13 research outputs found
Tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore La Jolla, Southern California
CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea-level fluctuations. Based on stratal geometry and acoustic character, we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences: an acoustically laminated estuarine unit deposited during early transgression, an infilling or âhealing-phaseâ unit formed during the transgression, and an upper transparent unit. Beneath the transgressive surface, steeply dipping reflectors with several dip reversals record faulting and folding along the La Jolla margin. Scripps Canyon is located at the crest of an antiform, where the rocks are fractured and more susceptible to erosion. La Jolla Canyon is located along the northern strand of the Rose Canyon Fault Zone, which separates Cretaceous lithified rocks to the south from poorly cemented Eocene sands and gravels to the north. Isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation. For example, the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the Holocene sea-level rise. The distribution of the infilling unit is controlled by pre-existing relief that records tectonic deformation and erosional processes. The thickness and distribution of the upper transparent unit are controlled by long-wavelength, tectonically induced relief on the transgressive surface and hydrodynamics
Current variability in a wide and open lacustrine embayment in Lake Geneva (Switzerland)
Field measurements and numerical simulations were used to determine the effects of dominant meteorological conditions on the hydrodynamics of a wide (aspect ratio ~2), relatively deep (seasonally stratified) and open lake embayment (Vidy Bay, Lake Geneva). A three-dimensional hydrodynamic model (Delft3D-FLOW) was employed to simulate flow in the lake. High-resolution maps of wind, temperature and humidity (over the lake) were applied as input to drive the model. Because wind was the main force driving flow in the lake, currents in the embayment were investigated systematically for different wind conditions and seasonal stratification. Satisfactory model validation was achieved using drifter and moored measurements within the embayment. Markedly different circulation patterns were measured within the embayment, with the transition from one pattern to another occurring abruptly for small changes in wind direction. These distinct patterns resulted from relatively small changes in the large gyre of Lake Genevaâs main basin, especially the angle between the current in front of the embayment and the embayment shoreline. The boundary between the embayment and the pelagic zone was defined by the largest gyre within the embayment. This study shows that, (i) in a large lake, complex current patterns can occur even within a minor embayment, and (ii) that these patterns can transition rapidly over a small range of wind directions. Near-shore gyre can occur for lengthy periods, which has implications for flushing of discharges within the embayment
De lâusage de certaines pĂȘcheries Ă lâĂąge du Bronze ancien dans lâarchipel de MolĂšne
International audienceThe abundant ichthyofauna on the archaeological site of Beg ar Loued reflects a high consumption of fish by people occupying the island of MolĂšne during the Early Bronze Age. This raises the question of fishing techniques employed, especially from nearby stone fish traps, which are very numerous on the foreshores of Brittany. This study provides an inventory of these structures on the foreshore of the archipelago of MolĂšne, based on aerial, pedestrian, underwater, and high-resolution bathymetric surveys. Functional stone fish traps during the Early Bronze Age were identified from their position in relation to former tide levels. A total of 36 (proven or likely) structures have been identified around the