References of "Borges, Alberto"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailBiogas (CO2, O-2, dimethylsulfide) dynamics in spring Antarctic fast ice
Delille, Bruno ULg; Jourdain, B.; Borges, Alberto ULg et al

in Limnology and Oceanography (2007), 52(4), 1367-1379

We studied the temporal variations of CO2, O-2, and dimethylsulfide (DMS) concentrations within three environments (sea-ice brine, platelet ice-like layer, and underlying water) in the coastal area of ... [more ▼]

We studied the temporal variations of CO2, O-2, and dimethylsulfide (DMS) concentrations within three environments (sea-ice brine, platelet ice-like layer, and underlying water) in the coastal area of Adelie Land, Antarctica, during spring 1999 before ice breakup. Temporal changes were different among the three environments, while similar temporal trends were observed within each environment at all stations. The underlying water was always undersaturated in O-2 (around 85%) and oversaturated in CO2 at the deepest stations. O-2 concentrations increased in sea-ice brine as it melted, reaching oversaturation up to 160% due to the primary production by the sea-ice algae community (chlorophyll a in the bottom ice reached concentrations up to 160 mu g L-1 of bulk ice). In parallel, DMS concentrations increased up to 60 nmol L-1 within sea- ice brine and the platelet ice- like layer. High biological activity consumed CO2 and promoted the decrease of partial pressure of CO2 (pCO(2)). In addition, melting of pure ice crystals and calcium carbonate (CaCO3) dissolution promoted the shift from a state of CO2 oversaturation to a state of marked CO2 undersaturation (pCO(2) < 30 dPa). On the whole, our results suggest that late spring land fast sea ice can potentially act as a sink of CO2 and a source of DMS for the neighbouring environments, i.e., the underlying water or/ and the atmosphere. [less ▲]

Detailed reference viewed: 69 (4 ULg)
See detailPlanktonic Archaea in Lake Kivu
Llirós, Marc; Darchambeau, François ULg; Plasencia, Anna et al

Conference (2007, June 12)

Detailed reference viewed: 7 (3 ULg)
See detailCarbon dioxide fluxes in Lake Kivu
Borges, Alberto ULg; Delille, Bruno ULg; Descy, Jean-Pierre et al

Conference (2007, June 12)

Detailed reference viewed: 2 (0 ULg)
Full Text
See detailDedication - Michel Frankignoulle
Borges, Alberto ULg; Delille, Bruno ULg

in Journal of Marine Systems (2007), 66(1-4), 4-5

Detailed reference viewed: 171 (9 ULg)
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 ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
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 ▲]

Detailed reference viewed: 21 (1 ULg)
Full Text
Peer Reviewed
See detailImportance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)
Bouillon, Steven; Middelburg, Jack J.; Dehairs, Frank et al

in Biogeosciences (2007), 4

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and ... [more ▼]

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, varied in phase with water height and was highest at low tide. Stable isotope data of POC and DOC displayed large variations in both pools, and similarly followed the variations in water height. Although the variation of 13CDOC (−23.8 to −13.8‰) was higher than that of 13CPOC (−26.2 to −20.5‰), due to the different endmember pool sizes, the 13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, however, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, 13C data on DIC indicate that the organic matter source for mineralization had a signature of −22.4‰. Hence, imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data demonstrate how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter transport are fundamentally different. [less ▲]

Detailed reference viewed: 36 (6 ULg)
Full Text
Peer Reviewed
See detailRapid decline of the CO2 buffering capacity in the North Sea and implications for the North Atlantic Ocean
Thomas, Helmuth; Prowe, A. E. Friederike; van Heuven, Steven et al

in Global Biogeochemical Cycles (2007), 21(GB4001),

New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO2 partial pressure (pCO2) in surface waters rose by 22 matm, thus faster than atmospheric pCO2, which in ... [more ▼]

New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO2 partial pressure (pCO2) in surface waters rose by 22 matm, thus faster than atmospheric pCO2, which in the same period rose approximately 11 matm. The surprisingly rapid decline in air-sea partial pressure difference (DpCO2) is primarily a response to an elevated water column inventory of dissolved inorganic carbon (DIC), which, in turn, reflects mostly anthropogenic CO2 input rather than natural interannual variability. The resulting decline in the buffering capacity of the inorganic carbonate system (increasing Revelle factor) sets up a theoretically predicted feedback loop whereby the invasion of anthropogenic CO2 reduces the ocean’s ability to uptake additional CO2. Model simulations for the North Atlantic Ocean and thermodynamic principles reveal that this feedback should be stronger, at present, in colder midlatitude and subpolar waters because of the lower present-day buffer capacity and elevated DIC levels driven either by northward advected surface water and/or excess local air-sea CO2 uptake. This buffer capacity feedback mechanism helps to explain at least part of the observed trend of decreasing air-sea DpCO2 over time as reported in several other recent North Atlantic studies. [less ▲]

