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See detailSnow cover and short-term synoptic events drive biogeochemical dynamics in winter Weddell Sea pack ice (AWECS cruise - June to August 2013)
Tison, J.-L.; Delille, Bruno ULg; Dieckmann, G. et al

Conference (2014, March)

This paper presents the preliminary results of an integrated multidisciplinary study of pack ice biogeochemistry in the Weddell Sea during the winter 2013 (June-August). The sea ice biogeochemistry group ... [more ▼]

This paper presents the preliminary results of an integrated multidisciplinary study of pack ice biogeochemistry in the Weddell Sea during the winter 2013 (June-August). The sea ice biogeochemistry group was one of the components of the AWECS (Antarctic Winter Ecosystem and Climate Study) cruise (Polarstern ANTXXIX-6). A total of 12 stations were carried out by the sea ice biogeochemistry group, which collected a suite of variables in the fields of physics, inorganic chemistry, gas content and composition, microbiology, biogeochemistry, trace metals and the carbonate system in order to give the best possible description of the sea ice cover and its interactions at interfaces. Samples were collected in the atmosphere above (gas fluxes), in the snow cover, in the bulk ice (ice cores), in the brines (sackholes) and in the sea water below (0m, 1m, 30 m). Here we present the results of basic physico-chemical (T°, bulk ice salinity, brine volumes, brine salinity, Rayleigh numbers) and biological (Chla) measurements in order to give an overview of the general status of the Weddell Sea winter pack ice encountered, and discuss how it controls climate relevant biogeochemical processes. Our results from the first set of 9 stations, mainly sampled along the Greenwich meridian and the easternmost part of the Weddell Sea definitively refute the view of a biogeochemically “frozen” sea ice during the Winter. This has already been demonstrated for the Spring and Summer, but we now see that sea ice sustains considerable biological stocks and activities throughout the Winter, despite the reduced amount of available PAR radiation. Accretion of the snow cover appears to play an essential role in driving biogeochemical activity, through warming from insulation, thus favouring brine transport, be it through potential convection, surface brine migration (brine tubes) or flooding. This results in a “widening” of the internal autumn layer (quite frequent in this rafting-dominated sea ice cover) and increase of the chla burden with age. Results from the second set of 3 stations in the western branch of the Weddell Sea gyre confirm that it comprises a mixture of older fast/second year ice floes with younger first-year ice floes. The older ice had the highest Chla concentrations of the entire cruise (>200 mgl-1), in an internal community enclosed within desalinized impermeable upper and lower layers. The first-year ice differs from that in the eastern Weddell Sea as it is dominated by columnar ice and (weak) algal communities are only found on the bottom or near the surface (no internal maximum). [less ▲]

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See detailEffect of melting Antarctic sea ice on the fate of microbial communities studied in microcosms
Lannuzel, D.; Schoenmann, V.; Dumont, I. et al

in Polar Biology (2013), 36(10), 1483-1497

Although algal growth in the iron-deficient Southern Ocean surface waters is generally low, there is considerable evidence that winter sea ice contains high amounts of iron and organic matter leading to ... [more ▼]

Although algal growth in the iron-deficient Southern Ocean surface waters is generally low, there is considerable evidence that winter sea ice contains high amounts of iron and organic matter leading to ice-edge blooms during austral spring. We used field observations and ship-based microcosm experiments to study the effect of the seeding by sea ice microorganisms, and the fertilization by organic matter and iron on the planktonic community at the onset of spring/summer in the Weddell Sea. Pack ice was a major source of autotrophs resulting in a ninefold to 27-fold increase in the sea ice-fertilized seawater microcosm compared to the ice-free seawater microcosm. However, heterotrophs were released in lower numbers (only a 2- to 6-fold increase). Pack ice was also an important source of dissolved organic matter for the planktonic community. Small algae (<10 μm) and bacteria released from melting sea ice were able to thrive in seawater. Field observations show that the supply of iron from melting sea ice had occurred well before our arrival onsite, and the supply of iron to the microcosms was therefore low. We finally ran a “sequential melting” experiment to monitor the release of ice constituents in seawater. Brine drainage occurred first and was associated with the release of dissolved elements (salts, dissolved organic carbon and dissolved iron). Particulate organic carbon and particulate iron were released with low-salinity waters at a later stage. [less ▲]

