Atmospheric and oceanic stable isotope signatures of a cold-air outbreakin Iceland during YOPP SOP1 and IGP

Publisher's version (útgefin grein)North-Atlantic Cold-air outbreaks are weather events characterised by extensive fluxes of latent heat to theatmosphere. Understanding the water budget of these weather events is important for the weather impact indownstream coastal areas. We use here observations of the stable isotopic composition of water vapour andprecipitation, expressed by the quantities dD, d18O, d17O and the secondary parameters d-excess and 17O-excess,to extract information about the origin and condensation history of water vapour evaporating during a period ofcold-air outbreaks north of IcelandIcelandic research institute (RANNÍS 152229

Archival of the water stable isotope signal in East Antarctic ice cores

The oldest ice core records are obtained from the East Antarctic plateau. Water stable isotopes records are key for reconstructions of past climatic conditions both over the ice sheet and at the evaporation source. The accuracy of such climate reconstructions crucially depends on the knowledge of all the processes affecting the water vapour, precipitation and snow isotopic composition. Atmospheric fractionation processes are well understood and can be integrated in Rayleigh distillation and complex isotope enabled climate models. However, a comprehensive quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing, especially for exchanges between vapour and snow. In low accumulation sites such as found on the East Antarctic Plateau, these poorly constrained processes are especially likely to play a significant role. This limits the interpretation of isotopic composition from ice core records, specifically at short time scales. Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from various sites of the East Antarctic Plateau. At the seasonal scale, we highlight a significant impact of metamorphism on surface snow isotopic signal compared to the initial precipitation isotopic signal. In particular, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five East Antarctic sites, we identify a common 20 cm cycle which cannot be attributed to the seasonal variability of precipitation. Altogether, the smaller range of isotopic compositions observed in the buried and in the surface snow compared to the precipitation, and also the reduced slope between surface snow isotopic composition and temperature compared to precipitation, constitute evidences of post-deposition processes affecting the variability of the isotopic composition in the snow pack. To reproduce these processes in snow-models is crucial to understand the link between snow isotopic composition and climatic conditions and to improve the interpretation of isotopic composition as a paleoclimate proxy

Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters

The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and O-17-excess) are related to delta O-18 and how they are controlled. d-excess increases in the interior of the continent (i.e., when delta O-18 decreases), due to the distillation process, whereas O-17-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the delta O-18 vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between delta O-18 and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to delta O-18 in most snow pits, the O-17-excess is no longer positively correlated to delta O-18 and even shows anti-correlation to delta O-18 at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes

The Incidence of AIDS-Defining Illnesses at a Current CD4 Count ≥200 Cells/µL in the Post-Combination Antiretroviral Therapy Era

The incidence of AIDS was higher in patients with a current CD4 count of 500-749 cells/µL compared to 750-999 cells/µL, but did not decrease further at higher CD4 levels. Results were similar in those virologically suppressed on combination antiretroviral therapy, suggesting immune reconstitution is incomplete until CD4 >750/µ

The Ancient Egypt, a civilization in front of a climatic change : the isotopic message of mummified living tissues

L'Egypte, territoire aride, dépend essentiellement du Nil pour l'irrigation de ses terres agricoles. La variabilité temporelle de la crue du fleuve a donc pu affecter directement la dynamique de la population égyptienne. Ici, cette hypothèse est testée en étudiant la variation du climat pendant l'Egypte ancienne parallèlement à des indicateurs du mode de vie des égyptiens. La variation dans le temps du δ18Ow de l'eau du Nil est reconstituée à partir des valeurs de δ18Op du phosphate de l'apatite de momies égyptiennes. L'augmentation de +3 ‰ du δ18Ow de l'eau du Nil entre la période Prédynastique (5500BP) et la période Gréco-Romaine (2000BP) est causée par une modification des conditions de précipitation au-dessus des sources du Nil. Elle traduit soit une hausse de température proche de 2°C soit une baisse des précipitations mensuelles d'environ 140 mm. Ici, l'hypothèse d'une aridification est privilégiée : en effet des mesures de δ18Op sur des poissons du Nil permettent de calculer une température du Nil à la période Gréco-Romaine comparable à l'actuelle. Le changement climatique constaté semble avoir peu d'impact sur la civilisation égyptienne. En effet la population égyptienne s'accroît nettement pendant la période considérée et le régime alimentaire est resté fondé sur les plantes en C3, peu adaptées aux milieux arides, avec une consommation rare de poissons et de protéines animales. La réduction de la crue a sans doute été compensée par les progrès technologiques de la civilisation égyptienne (chadouf, drainage) qui ont rendu possible la mise en culture de nouvelles terresEgypt is an arid territory, which essentially depends on the Nile river for the irrigation of its agricultural lands. The temporal variability of the river flood thus may have affected directly the dynamics of the Egyptian population. Here, this hypothesis is tested by studying the variation of the climate during Ancient Egypt concurrently to indicators of the life habits of the Egyptians. The variation with time of the δ18Ow of the Nile water is reconstructed from the δ18Op of the apatite phosphate of Egyptian mummies. The increase of +3 ‰ in the Nile water δ18Ow between the predynastic period (5500BP) and the Greco-Roman Period (2000BP) is caused by a change in the conditions of precipitation above the Nile sources. This increase can be the result of an increase in temperature of about +2 °C or of a decrease in the monthly amount of precipitation of about 140 mm. Here, the hypothesis of aridification is preferred: in effect, δ18Op measures on Nile fishes permit to infer a Nile water temperature at the Greco-Roman Period similar to the present-day one. The climatic change seems to have had little impact on the Egyptian civilization. In effect the Egyptian population increases considerably during the selected period and its diet remains funded on C3- plants, feebly adapted to arid environments, with a rare consumption of fishes or other animal protein. The decrease of the flood was admittedly compensated by the technological advances of the Egyptian civilization (shaduf, drainage) which allowed the cultivation of newly reclaimed land

