Geodynamic evolution of a Cadomian arc region: the northern Ossa-Morena zone, Iberian massif

Ductile deformation and polyphase metamorphism in the Ossa-Morena zone of the Iberian massif are related to two major tectonothermal episodes of Cadomian (late Neoproterozoic to early Cambrian) and Variscan age (middle to late Paleozoic). The available petrological, structural and geochronological data suggest that a number of tectono-metamorphic and magmatic episodes occurred during the 620–480 Ma interval that would comprise a complete Cadomian Wilson cycle. The geodynamic scenario was that of an Andean-type continental margin. An evolutionary model is presented for this orogeny comprising stages of volcanic arc generation, crustal thickening, back-arc extension, tectonic inversion and cratonization. A correlation with comparable areas from pre-Mesozoic massifs elsewhere in Europe is proposed, in particular with the Armorican massif of northern France.     

A Gravimetric Geoid Computation and Comparison with GPS Results in Northern Andalusia (Spain)

Two new GPS surveys have been carried out to check the accuracy of an existing gravimetric geoid in a test area located in northern Andalusia (Spain). The fast collocation method and the remove-restore procedure have been used for the computation of the quasigeoid model. The Spanish height system is based on orthometric heights, so the gravimetrically determined quasigeoid has been transformed to a geoid model and then compared to geoid undulations provided by GPS and levelling at benchmarks belonging to the Spanish first-order levelling network. The discrepancies between the gravimetric solution and GPS/levelling undulations amount to ±2 cm for one survey and ±5 cm for another after fitting a plane to the geoid model.     

Distribution and Acoustic Characteristics of Shallow Gas in the Korea Strait Shelf Mud off SE Korea

Shallow gas in the Korea Strait shelf mud (KSSM) off SE Korea, revealed by high-resolution subbottom profiles, is associated with acoustic blanking, acoustic turbidity, seepages with plumes in the water column, and seafloor depressions. The acoustic blanking, characterized by strong, consistent top reflection and wipeout below, is most dominant. The seaward edge of the acoustic blanking zone generally coincides with the 100-m water-depth contour, suggesting that the water depth (the pressure) may control the distribution of shallow gas. The acoustic turbidity, characterized by diffuse top reflection, is a dark smear, partially blanking the data below. The seepages with plumes, characterized by vertical smearing and disturbed seafloor, are seen only along the shallowest, landward edge of the acoustic blanking zone. This may suggest that the decreased gas solubility at shallow water depths, caused by the lowered pressure, increases the volume of free gas in the sediments, facilitating the gas escape. The seafloor depressions, interpreted as pockmarks, are accompanied by cone-shaped acoustic masking, which is probably the reflection from a narrow vent of gas. The gas-related acoustic anomalies appear to occur mostly in the upper, recent mud of the KSSM. Neither permeable beds nor faults, which can act as vertical migration pathways for deep thermogenic gas, are evident in the recent mud. We interpret that the bacterial degradation of organic matter in situ is the main source for the gas in the KSSM. The upwelling off SE Korea may be an important source for the increased organic matter in the area.     

Fracture characteristics and stress directions in the quaternary sediments of the Ulleung Basin,East Sea: Based on resistivity image log data

Abstract

Geophysical evidence indicating the presence of gas hydrate has been found in the Ulleung Basin, which lies off the east coast of the Korean Peninsula; however, hydrate distribution in the basin is not well understood. Logging-while-drilling data for 13 sites in the Ulleung Basin, East Sea, were obtained to investigate the distribution pattern of gas hydrate. Most of the sites yielded log data indicating the presence of gas hydrate. Prominent fractures (both resistive and conductive fractures) were clearly identified on the resistivity borehole images, particularly at seismic chimney sites. Resistive fractures, which contain large amounts of gas hydrate, are prominent in the seismic chimney sites. The strike and dip of each fracture was calculated and displayed on a stereographic plot and rosette diagram. From the fracture orientations on the stereographic plots, the maximum horizontal stress is NW–SE, reflecting the regional stress regime around the Ulleung Basin, although the fracture orientations are broadly distributed, indicating that the fracture pattern is not well-ordered on the rosette diagram. The fracture dips are between 36.46° and 63.66°; the range of dip azimuths is 0.94°–359°, and exhibit little change with depth. The dip azimuths are generally westerly to southwesterly.     

Spatial Simulation and Fuzzy Threshold Analyses for Allocating Restoration Areas

This paper presents a methodology for the evaluation of land condition and for the allocation of areas requiring restoration. It is based on spatial simulation analysis and fuzzy logic. The method is demonstrated in a restoration allocation problem within a military training area in Texas. Fuzzy logic is integrated with spatial analysis through Geographic Information Systems (GIS) to make land condition assessment geographically specific. Two sources of uncertainty in Land Condition Analysis are considered in this paper. First is the uncertainty due to incomplete information on land condition. Second is the uncertainty emanating from identifying the condition of a particular parcel of land. The first is addressed by using sequential Gaussian simulation, a geostatistical tool. Erosion status is selected as the land condition factor, and uncertainty associated with it is considered in this study. Land allocation is based on fuzzy logic to reflect the continuous transition between different land conditions and the minimization of loss that is expected to occur in the case of misallocation. Various forms of loss functions are used for allocating areas in need of restoration. An important result of the study is a map showing the areas allocated for restoration. The proposed method is compared to two alternative methods with varying degrees of determinism and uncertainty. The incorporation of uncertainty led to better allocation strategies and results that are more realistic.     

