First measurements from a deep-tow transient electromagnetic sounding system     

Spahr Webb  R. Nigel Edwards  Liming Yu 《Marine Geophysical Researches》1993,15(1):13-26

An electromagnetic sounding system has been developed to map the shallow electrical conductivity structure of the deep sea floor. The instrument consists of a magnetic source and several colinear magnetic receivers forming an array which is towed along the seafloor. The source generates a time varying magnetic field; the shape of the resulting magnetic field waveform at the receivers depends on the electrical conductivity below the seafloor between the receivers and the source. The instrument can be towed systematically over a study area under acoustic transponder or GPS navigation to construct a map of the electrical conductivity. Towing speeds of greater than 1 m s^–1 (2 knots) can be achieved without adversely effecting data quality. The instrument is sufficiently robust to survive continual contact with thinly sedimented, abrasive basalt. We present the first results from a deployment in August, 1990 near the Cleft Segment of the Juan de Fuca Ridge along an 8 km track to the west of the spreading center. Unforeseen problems with the instrument restricted the utility of the measurements for constructing detailed vertical conductivity profiles, but the measurements were adequate to determine an average conductivity in the upper 25 m, at more than 70 stations. The conductivity was found to vary from 0.1 to 0.4 S/m along the track.  相似文献   

Observations on the Burrows and Burrowing Behaviour of: Squilla mantis L. Crustacea: Stomatopoda     

R. J. A. ATKINSON  C. FROGLIA  E. ARNERI  B. ANTOLINI 《Marine Ecology》1997,18(4):337-359

Abstract. The burrows of Squilla mantis are described from polyester resin casts taken at two Adriatic sites near Ancona. Typically, burrows had two openings, one of which was larger than the other, and were basically U-shaped. An interesting association with the little-known caridean shrimp Athanas amazone was observed. The sediments occupied by S. mantis were silty sands and sandy muds. Field observations of S. mantis and other species on the same grounds are presented and some information on burrow density is given, derived from burrow counts using underwater television. Burrowing behaviour is described from observations of animals transferred to laboratory aquaria.  相似文献   

Little evidence for faunal zonation or communities in deep sea demersal fish faunas     

Richard L. Haedrich  Nigel R. Merrett   《Progress in Oceanography》1990,24(1-4)

Demersal fish data from 9 deep-sea surveys in the North Atlantic were examined to assess (1) the coherence and continuity of zones around the ocean basin, and (2) the persistence of structured communities over more than just a local scale. The 63 cruises took 96,779 specimens and 325 species in 692 benthic trawl hauls between 204 and 5345m depth. Measures of similarity and overlap applied to this faunal data did not produce patterns other than those reflecting the occurrence of two widespread and abundant species - Synaphobranchus kaupi at slope depths and Nematonurus armatus on the rise. Communities defined within a survey area by commonly-used analytical procedures cannot be identified from place to place over broader areas, and the concept along with its implication should be abandoned.  相似文献   

The use of ultra-sound in the preparation of carbonate and clay sediments for chironomid analysis     

Barbara Lang  Alan P. Bedford  Nigel Richardson  Stephen J. Brooks 《Journal of Paleolimnology》2003,30(4):451-460

Initial investigations of Holocene carbonate sediment from Hawes Water, Northwest England, yielded lower numbers of chironomid head capsules than anticipated. Standard techniques used to prepare sediment for chironomid analysis were ineffective in breaking up the coarse crystalline sediment structure sufficiently. This led to large amounts of sediment being retained and increased sample processing times. The low yield of head capsules also meant that more sediment was needed to produce adequate numbers of head capsules for analysis. The use of ultra-sound as part of the sediment processing was investigated. This technique reduced the amount of sediment left for sorting and yielded significantly more head capsules which were of equivalent structural condition and cleaner than those produced by conventional methods. The technique was extended to clay samples where similar results were obtained although shorter treatment times are recommended. The proportion of Tanytarsini and Tanypodinae heads increased significantly in carbonate and clay samples, respectively; both sediment types showed a significant decline in the proportion of Chironomini. The results indicate that ultra-sonic preparation of samples will yield a more accurate representation of chironomid assemblages in sediments leading to greater sensitivity and reliability in analysing past environmental conditions.  相似文献   

An Active Sun Throughout the Maunder Minimum     

Beer  Jürg  Tobias  Steven  Weiss  Nigel 《Solar physics》1998,181(1):237-249

Measurements of ¹⁰Be concentration in the Dye 3 ice core show that magnetic cycles persisted throughout the Maunder Minimum, although the Sun's overall activity was drastically reduced and sunspots virtually disappeared. Thus the dates of maxima and minima can now be reliably estimated. Similar behaviour is shown by a nonlinear dynamo model, which predicts that, after a grand minimum, the Sun's toroidal field may switch from being antisymmetric to being symmetric about the equator. The presence of cyclic activity during the Maunder Minimum limits estimates of the solar contribution to climatic change.  相似文献   

The application of single zircon evaporation and model Nd ages to the interpretation of polymetamorphic terrains: an example from the Proterozoic mobile belt of south India   总被引：7，自引：0，他引：7  

