Transparent exopolymer particles and dissolved organic carbon production by Emiliania huxleyi exposed to different CO2 concentrations: a mesocosm experiment

in Aquatic Microbial Ecology (2004), 34(1), 93-104

The role of transparent exopolymer particles (TEP) and dissolved organic carbon (DOC) for organic carbon partitioning under different CO2 conditions was examined during a mesocosm experiment with the ... [more ▼]

The role of transparent exopolymer particles (TEP) and dissolved organic carbon (DOC) for organic carbon partitioning under different CO2 conditions was examined during a mesocosm experiment with the coccolithophorid Emiliania huxleyi. We designed 9 outdoor enclosures (similar to11 m(3)) to simulate CO2 concentrations of estimated 'Year 2100' (similar to710 ppm CO2), 'present' (similar to410 ppm CO2) and 'glacial' (similar to190 ppm CO2) environments, and fertilized these with nitrate and phosphate to favor bloom development. Our results showed fundamentally different TEP and DOC dynamics during the bloom. In all mesocosms, TEP concentration increased after nutrient exhaustion and accumulated steadily until the end of the study. TEP concentration was closely related to the abundance of E. huxleyi and accounted for an increase in POC concentration of 35 +/- 2 % after the onset of nutrient limitation. The production of TEP normalized to the cell Abundance of E. huxleyi was highest in the Year 2100 treatment. In contrast, DOC concentration exhibited considerable short-term fluctuations throughout the study. In all mesocosms, DOC was neither related to the abundance of E. huxleyi nor to TEP concentration. A statistically significant effect of the CO2 treatment on DOC concentration was not determined. However, during the course of the bloom, DOC concentration increased in 2 of the 3 Year 2100 mesocosms and in 1 of the present mesocosms, but in none of the glacial mesocosms. It is suggested that the observed differences between TEP and DOC were determined by their different bioavailability and that a rapid response of the microbial food web may have obscured CO2 effects on DOC production by autotrophic cells. [less ▲]

Do we have enough pieces of the jigsaw to integrate CO2 fluxes in the Coastal Ocean ?

Poster (2004)

DIC dynamics in the Bay of Palma (NW Mediterranean)

Poster (2004)

Gas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt and Thames)

in Limnology & Oceanography (2004), 49(5), 1630-1641

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We ... [more ▼]

We measured the flux of CO2 across the air–water interface using the floating chamber method in three European estuaries with contrasting physical characteristics (Randers Fjord, Scheldt, and Thames). We computed the gas transfer velocity of CO2 (k) from the CO2 flux and concomitant measurements of the air–water gradient of the partial pressure of CO2 (pCO2). There was a significant linear relationship between k and wind speed for each of the three estuaries. The differences of the y-intercept and the slope between the three sites are related to differences in the contribution of tidal currents to water turbulence at the interface and fetch limitation. The contribution to k from turbulence generated by tidal currents is negligible in microtidal estuaries such as Randers Fjord but is substantial, at low to moderate wind speeds, in macrotidal estuaries such as the Scheldt and the Thames. Our results clearly show that in estuaries a simple parameterization of k as a function of wind speed is site specific and strongly suggest that the y-intercept of the linear relationship is mostly influenced by the contribution of tidal currents, whereas the slope is influenced by fetch limitation. This implies that substantial errors in flux computations are incurred if generic relationships of the gas transfer velocity as a function of wind speed are employed in estuarine environments for the purpose of biogas air–water flux budgets and ecosystem metabolic studies. [less ▲]

Alkenone carbon isotopes during a bloom of Emiliania huxleyi: Effects of CO2 concentration and production

Poster (2003, April 07)

The carbon isotopic composition of the C37-alkenones has been used in various paleoceanographic studies to estimate the ancient surface water CO2 concentration [CO2aq]. A number of recent culture, field ... [more ▼]

