Uncertainties in European summer precipitation changes: role of large scale circulation

Climate models suggest that anthropogenic emissions are likely to induce an important drying during summer over most of Europe in the late 21st century. However, the amplitude of the associated decrease in precipitation strongly varies among the different climate models. In order to reduce this spread, it is first necessary to identify its causes and the associated physical mechanisms. Consequently, the focus of this paper is to better estimate the role of large scale circulation (LSC) in precipitation changes over Europe using a multi-model framework and then to characterize the LSC changes using the weather regime paradigm. We show that LSC changes directly lead to a decrease of precipitation over northwestern Europe. This circulation-driven decrease in rainfall is mainly linked to an increase (decrease) of the occurrence of positive (negative) phase of the North Atlantic Oscillation regime. LSC is also responsible for a significant part of the models spread in precipitation changes over these regions. Over southern Europe, the role of LSC changes on multi-model mean precipitation changes is generally weak. We also show that the precipitation anomalies directly induced by LSC modifications seem to be further amplified through local feedbacks.     

Internal variability in a regional climate model over West Africa

Sensitivity studies with regional climate models are often performed on the basis of a few simulations for which the difference is analysed and the statistical significance is often taken for granted. In this study we present some simple measures of the confidence limits for these types of experiments by analysing the internal variability of a regional climate model run over West Africa. Two 1-year long simulations, differing only in their initial conditions, are compared. The difference between the two runs gives a measure of the internal variability of the model and an indication of which timescales are reliable for analysis. The results are analysed for a range of timescales and spatial scales, and quantitative measures of the confidence limits for regional model simulations are diagnosed for a selection of study areas for rainfall, low level temperature and wind. As the averaging period or spatial scale is increased, the signal due to internal variability gets smaller and confidence in the simulations increases. This occurs more rapidly for variations in precipitation, which appear essentially random, than for dynamical variables, which show some organisation on larger scales.     

Detection of non-radial pulsation and faint companion in the symbiotic star CH Cyg

We have detected asymmetry in the symbiotic star CH Cyg through the measurement of precision closure phase with the Integrated Optics Near-Infrared Camera (IONIC) beam combiner, at the infrared optical telescope array interferometer. The position of the asymmetry changes with time and is correlated with the phase of the 2.1-year period found in the radial velocity measurements for this star. We can model the time-dependent asymmetry either as the orbit of a low-mass companion around the M giant or as an asymmetric, 20 per cent change in brightness across the M giant. We do not detect a change in the size of the star during a 3-year monitoring period neither with respect to time nor with respect to wavelength. We find a spherical dust shell with an emission size of 2.2 ± 0.1 D _* full width at half-maximum around the M giant star. The star to dust flux ratio is estimated to be 11.63 ± 0.3. While the most likely explanation for the 20 per cent change in brightness is non-radial pulsation, we argue that a low-mass companion in close orbit could be the physical cause of the pulsation. The combined effect of pulsation and low-mass companion could explain the behaviour revealed by the radial velocity curves and the time-dependent asymmetry detected in the closure-phase data. If CH Cyg is a typical long secondary period variable then these variations could be explained by the effect of an orbiting low-mass companion on the primary star.     

Constraints on mantle plumes on Venus: Implications for volatile history

The analysis of Venus’ gravity field and topography suggests the presence of a small number of deep mantle plumes (～9). This study predicts the number of plumes formed at the core–mantle boundary, their characteristics, and the production of partial melt from adiabatic decompression. Numerical simulations are performed using a 3D spherical code that includes large viscosity variations and internal heating. This study investigates the effect of several parameters including the core–mantle boundary temperature, the amount of internal heating, and the mantle viscosity. The smallest number of plumes is achieved when no internal heating is present. However, scaling Earth’s radiogenic heating to Venus suggests a value of ～16 TW. Cases with internal heating produce more realistic lid thickness and partial melting, but produce either too many plumes or no plumes if a high mantle temperature precludes the formation of a hot thermal boundary layer. Mantle viscosity must be reduced to at least 10²⁰ Pa s in order to include significant internal heating and still produce hot plumes. In all cases that predict melting, melting occurs throughout the upper mantle. Only cases with high core temperature (>1700 K) produce dry melting. Over time the upper mantle may have lost significant volatiles. Depending on the water content of the lower mantle, deep plumes may contribute to present-day atmospheric water via volcanic outgassing. Assuming 50 ppm water in mantle, 10 plumes with a buoyancy flux of 500 kg/s continuously erupting for 4 myr will outgas an amount of water on the order of that in the lower atmosphere. A higher level of internal heating than achieved to date, as well as relatively low mantle viscosity, may be required to achieve simulations with ～10 plumes and a thinner lid. Alternatively, if the mantle is heating up due to the stagnant lid, the effect is equivalent to having lower rates of internal heating. A temperature increase of 110 K/byr is equivalent to ?13 TW. This value along with the internal heating of 3 TW used in this study may represent the approximate heat budget of Venus’ mantle.     

