Hypoxia in a Coastal Embayment of the Chesapeake Bay: A Model Diagnostic Study of Oxygen Dynamics     

Jian Shen  Taiping Wang  Julie Herman  Pam Mason  Gretchen L. Arnold 《Estuaries and Coasts》2008,31(4):652-663

Two distinct hypoxic patterns were revealed from high-frequency dissolved oxygen (DO) data collected from North Branch of Onancock Creek, a shallow coastal estuary of the Chesapeake Bay, from July to October 2004. Diurnal hypoxia developed associated with large DO swings during fair weather and hypoxia/anoxia developed for prolonged 2–5-day periods following rainfall events. A simplified diagnostic DO-algae model was used to investigate DO dynamics in the creek. The model results show that the modeling approach enables important features of the DO dynamics in the creek to be captured and analyzed. Large anthropogenic inputs of nutrients to the creek stimulated macroalgae blooms in the embayment. High DO production resulted in supersaturated DO in daytime, whereas DO was depleted at night as the high respiration overwhelmed the DO supply, leading to hypoxia. Unlike deep-water environments, in this shallow-water system, biological processes dominate DO variations. High macroalgae biomass interacting with low light and high temperature trigger the development of prolonged hypoxic/anoxic postrainfall events.  相似文献   

Matching carbon pools and fluxes for the Southern Ocean Iron Release Experiment (SOIREE)     

Dorothee C.E. Bakker  Philip W. Boyd  Edward R. Abraham  Matthew A. Charette  Mark P. Gall  Julie A. Hall  Cliff S. Law  Scott D. Nodder  Karl Safi  Dick J. Singleton  Kim Tanneberger  Thomas W. Trull  Anya M. Waite  Andrew J. Watson  John Zeldis 《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(12):1941-1960

The Lagrangian Southern Ocean Iron Release Experiment (SOIREE) allowed study of a gradually evolving iron-mediated phytoplankton bloom in water labelled with the inert tracer sulfur hexafluoride, SF₆. This article describes a pelagic carbon budget for the mixed layer in SOIREE and assesses the extent to which closure of the budget is achieved. Net community production (NCP) converted 837 mmol m⁻² of inorganic carbon to organic carbon in 12.0 d after the first iron addition. A large fraction (41%) of NCP remained as particulate organic carbon in the mixed layer of the iron-enriched patch, while 23% was lost by horizontal dispersion and 0–29% was exported. The closure of the carbon budget is hampered by the lack of measurements of dissolved organic carbon (DOC), by a major uncertainty in carbon export, and by use of empirical conversion factors in estimates of carbon biomass and metabolic rates. Lagrangian carbon-budget studies may be improved by direct measurement of all major carbon parameters and conversion factors. Carbon cycling in the SOIREE bloom resembled that in ‘natural’ algal blooms in the open Southern Ocean in some respects, but not in all. Daily NCP in the SOIREE bloom (70 mmol m⁻² d⁻¹) was higher than in natural blooms, partly because other studies did not account for horizontal dispersion, were for longer periods or included less productive areas. The build-up of POC stock and carbon export as a fraction of NCP in SOIREE were in the lower range of observations elsewhere.  相似文献   

Fluxes,sizes, morphology and compositions of particles in the Mt. Erebus volcanic plume,December 1983     

Chuan  Raymond L.  Palais  Julie  Rose  William I.  Kyle  Philip R. 《Journal of Atmospheric Chemistry》1986,4(4):467-477

