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81.
Abstract Uptake rates of ammonium (NH4 + ), nitrate (NO3 ? ), and urea by three subgroups of phytoplankton (< 200, < 20, < 2 μm) off Westland, were measured using 15 N tracer techniques in midwinter 1988, after a recent upwelling. For all size fractions at surface irradiance (I100), nitrogen (N) was taken up primarily as NO3 ?. This accounted for 67–85% of total N uptake (SρN), whereas at 40 and 7% of surface irradiance, the regenerated N (NH4 + ) and urea) made up 31–72% of SρN. Depth profile experiments for all three size components showed that uptake of NO3 ? was most light‐sensitive, followed by that of NH4 + and urea. The irradiance and nutrient availability plot indicated that light was substantially more important than the nutrient concentrations in controlling the assimilation of N by microplankton (20–200 μm). Nano‐ (2–20 μm) and picoplankton (< 2 μm) however, were not as sensitive to either light or nutrient concentrations. High winds and the resulting deep mixing, combined with offshore and alongshore advection in the midwinter, were suggested to be the major cause of the low biomass and N productivity. 相似文献
82.
Down-scaled regional ocean modeling system (ROMS) for high-resolution coastal hydrodynamics in Korea 总被引:1,自引:0,他引:1
A down-scaled operational oceanographic system is developed for the coastal waters of Korea using a regional ocean modeling system(ROMS).The operational oceanographic modeling system consists of atmospheric and hydrodynamic models.The hydrodynamic model,ROMS,is coupled with wave,sediment transport,and water quality modules.The system forecasts the predicted results twice a day on a 72 h basis,including sea surface elevation,currents,temperature,salinity,storm surge height,and wave information for the coastal waters of Korea.The predicted results are exported to the web-GIS-based coastal information system for real-time dissemination to the public and validation with real-time monitoring data using visualization technologies.The ROMS is two-way coupled with a simulating waves nearshore model,SWAN,for the hydrodynamics and waves,nested with the meteorological model,WRF,for the atmospheric surface forcing,and externally nested with the eutrophication model,CE-QUAL-ICM,for the water quality.The operational model,ROMS,was calibrated with the tidal surface observed with a tide-gage and verified with current data observed by bottom-mounted ADCP or AWAC near the coastal waters of Korea.To validate the predicted results,we used real-time monitoring data derived from remote buoy system,HF-radar,and geostationary ocean color imager(GOCI).This down-scaled operational coastal forecasting system will be used as a part of the Korea operational oceanographic system(KOOS) with other operational oceanographic systems. 相似文献
83.
为了解决振动水柱式波浪能转换装置收集多向波浪问题,本文设计了半球形多向聚合波道振荡水柱气室结构,以适合远海单点波浪能采集和发电。在规则波正向入射条件下,基于流体仿真分析软件(FLUENT)、流体动力学连续性假设和粘性不可压缩流体动量守恒的运动方程(Navier-Stokes方程)建立半球形振荡气室和三维数值波浪水槽模型。仿真结果表明:增设气室后壁,合理设计波道开口角度实现多向迎波捕获波浪能,优化前壁形状可降低波浪触底反射带来的能量耗散,同时提高了气室内空气压强和出气口速度,有效提升波浪能俘获效率,为后续发电的二次能量转换提供高效的空气动力。 相似文献
84.
Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April. 相似文献
85.
30ka以来南海东北部陆坡坡底沉积有机质的长链正构烷烃特征及其古植被意义 总被引:1,自引:0,他引:1
为探寻南海深海平原区的有机质组成特征、来源及其所反映的古气候/环境演化信息, 对南海东北部深水区的ZSQD289沉积柱状样品进行了正构烷烃组成及其单体稳定碳同位素的相关分析, 结合孢粉鉴定结果, 重点探讨该沉积区末次冰期以来陆源输入变化、源区的古植被演化及其气候响应因素。结果表明:30ka以来, 南海东北部深海陆坡坡底的沉积有机质以洋/陆混源为特征, 且以海洋自生生产力贡献为主, 其生源贡献存在明显的冰期/间冰期旋回变化特征, 冰期时陆源有机质输入明显高于全新世间冰期; 其陆源有机质应该主要由台湾南部河流输入, 在低海平面时通过海底峡谷搬运至此, 其过程中可能受到西太平洋底流和黑潮的影响。该沉积源区植被演化经历了C3/C4植物互为消长的变化过程, 但30ka以来主要还是以C3植物占优势, 由此推测末次冰期以来源区(台湾岛南部)不存在明显的干旱化, 冰期虽然温度较低但气候比较湿润。 相似文献
86.
87.
