Dating bedrock gorge incision in the French Western Alps (Ecrins-Pelvoux massif) using cosmogenic 10Be

We report in-situ produced ¹⁰Be data from the Gorge du Diable (French Western Alps) to date and quantify bedrock gorge incision into a glacial hanging valley. We sampled gorge sidewalls and the active channel bed to derive both long-term and present-day incision rates. ¹⁰Be ages of sidewall profiles reveal rapid incision through the late Holocene (ca 5 ka) at rates ranging from 6.5 to 13 mm yr⁻¹. Present-day incision rates are significantly lower and vary from 0.5 to 3 mm yr⁻¹ within the gorge. Our data imply either delayed initiation of gorge incision after final ice retreat from internal Alpine valleys at ca 12 ka, or post-glacial surface reburial of the gorge. Our results suggest that fluvial incision rates >1 cm yr⁻¹ into crystalline bedrock may be encountered in transient landscape features induced by glacial-interglacial transitions.     

Environmental conservation and the production of new territories: the example of French départements

Very important initiatives have been taken and policies have been adopted in the European Union to protect areas of great importance for threatened species and habitats. Protected areas differ broadly in terms of category, natural conditions and administrative organisation, from international initiative such as Biosphere Reserves, European ones with Natura 2000 network until the institution of national and regional protected areas. In France, the administrative subdivisions known as “départements” were created with the French Revolution in the end of the eighteenth century; in 1985 an original and autonomous procedure to establish special protected areas, called “Sensitive Natural Spaces” (SNS) was devolved to them. The scope of this paper is to present an overview of these devolved powers which enable French départements to create protected areas and to levy a departmental tax on sensitive natural spaces (DTSNS). We statistically studied some parameters by multivariate methods in order to explain the choices of this policy by the départements. The huge variations in the way these powers are implemented prove the development of new environmental territories.     

Bioturbation, short-lived radioisotopes, and the tracer-dependence of biodiffusion coefficients

Bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity. It is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes. In models, bioturbation is usually treated as a diffusive process where the biodiffusion coefficient (D_b) characterizes the biological mixing intensity. Biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle-bound radioisotopes. One peculiar observation is tracer-dependence: D_b values from short-lived tracers tend to be larger than those obtained from long-lived tracers from the same site. Recent theoretical work, based on random walk theory and Lattice Automaton Bioturbation Simulations (LABS), has suggested that this tracer-dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short-lived radioisotopes. Here we have compiled a global dataset of D_b values obtained from different radiotracers to assess tracer-dependence from a data perspective. Tracer-dependence is significant in low-mixing environments like slope and deep-sea sediments, but is not present in intensely mixed coastal areas. Tracer-dependence is absent when the number of mixing events is larger than 20, or the potential length scale is greater than 0.5 cm. Roughly this comes down to tracer-derived D_b values greater than 2 cm² yr⁻¹. This condition is met for 68%, 50%, and 8% of published D_b values obtained from coastal, continental slope, and abyssal environments, respectively. These results show that short-lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation.     

Interaction between tectonic and erosion processes on the morphogenesis of an Alpine valley: geological and geophysical investigations in the lower Romanche valley (Belledonne massif, western Alps)

In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides, from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone (SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited structures, the BMF and the SFZ.     

Spline models of contemporary, 2030, 2060 and 2090 climates for Mexico and their use in understanding climate-change impacts on the vegetation

Spatial climate models were developed for México and its periphery (southern USA, Cuba, Belize and Guatemala) for monthly normals (1961–1990) of average, maximum and minimum temperature and precipitation using thin plate smoothing splines of ANUSPLIN software on ca. 3,800 observations. The fit of the model was generally good: the signal was considerably less than one-half of the number of observations, and reasonable standard errors for the surfaces would be less than 1°C for temperature and 10–15% for precipitation. Monthly normals were updated for three time periods according to three General Circulation Models and three emission scenarios. On average, mean annual temperature would increase 1.5°C by year 2030, 2.3°C by year 2060 and 3.7°C by year 2090; annual precipitation would decrease ?6.7% by year 2030, ?9.0% by year 2060 and ?18.2% by year 2090. By converting monthly means into a series of variables relevant to biology (e. g., degree-days > 5°C, aridity index), the models are directly suited for inferring plant–climate relationships and, therefore, in assessing impact of and developing programs for accommodating global warming. Programs are outlined for (a) assisting migration of four commercially important species of pine distributed in altitudinal sequence in Michoacán State (b) developing conservation programs in the floristically diverse Tehuacán Valley, and (c) perpetuating Pinus chiapensis, a threatened endemic. Climate surfaces, point or gridded climatic estimates and maps are available at http://forest.moscowfsl.wsu.edu/climate/.     

Using climate information for supporting climate change adaptation in water resource management in South Africa

Water resources, and in particular run-off, are significantly affected by climate variability. At present, there are few examples of how the water management sector integrates information about changing intra-annual climate conditions in a systematic manner in developing countries. This paper, using the case study of Cape Town in the Western Cape, South Africa, identifies processes and products to facilitate increased uptake of seasonal climate forecasts among water resource managers. Results suggest that existing seasonal forecasts do not focus enough on specific users’ needs. In order to increase uptake, forecasts need to include information on the likely impact of precipitation variability on runoff and water availability. More opportunities are also needed for those with climate knowledge to interact with water resource managers, particularly in the developing country context where municipal managers’ capacity is strained. Although there are challenges that need to be overcome in using probabilistic climate information, seasonal forecast information tailored to the needs of water resource planners has the potential to support annual planning and is therefore a means of adapting to climate change.     

