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See detailPhylogéographie du complexe d'espèces Brassica oleracea
Aigoin, Delphine ULg

Master of advanced studies dissertation (2005)

The aim of this work is to clarify the genetic relationship between the species of the complex Brassica sect. oleracea and to suggest a historical scenario of cabbage domestication. We collected 79 ... [more ▼]

The aim of this work is to clarify the genetic relationship between the species of the complex Brassica sect. oleracea and to suggest a historical scenario of cabbage domestication. We collected 79 accessions, corresponding to 2 to 5 individus for each of the 11 taxons of this complex. Three types of molecular markers were studied on these individuals : two nuclear genes (sequencing of Adh and G3pdh genes), for microsatellite loci, and AFLP markers. Only the first two types of markers were used for phylogenetic reconstructions. Overall there is little consistency among markers and among studies. However a few solid results can be outlined, such as 1/ the grouping of endemic species from Sicilia (B. rupestris, B. villosa, B. macrocarpa), 2/ the grouping of cultivated accesions with the taxon B. oleracea, suggesting a unique domestication event. Considerations from the various phylogenetic reconstructions, from morphological data, and from historical records, suggest that such domestication event first occured in the mediterranean islands, and that the presently «wild» populations of the atlantic coast were in fact probably produced from these domesticated populations. [less ▲]

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See detailPhylogéographie mitochondriale du mulot sylvestre (Apodemus sylvaticus) dans la région paléarctique occidentale
Michaux, Johan ULg; Magnanou, Elodie; Nieberding, Caroline et al

in Biosystema, Systématique et biogéographie (2002), 20

We have sequenced 965 base pairs of the mitochondrial DNA cytochrome b from 102 woodmice (Apodemus sylvaticus) samples collected from 40 European localities. The aims of the study were to answer the ... [more ▼]

We have sequenced 965 base pairs of the mitochondrial DNA cytochrome b from 102 woodmice (Apodemus sylvaticus) samples collected from 40 European localities. The aims of the study were to answer the following questions: i) Did the Mediterranean peninsulas play a role as a refuge for small mammals? ii) Is the genetic variability of a small mammal like A. sylvaticus higher in the Mediterranean regions as compared with northern Europe? iii)Is it possible to find patterns of postglacial colonisation of Europe other than those presently recognised ? Sequence data were analysed using Distance and Maximum Parsimony phylogenetic reconstruction methods. A minimum spanning network was also calculated. Population genetic structure was determined by analysis of molecular variance (AMOVA). A "mismatch distribution" analysis was also performed to estimate the patterns of expansion. The results provide a clear picture of the impact of Quaternary glaciations on the genetic and geographic structure of the woodmouse. Analyses indicate a higher genetic variability for the woodmouse in the Mediterranean peninsulas as compared to northern Europe and the role of these peninsulas as refuge regions for small mammals. A new pattern of postglacial colonisation is also proposed where the Iberian and southern France refuge populations colonised almost all the European regions. The Sicilian population appears to be highly differentiated and highly variable. This result emphasises the importance of this island as a "hot spot" for the intraspecific genetic diversity of the woodmouse. Finally, populations of this species in North Africa originated from south-western Europe and are probably the result of a recent anthropogenic introduction. [less ▲]

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See detailPhylogeography and evolutionary history of Leopoldamys neilli, a Murinae rodent endemic to limestone karsts, in Thailand
Latinne, Alice ULg; Waengsothorn, Surachit; Herbreteau, Vincent et al

Conference (2012, May 15)

Limestone karsts are highly threatened biodiversity hotspots supporting high levels of endemic species. Karsts are patchy distributed within Southeast Asia and their isolation from one another give them ... [more ▼]

Limestone karsts are highly threatened biodiversity hotspots supporting high levels of endemic species. Karsts are patchy distributed within Southeast Asia and their isolation from one another give them the features of “islands on the continent” and has important consequences for the genetic structure of endemic taxa. In present study, we have studied the phylogeography of Neill’s Rat Leopoldamys neilli, a threatened Murinae rodent species endemic to limestone karsts of Thailand, on the basis of two mitochondrial markers, two nuclear fragments, as well as twelve microsatellite loci. Our study gave evidence of a complex and strong geographic structure of the genetic diversity for L. neilli. Several highly differentiated genetic lineages were observed throughout Thailand. These results suggest a severe fragmentation of L. neilli’s populations, correlated to the fragmented distribution of its habitat and highlight its high endemicity to limestone karsts. The evolutionary history of L. neilli was investigated using Approximate Bayesian computation (ABC) and our results suggest that the current phylogeographic pattern of this species result from several deep vicariant events during Plio-Pleistocene. To conclude, this study revealed an unexpected high level of intraspecific diversity within L. neilli. These results consolidate the importance to strengthen the protection of limestone habitats and to preserve not only their high interspecific but also intraspecific diversity. [less ▲]

