Three-year assessment of particulate organic carbon fluxes in Amundsen Gulf (Beaufort Sea): Satellite observations and sediment trap measurements

Surface concentrations and vertical fluxes of particulate organic carbon (POC) were assessed in the Amundsen Gulf (southeastern Beaufort Sea, Arctic Ocean) over the years 2004 to 2006 by using ocean color remote-sensing imagery and sequential sediment traps moored over the ca. 400 m isobath. Environmental conditions (sea ice, wind) and oceanographic variables (temperature, salinity, fluorescence and currents) were investigated to explain the variability of POC data. Annual downward POC fluxes in 2004, 2005 and 2006 cumulated, respectively, to 3.3, 4.2 and 6.0 g C m^?2 yr^?1 at ～100 m depth, and to 1.3, 2.2 and 3.3 g C m^?2 yr^?1 at ～210 m depth. The fraction of settling POC attributable to autochthonous processes occurring at or next to ice break-up was estimated to be 75–84% of the 100 m annual fluxes and to be 61–75% of the 210 m fluxes. Over the three ice-reduced seasons, distinct scenarios between ice conditions, surface POC pools and vertical POC export at 100 m were identified: (1) in 2004, despite a normal ice break-up, a weak primary production was measured and low vertical fluxes were collected as old ice moved across the region; (2) in 2005, a lengthened ice-free period allowed an extended season of surface POC production near-shore, while an intermediate increase of vertical fluxes was recorded offshore; and (3) in 2006, a late ice melt gave rise to a pulsed ice edge bloom and to large vertical fluxes also associated with extra ice-flushed material. Linear regressions of vertical POC fluxes against satellite-derived surface POC concentrations suggested that the pelagic POC retention in the upper 100 m of the Amundsen Gulf ranged from ca. 70% to 90% depending on the timing of ice cover melt. Regardless of the inter-annual variability, the estimated fraction of the surface POC reservoir reaching the 210 m water depth was reduced to ～5%. Therefore, as the Arctic Ocean warms up, our results support the expectation that the increasing extent of the seasonal ice zone will promote the POC pathways that benefit pelagic webs rather than benthic communities.     

Mechanisms of melt extraction during lower crustal partial melting

Progressive vapour‐absent partial melting of a closed rock system increases melt pressure due to an expansion in the volume of the mineral plus melt assemblage. For a locally closed system, we quantify the melt pressure increase per increment of partial melting of a metapelite using phase equilibria modelling and combine it with Mohr–Coulomb theory to examine the interplay between melt pressure and fracture behaviour. It is shown that very small increments of vapour‐absent partial melting (<1%) increase melt pore pressure by tens of MPa leading to inevitable brittle failure of locally closed systems. Fracturing will affect these systems, even if initially limited to the scale of a few grains, and a connected microfracture network will enhance permeability as partial melting progresses. This will lead to a conditionally open system, potentially limiting accumulation of melt in the source. Repeated and cyclic fracture as temperature progressively increases will drive migration of the melt into sites of low fluid pressure at all scales. Crystal‐plastic creep processes create deformation‐induced dilatancy gradients that dominate over buoyancy forces at all scales in the melt source. Brittle and ductile deformation therefore cooperate in the extraction of melt. Enhanced porosity and permeability in ductile shear zones result in lower fluid pressure, providing a potentially important driving force for melt migration and drainage ‘up’ shear zones and along larger scale fluid pressure gradients in the crust.     

Microbial diversity in contaminated soils along the T22 trench of the Chernobyl experimental platform

The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of ¹³⁷Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity.     

Redacted in Nebraska: the noises of conspiracy around nuclear power problems

This paper investigates a ‘small story’, the problems around the Fort Calhoun nuclear power plant (Nebraska) in the wet summer of 2011. Relying on materials from digital media, it presents the official and an alternative version of events. Utilizing a constructionist approach, it identifies the search for moral certainty, as well as the importance of blame and conspiracy theories, from which emerges the ‘big story’. Highlighting the important role of on-line media and digital communication, we document not only the official story but also an opposing version based on a coherent worldview emphasising the problems of big government, liberal views and denial of American individual rights—all framed as a conspiracy covering-up a threatening, human-made technology failure. We suggest why this worldview occurs, stressing a widespread emphasis on American values and history, ‘failed journalism’, public uncertainty, the complexity of nuclear technology, and the specific uses of digital communication.     