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See detailPredicting difficulty in PISA reading items : the process of describing item difficulty
Lumley, T.; Mendelovits, J.; Searle, D. et al

Conference (2010, April)

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See detailHow can we predict difficulty in PISA reading items ? The process of describing item difficulty
Alderson, C.; De Jong, J.; Kirsch, I. et al

Conference (2009, November)

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See detailHow can we predict difficulty in PISA reading items ? The process of describing item difficulty
Lumley, T.; Mendelovits, J.; Searle, D. et al

Conference (2009, September)

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See detailMicrobiological control on the cycling of Fe and its isotopes in Antarctic sea ice
Schoemann, V.; de Jong, J.; Lannuzel, D. et al

Poster (2008, July)

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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 detailIron microbial mats in Modern and Phanerozoic environments
Baele, J. M.; Boulvain, Frédéric ULg; De Jong, J. et al

in Instruments, Methods and Missions for Astrobioçlogy- Proc. of SPIE (2008), 7097

The recognition of iron microbial mats in terrestrial environments is of great relevance for the search for extraterrestrial life, especially on mars where significant iron minerals were identified in the ... [more ▼]

The recognition of iron microbial mats in terrestrial environments is of great relevance for the search for extraterrestrial life, especially on mars where significant iron minerals were identified in the subsurface. Most researches focused on very ancient microbial mats (e.g. BIFs) since they formed on Earth at a time where similar conditions are supposed to have prevailed on Mars too. However, environmental proxies are often difficult to use for these deposits on Earth which, in addition, may be heavily transformed due to diagenesis or even metamorphism. Here we present modern and phanerozoic iron microbial mats occurrences illustrating the wide variety of environments in which they form, including many marine settings, ponds, creeks, caves, volcanoes, etc. Contrarily to their Precambrian counterparts, Modern and Phanerozoic deposits are usually less affected by diagenesis and the environmental conditions likely to be better constrained. Therefore, their investigation may help for the search for morphological and geochemical biosignatures (e.g. iron isotopes) in ancient iron microbial occurrences on Earth but also on other Planets. In particular, many of the case studies presented here show that microstromatolithe-like morphologies may be valuable targets for screening potential biosignatures in various rock types. [less ▲]

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See detailCO2 dynamics and related air-ice-sea gas transfer in spring pack and land fast sea ice,
Delille, Bruno ULg; Schoemann, V.; Lannuzel, D. et al

Poster (2007, March)

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See detailCarbon dioxide dynamics in Antarctic pack ice and related air-ice CO2 fluxes
Delille, Bruno ULg; Trevena, A.; Schoemann, V. et al

Conference (2005, May)

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See detailIron distribution in a sea ice environment
Lannuzel, D.; de Jong, J.; Schoemann, V. et al

Poster (2004, October)

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See detailSIBClim: an Interdisciplinary Initiative on Sea Ice Biogeochemistry in a Climate Change Perspective
Tison, J.-L; Lancelo, C.; Chou, L. et al

Poster (2004, October)

Detailed reference viewed: 4 (0 ULg)
See detailLa lecture, moteur de changement : performances et engagement d'un pays à l'autre : résultats de PISA 2000
Kirsch, I.; De Jong, J.; Lafontaine, Dominique ULg et al

Book published by OCDE (2003)

Detailed reference viewed: 23 (4 ULg)
See detailReading for change : performance and engagement across countries : results of PISA 2000
Kirsch, I.; De Jong, J.; Lafontaine, Dominique ULg et al

Book published by OCDE (2003)

Detailed reference viewed: 52 (5 ULg)