Alimentation et mobilité dans la vallée du Nil, de la Préhistoire au Moyen Âge : perspectives isotopiques

In this article we summarize the isotopic analyses conducted on skeletons and mummies of the Nile Valley from Prehistory to the Middle Ages. This information makes it possible to study the mobility and environment of ancient populations. For example, isotopic ratios determine the proportions of different categories of food consumed by the inhabitants of the Nile Valley, and thus provide additional information compared to other methods. Surprisingly, the results suggest that the Nile fish has contributed little to the diet of the Nubians and Egyptians, regardless of time and social class considered. North/ South disparities exist in the types of cereals consumed along the valley, but records of Nubian diets have frequent spatial and temporal gaps that could be filled in with further studies. Oxygen isotope ratios indicate a gradual decrease in Egyptian rainfalls over time associated with the withdrawal of the monsoon to the South. This climate change, however, does not seem to have had a detrimental impact on agricultural practices in the Nile Valley, which came to be known as " the Granary of Rome" during the Roman Period.Par cet article, nous résumons l’ensemble des analyses isotopiques qui ont été conduites sur des squelettes et des momies de la vallée du Nil, de la préhistoire jusqu’au Moyen-Âge. Ces outils permettent d’étudier l’alimentation, la mobilité et l’environnement des populations anciennes. Les rapports isotopiques permettent par exemple de déterminer les proportions de différentes catégories d’aliments consommés par les habitants de la vallée du Nil, et viennent donc apporter un complément d’information par rapport à d’autres méthodes. De façon surprenante, ils suggèrent que le poisson du Nil a faiblement contribué à la table des Nubiens et des Égyptiens, quel que soit l’époque et la classe sociale considérées. Des disparités nord/ sud sont à relever quant aux types de céréales consommées le long de la vallée, mais l’enregistrement de l’alimentation des Nubiens présente de fréquentes lacunes spatio-temporelles qui pourront être comblées par des études ultérieures. Les rapports isotopiques de l’oxygène soulignent une diminution progressive des précipitations en Égypte au cours du temps, associée au retrait de la mousson vers le sud. Ce changement climatique ne semble cependant pas avoir eu d’impact néfaste sur les pratiques agricoles dans la vallée du Nil, dont la productivité est telle qu’au cours de la période romaine, l’Égypte sera connue sous le nom de «grenier à blé de Rome » .Jaouen Klervia, Touzeau Alexandra. Alimentation et mobilité dans la vallée du Nil, de la Préhistoire au Moyen Âge : perspectives isotopiques. In: Archéo-Nil. Revue de la société pour l'étude des cultures prépharaoniques de la vallée du Nil, n°28, 2018. pp. 43-55

Water isotope measurements from the Marginal Ice Zone and Fram strait during the INTAROS cruise, August 2018

Water vapour stable isotope composition (delta 18-O and delta 2-H) with respect to VSMOW have been measured continuously together with specific humidity, using a ship-mounted infrared spectrometer, during the INTAROS research cruise in August 2018 in the vicinity of Svalbard. In addition, stable water isotopes in precipitation, ocean surface water, and from CTD casts have been gathered at several occasions. The water isotope data are supplemented by continous measurements of meteorological parameters, including ambient pressure, air temperature, relative humidity, cloud height, visibility, wind speed, and wind direction, water temperature. All data have been collected during the INTAROS cruise on board KV Svalbard, lasting from 30 July to 18 August 2018. Water vapour isotope and meteorology data have been averaged at a 1 min resolution. The cruise started and ended at Longyearbyen, Svalbard, Norway, and covered part of the Fram strait to the west of Svalbard, and the Marginal Ice Zone north of the Svalbard Archipelago. A Picarro L2140-i water vapour isotope analyzer was installed onboard KV Svalbard during the INTAROS cruise with a heated inlet system at 10m above the ocean surface, flushed by a manifold pump at about 10 L per minute. Discrete water samples from precipitation were taken on an event basis in an open collector. Ocean surface water samples were taken from a bucket, and samples from CTD casts were taken from Niskin bottles. All liquid samples were analysed for delta 18-O and delta 2-H at FARLAB, University of Bergen, Norway. Data from corresponding CTD casts were used to extract salinity information at the depth of sea water isotope samples (doi:10.21335/NMDC-NERSC-1161526892). Meteorological data from the ship mounted meteorology payload have been provided by Meteorologisk Institutt, Oslo, Norway