Jessica M. Bartlett  Jon S. Dougherty-Page  Nigel B. W. Harris  Chris J. Hawkesworth  M. Santosh 《Contributions to Mineralogy and Petrology》1998,131(2-3):181-195

The technique of single zircon dating from the thermal evaporation of ²⁰⁷Pb/²⁰⁶Pb (Kober 1986, 1987) provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic assemblages. In contrast Nd model ages may provide a measure of the period of crustal residency for the sample or its protolith. These two techniques have been combined to elucidate the tectonic history of the Proterozoic mobile belt of southern India, exposed south of the Palghat-Cauvery Shear Zone that marks the southern boundary of the Archaean craton of Karnataka. The two main tectonic units of this mobile belt comprise the Madurai and Trivandrum Blocks, both of which are characterised by massive charnockite uplands and low-lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history throughout the Proterozoic. Evidence for early Palaeoproterozoic magmatism is restricted to the Madurai Block where single zircon evaporation ages from a metagranite (2436 ± 4 Ma) are similar to model Nd ages from a range of lithologies suggesting crustal growth at that time. The Trivandrum Block, to the south of the Achankovil shear zone, is comprised of the Kerala Khondalite Belt, the Nagercoil charnockites and the Achankovil metasediments. Single zircon evaporation ages, together with conventional zircon and garnet chronometry, suggest that all three units underwent upper-amphibolite facies metamorphism at ∼1800 Ma, an event unrecorded in the metagranite from the Madurai Block. This implies that the Madurai and Trivandrum blocks represent distinct terrains throughout the Palaeoproterozoic. Model Nd ages from the Achankovil metasediments are much younger (1500–1200 Ma) than those from the adjacent Kerala Khondalite Belt and Madurai Blocks (3000–2100 Ma), but there is no evidence for zircon growth in these metasediments during the Mesoproterozoic. Hence the comparatively young model Nd ages of the metasediments are indicative of a mixed provenance rather than a discrete period of crustal growth. Zircon overgrowths from the Madurai Block (547 ± 17 Ma) and Achankovil metasediments (530 ± 21 Ma) suggest that all tectonic units of the Proterozoic mobile belt of South India shared the same metamorphic history from the early Palaeozoic. This event has been recognised in the basement lithologies of Sri Lanka and East Antarctica, confirming that the constituent terrains of East Gondwana had assembled by this time. Received: 10 October 1995 / Accepted: 27 October 1997  相似文献   

Book reviews     

Trevor Langford‐Smith  Jim Walmsley  Sue Baker  Edward Linacre  Philip Hirsch  Nigel Thrift 《The Australian geographer》1989,20(2):202-216

GRIFFITH TAYLOR: Antarctic scientist and pioneer geographer (Carleton Library Series No. 145) by M. Sanderson. 15 x 23 cm, xi and 218 pages. Carleton University Press: Ottawa 1988 (ISBN 0 88629 068 6) $C24.95 (hard); (ISBN 0 88629 068 X) $C14.95 (soft) plus postage.

LAND, WATER AND PEOPLE: Geographical essays in Australian resource management edited by R. L. Heathcote and J. A. Mabbutt. 14 x 21 cm, xiii and 266 pages. Allen & Unwin: Sydney 1988 (ISBN 0 04 303008 4) $A24.95 (soft).

ENVIRONMENTAL GEOGRAPHY: Book One by J. Paine, H. McLean and G. Mayhew. 19 x 25 cm, 389 pages. Macmillan: Melbourne 1988 (ISBN 0 333 43073 5) $A28.95 (soft).

Climate Impact Assessment Program (1975) Impacts of climate change on the biosphere, Monograph No. 5, US Department of Transportation, Washington DC.

SMALL‐SCALE AGRICULTURE edited by J. Hirst, J. Overton, B. Allen and Y. Byron. 18 x 25 cm, xii and 210 pages. Commonwealth Geographical Bureau and Department of Human Geography, Australian National University: Canberra 1988 (ISBN 0 7316 3609 0) $A 10.00 (soft).

THE BRITTLE RIM: Finance, Business and the Pacific Region by M. T. Daly and M. I. Logan. 15 × 23 cm, 263 pages, Penguin Books: Ring‐wood 1989 (ISBN 0 14 012095 5) $A24.99 (soft)

THE END OF ORGANISED CAPITALISM by S. Lash and J. Urry. 15 x 23cm, 383 pages. Polity Press: Cambridge 1987 (ISBN 07456 00697) $A34.95 (soft).

THE POLITICS OF DEVELOPMENT: An Introduction to Global Issues by J. L. Seitz. 15 x 23 cm, xiii and 194 pages. Basil Blackwell: New York 1988 (ISBN 0 631 15801 4) $A27.95 (soft).

DEVELOPING WITH FOREIGN INVESTMENT edited by V. Cable and B. Persaud. 16 x 24 cm, viii and 327 pages. Croom Helm: London 1987 (ISBN 0 7099 4825 5) $A87.95 (hard).

PLANNING SYDNEY'S FUTURE by P. Spearritt and C. DeMarco, 21 x 27 cm, and 150 pages. Allen & Unwin: Sydney 1988 (ISBN 0 04 324014 3) $A17.95 (soft).