archipelago. Only 10 of them were functional at the Early Bronze Age. Other traps are located at a lower depth, indicating an earlier use, probably from the early Neolithic.La prĂ©sence dâune abondante ichtyofaune sur le site de Beg ar Loued tĂ©moigne dâune forte consommation de poissons par les populations ayant occupĂ© lâĂźle de MolĂšne Ă lâĂąge du Bronze ancien, soulevant la question des techniques de pĂȘche employĂ©es et la prĂ©sence Ă©ventuelle de barrages de pĂȘcherie Ă proximitĂ©. Cette Ă©tude dresse lâinventaire de ce type de structure sur les estrans de lâarchipel, en sâappuyant sur une sĂ©rie de prospections aĂ©riennes, pĂ©destres et subaquatiques, ainsi que sur un ensemble de relevĂ©s bathymĂ©triques Ă haute rĂ©solution. Les pĂȘcheries fonctionnelles Ă lâĂąge du Bronze ancien ont Ă©tĂ© repĂ©rĂ©es en se basant sur leur position par rapport aux anciens niveaux de marĂ©e. Un total de 36 structures, avĂ©rĂ©es ou possibles, a Ă©tĂ© identifiĂ© autour de lâarchipel. Seulement 10 d'entre elles Ă©taient fonctionnelles au Bronze ancien. Les autres piĂšges sont situĂ©s Ă une altitude plus basse, indiquant une utilisation plus ancienne, probablement dĂšs le dĂ©but du NĂ©olithique
De lâusage de certaines pĂȘcheries Ă lâĂąge du Bronze ancien dans lâarchipel de MolĂšne
International audienceThe abundant ichthyofauna on the archaeological site of Beg ar Loued reflects a high consumption of fish by people occupying the island of MolĂšne during the Early Bronze Age. This raises the question of fishing techniques employed, especially from nearby stone fish traps, which are very numerous on the foreshores of Brittany. This study provides an inventory of these structures on the foreshore of the archipelago of MolĂšne, based on aerial, pedestrian, underwater, and high-resolution bathymetric surveys. Functional stone fish traps during the Early Bronze Age were identified from their position in relation to former tide levels. A total of 36 (proven or likely) structures have been identified around the archipelago. Only 10 of them were functional at the Early Bronze Age. Other traps are located at a lower depth, indicating an earlier use, probably from the early Neolithic.La prĂ©sence dâune abondante ichtyofaune sur le site de Beg ar Loued tĂ©moigne dâune forte consommation de poissons par les populations ayant occupĂ© lâĂźle de MolĂšne Ă lâĂąge du Bronze ancien, soulevant la question des techniques de pĂȘche employĂ©es et la prĂ©sence Ă©ventuelle de barrages de pĂȘcherie Ă proximitĂ©. Cette Ă©tude dresse lâinventaire de ce type de structure sur les estrans de lâarchipel, en sâappuyant sur une sĂ©rie de prospections aĂ©riennes, pĂ©destres et subaquatiques, ainsi que sur un ensemble de relevĂ©s bathymĂ©triques Ă haute rĂ©solution. Les pĂȘcheries fonctionnelles Ă lâĂąge du Bronze ancien ont Ă©tĂ© repĂ©rĂ©es en se basant sur leur position par rapport aux anciens niveaux de marĂ©e. Un total de 36 structures, avĂ©rĂ©es ou possibles, a Ă©tĂ© identifiĂ© autour de lâarchipel. Seulement 10 d'entre elles Ă©taient fonctionnelles au Bronze ancien. Les autres piĂšges sont situĂ©s Ă une altitude plus basse, indiquant une utilisation plus ancienne, probablement dĂšs le dĂ©but du NĂ©olithique
Combining observations and models to enhance coastal resilience and adaptation.
International audienc
Suivi citoyen des indicateurs des alĂ©as dâĂ©rosion cĂŽtiĂšre et de submersion marine : crĂ©ation de lâapplication smartphone et tablette CoastAppli et expĂ©rimentation Ă GuissĂ©ny (FinistĂšre)
