Chokka squid (Loligo vulgaris reynaudii) abundance linked to changes in South Africa's Agulhas Bank ecosystem during spawning and the early life cycle     

Roberts  Michael J. 《ICES Journal of Marine Science》2005,62(1):33-55

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Grazing impact of mesozooplankton in an upwelling region off northern California, 2000–2003     

Anne M. Slaughter  Stephen M. Bollens  Gretchen Rollwagen Bollens   《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):3099

Mesozooplankton (>200 μm) grazing impact (% phytoplankton standing crop consumed d⁻¹) was determined by the gut fluorescence method during three springs (2000, 2001 and 2002) and two winters (2002 and 2003) in a coastal upwelling region off northern California. Wind events, in terms of both magnitude and duration, varied inter-annually and seasonally and included both upwelling-favorable and relaxation events. Grazing impact of mesozooplankton also varied inter-annually and seasonally, and was highest during June 2000 (mean=129% of standing crop d⁻¹), a prolonged period of wind “relaxation” and phytoplankton bloom. In contrast, mean grazing impact was lower during periods of stronger, more persistent winds, more active upwelling, greater cross-shelf transport, and lower chlorophyll concentration (25% and 38% in May–June 2001 and 2002, respectively). Wintertime conditions (January 2002 and 2003) were characterized by weakly upwelling or downwelling-favorable winds, low chlorophyll concentration, and lower mean mesozooplankton grazing impact (13% and 12%, respectively). The larger (>500 μm) size class contributed proportionally more to total mesozooplankton (>200 μm) grazing impact than the smaller (200–500 μm) size class during all sampling periods except spring 2002. These results suggest that mesozooplankton grazing impact is higher in spring than in winter, and that during the spring upwelling season, grazing is higher during periods of wind relaxation (weak upwelling) than during periods of stronger upwelling. Further, these results suggest an important role of mesozooplankton grazers on phytoplankton dynamics in the upwelling region off northern California.  相似文献   

南黄海夏季海水pCO2研究Ⅱ——下层海水涌升和长江冲淡水对海-气界面CO2通量的贡献     

《中国海洋大学学报(自然科学版)》2006,36(B05):147-152

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On vertical velocity fluctuations and internal tides in an upwelling region off the west coast of India     

A. S. Unnikrishnan  M. K. Antony 《Estuarine, Coastal and Shelf Science》1990,31(6)

Hourly fluctuations of vertical velocity in relation to components of flow and wind and temperature oscillations at a morring site in the shelf waters off the west coast of India are discussed. The vertical velocities were computed from a time series of vertical temperature profiles assuming that horizontal advection of temperature is negligible. The computed values at a depth of 40 m during the 72-h period of observation were of the order of 10⁻¹ to 10⁻²cm s⁻¹, with a mean value of −2·77 × 10⁻² cm s⁻¹ indicating a net upward movement of water. The computed vertical velocity showed fluctuations of about 2–3 h, in addition to weaker signals of about 12 h. Based on the spectral estimates, we speculate that these fluctuations of 2–3 h in the vertical velocity may be caused by the fluctuations in the along-shore wind. The oscillations of isotherms found in the temperaturedepth time series and the spectral estimates of temperature and cross-shore flow component showed a periodicity of about 12 h, which indicated the presence of semi-diurnal internal waves. The fact that these internal wave troughs were associated with the measured onshore flow suggested that the waves were propagating offshore. The computed stability parameters showed little evidence of instability or mixing. It was found that the isotherm troughs in the temperaturedepth time series at about 12-h period coincided with high vertical shear in the cross-shore direction and low values of Brunt Vaisälä frequency.  相似文献   

Gravity anomalies of the ridge-transform system in the South Atlantic between 31 and 34.5° S: Upwelling centers and variations in crustal thickness     

Ban-Yuan Kuo  Donald W. Forsyth 《Marine Geophysical Researches》1988,10(3-4):205-232