Use of an airborne quartz crystal microbalance cascade impactor instrument together with a correlation spectrometer has allowed the flux of particles and their size distribution to be determined at Mount Erebus. The plume contributes 21±3 metric tomnes/day of aerosol particles to the Antarctic upper troposphere. The aerosol particles consist of larger (5–25 m) particles of elemental sulfur and silica, a middle sized group of iron oxides and smaller particles (less than 1 m) of complex liquids. Unlike many volcanic plumes, the Erebus plume has only a small amount of sulfate particles. The concentrations of particles in the Erebus plumes was 70–370 m/m³. Limited sampling of the Antarctic atmosphere at 8 km altitude but hundreds of km away from Erebus obtained a few large particles of sulfur and silicates, suggesting a similarity with the Erebus plume. The fallout of these particles occurs slowly over a broad area of the Antarctic continent.  相似文献   

Prehistory of the Eastern Sahara : Fred Wendorf and Romuald Schild. Academic Press, New York, 1980     

Julie K. Stein 《Quaternary Research》1981,15(3):371-372

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Enriched back-arc basin basalts from the northern Mariana Trough: implications for the magmatic evolution of back-arc basins   总被引：1，自引：0，他引：1  

Robert J. Stern  Ping-Nan Lin  Julie D. Morris  Michael C. Jackson  Patricia Fryer  Sherman H. Bloomer  Emi Ito 《Earth and Planetary Science Letters》1990,100(1-3)

The composition of basalts erupted at the earliest stages in the evolution of a back-arc basin permit unique insights into the composition and structure of the sub-arc mantle. We report major and trace element chemical data and O-, Sr-, Nd-, and Pb- isotopic analyses for basalts recovered from four dredge hauls and one ALVIN dive in the northern Mariana Trough near 22°N. The petrography and major element chemistry of these basalts (MTB-22) are similar to tholeiites from the widest part of the Trough, near 18°N (MTB-18), except that MTB-22 have slightly more K₂O and slightly less TiO₂. The trace element data exhibit a very strong arc signature in MTB-22, including elevated K, Rb, Sr, Ba, and LREE contents; relatively lowK/Ba and highBa/La andSr/Nd. The Sr- and Nd- isotopic data plot in a field displaced from that of MTB-18 towards Mariana arc lavas, and the Pb-isotopic composition of MTB-22 is indistinguishable from Mariana arc lavas and much more homogeneous than MTB-18. Mixing of 50–90% Mariana arc component with a MORB component is hypothesized. We cannot determine whether this resulted from physical mixing of arc mantle and MORB mantle, or whether the arc component is introduced by metasomatism of MORB-like mantle by fluids released from the subducted lithosphere. The strong arc signature in back-arc melts from the Mariana Trough at 22°N, where the back-arc basin is narrow, supports general models for back-arc basin evolution whereby early back-arc basin basalts have a strong arc component which diminishes in importance relative to MORB as the back-arc basin widens.  相似文献   

Laboratory simulation of diffusion in contaminated marine sediments     

Julie A. Baron  Louis J. Thibodeaux  Danny D. Reible  Paul H. Templet  Charles B. Henry 《Estuaries and Coasts》1990,13(1):81-88

Wastes from offshore oil drilling activities are often discharged to the marine environment. Solid wastes that settle onto the bottom sediment may pose a health threat to marine organisms and eventually to man through the food chain. We need to understand their fate in order to predict the chemical concentration levels and life-times in the sediment and adjoining aquatic boundary layer. A laboratory simulation of selected in-bed processes that addresses contaminant leaching from the sediment is proposed. The process chosen for simulation in this study is the coupled desorption-diffusion of contaminants from the bed to the water column. A simple mathematical model of the process is also proposed. Preliminary results using organic chemicals for both the simulation and the model are presented. The results suggest that the experimental procedure represents a good way of estimating the diffusive leaching rates of hydrophobic compounds from contaminated sediments.  相似文献   

Reference Samples for Electron Microprobe Analysis*     

E. JAROSEWICH  J.A. NELEN  Julie A. NORBERG 《Geostandards and Geoanalytical Research》1980,4(1):43-47

The chemical analyses of twenty-six minerals, four natural glasses, and one synthetic glass prepared for use as microprobe reference samples are presented. New chemical analyses of minerals and revised analyses of several minerals published previously are included. Details of sample preparation are described and the homogeneity of the samples has been tested by the homogeneity index.  相似文献   

