Delayed and reduced coccolithophorid calcification under elevated PCO2

Poster (2004, May 10)

Numerous experiments to date have demonstrated that elevated PCO2 is detrimental to biogenic calcification rates. However, most of these experiments have been realized in batch or continuous cultures and ... [more ▼]

Numerous experiments to date have demonstrated that elevated PCO2 is detrimental to biogenic calcification rates. However, most of these experiments have been realized in batch or continuous cultures and give little information on the dynamics of calcification in natural conditions. The present work describes the development and decay of a nutrient-induced bloom of the coccolithophorid Emiliania huxleyi in a mesocosm experiment. The monitoring of Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TAlk) within the seawater enclosures allowed us to describe comprehensively day to day dynamics of both calcification and organic carbon production. Three atmospheric PCO2 conditions (glacial, present and next century) were simulated by bubbling CO2 mixtures, while total alkalinity was left to evolve from its present value. No conspicuous change of Net Community Production under elevated PCO2 was recorded while the production of inorganic carbon appeared to be affected in two ways. Firstly, the production rate of inorganic carbon appeared to be lowered by 40% in the next century PCO2 conditions, decreasing concomitantly the calcification to photosynthesis ratio from 0.75 (glacial conditions) to 0.45 (next century conditions). Secondly, the onset of calcification was delayed by 24~48h under elevated PCO2 conditions, reducing the overall length of calcification in the course of the bloom. These two effects would act to reduce the amount of precipitated CaCO3 by coccolithophorids in a High CO2 world [less ▲]

Variability of the gas transfer velocity of CO2 in a macrotidal estuary (The Scheldt)

in Estuaries (2004), 27(4), 593-603

We report a large set of 295 interfacial carbon dioxide (CO2) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant ... [more ▼]

We report a large set of 295 interfacial carbon dioxide (CO2) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant measurements of the air-water CO2 gradient, we computed the gas transfer velocity of CO2. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to the gas transfer velocity, using the conceptual relationship of O’Connor and Dobbins (1958). This allowed us to construct an empirical relationship to compute the gas transfer velocity of CO2 that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability of the gas transfer velocity in the Scheldt estuary was investigated.Water currents contribute significantly to the gas transfer velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability. [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 ▲]

SCHELDT - Airborne Hyperspectral Potential for Coastal Biogeochemistry of the Scheldt Estuary and Plume

Report (2003)

European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of ... [more ▼]

European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of dissolved CO2. The Scheldt basin covers one of the most populated and industrialised areas of Europe and its tributaries drain an area of about 21,860 km2. The amounts of nutrients discharged by the Scheldt increased considerably during the past 20 years. Due to the dilution and metabolic processes of the downstream river flow in the estuary, an important variability of several parameters can be observed amongst which phytoplankton species and concentration, particulate organic matter, colour dissolved organic matter and suspended matter. In the present days, researches on the functioning of estuarine and coastal ecosystems are based on highly time consuming, costly sea campaigns and laboratory analyses. Although optical spaceborne remote sensing already proved useful in such coastal ecosystem studies, hyperspectroscopy opened a new dimension by allowing improved distinction of various biogeochemical compounds through characteristic spectral signature identification. Water quality variables were examined in the Scheldt estuary and plume, using CASI-2 (Compact airborne Spectrographic Imager) hyperspectral sensor and in situ bio-optical observations. The numerous parameters and spectrum measured in each station were used for further remote sensing analysis, as well as to complete the interpretation of the observed environmental processes. Multiple regression approach has been used to derive correlation between classical ground truth measurements and the rich information provided by the numerous CASI spectral bands. From these relations, some synoptic maps of biogeochemical parameters could be derived in the Scheldt estuary and plume. [less ▲]

Airborne hyperspectral potential for coastal biogeochemistry of the Scheldt estuary and plume

Conference (2003, June)

Estuaries are obligate pathways for the transfer of dissolved and particulate material from the continent to the marine system. The tidal regime of some estuaries leads to an increased residence time of ... [more ▼]