First insights into the structure and environmental setting of cold-seep communities in the Marmara Sea

A brackish-water cold seep on the North Anatolian Fault (NAF) in the Marmara Sea was investigated with the Nautile submersible during the MarNaut cruise in 2007. This active zone has already been surveyed and revealed evidence of active seeping on the seafloor, such as bubble emissions, patches of reduced sediments, microbial mats and authigenic carbonate crusts. MarNaut was the first opportunity to sample benthic communities in the three most common microhabitats (bioturbated and reduced sediments, carbonate crust) and to examine their relationships with environmental conditions. To do so, faunal communities were sampled and chemical measurements were taken close to the organisms. According to diversity indices, the bioturbated microhabitat exhibited the highest taxonomic diversity and evenness despite a lower number of samples. Conversely, the reduced sediment microhabitat exhibited the lowest taxonomic diversity and evenness. The carbonate crust microhabitat was intermediate although it had the highest biomass. Multivariate analyses showed that (1) fauna were relatively similar within a single microhabitat; (2) faunal community structure varied greatly between the different microhabitats; (3) there was a link between faunal distribution and the type of substratum; and (4) chemical gradients (i.e. methane, oxygen and probably sulphides) may influence faunal distribution. The estimated fluid flow velocity (0.4–0.8 m/yr) confirmed the presence of fluid emission and provided evidence of seawater convection in the two soft-sediment microhabitats. Our results suggest that the reduced sediments may represent a harsher environment with high upward fluid flow, which restrains seawater from penetrating the sediments and inhibits sulphide production, whereas bioturbated sediments can be viewed as a bio-irrigated system with sulphide production occurring at greater depths. Therefore, the environmental conditions in reduced sediments appear to prevent the colonization of symbiont-bearing fauna, such as vesicomyid bivalves, which are more often found in bioturbated sediments. Fluid flow appears to control sulphide availability, which in turn influences the horizontal and vertical distribution patterns of fauna at small spatial scales as observed at other seep sites.     

Mid to Late Holocene hydroclimatic and geochemical records from the varved sediments of East Lake,Cape Bounty,Canadian High Arctic

A long sedimentary sequence from East Lake, Cape Bounty, Melville Island (74°55′N; 109°30′W) contains a 4200 year-long clastic varved record of paleohydrologic variations at high resolution. Sedimentary elemental geochemistry from micro X-ray fluorescence (μ-XRF) and sediment fabric variability reflect changes in sediment sources and lacustrine conditions through time. The sedimentary environment progressed from marine in the mid-Holocene, to estuarian from 2195 BC to 243 AD, to fully lacustrine source after 244 AD. Correlation with local meteorological data indicates that varve thickness (VT) is positively correlated with snow depth on May 1st and negatively correlated with mean Sept–May temperatures. Our paleoclimatic reconstruction from VT series revealed high snow accumulation and warm Sept–May months before 1350 BC, and a period of low snow accumulation and cold Sept–May between 1600–1900 AD that may correspond to the Little Ice Age. The general trends of VT series from Cape Bounty are in phase with the δ¹⁸O series in Agassiz Ice Cap, and in anti-phase with the VT series from Lower Murray Lake in the northeastern of Queen’s Elizabeth Islands (QEI). Low mean Arctic temperatures coincide with clusters of high sediment yield events at East, Nicolay and South Sawtooth Lakes, especially during 1600–1750 AD and 1810–1910 AD. The East Lake record also exhibits the signature of the Atlantic Multidecadal Oscillation (AMO) for periods: 600–850 AD, 1400–1550 AD and 1750–1850 AD.     

Mapping Coastal Aquifers by Joint Inversion of DC and TEM Soundings-Three Case Histories

Electrical and electromagnetic methods are well suited for coastal aquifer studies because of the large contrast in resistivity between fresh water-bearing and salt water-bearing formations. Interpretation models for these aquifers typically contain four layers: a highly resistive unsaturated zone; a surficial fresh water aquifer of intermediate resistivity; an underlying conductive, salt water saturated aquifer; and resistive substratum. Additional layers may be added to allow for variations in lithology within the fresh water and salt water layers. Two methods are evaluated: direct current resistivity and time domain electromagnetic soundings. Use of each method alone produces nonunique solutions for resistivities and/or thicknesses of the different layers. We show that joint inversion of vertical electric and time domain electromagnetic soundings produces a more tightly constrained interpretation model at three test sites than is produced by inversion methods applied to each data set independently.     

Error estimation and optimization of gravity surveys1

Gravity data are often acquired over long periods of time using different instruments and various survey techniques, resulting in data sets of non-uniform accuracy. As station locations are inhomogeneously distributed, gravity values are interpolated on to a regular grid to allow further processing, such as computing horizontal or vertical gradients. Some interpolation techniques can estimate the interpolation error. Although estimation of the error due to interpolation is of importance, it is more useful to estimate the maximum gravity anomaly that may have gone undetected by a survey. This is equivalent to the determination of the maximum mass whose gravity anomaly will be undetected at any station location, given the data accuracy at each station. Assuming that the maximum density contrast present in the survey area is known or can be reasonably assumed from a knowledge of the geology, the proposed procedure is as follows: at every grid node, the maximum mass whose gravity anomaly does not disturb any of the surrounding observed gravity values by more than their accuracies is determined. A finite vertical cylinder is used as the mass model in the computations. The resulting map gives the maximum detection error and, as such, it is a worst-case scenario. Moreover, the map can be used to optimize future gravity surveys: new stations should be located at, or near, map maxima. The technique is applied to a set of gravity observations obtained from different surveys made over a period of more than 40 years in the Abitibi Greenstone Belt in eastern Canada.