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31.
Kanchan Maiti Claudia R. Benitez-Nelson Yoshimi Rii Robert Bidigare 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1445
Mesoscale eddies may enhance primary production (PP) in the open ocean by bringing nutrient-rich deep waters into the euphotic zone, potentially leading to increased transport of particles to depth. This hypothesis remains controversial, however, due to a paucity of direct particle export measurements. In this study, we investigated particle dynamics using 234Th–238U disequilibria within a mesoscale cold-core eddy, Cyclone Opal, which formed in the lee of the Hawaiian Islands. 234Th samples were collected along two transects across Cyclone Opal as well as during a time-series within the eddy core during a decaying diatom bloom. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO2) fluxes at 150 m varied spatially and temporally within the eddy and strongly depended on the 234Th model formulation used (e.g., steady state versus non-steady state, inclusion of upwelling, etc.). Particle fluxes estimated from a steady state model assuming an upwelling rate of 2 m day−1 yielded the best fit to sediment-trap data. These 234Th-derived particle fluxes ranged from 332±14 to 1719±53 μmol C m−2 day−1, 27±3 to 114±12 μmol N m−2 day−1, and 33±20 to 309±73 μmol Si m−2 day−1. Although PP rates within Cyclone Opal were elevated by a factor of 2–3, PC and PN fluxes were the same, within error, inside and outside of Cyclone Opal. The ratio of PC export to PP remained surprisingly low at <0.03 and similar to those measured in surrounding waters. In contrast, bSiO2 fluxes within the eddy core were three times higher. Detailed analyses of 234Th depth profiles consistently showed excess 234Th at 100–175 m, associated with the remineralization and possible accumulation of suspended and dissolved organic matter from the surface. We suggest that strong microzooplankton grazing facilitated particulate organic matter recycling and resulted in the export of empty diatom frustules. Thus, while eddies may increase PP, they do not necessarily increase PC and PN export to deep waters. This may be a general characteristic of wind-driven cyclonic eddies of the North Pacific Subtropical Gyre and suggests that eddies may preferentially act as a silica pump, thereby playing an important role in promoting silicic-acid limitation in the region. 相似文献
32.
Lisa E. Collins William BerelsonDouglas E. Hammond Angela Knapp Richard SchwartzDoug Capone 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(8):898-914
Moored sediment traps were deployed from January 2004 through December 2007 at depths of 550 and 800 m in San Pedro Basin (SPB), CA (33°33.0′N, 118°26.5′W). Additionally, floating sediment traps were deployed at 100 and 200 m for periods of 12-24 h during spring 2005, fall 2007, and spring 2008. Average annual fluxes of mass, particulate organic carbon (POC), ??13Corg, particulate organic nitrogen (PON), ??15N-PON, biogenic silica (bSiO2), calcium carbonate (CaCO3), and detrital material (non-biogenic) were coupled with climate records and used to examine sedimentation patterns, vertical flux variability, and organic matter sources to this coastal region. Annual average flux values were determined by binning data by month and averaging the monthly averages. The average annual fluxes to 550 m were 516±42 mg/m2 d for mass (sdom of the monthly averages, n=117), 3.18±0.26 mmol C/m2 d for POC (n=111), 0.70±0.05 mmol/m2 d for CaCO3 (n=110), 1.31±0.21 mmol/m2 d for bSiO2 (n=115), and 0.35±0.03 mmol/m2 d for PON (n=111). Fluxes to 800 and to 550 m were similar, within 10%. Annual average values of ??13Corg at 550 m were −21.8±0.2‰ (n=108), and ??15N averages were 8.9±0.2‰ (n=95). The timing of both high and low flux particle collection was synchronous between the two traps. Given the frequency of trap cup rotation (4-11 days), this argues for particle settling rates ≥83 m/d for both high and low flux periods. The moored traps were deployed over one of the wettest (2004-2005, 74.6 cm rainfall) and driest (2006-2007, 6.6 cm) rain years on record. There was poor correlation (Pearson's correlation coefficient, 95% confidence interval) of detrital mass flux with: Corg/N ratio (r=0.10, p=0.16); ??15N (r=−0.19, p=0.02); and rainfall (r=0.5, p=0.43), suggesting that runoff does not immediately cause increases in particle fluxes 15 km offshore. ??13Corg values suggest that most POC falling to the basin floor is marine derived. Coherence between satellite-derived chlorophyll a records from the trap location (±9 km2 resolution) and SST data indicates that productivity and export occurs within a few days of upwelling and both of these parameters are reasonable predictors of POC export, with a time lag of a few days to 2 weeks (with no time lag—SeaWiFS chlorophyll a and POC flux, r=0.25, p=0.0014; chlorophyll a and bSiO2 flux, r=0.28, p=0.0002). 相似文献
33.
本文阐述了大客车的噪声识别和分析,在大型客车噪声控制中,用声强法声场分析和噪声谱分析法识别主要噪声源。 相似文献
34.
