Benthic foraminifera as tracers of brine production in the Storfjorden "sea ice factory"

Abstract. The rapid response of benthic foraminifera to environmental factors (e.g. organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such an approach, however, requires a thorough knowledge of their modern ecology in such extreme settings. To this aim, seven stations along a north–south transect across the Storfjorden (Svalbard archipelago) have been sampled using an interface multicorer. This fjord is an area of intense sea ice formation characterised by the production of brine-enriched shelf waters (BSW) as a result of a recurrent latent-heat polynya. Living (rose bengal-stained) foraminiferal assemblages were analysed together with geochemical and sedimentological parameters in the top 5 cm of the sediment. Three major biozones were distinguished. (i) The "inner fjord" zone, dominated by typical glacier proximal calcareous species, which opportunistically respond to fresh organic matter inputs. (ii) The "deep basins and sill" zone, characterised by glacier distal agglutinated fauna; these are either dominant because of the mostly refractory nature of organic matter and/or the brine persistence that hampers the growth of calcareous species and/or causes their dissolution. (iii) The "outer fjord" zone, characterised by typical North Atlantic species due to the intrusion of the North Atlantic water in the Storfjordrenna. The stressful conditions present in the deep basins and sill (i.e. acidic waters and low food quality) result in a high agglutinated ∕ calcareous ratio (A∕C). This supports the potential use of the A∕C ratio as a proxy for brine persistence and overflow in Storfjorden

Benthic and Planktic Foraminifera as Indicators of Late Glacial to Holocene Paleoclimatic Changes in a Marginal Environment: An Example from the Southeastern Bay of Biscay

Benthic and planktic foraminiferal assemblages from two sediment cores (2000 m depth, 44°33′N-2°45′W) were analyzed to first compare modern and dead faunas and next to study changes in the hydrology of the southeastern Bay of Biscay (SE BoB) over the last 12.8 cal ka BP. Considering benthic ecosystem characteristics, the first part of the paleorecord (12.8–7.6 cal ka BP) is composed of laminated sediments that may have resulted from turbiditic overflow events, whereas occurrences of transported species (e.g. Nonionella sp., Cassidulina carinata) attest of continental influence at the core location. After 7.6 cal ka BP, the sediment becomes bioturbated concomitantly to the stabilization of the sea-level. The benthic foraminiferal fauna is largely dominated by Uvigerina peregrina suggesting a high seasonality with seasonal pulsed organic matter fluxes to the seafloor. On the other hand, the planktic foraminiferal composition indicates that surface water masses were under the influence of the polar front in the early record, which retreated at about 11.5 cal ka BP. The early Holocene is characterized by relatively warm and stratified water masses at 8.4–4.8 cal ka BP. The last 4.8 cal ka BP records a gradual sea surface water cooling trend and enhanced foraminiferal production from ~2.6 cal ka BP until present. The early (12.8–10.5 cal ka BP) and late (2.3–1.7 cal ka BP) Holocene are characterized by the presence of the planktic species Globigerinoides ruber probably caused by intrusions of the Iberian Poleward Current (IPC), and a negative state of the North Atlantic Oscillation (NAO)

Barents Sea plankton tows and surface sediment planktonic foraminifera assemblages

Concentration and relative abundances of planktonic foraminifera in plankton tows and surface sediments of the the Barents Sea, from 69°50,686 N to 75°36,095 N

Relative abundances of living planktonic foraminifera in surface sediments from the Barents Sea

Concentration and relative abundances of planktonic foraminifera in plankton tows and surface sediments of the the Barents Sea, from 69°50,686 N to 75°36,095 N

Ecologie des foraminifères planctoniques du golfe de Gascogne (variations spatio-temporelles des assemblages et géochimie de leurs tests)

