共查询到20条相似文献，搜索用时 31 毫秒
1.
Brian DzwonkowskiKyeong Park Ho Kyung Ha William M. Graham Frank J. HernandezSean P. Powers 《Continental Shelf Research》2011,31(9):939-950
Hydrographic variability on the Alabama shelf just outside of Mobile Bay, a major source of river discharge into the Gulf of Mexico, is examined using time series of water column temperature and surface and bottom salinity from a mooring site with a depth of 20 m in conjunction with a series of across-shelf CTD surveys. The time series data show variability in a range of time scales. The density variation is affected by both salinity and temperature, with its relatively strong annual signal mostly determined by temperature and its year to year variability mostly determined by salinity. Seasonal mean structures of temperature, salinity, and density show a transition from estuarine to shelf conditions in which three regions with distinct seasonal characteristics in their horizontal and vertical gradient structures are identified. Correlation analysis with the available forcing functions demonstrates the influence of Mobile Bay on the variability at the mooring site. At low frequencies, river discharge from Mobile Bay has a varying influence on salinity, which is absent during the periods with unusually low discharge. At shorter synoptic time scales, both the estuarine response to the across-shelf wind stress and the shelf response to the along-shelf wind stress are significantly correlated with temperature/salinity variability: the former becoming important for the surface layer during winter whereas the latter for the bottom layer during both winter and summer. These forcing functions are important players in determining the estuarine-shelf exchange, which in turn is found to contribute to the shelf hydrographic structure. 相似文献
2.
Daisuke Takahashi Kazuo Kido Yoshinori Nishida Naoto Kobayashi Naoyuki Higaki Hideo Miyake 《Continental Shelf Research》2007
We conducted hydrographic observations in 2002 to investigate the anticyclonic eddy that emerges every summer in Funka Bay, Hokkaido, Japan, and elucidate dynamical structure and wind-driven upwelling within the eddy. The anticyclonic eddy has a vertical scale of 32 m and is characterized by a strong baroclinic flow and a sharp pycnocline with a concave isopycnal structure. The sharp pycnocline occurs below a warm and relatively low-salinity water termed summer Funka Bay water (FS), which is formed by heating from solar radiation and dilution from river discharge in summertime Funka Bay. Flow of the anticyclonic eddy rotates as a rigid body at each layer, and the horizontal scale and rotation period of the eddy in the surface layer are about 15 km and 2.2 days, respectively. The dynamical balance of the anticyclonic eddy is well explained by the gradient flow balance. The contribution of centrifugal force to the gradient flow balance is about 27%. Therefore, the effect of the nonlinear term associated with centrifugal force cannot be neglected in considering the dynamics of the anticyclonic eddy in summertime Funka Bay. In addition, upwelling of subsurface water was observed in the surface layer of the central part of the eddy. The formation mechanism of this upwelling is consistent with interaction between horizontal uniform wind and the eddy. This upwelling is driven by upward Ekman pumping velocity related to the horizontal divergence of Ekman transport. In summertime Funka Bay, there are two wind effects that affect the anticyclonic eddy: a decay effect of the upwelling of subsurface water resulting from horizontal uniform wind (mainly northwesterly wind), and a maintenance or spin-up effect of horizontal non-uniform wind (mainly southerly–southeasterly seasonal wind) with negative wind stress curl. 相似文献
3.
