Kappa Distributions: Theory and Applications in Space Plasmas

The plasma particle velocity distributions observed in the solar wind generally show enhanced (non-Maxwellian) suprathermal tails, decreasing as a power law of the velocity and well described by the family of Kappa distribution functions. The presence of non-thermal populations at different altitudes in space plasmas suggests a universal mechanism for their creation and important consequences concerning plasma fluctuations, the resonant and nonresonant wave – particle acceleration and plasma heating. These effects are well described by the kinetic approaches where no closure requires the distributions to be nearly Maxwellian. This paper summarizes and analyzes the various theories proposed for the Kappa distributions and their valuable applications in coronal and space plasmas.     

Air temperature trend and the impact on winter wheat phenology in Romania

Air temperature variability and trends in Romania were analysed using monthly, seasonal, and annual datasets. Temperature data of winter wheat season were also analysed. The Mann-Kendall test, Sen’s slope estimate, the sequential version of the Mann-Kendall test, the Pettitt test and spatial and temporal hierarchical cluster analyses were used. First, the datasets were checked for changing points. The 106-year period was divided into two long periods of 100 years each to verify the importance of a very short interval in changing of general trends; after that it was divided into three shorter periods of 35–36 years each. The main conclusions are as follows: the 6 years making up the difference between the two long periods are very important in the context of the recent global warming; the three shorter periods analysis indicate some fluctuations rather than continuous warming. The latest short period is the most relevant for global warming. Spatial hierarchical cluster analysis indicated the existence of two distinctive groups. One of them, which includes stations in the south-east part of the country, seems to be influenced by the Black Sea surface temperature. Temporal hierarchical cluster analysis reveals that annual data series have the closest relation with the summer data series. Further, the impact of temperature changes on winter wheat phenology was determined using a phenology simulation performed with the model from the Decision Support System for Agrotechnology Transfer v. 4.0.2.0 platform. Earlier occurrences of anthesis and maturity were noticed for several regions in the country.     

Subduction, collision and initiation of hominin dispersal

Subduction is the main driving force of plate tectonics controlling the physiography of the Earth. The northward subduction of the Sinai plate was interrupted during the Early Pleistocene when the Eratosthenes Seamount began to collide with the Cyprian arc. A series of synchronous structural deformations was triggered across the entire eastern Mediterranean, and local topography was drastically accentuation along the Levantine corridor – one of the main pathways of hominin dispersal out of Africa. However, the choice of this preferred pathway and timing of dispersal has not been resolved. Though causes for dispersal out of Africa are in debate, we show that the transition from subduction to collision in the eastern Mediterranean set the route.     

Loggerhead sea turtles (Caretta caretta) as bioturbators in neritic habitats: an insight through the analysis of benthic molluscs in the diet

Molluscs are a diverse and ubiquitous group of organisms which contribute to the formation of biogenic sediments and are one of the major prey taxa for the neritic‐stage loggerhead sea turtles (Caretta caretta) worldwide. Here we investigated to what degree molluscs contribute to the diet of individual turtles, and what role the feeding strategy of loggerheads might play in bioturbation, one of the key processes in nutrient transport in marine ecosystems. We performed a detailed analysis of benthic molluscs from the digestive tracts of 62 loggerhead sea turtles (curved carapace length: 25.0–85.4 cm) found in the Northern Adriatic Sea. From 50 of the turtles that contained benthic molluscs, we identified 87 species representing 40 families and three classes (Gastropoda, Bivalvia and Scaphopoda), including 72 new dietary records for loggerhead turtle. Most of the identified molluscs were small‐sized species (shell length ≤ 3 cm) and were often found in a subfossil condition. Their intake may be considered a byproduct of infaunal mining, while larger molluscs were mainly found crushed into smaller fragments. Through such foraging behaviour loggerheads actively rework sediments, increase the surface area of shells and the rate of shells disintegration, acting as bioturbators in this system. We conservatively estimate that loggerheads in the neritic zone of the Adriatic Sea bioturbate about 33 tonnes of mollusc shells per year, and hypothesize about the possible effects of bioturbation reduction on environmental changes in the Northern Adriatic ecosystem.     

Ra and Th adsorption coefficients in lakes—Lake Kinneret (Sea of Galilee) “natural experiment”

