HRTEM study of Popigai impact diamond: heterogeneous diamond nanostructures in native amorphous carbon matrix

High-resolution transmission electron microscopy was applied for the detailed nanostructural investigation of Popigai impact diamonds with the aim of revealing the nature of the amorphous carbon of the matrix. The successful application of two complementary specimen preparation methods, focused ion beam (FIB) milling and mechanical cleavage, allowed direct imaging of nanotwinned nanodiamond crystals embedded in a native amorphous carbon matrix for the first time. Based on its stability under the electron beam, native amorphous carbon can be easily distinguished from the amorphous carbon layer produced by FIB milling during specimen preparation. Electron energy loss spectroscopy of the native amorphous carbon revealed the dominance of sp ²-bonded carbon and the presence of a small amount of oxygen. The heterogeneous size distribution and twin density of the nanodiamond crystals and the structural properties of the native amorphous carbon are presumably related to non-graphitic (organic) carbon precursor material.     

Adaptive variability to low‐pH river discharges in Acartia tonsa and stress responses to high PCO2 conditions

Environmental transitions leading to spatial physical–chemical gradients are of ecological and evolutionary interest because they are able to induce variations in phenotypic plasticity. Thus, the adaptive variability to low‐pH river discharges may drive divergent stress responses [ingestion rates (IR) and expression of stress‐related genes such as Heat shock protein 70 (Hsp70) and Ferritin] in the neritic copepod Acartia tonsa facing changes in the marine chemistry associated to ocean acidification (OA). These responses were tested in copepod populations inhabiting two environments with contrasting carbonate system parameters (an estuarine versus coastal area) in the Southern Pacific Ocean, and assessing an in situ and 96‐h experimental incubation under conditions of high pressure of CO₂ (_PCO₂ 1200 ppm). Adaptive variability was a determining factor in driving variability of copepods' responses. Thus, the food‐rich but colder and corrosive estuary induced a traits trade‐off expressed as depressed IR under in situ conditions. However, this experience allowed these copepods to tolerate further exposure to high _PCO₂ levels better, as their IRs were on average 43% higher than those of the coastal individuals. Indeed, expression of both the Hsp70 and Ferritin genes in coastal copepods was significantly higher after acclimation to high _PCO₂ conditions. Along with other recent evidence, our findings confirm that adaptation to local fluctuations in seawater pH seems to play a significant role in the response of planktonic populations to OA‐associated conditions. Facing the environmental threat represented by the inter‐play between multiple drivers of climate change, this biological feature should be examined in detail as a potential tool for risk mitigation policies in coastal management arrangements.     

Book reviews

AN INTRODUCTION TO URBAN GEOGRAPHIC INFORMATION SYSTEMS by W.E. Huxhold. 16 x 23 cm, xxiii and 337 pages. Oxford University Press, New York, 1991. (ISBN 0 19 506535 2) $44.95 (soft).

INDONESIA: resources, ecology and environment (Natural Resources of South‐East Asia Series) edited by J. Hardjono. 14 × 22 cm, xvi and 262 pages. Oxford University Press, Oxford, 1991. (ISBN 0 19 588992 4) $39.95 (hard).

THE UNIQUE CONTINENT: an introductory reader in Australian environmental studies edited by J. Smith. 13 × 20 cm, vi and 282 pages. University of Queensland Press, Brisbane, 1992. (ISBN 0 7022 2475 8) $14.95 (soft).

SPECIAL INTEREST TOURISM edited by B. Weiler and C.M. Hall. 15 × 23 cm, xi and 214 pages. Belhaven, London, 1992. (ISBN 1 85293 072 1) £35.00 (hard).

REMOTE POSSIBILITIES: the Aboriginal domain and the administrative imagination by T. Rowse. 18 × 25 cm, viii and 117 pages. North Australian Research Unit, Australian National University, Darwin, 1992. (ISBN 0 7315 1345 2) $15.00 (soft).

ANTARCTICA: an economic history of the last continent by M. Wilder. 21 × 29 cm, viii and 155 pages. Department of Economic History, University of Sydney, Sydney, 1992. (ISBN 0 86758 616 8) $20.00 (soft).

AUSTRALIAN RAINFORESTS (Oxford Monographs on Biogeography No. 6) by P. Adam. 19 × 25 cm, xiv and 308 pages. Oxford Science Publications/Clarendon Press, Oxford, 1992. (ISBN 0 19 854223) $170.00 (hard).     

Stability of planetary orbits in binary systems

The possible existence of stable orbits is investigated in binary systems using Hill's method. Analytical stability conditions are established for satellites, for inner planets and for outer planets, allowing arbitrary values for the mass-ratio of the binary.Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978.     

Changing Geographies and the Geography of Change: Some Reflections

To celebrate the 50th anniversary of the Singapore Journal of Tropical Geography and the 75th anniversary of the teaching of geography in the Department of Geography, National University of Singapore, the home of the Journal, this article, based on personal reflections and "objective" academic materials, provides an overview of developments in geography in the Department and Journal. The paper argues that the department's and Journal's"identities", since the post-World War II period, have been shaped by Singapore's changing domestic politics, the changing university academic environment, the personalities and academic interests of heads of the department and the Journa's editors, the state of the changing regional and global political economic environment, and the individual research interests of faculty in the department, and reflects a complex mix of colonial/post-colonial, modern/post-modern, North-South and East-West discourses. While a defined Singapore school of geography has yet to emerge, the article shows that both the department and the Journal have made major strides in meeting the challenges of globalisation and, in the process, have gained international visibility and academic legitimacy. In particular, the Journal has consolidated its position as a major voice for academics in lesser developed countries, its platform for "tropical world" discourse and maintaining its edge in the colonial/post-colonial and modern/post-modern discourses of states within the tropics.     

