Freshwater inflow and estuarine variability in the Gamtoos Estuary, South Africa     

Eckart H. Schumann  Meryl W. Pearce 《Estuaries and Coasts》1997,20(1):124-133

The Gamtoos is a shallow flood-tidal estuary located on the south coast of South Africa. Even though it has an extensive catchment area, dams limit runoff and mean freshwater inflow is estimated at less than 1 m³ s^?1, and the flood tidal deltas constrict and at times even close the mouth. The results presented here derive from an intensive measurement program carried out over a 3-wk period at the end of 1992, immediately after good rains in the Gamtoos catchment region. Freshwater inflow increased to more than 10 m³ s^?1, driving the salt wedge downstream and resulting in intense haloclines in the mid-estuary region. The program monitored the return to more average estuarine structures, and even though tidal exchange was restricted, marked differences occurred in stratification at neap and spring tides; tidal exchanges provided the dominant mixing forces. It is found that the shallower upper reaches of the estuary are flushed with relatively small increases in freshwater inflow, though a balance exists with the tidal exchanges through the constricted mouth. The variation in the position of the salt wedge and in the salinity stratification can have substantial implications for biota.  相似文献   

`Protecting the Polar Marine Environment: Law and Policy for Pollution Prevention' by Davor Vidas (Ed.). Cambridge University Press, 2000, 276 pages. ISBN 0-521-66311-3, Price US $69.95 cloth.     

Jack B Pearce 《Marine pollution bulletin》2002,44(8):833

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Late Quaternary evolution of the Madeira Abyssal Plain,Canary Basin,NE Atlantic     

R. G. Rothwell  T. J. Pearce  P. P. E. Weaver 《Basin Research》1992,4(2):103-131

The deepest part of the Canary Basin, the Madeira Abyssal Plain, receives allochthonous sediments derived from a large drainage basin which, if its subaerial continuation is included, covers an area of 3.36 times 10⁶ km². An international research effort over the last 10 years has recovered over 160 sediment cores from the plain, and the development of a high-resolution stratigraphy has enabled individual turbidites to be correlated layer by layer. Sedimentation on the Madeira Abyssal Plain during the late Quaternary is dominated by thick turbidite muds separated by thin pelagic intervals. The core density has allowed the mapping of each sedimentary unit throughout the abyssal plain, thus building up a layer by layer picture of sediment accumulation. Over the last 300 kyr, 600 km³ of turbidites compared to 60 km³ of pelagic sediments have been deposited on the plain. Sedimentary structures developed in the coarse basal facies of the larger turbidites are more complex than simple models predict due to surging flows, fluctuating flow velocities and reflection from adjacent high ground. Over the last 300 kyr, there has been a switching of entry points for turbidity currents entering the abyssal plain. From 300 ka to 200 ka, organic-rich turbidites were emplaced predominantly from the south but around 200 ka this source switched off and subsequent organic- and volcanic-rich turbidites, which included units deposited by giant, possibly hyperconcentrated flows, were emplaced from northern or eastern sources. Although restricted to the late Quaternary, the data presented provides a detailed case study of the evolution of an oceanic basin fill.  相似文献   

Origin of magnetization in lunar breccias: An example of thermal overprinting     

W.A. Gose  D.W. Strangway  G.W. Pearce 《Earth and Planetary Science Letters》1978,38(2):373-384

Twenty six samples from seven hand specimens, collected from the station 6 boulder at the Apollo 17 landing site, were studied magnetically. The boulder is a breccia consisting of three lithologic units distinguished by their clast population. The direction of magnetization of samples from unit B which is almost devoid of large clasts cluster fairly well after alternating field demagnetization. Samples from unit C which is characterized by abundant large clasts up to 1 m in size do not contain a uniform direction of magnetization but the distribution is not random. Based on these data we propose that the natural remanent magnetization (NRM) in these breccias is the vector sum of two magnetizations, a pre-impact magnetization and a partial thermoremanence acquired during breccia formation. The relative contribution of the two components is controlled by the thermal history of the ejecta, which in turn is determined by its clast population. Depending on the clast population, the NRM can be a total thermoremanence, a partial thermoremanence plus a pre-impact magnetization, or a pre-impact magnetization. This model of thermal overprinting might be applicable to all lunar breccias of medium and higher metamorphic grade.  相似文献   

