A major sulphur isotope event at c. 510 Ma: a possible anoxia–extinction–volcanism connection during the Early–Middle Cambrian transition?     

M.L. Hough  G.A. Shields  L.Z. Evins  H. Strauss  R.A. Henderson  S. Mackenzie 《地学学报》2006,18(4):257-263

A new approach to constraining seawater δ³⁴S and sulphate concentration using francolite‐bound sulphate reveals an abrupt increase in δ³⁴S to +50‰ around the Early–Middle Cambrian boundary. Such high δ³⁴S values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500–700 μgL^?1. We argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the Kalkarindji Large Igneous Province of northern Australia and that it triggered the collapse of early metazoan reef ecosystems during the latest Early Cambrian. Mass extinctions of the last 260 Myr have all coincided with enhanced volcanic activity, while several are also associated with positive shifts in seawater δ³⁴S. Extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution. Terra Nova, 18, 257–263, 2006  相似文献   

Operational predictability of monthly average maximum temperature over the Iberian Peninsula using DEMETER simulations and downscaling   总被引：1，自引：0，他引：1  

M. DOLORES FRÍAS  JESÚS FERNÁNDEZ  JON SÁENZ  CONCEPCIÓN RODRÍGUEZ-PUEBLA 《地球，A辑:动力气象学与海洋学》2005,57(3):448-463

  相似文献   

CO2 air–sea exchange due to calcium carbonate and organic matter storage, and its implications for the global carbon cycle     

Abraham Lerman  Fred T. Mackenzie 《Aquatic Geochemistry》2006,12(4):389-390

  相似文献   

Experimental study of igneous and sedimentary apatite dissolution: Control of pH, distance from equilibrium, and temperature on dissolution rates     

Michael W. Guidry  Fred T. Mackenzie 《Geochimica et cosmochimica acta》2003,67(16):2949-2963

Apatite dissolution experiments were conducted using both a fluidized bed and stirred tank reactor over a range of pH, temperature, solution saturation state, and on non-carbonated and carbonated apatite compositions: igneous fluorapatite (FAP) and sedimentary carbonate fluorapatite (CFA), respectively. From 2 <pH <6, the rate of release from dissolution of all apatite components [calcium (Ca), phosphorus (P), and fluoride (F)] increased with decreasing pH for FAP. From 6 < pH < 8.5, the FAP dissolution rate is pH independent. Measuring apatite dissolution rates at pH > 8.5 were not possible due to detection limits of the analytical techniques used in this study and the high insolubility of FAP. For the CFA compositions studied, the dissolution rate decreased with increasing pH from 4 < pH < 7. During early stages of the dissolution reaction for both FAP and CFA, mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P and Ca:F being greater than mineral stoichiometric ratios, suggesting that Ca was preferentially released compared to P and F from the mineral structure during the early stages of dissolution. An increase in reacted solution pH accompanies this early elevated release of Ca. As the dissolution reaction proceeded to steady state, dissolution became congruent. When normalized to BET measured surface area, FAP dissolved faster from 4 < pH < 7 compared to CFA. The apparent Arrhenius activation energy (E_a) of FAP dissolution over the temperature range of 25-55°C at pH = 3.0, I = 0.1, and pCO₂ = 0 is 8.3 ± 0.2 kcal mol⁻¹. Both the apparent exchange of solution H⁺ for solid-bound Ca at low pH in the early stage of dissolution and the E_a of dissolution suggest a surface and not a diffusion controlled dissolution reaction for FAP and CFA. The degree of undersaturation of the solution, ΔG_R, with respect to FAP was important in determining the dissolution rate. At pH = 3.0, I = 0.1, and pCO₂ = 0, the dissolution rate of FAP was ∼ 5× greater in the far-from-equilibrium region compared to the near-equilibrium slope region.A simple apatite weathering model incorporating the experimental results from this study was constructed, and numerical calculations suggest that during the Phanerozoic both the surface area of igneous rock available for weathering and the average global temperature were important factors in determining the P weathering flux from apatite dissolution. It is possible that elevated global temperatures coupled with relatively high surface area of igneous rock during the early- to mid-Paleozoic resulted in elevated P weathering fluxes, which along with climatic evolutionary pressures of the Neoproterozoic, facilitated the radiation of multicellular organisms, large-scale phosphorite deposition, and abundance of calcium phosphate shelled organisms during the early Cambrian.  相似文献   

A geopotential error analysis for a non planar satellite to satellite tracking mission   总被引：1，自引：0，他引：1  

R. Mackenzie  P. Moore 《Journal of Geodesy》1997,71(5):262-272

This study is concerned with gravity field recovery from low-low satellite to satellite range rate data. Compared against a coplanar mission an improvement is predicted in errors associated with certain parts of the geopotential by the separation of the orbital planes of the two satellites. Using Hill's equations an analytical scheme is developed to model the range rate residuals. It is flexible enough to model the residuals between pairs of satellites in the same orbital plane or whose planes are separated in right ascension. This scheme should allow the possibility of larger planar separations than previously since no small angle approximation is made. The effects of such an orientation on gravity field recovery can therefore be analysed by means of an extensive error analysis. The results of this analysis indicate that a significant improvement in the errors of the near sectorial coefficients are obtained when the satellite's orbital planes are separated. Received: 9 April 1996; Accepted: 26 September 1996  相似文献   

Petrology,Igneous, Sedimentary and Metamorphic by Ernest G. E. Ehlers and Harvey Blatt. W. H. Freeman & Co., San Francisco, 1982. No. of pages: 732. Price: £21.95     

