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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 detailBiogeochemical study of a coccolithophore bloom in the northern Bay of Biscay (NE Atlantic Ocean) in June 2004
Harlay, Jérôme ULg; Borges, Alberto ULg; Van Der Zee, Claar et al

in Progress in Oceanography (2010), 86(3-4), 317-336

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the ... [more ▼]

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the different stages of a coccolithophore bloom dominated by Emiliania huxleyi. The cruise was carried out after the main spring phytoplankton bloom that started in mid-April and peaked in mid-May. Consequently, low phosphate (PO4<0.2 μM) and silicate (DSi<2.0 μM) concentrations, low partial pressure of carbon dioxide (pCO2) and high calcite saturation degree in surface waters combined with thermal stratification, probably favoured the blooming of coccolithophores. During the period of the year our cruise was carried out, internal tides induce enhanced vertical mixing at the continental shelf break leading to the injection of inorganic nutrients to surface waters that probably trigger the bloom. The bloom developed as the water-column stratified and as the water mass was advected over the continental shelf, following the general residual circulation in the area. The most developed phase of the bloom was sampled in a remote sensed high reflectance (HR) patch over the continental shelf that was characterized by low chlorophyll-a (Chl-a) concentration in surface waters (<1.0 μg L-1), high particulate inorganic carbon (PIC) concentration (~8 μmol L-1) and coccolithophore abundance up to 57×106 cells L-1. Transparent exopolymer particles (TEP) concentrations ranged between 15 and 120 μg Xeq L-1 and carbon content of TEP represented up to 26% of the particulate organic carbon (POC; maximum concentration of 15.5 μmol L-1 in the upper 40 m). Integrated primary production (PP) ranged between 210 mg C m-2 d-1 and 680 mg C m-2 d-1 and integrated calcification (CAL) ranged between 14 and 140 mg C m-2 d-1, within the range of PP and CAL values previously reported during coccolithophore blooms in open and shelf waters of the North Atlantic Ocean. Bacterial protein production (BPP) measurements in surface waters (0.3 to 0.7 μg C L-1 h-1) were much higher than those reported during early phases of coccolithophore blooms in natural conditions, but similar to those during peak and declining coocolithophorid blooms reported in mesocosms. Total alkalinity anomalies with respect to conservative mixing (ΔTA) down to -49 μmol kg-1 are consistent with the occurrence of biogenic precipitation of calcite, while pCO2 remained 15 to 107 μatm lower than atmospheric equilibrium (372 μatm). The correlation between ΔTA and pCO2 suggested that pCO2 increased in part due to calcification, but this increase was insufficient to overcome the background under-saturation of CO2. This is related to the biogeochemical history of the water masses due to net carbon fixation by the successive phytoplankton 2 [less ▲]

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See detailParticle export with coccolithophorid Emiliania huxleyi blooms in the Bay of Biscay. XII International Symposium on Oceanography of the Bay of Biscay
Schmidt, Sabine; Harlay, Jérôme ULg; Roevros, Nathalie et al

Conference (2010, May 03)

Coccolithophores, one of the most productive calcifying phytoplanktonic groups, often form massive blooms in the temperate and sub-polar oceans, and in particular at continental margins and in shelf seas ... [more ▼]

Coccolithophores, one of the most productive calcifying phytoplanktonic groups, often form massive blooms in the temperate and sub-polar oceans, and in particular at continental margins and in shelf seas. 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 also a major producer of dimethyl sulphide (DMS), whose oxidation products of DMS affect the number and size distribution of tropospheric cloud condensation nuclei, with possible consequences for cloud albedo and heat balance. Coccolithophores are further known to produce transparent exopolymer particles (TEP) that promote particle aggregation and sinking. Coccolithophores play thus key roles in the global carbon, carbonate and sulphur cycles, and, in turn, in climate regulation. The objectives of the Belgian CCCC project (Role of Oceanic Production and Dissolution of Calcium Carbonate in Climate Change) was to evaluate the role in climate regulation of calcification, primary production and export processes during coccolithophorid blooms. Field investigations, supported by remote sensing data, were conducted in the Northern Gulf of Biscay on the continental shelf and slope region (47°- 50°30'N, 5°-11°W) where coccolithophorid blooms are frequently and recurrently observed. During the cruises in May 2002 and 2003 on board the r/v Belgica, fundamental variables (temperature, salinity, primary production, Chl. a, particulate organic carbon) were measured in the water column. To estimate the spatial variability of particle dynamics in surface waters in relation with the coccolithophorid bloom development, we had employed the natural radionuclide 234Th. The preferential scavenging of the particle-reactive daughter 234Th (t1/2= 24.1 days) while its soluble parent, 238U, remains nearly constant, provides an appropriate tool for assessing temporal variations of the removal of particles from surface waters, at a time scale of weeks. The two cruises have permitted to sample two different situations; in particular in May 2002, it was possible to sample a well-developed bloom. As a result, 234Th present contrasted profiles in the upper 0-80 m during the two investigations. In May 2003, 234Th was nearly in equilibrium with 238U (its radioactive parent) along with high particulate activities: this seems to indicate an early bloom situation with low grazing fluxes. On the opposite, in May 2002, deficits of 234Th toward 238U were indicating more efficient particle export from upper waters. Synthesis of the acquired data will be discussed to compare particle dynamics and the magnitude of particulate carbon export using 234Th and POC data at different states of coccolithophorid bloom in the Northern Gulf of Biscay. [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 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 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 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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See detailBiogeochemistry of a late marginal coccolithophorid bloom in the Bay of Biscay
Harlay, Jérôme ULg; de Bodt, Caroline; d'Hoop, Quentin et al

