Stream sediment geochemistry of the upper Cheyenne River watershed within the abandoned uranium mining region of the southern Black Hills,South Dakota,USA     

Rohit K. Sharma  Keith D. Putirka  James J. Stone 《Environmental Earth Sciences》2016,75(9):823

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The 2dF Galaxy Redshift Survey: power-spectrum analysis of the final data set and cosmological implications     

Shaun Cole  Will J. Percival  John A. Peacock  Peder Norberg  Carlton M. Baugh  Carlos S. Frenk  Ivan Baldry  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Matthew Colless  Chris Collins  Warrick Couch  Nicholas J. G. Cross  Gavin Dalton  Vincent R. Eke  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Karl Glazebrook  Carole Jackson  Adrian Jenkins  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren Madgwick  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,362(2):505-534

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Phytoplankton biornass in relation to the surface hydrography of southern New Zealand and possible effects on the food chain     

Janet M. Bradford  H. John Cranfield  Keith P. Michael 《新西兰海洋与淡水研究杂志》2013,47(2):133-144

Abstract

The surface distribution of salinity, temperature, nitrate‐nitrogen (N0₃‐N), and chlorophyll a in the southern New Zealand, Foveaux Strait region in February 1977, 1978, 1979, and 1980 was highly variable. The source of new nitrogen appears to be incursions of high‐salinity water west and east of Stewart Island. Although it seems likely that the source of this high‐nutrient, high‐salinity water is vertical, a horizontal advective source cannot be ruled out The chlorophyll a content of surface waters was not related directly to the NO3‐N concentrations. This lower food chain variability may be linked to variability in economically important species. Oysters grew twice as fast in the summer of 1978/79 as they did in 1979/80. But the mean chlorophyll a values were very similar for February of both years (2.5 and 2.2 μg 1^?1, respectively). The elevated NO₃‐N levels in 1979 may have resulted in much higher phytoplankton levels later that summer and resulted in the higher oyster growth rate that year. The mechanisms driving this variability have yet to be determined.  相似文献   

Sediment-transport modeling on Southern Californian shelves: A ROMS case study     

Meinte Blaas  Changming Dong  Patrick Marchesiello  James C. McWilliams  Keith D. Stolzenbach 《Continental Shelf Research》2007

Suspended sediment-transport processes in Santa Monica and San Pedro Bay are analyzed using the sediment-transport capabilities of the Regional Oceanic Modeling System (roms). A one-month simulation for December 2001 has been carried out with a set of nested domains. The model inputs include tides, winds, surface waves, and idealized initial sediment conditions for sand and non-cohesive silt. Apart from the control run, the sensitivity of the results to surface waves, ripple roughness and bed armoring has been analyzed. From the control experiment, the horizontal transport of sand turns out to be limited to within a few km of the nearshore erosion zones. During high wave events, silt is transported over further distances and also partly offshelf in distinct plumes. The effectiveness of horizontal silt transport depends strongly on vertical mixing due to both surface wind stress and wave-enhanced bottom stress. High wave events coincident with strong winds (hence strong vertical mixing) are the most optimal conditions for sediment-transport. Excluding wave effects in the simulation shows that surface waves are the dominant factor in resuspending bed material on the Southern Californian shelves. The sensitivity experiments also show that the direct influence of additional ripple roughness on erosion and deposition is relatively weak. Switching off bed armoring locally results in increases of near-bottom concentrations by a factor of 20 for silt and a factor of 5 for sand as well as stronger spatial gradients in grain size.  相似文献   

Using chloride and other ions to trace sewage and road salt in the Illinois Waterway     

Walton R. Kelly  Samuel V. Panno  Keith C. Hackley  Hue-Hwa Hwang  Adam T. Martinsek  Momcilo Markus 《Applied Geochemistry》2010

Chloride concentrations in waterways of northern USA are increasing at alarming rates and road salt is commonly assumed to be the cause. However, there are additional sources of Cl⁻ in metropolitan areas, such as treated wastewater (TWW) and water conditioning salts, which may be contributing to Cl⁻ loads entering surface waters. In this study, the potential sources of Cl⁻ and Cl⁻ loads in the Illinois River Basin from the Chicago area to the Illinois River’s confluence with the Mississippi River were investigated using halide data in stream samples and published Cl⁻ and river discharge data. The investigation showed that road salt runoff and TWW from the Chicago region dominate Cl⁻ loads in the Illinois Waterway, defined as the navigable sections of the Illinois River and two major tributaries in the Chicago region. Treated wastewater discharges at a relatively constant rate throughout the year and is the primary source of Cl⁻ and other elements such as F⁻ and B. Chloride loads are highest in the winter and early spring as a result of road salt runoff which can increase Cl⁻ concentrations by up to several hundred mg/L. Chloride concentrations decrease downstream in the Illinois Waterway due to dilution, but are always elevated relative to tributaries downriver from Chicago. The TWW component is especially noticeable downstream under low discharge conditions during summer and early autumn when surface drainage is at a minimum and agricultural drain tiles are not flowing.  相似文献   

Iron isotope compositions of carbonatites record melt generation, crystallization, and late-stage volatile-transport processes   总被引：2，自引：0，他引：2  

Clark M. Johnson  Keith Bell  Brian L. Beard  Aaron I. Shultis 《Mineralogy and Petrology》2010,98(1-4):91-110

Carbonatites define the largest range in Fe isotope compositions yet measured for igneous rocks, recording significant isotopic fractionations between carbonate, oxide, and silicate minerals during generation in the mantle and subsequent differentiation. In contrast to the relatively restricted range in δ⁵⁶Fe values for mantle-derived basaltic magmas (δ⁵⁶Fe?=?0.0?±?0.1‰), calcite from carbonatites have δ⁵⁶Fe values between ?1.0 and +0.8‰, similar to the range defined by whole-rock samples of carbonatites. Based on expected carbonate-silicate fractionation factors at igneous or mantle temperatures, carbonatite magmas that have modestly negative δ⁵⁶Fe values of ~ ?0.3‰ or lower can be explained by equilibrium with a silicate mantle. More negative δ⁵⁶Fe values were probably produced by differentiation processes, including crystal fractionation and liquid immiscibility. Positive δ⁵⁶Fe values for carbonatites are, however, unexpected, and such values seem to likely reflect interaction between low-Fe carbonates and Fe³⁺-rich fluids at igneous or near-igneous temperatures; the expected δ⁵⁶Fe values for Fe²⁺-bearing fluids are too low to produced the observed positive δ⁵⁶Fe values of some carbonatites, indicating that Fe isotopes may be a valuable tracer of redox conditions in carbonatite complexes. Further evidence for fluid-rock or fluid-magma interactions comes from the common occurrence of Fe isotope disequilibrium among carbonate, oxide, silicate, and sulfide minerals in the majority of the carbonatites studied. The common occurrence of Fe isotope disequilibrium among minerals in carbonatites may also indicate mixing of phenocyrsts from distinct magmas. Expulsion of Fe³⁺-rich brines into metasomatic aureols that surround carbonatite complexes are expected to produce high-δ⁵⁶Fe fenites, but this has yet to be tested.  相似文献   

Middle Pleistocene environments,landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley     

Jenni E. Sherriff  Keith N. Wilkinson  Poppy Harding  Hayley Hawkins  Rhys G. O. Timms  Daniel S. Adler  Emily J. Beverly  Simon P. E. Blockley  Boris Gasparyan  Christina J. Manning  Darren Mark  Samvel Nahapetyan  Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.  相似文献