Desert margins near the Chinese Loess Plateau during the mid-Holocene and at the Last Glacial Maximum: a model–data intercomparison

Expansion and contraction of desert margins around the globe have been inferred from a variety of proxy data and have since been linked, particularly in northern China and in the sub-Sahel, to changes in freshwater flux, vegetation cover, sea surface temperatures and, perhaps most importantly, monsoon circulations. We present a direct comparison of results from numerical general circulation model experiments for the mid-Holocene and for the Last Glacial Maximum (LGM) with the climatic conditions that have been inferred from loess–paleosol sequences taken from the Chinese Loess Plateau.During the mid-Holocene in northern China, the northwestward migration of the southeast desert margin that has been suggested by grain size analysis is also expressed in the model results. There is a statistically significant wetting of the Plateau region, and increased soil moisture is a consequence of an enhanced summer monsoon whose latent heat release deepens the cyclonic Tibetan low and brings increased low-level convergence and precipitation to the area. North of the desert region, this circulation dries the soil through enhanced atmospheric subsidence, although the northern margin of the desert does not migrate significantly.Expansion of the desert margin toward the southeast at the LGM is small, but there is a statistically significant drying of the Plateau. The local hydrological cycle is reduced, and there is an increase in large-scale atmospheric subsidence over the region that is caused by the presence of the Fennoscandian ice sheet upwind. Model results therefore suggest that, in addition to local micro- and mesoclimatic conditions, regional effects, such as monsoon circulations and distal orography, are also important factors in determining the location of desert margins.     

Reviews

GEOMORPHOLOGY by R. J. Chorley, S. A. Schumm and D. E. Sugden.’ 19 × 25 cm, xxiii and 605 pages. Methuen: London 1984 (ISBN 0 416 32590 4) $A39.95 (cloth).

THEMES IN GEOMORPHOLOGY edited by A. F. Pitty. 13 × 21 cm, 280 pages. Croom Helm: London 1985 (ISBN 0 7099 2066 0) $A49.50 (cloth).

DESERTS AND ARID LANDS edited by F. El‐Baz. 16 × 25 cm, vi and 222 pages. Nijhoff: The Hague 1984 (ISBN 90 247 2850 9) $US46.00 (cloth).

COASTAL GEOMORPHOLOGY IN AUSTRALIA edited by B. G. Thorn. 16 × 24 cm, xv and 349 pages. Academic Press: Sydney 1984 (ISBN 0 12 687880 3) $A49.50 (cloth).

KWONGAN: Plant Life on the Sandplain edited by J. S. Pate and J. S. Beard. University of Western Australia Press: Nedlands 1984 (ISBN 0 85564 230 0) $A25.00 (limp).

THEMES IN BIOGEOGRAPHY edited by J. A. Taylor. 22 × 14 cm, xxvii and 404 pages. Croom Helm: London 1984 (ISBN 0 7099 2428 3) $A25.95 (limp).

ENVIRONMENTAL IMPACT ASSESSMENT: A Practical Guide by C. F. Porter. 22 × 15 cm, xiii and 269 pages. University of Queensland Press: St Lucia 1985 (ISBN 0 7022 1699 2) $A35.00 (cloth).

THE CLIMATIC SCENE edited by M. J. Tooley and G. M. Sheail. 16 × 24 cm, xx and 306 pages. George Allen and Unwin: London 1985 (ISBN 0 04 551089 X) $A59.95 (cloth).

VOLCANIC HAZARDS: A Sourcebook on the Effects of Eruptions by R. J. Blong. 24 × 15 cm, xvi and 424 pages. Academic Press: Sydney 1984 (ISBN 0 12 107180 4) $A68.00 (cloth).

THE ECONOMICS OF BUSHFIRES: The South Australian Experience edited by D. T. Healey, F. G. Jarrett and J. M. McKay. 22 × 15 cm, x and 152 pages. Oxford University Press: Melbourne 1985 (ISBN 0 19 554669 5) $A19.99 (cloth).     

Geology and geotechnical characteristics of sediments in east bay area,Mississippi delta

Abstract

Deltaic sedimentation has produced an accumulation of clay and silt with a maximum thickness of 90 m in East Bay area. Sediments in the upper 50 m grade from interbedded sand, silt, and clay near South Pass and Southwest Pass to predominantly clay in the central part of the area. The variation in the types of sediments and rates of deposition greatly affected the engineering properties of these deposits. Sediments from boreholes in the central part of the area have shear strengths of less than 10 kPa to a depth of at least 50 m. Near the distributaries, shear strength increases with depth; values as high as 43 kPa were measured in sediments in the upper 50 m. These sediments are generally stronger and coarser, and have a lower water content and liquid limit than do sediments at comparable depths in the central part of the area.     

