Late Holocene current patterns in the northern Patagonian fjords recorded by sediment drifts in Aysén Fjord

Present-day circulation patterns in the southeastern Pacific Ocean are driven by the Antarctic Circumpolar Current, directing subantarctic surface water into the Patagonian fjords since at least the early Holocene. In this way, bottom current patterns in the area are regulated by the regional climate, although the complex bathymetry of the fjords has a significant impact as well. To understand the potential interplay of climate, seafloor topography and circulation patterns, we study the sedimentary infill of Aysén Fjord (~45°S) and reveal the first active sediment drifts in the region. These allow constraining the present-day circulation patterns in northern Patagonia and show an incoming (southward) as well as returning (northward) flow direction. While the general sedimentary evolution of the fjord (and thus also the sediment drifts) is climate-driven (i.e., it reflects variability in southern westerly wind strength), the onset of drift formation at ~3.7 ka does not seem to have originated from an abrupt change in regional climate. Instead, we propose that a megathrust earthquake described in paleoseismic records in the area could have resulted in subsidence of one (or more) of the many bathymetric highs in the Patagonian fjords, thus contributing to enhanced spilling of subantarctic water into the fjord. This study underscores the importance of multidisciplinary research to understand past and present bottom current circulation patterns and disentangle different possible feedback mechanisms

Etude des variations de la mousson nord africaine et de l'hydrologie de l'Atlantique à la transition mio-pliocène (relations avec la crise de salinité messinienne en Méditerranée)

Un bilan minéralogique et géochimique des sédiments du Site ODP 659 a permis d établir un nouveau modèle de dépôt des sédiments au niveau du plateau du Cap Vert qui constitue une zone clé dans la restitution des apports éoliens à l Atlantique depuis le continent africain. Nous avons apporté des contraintes supplémentaires sur les zones d alimentation et les voies de transport du matériel sédimentaire au plateau du Cap Vert et montré un lien étroit entre la sédimentation de cette zone et les changements de la mousson Nord africaine. Nous avons ainsi établi de nouveaux traceurs minéralogiques et géochimiques des changements passés de la mousson africaine. Outre un contrôle très étroit de la mousson africaine par l insolation reçue par la Terre aux basses latitudes, nous avons mis en évidence l existence de changements du régime de la mousson qui échappe à tout contrôle orbital. Ceux-ci semblent liés aux changements paléogéographiques du domaine méditerranéen en liaison avec l assèchement progressif et la remise en eau du bassin de la Méditerranée lors des évènements majeurs de la crise de salinité messinienne. Les isotopes stables de l oxygène et du carbone des foraminifères benthiques Cibicides wuellerstorfi ont également permis de restituer, sur une échelle d âge orbitale, les variations de l hydrologie profonde en Atlantique ainsi que les variations du niveau marin. Plus particulièrement, nous avons confirmé que la fermeture des ponts océaniques entre la Méditerranéen et l Atlantique au cours de la crise de salinité messinienne n est pas contrôlée par les variations du niveau marin mais bien par la tectonique.Mineralogical and geochimical results on sediments of Site ODP 659 permitted to establish a new model of sediment deposit in Cap Verde rise which constitute a key area on restitution of eolian input from Africa to Atlantic Ocean. We brought additional constraints on feeding zones and detritals inputs of the sedimentary material to the Cap Verde rise and shown a close link between the sedimentation of this zone and the variations of African Northern monsoon. We thus established new mineralogical and geochemical tracers of the last changes of African monsoon. In addition to a very narrow control of African monsoon by the insolation received by the Earth at the low latitudes, we highlighted the existence of changes in the monsoon which escapes of orbital control. Those seem related to the palaeogeographic changes of the Mediterranean field in connection with the progressive draining and drought of the Mediterranean Sea at the time of the major events of the messinian salinity crisis. On an orbital timescale, study of oxygen and carbon stable isotopes obtained on benthic Foraminifera Cibicides wuellerstorfi permit to reconstruct the variations of major hydrology in the Atlantic as well as the variations of world sea level. More particularly, we confirmed that the closing of the oceanic bridges between the Mediterranean Sea and the Atlantic Ocean during the messinian salinity crisis are not controlled by the variations of the sea level but well by tectonic movements.ORSAY-PARIS 11-BU Sciences (914712101) / SudocPARIS-Museum-Bib. de géologie (751055215) / SudocSudocFranceF

Investigation on the capability of polysulphone for measuring biologically effective solar UV exposures

Polysulphone (PS) dosimetry is a well-known technique broadly used to assess the erythemally effective solar UV dose received by anatomical sites (personal exposure). We investigate the capability of PS dosimetry to convert doses absorbed by PS badges into biologically effective solar UV exposures taking as examples two relevant effects for human skin: erythema induction and pre-vitamin D3 production. PS calibration curves for erythemal and pre-vitamin D3 were distinctly determined by using an empirical relationship between the biologically effective UV exposures and the PS absorbance change. This relationship is parameterized by a coefficient, distinct for each of the two considered biological effects, multiplying the same cubic polynomial function. It is shown how the multiplying coefficient is related to the ratio between the biologically effective and the PS weighted irradiances which is the prevailing factor affecting the accuracy of the calibration and, consequently, the capability of PS films for measuring biologically effective solar UV exposures. The points addressed in this paper can be extended to other biological effects of interest whose action spectra have some similarity with the PS film response