Longevity and progressive abandonment of the Rocky Flats surface, Front Range, Colorado

The post-orogenic evolution of the Laramide landscape of the western U.S. has been characterized by late Cenozoic channel incision of basins and their adjacent ranges. One means of constraining the incision history of basins is dating the remnants of gravel-capped surfaces above modern streams. Here, we focus on an extensive remnant of the Rocky Flats surface between Golden and Boulder, Colorado, and use in situ-produced ¹⁰Be and ²⁶Al concentrations in terrace alluvium to constrain the Quaternary history of this surface. Coal and Ralston Creeks, both tributaries of the South Platte River, abandoned the Rocky Flats surface and formed the Verdos and Slocum pediments, which are cut into Cretaceous bedrock between Rocky Flats and the modern stream elevations. Rocky Flats alluvium ranges widely in age, from > 2 Ma to  400 ka, with oldest ages to the east and younger ages closer to the mountain front. Numerical modeling of isotope concentration depth profiles suggests that individual sites have experienced multiple resurfacing events. Preliminary results indicate that Verdos and Slocum alluvium along Ralston Creek, which is slightly larger than Coal Creek, is several hundred thousand years old. Fluvial incision into these surfaces appears therefore to progress headward in response to downcutting of the South Platte River. The complex ages of these surfaces call into question any correlation of such surfaces based solely on their elevation above the modern channel.     

Use of continuous measurements of dissolved organic matter fluorescence in groundwater to characterize fast infiltration through an unstable fractured hillslope (Valabres rockfall, French Alps)

Continuous measurements of natural fluorescence of dissolved organic matter (DOM) in groundwater have been used to characterize infiltration through an unstable fractured hillslope at the event time scale. Within the gneissic Valabres rockfall area in the southern French Alps, two sites, in the unstable massif and in the collapse area, were continuously monitored for electrical conductivity and for DOM natural fluorescence using a field fluorometer, and analyzed weekly for hydrochemical data. Two main results were found. From a methodological point of view, DOM natural fluorescence was a relevant tracer of fast infiltration in fissured media, knowing that continuous measurements improved the study of infiltration processes at the event time scale. From a hydrogeological point of view, the unstable fractured massif showed delayed dilution phenomena and the collapse areas showed fast and slow infiltration by piston-type flows via more or less open fractures. Consequently, from this conceptual model one may suppose that, unlike the collapse zones, the fractured hillslope threatening the valley is not submitted to strong pore-water pressure variations.     

Precipitation retrieval from space: An overview

During the last decade, satellite observations have allowed significant advances in quantifying precipitation, especially with the contribution of the TRMM mission. Observations at different wavelengths (visible, infrared, and microwaves), in both active and passive microwave modes, are analyzed, and eventually coupled to produce records of precipitation estimates over the globe, with up to hourly time sampling. This article provides an overview of the techniques, the results and the perspectives.     

Uncertainty analysis of statistical downscaling models using Hadley Centre Coupled Model

Regression-based statistical downscaling is a method broadly used to resolve the coarse spatial resolution of general circulation models. Nevertheless, the assessment of uncertainties linked with climatic variables is essential to climate impact studies. This study presents a procedure to characterize the uncertainty in regression-based statistical downscaling of daily precipitation and temperature over a highly vulnerable area (semiarid catchment) in the west of Iran, based on two downscaling models: a statistical downscaling model (SDSM) and an artificial neural network (ANN) model. Biases in mean, variance, and wet/dry spells are estimated for downscaled data using vigorous statistical tests for 30 years of observed and downscaled daily precipitation and temperature data taken from the National Center for Environmental Prediction reanalysis predictors for the years of 1961 to 1990. In the case of daily temperature, uncertainty is estimated by comparing monthly mean and variance of downscaled and observed daily data at a 95 % confidence level. In daily precipitation, downscaling uncertainties were evaluated from comparing monthly mean dry and wet spell lengths and their confidence intervals, cumulative frequency distributions of monthly mean of daily precipitation, and the distributions of monthly wet and dry days for observed and modeled daily precipitation. Results showed that uncertainty in downscaled precipitation is high, but simulation of daily temperature can reproduce extreme events accurately. Finally, this study shows that the SDSM is the most proficient model at reproducing various statistical characteristics of observed data at a 95 % confidence level, while the ANN model is the least capable in this respect. This study attempts to test uncertainties of regression-based statistical downscaling techniques in a semiarid area and therefore contributes to an improvement of the quality of predictions of climate change impact assessment in regions of this type.