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See detailPhylogeography and taxonomy of woodmice (Apodemus sylvaticus) populations from Western Palearctic: RFLP of the mtDNA variability
Michaux, JR; Libois, Roland ULg; Ramalhinho, Maria da Graça et al

in Ylönen, Hannu; Hentonnen, Heikki; Laajalahti, Päivi (Eds.) et al 3rd European congress of mammalogy (1999, May)

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See detailPhylogeography of a nematode (Heligmosomoides polygyrus) in the western Palearctic region: persistence of northern cryptic populations during ice ages?
Nieberding, Caroline M. ULg; Libois, Roland ULg; Douady, C. J. et al

in Molecular Ecology (2005), 14(3), 765-79

This study establishes the continental phylogeographical pattern of a European nematode, Heligmosomoides polygyrus (Dujardin, 1845; Heligmosomoidea). We sequenced 687 base pairs of the mitochondrial DNA ... [more ▼]

This study establishes the continental phylogeographical pattern of a European nematode, Heligmosomoides polygyrus (Dujardin, 1845; Heligmosomoidea). We sequenced 687 base pairs of the mitochondrial DNA (mtDNA) cyt b gene for 136 individuals collected in 22 localities. The results revealed that H. polygyrus populations are separated into five major units corresponding to the Italian, northern European (Denmark and Ireland), Iberian, western European, and Balkan populations. Different subclades were also observed within the first two groups. Based on the rate of molecular evolution of H. polygyrus cyt b gene-estimated to 3.5%-3.7% divergence per million years (Myr) in a previous study--the isolation time of the five clades was estimated between 2.5 +/- 0.24 and 1.5 +/- 0.23 million years ago. Moreover, H. polygyrus presents a higher genetic variability in the Mediterranean peninsulas as compared to northwestern Europe, highlighting the role of these regions as refuge areas. Like its specific host, the wood mouse Apodemus sylvaticus, H. polygyrus' pattern of postglacial recolonization of northwestern Europe was initiated from Iberian populations, while Italian and Balkan populations did not expand to the north. The results also suggest the existence of forested and temperate refuges in the southern British Isles during the Quaternary. Finally, the genetic diversity as well as the level of genetic divergence between the lineages of H. polygyrus are compared to those observed in other vertebrate and invertebrate phylogeographical studies: the existence of highly differentiated lineages in H. polygyrus (5%-10% of genetic divergence) highlights that the effects of Pleistocene climate changes on free-living organisms are also reflected in their obligate parasites. [less ▲]

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See detailPhylogeography of african timber trees
Hardy, Olivier; Daïnou, Kasso ULg; Debout, Gabriel et al

Conference given outside the academic context (2012)

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See detailPhylogeography of Harbour Porpoise (Phocoena phocoena) in the Eastern North Atlantic and in the Black Sea Explored by the Analyses of Nuclear and Mitochondrial DNA
Fontaine, Michaël; Baird, C.; Stuart, J. E. et al

Poster (2005)

Study of the genetic population structure and the demographic history of the harbour porpoise (Phocoena phocoena) has been nearly comprehensive throughout its distribution in North Atlantic, most studies ... [more ▼]

Study of the genetic population structure and the demographic history of the harbour porpoise (Phocoena phocoena) has been nearly comprehensive throughout its distribution in North Atlantic, most studies using the mitochondrial control region as a genetic marker. Although these studies have shown population structure in some parts of the North Atlantic, mitochondrial DNA is a single, maternally inherited locus and therefore insufficient to fully characterize population structure and history. Polymorphism at 11 microsatellite loci was analyzed in harbour porpoises collected throughout the range of the species in the Central and Eastern North Atlantic from the Iberian peninsula northward to Arctic waters (Portugal, Spain, bay of Biscay, Irish waters, English Channel, the southern bay of the North Sea, Norway, Faroe Islands, and Iceland) and also along the coasts of the Black Sea (Turkey, Ukraine, Bulgaria and Georgia). Multilocus tests for allele frequency differences and population structure estimates indicate complete genetic isolation between Atlantic and Black Sea porpoises. No fine population structure was observed within the Black Sea, and this population displayed a low genetic diversity compared to those of Atlantic. These results can be interpreted in the light of the demographic history of this relict population and the strong founder effect and bottleneck it may have undergone in its past evolution. In Eastern North Atlantic waters, microsatellite data revealed fine scale partitioning of the genetic variation. These results will be compared to the pattern previously reported based on the analysis of the mtDNA control region, and seem to correlate with variation in oceanographic features. [less ▲]

