Separate and Combined Effects of Estuarine Stress Gradients and Disturbance on Oyster Population Development on Restored Reefs

Disturbance combined with the effects of multiple stress gradients can produce biotic outcomes that are complex and perhaps not predictable based on knowledge of the individual stress variables. We analyzed oyster (Crassostrea virginica) colonization of novel substrate via structural equation modeling (SEM) to test cause-and-effect multivariate models posed a priori as hypotheses. We separately analyzed long-term data on water quality (WQ), canal flow, and rainfall to determine drivers of chlorophyll a for use in the oyster SEM. The best oyster SEM for adult (R ² = 0.74) and small <20-mm (R ² = 0.48) oyster abundances combined WQ stress gradients produced by normal canal flow with disturbance caused by extremely high flow. There was a ?0.26 direct negative effect of increasing salinity during normal canal flow on the small oyster size class possibly reflecting undocumented increases in marine predators and a negative total effect (negative indirect + direct effects) of the salinity gradient on adult oysters. Very low salinity occurring during extreme (disturbance) canal flows produced large negative direct and total effects on small oysters, but no significant total effect for adult oysters. Chlorophyll a (Chl-a) during normal canal flow had negative total effects on small oysters but positive total effects on adult oysters. The effect of max Chl-a on adult oysters was strongly negative during disturbance-level canal flow. Turbidity during normal canal flow had no effect on small or adult oysters. However, during disturbance flows, the maximum turbidity had strong negative effects. Stress and disturbance from freshwater releases impacted oyster recruitment and survival, affecting the colonization and growth of oysters.     

The effects of diagenesis on the redistribution of strontium isotopes in shales

The rubidium-strontium method has often been used in attempts to date shales, but has yielded mixed results. In order to explore the effects of diagenesis on this system, samples of a Miocene shale section collected from an oil well drilled in coastal Louisiana were separated into fractions and analyzed for Sr⁸⁷/Sr⁸⁶, Rb and Sr. The diagenetic changes involve the destruction of detrital mica and feldspar and the formation of an illite-rich clay from smectite. Strontium from interstitial waters, calcium carbonate and adsorbed on the clay minerals is released and then sequestered by the newly forming phases, together with the strontium mobilized from the silicate minerals. Attending these changes there is a trend towards the homogenization of the shale with respect to its strontium isotopes, but diagenesis and homogenization are not complete in the deepest part (5523 m) of the section studied. Therefore, the interpretation of rubidium-strontium shale dates remains uncertain, but the dates in many cases most probably represent the time equal to or younger than the time of the major construction of new phases and the attendant homogenization of the strontium isotopes.     

Do stony meteorites come from comets?

The place of origin of stony meteorites can be determined from their trapped solar-wind gases. “Gas-rich” meteorites have only 10^?3?10^?4 the solar noble gas content and ?10^?2?10^?4 the surface exposure age of lunar soils. These differences suggest that the gas implantation took place between 1 and 8 AU from the Sun, in a region where the cratering rate was 10²?10³ times higher than at 1 AU. Both characteristics point to the asteroid belt. The predicted Ne²⁰ content a gas-rich meteorite formed at 2.5 AU is 1.2 × 10^?5 cc STP g^?1, compared to an observed mean for H-chondrites of 0.5 × 10^?5 cc STP g^?1. The observed prevalence of gas-rich meteorites (40–100% among carbonaceous chondrites, 2–33% among other classes) requires that the parent body remained long enough in the asteroid belt to develop a substantial regolith. This condition can be met by asteroids (～ 10% of mass converted to regolith.in 4.5 × 10⁹ yr), but not by short period comets (～0.04% converted in 10⁷ yr). It appears that a cometary origin can be ruled out for all stony meteorite clases that have gas-rich members. This includes carbonaceous chondrites.     

Precise calculation of the magnetosphere surface for a tilted dipole

The shape of the magnetosphere has been calculated self-consistently for inclinations of the Earth's magnetic dipole from perpendicular to the solar wind. Inclination angles of 0–35° have been chosen in steps of 5° and various smooth trends in the surface characteristics with increasing inclination angle noted. The surface points and the complete field at the surface points have been calculated for the entire surfaces. The neutral point region has been given precise study in one degree steps and is found to be tangent to the solar wind velocity and to have a smooth continuous curvature. The inclusion of the Earth's bow shock pressure and other sources of current have not been included at this stage of our program.     

Magnetic and ionospheric storms

Summary The characteristic ionospheric storm variation of F₂ Layer ionisation at a temperate latitude station is described and compared with corresponding effects at other latitudes. The well known marked variability of the F₂ Layer critical frequency is attributed, in part, to the operation of the ionospheric storm mechanism. The lack of correlation between variations of F₂ ionisation at two sites, at a considerable distance apart, is due to the fact that ionospheric storm manifestation is found to vary, in sign and magnitude, with geomagnetic latitude, and is also subject to a diurnal control determined by local time.

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Zusammenfassung Die charakteristische Ionosphärensturmvariation der Ionisation der F₂-Schicht an einer Station der gemäßigten Breite wird beschrieben und mit entsprechenden Vorgängen in anderen Breiten verglichen. Die bekannte eindeutige Veränderlichkeit der kritischen Frequenz der F₂-Schicht wird teilweise der Wirkung des Mechanismus der Ionosphärenstürme zugeschrieben. Das Fehlen einer Korrelation zwischen den Variationen der F₂-Schicht an zwei in beträchtlicher Entfernung voneinander gelegenen Orten erklärt sich aus der Tatsache, daß das Auftreten der Ionosphärenstürme nach Vorzeichen und Ausmaß mit der geomagnetischen Breite variiert und außerdem einem ortszeitlich bedingten Tageseinfluß unterliegt.

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Résumé On décrit la variation la variation caractéristique d'ionisation de la couche F₂ lors des tempêtes ionosphériques observées à une station de latitude moyenne et on la compare aux phénomènes analogues à d'autres latitudes. La variabilité marquée et bien connue de la fréquence critique de la couche F₂ est partiellement attribuée au mécanisme des tempêtes ionosphériques. L'absence de corrélation entre les variations de la couche F₂ en deux endroits considérablement éloignés l'un de l'autre s'explique par le fait que l'apparition des tempêtes ionosphériques varie en signe et en intensité avec la latitude

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With 4 figures.

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Dedicated to Professor Dr.H. Benndorf on the occasion of his eightieth birthday.