TRACING BY GRAVITY OF A NARROW BURIED GRABEN STRUCTURE,DETECTED BY SEISMIC REFRACTION,FOR GROUND-WATER INVESTIGATIONS IN NORTH CHILE*

In the Andes mountains of North Chile seismic refraction measurements revealed the existence of a buried graben structure. The special geological environment permitted the deduction, by detailed analyses of diffraction patterns and delayed arrival times, of a low velocity layer underneath a high velocity ignimbritic sheet. The gravity method was chosen as an economic secondary aid to trace the course of the buried structure. This unusual combination of detailed gravity measurements following a general seismic survey was not only successful in detecting and tracing a buried structure, but also provided complementary data about the deeper subsurface conditions.     

The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye

Summary. A palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of Skye, Scotland, by the Sound of Sleat.
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here.     

Hydrogen and helium spectra in large magnetic fields

The energy levels and wave functions of hydrogen and helium atoms in the presence of large (10⁷G) magnetic fields are found by assuming that the eigenvalues and eigenvectors may be approximated by those of a truncated Hamiltonian matrix. In these atoms, fields of this size produce, in addition to the usual Paschen-Back effect, a quadratic Zeeman effect. This contributes an upward shift to the energy of all levels, which at sufficiently high fields dominates the Paschen-Back splitting.The behavior of a number of eigenvalues and wave functions as a function of magnetic field is presented. The effects of the field on the wavelengths and strengths of the components of H and the helium lines 4471, 4026 and 4120 as well as the forbidden 4025 are examined. In hydrogen the lines are split into components attributed to the now nondegenerate transitionsnlm _lnlm_l. In helium forbidden lines are excited, which may develop strengths larger than those of the allowed lines.     

Effects of grazing by Daphnia on algal carotenoids: Implications for paleolimnology

Reverse-phase thin layer chromatography was used to quantify algal carotenoid degradation resulting from grazing by Daphnia magna in suspensions of lyophilized Oscillatoria utermöhlii, O. limnetica, Anabaena flos-aquae and Synechococcus sp. Three samples were removed every 24 h from 0 h to 144 h and the carotenoid, carbon and nitrogen content of the remaining algal-fecal mixture was determined. Grazing by Daphnia reduced carotenoid concentrations by 30%–80% after 144 h, with myxoxanthophyll being the most labile pigment in experiments with filamentous cyanophytes. However, as a group, the carotenoids were more resistant to the combined effects of grazing by Daphnia and bacterial action than were particulate algal carbon (78% to 82% lost by 144 h) or nitrogen (86%–90%) during the period in which easily digestible material remained. The maximal extent of carotenoid enrichment relative to particulate carbon ranged from 150% to 300% of initial pigment concentrations but declined with repeated coprophagy. On the basis of these results and published pigment budgets, we conclude both that fecal transportation of pigments may be an important determinant of carotenoid accumulation rates and that carotenoid stratigraphies should record predator-mediated changes in zooplankton community structure, especially in oligotrophic conditions.     

Saturn's electrostatic discharges: Could lightning be the cause?

It is proposed that Saturn's electrostatic discharges (SED) might be generated in the planet's equatorial atmosphere, perhaps as lightning from a storm system. The 10^h10^m periodicity of the signal envelope duplicates that of Saturn's equatorial jet. The rings shield the atmosphere from solar EUV photons, and thereby substantially reduce the local ionospheric cutoff frequency to allow low-frequency SED to leak out. Many of the unusual properties of SED could be explained in terms of changes in the storm system, the relative spacecraft position in the beaming pattern of the source, local refraction of the signal by the highly disturbed ionosphere, and the influence of the ring particles on the highest frequency component of SED. A comparison of SED with planetary lightning on other planets shows that the two are similar in general character and some time behavior; the power output of SED may be higher than most planetary lightnings but that is unclear because of uncertainties in the measurements and variations in the signal's spectrum. Our simple discussion suggests that lightning could be a viable source for SED and that exotic ring mechanisms are not necessarily required.