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See detailPhylogeography of the flathead mullet Mugil cephalus in the north-west Pacific as inferred from the mtDNA control region
Jamandre, Brian Wade ULg; Durand, J.-D.; Tzeng, W. N.

in Journal of Fish Biology (2009), 75(2), 393-407

The population genetic structure and historical demography of the flathead mullet Mugil cephalus were investigated using the mtDNA control region (CR) sequences (909-1015 bp) of 126 individuals collected ... [more ▼]

The population genetic structure and historical demography of the flathead mullet Mugil cephalus were investigated using the mtDNA control region (CR) sequences (909-1015 bp) of 126 individuals collected from seven locations in the north-west Pacific between 2005 and 2007. Haplotype diversity (h = 0·9333-1·000) and nucleotide diversity (π = 0·0046-0·1467) varied greatly among the sampling locations. Phylogenetic analysis of the CR sequences indicated that M. cephalus in the north-west Pacific belongs to two highly divergent lineages (lineages 1 and 2), with the inferred population structure being closely associated with the distribution of both lineages. Two populations were identified, one from the East China Sea and the other from the South China Sea. The former samples were obtained from Taiwan and Qingdao of north China and associated with lineage 1 haplotypes. The latter samples were collected from the Philippines, Pearl River of South China and two samples from Japan, all of which were associated with lineage 2. Japanese samples from Okinawa and Yokosuka had different degrees of mixing between lineages 1 and 2. Historical demographic variables in both populations indicated that Pleistocene glaciations had a strong impact on M. cephalus in the north-west Pacific, resulting in a recent demographic decline of the East China Sea population but in demographic equilibrium for the South China Sea population. Japan appears to be a contact zone between lineages 1 and 2, but it may also be indicative of coexistence between resident and migratory populations. Further global studies are required to clarify the taxonomic status of this cosmopolitan species. © 2009 The Fisheries Society of the British Isles. [less ▲]

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See detailPhylogeography of the garden dormouse Eliomys quercinus in the western Palearctic region
Perez, Grégoire; Libois, Roland ULg; Nieberding, Caroline

in Journal of Mammalogy (2013), 94(1),

The garden dormouse, Eliomys quercinus (Rodentia, Gliridae), displays a surprisingly high karyotypic diversity, with the number of chromosomes varying between 2N ¼ 48 and 2N ¼ 54. We aimed to assess ... [more ▼]

The garden dormouse, Eliomys quercinus (Rodentia, Gliridae), displays a surprisingly high karyotypic diversity, with the number of chromosomes varying between 2N ¼ 48 and 2N ¼ 54. We aimed to assess whether the karyotypic diversity is congruent with the mitochondrial differentiation of the populations; improve our understanding of the taxonomic relationships between garden dormouse populations based on both chromosomal and mitochondrial information; and establish the phylogeographic history of the species and the time of differentiation of mitochondrial lineages of E. quercinus and E. melanurus. For this purpose we sequenced the mitochondrial cytochrome-b (Cytb) gene for 62 E. quercinus and 4 E. melanurus from 27 localities representing all the known chromosomal races of the genus Eliomys in the western Palearctic region. Our results 1st showed that populations of E. quercinus are separated into 4 evolutionarily significant units partially congruent with the chromosomal races and corresponding to Iberian (2N¼48), Italian (2N¼48 or 50), western European (2N¼48, 49, or 50), and Alpine (2N ¼ 52 or 54) mitochondrial lineages or clades. The existence of hybrid individuals between chromosomal races and the presence of several chromosomal races within each mitochondrial lineage both indicate that gene flow persists between chromosomal races. Second, we estimated that the major mitochondrial lineages differentiated from each other around 4.2 6 SD 1 million years ago, thus predating the Quaternary glaciations. Third, E. quercinus displayed a higher haplotypic variability in the Mediterranean peninsula than in the northwestern European populations. However, E. quercinus did not show a pattern of ostglacial recolonization of northwestern Europe from Iberian or Italian populations. Our results also suggest that additional, unexpected refuge regions around the Alps exist for the species. Such information will be useful for deciphering the priorities for the protection of E. quercinus, which is listed as ‘‘Near Threatened’’ on the International Union for the Conservation of Nature Red List of Threatened Species and is protected by Appendix III of the Bern Convention. [less ▲]

