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See detailTemporal evolution of decaying summer first-year sea ice in the Western Weddell Sea, Antarctica
Tison, J. L.; Worby, A.; Delille, Bruno ULg et al

in Deep-Sea Research Part II, Topical Studies in Oceanography (2008), 55(8-9), 975-987

The evolution of the main physico-chemical properties of the unflooded 90-cm-thick first-year sea-ice cover at the Ice Station POLarstern (ISPOL) "clean site" is described. ISPOL was an international ... [more ▼]

The evolution of the main physico-chemical properties of the unflooded 90-cm-thick first-year sea-ice cover at the Ice Station POLarstern (ISPOL) "clean site" is described. ISPOL was an international experiment of the German research icebreaker R.V. Polarstern. The vessel was anchored to an ice floe for an observation period of 5 weeks, during the early summer melt onset in the Western Weddell Sea. The "clean site" was specially designed and accessed so as to prevent any trace metal contamination of the sampling area. Observations were made at 5-day intervals during December 2004 in the central part of the main floe. Results show the succession of two contrasting phases in the behavior of the brine network (brine channels, pockets, and tubes). Initially, brine salinity was higher than that of sea-water, leading to brine migration and a decrease in the mean bulk salinity of the ice cover. This process is highly favored by the already high bulk porosity (14%), which ensures full connectivity of the brine network. Gravity drainage rather than convection seems to be the dominant brine transfer process. Half-way through the observation period, the brine salinity became lower than that of the sea-water throughout the ice column. The brine network therefore switched to a "stratified" regime in which exchange with sea-water was limited to molecular diffusion, strongly stabilizing the bulk mean sea-ice salinity. During the transition between the two regimes, and in areas closer to ridges, slush water (resulting from a mixture of snow meltwater and sea water accumulated at the snow-ice interface) penetrated through the growing "honeycomb-like structure" and replaced the downward draining brines. This resulted in a slight local replenishment of nutrients (as indicated by dissolved silicic acid). However, as a whole, the described decaying regime in this globally unflooded location with limited snow cover should be unfavorable to the development of healthy and active surface and internal microbial communities. The switch from gravity to diffusion controlled transport mechanisms within the ice column also should affect the efficiency of gas exchange across the sea-ice cover. The observed late build-up of a continuous, impermeable, superimposed ice layer should further significantly hamper gas exchange. Statistical estimates of the evolution of the ice thickness during the observation period and salinity trends of the under-ice water salinity down to 30m corroborate model predictions of a moderate bottom melting (5-10cm) from ocean heat fluxes. (C) 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCarbon dioxide dynamics in lake Kivu during the dry and wet seasons
Borges, Alberto ULg; Delille, Bruno ULg; Descy, J.-P. et al

Poster (2008)

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See detailInter-annual variability of the carbon dioxide oceanic sink south of Tasmania
Borges, Alberto ULg; Tilbrook, B.; Metzl, N. et al

Poster (2008)

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See detailSeasonal variability of CO2 fluxes in the tropical lagoons of Ivory Coast
Koné, Y. J. M.; Gourene, G.; Abril, G. et al

Poster (2008)

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See detailA dynamic model of an experimental bloom of coccolithophores Emiliania huxleyi
Joassin, Pascal ULg; Borges, Alberto ULg; Chou, Lei et al

Conference (2007, November 27)

A dynamic model has been developed to represent biogeochemical events observed during an experimentally induced bloom of coccolithophores Emiliania huxleyi. This bloom occurred in a mesocosm experiment ... [more ▼]

A dynamic model has been developed to represent biogeochemical events observed during an experimentally induced bloom of coccolithophores Emiliania huxleyi. This bloom occurred in a mesocosm experiment (Bergen 2001 experiment) during which ecosystem development was followed over a 23-days period through changes of the stocks of inorganic nutrients (nitrate, ammonium and phosphate), dissolved inorganic carbon and pCO2, O2 concentration, pigments, particulate organic carbon and nitrogen, dissolved organic carbon, the production of Transparent Exopolymeric Particles (TEP), primary production, alkalinity, calcification and particulate inorganic carbon. The dynamic model is based on unbalanced algal growth and balanced growth for bacteria as described in Van den Meersche et al. (2004). In addition, in order to adequately reproduce the observations, the model has been extended by including an explicit description of calcification, T.E.P production and an enhanced mortality due to viruses. This last process, based on a critical promiscuity between cellular hosts and viral agents, successfully contributed to reproduce the bloom extinction as observed in the mesocosm experiment. This model will be implemented in a coupled physical-biogeochemical model of the Black Sea ecosystem in the framework of the EU Sesame project and in the Gulf of Biscay in the frame of the Belgian PEACE project. [less ▲]

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See detailPlanktonic Archaea in Lake Kivu
Llirós, Marc; Darchambeau, François ULg; Plasencia, Anna et al

Conference (2007, September 02)

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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 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 ▲]

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See detailPlanktonic Archaea in Lake Kivu
Llirós, Marc; Darchambeau, François ULg; Plasencia, Anna et al

Conference (2007, June 12)

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See detailCarbon dioxide fluxes in Lake Kivu
Borges, Alberto ULg; Delille, Bruno ULg; Descy, Jean-Pierre et al

Conference (2007, June 12)

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See detailDedication - Michel Frankignoulle
Borges, Alberto ULg; Delille, Bruno ULg

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

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See detailSpatial and temporal variation of bacterioplankton in a sub-Antarctic coastal area (Kerguelen Archipelago)
Delille, Daniel; Gleizon, Fabien; Delille, Bruno ULg

in Journal of Marine Systems (2007), 68(3-4), 366-380

Bacterial abundance and production were measured monthly for one year along cross-shore transects in 3 sub-Antarctic fjords of the Kerguelen Archipelago (seven stations each). Mean values of the 3 most ... [more ▼]

Bacterial abundance and production were measured monthly for one year along cross-shore transects in 3 sub-Antarctic fjords of the Kerguelen Archipelago (seven stations each). Mean values of the 3 most coastal (inside) and most offshore (outside) stations were used to describe the relationship between temperature, phytoplankton biomass, bacterial abundance and bacterial production over a one year annual cycle. The entire sampling protocol was repeated twice during each cruise: once at noon and once at midnight. Over the whole sampling period, the temperature ranged from 2.1 to 7.4 degrees C, while chlorophyll a concentrations varied by a factor of 10, and bacterial abundance and production varied by factors of 12 and 30, respectively. Within one day, all of these parameters sometimes varied by a factor of 4 between noon and midnight. A clear seasonality was observed for all of the parameters. However, while variations of phytoplankton and bacterial production paralleled those of temperature, bacterial abundance was low in midsummer and maximum in autumn. While no general pattern could be observed from the total data set, spatial gradients could interfere strongly with temporal changes. (C) 2007 Elsevier B.V All rights reserved. [less ▲]

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See detailCarbon dioxide in European coastal waters
Borges, Alberto ULg; Schiettecatte, L.-S.; Abril, G. et al

Poster (2007)

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See detailDissolved inorganic carbon dynamics in the Gulf of Biscay (June 2006)
Suykens, K.; Delille, Bruno ULg; Borges, Alberto ULg

Poster (2007)

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