The adsorption rate constants of Ra and Th were estimated from empirical data from a freshwater lake and its feeding saline springs. We utilized the unique setting of Lake Kinneret (Sea of Galilee, northern Israel) in which most of the Ra and Th nuclides are introduced into the lake by saline springs with high ²²⁶Ra activities and a high ²²⁴Ra/²²⁸Ra ratio of 1.5. The mixing of the Ra enriched saline waters and freshwater in the lake causes the ²²⁴Ra/²²⁸Ra ratio to drop down to 0.1 in the Kinneret due to preferential adsorption of ²²⁸Th. These conditions constitute a “natural experiment” for estimating adsorption rates. We developed a simple mass-balance model for the radionuclides in Lake Kinneret that accurately predicted the Ra isotope ratios and the ²²⁶Ra activity in the lake. The model is comprised of simultaneous equations; one for each radionuclide. The equations have one input term: supply of radionuclides from the saline springs; and three output terms: adsorption on particles in the lake, radioactive decay and outflow from the lake. The redundancy in the analytical solutions to the mass balance equations for the relevant nuclides constrained the values of Ra and Th adsorption rate constants to a very narrow range. Our results indicate that the adsorption rate constant for Ra is between 0.005 d⁻¹ and 0.02 d⁻¹. The rate constant for Th is between 0.5 d⁻¹ and 1 d⁻¹, about fifty to a hundred times higher. The estimated desorption rate coefficient for Ra is about 50-100 times larger than its adsorption rate constant. The mass-balance equations show that the residence times of all Ra isotopes (²²⁶Ra, ²²⁸Ra,²²³Ra, ²²⁴Ra) and of ²²⁸Th in the lake are about 95, 92, 14, 6 and 1 d, respectively. These residence times are much shorter than the residence time of water in the lake (about 5.5 y). The steady state activity ratios in Lake Kinneret depend mainly on the adsorption rate constants, decay constants, the outflow rate from the lake and the activity ratios in the saline springs. The activity ratios are independent of the saline springs flow rate.     

Copper complexing capacity of seawater: A critical appraisal of the direct ASV method

The break-point in the Cu(II) titration curve obtained by anodic stripping voltammetry (ASV) is usually attributed to the formation of strong organo-copper complexes. This interpretation is the basis for the direct determination by ASV of the copper complexing capacity of natural waters. The present study suggests, however, that the break in the Cu(II) titration curve in seawater, as determined by ASV, could be due to the formation of a ZnCu intermetallic compound (IC) formed in the mercury during the deposition stage of the ASV procedure.     

Hydrogeological modeling as a tool supporting the interpretation of pollen proxies for palaeoclimate reconstitution: The Senegalese “niayes” case-study

The Niayes of Senegal are sahelian interdunal fens, that hosted an azonal subguinean vegetation during the Holocene thanks to the availability of fresh groundwater despite contrasted climatic conditions. Exploratory scenario-based modeling of the zonal hydrogeology has been conducted for different periods with the Cast3M code. The results show that the delay in the onset of humid vegetation ca. 10 ky cal. BP could be ecosystemic and denote a start of the African Humid Period (AHP) ca. 11.5 ky cal. BP. Alternatively, the AHP could have started earlier while its beneficial effects would have been canceled by low sea levels. Vegetation degradation around 7.5 ky cal. BP is shown to have resulted from a climate minoration, that possibly alleviated until 4 ky cal. BP. The rising watertable allowed the degraded forest to persist during that period however. The forest expansion that followed ca. 3.5 ky cal. BP had then clearly a climatic origin. The interpretation of pollens for climate research requires a careful filtering-out of local groundwater availability.     

Biased monitoring of fresh water-salt water mixing zone in coastal aquifers

In coastal aquifers, significant vertical hydraulic gradients are formed where fresh water and underlying salt water discharge together upward to the seafloor. Monitoring boreholes may act as "short circuits" along these vertical gradients, connecting between the higher and the lower hydraulic head zones. When a sea tide is introduced, the fluctuations of both the water table and the depth of the mixing zone are also biased due to this effect. This problem is intensified in places of long-screen monitoring boreholes, which are common in many places in the world. For example, all approximately 500 boreholes of the fresh water-salt water mixing zone in the coastal aquifer of Israel are installed with 10 to 50 m long screens. We present field measurements of these fluctuations, along with a three-dimensional numerical model. We find that the in-well fluctuation magnitude of the mixing zone is an order of magnitude larger than that in the porous media of the actual aquifer. The primary parameters that affect the magnitude of this bias are the anisotropy of the aquifer conductivity and the borehole hydraulic parameters. With no sea tide, borehole interference is higher for the anisotropic case because the vertical hydraulic gradients are high. When tides are introduced, the amplitude of the mixing zone fluctuation is higher for the isotropic case because the overall effective hydraulic conductivity is greater than the conductivity in the anisotropic case. In the aquifer, the fresh water-salt water mixing zone fluctuations are dampened, and tens of meters inland from the shoreline, the fluctuations are on the order of few centimeters.     

Étude de la variation spatio-temporelle des paramètres physico-chimiques caractérisant la qualité des eaux d'une lagune côtière et ses zonations écologiques : cas de Moulay Bousselham,Maroc

Our interest is related to the hydrological characteristics of the Moulay Bousselham lagoon. Water samples were taken monthly from July 2001 to June 2002 in 15 stations distributed along the lagoon. The various measured hydrological parameters (temperature, salinity, suspended matter, chlorophyll a) showed significant monthly variations ($p<0.001$), whereas spatially among all sampled stations, only the salinity showed significant variations. The variability analysis approached by the analysis of the normalized principal components combined with discriminate analysis showed very small inter-stations variability. Its percentage is 11% and 9% of the total variance during high and low tide, respectively. To cite this article: H. Labbardi et al., C. R. Geoscience 337 (2005).