Conference (2007, April 15)

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s oceans. Within the ... [more ▼]

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s 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 multidisciplinary investigation of a late-spring bloom dominated by Ehux. Field sampling was assisted by daily transmission to the RV Belgica of remote sensing images, indicating the bloom development in the area. Various stations on the shelf and the shelf-break were sampled for the vertical distributions of nutrients, Transparent Exopolymer Particles (TEP), chlorophyll-a and particulate carbon concentrations. These data will be presented, here, in relation with 14C based integrated primary production, dissolved esterase activity and the bacterial community structure to emphasize the importance of coccolithophorid blooms in the biogeochemistry of the Northern Atlantic’s continental shelf. [less ▲]

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See detailCoccolithophorid calcium carbonate dissolution in surface waters
Harlay, Jérôme ULg; Koch, Craig; Young, Jeremy R et al

Poster (2007, March 06)

The role of calcifying organisms in the ocean biogeochemistry has been receiving increasing attention since CO2-related global change issues such as ocean acidification were pointed out by the scientific ... [more ▼]

The role of calcifying organisms in the ocean biogeochemistry has been receiving increasing attention since CO2-related global change issues such as ocean acidification were pointed out by the scientific community. The implications of changing oceanic pH in modifying ecosystems dominated by planktonic calcifiers have been shown by mesocosm and laboratory experiments based on CO2 manipulations. The major concern of such experiments focussed on variations in the rates of ecosystem primary production and calcification due to changes in algal physiology or specific composition. Our results, from an interdisciplinary survey of coccolithophore-dominated blooms in the northern Bay of Biscay (NE Atlantic), suggest that biogenic calcite dissolution is occurring in the photic zone where surface waters are oversaturated with respect to calcite. The dissolution of CaCO3 in surface waters, evidenced by scanning electron microscopy observations, has an impact on the preservation and export of carbon in coccolithophore-dominated ecosystems and on the exchange of CO2 across the ocean-atmosphere interface. Both aspects of suspended calcite concentration reduction in natural environments (lower rates of production or dissolution) could be considered as a perturbation of the oceanic carbon cycle. We aim at presenting here a biogeochemical description of processes, including integrated primary production, calcification, and parameters such as transparent exopolymer particles concentration and particulate inorganic carbon profiles, during field studies. A mechanism for calcite dissolution, based on biological activity in microenvironments (including grazing, bacterial respiration and DMS production) is presented as a conceptual model in coccolithophore blooms. [less ▲]

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See detailBiogeocehmical study of a coccolithophore bloom at the continental margin in the Northeast Atlantic
Harlay, Jérôme ULg; van der Zee, Claar; Schiettecatte, Laure-Sophie et al

Conference (2005, June 14)

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s oceans. The continental ... [more ▼]

Coccolithophores, among which Emiliania huxleyi (Ehux) is the most abundant and widespread species, are the dominant calcifying phytoplankton in the temperate zone of the world’s oceans. The continental margin in the Northern Bay of Biscay (North Atlantic Ocean) was visited in June 2004 during a multidisciplinary investigation of a late-spring bloom dominated by Ehux. Field sampling was assisted by daily transmission to the RV Belgica of remote sensing images, indicating the bloom development in the area. Primary production and calcification were measured by 14C incubations and zooplankton grazing experiments were performed. Vertical distributions of transparent exopolymer (TEP) concentration and bacterial density, as well as the bacterial production in surface waters, were also determined to elucidate the fate of biogenic carbonate production. The organic and inorganic carbon fluxes are evaluated in terms of relevant processes and discussed in relation with the DIC and nutrient dynamics. [less ▲]

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