The carbon isotopic composition of the C37-alkenones has been used in various paleoceanographic studies to estimate the ancient surface water CO2 concentration [CO2aq]. A number of recent culture, field and sediment studies, however, indicate that the carbon isotopic fractionation in haptophyte algae is predominantly controlled by physiological processes and environmental factors other than the ambient [CO2aq]. The most prominent factors are algal growth rate, nutrient availability, light intensity, the carbon uptake mechanism (passive/active), and the carbon source (CO2aq/bicarbonate). To what extent these different factors might affect the carbon isotopic signal of alkenones ultimately preserved in the sediment is still under debate. A cause of uncertainty are the individual strenghts and weaknesses of the different methodological approaches. Culture experiments, for example, cannot perfectly recreate the sum of natural growth conditions and physical processes affecting the carbon isotopic signal in the field and its preservation in the sediment. On the other hand, core-top data represent several hundred to a couple of thousand years and therefore only reflect an average. Here, we present the first study testing the effects of [CO2aq] on the alkenone isotopic signal under natural bloom conditions in a semi-closed system. In a series of 9 floating mesocosms in a Norwegian fjord a bloom of Emiliania huxleyi was followed over a three week period. The mesocosms were covered by gas tight domes to adjust and maintain 3 different CO2 partial pressures in the tent atmosphere ranging from pre-industrial (190 ppmv) to year 2100 levels (680 ppmv) as predicted by the IPCC’s report. We found that during the exponential growth phase the isotopic fractionation of alkenones decreased by 5 to 7 per mill and reached a plateau during the stationary phase. During the stationary phase the alkenone content per cell increased from 1-2 pg/cell to 6-8 pg/cell. Between the [CO2aq] treatments we observed an alkenone isotopic difference of only 2 per mill. These results indicate that changes in algal physiology and/or environmental conditions occuring during the course of an algal bloom strongly affect alkenone isotope fractionation. This effect overrides a comparatively small variation in the alkenone isotopic signal due to [CO2aq]. Implications for alkenone isotopic fractionation as a paleo-production or paleo-nutrient proxy will be discussed. [less ▲]

On the coupling of primary production and calcification during a field experiment in the northeastern Atlantic

Poster (2003, April 06)

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of ... [more ▼]

The role of calcifying phytoplanktonic organisms in ocean carbon biogeochemistry and in climate change has received increasing attention in the marine community. The quantification of the production of biogenic calcium carbonate and associated organic matter in the photic zone and of their fate during settling is essential for a better assessment of the oceanic carbon cycle. In the framework of the Belgian global change programme, we conducted a field experiment on board the R/V Belgica in Spring 2002 along the Northern Bay of Biscay margin during successive coccolithophorid Emiliania huxleyi (Ehux) blooms. We aim, in particular, at quantifying the role of calcifying phytoplanktonic organisms in sequestering carbon. With near real-time transmission of remote sensing data during the survey, we were able to track the position and evolution of the various coccolithophore blooms along the shelf break. Bio-optical measurements were performed for modelling purpose and for calibration of the recently launched MERIS Sensor. During the field campaign, special attention was paid to the precise determination of the dissolved inorganic carbon chemistry. Primary production and rate of calcification were measured using C14 incorporation experiments and the organic to inorganic particulate carbon ratio quantified. Phytoplankton speciation was determined by microscopic examination, flow cytometry and HPLC pigment analyses. Zooplankton grazing experiments on phytoplankton were also performed. Suspended particles were characterised by their chemical composition and morphology. Th234 was used to quantify particle residence times and particulate organic carbon fluxes in surface waters. The results indicate significant particle export during the sampling period, with particle residence times in the upper 80 m ranging from 15 to 45 days. In this presentation, we will integrate the results obtained from remote sensing, biooptical investigation, water chemistry and process studies to elucidate the coupling of primary production and calcification during Ehux blooms and its importance in the marine biogeochemical cycle of carbon. [less ▲]

Assessment of the importance of the carbonate pump in surface waters of the Bay of Biscay

Poster (2003, January 07)

Marine carbon research in the past decade has been mainly devoted to the understanding and quantification of processes controlling the fluxes of organic matter in the ocean. Little attention has been paid ... [more ▼]