International audienceLes alĂ©as cĂŽtiers (Ă©rosion, submersion, migration dunaire) et les dynamiques cĂŽtiĂšres sont souvent mĂ©connus par le grand public. Or, dans un contexte de changement climatique et dâĂ©volution de la lĂ©gislation (loi « Climat et rĂ©silience » en 2021) sur la gestion des alĂ©as et des risques cĂŽtiers (risque(s) combinant alĂ©a(s) et enjeu(x)), le suivi de lâĂ©volution du littoral au travers dâindicateurs des alĂ©as cĂŽtiers (position du trait de cĂŽte, niveau de la plage, niveau dâeau sur un repĂšre lors dâune submersion, etc.) devrait ĂȘtre lâaffaire de tous. JusquâĂ prĂ©sent, aucune application citoyenne pour smartphone ou tablette ne permettait de suivre conjointement les indicateurs des alĂ©as cĂŽtiers dâĂ©rosion et de submersion, alors que ces deux alĂ©as sont souvent liĂ©s. Pour y remĂ©dier, dans le cadre dâun projet de recherche et de formation (2019-2022) regroupant des Ă©tudiants en gĂ©ographie, en biologie et en informatique, nous avons crĂ©Ă© lâapplication Android CoastAppli. CoastAppli, qui vise un public large (habitants, touristes, scolaires, gestionnaires du littoral, etc.) et a Ă©tĂ© expĂ©rimentĂ©e Ă GuissĂ©ny (FinistĂšre) entre janvier et octobre 2022 auprĂšs de 86 personnes, permet de rĂ©aliser un suivi citoyen des indicateurs dâalĂ©as cĂŽtiers. GrĂące Ă lâimplication des utilisateurs sur les quatre sites de cette commune, les rĂ©sultats soulignent la fiabilitĂ© des donnĂ©es quantitatives (jusquâĂ une erreur globale de ± 4 cm) et/ou qualitatives, ainsi que la haute frĂ©quence dâacquisition (mensuelle). Par ailleurs, cela semble un bon moyen pour comprendre, discuter et rĂ©flĂ©chir entre acteurs du territoire aux dĂ©fis de gestion du littoral dâaujourdâhui et de demain
Suivi citoyen des indicateurs des alĂ©as dâĂ©rosion cĂŽtiĂšre et de submersion marine : crĂ©ation de lâapplication smartphone et tablette CoastAppli et expĂ©rimentation Ă GuissĂ©ny (FinistĂšre)
International audienceLes alĂ©as cĂŽtiers (Ă©rosion, submersion, migration dunaire) et les dynamiques cĂŽtiĂšres sont souvent mĂ©connus par le grand public. Or, dans un contexte de changement climatique et dâĂ©volution de la lĂ©gislation (loi « Climat et rĂ©silience » en 2021) sur la gestion des alĂ©as et des risques cĂŽtiers (risque(s) combinant alĂ©a(s) et enjeu(x)), le suivi de lâĂ©volution du littoral au travers dâindicateurs des alĂ©as cĂŽtiers (position du trait de cĂŽte, niveau de la plage, niveau dâeau sur un repĂšre lors dâune submersion, etc.) devrait ĂȘtre lâaffaire de tous. JusquâĂ prĂ©sent, aucune application citoyenne pour smartphone ou tablette ne permettait de suivre conjointement les indicateurs des alĂ©as cĂŽtiers dâĂ©rosion et de submersion, alors que ces deux alĂ©as sont souvent liĂ©s. Pour y remĂ©dier, dans le cadre dâun projet de recherche et de formation (2019-2022) regroupant des Ă©tudiants en gĂ©ographie, en biologie et en informatique, nous avons crĂ©Ă© lâapplication Android CoastAppli. CoastAppli, qui vise un public large (habitants, touristes, scolaires, gestionnaires du littoral, etc.) et a Ă©tĂ© expĂ©rimentĂ©e Ă GuissĂ©ny (FinistĂšre) entre janvier et octobre 2022 auprĂšs de 86 personnes, permet de rĂ©aliser un suivi citoyen des indicateurs dâalĂ©as cĂŽtiers. GrĂące Ă lâimplication des utilisateurs sur les quatre sites de cette commune, les rĂ©sultats soulignent la fiabilitĂ© des donnĂ©es quantitatives (jusquâĂ une erreur globale de ± 4 cm) et/ou qualitatives, ainsi que la haute frĂ©quence dâacquisition (mensuelle). Par ailleurs, cela semble un bon moyen pour comprendre, discuter et rĂ©flĂ©chir entre acteurs du territoire aux dĂ©fis de gestion du littoral dâaujourdâhui et de demain
Precipitation as driver of carbon fluxes in 11 African ecosystems
This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments. Values for maximum net carbon assimilation rates (photosynthesis) ranged from -12.5 mu mol CO2 m(-2) s(-1) in a dry, open Millet cropland (C-4-plants) up to -48 mu mol CO2 m(-2) s(-1) for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r(2)=0.74). Maximum photosynthetic uptake rates (Fp(max)) were positively related to satellite-derived f(APAR). Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C-3-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa