Influence of plankton concentration on gametogenesis and spawning of the black lip pearl oyster Pinctada margaritifera in Ahe atoll lagoon (Tuamotu archipelago, French polynesia)

Pearl culture industry represents one of the dominant business sector of French Polynesia. However, it still entirely relies on unpredictable spat collection success. Our aim was to assess the influence of natural plankton concentration fluctuations on maturation and spawning of the black lip pearl oyster Pinctada margaritifera, during a 4months survey conducted in Ahe atoll lagoon. Plankton concentration was assessed by chlorophyll a extraction and by microscope counts while gonadic index, gonado-visceral dry weights and histology were used to measure pearl oysters reproduction activity. We found that (i) plankton concentration fluctuations were mainly related to wind regime, (ii) gametogenesis rate was mainly related to plankton concentration, (iii) spawning occurred when maximal gonad storage was reached, (iv) plankton concentration was the main spawning synchronizing factor. These results contribute explaining P. margaritifera spat collection variability in French Polynesian atoll lagoon.     

Giant gas bubbles in a rheomorphic vent fill at the Las Cañadas caldera,Tenerife (Canary Islands)

During rheomorphism subsequent to fallout deposition, a portion of the densely welded fallout of the La Grieta Member flowed back into the vent from where it was erupted, while the rest of it flowed down the outer slopes of the Las Cañadas caldera in Tenerife. The welded fallout and conduit-vent structure are physically connected and constitute a rare example of this type of deposits rooted to its feeder conduit and exposed in the caldera wall. The lower part of the vent-filling rheomorphic rocks shows gas bubbles and cavities that increase in size (up to 4 m) down vent. Bubbles are deformed against other bubbles, against the steep vent walls, flattened parallel to the flow foliation planes, and elongated parallel to the flow lineation and flow fold axes. The preservation of such giant bubbles, rather than their formation, seems to be a pretty unique feature of the phonolitic products investigated here and it is likely the result of the combination of factors that acted to preserve, in the surrounding of the glass transition interval, the sealing and the late stage cooling of a pressurized system. In addition, strain drop at the base of the vent-filling rheomorphic flow caused by flow stopping against vertical vent walls may have promoted rapid gas exsolution and the formation of large bubbles.     

Trace element geochemistry of K-rich impact spherules from howardites

The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired.The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.     

Chemical composition and evolution of tourmaline-supergroup minerals from the Sb hydrothermal veins in Rožňava area,Western Carpathians,Slovakia

Mineralogy and Petrology - Tourmaline-supergroup minerals are common gangue minerals in Sb-hydrothermal veins on Betliar – Straková, Čučma – Gabriela and...     

Modelling the dynamics of snow cover, soil frost and surface ice in Norwegian grasslands

Studying the winter survival of forage grasses under a changing climate requires models that can simulate the dynamics of soil conditions at low temperatures. We developed a simple model that simulates depth of snow cover, the lower frost boundary of the soil and the freezing of surface puddles. We calibrated the model against independent data from four locations in Norway, capturing climatic variation from south to north (Arctic) and from coastal to inland areas. We parameterized the model by means of Bayesian calibration, and identified the least important model parameters using the sensitivity analysis method of Morris. Verification of the model suggests that the results are reasonable. Because of the simple model structure, some overestimation occurs in snow and frost depth. Both the calibration and the sensitivity analysis suggested that the snow cover module could be simplified with respect to snowmelt and liquid water content. The soil frost module should be kept unchanged, whereas the surface ice module should be changed when more detailed topographical data become available, such as better estimates of the fraction of the land area where puddles may form.     

Etropus crossotus, an annual flatfish species; age and growth of the fringed flounder in South Carolina

Fringed flounder, Etropus crossotus, a small flatfish common along the southeastern coast of the US, were collected along the South Carolina coast in the fall of 1992, and in the North Inlet estuary from August 1992 until July 1994. Standard length was 82% of total length and the relationship between standard length and wet weight showed near-isometric growth with no significant differences between males and females. Dry weight was 21% of wet weight and ash-free dry weight 14% of wet weight with no significant differences between sexes. Daily increments in the sagittal otoliths were used for age determination. No annual structures could be identified. The maximum age was about 14.5 months. Age-at-length was not different between the sexes. The relationship between age and length was exponential, with age (in days) equalling an e power of 4.242 + 0.135 × standard length (in cm). Back-calculated hatch dates and catches of early juveniles indicated a spawning season that lasted from March to October. Females started to be sexually mature at 7 to 7.5 cm standard length, but 50% maturity was reached at 8 to 8.5 cm. Females could grow to that size within one spawning season. Individuals hatched early in the spawning season could produce eggs in the latter portion of that season's spawning period.     

Process-based modeling of the overflow-induced growth of erosional channels

A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a non-cohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the channel growth both vertically and laterally.     

Dissipative MHD solutions for resonant AlfvÉn waves in 1-dimensional magnetic flux tubes

The present paper extends the analysis by Sakurai, Goossens, and Hollweg (1991) on resonant Alfvén waves in nonuniform magnetic flux tubes. It proves that the fundamental conservation law for resonant Alfvén waves found in ideal MHD by Sakurai, Goossens, and Hollweg remains valid in dissipative MHD. This guarantees that the jump conditions of Sakurai, Goossens, and Hollweg, that connect the ideal MHD solutions for _r , andP across the dissipative layer, are correct. In addition, the present paper replaces the complicated dissipative MHD solutions obtained by Sakurai, Goossens, and Hollweg for _r , andP in terms of double integrals of Hankel functions of complex argument of order with compact analytical solutions that allow a straightforward mathematical and physical interpretation. Finally, it presents an analytical dissipative MHD solution for the component of the Lagrangian displacement in the magnetic surfaces perpendicular to the magnetic field lines which enables us to determine the dominant dynamics of resonant Alfvén waves in dissipative MHD.