Collisional processes in stellar systems

The theory of collisional relaxation in stellar systems is discussed in terms of an expansion in powers of 1/N, the inverse of the total number of stars. The results are expressed in terms of the concept of gravitational polarization.     

The offshore east African rift system: new insights from the Sakalaves seamounts (Davie Ridge,SW Indian Ocean)

The offshore branch of the East African Rift System (EARS) has developed during Late Cenozoic time along the eastern Africa continental margin. While Neogene–Pleistocene extensional tectonic deformation has been evidenced along the northern segment of the Davie Ridge, the spatial extent of deformation further south remains poorly documented. Based on recent and various oceanographic datasets (bathymetric surveys, dredge samples and seismic profiles), our study highlights active normal faulting, modern east–west extensional tectonic deformation and Late Cenozoic alkaline volcanism at the Sakalaves Seamounts (18°S, Davie Ridge) that seem tightly linked to the offshore EARS development. In parallel, rift‐related tectonic subsidence appears responsible for the drowning of the Sakalaves Miocene shallow‐water carbonate platform. Our findings bring new insights regarding the development of the EARS offshore branch and support recent kinematic models proposing the existence of a plate boundary across the Mozambique Channel.     

Geomorphic controls of perched groundwater interaction with natural ridge-top depressional wetlands

Geographically isolated wetlands (GIWs) are commonly reported as having hardpan or low hydraulic conductivity units underneath that produce perched groundwater, which can sustain surface water levels independently of regional aquifer fluctuations. Despite the potential of GIW-perched aquifer systems to provide important hydrological and ecological functions such as groundwater storage and native amphibian habitat, little research has studied the hydrologic controls and dynamics of these systems. We compared several ridge-top depressional GIW-perched groundwater systems to investigate the role of watershed morphology on hydroregime and groundwater-surface water interaction. Ridge-top depressional wetlands in the Daniel Boone National Forest, Kentucky were chosen because they offer natural controls such as lack of apparent connection to surface water bodies, similar climate, and similar soils. Three wetlands with different topographic slopes and hillslope structures were mapped to distinguish key geomorphic parameters and monitored to characterize groundwater-surface water interaction. Wetlands with soil hummocks and low upland slopes transitioned from infiltration to groundwater discharge conditions in the spring and during storm events. The magnitude and duration of this transition fell along a continuum, where higher topographic slopes and steeper uplands produced comparably smaller and shorter head reversals. This demonstrates that ridge-top GIW-perched groundwater systems are largely sensitive to the runoff-recharge relationship in the upland area which can produce significant groundwater storage on a small-scale.     

Trends and low-frequency variability of storminess over western Europe, 1878–2007

This study analyzes extremes of geostrophic wind speeds derived from sub-daily surface pressure observations at 13 sites in the European region from the Iberian peninsula to Scandinavia for the period from 1878 or later to 2007. It extends previous studies on storminess conditions in the Northeast (NE) Atlantic-European region. It also briefly discusses the relationship between storminess and the North Atlantic Oscillation (NAO). The results show that storminess conditions in the region from the Northeast Atlantic to western Europe have undergone substantial decadal or longer time scale fluctuations, with considerable seasonal and regional differences (especially between winter and summer, and between the British Isles-North Sea area and other parts of the region). In the North Sea and the Alps areas, there has been a notable increase in the occurrence frequency of strong geostrophic winds from the mid to the late twentieth century. The results also show that, in the cold season (December–March), the NAO-storminess relationship is significantly positive in the north-central part of this region, but negative in the south-southeastern part.     

Renewed Geoarchaeological Investigations of Mwanganda's Village (Elephant Butchery Site), Karonga,Malawi

The site of Mwanganda's Village, located along a paleochannel in northern Malawi, is one of only a few sites that have characterized the Middle Stone Age (MSA) of Malawi for decades (Clark & Haynes, 1970 ; Clark et al., 1970 ; Kaufulu, 1990 ). The Malawi Earlier‐Middle Stone Age Project has re‐examined the site using new mapping and chronometric tools in order to reinterpret the site's significance within the context of current debates surrounding human origins and the potential role the environment played in shaping human behavior. The new data do not support the previous hypothesis that the site was an elephant butchery location (contra Clark & Haynes, 1970 ; Clark et al., 1970 ; Kaufulu, 1990 ). Instead, the evidence shows successive colonization of riparian corridors by MSA hunter‐gatherers focused on exploiting localized resources during periods of generally humid climates while other lakes desiccated across Africa. We challenge the hypothesis that stable and intermediately high lake levels within the African Rift Valley System (sensu Trauth et al., 2010 ) catalyzed the evolution of regional interaction networks between 42 and 22 ka. Instead, we interpret the evidence to suggest that regional variants of technology persist into the late MSA as foragers focused on exploiting resources from local catchments.     

Nutrient Loading and Transformations in the Columbia River Estuary Determined by High-Resolution In Situ Sensors

The Columbia River estuary is characterized by relatively large tidal currents and water residence times of a few days or less. These and other environmental conditions tend to suppress water column productivity and favor the export of riverborne nutrients to the coastal ocean. However, hotspots of biological activity may allow for significant nutrient transformation and removal within the estuary, but these processes have previously been difficult to quantify due to the challenges of obtaining measurements at appropriate frequency and duration. In this study, nutrient biogeochemical dynamics within the salt-influenced region of the estuary were quantified using high-resolution in situ observations of nutrients and physical water properties. During 2010, three autonomous nutrient sensors (Satlantic SUNA, SubChem Systems Inc. APNA, WET Labs Cycle-PO4) that together measured nitrate?+?nitrite, orthophosphate, ammonium, silicic acid, and nitrite were deployed on fixed observatory platforms. Hourly measurements captured tidal fluctuations and permitted an analysis of river and ocean end-member mixing. The results suggested that during summer, the lower estuary released high concentrations of ammonium and phosphate despite low concentrations in the river and coastal ocean. This was likely a result of organic matter accumulation and remineralization in the estuarine turbidity maximum and the lateral bays adjacent to the main channel.     

Solar Orbiter

The heliosphere represents a uniquely accessible domain of space, where fundamental physical processes common to solar, astrophysical and laboratory plasmas can be studied under conditions impossible to reproduce on Earth and unfeasible to observe from astronomical distances. Solar Orbiter, the first mission of ESA’s Cosmic Vision 2015?–?2025 programme, will address the central question of heliophysics: How does the Sun create and control the heliosphere? In this paper, we present the scientific goals of the mission and provide an overview of the mission implementation.