Impact of swell on simulations using a regional atmospheric climate model

When long, fast swell waves travel in approximately the same direction as the wind, the surface stress is reduced compared with under wind-sea conditions. Using measurements from the Östergarnsholm site in the Baltic Sea, new expressions of the roughness length were developed for wind sea and swell. These new expressions were implemented in the RCA3 regional climate model covering Europe. A 3-year simulation and two case studies using the wavefield from the ECMWF reanalysis (ERA-40) were analysed using the improved formulations. Wind-following swell led to a significant reduction of mean wind stress and heat fluxes. The mean surface layer wind speed was redistributed horizontally and the marine boundary layer cooled and dried slightly. This cooling was most pronounced over North Sea and the Norwegian Sea (almost 0.2 °C annually on average) whereas the drying was most pronounced over the Mediterranean Sea (almost 0.4 g kg⁻¹). Somewhat less convective precipitation and low-level cloudiness over the sea areas were also indicated, in particular over the Mediterranean Sea. The impact on the atmosphere, however, is significantly locally greater in time and space.     

Radio geology

BBC Education has produced a series of six radio programmes on geology, to be broadcast in March 1988 on Radio 4 VHF. The programmes are supported by 117 slides (two of which are used - in black-and-white form-to illustrate this article) and three computer programs.     

The use of digital map data in the segmentation and classification of remotely-sensed images

Abstract

Remotely-sensed data constitute a major potential source of input to geographical information systems (GIS)However, these data often have a relatively poor classification accuracy compared with that of the cartographic data from maps with which they may be combined in the course of GIS analysis. The possibility exists of using data sets (in the form of digital maps) resident within a GIS in order to improve this accuracy, before the classified image is incorporated into the GIS. Results are discussed from a British Alvey Information Technology project to develop a system for the knowledge-based segmentation and classification of remotely-sensed terrain images, in which the knowledge contained in digital map     

Calorific value, lipid content and radioactivity of common species from Hornsund, Southwest Spitsbergen

In the summer of 1981 the common flora and fauna of 28 species from Hornsund were collected, and the energy value, lipid content and global activity determined. It was found that the plants had low energy values, varying from 12.26 ± 0.42 kJ g⁻¹ dry weight to 15.45 ±1.00kJ'dry weight. The highest values in animals were noted in Liparis liparis (Pisces) 22.15 ± 0.89 kJg⁻¹ dry weight, and Sagitta elegans (Chae-tognatha) 20.64 ± 0.49kJg⁻¹, the lowest being in Orchomene minuta (Amphipoda) 11.30 ± 0.74kJg⁻¹d.w. The lipid contents in the species studied were mostly low, the mean range from lowest to highest being 1.37-8.60% for plants and 7.14–31.93% for animals, and they were proportional to the energy value. Both the energy values and lipid contents were comparable to those in similar species from other waters. The global fi activity in the organisms analysed was not high; at the same time plants had a higher content of radioactive isotopes, 1.97-61.9pCi g⁻¹ d.w., than animals, 5.2-17.8pCi g⁻¹ d.w.     

Depositional environments in an extensive tide-influenced delta plain, Middle Devonian Gauja Formation, Devonian Baltic Basin

The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide‐influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo‐shoreline, separated by muddy intra‐channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross‐stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse‐grained sediment input. The Gauja Formation contrasts with established models for tide‐influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)‐directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger‐scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation.     

Discontinuous Melt Extraction and Weak Refertilization of Mantle Peridotites at the Vema Lithospheric Section (Mid-Atlantic Ridge)

Melting processes beneath the Mid-Atlantic Ridge were studiedin residual mantle peridotites sampled from a lithospheric sectionexposed near the Vema Fracture Zone at 11°N along the Mid-AtlanticRidge. Fractional and dynamic melting models were tested basedon clinopyroxene rare earth element and high field strengthelement data. Pure fractional melting (non-modal) cannot accountfor the observed trends, whereas dynamic melting with criticalmass porosity <0·01 fits better the measured values.Observed microtextures suggest weak refertilization with 0·1–1%quasi-instantaneous or partially aggregated melts trapped duringpercolation. The composition of the melts is evaluated, togetherwith their provenance, with respect to the garnet–spineltransition. Partial melts appear to be aggregated over shortbut variable intervals of the melting column. Deep melts (generatedwithin the garnet stability field at the base of the meltingcolumn) escape detection, being separated from the residuesby transport inside conduits or fractures. The temporal evolutionof the melting process along the exposed section shows a steadyincrease of mantle temperature from 20 Ma to present. KEY WORDS: mantle partial melting; abyssal peridotite; trace element; refertilization; Vema Fracture Zone     

Origin of black coloured laminae in speleothems from the Kraków-Wieluń; Upland, Poland

Black coloured laminae have been detected inside speleothems from nine caves situated in the Kraków-Wieluń Upland. The black colour results from the occurrence of charcoal particles and organic compounds. These particles originated inside the caves during wood combustion caused by prehistoric human activity. The ultrastructures of charcoal particles prove that most originated in temperatures ranging from 400 up to 600°C, suggesting that the charcoal is connected with domestic fires rather than torches. Although the laminae are proof of human activity in the caves, the occurrence of one particular lamina cannot be associated with a single episode of human occupation. It is due to the fact that depositional processes and corrosion control the number and thickness of the laminae discussed. The presence of black coloured laminae within the studied Holocene speleothems indicates that the investigated caves were settled in the Neolithic, the Bronze Age and later periods. This is consistent with the former archaeological data.