To decipher the distribution of mass anomalies near the earth's surface and their relation to the major tectonic elements of a spreading plate boundary, we have analyzed shipboard gravity data in the vicinity of the southern Mid-Atlantic Ridge at 31–34.5° S. The area of study covers six ridge segments, two major transforms, the Cox and Meteor, and three small offsets or discordant zones. One of these small offsets is an elongate, deep basin at 33.5° S that strikes at about 45° to the adjoining ridge axes.By subtracting from the free-air anomaly the three-dimensional (3-D) effects of the seafloor topography and Moho relief, assuming constant densities of the crust and mantle and constant crustal thickness, we generate the mantle Bouguer anomaly. The mantle Bouguer anomaly is caused by variations in crustal thickness and the temperature and density structure of the mantle. By subtracting from the mantle Bouguer anomaly the effects of the density variations due to the 3-D thermal structure predicted by a simple model of passive flow in the mantle, we calculate the residual gravity anomalies. We interpret residual gravity anomalies in terms of anomalous crustal thickness variations and/or mantle thermal structures that are not considered in the forward model. As inferred from the residual map, the deep, major fracture zone valleys and the median, rift valleys are not isostatically compensated by thin crust. Thin crust may be associated with the broad, inactive segment of the Meteor fracture zone but is not clearly detected in the narrow, active transform zone. On the other hand, the presence of high residual anomalies along the relict trace of the oblique offset at 33.5° S suggests that thin crust may have been generated at an oblique spreading center which has experienced a restricted magma supply. The two smaller offsets at 31.3° S and 32.5° S also show residual anomalies suggesting thin crust but the anomalies are less pronounced than that at the 33.5° S oblique offset. There is a distinct, circular-shaped mantle Bouguer low centered on the shallowest portion of the ridge segment at about 33° S, which may represent upwelling in the form of a mantle plume beneath this ridge, or the progressive, along-axis crustal thinning caused by a centered, localized magma supply zone. Both mantle Bouguer and residual anomalies show a distinct, local low to the west of the ridge south of the 33.5° S oblique offset and relatively high values at and to the east of this ridge segment. We interpret this pattern as an indication that the upwelling center in the mantle for this ridge is off-axis to the west of the ridge.  相似文献   

Numerical Simulations of Sea Surface Cooling by a Mixed Layer Model during the Passage of Typhoon Rex   总被引：3，自引：0，他引：3  

Wada  Akiyoshi 《Journal of Oceanography》2005,61(1):41-57

In order to investigate the formation mechanism of rapid decrease of maritime sea surface temperature (SST) observed by R/V Keifu Maru, the ocean response to Typhoon Rex is simulated using a mixed layer model. The rapid decrease of the maritime SST is successfully simulated with realistic atmospheric forcing and an entrainment scheme of which sources of turbulent kinetic energy (TKE) are production due to wind stress, generation during free convection, and production due to current shear. The rapid decrease at the observed station by R/V Keifu Maru is not produced by instant atmospheric forcing but is mainly produced by entrainment on the right side of the running typhoon as a part of cooling area during its passage, and remained during a few days. The sea surface cooling (SSC) is evident along the track and on the right side of the running typhoon, which is similar to the SSC of satellite observation by TRMM/TMI. The conspicuous SSC produced by both entrainment and upwelling is situated just under the track of typhoon when the typhoon moves slower. Intercomparison of entrainment schemes of the mixed layer model is implemented. Frictional velocity and buoyancy effects are effective for a gradual SSC covering the wide region. In contrast, the effect of current shear at the mixed layer base is related to the amount of SSC and the sharp horizontal gradient of SSC. The entrainment scheme including all three TKE sources has the best performance for SSC simulation.  相似文献   

Numerical modelling and analysis of temperature controlled density currents in Tomales Bay, California     

J.-L. Harcourt-Baldwin  G.P.J. Diedericks 《Estuarine, Coastal and Shelf Science》2006,66(3-4):417-428