THE RICHEST LODE: Broken Hill 1888–1988 by R. J. Solomon. 22 x 28 cm, 424 pages. Hale & Iremonger: Sydney 1988 (ISBN 0 86806 333 9).

CONTEMPORARY ISSUES IN DEVELOPMENT (North Australia: Progress and Prospects, Volume 1) edited by D. Wade‐Marshall and P. Loveday. xiii and 310 pages. North Australia Research Unit, Australian National University: Darwin 1988 (ISBN 07315 0335 X).

NEW CALEDONIA OR KANAKY? The Political History of a French Colony (Pacific Research Monograph No. 16) by J. Connell. National Centre for Development Studies, Australian National University: Canberra 1987 (ISBN 0 7315 05123).

DISEASE ECOLOGY by Andrew Learmonth. 15 x 23 cm, 456 pages. Basil Blackwell: Oxford 1988 (ISBN 0 631 15799 9) $A46.00 (soft).

QUALITATIVE METHODS IN HUMAN GEOGRAPHY edited by J. Eyles and D. M. Smith. 15 x 23 cm, xiii and 272 pages. Polity Press: Cambridge 1988 (ISBN 0 7456 0371 8) $A34.95 (soft).

GEOGRAPHICAL SYSTEMS AND SYSTEMS OF GEOGRAPHY: Essays in Honour of William Warntz edited by W. J. Coffey. 14 x 21 cm, 211 pages. Department of Geography, University of Western Ontario: London, Ontario 1988 (ISBN 0 7714 09747) $C30.00 (soft).  相似文献   

Sediment balances in the Blue Nile River Basin   总被引：2，自引：1，他引：1  

Yasir SAALI  Alessandra CROSATO  Yasir AMOHAMED  Seifeldin HABDALLA  Nigel GWRIGHT 《国际泥沙研究》2014,29(3):316-328

Rapid population growth in the upper Blue Nile basin has led to fast land-use changes from natural forest to agricultural land.This resulted in speeding up the soil erosion process in the highlands and increasing sedimentation further downstream in reservoirs and irrigation canals.At present,several dams are planned across the Blue Nile River in Ethiopia and the Grand Ethiopian Renaissance Dam is currently under construction near the border with Sudan.This will be the largest hydroelectric power plant in Africa.The objective of this paper is to quantify the river flows and sediment loads along the Blue Nile River network.The Soil and Water Assessment Tool was used to estimate the water flows from un-gauged sub-basins.To assess model performance,the estimated sediment loads were compared to the measured ones at selected locations.For the gauged sub-basins,water flows and sediment loads were derived from the available flow and sediment data.To fill in knowledge gaps,this study included a field survey in which new data on suspended solids and flow discharge were collected along the Blue Nile and on a number of tributaries.The comparison between the results of this study and previous estimates of the sediment load of the Blue Nile River at El Deim,near the Ethiopian Sudanese border,show that the sediment budgets have the right order of magnitude,although some uncertainties remain.This gives confidence in the results of this study providing the first sediment balance of the entire Blue Nile catchment at the sub-basin scale.  相似文献   

Short communication: Recognising the perils of landslide-generated tsunamis in the Asia–Pacific region     

Terry  James P.  Goff  James  Winspear  Nigel  Bongolan  Vena Pearl 《Natural Hazards》2019,96(3):1413-1428

The objective of the paper was to characterise the temporal and spatial variability of winter warm spells in Central Europe in the years 1966/1967–2015/2016 and to determine the circulation conditions of their occurrence. The applied data were obtained from the Polish Institute of Meteorology and Water Management, Deutscher Wetterdienst and the National Centre for Environmental Prediction/National Centre for Atmospheric Research. A warm spell was defined as a sequence of at least three warm days, i.e. when the maximum air temperature is higher than the 95th percentile of the probability density function designated from observation. The research has proven that over the study period the air temperature increased in the winter season in Central Europe and this translated into an increase in the number of warm days. An average of 3–5 warm spells was recorded per 10 years. The most numerous warm spells occurred during three winter seasons, i.e. 1989/1990, 2006/2007 and 2015/2016. The occurrence of warm spells was related to positive anomalies of geopotential heights over the study area in the cross section of the entire troposphere. Maximum anomalies appeared at 250 hPa geopotential height, and they developed on average 9 days before the commencement of warm spells over the study area.

  相似文献   

Marine Controlled Source Electromagnetics: Principles,Methodologies, Future Commercial Applications   总被引：10，自引：1，他引：9  

Nigel?EdwardsEmail author 《Surveys in Geophysics》2005,26(6):675-700

The exploration community, from the earth scientist to the investment manager, has surely recognized the recent surge of interest in the use of controlled source electromagnetics for offshore hydrocarbon detection and assessment. The targets, petroleum, natural gas and gas hydrate, are resistive zones in an otherwise conductive background. I trace the academic and commercial development of marine methods from basic theory through experimental design to the few published relevant exploration case histories. Invited review paper presented at the 17th Electromagnetic Induction Workshop. Hyderabad, India, 18–23 October, 2004.  相似文献