On the radio-frequency emission from the Geminga pulsar

The famous neutron star Geminga was until quite lately the only pulsar undetected in the radio regime, though observed as a strong pulsating γ- and X-ray source. Three independent groups from the Pushchino Radio Astronomy Observatory (Russia) reported recently the detection of pulsed radio emission from Geminga at 102.5 MHz, i.e., the first detection of the radio pulsar PSR J0633 + 1746 by Kuz'min &38; Losovskii, Malofeev &38; Malov and Shitov &38; Pugachev. This pulsar exhibits the weakest radio luminosity known. Its average pulse profile appears to be very wide, filling an entire 360° pulse window according to Kuz'min &38; Losovskii.   We present a model explaining the peculiarities of the Geminga radio pulsar, based on the assumption that it is an almost aligned rotator. The electromagnetic waves generated in the inner magnetosphere reach the region within the light cylinder with a weak magnetic field (at distances of a few light cylinder radii), where they are strongly damped due to the cyclotron resonance with particles of magnetospheric electron–positron plasma. The lowest frequencies that can escape are determined by the value of the magnetic field in the region where the line of sight passes through the light cylinder. The specific viewing geometry of an almost aligned rotator implies that the observer's line of sight probes the emission region near the bundle of the last open field lines. This explains the unusually weak emission from Geminga's low-frequency radio pulsar.     

Geoid determination in central Spain from gravity and height data

Summary The least-squares collocation method has been used for the computation of a geoid solution in central Spain, combining a geopotential model complete to degree and order 360, gravity anomalies and topographic information. The area has been divided in two 1°× 1° blocks and predictions have been done in each block with gravity data spacing about 5 × 5 within each block, extended 1/2°. Topographic effects have been calculated from 6 × 9 heights using an RTM reduction with a reference terrain model of 30 × 30 mean heights.     

Trichodesmium spp. population structure in the eastern North Atlantic subtropical gyre

Trichodesmium spp. population structure was studied based on a transect in the eastern subtropical North Atlantic in October 2006, covering a gradient from near-temperate conditions up to fully subtropical, oligotrophic waters. Trichodesmium spp. trichomes were counted and measured, distinguishing free trichomes from those forming macroscopic colonies (“puffs” or “tufts”). Moreover, for both free and colonial individuals, abundance and size structure variation were quantified from single trichome-level data. Nitrogen fixation rates were estimated using an empirical approach based on abundance observations and a heuristic approach to incorporate variation in trichome size and environmental temperature. A gradual change towards greater sizes and increased abundances was observed as physical conditions became subtropical. An extreme response was detected at one station (29.8°W, 26.3°N), in which both in situ and remote sensing data revealed the presence of a Trichodesmium bloom. Despite the presence of a mesoscale anticyclonic eddy, a close examination of prior surface conditions using altimeter data indicated that the bloom was related to the advection of southern waters. In general, our results highlighted the importance of free trichomes in Trichodesmium spp. populations in this part of the North Atlantic. Furthermore, they suggested a possible role of both size and population structure on the wide range of N₂ fixation estimates currently available in the literature.     

Trace metal concentrations in southern right whale (Eubalaena australis) at Península Valdés, Argentina

The presence of essential (Fe, Mn, Zn, Cu, Ni and Al) and non-essential trace metals (Cd and Pb) was tested in liver (N=26) and kidney (N=42) from dead Southern Right Whale (SRW--Eubalaena australis) calves found beached in Península Valdés, Argentina. Essential metals were detected in all samples, particularly in hepatic tissue; though Ni and Al were accumulated mainly in the kidney. Cd and Pb were not detected in any samples. Sex and length of calves did not influence metal levels found, nor did the geographic location of carcasses. Our findings for essential metals were similar to those reported for mysticetes in other parts of the world. Except for a previous report on one SRW calf, this is the first data on trace metals for this species in Patagonia. This information is vital for SRW management considering increasing human pressures impacting their feeding and breeding grounds.     

Eutrophic waters, algal bloom and fish kill in fish farming areas in Bolinao, Pangasinan, Philippines

The coastal waters of Bolinao, Pangasinan, Philippines experienced environmental changes over a 10-year period (1995-2005), the most significant effect of which was the major fish kill event in 2002 that coincided with the first reported Philippine bloom of a dinoflagellate Prorocentrum minimum. Days before the bloom, dissolved oxygen was < 2.0 mg/l in the waters that were stratified. These conditions may be linked to the uncontrolled proliferation of fish pens and cages to more than double the allowable limit of 544 units for Bolinao waters. Mariculture activities release organic matter from unconsumed feed and fecal material that accumulate in the water and sediments. In over 10 years, water quality conditions have become eutrophic with ammonia increasing by 56%, nitrite by 35%, nitrate by 90%, and phosphate by 67%. The addition of more fish pens and cages placed additional stress to this poorly flushed, shallow area that affected water quality due to changes in the water residence time.