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See detailPhylogeography of the Southeast Asian sundaicus complex inferred by differential evolution markers
Dusfour, Isabelle; Michaux, Johan ULg; Manguin, Sylvie

in American Journal of Tropical Medicine and Hygiene (The) (2006), 75(5), 590

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See detailPhylogeography, risk factors and genetic history of hepatitis C virus in Gabon, central Africa.
Njouom, Richard; Caron, Melanie; Besson, Guillaume et al

in PLoS ONE (2012), 7(8), 42002

BACKGROUND: The epidemiological and molecular characteristics of hepatitis C virus (HCV) infection in the general population have been poorly investigated in Africa. The aim of this study was to determine ... [more ▼]

BACKGROUND: The epidemiological and molecular characteristics of hepatitis C virus (HCV) infection in the general population have been poorly investigated in Africa. The aim of this study was to determine the prevalence, genotype distribution and epidemic history of HCV in the Gabonese general population. METHODS/PRINCIPAL FINDINGS: A total of 4042 sera collected from adults in 220 villages in all nine administrative areas of the country were screened for antibodies to HCV. HCV NS5B region sequencing was performed for molecular characterization and population genetic analyses. Of 4042 tested sera, 455 (11.2%) were positive. The seroprevalence of HCV varied significantly by administrative area, with the highest rate in Ogooue-Lolo province (20.4%) and the lowest in Ogooue-Maritine province (3.7%). History of parenteral injections, past hospital admission and age over 55 years were independent risk factors for HCV infection (p<0.0001). Phylogenetic analyses showed that 91.9% of the strains were genotype 4 (HCV-4), 5.7% genotype 1 and 2.2% genotype 2. HCV-4 strains were highly heterogeneous, with more than eight subtypes; subtype 4e predominated (57.3%). Coalescence analyses indicated that subtype 4e was the oldest, with an estimated most recent common ancestor of 1702 [95% CI, 1418-1884]. The epidemic profile indicated that it spread exponentially during the first part of the 20th century, probably by iatrogenic transmission. CONCLUSIONS/SIGNIFICANCE: These results confirm the endemicity of HCV subtype 4e in Gabon and show that its spread is due to a cohort effect, with previous, possibly iatrogenic events. More extensive epidemiological studies are needed to better characterize the route of transmission and the dissemination of HCV in Gabon. [less ▲]

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See detailPhysical activity and cardiovascular risk factors in children. The Belgian Luxembourg Child Study.
Guillaume, Michèle ULg; Lapidus, L.; Bjorntorp, P.

in Obesity Research (1997)

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See detailPhysical activity patterns of children after neonatal arterial switch operation.
Massin, Martial M; Hovels-Gurich, Hedwig H; Gérard, Paul ULg et al

in Annals of Thoracic Surgery (2006), 81(2), 665-70

BACKGROUND: Physical inactivity is a major atherosclerosis risk factor. The exercise tolerance is usually excellent after neonatal arterial switch operation, but those patients in whom coronary anomalies ... [more ▼]