In Situ Surfactant Washing of Polychlorinated Biphenyls and Oils from a Contaminated Site   总被引：5，自引：0，他引：5  

A. S. Abdul  T. L. Gibson  Carolina C. Ang  Julie C. Smith  R. E. Sobczynski 《Ground water》1992,30(2):219-231

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Modeling the attenuated total reflectance infrared (ATR-FTIR) spectrum of apatite     

Julie Aufort  Loïc Ségalen  Christel Gervais  Christian Brouder  Etienne Balan 《Physics and Chemistry of Minerals》2016,43(9):615-626

Attenuated total reflectance (ATR) infrared spectra were measured on a synthetic and a natural fluorapatite sample. A modeling approach based on the computation of the Fresnel reflection coefficient between the ATR crystal and the powder sample was used to analyze the line shape of the spectra. The dielectric properties of the samples were related to those of pure fluorapatite using an effective medium approach, based on Maxwell–Garnett and Bruggeman models. The Bruggeman effective medium model leads to a very good agreement with the experimental data recorded on the synthetic fluorapatite sample. The poorer agreement observed on the natural sample suggests a more significant heterogeneity of the sample at a characteristic length scale larger than the mid-infrared characteristic wavelength, i.e., about 10 micrometers. The results demonstrate the prominent role of macroscopic electrostatic effects over fine details of the microscopic structure in determining the line shape of strong ATR bands.  相似文献   

Sedimentology,clay mineralogy and grain-size as indicators of 65 ka of climate change from El’gygytgyn Crater Lake,Northeastern Siberia   总被引：2，自引：0，他引：2  

Celeste A. Asikainen  Pierre Francus  Julie Brigham-Grette 《Journal of Paleolimnology》2007,37(1):105-122

El’gygytgyn Crater Lake, NE Siberia was investigated for sedimentological proxies for regional climate change with a focus on the past 65 ka. Sedimentological parameters assessed relative to magnetic susceptibility include stratigraphy, grain size, clay mineralogy and crystallinity. Earlier work suggests that intervals of high susceptibility in these sediments are coincident with warmer (interglacial-like) conditions and well-mixed oxygenated bottom waters. In contrast, low susceptibility intervals correlate with cold (glacial-like) conditions when perennial ice-cover resulted in anoxia and the dissolution of magnetic carrier minerals. The core stratigraphy contains both well-laminated to non-laminated sequences. Reduced oxygen and lack of water column mixing preserved laminated sequences in the core. A bioturbation index based upon these laminated and non- laminated sequences co-varies with total organic carbon (TOC) and magnetic susceptibility. Clay mineral assemblages include illite, highly inter-stratified illite/smectite, and chlorite. Under warm or hydrolyzing conditions on the landscape around the lake, chlorite weathers easily and illite/smectite abundance increase, which produces an inverse relationship in the relative abundance of these clays. Trends in relative abundance show distinct down-core changes that correlate with shifts in susceptibility. The mean grain-size (6.92 μm) is in the silt-size fraction, with few grains larger than 65 μm. Terrigenous input to the lake comes from over 50 streams that are filtered through storm berms, which limits clastic deposition into the lake system. The sedimentation rate and terrigenous input grain-size is reduced during glacial intervals. Measurements of particle-size distribution indicate that the magnetic susceptibility fluctuations are not related to grain size. Lake El’gygytgyn’s magnetic susceptibility and clay mineralogy preserves regional shifts in climate including many globally recognized␣events like the Younger Dryas and Bolling/Allerod. The sedimentary deposits reflect the climatic transitions starting with MIS4 through the Holocene transition. This work represents the first extensive sedimentological study of limnic sediment proxies of this age from Chukotka (Fig. 1). This is the tenth in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.  相似文献