The TiO₂–K₂O–P₂O₅ diagram: A method of discriminating between oceanic and non-oceanic basalts     

T.H. Pearce  B.E. Gorman  T.C. Birkett 《Earth and Planetary Science Letters》1975,24(3):419-426

The TiO₂–K₂O–P₂O₅ ternary diagram is proposed as a method of discriminating between oceanic and non-oceanic (continental) basalts. This diagram is effective for non-alkaline “primitive” basalts: fractionated rocks cannot be adequately discriminated. Suitable analyses are those which have total alkalies ≤ 20% in an (Fe₂O₃ + FeO)–MgO–(Na₂O + K₂O) diagram. The proposed dividing line separates 93% of 222 ocean-floor and ocean-ridge basalts into the oceanic field and > 80% of continental basalt analyses into the non-oceanic field. Two exceptions are the Tertiary basalts of Greenland and the Deccan Traps which have oceanic affinities. “Continental” suites displaying an oceanic affinity in the TiO₂–K₂O–P₂O₅ diagram may be a result of abortive attempts to generate new sea floor. Preliminary results for dike swarms and Archean basalts suggest preponderant oceanic affinities. Alteration and metamorphism of oceanic basalts generally occasion enrichment of K₂O relative to TiO₂ and P₂O₅.  相似文献   

3rd International Biodegradation Symposium     

James S. Young  John B. Pearce 《Marine pollution bulletin》1975,6(7):101-105

Dumping grounds in New York Bight receive very large quantities of sewage sludge. Lobsters and rock crabs collected in or near the dumping grounds sometimes show various pathological conditions of the shell and gills. In this study the histopathology of ‘shell disease’, the causative agents and its effects on respiration are discussed in connexion with a possible association with the disposal of solid wastes into the ocean.  相似文献   

Trace metals in sediments of New York Bight     

D.J. Carmody  J.B. Pearce  W.E. Yasso 《Marine pollution bulletin》1973,4(9):132-135

Concentrations of chromium, copper, lead, nickel and zinc in superficial sediments in New York Bight are ten to a hundred times greater near waste disposal areas than in uncontaminated sediments. Some wastes are transported by currents north-east towards Long Island and south-east along the Hudson Submarine Valley.  相似文献   

A contribution to the theory of variation diagrams   总被引：9，自引：0，他引：9  

T. H. Pearce 《Contributions to Mineralogy and Petrology》1968,19(2):142-157

Harker diagrams and other ternary weight per-cent diagrams distort genetic trends by changing their slopes. They can not be readily used to discriminate between rival hypotheses. Two theorems have been proven which show the desirability of using certain types of ratios, instead of per-cent values, for comparisons. It is suggested that, when it is desired to discriminate between rival hypotheses, or to determine the exact variation between components, weight per-cent comparisons be discontinued (wherever possible) in favour of molar ratio comparisons in which one of the components (the divisor) is a constant. Variation diagrams of this type offer reliable discrimination between rival hypotheses, and yield the true relationship between variables in every case. An example involving crystal fractionation of olivine and pyroxene from a basic sill is developed in detail, and other potential uses are mentioned. This technique is completely general and is not restricted to chemical components, or to any scale of system, or to any field of study, providing certain essential conditions are fulfilled.  相似文献   

The effect of noise on seismograms     

R. G. Pearce  B. J. Barley 《Geophysical Journal International》1977,48(3):543-547

Summary. We describe a method which provides an estimate of the accuracy to which time-domain features of seismic signals can be measured in the presence of noise. Observed seismograms are simulated by adding random noise with the same frequency spectrum and signal-to-noise ratio to matching synthetic seismograms. The effect of noise on synthetic and observed P -wave first motions is used as an illustration. It is shown that the apparent reliability of such observations, as determined by visual estimation, is often illusory.  相似文献   

Key(s) to marine ecology and understanding pollution impacts--a tribute to Dr. Howard Sanders, marine benthic biologist extra-ordinaire     

Pearce JB  Wells PG 《Marine pollution bulletin》2002,44(3):179-180

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