BACKGROUND: Physical inactivity is a major atherosclerosis risk factor. The exercise tolerance is usually excellent after neonatal arterial switch operation, but those patients in whom coronary anomalies remain the main late complication, risk developing atherosclerotic coronary disease owing to perceived physical activity restrictions. METHODS: We investigated physical activity patterns of 52 unselected children 7 to 14 years after neonatal arterial switch operation for transposition of the great arteries by 24-hour continuous heart rate monitoring. The percentage of heart rate reserve was used to measure the amounts of activities. Comparisons were made with 35 children with repaired atrial or ventricular septal defect and with 127 age-matched healthy children. RESULTS: Children after arterial switch operation accumulated 167.3 +/- 70.6, 25.3 +/- 12.9, and 15.7 +/- 11.3 minutes a day (mean +/- SD) of light, moderate, and vigorous physical activities, respectively. At the same activity levels, children with repaired septal defect accumulated 165.2 +/- 82.2, 26.2 +/- 11.7, and 16.2 +/- 9.1 minutes a day, and their healthy peers 164.8 +/- 74.5, 31.8 +/- 13.9, and 21.9 +/- 11.3 minutes a day. Both cardiac groups were significantly less active than the control group when considering moderate (p = 0.026) and vigorous activities (p = 0.006). Only 19% and 27% of the children after arterial switch operation engaged, respectively, in more than 30 minutes a day of moderate activity and 20 minutes a day of vigorous activity. CONCLUSIONS: Children after arterial switch operation, just like other cardiac children, do not meet the guidelines for physical activity. We should encourage regular physical activity to offset adult sedentary behavior and to prevent atherosclerotic cardiovascular disease in those patients whose long-term function of the coronary arteries remains a matter of concern. [less ▲]

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See detailPhysical activity promotion among older adults: Short term effects of a neighbourhood environment internet-based intervention
Mouton, Alexandre ULg; Rompen, Jérôme ULg; Cloes, Marc ULg

Poster (2013, May)

Purpose. Recent research suggests that internet-based physical activity interventions can be suitable and effective, even for older adults. Besides, neighbourhood environment internet-based interventions ... [more ▼]

Purpose. Recent research suggests that internet-based physical activity interventions can be suitable and effective, even for older adults. Besides, neighbourhood environment internet-based interventions are currently considered as more effective than traditional motivational interventions. Therefore, the main purpose of this study was to explore the effects of a neighbourhood environment internet-based intervention on physical activity behaviours of older adults. Methods. At baseline, 87 older adults (60.69 ± 7.85 years) from the same district were assigned to an intervention (n = 41) or a control (n = 46) group. The two months intervention was composed of a comprehensive physical activity promotion website, with an emphasis on neighbourhood environment contents, and a monthly personalized email based on the stage of change theory. Physical activity behaviours were assessed by the IPAQ short-form and the stage of change questionnaire at baseline, after one and two month of the intervention, and after one month follow-up. Results. Significant improvements were observed for the stage of change questionnaire in the intervention group from baseline to the end of the intervention (p = 0.003), they remained at follow-up (p = 0.012) while the control group remained unchanged. Physical activity level declined progressively in the control group as it remained constant in the intervention group, with as significant difference between groups after two months intervention (p = 0.027). Conclusions. These findings suggest that a neighbourhood environment internet-based intervention can improve physical activity behaviours in older adults. Further research on this topic is needed to examine longer term effects with larger sample. [less ▲]

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See detailPhysical Activity Promotion In Overweight/Obese Children. A Project Implemented In A Hospital Context
Cloes, Marc ULg; Dewandre, Anne-Cécile; LEBRETHON, Marie-Christine ULg

Conference (2012)

BACKGROUND. Overweight and obesity in youth must be combated through a multiple approach combining management principles in nutrition and physical activity (PA). In the hospital context, medical staff ... [more ▼]

BACKGROUND. Overweight and obesity in youth must be combated through a multiple approach combining management principles in nutrition and physical activity (PA). In the hospital context, medical staff seems to be more focused on nutrition. AIM. In this study, we proposed to implement a specific intervention focusing on PA in parallel with traditional paediatric and dietetic visits designed to 6-12 year-old children. METHODS. Data were collected in three steps: (1) after a visit at the hospital, subjects and their parents answered to a questionnaire (lifestyle, representation about PA) and attended to a meeting during which they received written (illustrated booklet) and oral cues about PA as well as an invitation to use a PA diary and a pedometer; (2) before the next visit (almost 8 weeks interval), they were free to apply the recommendations; (3) after the next visit to the hospital, subjects analyzed the diary with one of the researchers and answered to questions about their current lifestyle and representations about PA. 34 children respected the whole protocol. FINDINGS. Among the children and their parents, representations of PA changed between the visits (PA was no longer regarded merely as sport). Major changes were also identified in children’s lifestyle (increase of number of weekly PA, family PA, weekly PA time; decrease of inactivity time like TV or video games). Only 27 children out of 34 used the PA diary at least once (information were recorded for a mean of 18 days/child between the 2 visits – a third of the duration of the interval). The pedometer has been used by 15 children and was considered as a motivating tool. 58.5% of comments collected at the end of the second meeting were positive and emphasized the interest of the intervention; 24.6% were negative and mainly focused the PA diary). DISCUSSION. This study underlines the need to improve the family's representations about PA in paediatric and dietetic visits. It supports PA experts' integration in the staff. [less ▲]

