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The potential for carbon export and the role of siliceous plankton in the cycling of C and N was assessed in natural plankton assemblages in the Santa Barbara Basin, California, by examining uptake rates of inorganic carbon, nitrate and silicic acid. In April–August 1997, the concentrations of chlorophyll a, particulate organic carbon, particulate organic nitrogen and biogenic silica were measured twice monthly, and results revealed the occurrence of at least three blooms, the largest in June. Particulate elemental ratios of C, N and Si were similar to ratios of nutrient-replete diatoms, suggesting that they dominated this bloom. Mean integrated rates of carbon, nitrate and silicon uptake during the 4-month study period are similar to other productive coastal and upwelling regions (103, 8.3 and 13 mmol m−2 day−1, respectively). New production rates were twice as high as previously reported in this region and indicate that high rates of new production along eastern boundary currents are not confined to the major coastal upwelling regions. C/NO3−, Si/NO3− and Si/C uptake ratios varied widely, and mean integrated ratios were 14±5.4, 1.6±1.0 and 0.12±0.07 (S.D.), respectively. That mean C/NO3− uptake ratio corresponds to an f-ratio of about 0.5 indicating a large potential for particulate export. Based on the average Si/NO3− and Si/C uptake ratios, diatoms could perform all of the primary production and nitrate uptake that occurred during the study; these rates also suggest that export is controlled by diatoms in this system. The mean Si/C biomass ratio was lower than the mean Si/C uptake ratio, consistent with the preferential export of Si relative to C observed in sediment traps in the basin. The study took place during a period of surface-water warming, with nitrate and silicic acid concentrations decreasing throughout the onset of the 1997–1998 El Niño conditions. Although diatoms contributed less to particulate biomass during the low nutrient conditions, high f-ratios (0.33–0.66) were maintained. 相似文献
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Within the framework of several local and international programs, a quasi-operational ocean-forecasting system for the Southeastern Mediterranean Sea has been established and evaluated through a series of preoperational tests. The Princeton Ocean Model (POM) is used for simulating and predicting the hydrodynamics while the Wave Model (WAM) is used for predicting surface waves. Both models were set up to allow varying resolution and multiple nesting. In addition, POM was set up to be easily relocatable to allow rapid deployment of the model for any region of interest within the Mediterranean Sea. A common requirement for both models is the need for atmospheric forcing. Both models require time varying wind or wind stress. In addition, the hydrodynamic model requires initial conditions as well as time dependent surface heat fluxes, fresh water flux, and lateral boundary conditions at the open boundaries. Several sources of atmospheric forcing have been assessed based on their availability and their impact on the quality of the ocean models' forecasts. The various sources include operational forecast centers, other research centers, as well as running an in-house regional atmospheric model. For surface waves, higher spatial and temporal resolution of the winds plays a central role in improving the forecasts in terms of significant wave height and the timing of various high wave events. For the hydrodynamics, using the predicted wind stress and heat fluxes directly from an atmospheric model can potentially produce short range ocean forecasts that are nearly as good as hindcasts forced with gridded atmospheric analyses. Finally, a high-resolution, nested version of the model has shown to be stable under a variety of forcing conditions and time scales, thus indicating the robustness of the selected nesting strategy. For the southeastern corner of the Mediterranean, at forecast lead times of up to 4 days the high-resolution model shows improved skill over the coarser resolution driving model when compared to satellite derived sea surface temperatures. Most of the error appears to be due to the analysis error inherent in the initial conditions. 相似文献
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研究目的:新建红柳至一里坪铁路位于敦煌至格尔木铁路红柳站与柴达木盆地腹地一里坪之间,沿途经过盐沼盆地、早期湖积盆地、雅丹地貌三个地质地貌单元,交错分布有风沙、岩溶、地震、崩塌、软土、盐渍土、盐岩及盐渍岩、季节性冻土等地质现象,生态环境脆弱,水文环境、地质环境复杂多变。地质工作需查明控制线路方案的地质因素,综合分析其危害,预测其对工程可能产生的不利影响,为线路选择及工程设置提供依据。研究结论:(1)柴达木湖积盆地以盐为本,以水、风为介质,盐的搬运、沉积在相对封闭的盆地内循环不止;(2)祁连山、昆仑山坡麓一带的盐沼湖,水补给充足,湖内软土、季节性冻土、岩溶发育,难以治理,线路采用了绕避方案;(3)雅丹地区,地表多被"盐被"覆盖,部分沙漠化,采用桥方案短距离通过风沙地带;(4)早期干湖积盆地内地质条件相对较好,线路长段通过;(5)工程建设应以盐治沙,保护"盐被",保持水环境的稳定;(6)本研究可为相似地质特征的选线及工程设计提供一定的参考价值。 相似文献
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The water mass, circulation and chemical properties of the Cilician Basin, the northeastern Levantine Sea, are described on the basis of three hydrographic cruises performed during May 1997 (spring), July 1998 (summer) and October 2003 (autumn). The hydrographic data reveal the presence of Levantine Surface Water (LSW) and Modified Atlantic Water (MAW) within the upper 90 m layer, Levantine Intermediate Water (LIW) between 90 and 250 m, and Transitional Mediterranean Water (TMW) further below. The temporal variability of the circulation system is manifested by a change in shape, size and intensity of eddies as well as the pathways of the Lattakia Basin coastal current system. The nutrient concentrations varied between nitrate + nitrite = 0.16–0.31 μM, phosphate = 0.02–0.03 μM and silicate = 0.95–1.2 μM for the surface layer during sampling periods. Dissolved nutrient concentrations in the Transitional Mediterranean Water were: 2.1–5.3 μM for NO3 + NO2, 0.10–0.21 μM for PO4 and 5.7–10 μM for Si. The molar ratios of nitrate to phosphate in the water column range between 5 and 20 in the surface layer and reach up to a value of 45 at the top of the nutricline at the depths of 29.05 kg/m3 isopycnal surface for most of the year. Below the nutricline the N / P ratios retain the values around 24–28. 相似文献