Estuaries are obligate pathways for the transfer of dissolved and particulate material from the continent to the marine system. The tidal regime of some estuaries leads to an increased residence time of the freshwater in the estuarine mixing zone and pronounced changes in the speciation of elements. European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of dissolved CO2. The Scheldt basin covers one of the most populated and industrialised areas of Europe and its tributaries drain an area of about 21,860 km2. The amounts of nutrients discharged by the Scheldt increased considerably during the past 20 years. Due to the dilution and metabolic processes of the downstream river flow in the estuary, an important variability of several parameters can be observed amongst which phytoplankton species and concentration, particulate organic matter, colour dissolved organic matter and suspended matter. In the present days, researches on the functioning of estuarine and coastal ecosystems are based on highly time consuming, costly sea campaigns and laboratory analyses. Although optical spaceborne remote sensing already proved useful in such coastal ecosystems studies, hyperspectroscopy opened a new dimension by allowing improved distinction of various biogeochemical compounds through characteristic spectral signature identification. The goal of this research is to explore the potential of CASI-SWIR airborne hyperspectroscopy in retrieving some of the biogeochemical parameters of interest in the Schedlt estuary and plume (Belgium-Netherlands coastal zone). A 13 sampling stations field survey was realised in order to cover as quickly as possible the wide range of water quality encountered from the mouth of the estuary to the outer limit of the plume. The numerous parameters and spectrum measured in each station were used for further remote sensing analysis, as well as to complete the interpretation of the observed environmental processes. Correlation was searched between classical ground truth measurements and the rich information provided by numerous CASI-SWIR spectral bands carefully chosen. These relations were used as an attempt to derive synoptic view of the spatial distribution of various biogeochemical parameters in the Scheldt estuary and plume. Synthesis of these hyperspectral-mapping products with other complementary satellite maps and ground data set may allow ocean scientists to derive substantial information about ecosystem processes in the Scheldt estuary and adjacent coast. [less ▲]

Distribution of surface carbon dioxide and air-sea exchange in the English Channel and adjacent areas

in Journal of Geophysical Research (2003), 108(C5),

In the present paper we report the distribution of the partial pressure of CO2 (pCO2) in surface waters along 13 transects in the English Channel, covering the four seasons. The spatial and temporal ... [more ▼]

In the present paper we report the distribution of the partial pressure of CO2 (pCO2) in surface waters along 13 transects in the English Channel, covering the four seasons. The spatial and temporal variability of pCO2 is controlled by a complex combination of primary production (from May to June), degradation of organic matter, temperature change, and freshwater inputs. Preliminary air-sea CO2 exchange computations suggest that the Channel is not a major sink of atmospheric CO2 and is probably neutral from the point of view of atmospheric coupling. This is mainly related to a relatively low export and/or burial of organic carbon and intense benthic calcification. [less ▲]

CO2 emission from mangroves’ surrounding waters

Poster (2003)

Inorganic and organic carbon biogeochemistry in the Gautami Godavari estuary (Andhra Pradesh, India) during pre-monsoon : the local impact of extensive mangrove forests

in Global Biogeochemical Cycles (2003), 17(4),

[1] The distribution and sources of organic and inorganic carbon were studied in the Gautami Godavari estuary (Andhra Pradesh, India) and in a mangrove ecosystem in its delta during pre-monsoon. In the ... [more ▼]

[1] The distribution and sources of organic and inorganic carbon were studied in the Gautami Godavari estuary (Andhra Pradesh, India) and in a mangrove ecosystem in its delta during pre-monsoon. In the oligohaline and mesohaline section (salinity 0–15) of the estuary, internal production of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) was recorded, and the d13CDIC profile suggests that carbonate dissolution may be an important process determining the DIC dynamics in this section of the Godavari. The partial pressure of CO2 (pCO2) was fairly low along the entire salinity gradient, (293–500 ppm), but much higher and more variable (1375–6437 ppm) in the network of tidal mangrove creeks in the delta. Here, variations in the concentration and d13C of the DIC pool were shown to result largely from the mineralization of organic matter. The present study clearly identifies the mangrove creeks as an active site of mineralization and CO2 efflux to the atmosphere, but shows that these changes in the aquatic biogeochemistry are a localized feature, rapidly fading in the adjacent Kakinada Bay. Our data indicate that mineralization of dissolved organic carbon (DOC) of mangrove origin, and its subsequent efflux as CO2 to the atmosphere may represent an important fate for mangrove carbon. Although further quantification of this process in a variety of systems is required, we suggest that some of the current ideas on the role of mangroves in the carbon budget of the coastal zone may need to be reconsidered. [less ▲]