Dispersive O+ conics observed in the plasma-sheet boundary layer with CRRES/LOMICS during a magnetic storm

We present initial results from the Low-energy magnetospheric ion composition sensor (LOMICS) on the Combined release and radiation effects satellite (CRRES) together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion species (H⁺, He⁺⁺, He⁺, O⁺⁺, O⁺) simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the time resolution afforded by the spacecraft spin period of 30 s. During the geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT to 0816 UT) the LOMICS ion mass spectrometer observed an apparent O⁺ conic flowing away from the southern hemisphere with a bulk velocity that decreased exponentially with time from 300 km/s to 50 km/s, while its temperature also decreased exponentially from 700 to 5 eV. At the onset of the O⁺ conic, intense low-frequency electromagnetic wave activity and strong pitch-angle scattering were also observed. At the time of the observations the CRRES spacecraft was inbound at L\approx7.5 near dusk, magnetic local time (MLT), and at a magnetic latitude of -23°. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary layer (PSBL) when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particle interactions. We are unable to conclude whether the conic was causally associated with spatial structures of the PSBL or the central plasma sheet.     

Tectonic geomorphology of the Ash Hill fault, Panamint Valley, California

ABSTRACT
Panamint Valley, in eastern California, is an extensional basin currently bounded by active, dextral-normal oblique-slip faults. There is considerable debate over the tectonic and topographic evolution of the valley. The least-studied structure, the Ash Hill fault, runs for some 50 km along the valley's western edge, and active strands of the fault continue south into the neighbouring Slate Range. Vertical displacement on the fault is valley-side up, creating topography that conflicts with the gross morphology of the valley itself. We use this topography, along with kinematic and geological markers, to constrain the Quaternary slip rate and orientation of the Ash Hill fault. The fault offsets all but the active channel deposits in the valley, and slickenlines indicate a strike-slip to dip-slip ratio of 3.5:1. An offset volcanic unit dated at 4 Ma provides a minimum slip rate of 0.3±0.1 mm yr⁻¹, and a long-term strike-slip to dip-slip ratio of 5.2:1. Slip on the fault has warped a palaeolake shoreline within the valley. Simple elastic dislocation modelling of the vertical deformation of the shoreline suggests total fault slip of ≈60 m, valley-side up. The shoreline probably dates to 120–150 ka, implying a late Quaternary slip rate of 0.4–0.5 mm yr⁻¹. We suggest two possible mechanisms for the apparently anomalous slip behaviour of the Ash Hill fault. The fault may be a listric structure related to the proposed low-angle fault underlying Panamint Valley. Alternatively, the Ash Hill fault is a high-angle fault, implying that the valley is currently bounded by high-angle dextral-slip faults. Lack of detailed subsurface information precludes any knowledge of the true relationships between the presently active faults.     

Reflectance of amorphous-cubic NH3 frosts and amorphous-hexagonal H2O frosts at 77K from 1400 to 3000Å

The directional hemispherical reflectance of ammonia and water frosts in the range from 1400 to 3000 Å was measured at 77K. Amorphous and cubic ammonia frosts and amorphous and hexagonal water frosts were studied. The amorphous frosts were grown on a liquid-nitrogen (LN₂)-cooled stainless steel substrate until they were optically thick for 3000 Å radiation. For both gases, deposition at 77K and a pressure of 1.0 × 10^?4 torr resulted in an amorphous frost. The cubic ammonia and the hexagonal water frosts were formed by warming their respective amorphous frosts to 180K. The frosts were then recooled to 77K before radiometric data were recorded. Following frost formation, the reflectance was measured for decreasing wavelengths until it fell below two percent. The amorphous and hexagonal water frosts had continuum reflectances above eighty percent for wavelengths between 2300 and 3000 Å and an absorption cutoff near 1800 Å. The hexagonal water frosts showed an absorption feature with a 100 Å half-width at 1959 Å which had not been previously observed. The amorphous and cubic ammonia frosts also had reflectances above 80% for wavelengths between 2300 and 3000 Å, but their absorption cutoff occurred near 2175 and 2075 Å, respectively. Frost thickness ranged from 2 to 5 mm.     

A theoretical study of the ionospheric F region equatorial anomaly—I. Theory

When observed noontime values of the maximum electron density, NMAX(F2), in the ionospheric F2 region are plotted as a function of magnetic latitude, a curve is produced which has two peaks, one on either side of the dip equator at ± 16° dip latitude. This paper theoretically investigates the daily variation of this latitudinal distribution of NMAX(F2) (the so-called Appleton or equatorial anomaly) and specifically attempts to account for the longitudinal differences observed between the American and Asian sectors.Part I outlines the theory involved in solving the time-dependent plasma continuity equation in which production, loss, and transport of ionization are taken into account, where the effects of neutral wind, ambipolar diffusion and $\text{E}\text{×}\text{B}$ drift are included in the transport term. By describing the geomagnetic field in two equivalent ways, $\text{B}\text{= ? ▽γ}$ and $\text{B}\text{= ▽α × ▽β}$, where α, β and γ are known magnetic scalar potentials, the spherical r, θ and φ space coordinates of the continuity equation are transformed to coordinates which define directions parallel and perpendicular to the magnetic field thus putting the equation in a form suitable for numerical integration.     