Daisuke Takahashi Hideo Miyake Takeyasu Nakayama Naoto Kobayashi Kazuo Kido Yoshinori Nishida 《Continental Shelf Research》2010
Flow fluctuations inside an anticyclonic eddy in summertime Funka Bay were examined using three moorings and hydrographic data. The flow pattern above a sharp pycnocline with a concave isopycnal structure during the mooring period was characterized by high mean kinetic energy and relatively low eddy kinetic energy. The ratios of eddy to mean kinetic energy were equal to or less than one, and the mean flow field and isopycnal structure indicated the existence of a stable anticyclonic eddy above the sharp pycnocline under approximate geostrophic balance. Larger flow fluctuations with periods longer than 7 days were dominant inside the eddy. The low-frequency flow fluctuations are accompanied by north to northeastward movement of the eddy with deepening of the pycnocline and spin-up of the anticyclonic circulation. The wind field over Funka Bay is characterized by bay-scale wind fluctuations. The bay-scale winds are greatly influenced by the land topography around Funka Bay, resulting in non-uniform structure with significant wind stress curl. The bay-scale wind fluctuations are termed “locally modified wind” in the present study. The locally modified wind has a negative (positive) wind stress curl in the central–northeastern (southwestern) region of Funka Bay. The north to northeastward movement of the eddy is caused by horizontal non-uniform supply of vorticity from the locally modified wind forcing by the Ekman pumping process. Through this process, the anticyclonic circulation is enhanced (weakened) in the central–northeastern (southwestern) part of the eddy, resulting in the eddy moving north to northeastward with the pycnocline deepening and spin-up of the anticyclonic circulation. The locally modified wind forcing induces low-frequency flow fluctuations through the movement of the eddy in summertime Funka Bay. 相似文献
4.
Wind-induced hydrodynamic changes impact on sediment resuspension for large,shallow Lake Taihu,China
Abdul Jalil Yiping Li Ke Zhang Xiaomeng Gao Wencai Wang Hafiz Osama Sarwar Khan Baozhu Pan Salar Ali Kumud Acharya 《国际泥沙研究》2019,34(3):205-215
The internal sediment release is a key factor controlling eutrophication processes in large,shallow lakes.Sediment resuspension is associated with the wave and current induced shear stress in large,shallow lakes.The current study investigated the wind field impacts on sediment resuspension from the bottom at Meiliang Bay of large,shallow Lake Taihu.The impacts of the wind field on the wave,current,and wave-current combined shear stresses were calculated.The critical wind speed range was 4–6 m/s after which wave and current shear stress started to increase abruptly,and onshore wind directions were found to be mainly responsible for greater shear stress at the bottom of Lake Taihu.A second order polynomial fitting correlation was found between wave(R^2 0.4756)and current(R^2 0.4466)shear stresses with wind speed.Wave shear stress accounted for 92.5% of the total shear stress at Meiliang Bay.The critical wave shear stress and critical total shear stress were 0.13 N/m^2 for sediment resuspension whereas the current shear stress was 0.019 N/m^2 after which suspended sediment concentrations(SSC)increased abruptly.A second order polynomial fitting correlation was found between wave(R^2 0.739),current(R^2 0.6264),and total shear stress(R^2 0.7394)with SSC concentrations at Meiliang Bay of Lake Taihu.The sediment resuspension rate was 120 to 738 g/m^2/d during 4–6 m/s onshore winds while offshore winds contributed ≥ 200 g/m^2/d.The study results reveal the driving mechanism for understanding the role of the wind field in sediment resuspension while considering wind speed and direction as control parameters to define wave and current shear stresses. 相似文献
5.
Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average
depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx.
2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from rivers that drain into the
bay. The hydro- and thermodynamical structures of Hervey Bay and their variability are presented here for the first time,
using a combination of four-dimensional modelling and observations from field studies. The numerical studies are performed
with the Coupled Hydrodynamical Ecological Model for Regional Shelf Seas (COHERENS). Due to the high tidal range (>3.5 m),
the bay is considered as a vertically well-mixed system, and therefore, only horizontal fronts are likely. Recent field measurements,
but also the numerical simulations, indicate characteristic features of an inverse/hypersaline estuary with low salinity (35.5 psu)
in the open ocean and peak values (>39.0 psu) in the head water of the bay. The model further predicts a nearly persistent
mean salinity gradient of 0.5 psu across the bay (with higher salinities close to the shore). The investigation further shows
that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation
and the strength of the salinity gradient across the bay. Due to an ongoing drying trend, the occurrence of severe droughts
at the central east coast of Australia and, therefore, a reduction in freshwater supply, the salinity flux out of the bay
has increased, and the inverse circulation has also strengthened. 相似文献
6.