Yin Xiulan China Institute of Geo-environmental Monitoring Beijing China Hu Ping Faculty of Earth Sciences China University of Geosciences Wuhan China Northeastern Illinois University Chicago IL USA Li Dien Division of Earth Environmental Sciences Los Alamos National Laboratory Los Alamos NM USA 《中国地质大学学报(英文版)》2004,15(4):355-360
The sorption of Eu species onto nano-size silica-water interfaces was investigated using fluorescence spectroscopy for Ph ranges of 1-8.5 and an initial Eu concentration (Ceu) of 2×10-4 M. The sorption rate of Eu was initially low, but significantly increased at Ph>4. The sorption density of Eu species on a silica surface was ~1.58×10-7 mol/m2 when the dissolved Eu species were completely sorbed onto silica-water interfaces at Ph=~5.8. The sorbed Eu species at Ph<6 is aquo Eu3 , which is sorbed onto silica-water interfaces as an outer-sphere complex at Ph<5, but may be sorbed as an inner-sphere bidentate complex at 5相似文献
35.
采用2. 0 mol/dm~3Na_2CO_3溶液5h单点化学提取-硅钼蓝连续分光光度分析法分别测定了大亚湾西部海域13个表层沉积物和1个沉积物岩芯中生物硅的含量.表层沉积物和沉积物岩芯中生物硅含量占比分别为0. 69%~2. 02%和1. 24%~2. 05%,平均值分别为1. 42%和1. 60%.结果证实西大亚湾沉积物中生物硅含量水平与我国南海近岸海域基本一致.在210Pbex测年的基础上,通过分析沉积物岩芯中生物硅、有机物、无机碳等多指标,揭示近百年来大亚湾周边环境变化对海洋环境的影响,证实了上世纪80年代以来西大亚湾周边农业、海水养殖业和工业发展等人类活动加剧了该海域生态环境变化,尤其90年代核电站运行对海洋生态变化造成一定的影响. 相似文献
36.
Giorgio Bavestrello Riccardo Cattaneo-Vietti Carlo Cerrano Stefania Cerutti Michele Sará 《Marine Ecology》1996,17(1-3):41-50
Abstract. The importance of sponge spicules in the turnover of biogenic silica (BSi) in the detritic bottoms of the Eastern Ligurian Riviera was evaluated by studying sediment cores and the detrital matter collected by a trap over a one year period.
This study made evident that: i) Sponge spicules represent the main component of the BSi both in the sediments and in the trapped matter; ii) A correlation exists between the sponge biomass present on the overhanging cliff and the amount of sponge spicules found in the sediment below; iii) Inside the sediments, a superficial layer (10 cm deep) characterized by intensive silica dissolution processes can be observed; and iv) The amount of spicules collected using the trap is not constant throughout the year, but shows a characteristic trend with low values in spring and summer and high values in autumn and winter. 相似文献
This study made evident that: i) Sponge spicules represent the main component of the BSi both in the sediments and in the trapped matter; ii) A correlation exists between the sponge biomass present on the overhanging cliff and the amount of sponge spicules found in the sediment below; iii) Inside the sediments, a superficial layer (10 cm deep) characterized by intensive silica dissolution processes can be observed; and iv) The amount of spicules collected using the trap is not constant throughout the year, but shows a characteristic trend with low values in spring and summer and high values in autumn and winter. 相似文献
37.
秦岭泥盆系硅岩岩石类型对比研究 总被引:2,自引:0,他引:2
硅岩可以通过化学沉积(真溶液或胶体沉淀)和内碎屑堆积而成。由于热水有较强的化学活动性,因而在水岩界面附近也会形成交代成因的硅岩。在许多情况下,硅岩既具有沉积岩的岩石学特征,又具有交代岩的岩石学特征,其成岩环境十分特殊。因此,虽然有许多地球化学方法可以区分不同类型的硅岩,但岩石学特征是最基本的和最直接的标志。 相似文献
38.
A convenient and effective procedure was developed for the conversion of alcohol to olefin by tosylation and subsequent β-elimination promoted by silica gel in this study. Treatment of the alcohols with p-toluenesulfonyl chloride in pyridine at 0℃ affords tosylates which undergo β-elimination with silica gel in dichloromethane or chloroform at room temperature, yielding olefinswith high productivity. 相似文献
39.
40.
Synthesis and characterization of zeolite X obtained from kaolin for adsorption of Zn(Ⅱ) 总被引:4,自引:0,他引:4
I. S. Ismael 《中国地球化学学报》2010,29(2):130-136
This study deals with the synthesis and characterization of low-silica zeolite X, from calcined Kalabsha kaolin, for adsorption of Zn(Ⅱ) ions from aqueous solution. The synthesis processes is performed under hydrothermal treatment in alkaline solutions. The obtained zeolite samples are characterized using X-ray diffraction, grain size distribution, surface area, and SEM. The critical molar ratios of both SiO2/Al2O3 and K2O/Na2O are about 2.9 and 0.16, respectively. Those ratios are needed to give individual low silica zeolite X in a minimum reaction time. The adsorption capacity of the synthesized products is determined by adsorption of Zn(Ⅱ) ions from solution. The results suggest that the zeolite obtained could be converted to a beneficial product, which will be used in future as an ion exchanger in removing heavy metals from wastewaters. 相似文献