A renaissance in studies of ancient life     

J. William Schopf  Anatoliy B. Kudryavtsev 《Geology Today》2010,26(4):140-145

In the Origin of Species, published a century‐and‐a‐half ago, Darwin was mystified by the lack of a ‘pre‐Cambrian’ fossil record, the existence of which he regarded as pivotal to his theory of evolution. For the next 100 years, this ‘missing’ fossil record—unknown and thought unknowable'stood out as arguably the single greatest blemish to Darwin's theory. Beginning in the 1950s, the answer to Darwin's problem began to be unearthed, a Precambrian record of flourishing communities of microscopic organisms now known to extend to 3500 million years ago. During recent years, studies of such ancient microbes have markedly increased, spurred by an influx of new workers and, especially, by the introduction of new analytical techniques, three of which are featured here: confocal laser scanning microscopy, and Raman‐spectral and fluorescence‐spectral imagery. Used together, these techniques provide evidence of the three‐dimensional form, cellular anatomy, and molecular structure of rock‐embedded microscopic fossils and of the minerals in which they are entombed that is unavailable by any other means.  相似文献   

A) A. I. H. S. / A) I. A. S. H.     

Herbert B. OSBORN  William N. REYNOLDS 《水文科学杂志》2013,58(3):71-78

Abstract

In the Southwestern intermountain and high plains areas, precipitation is seasonal, with the major part of the rainfall occurring in the summer. Most winter precipitation occurs as low-intensity rain or snow along slow-moving cold fronts. Most summer precipitation occurs as short-duration, high-intensity thunderstorms from purely convective buildup or from convective cells developing along a weak fast-moving cold front. Almost all runoff occurs from the summer convective storms.

Since runoff-producing precipitation is of primary interest at the Southwest Watershed Research Center, Agricultural Research Service, Tucson, Arizona, the convective storms have been most thoroughly analyzed. Duration, intensity, areal extent, movement, character, and return frequencies for varying volumes and intensities of these convective storms are analyzed from records from dense networks of recording rain gages in four study areas in Arizona and New Mexico. The primary study areas are the 58-square-mile Walnut Gulch Experimental Watershed at Tombstone, Arizona, and the 67-squaremile Alamogordo Creek Watershed near Santa Rosa, New Mexico. Three “record” storms of differing character occurring in 1960 and 1961 on Alamogordo Creek Watershed and one “record” storm in 1961 on the Wlanut Gulch Watershed are analyzed and compared in detail.  相似文献   

Breaking wave loads at vertical seawalls and breakwaters     

Giovanni Cuomo  William Allsop  Tom Bruce  Jonathan Pearson 《Coastal Engineering》2010

This paper presents recent advances in knowledge on wave loads, based on experimental work carried out in the CIEM/LIM large flume at Barcelona within the framework of the VOWS (Violent Overtopping by Waves at Seawalls) project. Both quasi-static and impact wave forces from the new data set have been compared with predictions by empirical and analytical methods. The scatter in impact forces has been found to be large over the whole range of measurements, with no existing method giving especially good predictions. Based on general considerations, a simple and intuitive set of prediction formulae has been introduced for quasi-static and impact forces, and overturning moments, giving good agreement with the new measurements. New prediction formulae have been compared with previous measurements from physical model tests at small and large scale, giving satisfactory results over a relatively wide range of test conditions. The time variation of wave impacts is discussed, together with pressure distribution up the wall, which shows that within experimental limitations the measured pressures are within existing limits of previous study.  相似文献   

Spatial and temporal patterns in the hyperbenthic community structure in a warm temperate southern African permanently open estuary     

Elodie Heyns  William Froneman 《Estuarine, Coastal and Shelf Science》2010

The spatial and temporal patterns in the hyperbenthic community structure (>500 μm) in the warm temperate, permanently open Kariega Estuary situated along the south-eastern coastline of South Africa was investigated monthly over a period of twelve months. Data were collected using a modified hyperbenthic sledge at six stations along the length of the estuary. Physico-chemical data indicate the presence of a constant reverse salinity gradient, with highest salinities measured in the upper reaches and lowest at the mouth of the estuary. Strong seasonal patterns in temperature, dissolved oxygen and total chlorophyll-a (chl-a) concentration were evident. Total average hyperbenthic densities ranged between 0.4 and 166 ind.m⁻³ in the lower net and between 0.2 and 225 ind.m⁻³ in the upper net. Hyperbenthic biomass values ranged between 0.02 and 11.9 mg.dry weight.m⁻³ in the lower net and between 0.02 and 17.4 mg.dry weight.m⁻³ in the upper net. Both the lower and upper nets were numerically dominated by decapods (mainly brachyuran crab zoea) with the exception of June and July 2008 when mysids (mainly Mesopodopsis wooldridgei) dominated, comprising up to 72.4 ± 58.14% of the total abundance in the lower net. A redundancy analysis (RDA) indicated that 99.2% of the variance in the hyperbenthic community structure could be explained by the first two canonical axes. Axis one, which accounted for 96.8% of the total variation detected in the ordination plot was highly correlated with sedimentary organic content and to a lesser extent the chl-a concentration within the Kariega Estuary. The correlations with the second canonical axis (2.4%) were less obvious, however, salinity and seston concentration were weakly correlated with this axis.  相似文献   