《Continental Shelf Research》1986,5(5):579-610
The solution of the hydrodynamic equations describing wind drift currents in an idealized stratified sea is developed using a modal expansion in the vertical. The influence of the magnitude of wind induced surface eddy viscosity, within the surface mixed layer, and reduced eddy viscosity at depth associated with a stable pycnocline, upon wind induced current structure is examined.Changes in modal structure with eddy viscosity, mixed layer depth, pycnocline thickness and total water depth are considered. It is evident from the modal equations that the time variation of the contribution of each mode to current structure is determined by the modal eigenvalue, mean eddy viscosity, water depth and the vertical integral of the mode squared.Calculations show that the magnitude and direction of steady state surface currents under strongly stratified conditions, are significantly influenced by mixed layer depth and pycnocline thickness. Surface eddy viscosity is also important, and in weakly stratified conditions eddy viscosity within and below the pycnocline influences surface current.The presence of a thin near surface ‘wall layer’ is shown to influence significantly the direction of surface current, but to have little effect upon currents below this surface layer. 相似文献
7.
Studies of a wind mechanism influencing the recruitment of blue crabs in the Middle Atlantic Bight 总被引：1，自引：0，他引：1
This report forms part of an on-going effort to understand the large yearly variations in blue crab harvest of Chesapeake Bay. Recent sampling programs have indicated that the larvae are transported out of the bay immediately after being spawned, and spend their first month offshore at the sea surface. Although it is well established that a mid and outer shelf southward flow occurs during all seasons in the Middle Atlantic Bight, very little is known of the nearshore currents. This study constitutes an effort to determine if the characteristically light, but northward, wind stress during the critical summer months is sufficient to drive northward counter flow at the surface and, hence, to reduce the chances that the larvae are being advected south and lost from the area of Chesapeake Bay.We investigate a local model of wind-driven currents on the continental shelf with vertical decoupling at the pycnocline. Additional driving forces include an alongshore sea surface slope and horizontal pressure gradients. With characteristic forcing values, it is found that the wind stress is indeed sufficient to drive a light northward flow within 25 to 50 km of the shoreline. We expect, then, that blue crab larval recruitment back to Chesapeake Bay may be partially dependent on summer wind stress. A comparison between a wind index time series and harvest several years later is strongly suggestive of such a dependency. 相似文献
8.
水库或湖泊的热分层结构是其动力与环境过程的重要研究方面,虽然很多学者针对水体分层结构和演变机理开展了大量研究,但水体通过水-气界面与大气进行热交换的过程,各气象因子的贡献机理等研究成果还很缺乏。本文基于三峡水库香溪河库湾2019年3月-2020年2月期间的水温、水位及气象等监测数据,针对水-气界面热交换过程如何影响水温垂向结构及表层水体湍流混合作用开展研究。结果表明,(1)香溪河水体年内呈高温期分层、低温期混合的基本特征,高温期混合层深度小于8 m,低温期混合层深度超过30 m。(2)太阳短波辐射是香溪河水体的主要热源,潜热通量和长波辐射是香溪河水体的主要冷源,感热通量贡献极小。(3)香溪河平均风速较弱,约为1.6 m/s,主要通过增强潜热和感热通量的方式影响水体垂向稳定性结构特征,其机械扰动作用较弱。(4)表层水体湍能通量在高温期较低(10-7m3/s3量级),此时水体处于分层状态,风应力大概率主导表层水体湍流发育;低温期表层水体湍能通量较高(10-6 m3/s3<... 相似文献
9.
10.