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See detailPhysical activity, obesity, and cardiovascular risk factors in children. The Belgian Luxembourg Child Study II.
Guillaume, Michèle ULg; Lapidus, L.; Bjondorp, P. et al

in Obesity Research (1997), 5(6), 549-56

Physical activity was measured in relation to cardiovascular (CV) risk factors in a randomly selected population of 1028 children from Province de Luxembourg in Belgium, a mainly rural area with a high ... [more ▼]

Physical activity was measured in relation to cardiovascular (CV) risk factors in a randomly selected population of 1028 children from Province de Luxembourg in Belgium, a mainly rural area with a high prevalence of such risk factors among adults and children. Physical activity was estimated as participation in sport activities, a major indicator of leisure-time physical activity in schoolchildren, and physical inactivity was estimated as frequency and duration of television (TV) watching. Boys participated more frequently in sport activities than girls did (p = 0.001). A majority of the children watched TV daily. After age adjustment, bodyweight (girls, p < 0.012; boys, p < 0.027) and, in boys, body mass index (BMI) (p < 0.039) were related to days per week of TV watching. No significant relationships with other CV risk factors remained after adjustments for BMI. In analyses of independent contributions of age, TV watching, and sports activity on CV risk factors, age showed highly significant relationships. In boys, TV showed relationships with BMI (p < 0.04) and (borderline) with systolic blood pressure, independent of age and sports activity, whereas the latter was significantly related to subscapular skinfold (p < 0.04) and (borderline) with triceps skinfold and cholesterol. In girls, no significant independent contributions to risk factor associations were found. The father's education was directly associated with sports activities, whereas the mother being a housewife showed negative relationships to physical activity and positive to TV watching in their children, suggesting socioeconomic influence on the activity patterns of children. Furthermore, registrations suggested less physical activity in the most rural part of the area. It is concluded that children in this mainly rural area watch TV frequently. In boys, physical inactivity, measured both as TV watching and as registrations of sports activities, contributes independently to body fat mass. In girls, no contribution or weaker contributions of physical inactivity were found. This suggests that contributory factors leading to obesity might be different in girls and boys. [less ▲]

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See detailPhysical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment
Zhou, Jiayun ULg; Delille, Bruno ULg; Kaartokallio, Hermanni et al

in Marine Chemistry (2014), 166

We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day ... [more ▼]

We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of -14 °C for 14 days after which ice decay was induced by increasing the air temperature to -1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicate that there was a succession of 3 stages in the brine dynamics: forced-convection, followed by bottom convection during ice growth, and then brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves. [less ▲]

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See detailPhysical and biogeochemical properties in landfast sea ice (Barrow, Alaska): insights on brine and gas dynamics across seasons
Zhou, Jiayun ULg; Delille, Bruno ULg; Eicken, H. et al

in Journal of Geophysical Research (2013), 118(6), 3172-3189

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages ... [more ▼]

The impacts of the seasonal evolution of sea-ice physical properties on ice-ocean biogeochemical exchanges were investigated in landfast ice at Barrow (Alaska) from January through June 2009. Three stages of brine dynamics across the annual cycle have been identified based on brine salinity, brine volume fraction and porous medium Rayleigh number [less ▲]

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See detailPhysical and biological controls on DMS,P dynamics in ice-shelf influenced fast ice during a winter-spring and a spring-summer transitions
Carnat, G.; Zhou, Jiayun ULg; Papakyriakou, T. et al

in Journal of Geophysical Research. Oceans (2014), 119

We report the seasonal and vertical variations of dimethylsulphide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer ... [more ▼]

We report the seasonal and vertical variations of dimethylsulphide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover, with emphasis on the ice texture and brine dynamics. Isolated DMS and DMSP maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture. We show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates (strong DMSP producers) in the ice cover. We also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of DMS,P concentrations. We show that during the winter-spring transition in 2012, the DMS,P profiles were strongly influenced by the development and decline of a diatom dominated bloom in the bottom ice, with DMSP variations remarkably following chl a variations. During the spring-summer transition in 2011, the increase in brine volume fraction (influencing ice permeability) on warming was shown to trigger (1) an important release of DMS to the under-ice water through brine convection (2) a vertical redistribution of DMSP across the ice [less ▲]

