Active tectonic morphology and submarine deformation of the northern Gulf of Eilat/Aqaba from analyses of multibeam data

A high-resolution marine geophysical study was conducted during October-November 2006 in the northern Gulf of Aqaba/Eilat, providing the first multibeam imaging of the seafloor across the entire gulf head spanning both Israeli and Jordanian territorial waters. Analyses of the seafloor morphology show that the gulf head can be subdivided into the Eilat and Aqaba subbasins separated by the north-south-trending Ayla high. The Aqaba submarine basin appears starved of sediment supply, apparently causing erosion and a landward retreat of the shelf edge. Along the eastern border of this subbasin, the shelf is largely absent and its margin is influenced by the Aqaba Fault zone that forms a steep slope partially covered by sedimentary fan deltas from the adjacent ephemeral drainages. The Eilat subbasin, west of the Ayla high, receives a large amount of sediment derived from the extensive drainage basins of the Arava Valley (Wadi ’Arabah) and Yutim River to the north–northeast. These sediments and those entering from canyons on the south-western border of this subbasin are transported to the deep basin by turbidity currents and gravity slides, forming the Arava submarine fan. Large detached blocks and collapsed walls of submarine canyons and the western gulf margin indicate that mass wasting may be triggered by seismic activity. Seafloor lineaments defined by slope gradient analyses suggest that the Eilat Canyon and the boundaries of the Ayla high align along north- to northwest-striking fault systems—the Evrona Fault zone to the west and the Ayla Fault zone to the east. The shelf–slope break that lies along the 100 m isobath in the Eilat subbasin, and shallower (70–80 m isobaths) in the Aqaba subbasin, is offset by approx. 150 m along the eastern edge of the Ayla high. This offset might be the result of horizontal and vertical movements along what we call the Ayla Fault on the east side of the structure. Remnants of two marine terraces at 100 m and approx. 150 m water depths line the southwest margin of the gulf. These terraces are truncated by faulting along their northern end. Fossil coral reefs, which have a similar morphological appearance to the present-day, basin margin reefs, crop out along these deeper submarine terraces and along the shelf–slope break. One fossil reef is exposed on the shelf across the Ayla high at about 60–63 m water depth but is either covered or eroded in the adjacent subbasins. The offshore extension of the Evrona Fault offsets a fossil reef along the shelf and extends south of the canyon to linear fractures on the deep basin floor.     

New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.     

Measurement of seabed sound speeds from head waves in shallow water

Acoustic signals from small explosive charges have been measured with sonobuoys on twelve tracks in Australian northern shallow waters with the aim of assessing whether useful geoacoustic information could be obtained. Using the frequency band from 14 to 70 Hz, travel times of head waves were monitored, and the sound speeds and depths of corresponding interfaces in the seabed were derived. The water sound speed varied a little with range, and its depth dependence was allowed for by using its average value. Head waves from interfaces indistinguishable from the seafloor (the water/seabed interface) were detected on only three of the tracks, with derived sound speeds of 2100 to 2300 m/s. The first sub-bottom interfaces were from 50 to 600 m beneath the seafloor, and their sound speeds ranged from around 2000 m/s to 6400 m/s. Thus the head waves were from chalk or limestone, cemented sediments in which sound-speed gradients would be small. The amount of data obtained for the seafloor was limited by incoherence of the signals and, for some tracks, by excessive spacing between shots. The incoherence is generally attributed to multiple head waves that are individually unresolvable, while on two tracks there were indications of medal ground waves. Occasional anomalous data were obtained, but generally the assumptions of the simple interpretation method were found to be valid. Since no curvature in the range-time lines was observed, there was no evidence of sub-bottom sound-speed gradients being significant     

Glacial Lake Victoria,a high‐level Antarctic Lake inferred from lacustrine deposits in Victoria Valley

We present evidence of a large lake (Glacial Lake Victoria) that existed in Victoria Valley in the dry valleys region of Antarctica between at least 20 000 and 8600 ¹⁴C yr BP. At its highstands, Glacial Lake Victoria covered 100 km² and was ca. 200 m deep. The chronology for lake‐level changes comes from 87 AMS radiocarbon dates of lacustrine algae preserved in deltas and glaciolacustrine deposits that extend up to 185 m above present‐day lakes on the valley floor. The existence of Glacial Lake Victoria, as well as other large lakes in the dry valleys, indicates a climate regime significantly different from that of today at the last glacial maximum and in the early Holocene. Copyright © 2002 John Wiley & Sons, Ltd.     

