Impact of suboxia on sinking particulate organic carbon: Enhanced carbon flux and preferential degradation of amino acids via denitrification     

Benjamin A.S Van Mooy  Richard G KeilAllan H Devol 《Geochimica et cosmochimica acta》2002,66(3):457-465

Fluxes of particulate organic carbon (POC) through the oxygen deficient waters in the eastern tropical North Pacific were found to be relatively less attenuated with depth than elsewhere in the eastern North Pacific. The attenuation coefficient (b) for the flux was found to be 0.40 versus the composite value of 0.86 determined by Martin et al. (1987). To examine this further, sinking POC was collected using sediment traps and allowed to degrade in oxic and suboxic experiments. Using a kinetic model, it was found that degradation proceeded at similar rates (roughly 0.8 day⁻¹) under oxic and suboxic conditions, but a greater fraction of bulk POC was resistant to degradation in the suboxic experiments (61% vs. 23%). Amino acids accounted for 37% of POC collected at 75m, but following degradation the value dropped to 17% and 16% in the oxic and suboxic experiments respectively. POC collected from 500m was 10% amino acids. The non-AA component of POC collected at 75m was not degraded under suboxic conditions, while under oxic conditions it was. These results suggest that microbes degrading OC under suboxic conditions via denitrification preferentially utilize nitrogen-rich amino acids. This preferential degradation of amino acids suggests that 9% more nitrogen may be lost via water column denitrification than is accounted for when a more “Redfieldian” stoichiometry for POC is assumed.  相似文献   

Surface chemistry and reactivity of biogenic silica   总被引：2，自引：0，他引：2  

Suvasis Dixit  Philippe Van Cappellen 《Geochimica et cosmochimica acta》2002,66(14):2559-2568

The surface chemistry of cultured diatoms was compared to that of biosiliceous material in Southern Ocean sediments, using potentiometric titrations and aluminum adsorption experiments. Aerosil 200, a well-studied synthetic amorphous silica, served as reference solid. Surface charge development and aluminum adsorption on cultured diatom shells were comparable to Aerosil. The surface chemical properties of biosiliceous material buried to depths of 15-25 cm in Southern Ocean sediments, however, deviated markedly from those of the cultured diatoms. In pH range 4-8.5, the surface charge density was systematically lower for biogenic silica from the sediments. In addition, the aluminum adsorption edge on the biosiliceous sediments was shifted to higher pHs by about 0.4 units. The results indicate that ionizable surface silanol groups on diagenetically altered diatom shells are less abundant and, possibly, less acidic than on freshly cultured diatoms. The observed differences in surface chemical structure are consistent with the progressive loss of reactivity, or aging, of biogenic silica which promotes its preservation in sediments.  相似文献   

U-series dating of bone using the diffusion-adsorption model     

A.W.G. PikeR.E.M. Hedges  P. Van calsteren 《Geochimica et cosmochimica acta》2002,66(24):4273-4286

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分形在地貌学中应用的几个问题的分析   总被引：5，自引：0，他引：5  

李锰  朱令人  龙海英 《地震研究》2002,25(2):155-162

就实际地貌分形研究工作中经常遇到的截面约定、自仿射分形局域维与渡越长度、分维的比较以及过渡分形等几个问题进行了分析和探讨，并提出了在应用过程中的注意事项和解决方案。  相似文献   

Wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation   总被引：3，自引：0，他引：3  

Nam H. Pham  †  José M. Carcione  Hans B. Helle  Bjørn Ursin 《Geophysical Prospecting》2002,50(6):615-627

We obtain the wave velocities and quality factors of clay‐bearing sandstones as a function of pore pressure, frequency and partial saturation. The model is based on a Biot‐type three‐phase theory that considers the coexistence of two solids (sand grains and clay particles) and a fluid mixture. Additional attenuation is described with the constant‐Q model and viscodynamic functions to model the high‐frequency behaviour. We apply a uniform gas/fluid mixing law that satisfies the Wood and Voigt averages at low and high frequencies, respectively. Pressure effects are accounted for by using an effective stress law. By fitting a permeability model of the Kozeny– Carman type to core data, the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies, including the effects of partial saturation. Testing of the model with laboratory data shows good agreement between predictions and measurements.  相似文献   