Cette thèse a été réalisée dans le cadre du projet de recherche ANR FORCLIM. L'objectif fondamental de ce travail était d'effectuer une étude poussée de l'écologie des foraminifères planctoniques dans les écosystèmes actuels du Golfe de Gascogne, à partir des filets à plancton et des données hydrologiques recueillies au cours de 5 missions océanographiques. Les résultats montrent des variations saisonnières importantes de leurs densités, mais aussi de leurs assemblages spécifiques. Des assemblages se succèdent au cours des saisons, avec de grandes concentrations de N. pachyderma dextre, G. inflata, G. scitula et G. glutinata en fin d'hiver-début printemps, T. quinqueloba, G. uvula, G. bulloides et G. glutinata se manifestent en grandes densités au cours du bloom phytoplanctonique printanier. Ces espèces sont progressivement remplacées par des espèces, comme O. universa et G. trilobus en surface et G. scitula en profondeur en été. De Mars à Juin, le long d'un transect bathymétrique, on remarque une décroissance des concentrations des foraminifères planctoniques vers la côte. Mais les apports saisonniers de nutriments par les fleuves, ainsi que l'influence hydrologique d'un canyon sous marin peuvent contrarier ce gradient de décroissance large-côte. En Novembre, G. calida apparaît en très grande abondance dans les stations les plus côtières, pouvant marquer un évènement de bloom automnal côtier. Une analyse automatique des tailles des spécimens vivants et morts indique de plus grandes tailles dans les eaux estivales. Néanmoins, la température ne semble pas être un facteur majeur direct des variations de tailles des foraminifères. La disponibilité en nourriture serait un des facteurs majeurs, avec l'un des facteurs covariant à la salinité, comme la turbidité. Les rapports isotopiques en oxygène des tests de foraminifères planctoniques vivants indiquent des populations de Juin manifestement plus faibles que ceux mesurés en Mars et Avril, suggérant qu'il s'agirait de générations différentes.This PhD was realised within the framework of the research project ANR FORCLIM. The fundamental aim of this study focused on the ecology of planktic foraminifera in the recent ecosystem of the Bay of Biscay. Samples from plankton tows and hydrological data were collected during 5 cruises. Results show a strong seasonal variation in planktic foraminiferal densities and species assemblages. Faunal assemblages changed in quantity and quality on a seasonal scale. High concentrations of N. pachyderma dextral, G. inflata, G. scitula, and G. glutinata marked the end of winter and the beginning of spring in the plankton community. T. quinqueloba, G. uvula, G. bulloides and G. glutinata were abundant during the spring phytoplanktonic bloom. During the summer, these species were progressively replaced by others species, such as O. universa and G. trilobus at low water depths, and G. scitula at greater depths. From March to June, along a bathymetric transect, planktic foraminiferal concentrations decreased toward the coast. Seasonal variability of nutrients derived from river discharge, or hydrological effects caused by sub marine canyons did affect the distribution of planktic foraminifers. In November, G. calida was abundant at onshore stations, marking an autumn bloom event. Size analysis of living and dead specimens showed that planktonic foraminifera were larger during summer. Temperature did not seem to significantly affect size variation of planktic foraminifers. It can be assumed that food supply, salinity and turbidity do affect the distribution of planktic foraminifers. Stable oxygen isotope ratios from tests of living planktic foraminifers indicate that populations in June were clearly lower than March and April populations, suggesting that they are from different generations.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Seasonal record of foraminiferal export fluxes in the Bay of Biscay

Date du colloque : 05/2008International audienc

Seasonal export of plankton foraminifera in the Bay of Biscay

Date du colloque : 04/2008International audienc

Swash platform morphology in the ebb-tidal delta of the Barra Nova inlet, South Portugal

International audienceAn artificially created inlet cut in the barrier island system of the Ria Formosa (South Portugal) was studied by performing fieldwork from January to March 1999. This study focuses on the updrift swash platform associated with the ebb-tidal delta. The area was monitored during a month with fair weather conditions studying morphodynamics, sedimentary dynamics and hydrodynamic measurements. The results were used to establish a sedimentary budget of the swash platform and to quantify the morphodynamics. A strong accretion was observed on the swash platform, which corresponds to the volume of sediment provided by the longshore drift on the adjacent updrift coast. A redistribution of sediment was observed on the platform, changing the orientation of the main swash platform axis. The swash bars forming this area are very dynamic (20m migration in 8 days), and the entire swash platform is migrating toward the inlet resulting in progressive closure of the system. Characteristics of the inlet and morphodynamics of the swash platform were used to validate a conceptual model of by-passing by ebb-tidal delta breaching for this system