Detailed reference viewed: 57 (3 ULg)
Full Text
Peer Reviewed
See detailHigh temporal coverage of carbon dioxide measurements in the Southern Bight of the North Sea
Schiettecatte, L. S.; Thomas, H.; Bozec, Y. et al

in Marine Chemistry (2007), 106(1-2), 161-173

A monthly survey of the partial pressure of CO2 (pCO2) was carried in the Southern Bight of the North Sea (SBNS) from June 2003 to May 2004. The spatial variability of the surface distribution of the pCO2 ... [more ▼]

A monthly survey of the partial pressure of CO2 (pCO2) was carried in the Southern Bight of the North Sea (SBNS) from June 2003 to May 2004. The spatial variability of the surface distribution of the pCO2 was relatively small (within a range of 10–70 μatm) compared to the amplitude in the seasonal signal (∼260 μatm). On an annual scale, the pCO2 dynamics appeared to be controlled by biological processes (primary production in springtime and respiratory processes in summer), rather than temperature (in summer). The comparison with measurements carried out in 2001 and 2002 (13 cruises) shows that the inter-annual variability of pCO2 was close to the range of the spatial variability and mostly observed in spring, associated to biological processes (primary production). Net ecosystem production estimated from dissolved inorganic carbon (DIC) temporal variations showed that the SBNS is autotrophic, at an annual rate of 6.3 mol C m−2 yr−1. The decoupling in time between autotrophy in spring and heterotrophy in summer, associated to the relatively rapid flushing time of the water mass in the area (∼70 days), might allow the export of a fraction of the springtime synthesized organic matter to the adjacent areas of the North Sea. The SBNS was on a yearly basis a sink of atmospheric CO2 at a rate of −0.7 mol C m−2 yr−1. [less ▲]

Detailed reference viewed: 26 (2 ULg)
Full Text
Peer Reviewed
See detailAn artificial neural network analysis of factors controlling ecosystem metabolism in the coastal ocean
Rochelle Newall, Emma J.; Winter, Christian; Barrón, Cristina et al

in Ecological Applications (2007), 17(5), 185196

Knowing the metabolic balance of an ecosystem is of utmost importance in determining whether the system is a net source or net sink of carbon dioxide to the atmosphere. However, obtaining these estimates ... [more ▼]

Knowing the metabolic balance of an ecosystem is of utmost importance in determining whether the system is a net source or net sink of carbon dioxide to the atmosphere. However, obtaining these estimates often demands significant amounts of time and manpower. Here we present a simplified way to obtain an estimation of ecosystem metabolism. We used artificial neural networks (ANNs) to develop a mathematical model of the gross primary production to community respiration ratio (GPP:CR) based on input variables derived from three widely contrasting European coastal ecosystems (Scheldt Estuary, Randers Fjord, and Bay of Palma). Although very large gradients of nutrient concentration, light penetration, and organic-matter concentration exist across the sites, the factors that best predict the GPP:CR ratio are sampling depth, dissolved organic carbon (DOC) concentration, and temperature. We propose that, at least in coastal ecosystems, metabolic balance can be predicted relatively easily from these three predictive factors. An important conclusion of this work is that ANNs can provide a robust tool for the determination of ecosystem metabolism in coastal ecosystems. [less ▲]

Detailed reference viewed: 72 (9 ULg)
Full Text
Peer Reviewed
See detailCarbon dioxide dynamics in rivers and coastal waters of the ABig Island@ of Hawaii, USA, during baseline and heavy rain condition
Paquay, F. S.; Mackenzie, F. T.; Borges, Alberto ULg

in Aquatic Geochemistry (2007), 13(1), 1-18

The distributions of the partial pressure of carbon dioxide (pCO2) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo Bay on the west ... [more ▼]

The distributions of the partial pressure of carbon dioxide (pCO2) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed an oversaturation in CO2 with respect to atmospheric equilibrium and a CO2 undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO2 values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO2 from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are the predominant drivers of the spatial and temporal patterns in the distribution of pCO2. In Hilo Bay, CO2 oversaturation dominates and the bay was a source of CO2 to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the bay is not a significant source of CO2 to the atmosphere. [less ▲]

Detailed reference viewed: 28 (2 ULg)
Full Text
Peer Reviewed
See detailBiogeochemistry of the Tana estuary and delta (northern Kenya)
Bouillon, Steven; Dehairs, Frank; Schiettecatte, Laure-Sophie et al

in Limnology & Oceanography (2007), 52(1), 45-59

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and ... [more ▼]