W. S. Mackenzie  A. E. Adams 《Geological Journal》1983,18(1):101-101

  相似文献   

Pressure image assimilation for atmospheric motion estimation     

THOMAS CORPETTI  PATRICK HÉAS  ETIENNE MÉMIN  NICOLAS PAPADAKIS 《地球，A辑:动力气象学与海洋学》2009,61(1):160-178

The complexity of the laws of dynamics governing 3-D atmospheric flows associated with incomplete and noisy observations make the recovery of atmospheric dynamics from satellite image sequences very difficult. In this paper, we address the challenging problem of estimating physical sound and time-consistent horizontal motion fields at various atmospheric depths for a whole image sequence. Based on a vertical decomposition of the atmosphere, we propose a dynamically consistent atmospheric motion estimator relying on a multilayer dynamic model. This estimator is based on a weak constraint variational data assimilation scheme and is applied on noisy and incomplete pressure difference observations derived from satellite images. The dynamic model is a simplified vorticity-divergence form of a multilayer shallow-water model. Average horizontal motion fields are estimated for each layer. The performance of the proposed technique is assessed using synthetic examples and using real world meteorological satellite image sequences. In particular, it is shown that the estimator enables exploiting fine spatio-temporal image structures and succeeds in characterizing motion at small spatial scales.  相似文献   

The effect of maturation on the configurations of acyclic isoprenoid acids in sediments     

A.S. Mackenzie  R.L. Patience  D.A. Yon  J.R. Maxwell 《Geochimica et cosmochimica acta》1982,46(5):783-792

Within a variety of sedimentary rocks of differing maturity, the configurations of a suite of acyclic isoprenoid acids have been examined by gas Chromatographic (in a few cases also by combined gas chromatography-mass spectrometry) analysis of their diastereoisomeric methyl and (?)-menthyl esters. The samples include the Eocene Messel (Germany) and Green River (U.S.) shales, the Permian Irati shale (Brazil) and a number of Lower Toarcian shales from the Paris Basin. The isomer distributions show that isomerisation occurs at the chiral centres with increasing maturation (to increase the number of isomers) and that the rate of isomerisation increases for centres (C-2,C-3) closest to the carboxyl group. These results suggest that adsorption of the carboxyl group to a catalyst surface may control the isomerisation rates by way of access to the catalyst.  相似文献   

Organic geochemistry and pore water chemistry of sediments from Mangrove Lake,Bermuda     

Patrick G. Hatcher  Bernd R.T. Simoneit  Fred T. Mackenzie  A.Conrad Neumann  Donald C. Thorstenson  Sol M. Gerchakov 《Organic Geochemistry》1982,4(2):93-112

Mangrove Lake, Bermuda, is a small coastal, brackish-water lake that has accumulated 14 m of banded, gelatinous, sapropelic sediments in less than 10⁴ yr. Stratigraphic evidence indicates that Mangrove Lake's sedimentary environment has undergone three major depositional changes (peat, freshwater gel, brackish-water gel) as a result of sea level changes. The deposits were examined geochemically in an effort to delineate sedimentological and diagenetic changes. Gas and pore water studies include measurements of sulfides, ammonia, methane, nitrogen gas, calcium, magnesium, chloride, alkalinity, and pH. Results indicate that sulfate reduction is complete, and some evidence is presented for bacterial denitrification and metal sulfide precipitation. The organic-rich sapropel is predominantly algal in origin, composed mostly of carbohydrates and insoluble macromolecular organic matter called humin with minor amounts of proteins, lipids, and humic acids. Carbohydrates and proteins undergo hydrolysis with depth in the marine sapropel but tend to be preserved in the freshwater sapropel. The humin, which has a predominantly aliphatic structure, increases linearly with depth and composes the greatest fraction of the organic matter. Humic acids are minor components and are more like polysaccharides than typical marine humic acids. Fatty acid distributions reveal that the lipids are of an algal and/or terrestrial plant source. Normal alkanes with a total concentration of 75 ppm exhibit two distribution maxima. One is centered about n-C₂₂ with no odd/even predominance, suggestive of a degraded algal source. The other is centered at n-C₃₁ with a distinct odd/even predominance indicative of a vascular plant origin. Stratigraphic changes in the sediment correlate to observed changes in the gas and pore water chemistry and the organic geochemistry.  相似文献   

Pleistocene volcanic rocks from the Fly-Highlands province of western Papua New Guinea: A note on new Sr and Nd isotopic data and their petrogenetic implications     

P.J. Hamilton  R.W. Johnson  D.E. Mackenzie  R.K. O'Nions 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

RB-Sr and Sm-Nd isotopic and trace-element-abundance values have been determined for 15 mafic and intermediate rocks from six Pleistocene volcanic centres of the Fly-Highlands province. ⁸⁷Sr/⁸⁶Sr and _{N d} values range from 0.70362 to 0.70540, and +1.9 to +5.9, respectively. These new data can be accounted for by contamination of mantle-derived magmas by the continental crust through which the magmas have risen. They do not, however, preclude derivation of some of the Sr and Nd from subducted crust, nor are they inconsistent with Sr and Nd enrichments having taken place by means of mantle metasomatic events. Nevertheless, there is no Benioff zone beneath the Fly-Highlands province (although there is geological evidence for Cretaceous subduction). A preferred interpretation is that uncontaminated, mantle-derived magmas are related to the Pliocene crustal uplift that caused the development of the highlands and which formed in response to a mid-Tertiary continent/island-arc collision.  相似文献