The Nippon/Norway Svalbard Meteor Radar: First results of small-scale structure observations

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Rainfall interception by trees of Pinus radiata,and Eucalyptus viminalis,in a 1300 mm rainfall area of southeastern New South Wales: I. Gross losses and their variability

Interception loss, I, was determined by continuous concurrent measurements of the canopy precipitation balances of a mature seed orchard tree of Pinus radiata, and a dominant tree of Eucalyptus viminalis at a mountainous high rainfall site (900 m a.s.l.) in Tallaganda State Forest of the Upper Shoalhaven Catchment. Approximate canopy storage capacity (Sc) of the pine was 54 l, and that of the eucalypt was 11·3 l. Gross pine I was 26·5 per cent and eucalypt I was 8·3 per cent of total incident rainfall over a period of 18 months, from June 1975 to December 1976. The exponential model that provided the best fit to overall data relating I to gross rainfall (P_g) was of good precision for the pine (r² = 0·73) but rather poor precision for the eucalypt (r² = 0·27). A consistent pattern in interception data of the two canopy types suggested that variation in I was related to change in pervasive conditions influencing rates of evaporation from wet canopies during rainfall. Multiple regression analyses confirmed that factors such as rainfall intensity and windspeed explained some of the variation in eucalypt I but little in pine I. Negative eucalypt I and corresponding low values of pine I over a wide range of P_g (up to 20 mm) suggest that capture of wind-borne precipitation (cloud, mist, or fog) had also complicated the canopy precipitation balances.     

Geomagnetic secular variation and secular acceleration in the Red Sea area

Summary. Estimates of the secular variation in the Red Sea over the period 1959 to 1972 have been obtained from an analysis of marine magnetic data. A total of 318 crossings of ships' tracks were used to determine the mean secular variation for the intervals 1959–72, 1959–65 and 1965–72. The mean secular variation 1959–72 shows a marked northward increase from approximately -10 nT/yr at 13°N to +27 nT/yr at 24°N. North of this, the data suggest a small decrease to + 25 nT/yr at 27° N. These values are consistent with the secular variation recorded at the nearby geomagnetic observatory at Helwan, Egypt, but less than those predicted by the 1965 IGRF for the same period.
Comparison of the mean secular variations for 1959–65 and 1965–72 yields a rough estimate of the secular acceleration of - 1.5 nT yr⁻². Analysis of the cross-over information, corrected for the latitude dependence of the secular variation, shows a regular decrease in the secular change over the period 1959–72 at all latitudes of about -1 nTyr⁻². This secular acceleration makes a substantial contribution to the overall secular change in the Red Sea and as such must be included in the correction of magnetic data covering more than a few years.     

A study of the long-term variability in radio emission of active galaxies

A long-term study of 13 active galaxies has been carried out at 10.7 GHz over the period September 1980 to April 1982. The sources were observed at approximately monthly intervals and most of them were selected because they are also X-ray sources. The data obtained are used to measure their respective variabilities and to search for any correlations with other source parameters. No obvious relationship to radio or X-ray luminosity was found, though there does appear to be two distinct levels of radio variability for these sources and clear evidence of higher X-ray than radio variability.     

A paleomagnetic study of the Mull lava succession

Summary. A paleomagnetic study has been made of a succession of 139 non-overlapping basaltic lavas, representing 91 per cent of the longest remaining succession of flows associated with the Paleogene Mull volcano. All the lavas have experienced considerable hydrothermal alteration, probably at up to several million years after initial magnetization and frequently with alteration to the opaque minerals and the production of new potentially magnetic phases. The question of whether directional remagnetization has taken place while preserving within-unit directional consistency and discreteness of unit mean direction is discussed. Extensive directional remagnetization is excluded as an explanation for the data. If stable directions obtained by alternating field remanence cleaning coincide with original TRM directions then a mean pole position for all temporally independent lava directions from the British Tertiary igneous province is at 71.9° N, 167.2° E, with k:22 and α₉₅:3.0°. This pole is significantly different from the geographic pole. If the difference in palaeomagnetic and geographic poles is interpreted in terms of absolute plate motion, then 2010 km of northwards motion of the western part of the Eurasian Plate, at 3.7 cm/yr, has taken place over the last 55 Myr. This motion has implications for the geological history of the Arctic and for the complexity of mantle motions.