The estuarine mixing zone of the Tana River (northern Kenya) and an extensive deltaic area just south of the estuary were sampled in April 2004 with the aim of identifying the distribution, sources, and processing of particulate and dissolved organic carbon (POC, DOC) and inorganic carbon (DIC). C4 inputs from the catchment contributed ,50% to the POC pool in the Tana River and estuary, and in the mangrove creek water column and intertidal sediments. The d13C values of DOC, however, were typically much more negative than that of POC, indicating a substantially higher contribution by C3 and/or mangrove-derived carbon in the DOC pool. The undersaturation of O2, high pCO2, and the nonconservative nature of DIC and d13CDIC suggest a strongly heterotrophic water column, particularly in the freshwater part of the Tana and in the tidal creeks in the delta, where high additional inputs of organic matter were observed. However, some of these sites showed d18ODO signatures lower than the atmospheric equilibrium (i.e., +24.2%) indicative of significant O2 production by photosynthesis. Therefore, the heterotrophic signature in the water column is likely the result of a strong interaction with the large intertidal areas, whereby respiratory activity in sediments and in the overlying water column during tidal inundation leave a marked signature on the water column. This is confirmed by the covariation between salinity-normalized total alkalinity and DIC, whose slope indicates an important role for anaerobic diagenetic processes. If our data are representative for other large river systems in the region, current estimates are likely to underestimate suspended matter and both inorganic and organic C fluxes to the Indian Ocean from tropical east Africa. [less ▲]

Detailed reference viewed: 34 (2 ULg)
Full Text
Peer Reviewed
See detailDynamics of organic and inorganic carbon across contiguous mangrove and seagrass systems (Gazi bay, Kenya)
Bouillon, Steven; Dehairs, Frank; Velimirov, Branko et al

in Journal of Geophysical Research. Biogeosciences (2007), 112(G02018),

We report on the water column biogeochemistry in adjacent mangrove and seagrass systems in Gazi Bay (Kenya), with a focus on assessing the sources and cycling of organic and inorganic carbon. Mangrove and ... [more ▼]

We report on the water column biogeochemistry in adjacent mangrove and seagrass systems in Gazi Bay (Kenya), with a focus on assessing the sources and cycling of organic and inorganic carbon. Mangrove and seagrass-derived material was found to be the dominant organic carbon sources in the water column, and could be distinguished on the basis of their d13C signatures and particulate organic carbon:total suspended matter (POC/TSM) ratios. Spatially, a distinct boundary existed whereby the dominance of mangrove-derived material decreased sharply close to the interface between the mangrove forest and the dense seagrass beds. The latter is consistent with the reported export of mangrove-derived material, which is efficiently trapped in the adjacent seagrass beds. There were significant net inputs of POC and dissolved organic carbon (DOC) along the Kidogoweni salinity gradient, for which the d13CPOC signatures were consistent with those of mangroves. DOC was the dominant form of organic carbon in both mangrove and seagrass beds, with DOC/POC ratios typically between 3 and 15. Dynamics of dissolved inorganic carbon in the creeks were strongly influenced by diagenetic C degradation in the intertidal mangrove areas, resulting in significant CO2 emission from the water column to the atmosphere. Although highest partial pressure of CO2 (pCO2) values and areal CO2 flux rates were observed in the mangrove creeks, and the water column above the seagrass beds was in some locations a net sink of CO2, most of the ecosystems’ emission of CO2 to the atmosphere occurred in the seagrass beds adjacent to the mangrove forest. The presence of dense seagrass beds thus had a strong effect on the aquatic biogeochemistry, and resulted in trapping and further mineralization of mangrove-derived POC, intense O2 production and CO2 uptake. The adjacent seagrass beds provide a large area with conditions favorable to exchange of CO2 with the atmosphere, thereby limiting export of mangrove-derived organic and inorganic carbon toward the coastal ocean. [less ▲]

Detailed reference viewed: 53 (7 ULg)
Full Text
See detailCarbon dioxide in European coastal waters
Borges, Alberto ULg; Schiettecatte, L.-S.; Abril, G. et al

Poster (2007)

Detailed reference viewed: 2 (0 ULg)
Full Text
See detailDissolved inorganic carbon dynamics in the Gulf of Biscay (June 2006)
Suykens, K.; Delille, Bruno ULg; Borges, Alberto ULg

Poster (2007)

Detailed reference viewed: 1 (0 ULg)
Full Text
See detailCarbon dioxide dynamics in the tropical Ebrié lagoon (Ivory Coast)
Koné, Y. J. M.; Delille, Bruno ULg; Borges, Alberto ULg

Poster (2007)

Detailed reference viewed: 8 (0 ULg)