Distant modulation of electron intensity during the expansion phase of an auroral substorm

Pulses in electron intensity, occurring during the expansion phase of an auroral substorm, were studied using a Skylark sounding rocket launched from Kiruna, Sweden at 2226:50 UT on 2 March 1972. The pulses were typically of 5 s duration and occurred sporadically with a typical interval of 15 s. The rocket carried main and ejected payloads, and the pulses, occurring simultaneously at both, are found to be temporal rather than spatial in origin. Pitch-angle distributions changed little during a pulse, remaining slightly peaked towards larger pitch-angles. Precipitation is thought to be caused by pitch-angle diffusion under conditions where scattering angles are large compared with the opening angle of the loss cone. Enhanced scattering and variations in the temperature of the source plasma are both considered as possible causes of the pulse-like modulation. A dispersion in the times of occurrence of the pulses at different electron energies (3·8, 5·7, 9·0, > 18 and > 48 keV) indicates that the pulses originated at distances which varied between 41,000 ± 4000 km and 90,000 ± 7000 km during the flight. The larger distances are seen as evidence for temporary distortion of the local (L = 5·4) geomagnetic field lines whereby they are stretched to twice their normal (near-dipole) length. It appears that over a period of 100 s the field lines expanded and contracted at a speed of approximately 1000 km s^?1. The further observation that the electron energy spectra were approximately Maxwellian, with a temperature equivalent to ～3 keV, helps to confirm the indications that the precipitation and its modulation were controlled directly by processes taking place in the plasma sheet. Other possible causes of the variable dispersion are considered, but found to be inconsistent with the present results.     

Giant Maps as Pedagogical Tools for Teaching Geography and Mathematics

Giant maps offer a potentially useful pedagogical tool for teaching mathematics and map skills. In this pilot study, giant maps were distributed to elementary schools in Colorado and New Hampshire and teachers were provided with guided activities designed to integrate mathematics and geography skills. In an assessment of student skills, it was found that there were improvements in map-use skills and that students improved in some skills more than others. Additionally, there were differences in gender; girls improved more in their scores for some skills and less than boys in others. The teaching benefits of giant maps merit additional investigation.     

The wollongong lead study: an investigation of the blood lead levels of pre‐school children and their relationship to soil lead levels

The Wollongong Lead Study was undertaken in 1989–90 by the Pollution Task Force of Healthy Cities Illawarra and the Health Promotion Unit of the Illawarra Area Health Service. It was done in response to community concern in the Port Kembla area about the health effects of known high atmospheric lead levels, which result from the emissions from the Electrolytic Refining & Smelting Pty Ltd (now Southern Copper) smelter. It followed procedures similar to those used in the extensive and long‐term studies of the consequences of emissions from the lead smelter at Port Pirie in South Australia and concentrated on the highest risk group identified by the Port Pirie work, namely very young children (mainly 1–3 years). This paper reports the aspects of the study related to soil‐blood level relationships.

Two areas were compared: a southern area near the smelter; and a northern area near Bellambi which was used as a control because it is not usually affected by air pollution from the industrial zone at Port Kembla. A total of 164 soil samples and 83 blood samples were collected from the southern area, together with 79 soil samples and 30 blood samples from the northern area. Soil lead levels were not high by world standards in either region. The southern area had greater levels than the northern area. While there was no apparent pattern in the northern area, soil lead levels rose significantly towards the smelter at Port Kembla. Blood lead levels were also higher in the southern area. Here they rose from the south towards the industrial area generally, rather than peaking near the smelter. In the northern area there was no pattern apparent. Soil levels were significantly correlated with blood levels (significance level >0.05) and explained 29 per cent of the variation in the blood data. Soil lead levels can be used, therefore, as a general indicator of likely high blood lead levels in young children. Seven children (8%) in the southern area and two children (7%) in the northern area had blood lead levels above the NH&MRC recommended level of concern (25 μg/dL).     

Explaining State‐Environmental NGO Relations in the Philippines and Indonesia

This paper explains how the notion of “critical engagement” has been a popular basis for NGO‐state relations in the Philippines and Indonesia. It has been used, moreover, in both liberal democratic (post‐1985 Philippines) and authoritarian (late 1960s to late 1990s Indonesia) political regimes. For both states and reform‐minded NGOs, critical engagement has represented a flexible means by which to pursue assorted political, economic and social ends. In a context of regional political and economic upheaval, it is likely to remain popular with both states and many NGOs for the foreseeable future.     

Acoustic backscatter and sediment textural properties of inner shelf sands,northeastern Gulf of Mexico

The relationship between spatial variations of the properties of sea-floor sediments and acoustic backscatter from the surface of the sea floor on the continental shelf off of Panama City, Florida, USA, is investigated using surficial sediment grab samples and digital side-scan sonar data. Acoustic backscatter strength has a high, direct correlation with the mean grain size of the sediments. Acoustic backscatter strength also correlates directly with the carbonate content of the sediments, particularly in medium-and coarse-sand facies, because large, irregularly shaped, carbonate particles affect both the mean grain size of the sediments and the roughness of the surface of the sea floor.     

Physiographic features on the northern Gulf of Mexico continental slope

The continental slope of the northern Gulf of Mexico is diapirically controlled and is comprised of coalescing salt sheets, salt withdrawal basins, salt ridges, salt tongues and sills, and submarine canyons. Bathymetric information from single-beam data has resulted in several published maps. Many of the map areas have been remapped, using multibeam surveys, by the US National Ocean Service, and names have been given to the major physiographic features. The multibeam program was discontinued before complete coverage of the slope was accomplished. We provide charts of the remaining areas with names of features that have been accepted by the US Board of Geographic Names.