Understanding the O-17 excess glacial-interglacial variations in Vostok precipitation

International audienceCombined measurements of delta O-18, delta O-17, and delta D in ice cores, leading to d excess and O-17 excess, are expected to provide new constraints on the water cycle and past climates. We explore different processes, both in the source regions and during the poleward transport, that could explain the O-17 excess increase by 20 per meg observed from the Last Glacial Maximum (LGM) to Early Holocene (EH) at the Vostok station. Using a single-column model over tropical and subtropical oceans, we show that the relative humidity at the surface is the main factor controlling O-17 excess in source regions. Then, using a Rayleigh-type model, we show that the O-17 excess signal from the source region is preserved in the polar snowfall, contrary to d excess. Evaporative recharge over mid and high latitudes and delta O-18 seasonality in polar regions can also affect the Vostok O-17 excess but cannot account for most of the 20 per meg deglacial increase from LGM to EH. On the other hand, a decrease of the relative humidity at the surface (rh(s)) by 8 to 22% would explain the observed change in O-17 excess. Such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity, if the surface thermodynamic disequilibrium decreased by 4 degrees C. Such a change in rh(s) would affect source and polar temperatures reconstructions from delta O-18 and d excess measurements, strengthening the interest of O-17 excess measurements to better constrain such changes

Réconciliation des enregistrements isotopiques dans les spéléothèmes et les glaces en Amérique du Sud tropicale et subtropicale: nouveaux éléments sur la séquence des événements pendant la dernière déglaciation

International audienceNous présentons ici une révision de la datation de la carotte de glace d’Illimani, forée en 1999 en Bolivie(16°S, 6300 m), sur sa partie profonde (les derniers mètres). Les mesures de la composition isotopique enoxygène 18 de l’oxygène des bulles d’air sur le fond de cette carotte peuvent aujourd’hui être comparées àdes enregistrements haute résolution de ce traceur isotopique dans les glaces polaires. Il en ressort nettementque le fond de la carotte serait plus jeune d’environ 2000 ans qu’initialement suggéré (18 000 ans). Cettecomparaison vient confirmer des mesures en carbone 14 réalisées sur une carotte forée par une équipe suissesur le même glacier et la même année. L’enregistrement isotopique glaciaire (oxygène 18 ou deutérium) ainsire daté montre un minimum aux alentours de 16 000 ans, davantage synchrone avec les enregistrementsisotopiques en oxygène 18 issus des spéléothèmes se situant à proximité. Ce résultat est plus cohérent avecnotre compréhension du cycle des isotopes stables de l’eau dans cette région : à ces latitudes, la compositionisotopique en oxygène 18 des carottes de glace et des spéléothèmes est reliée au cycle de l’eau atmosphériqueet devrait donc être synchrone d’une archive à l’autre sur des échelles de temps longues. Ce minimumisotopique dans les enregistrements de cette région tropicale de l’Amérique du Sud est beaucoup plus jeuneque le minimum de température enregistré aux alentours de 21 000 ans dans les carottes de glace polaireset est certainement à relier à une ré organisation du cycle hydrologique lors de l’événement de Heinrich 1.Nous discuterons lors de la présentation de la séquence des évènements pendant la déglaciation sur plusieursenregistrements en Amérique du Sud tropicale et subtropicale, localisés plus au Sud et plus au Nord que lacarotte d’Illimani

What controls the triple isotopic composition of water in Bolivian precipitation?

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Dynamic of the atmospheric boundary layer from the isotopic composition of surface water vapor at the Maïdo Observatory (LaRéunion, Indian Ocean)

International audienceProjections of tropical and subtropical precipitation strongly differ from one climate model to another, both insign and in amplitude. This is the case for example in some parts of the West Indian Ocean. The causes of thoseuncertainties are numerous and a better understanding of humid processes in the tropical atmosphere is needed.We propose to address this burning question by using water stables isotopes.We have been measuring the isotopic composition of surface water vapor at the atmospheric Observatoryof Maïdo located at La Reunion Island (21◦S, 55◦E, 2200m a.s.l) since November 2014. Our results exhibit astrong diurnal cycle all over the year (except during cyclonic activity), with almost constant isotopic values duringthe day (around -13.5±0.6h for oxygen 18 from November 2014 to November 2015) and variable and verydepleted isotopic values during the night (down to -35h for oxygen 18 over the same period) associated with lowhumidity levels. We will show in this presentation that the diurnal isotopic variations are associated to a strongair masses mixing. During the day, the isotopic composition of the vapor is typical of marine boundary layer(BL) moisture transported from the close Ocean and lifted up to the Maïdo station. During the night, the depletedvalues and the low humidity could trace free troposphere moisture, which is consistent with previous studiessuggesting that the Maïdo Observatory is above the BL during the night. We will explore the influence of the dailyBL development on our observations, using a set of atmospheric vertical profiles done on site in May 2015 duringthe BIOMAIDO campaign. At last, we will discuss the most isotopic depleted values recorded in our observationsduring the night as a possible consequence of regional strong subsidences

A 1-year long delta O-18 record of water vapor in Niamey (Niger) reveals insightful atmospheric processes at different timescales

International audienceWe present a 1-year long representative delta O-18 record of water vapor (delta O-18(v)) in Niamey (Niger) using the Wavelength Scanned-Cavity Ring Down Spectroscopy (WS-CRDS). We explore how local and regional atmospheric processes influence delta O-18(v) variability from seasonal to diurnal scale. At seasonal scale, delta O-18(v) exhibits a W-shape, associated with the increase of regional convective activity during the monsoon and the intensification of large scale subsidence North of Niamey during the dry season. During the monsoon season, delta O-18(v) records a broad range of intra-seasonal modes in the 25-40-day and 15-25-day bands that could be related to the well-known modes of the West African Monsoon (WAM). Strong delta O-18(v) modulations are also seen at the synoptic scale (5-9 days) during winter, driven by tropical-extra-tropical teleconnections through the propagation of a baroclinic wave train-like structure and intrusion of air originating from higher altitude and latitude. delta O-18(v) also reveals a significant diurnal cycle, which reflects mixing process between the boundary layer and the free atmosphere during the dry season, and records the propagation of density currents associated with meso-scale convective systems during the monsoon season. Citation: Tremoy, G., F. Vimeux, S. Mayaki, I. Souley, O. Cattani, C. Risi, G. Favreau, and M. Oi (2012), A 1-year long delta O-18 record of water vapor in Niamey (Niger) reveals insightful atmospheric processes at different timescales, Geophys. Res. Lett., 39, L08805, doi:10.1029/2012GL051298

Black carbon emission and deposition fluxes reconstructed from shallow Illimani firn core (Bolivia)

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Origin and fate of hydrothermal fluids at Piton des Neiges volcano (Réunion Island): A geochemical and isotopic (O, H, C, Sr, Li, Cl) study of thermal springs

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