An Experimental Investigation of the Palatability of Kelp Bed Algae to the Sea Urchin Parechinus angulosus LESKE

Abstract. The relative palatability of 13 algae common in the kelp beds of the west coast of the Cape Peninsula, South Africa, is experimentally investigated with respect to feeding by the sea urchin Parechinus angulosus.
We investigated 2 hypotheses: 1) that this important herbivore would feed selectively on these algae and 2) that Desmarestia firma, one of these algae, would be unattractive to Parechinus on account of the H₂S0₄ in the thallus.
Algal preferences are determined from 3 types of feeding experiment, results of which support our first hypothesis, and allow us to group the algae into 3 arbitrary categories: "preferred", "intermediate", and "non-preferred". To explain these patterns, we measured "relative astringen-cy" of each species (essentially a phenol measurement), and phenol content of 4 species (FOUN-DENIS method). Rates of feeding on single species are negatively correlated with relative astringen-cies (r = 0.76, P = 0.99). The high relative astringency of D. firma is caused by its high (18 % per dry mass) H₂S0₄ content, and it is non-preferred. Our results therefore support our second hypothesis. Other implications of these results are discussed.     

Zooplankton Grazing during Dinoflagel-late Blooms in a Cape Cod Embayment, with Observations of Predation upon Tin-tinnids by Copepods

Abstract. The patterns and rates of feeding by the copepod Acartia hudsonica and larvae of the polychaete Polydora sp. were investigated during the spring in an estuarine embayment. These dominant macrozooplankters fed upon the natural particulate assemblages (predominantly dino-flagellates) spiked with the toxic dinoflagellate Gonyaulax tamarensis. G. tamarensis was ingested by both zooplankters, as was Heterocapsa triquetra , the most abundant alternative food item. Ingestion rates generally increased as dinoflagellate concentrations increased, resulting in a relatively constant (and low) filtration rate for each grazer. Dinophysis acuminata , another dominant dinoflagellate, was essentially ungrazed. Thus, the zooplankters did not ingest one dinoflagellate and consumed others in proportion to their availability but at low rates. Based on these low rates and the small number of A. hudsonica observed during the spring, we infer minima! grazing impact on a 1980 G. tamarensis bloom. In contrast, the impact of polychaete larvae may have been substantial, since their extreme numerical abundance more than compensated for low filtration rates.
In one instance, the tintinnid Eutintinnus pectinis was accidentally included in a grazing experiment. Our ingestion data demonstrate that A. hudsonica , when presented with a combination of tintinnids and several species of phytoplankton (G. tamarensis and D. acuminata) ingested the tintinnids at high rates, in proportion to their high abundance. Since the nanoflagellate Chroomonas amphioxea was found within the loricae of many of the surviving tintinnids, this also provided a qualitative demonstration of the often-hypothesized nanoplankton to tintinnid to copepod link in a marine food chain.     

Metabolism of a model environmental carcinogen by bivalve molluscs

Bivalve molluscs have been used as monitors of marine pollution because they concentrate xenobiotics of many kinds in their tissues. Marine pollutants often produce stress responses such as reduced scope for growth, lysosomal destabilization, altered immune responsiveness and other sequelae. The ability of bivalves to metabolize organic compounds via mixed-function oxygenases (MFO) was demonstrated by the epoxidation of aldrin¹ and benzo[a]pyrene (BP);² this work has been corroborated and extended in many subsequent studies. Biotransformation of BP and other environmental procarcinogens can generate either activated or detoxified metabolites. In this paper the BP metabolites produced by digestive gland homogenates of the clam (Mercenaria mercenaria) and the oyster (Crassostrea virginica) are described. Control bivalves produced the proximate carcinogen (BP 7,8-dihydrodiol), as well as various minimally reactive BP diols and monohydroxylated metabolites. Seven days after injection of the potent inducer of mammalian MFO, Aroclor 1254, BP 7,8-diol production was augmented in Mercenaria, and atypical quinones and phenols were seen in both species. However, in the Ames bacterial mutagenicity assay, homogenates from Aroclor-treated clams failed to activate benzo[a]pyrene. The biological significance of BP metabolism in bivalves is unknown; however, it may prove to be a useful index of pollution.     

X-ray tomographic analysis of sediment macrostructure in Eckernförde Bay,western Baltic Sea

X-ray computed tomography analysis of sediment cores from Eckernförde Bay (western Baltic Sea) indicates that the primary macrostructures and sources of physical property variability are feeding pockets and laminae. Burrowing produces easily discernible macrostructures, yet has a nominal effect overall on sediment property variability. Grain-size distribution is a dominant parameter determining the sediment macrostructure—physical property relationship: the largest variation in sediment properties was associated with sandy sediment and the smallest with muds. However, equally significant is the sorting or spatial distribution of grains within a particular sediment horizon, i.e., whether spatially uniform or patchy.