A new natural,super-hard,transparent polymorph of carbon from the Popigai impact crater,Russia

A natural shockwave event led to the formation of a new crystalline polymorph of carbon in gneisses from the Popigai crater, Russia. The new species occupies the interior of a multiphase assemblage and is entirely enveloped by lonsdaleite and graphite. Polishing hardness of this new phase is greater than that of lonsdaleite. Micro-beam synchrotron X-ray diffraction, imaging and fluorescence studies revealed a pure transparent carbon phase. The diffraction pattern is indexed in terms of a cubic cell (a=14.697 Å, space group Pm3m.). This species was neither encountered in static or dynamic high-pressure experiment nor predicted by theoretical calculations. To cite this article: A. El Goresy et al., C. R. Geoscience 335 (2003).     

Experimental research on critical point hypothesis

According to the critical point hypothesis (CPH), energy release would accelerate in power law before occurrence of large earthquakes or failure of brittle materials. In the paper, CPH was studied by acoustic emission experiments of large-scale rock samples. Three kinds of rock samples were used in the experiments. The tri-axial loading condition was applied under different loading histories. The released elastic energy (Acoustic emission) was recorded with acoustic emission technique as microcracks emerged and developed inside the rock samples. The experimental results gave a further verification on the CPH. The elastic energy release of rock samples would accelerate before the failure even under different experimental conditions. Primary studies were also made on medium-term earthquake prediction by using accelerating energy release (AER) in the paper. Foundation item: Project of Natural Sciences Foundation of China (10232050), Project of State Key Basic Research (2002CB412706) and Project of Computer Network Information Center, Chinese Academy of Sciences (2002CB412706).     

Denitrification in the Arabian Sea: A 3D ecosystem modelling study

A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr⁻¹,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m⁻² d⁻¹) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m⁻² d⁻¹). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the ²³⁴Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.     

Trophic pathways and carbon flux patterns in the Laptev Sea

The Laptev Sea is a high-Arctic epicontinental sea north of Siberia (Russia) that is one of the least understood regions of the world’s ocean. It is characterized by a shallow and broad shelf plateau, high influx of river water, sediments and nutrients during summer, long-lasting sea-ice cover from October to May, and the formation of a narrow flaw-lead polynya off the fast-ice edge during winter.Here, we describe results of a German–Russian research project (1993-present), presenting the distribution patterns and dynamics of its marine flora and fauna, as well as pathways and processes of coupling between sea-ice, water-column and sea-floor biota.Three ecological zones are distinguished along a combined east–west and Lena-impact gradient, differing in the composition of pelagic and benthic communities. In general, high Chl a concentrations in the sediments indicate a tight coupling between sympagic and pelagic primary production and nutrient supply to the benthos throughout the entire Laptev Sea. However, there were pronounced regional differences between the ecological zones in magnitude of primary production and trophic dynamics. Primary production during the ice-free summer was highest in the estuarine zone most strongly influenced by the Lena River (210 mg C m⁻² day⁻¹). The western and northeastern Laptev Sea yielded 55 and 95 mg C m⁻² day⁻¹, respectively. Moreover, the zones differed in the partitioning of carbon flux between zooplankton and benthic food webs. In the Lena zone zooplankton carbon demand was about 31 mg C m⁻² day⁻¹ whereas in the western zone it was 21 mg C m⁻² day⁻¹ and in the eastern zone 4 mg C m⁻² day⁻¹. Total benthic carbon demand was 32 mg C m⁻² day⁻¹ for the Lena zone, 56 mg C m⁻² day⁻¹ in the western zone and 100 mg C m⁻² day⁻¹ in the northeastern zone.A carbon budget constructed for the Laptev Sea indicates that (1) a high proportion of primary production is channelled through the benthic trophic web, bypassing the pelagic trophic web, and (2) autochthonous primary production in the northeastern and western Laptev Sea might not be sufficient to fuel both pelagic and benthic secondary production and, hence, input of allochthonous organic carbon is required to balance the overall carbon demand.     

Remote acoustic sensing methods for studies in oceanology

In this paper, the lines of investigation on a problem of the development of remote acoustic sensing methods in oceanology are formulated. This paper summarizes the results of investigations into the possibilities for monitoring temperature and flow fields in shallow seas. In the discussed experiments, the instrumentation being constituents of the complex for longduration remote monitoring of marine medium climatic variability and that of the acoustic tomography of shallow sea dynamic processes is used. The acoustic instruments were located on the POI FEB RAS acousto-hydrophy sical polygon (Pacific Oceanological Institute, Far Eastern Branch of the Russian Academy o f Sciences) near the Gamov Peninsula. Acoustic receiving and transmitting systems operating with multiplex phase-manipulated signals (of M-codes) at frequency range 250-2500 Hz form the basis for this complex.