exudation, cell lysis or leakage to the dissolved organic matter pool. Concentrations of total hydrolyzable neutral sugars range from 200-800nM and 20-170nM in surface and deep waters, respectively (Benner, 2002). It has been shown that CCHO, in particular acidic polysaccharides, are involved in aggregation processes, e.g. the formation of transparent exopolymer particles (TEP). Recently, it has been suggested that ocean acidification increases TEP production, and therefore potentially enhances particle aggregation (Engel 2002, Mari 2008). Here, we present data on the abundance and composition of neutral and acidic CCHO and on TEP, obtained from field investigations and from CO2-controlled chemostat experiments that were conducted during a coccolithophore bloom in the Bay of Biscay 2006. Based on our findings, we discuss the partitioning of CCHO into gel particles, potential effects of ocean acidification and related consequences for organic matter export. [less ▲]

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See detailAbundance and size distribution of transparent exopolymer particles (TEP) in a coccolithophorid bloom in the northern Bay of Biscay
Harlay, Jérôme ULg; De Bodt, Caroline; Engel, Anja et al

in Deep-Sea Research Part I, Oceanographic Research Papers (2009), 56(8), 1251-1265

The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a ... [more ▼]

The distribution of transparent exopolymer particles (TEP) was investigated during a coccolithophorid bloom in the northern Bay of Biscay (North Atlantic Ocean) in early June 2006. MODIS chlorophyll-a (Chl-a) and reflectance images before and during the cruise were used to localize areas of important biological activity and high reflectance (HR). TEP profiles along the continental margin, determined using microscopic (TEPmicro) and colorimetric (TEPcolor) methods, showed abundant (6.1 x 10(6)-4.4 x 10(7) L-1) and relatively small (0.5-20 mu m) particles, leading to a low total volume fraction (0.05-2.2 ppm) of TEPmicro and similar vertical profiles of TEPcolor Estimates of carbon content in TEP (TEP-C) derived from the microscopic approach yielded surface concentration of 1.50 mu mol CL-1. The contribution of TEP-C to particulate organic carbon (POC) was estimated to be 12% (molar C ratio) during this survey. Our results suggest that TEP formation is a probable first step to rapid and efficient export of C during declining coccolithophorid blooms. (C) 2009 Elsevier Ltd. All rights reserved. [less ▲]

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See detailBiogeochemical Investigations of Coccolithophore Blooms along the Continental Margin of the Northern Bay of Biscay: Highlights of the PEACE Project
Chou, Lei; Harlay, Jérôme ULg; De Bodt, Caroline et al

Poster (2008, October 06)

Recent studies have demonstrated that changing ocean chemistry due to ocean acidification poses a growing threat for marine organisms such as corals, coccolithophores and many others that form calcareous ... [more ▼]

Recent studies have demonstrated that changing ocean chemistry due to ocean acidification poses a growing threat for marine organisms such as corals, coccolithophores and many others that form calcareous skeletons. Its biogeochemical feedbacks and impact on the oceanic carbon cycle are yet to be quantified. Coccolithophores are the major calcifying phytoplankton in the sub-polar and temperate regions of the world’s ocean. They produce furthermore transparent exopolymer particles (TEP), which are known to promote aggregate formation. Combined with the CaCO3 ballast effect, large-scale coccolithophore blooms could thus contribute to the export of organic carbon to deep waters on relatively short time scales. During the Belgian PEACE project, we have conducted yearly interdisciplinary biogeochemical surveys, assisted by remote sensing, along the continental margin of the northern Bay of Biscay where coccolithophore blooms dominated by Emiliania huxleyi are frequently and recurrently observed (Figure 1). Rates of various processes governing the coccolithophore ecosystem dynamics have been determined and associated biogeochemical parameters analysed. The overall objective is to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophore blooms. Here we report the principal results obtained during the 2006 campaign. [less ▲]

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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 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 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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