Earthquake—generating Structure Revealed by 1999 Sichuan mianzhu Earthquake Sequence with Ms=5.0     

Zhao Zhu  Wang Bilan  Long Sisheng 《中国地震研究》2002,16(2):147-154

Through the accurate determination of hypocenter location,the measurement of the main focal mechanism solutions and the analyses of time dependent processes for Sichuan Mianzhu earthquake sequence with Ms=5.0 occurred along the middle segment of Longmenshan fault zone on November 30,1999,the distribution of focal depth section,the stress relase and seismicity features are given to reveal the earthquake-geneating structure of the earthquake sequence.The obtained results show the activity features for this sequence as follows:(1) There is no obvious foreshock,the accumulated strain energy releases in nearly pulse way,fluctuation of the seismic activity level is not quite evident during the duration of the sequence,and the statistical relation between the large events and the small events is less compatible with the traditional G-R estimation;(2) The epicenters of the earthquake sequence are not distributed on the main Longmenshan piedmont faults emerging out ground,but near the hidden Longmenshan piedmont faults.The direction of epicenter distribution is not very coincident with the fault strikes.The microscopic epicenters are relatively far from the macroscopic epicenters,The focal depths range from 5km to 16km;(3) The fractures of focal fault plane with the NE strike appear out the strike-slip displacement with a few overthrust components under the major principal compressive stress of NNE direction.From these,we consider it should be paid more attentions to the underground hidden faults near the ground fault zone on a large scale for their generating earthquake risk.  相似文献   

Uniform postglacial slip-rate along the central 600 km of the Kunlun Fault (Tibet), from ²⁶Al, ¹⁰Be, and ¹⁴C dating of riser offsets, and climatic origin of the regional morphology     

Jerome Van Der Woerd  Paul Tapponnier  Frederick J. Ryerson  Anne-Sophie Meriaux  Bertrand Meyer  Yves Gaudemer  Robert C. Finkel  Marc W. Caffee  Zhao Guoguang  Xu Zhiqin 《Geophysical Journal International》2002,148(3):356-388

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鄂尔多斯高原景观格局变化分析--以伊金霍洛旗为例     

贾宝全  孙鹏森  王国  慈龙骏 《干旱区地理》2003,26(3):202-207

以位于内蒙古鄂尔多斯高原上的伊金霍洛旗为研究区域，以景观生态学的数量分析方法为基本手段，在土地利用现状分类体系下，以其1984、1991和1998年3个年度的土地利用图为基础。从区域和斑块类型两个尺度上，对其景观格局进行了数量分析。结果表明，在三个典型年度。天然草地为伊金霍洛旗的景观基质，景观格局指数的所有变化均是在此基础上发生和演变的。从整个景观尺度的格局指数变化情况显示，伊金霍洛旗景观的破碎化程度在增加；同时景观的异质性程度在下降，景观愈来愈有少数景观斑块类型所控制。而在斑块类型这一尺度上的格局指数变化说明，不同类型斑块的复杂性的变化趋势基本相同，即均有不同程度的增长，但增加幅度有限；同时还说明，不同类型斑块内部其大小差异的幅度在不断缩小。但从不同年度的变化情况来看，无论是区域还是不同的斑块类型，其格局指数的变化并不与总体的变化趋势同步。  相似文献   

宁芜地区大平山铜矿、天台山黄铁矿与古火山机构关系的探讨     

侯龙海 《江苏地质》2003,27(1):12-18

以大平山铜矿、天台山黄铁矿矿为例，阐述了该区的矿区、矿床地质及火山机构特征，并从成矿时间、空间及成因三个方面论述了矿床成矿与古火山机构的关系。  相似文献   

土屋-延东斑岩型铜(钼)矿床多源信息找矿模型   总被引：5，自引：2，他引：5       下载免费PDF全文

朱裕生  王福同  龙宝林  薛迎喜  肖克炎  冯京  庄道泽  姜立丰 《矿床地质》2003,22(3):287-294

为提高东天山铜镍成矿带内的矿产勘查效益，文章综合了区域成矿环境、矿床特征、地球物理场、地球化学场等成矿信息，尝试建立了土屋—延东斑岩型铜钼矿床的多源信息找矿模型。认为成矿带内铜矿资源远景良好，必将成为我国又一个铜矿资源潜力区。  相似文献