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See detailThe physical and biological controls on the distribution of gases and solutes in sea ice from ice growth to ice decay
Zhou, Jiayun ULg

Doctoral thesis (2014)

Les changements dans l’extension et les propriétés de la glace de la mer, liés au réchauffement climatique, affectent l’écosystème polaire, ainsi que les interactions entre l’atmosphère, la glace de mer ... [more ▼]

Les changements dans l’extension et les propriétés de la glace de la mer, liés au réchauffement climatique, affectent l’écosystème polaire, ainsi que les interactions entre l’atmosphère, la glace de mer et l’eau sous-jacente. Cependant, des incertitudes subsistent quant aux changements potentiels qui affecteront la biogéochimie de la glace de mer dans un futur proche. Afin de mieux comprendre les changements potentiels qui affecteront la biogéochimie de la glace de mer, nous avons étudié les facteurs qui influencent la distribution de certains composés dissouts (e.g., nutriments, matière organique dissoute (DOM)) et gazeux (e.g., Ar, O2, N2, CH4) au sein de la glace de mer, depuis la croissance de la glace, jusqu’à sa fonte. Les résultats ont été obtenus à partir d’une expérience de 19 jours dans un bassin expérimental à Hambourg (Allemagne) et une étude de terrain de 5 mois à Barrow (Alaska). Ils ont été ensuite comparés aux propriétés physiques de la glace (température, salinité et autres paramètres dérivés) et à des paramètres biologiques (activité bactérienne, abondance bactérienne, chlorophylle-a et phaeopigments). Nos travaux ont montré que les propriétés physiques de la glace exercent une forte influence sur la répartition des composes biogéochimiques dans la glace de mer, à travers leur impact sur la dynamique des saumures, la formation de bulles de gaz et la perméabilité de la glace. Nous avons décrit 4 stades dans la dynamique des saumures qui influencent la distribution des composés dissouts (e.g., silice et DOM) dans la glace. Cependant, le gaz inerte étudié (Ar) montre une dynamique différente de celle des composés dissouts, indiquant un mécanisme de transport différent. Nous suggérons que la formation de bulles de gaz dans la glace de mer est le mécanisme responsable de cette différence, parce que les bulles de gaz devraient migrer vers le haut, à cause de leur différence de densité par rapport aux saumures, alors que les saumures sont drainées vers le bas à cause de la gravité. Nos observations montrent également que le seuil critique de perméabilité pour l’ascension des bulles de gaz devrait se trouver entre 7.5 et 10 % de volume relatif en saumure ; seuil qui est plus élevé que les 5 % suggérés pour le transport de saumure vers le bas. L’augmentation de la perméabilité de la glace et les échanges de gaz prolongés tendent à amener les concentrations de gaz vers leur valeur de solubilité, sauf lorsque l’eau sous-jacente présente une sursaturation par rapport à l’atmosphère (e.g., CH4), ou lorsque une production in-situ se produit au sein de la glace (e.g., O2). Etant donné que l’ammonium et O2 s’accumulent clairement dans les couches de glace où la convection est limitée, nous suggérons que les variations de ces composés biogéochimiques dans la glace dépendent de la balance entre le transport physique et l’activité biologique ; l’impact de cette dernière sur les composés biogéochimiques est particulièrement visible lorsque le taux de production biologique du composé excède largement la vitesse d’élimination du composé par le transport physique. Nous avons ensuite discuté du potentiel d’utiliser Ar et N2 comme traceurs inertes pour corriger l’impact des processus physiques sur les variations de O2, afin de déterminer la production communautaire nette dans la glace de mer. Les propriétés chimiques de certains composés biogéochimiques (e.g., nitrate, ammonium, DOM) pourraient également influencer leur répartition au sein de la glace de mer, en plus des processus physiques et biologiques. Cependant, il est nécessaire d’avoir plus d’études à ce sujet pour confirmer cela. Enfin, sur base de nos résultats, nous présentons une mise à jour des processus qui régulent la répartition des gaz dans la glace de mer, avec des références à des observations récentes qui illustrent chacun des processus. Nous donnons également un aperçu des changements qui pourraient affecter la biogéochimie de la glace de mer à l’avenir, et des pistes de recherches pour une quantification précise de ces changements. [less ▲]

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