Impact of Alaskan Stream eddies on chlorophyll distribution in the North Pacific   总被引：1，自引：0，他引：1  

Hiromichi Ueno  William R. Crawford  Hiroji Onishi 《Journal of Oceanography》2010,66(3):319-328

The impact of the Alaskan Stream (AS) eddies on the chlorophyll a (chl-a) distribution in the central subarctic North Pacific was investigated through analysis of chl-a and altimetry data from satellite observations. Altimetry observations provided the locations of mesoscale eddies in time and space within the maps of chlorophyll distributions. The climatological chl-a distributions averaged in the area and time showing presence of AS eddies suggested that AS eddies contributed significantly to the chl-a distribution in the deep-sea region of the subarctic North Pacific. The chl-a distribution was closely related to the AS eddies regardless of whether the eddy was located in or detached from the AS. A combination of two or three AS eddies sometimes formed high chl-a concentration belts that injected chlorophyll and coastal nutrient-rich waters southward from the Aleutian Islands far into the deep-sea region of the subarctic North Pacific. These results indicate that chl-a distribution in the central subarctic North Pacific was strongly impacted by AS eddies.  相似文献   

Hanford tank residual waste – Contaminant source terms and release models     

William J. Deutsch  Kirk J. Cantrell  Kenneth M. Krupka  Michael L. Lindberg  R. Jeffery Serne 《Applied Geochemistry》2011,26(9-10):1681-1693

Residual waste is expected to be left in 177 underground storage tanks after closure at the US Department of Energy’s Hanford Site in Washington State, USA. In the long term, the residual wastes may represent a potential source of contamination to the subsurface environment. Residual materials that cannot be completely removed during the tank closure process are being studied to identify and characterize the solid phases and estimate the release of contaminants from these solids to water that might enter the closed tanks in the future. As of the end of 2009, residual waste from five tanks has been evaluated. Residual wastes from adjacent tanks C-202 and C-203 have high U concentrations of 24 and 59 wt.%, respectively, while residual wastes from nearby tanks C-103 and C-106 have low U concentrations of 0.4 and 0.03 wt.%, respectively. Aluminum concentrations are high (8.2–29.1 wt.%) in some tanks (C-103, C-106, and S-112) and relatively low (<1.5 wt.%) in other tanks (C-202 and C-203). Gibbsite is a common mineral in tanks with high Al concentrations, while non-crystalline U–Na–C–O–P ± H phases are common in the U-rich residual wastes from tanks C-202 and C-203. Iron oxides/hydroxides have been identified in all residual waste samples studied to date. Contaminant release from the residual wastes was studied by conducting batch leach tests using distilled deionized water, a Ca(OH)₂-saturated solution, or a CaCO₃-saturated water. Uranium release concentrations are highly dependent on waste and leachant compositions with dissolved U concentrations one or two orders of magnitude higher in the tests with high U residual wastes, and also higher when leached with the CaCO₃-saturated solution than with the Ca(OH)₂-saturated solution. Technetium leachability is not as strongly dependent on the concentration of Tc in the waste, and it appears to be slightly more leachable by the Ca(OH)₂-saturated solution than by the CaCO₃-saturated solution. In general, Tc is much less leachable (<10 wt.% of the available mass in the waste) than previously predicted. This may be due to the coprecipitation of trace concentrations of Tc in relatively insoluble phases such as Fe oxide/hydroxide solids.  相似文献   

The Chalk area of North-East Surrey     

George William Young 《Proceedings of the Geologists' Association. Geologists' Association》1905,19(4):188-IN1

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Excursion to Gerrard's Cross,Bucks: Saturday,April 1st, 1905     

R.C. Sikes  A.H. William 《Proceedings of the Geologists' Association. Geologists' Association》1905,19(3):107-108

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Excursion to Knockholt and Sevenoaks: Saturday,May 24th, 1879. (Second of the Weald Series.)     

J. Logan Lobley  William Fawcett 《Proceedings of the Geologists' Association. Geologists' Association》1880,6(5):194-196

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Ordinary meeting,April 6th, 1877     

William Carruthers 《Proceedings of the Geologists' Association. Geologists' Association》1877,5(3):113-114

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