The study of water masses is important as they transport water properties affecting the biosphere and ocean dynamics. In this study, we revisit water masses in the Caribbean Sea using climatology and 11 months of observations at different depths from 3 moorings placed in the Guajira upwelling region, providing some new findings. The Caribbean Surface Water (CSW) seasonal variability is studied at the mixed layer depth. Salinity differences between CSW and the saltier North Atlantic Subtropical Underwater (SUW) determine static stability spatial and temporal variations, with implications for regional ocean dynamics. Besides, we assess the climatologic distribution of water masses below the salinity maximum using the optimum multiparameter analysis and the Thermodynamic Equation of Seawater 2010, defining their source water indices when entering the Caribbean Sea. The SUW, with its core at ~ 150 m depth, occupies 16% of the Caribbean Sea volume, complemented by 38% of Antarctic Intermediate Water, with its core at ~ 700 m depth and North Atlantic Deep Water, which as bottom water occupies 46% of the volume. Hydrographic observations do not differ from climatology, regardless of their large sub-annual variations decreasing with depth. Daily time series of dominant water fractions at different depths correlate at each mooring, indicating a common forcing. Besides, rotated wind stress, which is an indicator of the Guajira upwelling, correlates regularly with water mass fractions down to 700 m depth. However, during strong wind shifts, upwelling seems to affect them down to 1450 m depth.
相似文献11.
Spatial variability in organic material sinking export in the Hudson Bay system,Canada, during fall 总被引：1，自引：0，他引：1
Amandine Lapoussière Christine Michel Michel Gosselin Michel Poulin 《Continental Shelf Research》2009
Spatial variations in the sinking export of organic material were assessed within the Hudson Bay system (i.e., Hudson Bay, Hudson Strait and Foxe Basin) during the second oceanographic expedition of ArcticNet, on board the CCGS Amundsen in early fall 2005. Sinking fluxes of particulate organic material were measured using short-term free-drifting particle interceptor traps deployed at 50, 100 and 150 m for 8–20 h at eight stations. Measurements of chlorophyll a (chl a), pheopigments (pheo), particulate organic carbon (POC), biogenic silica (BioSi), protists, fecal pellets and bacteria were performed on the collected material. In parallel, sea surface salinity and temperature were determined at 121 stations in the Hudson Bay system. Three hydrographic regions presenting different sedimentation patterns were identified based on average surface salinity and temperature. Hudson Strait was characterized by a marine signature, with high salinity (average=32.3) and low temperature (average=2.1 °C). Eastern Hudson Bay was strongly influenced by river runoff and showed the lowest average salinity (26.6) and highest average temperature (7.6 °C) of the three regions. Western Hudson Bay showed intermediate salinity (average=29.4) and temperature (average=4.4 °C). Sinking fluxes of total pigments (chl a+pheo: 3.37 mg m−2 d−1), diatom-associated carbon (19.8 mg m−2 d−1) and BioSi (50.2 mg m−2 d−1) at 50 m were highest in Hudson Strait. Eastern Hudson Bay showed higher sinking fluxes of total pigments (0.52 mg m−2 d−1), diatom-associated carbon (3.29 mg m−2 d−1) and BioSi (36.6 mg m−2 d−1) compared to western Hudson Bay (0.19, 0.05 and 7.76 mg m−2 d−1, respectively). POC sinking fluxes at 50 m were low and relatively uniform throughout the Hudson Bay system (50.0–76.8 mg C m−2 d−1), but spatial variations in the composition of the sinking organic material were observed. A large part (37–78%) of the total sinking POC was unidentifiable by microscopic observation and was qualified as amorphous detritus. Considering only the identifiable material, the major contributors to the POC sinking flux were intact protist cells in Hudson Strait (28%), fecal pellets in eastern Hudson Bay (52%) and bacteria in western Hudson Bay (17%). A significant depth-related attenuation of the POC sinking fluxes (average loss between 50 and 150 m=32%) and a significant increase in the BioSi:POC ratio (average increase between 50 and 150 m=76%) were observed in Hudson Strait and eastern Hudson Bay. For all other sinking fluxes and composition ratios, we found no statistically significant difference with depth. These results show that during fall, the sinking export of total POC from the euphotic zone remained fairly constant throughout the Hudson Bay system, whereas other components of the organic sinking material (e.g., chl a, BioSi, fecal pellets, protist cells) showed strong spatial variations. 相似文献
12.