A shakemap system providing rapid estimates of strong ground shaking could be useful for emergency response providers in a
damaging earthquake. A hybrid procedure, which combines site-dependent ground motion prediction models and the limited observations
of the Real-Time Digital stream output system (RTD system operated by Central Weather Bureau, CWB), was set up to provide
a high-resolution shakemap in a near-real-time manner after damaging earthquakes in Taiwan. One of the main factors that affect
the result of ground motion prediction analysis is the existence of site effects. The purpose of this paper is to investigate
the local site effects and their influence in the ground shaking and then establish an early estimation procedure of potential
hazard for damaging earthquakes. Based on the attenuation law, the site effects of each TSMIP station are discussed in terms
of a bias function that is site and intensity-level dependent function. The standard deviation of the site-dependent ground
motion prediction model can be significantly reduced. The nonlinear behavior of ground soil is automatically taken into account
in the intensity-level dependent bias function. Both the PGA and the spectral acceleration are studied in this study. Based
on the RTD data, event correctors are calculated and applied to precisely estimate the shakemap of damaging earthquakes for
emergency response. 相似文献
88.
Effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock: Implication on mechanism of borehole breakouts 总被引:1,自引:0,他引:1
We conducted laboratory true triaxial experiments in the nearly impermeable Pohang rhyolite to investigate failure mechanisms under ‘dry’ and ‘wet’ rock conditions. Under ‘dry’ conditions prismatic specimens were jacketed all around to prevent confining fluid penetration. Under ‘wet’ conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid (kerosene) applying the least principal stress in an attempt to simulate the case of an unlined borehole wall. In both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises. The unjacketed rhyolite strength is, however, only 60 to 85% of the strength under dry conditions, depending on the magnitude of the intermediate principal stress. In dry rhyolite the failure process begins upon dilatancy onset, followed by microcrack localization, and ending in a steeply dipping shear fracture. On the other hand, brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through-going extensile fractures subparallel and adjacent to one of the unjacketed faces, resembling the extensile cracks leading to borehole breakouts in crystalline rocks. We infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress-induced microcracks subparallel to the unjacketed faces, leading to ‘early’ failure. 相似文献
89.
Dev Niyogi Hsin-I Chang Fei Chen Lianhong Gu Anil Kumar Surabi Menon Roger A. Pielke Sr. 《Natural Hazards》2007,42(2):345-359
Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon region. In this paper, we propose
that another pathway by which aerosols can modulate the multi-scale aspect of Indian monsoons is by altering the land–atmosphere
interactions. The nonlinear feedbacks due to aerosol/diffuse radiation on coupled interactions over the Indian monsoon region
are studied by: (1) reviewing recent field measurements and modeling studies, (2) analyzing the MODIS and AERONET aerosol
optical depth datasets, and (3) diagnosing the results from sensitivity experiments using a mesoscale modeling system. The
results of this study suggest that the large magnitude of aerosol loading and its impact on land–atmosphere interactions can
significantly influence the mesoscale monsoonal characteristics in the Indo-Ganges Basin. 相似文献
90.
Johnson Simon P.; de Waele Bert; Tembo Francis; Katongo Crispin; Tani Kenichiro; Chang Qing; Iizuka Tsuyoshi; Dunkley Daniel 《Journal of Petrology》2007,48(7):1411-1441
The southern Irumide Belt (SIB) is an ENEWSW-trending,late Mesoproterozoic orogenic belt located between the CongoTanzaniaBangweulu(CTB) and Kalahari cratons in central southern Africa. It isseparated from the late Mesoproterozoic Irumide Belt (IB) tothe north by Permo-Triassic graben, raising the possibilitythat the younger rifts reactivated a suture between the twobelts that has been rendered cryptic as a result of youngerKaroo cover. Both belts are dominated by calc-alkaline gneisses,but in addition the SIB contains abundant metavolcanic and metasedimentaryrocks. In this study we present detailed geochemical, isotopicand geochronological data for volcanic and plutonic lithologiesfrom the southernmost part of the SIB, the CheworeRufunsaTerrane. This terrane comprises a wide variety of supracrustalto mid-crustal rocks that have major- and trace-element compositionssimilar to magmas formed in present-day subduction zones. Chondrite-normalizedrare earth element (REE) profiles and whole-rock SmNdisotope compositions indicate that the parental supra-subductionmelts interacted with, and were contaminated by sialic continentalcrust, implying a continental-margin-arc setting. Secondaryionization mass spectrometry dating of magmatic zircon has yieldedcrystallization ages between c. 1095 and 1040 Ma, similar toelsewhere in the SIB. UPb dating and in situ LuHfisotopic analyses of abundant xenocrystic zircon extracted fromthe late Mesoproterozoic granitoids indicate that the contaminantcontinental basement was principally Palaeoproterozoic in ageand had a juvenile isotopic signature at the time of its formation.These data are in contrast to those for the IB, which is characterizedby younger, c. 1020 Ma, calc-alkaline gneisses that formed bythe direct recycling of Archaean crust without significant additionof any juvenile material. We suggest that the SIB developedby the subduction of oceanic crust under the margin of an unnamedcontinental mass until ocean closure at c. 1040 Ma. Subsequentcollision between the SIB and the CTB margin led to the cessationof magmatism in the SIB and the initiation of compression andcrustal melting in the IB. KEY WORDS: geochemistry; Mesoproterozoic; SHRIMP zircon UPb dating; SmNd isotopes; Southern Irumide Belt 相似文献