The coastal region adjacent to Tomales Bay, California is dominated by wind-driven upwelling during spring and summer and the cold, upwelled water is moved towards Tomales Bay, entering the estuary with the flood tide. If the tidal excursion is ≥6 km and the cold water subducts beneath the warmer, less dense estuarine water, a temperature controlled density current may form and intrude towards the head of the estuary as a thermally stratified bottom layer. The numerical modelling was aimed at determining the capability of the Delft3D-FLOW model to reproduce the cold ocean water intrusion events, the response (development and progression) of these intrusions to differing physical scenarios and the comparative importance of the parameters to the intrusions. The numerical model successfully reproduced the density intrusions and showed that the persistence and break down of the density intrusions were affected by a number of physical parameters, to varying degrees. The sensitivity analysis showed that density intrusion formation is controlled by tidal conditions and ocean water temperature. The strength and persistence of the developed density intrusions are influenced by wind, insolation and estuary depth. Fresh water inflow at the head of the estuary had no impact on the density intrusions. Three-dimensional numerical modelling is thus a valuable tool in understanding the estuary and its functioning.  相似文献   

Scyphomedusae in surface waters near the Oregon coast, May–August 1981     

Jonathan M. Shenker 《Estuarine, Coastal and Shelf Science》1984,19(6):619-632

The scyphomedusae of the surface waters off Oregon and southern Washington were collected with commercial purse seines from May–August 1981. Twelve east-west transects, located from north of the Columbia River to south of Coos Bay were sampled from the 37 m isobath to distances up to 48 km from shore. Chrysaora fuscescens was the dominant species collected in each month. Maximum sampled abundances reached 18001 of medusae per 10⁵ m³. Using an estimated carbon content of 0·280% of wet weight, this medusa density was calculated to contain approximately 50 mg Cm⁻³. Seven of the 263 samples contained so many medusae that they exceeded the capacity of the sampling gear. In all months but May, when medusa densities were relatively low, the density of C. fuscescens was greatest closest to shore and decreased rapidly offshore. Mean umbrella diameter increased from 8·6 cm in May to 18·5 cm in August, while the largest specimens increased from 19 cm in May to 37 cm in August. Aurelia aurtia, Cyanea capillata and Phacellophora camtschatica were also collected, but were much less abundant than C. fuscescens. The relative abundance of C. fuscescens was compared with the maximum abundance of copepods off the Oregon coast, and the hydrographic features influencing medusa distribution patterns are discussed.  相似文献   

Physical forcing of onshore transport of crab megalopae in the northern Portuguese upwelling system     

Maria Joo Almeida  Henrique Queiroga 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1091-1102

Wind-driven circulation is a mechanism that may be involved in the shoreward transport of invertebrate larvae. This study investigated the temporal variability of the supply of crab megalopae to an estuary located in the northwest coast of Portugal, which is affected by seasonal upwelling, and related variations in supply to several upwelling indices. Megalopae of the European common shore crab Carcinus maenas (L.). were collected daily, using artificial settlement substrates, during a 3-month period, from March 15 to June 15, 2000. Two settlement episodes were detected, which were consistent with the variation in abundance and size of juvenile crabs. Variations in subtidal sea level and sea surface temperature anomaly were correlated with the strength of along-shore wind stress and consistent with upwelling theory. Contingency analyses showed positive significant associations between increasing intensity of southerly winds and megalopal supply, for time lags of 0–6 d, indicating that shoreward transport occurred during relaxation or reversal of upwelling favourable winds. Associations between megalopal supply and tidal range or the duration of nocturnal flood were not detected. Compared to other studies of the supply of crab megalopae to coastal habitats that used a similar methodology, very low numbers of megalopae were collected during this study. The paucity of C. maenas megalopae in the Ria de Aveiro is in agreement with the low densities of this larval stage in the plankton, and indicates that maintenance of the population is achieved despite a low supply of megalopae.  相似文献   

珠江口以西陆架海域环流研究Ⅱ.   总被引：1，自引：0，他引：1  

伍伯瑜 《台湾海峡》1990,(1)

本文讨论了珠江口以西陆架海域夏季(6—9月)的上升流现象,文中选用了部分水文断面和温度递减量的图解,讨论了该海域上升流的影响范围、强度和位置及其特征。  相似文献