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.     

Spectroscopy, morphometry, and photoclinometry of Titan's dunefields from Cassini/VIMS

Fine-resolution (500 m/pixel) Cassini Visual and Infrared Mapping Spectrometer (VIMS) T20 observations of Titan resolve that moon's sand dunes. The spectral variability in some dune regions shows that there are sand-free interdune areas, wherein VIMS spectra reveal the exposed dune substrate. The interdunes from T20 are, variously, materials that correspond to the equatorial bright, 5-μm-bright, and dark blue spectral units. Our observations show that an enigmatic “dark red” spectral unit seen in T5 in fact represents a macroscopic mixture with 5-μm-bright material and dunes as its spectral endmembers. Looking more broadly, similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes. The presence of interdunes indicates that Titan's dunefields are both mature and recently active. The spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of Titan; various organics are consistent with the dunes' measured reflectivity. We measure a mean dune spacing of 2.1 km, and find that the dunes are oriented on the average in an east-west direction, but angling up to 10° from parallel to the equator in specific cases. Where no interdunes are present, we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m. These results pave the way for future exploration and interpretation of Titan's sand dunes.     

The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake,Utah, USA

The Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 ¹⁴C bp ) and the shallow Great Salt Lake (since 11 500 ¹⁴C bp ). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca²⁺, Mg²⁺ and HCO₃^? concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.     

Prediction of the calcium carbonate budget in a sedimentary basin: A “source-to-sink” approach applied to Great Salt Lake,Utah, USA

Most source-to-sink studies typically focus on the dynamics of clastic sediments and consider erosion, transport and deposition of sediment particles as the sole contributors. Although often neglected, dissolved solids produced by weathering processes contribute significantly in the sedimentary dynamics of basins, supporting chemical and/or biological precipitation. Calcium ions are usually a major dissolved constituent of water drained through the watershed and may facilitate the precipitation of calcium carbonate when supersaturating conditions are reached. The high mobility of Ca²⁺ ions may cause outflow from an open system and consequently loss. In contrast, in closed basins, all dissolved (i.e. non-volatile) inputs converge at the lowest point of the basin. The endoreic Great Salt Lake basin constitutes an excellent natural laboratory to study the dynamics of calcium on a basin scale, from the erosion and transport through the watershed to the sink, including sedimentation in lake's waterbody. The current investigation focused on the Holocene epoch. Despite successive lake level fluctuations (amplitude around 10 m), the average water level seems to have not been affected by any significant long-term change (i.e. no increasing or decreasing trend, but fairly stable across the Holocene). Weathering of calcium-rich minerals in the watershed mobilizes Ca²⁺ ions that are transported by surface streams and subsurface flow to the Great Salt Lake (GSL). Monitoring data of these flows was corrected for recent anthropogenic activity (river management) and combined with direct precipitation (i.e. rain and snow) and atmospheric dust income into the lake, allowing estimating the amount of calcium delivered to the GSL. These values were then extrapolated through the Holocene period and compared to the estimated amount of calcium stored in GSL water column, porewater and sediments (using hydrochemical, mapping, coring and petrophysical estimates). The similar estimate of calcium delivered (4.88 Gt) and calcium stored (3.94 Gt) is consistent with the premise of the source-to-sink approach: a mass balance between eroded and transported compounds and the sinks. The amount of calcium deposited in the basin can therefore be predicted indirectly from the different inputs, which can be assessed with more confidence. When monitoring is unavailable (e.g. in the fossil record), the geodynamic context, the average lithology of the watershed and the bioclimatic classification of an endoreic basin are alternative properties that may be used to estimate the inputs. We show that this approach is sufficiently accurate to predict the amount of calcium captured in a basin and can be extended to the whole fossil record and inform on the storage of calcium.     

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ).     

Access routes to high mountain huts facing climate-induced environmental changes and adaptive strategies in the Western Alps since the 1990s

ABSTRACT

In the European Alps, high mountain environments are subject to major impacts resulting from climate change, which strongly affect human activities such as mountaineering. The purpose of the study was to examine changes in access routes to 30 high mountain huts in the Western Alps since the 1990s. Data were derived from the use of two different methods, geo-historical studies and a questionnaire, and were used to identify both the climate-related processes affecting the climbing routes and the strategies implemented by public entities, Alpine clubs, guide companies, and hut keepers to maintain acceptable safety and technical conditions. The case studies revealed issues affecting three access routes and the results from the questionnaire showed that the main processes affecting access routes were loss of ice thickness and retreat from the front of the glaciated areas. Commonly, in situ equipment was installed to facilitate access for mountaineers and/or a part of a route was relocated to a safer area. The authors conclude that in most cases, the measures were effective but they were limited by financial, ethical and legal issues, especially in protected or classified areas that could jeopardise their durability and effectiveness.