Marine carbon research in the past decade has been mainly devoted to the understanding and quantification of processes controlling the fluxes of organic matter in the ocean. Little attention has been paid until now to the particulate inorganic carbon whose net fluxes to the sediments are comparable to those of the organic matter. There remains still a large uncertainty in the production and the fate of biogenic calcium carbonate in the oceanic carbon cycle. In the framework of the Belgian global change programme, we have developed a project devoted to the study of the inorganic carbon cycle in the Bay of Biscay where coccolithophorid blooms occur frequently. The study focuses on processes associated with the oceanic production and dissolution of calcium carbonate, by combining field investigations, laboratory experiments and modelling efforts. The rate of primary production and of calcification by phytoplankton is evaluated by 14C incubation experiments during a coccolithophorid bloom-forming period in the area of investigation. The relative production of organic matter and calcium carbonate in the photic zone along a transect from the continental shelf across the slope to deep waters will be presented. A tentative mass balance of the carbon fluxes for this area will be constructed. These preliminary results confirm the importance that the calcium carbonate pump may play in open ocean. [less ▲]

Gas transfer velocities of CO2 in three European estuaries (Randers Fjord, Scheldt and Thames)

Poster (2003)

Fronts and mesoscale variability in the southern Indian Ocean as inferred from the TOPEX/POSEIDON and ERS-2 altimetry data

in Oceanology (2003), 43(5, SEP-OCT), 632-642

Charts of sea level anomalies (SLA) based on the combined altimetry data from the TOPEX/POSEIDON and ERS-2 satellites, as well as the corresponding charts of the sea surface dynamic heights (constructed ... [more ▼]

Charts of sea level anomalies (SLA) based on the combined altimetry data from the TOPEX/POSEIDON and ERS-2 satellites, as well as the corresponding charts of the sea surface dynamic heights (constructed by the superposition of SLA distributions over the climatic dynamic topography) and the temperature gradients at the ocean surface on the basis of the satellite Multi-Channel Sea Surface Temperature (MCSST) data, were used to study the mesoscale variability related to the fronts in the Southern Indian Ocean (30degrees-60degrees S, 20degrees-150degrees E). An analysis of these three types of satellite information for the central weeks of each month during the period from 1997 to 1999 allowed us to distinguish zones of enhanced meandering (eddy formation) within the basin under study, as well as the contributions of individual fronts and their interaction to the regional mesoscale variability. The problems of the correlation between the intensity of mesoscale variability and peculiarities of the local bottom topography and seasonal/interannual variability of mesoscale dynamics are addressed. [less ▲]

Carbonate dissolution in the turbid and eutrophic Loire estuary

in Marine Ecology. Progress Series (2003), 259

We measured particulate and dissolved organic carbon (POC and DOC), chlorophyll, oxygen, partial pressure of Co-2, pH, total alkalinity (TAlk) and particulate inorganic carbon (PIC) during a late summer ... [more ▼]

We measured particulate and dissolved organic carbon (POC and DOC), chlorophyll, oxygen, partial pressure of Co-2, pH, total alkalinity (TAlk) and particulate inorganic carbon (PIC) during a late summer cruise in the eutrophic Loire estuary. These parameters reveal an intense mineralisation of organic matter in the estuarine maximum turbidity zone (MTZ) that results in oxygen deficits (down to 20% of the saturation level) and high CO2 oversaturations (pCO(2) up to 2900 muatm). Several facts revealed the occurrence of carbonate dissolution in the Loire MTZ: large amounts of alkalinity were produced in the upper estuary, increasing its transfer to the ocean by 30%; the calculated saturation index showed a net undersaturation for aragonite and a slight undersaturation for calcite in the MTZ; and PIC decreased from 2.1% (% dry weight) in riverine suspension to 0.4% in the MTZ. A stoichiometric approach is used to assess the coupling between aerobic respiration and carbonate dissolution, where apparent oxygen utilisation, excess CO2, TAlk and dissolved inorganic carbon are compared quantitatively. About 20%, of the CO2 generated by respiration was involved in carbonate dissolution. The loss of PIC at the river-estuary transition quantitatively corresponds to the amount of authigenic calcite precipitated upstream in the highly eutrophic river. This suggests that CO2 exchange with the atmosphere along the eutrophic river-estuary continuum is buffered by carbonate precipitation in the autotrophic river and its dissolution in the heterotrophic estuary. [less ▲]