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991.
A quasi-two dimensional model of the carbon and nitrogen cycling above the 70m isobath of the southeastern Bering Sea at 57°N replicates the observed seasonal cycles of nitrate, ammonium, ΣCO2, pCO2, light penetration, chlorophyll, phytoplankton growth rate, and primary production, as constrained by changes in wind, incident radiation, temperature, ice cover, vertical and lateral mixing, grazing stress, benthic processing of phytodetritus and zooplankton fecal pellets, and the pelagic microbial loop of DOC, bacteria, and their predators. About half of the seasonal resupply of nitrate stocks to their initial winter conditions is derived from in situ nitrification, with the rest obtained from deep-sea influxes. Under the present conditions of atmospheric forcing, shelf-break exchange, and food web structure, this shelf ecosystem serves as a sink for atmospheric CO2, with storage in the forms of exported DOC, DIC, and unutilized POC (phytoplankton, bacteria, and fecal pellets).As a consequence of just the rising levels of atmospheric pCO2 since the the Industrial Revolution, however, the biophysical CO2 status of the Southeastern Bering Sea shelf may have switched over the last 250 years, from a prior source to the present sink, since this relatively pristine ecosystem has unergone little eutrophication. Such fluctuations of CO2 status may thus be reversed by the physical processes of : (1) reduction of atmospheric pCO2, (2) increased on welling of deep-sea ΣCO2, and (3) warming of shelf waters. Based on our application of this model to the Chukchi Sea and the Gulf of Mexico, about 1.0–1.2 gigatons C y-1 of atmospheric CO2 may now be sequestered by temperate and polar shelf ecosystems. When tropical systems are included, however, a positive net sink of only 0.6–0.8. × 1015g C y−1 may prevail over all shelves. 相似文献
992.
九龙江河口区水体中的226Ra和228Ra 总被引:8,自引:0,他引:8
用MnO2-纤维富集大体积水样中的Ra同位素,并用直接射气法测定226Ra和228Ac的β计数法测定228Ra的方法,研究了九龙江河口区226Ra,228Ra的行为,结果表明:在该河口区226Ra,228Ra均呈非保守行为,226Ra,228Ra的最高值分别在盐度为19和9处测得。228Ra/226Ra)A.R.值在盐度小于19的区域约为3左右。与世界其他河口区相比,九龙江河口区的226Ra,22 相似文献
993.
994.
Trends in biomass, density and diversity of North Sea macrofauna 总被引:6,自引:2,他引:6
995.
Wave direction measurements using pitch-roll buoys 总被引:2,自引:0,他引:2
996.
Fluxes of particulate carbon, nitrogen, phytoplankton pigments, biogenic silica and dry mass were measured using free-floating and moored sediment trap arrays in the Santa Monica Basin during the period from October 1985 to August 1990 as part of the California Basin Study (CaBS) Program. In field testing for potential sources of sediment trap biases, we found little significant or consistent difference in rate estimates between short-term drifting traps and long-term moored traps, between preserved and unpreserved traps in short-term experiments, between different preservatives (mercury or formalin) in long-term experiments, between different designs of small cylindrical traps, and between deep-moored cylindrical traps and large conical traps. We did, however, find that sediment trap samples collected and analyzed on 0.45 μm silver filters gave estimates of carbon and nitrogen fluxes about 25% higher than samples collected on GF/F glass-fiber filters. Concurrent trap deployments at two stations 18km apart revealed low mesoscale variability in flux estimates. Seasonal patterns in carbon and nitrogen flux were not evident in our data, but strong seasonality, with spring maxima and summer minima, were observed for fluxes of phaeopigments and biogenic silica out of the euphotic zone.Time-averaged rates of particulate flux for long-term trap deployments from January to August 1990, were 121, 18.8, 1.5, 67 and 633mg m−2d−1 at 110–135m for carbon, nitrogen, phaeopigment, biogenic silica and mass, respectively. Flux estimates to the basin floor (835–860m) were 50, 6.5, 0.64, 41.6 and 575mg m−2d−1 for the same parameters. The former estimates are constrained by and in good agreement with independent assessments of new production from nitrate uptake in the euphotic zone. The latter agree with rates previously inferred from the sedimentary record using 210Pb as a tracer. In addition, the difference in carbon estimates in the water column between the euphotic zone and the basin floor is consistent with the requirements for bacterial growth and metabolism at intermediate depths as measured by the thymidine method. 相似文献
997.
This paper considers the threshold of motion of sediment in shallow coastal waters under breaking and non-breaking waves. A simple model, representing conditions at the fluid/sediment interface, is developed. The representation of a breaking wave is based on bore theory, and the shear stress at the bed is based on the friction formula of O'Connor and Yoo. A threshold formula is presented based on the use of energy dissipation. The threshold data is also related to the Shields threshold criterion. 相似文献
998.
The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used in port, coastal and off-shore works. The method for stability analysis of the large-diameter cylinder structure, especially for stability analysis of the embedded large-diameter cylinder structure, is an important issue. In this paper, an idea is presented that is, em-bedded large-diameter cylinder quays can be divided into two types, i.e. the gravity wall type and the cylinder pile wall type. A method for stability analysis of the large-diameter cylinder quay of the cylinder pile wall type is developed and a method for stability analysis of the large-diameter cylinder quay of the gravity wall type is also proposed. The effect of sig-nificant parameters on the stability of the large-diameter cylinder quay of the cylinder pile wall type is investigated through numerical calculation. 相似文献
999.
A Computational Model for Velocity Separation in Shallow Sea 总被引:1,自引:0,他引:1
Based on the hydrodynamical feature and the theoretical velocity profiles of tidal flow and vvind-induced flow in shal-low sea, a computational model is established for the first time, which can separate observed velocity into tidal velocity and wind-induced velocity by use of the least square method. With the model, not only the surface velocities of tidal flow and vvind-induced flow are obtained, but also the bed roughness height is determined and the wind velocity above the wa-ter surface is estimated. For verification of the model, the observed velocity in the Yellow River Estuary and the laborato-ry test is separated, then it is applied to the Yangtze River Estuary. All the results are satisfactory. The research results show that the model is simple in method, feasible in process and reasonable in result. The model is a valid approach to analysis and computation of field dala, and can be applied to separate the observed velocity in shallow sea; at the same time, reasonable boundary conditions of th 相似文献
1000.
Erkan G?ka?an Cem Gazio?lu Bedri Alpar Zeki Yücel ?ükrü Ersoy O?uz Gündo?du Cenk Yalt?rak Buser Tok 《Geo-Marine Letters》2002,21(4):183-199
Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies. 相似文献