The eddy pair off eastern Vietnam: Interannual variability and impact on thermohaline structure 总被引：4，自引：0，他引：4
The main features, interannual variability of the eddy pair (an anti-cyclonic southern eddy and a cyclonic northern eddy) off eastern Vietnam and its impact on local thermohaline structure are analyzed using altimeter data, the Simple Ocean Data Assimilation (SODA) data, and the Medium-Range Weather Forecasts (ECWMF) data. The results show that the eddy pair is a seasonal phenomenon usually found in the summer to fall. It can reach downward to about 400 m depth but is strongest at the upper 100 m depth. In addition, the eddy pair displays a remarkable interannual variability with periods of 5.6 and 3.6 years. The local wind stress curl plays an important role in the interannual variability of eddy pair. Moreover, the eddy pair has an obvious impact on the thermohaline structure of the local upper ocean. The eddy pair can lead to stronger temperature variability in the upper 380 m but stronger salinity variability only in the upper 150 m depth. When the eddy pair is strong, the anti-cyclonic eddy deepens the thermocline, while the cyclonic eddy shoals the thermocline. Taking the depth of 20 °C isotherm as the thermocline depth, we find that in September, the thermocline drops downward to 110–140 m depth in the anti-cyclonic eddy but rises up to 50–80 m depth in the cyclonic eddy. 相似文献
13.
《Continental Shelf Research》1987,7(7):715-733
Temperature and salinity data for the years 1939–1983 are used to investigate seasonal and interannual scales of the hydrographic variability across the Guaymas Basin, which is located between 27° and 28°N in the Central Gulf of California. Winter conditions extend from December to April and summer conditions from June to October, with transition periods in May and November. Sea surface temperature increases from about 16°C in February–March to 31°C in August. No clear seasonal cycle in surface salinity was found. Typical values are above 35.1‰ even in winter, and up to 35.5‰ in November.Relatively cold and low salinity near-surface waters observed in June 1957 and in June 1982, suggest advection of California Current Water to the Guaymas Basin. Subtropical Subsurface Water may occur around the year, but is obscured by vertical mixing with Gulf Water mainly during winter, when vertical stratification is weaker. The Intermediate and Deep Pacific Water masses successively fill the Guaymas Basin to the bottom (2000 m), showing very stable T-S characteristics.Positive sea level anomalies at Guaymas increases during El Nin˜o years, and anomalous low salinity and high temperature at the surface indicate the presence in the Guaymas Basin of water from the south. Observed differences reached 0.4‰ in surface salinity and 3°–5°C in surface temperature. There is evidence that the observed low salinities could not be due to abundant precipitation. An additional effect is a deepening of the winter pycnocline down about 200 m, compared to the usual depth of <100 m. In summer, this effect is not as clear as in winter, due to the strong stratification. The effects of the very strong 1982–1983 and 1957–1958 ENSO episodes may have lasted for one and two years, respectively. It is argued that during an ENSO event the Transition Water of the California Current meet and mix near the Gulf entrance with the Tropical Surface Water of the Costa Rica Coastal Current. This mixed water could have been carried north into the Gulf by local surface circulation. In 1983 it was found at the surface in the Guaymas Basin above the southeastward flow of the colder and saltier Gulf Water. 相似文献
14.
Pramanik Saikat Sil Sourav Mandal Samiran Dey Dipanjan Shee Abhijit 《Ocean Dynamics》2019,69(11):1253-1271
Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11°N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at ~ 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October–December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.
