Mineralogy and chemistry of cobbles at Meridiani Planum, Mars, investigated by the Mars Exploration Rover Opportunity

Numerous loose rocks with dimensions of a few centimeters to tens of centimeters and with no obvious physical relationship to outcrop rocks have been observed along the traverse of the Mars Exploration Rover Opportunity. To date, about a dozen of these rocks have been analyzed with Opportunity’s contact instruments, providing information about elemental chemistry (Alpha Particle X‐ray Spectrometer), iron mineralogy and oxidation states (Mössbauer Spectrometer) and texture (Microscopic Imager). These “cobbles” appear to be impact related, and three distinct groups can be identified on the basis of chemistry and mineralogy. The first group comprises bright fragments of the sulfate‐rich bedrock that are compositionally and texturally indistinguishable from outcrop rocks. All other cobbles are dark and are divided into two groups, referred to as the “Barberton group” and the “Arkansas group,” after the first specimen of each that was encountered by Opportunity. Barberton group cobbles are interpreted as meteorites with an overall chemistry and mineralogy consistent with a mesosiderite silicate clast composition. Arkansas group cobbles appear to be related to Meridiani outcrop and contain an additional basaltic component. They have brecciated textures, pointing to an impact‐related origin during which local bedrock and basaltic material were mixed

Oceanic hindcast simulations at high resolution suggest that the Atlantic MOC is bistable

All climate models predict a freshening of the North Atlantic at high latitude that may induce an abrupt change of the Atlantic Meridional Overturning Circulation (hereafter AMOC) if it resides in the bistable regime, where both a strong and a weak state coexist. The latter remains uncertain as there is no consensus among observations and ocean reanalyses, where the AMOC is bistable, versus most climate models that reproduce a mono-stable strong AMOC. A series of four hindcast simulations of the global ocean at 1/12° resolution, which is presently unique, are used to diagnose freshwater transport by the AMOC in the South Atlantic, an indicator of AMOC bistability. In all simulations, the AMOC resides in the bistable regime: it exports freshwater southward in the South Atlantic, implying a positive salt advection feedback that would act to amplify a decreasing trend in subarctic deep water formation as projected in climate scenarios

Framing, Context, and Methods (Chapter 1)

Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) assesses the current evidence on the physical science of climate change, evaluating knowledge gained from observations, reanalyses, paleoclimate archives and climate model simulations, as well as physical, chemical and biological climate processes. This chapter sets the scene for the WGI Assessment, placing it in the context of ongoing global and regional changes, international policy responses, the history of climate science and the evolution from previous IPCC assessments, including the Special Reports prepared as part of this Assessment Cycle. This chapter presents key concepts and methods, relevant recent developments, and the modelling and scenario framework used in this Assessment

Using eDNA to detect the distribution and density of invasive crayfish in the Honghe-Hani rice terrace World Heritage site

The Honghe-Hani landscape in China is a UNESCO World Natural Heritage site due to the beauty of its thousands of rice terraces, but these structures are in danger from the invasive crayfish Procambarus clarkii. Crayfish dig nest holes, which collapse terrace walls and destroy rice production. Under the current control strategy, farmers self-report crayfish and are issued pesticide, but this strategy is not expected to eradicate the crayfish nor to prevent their spread since farmers are not able to detect small numbers of crayfish. Thus, we tested whether environmental DNA (eDNA) from paddy-water samples could provide a sensitive detection method. In an aquarium experiment, Real-time Quantitative polymerase chain reaction (qPCR) successfully detected crayfish, even at a simulated density of one crayfish per average-sized paddy (with one false negative). In a field test, we tested eDNA and bottle traps against direct counts of crayfish. eDNA successfully detected crayfish in all 25 paddies where crayfish were observed and in none of the 7 paddies where crayfish were absent. Bottle-trapping was successful in only 68% of the crayfish-present paddies. eDNA concentrations also correlated positively with crayfish counts. In sum, these results suggest that single samples of eDNA are able to detect small crayfish populations, but not perfectly. Thus, we conclude that a program of repeated eDNA sampling is now feasible and likely reliable for measuring crayfish geographic range and for detecting new invasion fronts in the Honghe Hani landscape, which would inform regional control efforts and help to prevent the further spread of this invasive crayfish

Seasonal variation in environmental DNA detection in sediment and water samples

The use of aquatic environmental DNA (eDNA) to detect the presence of species depends on the seasonal activity of the species in the sampled habitat. eDNA may persist in sediments for longer than it does in water, and analysing sediment could potentially extend the seasonal window for species assessment. Using the great crested newt as a model, we compare how detection probability changes across the seasons in eDNA samples collected from both pond water and pond sediments. Detection of both aquatic and sedimentary eDNA varied through the year, peaking in the summer (July), with its lowest point in the winter (January): in all seasons, detection probability of eDNA from water exceeded that from sediment. Detection probability of eDNA also varied between study areas, and according to great crested newt habitat suitability and sediment type. As aquatic and sedimentary eDNA show the same seasonal fluctuations, the patterns observed in both sample types likely reflect current or recent presence of the target species. However, given the low detection probabilities found in the autumn and winter we would not recommend using either aquatic or sedimentary eDNA for year-round sampling without further refinement and testing of the methods

Accuracy and performance of optimized Bayesian source separation for hyperspectral unmixing

International audienc

Modifications of gyre circulation by sub-mesoscale physics

The large-scale impacts of sub-mesoscale physics are addressed by comparing mean characteristics of basin-scale, seasonally varying, subtropical and subpolar gyres in a suite of numerical experiments varying in horizontal resolution (1°, 1/9° and 1/54°) and accordingly, in sub-grid scale mixing. After 100 years of simulation, and as suggested from earlier studies, the mean circulation and the mean structure of the ventilated thermocline strongly differ when switching from 1° to 1/9° resolution. Our results emphasize that increasing the resolution from 1/9° to 1/54° leads to major further changes. These changes ensue from the emergence of a denser and more energetic vortex population at 1/54°, occupying most of the basin and sustained by sub-mesoscale physics. Non-linear effects of this turbulence strongly intensify the jet that separates the two gyres, thus steepening the isopycnals and counter-balancing the strong eddy-driven heat transport that tends to flatten them. The jet is more zonal, penetrates further to the east, and is shifted southward by a few degrees, which significantly alters the shape and position of the gyres. The strengthening of the main jet comes together with the emergence of a regime of energetic secondary zonal jets, associated with complex recirculations. In parallel, sub-mesoscales restratify both the seasonal and the main thermocline, inducing in particular a reduction of deep convection and the modification of the water masses involved in the meridional overturing circulation. Although the results presented here are presumably highly constrained by the idealized geometry of our basin, they suggest that sub-mesoscale processes play an important role on the mean circulation and mean transports at the scale of oceanic basins. At the highest resolution presented here (1/54°), momentum effects are becoming important so that eddies do not simply cause the slumping of isopycnals but can arrange the flow to form jet-like structures with steeper isopycnals in places

Applying new spectral unmixing technique to Martian hyperspectral data

International audienc