相似文献15.
Temporal-spatial variations of euphotic depth of typical lake regions in Lake Taihu and its ecological environmental significance 总被引：5，自引：0，他引：5
ZHANG Yunlin QIN Boqiang HU Weiping WANG Sumin CHEN Yuwei CHEN Weimin 《中国科学D辑(英文版)》2006,49(4):431-442
Euphotic depth can be defined as the portion of wa- ter column that supports the net primary productivity. Its lower end is the critical depth, namely, the depth measured when the daily net primary productivity is zero[1]. In the ecosystems of oceans, lakes and rivers, phytoplankton live in the euphotic depth and euphotic depth is usually taken as the lower boundary, when studying the primary productivity and biomass of phytoplankton; therefore the corresponding depth is sometimes called the t… 相似文献
16.
S. Retailleau H. Howa R. Schiebel F. Lombard F. Eynaud S. Schmidt F. Jorissen L. Labeyrie 《Continental Shelf Research》2009,29(8):1123-1135
The distribution of planktic foraminifera from the continental slope onto the shelf of the south-eastern Bay of Biscay is discussed in relation to environmental factors. Samples were obtained between March and November, 2006–2008, along a bathymetric transect from 2000 to 145 m water depth, from 50 km off the shelf-break onto the outer shelf. Live specimens and empty tests (>100 μm) were collected with vertical plankton tows from the sea surface to a maximum water depth of 700 m, and temperature, salinity, oxygen concentration, and fluorescence/chlorophyll-a concentration were recorded. Additional data on chlorophyll-a concentration and sea surface temperature were derived from satellite imagery (Aqua MODIS and SeaWIFS). Planktic foraminifera were most abundant in the upper 80 m of the water column at all locations, with decreasing numbers towards the coast in March, April, and June. In November, maximum numbers of live specimens occurred at the outer shelf location. In July, planktic foraminiferal standing stocks were low throughout the sampling area.Chlorophyll-a concentration (i.e., food) and fresh water input were found to affect the abundance of planktic foraminifera along the transect; however we found no influence of water depth or proximity to the shelf. 相似文献
17.
Takeshi Izumo 《Ocean Dynamics》2005,55(2):110-123
The equatorial undercurrent (EUC), the shallow meridional overturning cells feeding it, and their role in El Niño and decadal variability in the equatorial Pacific are studied using both in situ data and an ocean general circulation model. Using temperature and current data from the TAO/TRITON moorings at the equator, their data gaps are filled and it was shown that continuous time series of mass transport, temperature, depth, and kinetic energy of the EUC could be constructed for the period 1980–2002 with an excellent accuracy. This dataset was analysed and used to validate the output from an oceanic general circulation model (OGCM). The OGCM was then used to find that variations in the strength of the EUC, shallow meridional overturning (pycnocline convergence and surface divergence), and equatorial upwelling had the same variations in mass transport on interannual and longer time scales within the period 1951–1999. These variations are all caused by variations of the zonal wind stress zonally integrated, in agreement with simple linear and steady dynamics theories. Impact of these mass transport variations and of temperature variations on heat budgets in the entire equatorial band of the Pacific and in its eastern part are quantified. 相似文献
18.
The validation and subsequent application of the current three-dimensional numerical hydrodynamic model of Chesapeake Bay is presented. The numerical model solves conservation equations for water mass, momentum, salinity, and heat on a boundary-fitted grid in the horizontal plane and a Cartesian z-grid in the vertical. A generalized ADI finite difference scheme is employed in conjunction with mode splitting technique, solving external and the internal modes. The 10-year boundary conditions including tide, slinity, temperature, wind, heat exchange coefficient, river and non-point source flows were constructed. Model validation was accomplished by demonstrating the model's ability to reproduce observed data over time scales ranging from tidal to seasonal periods. The major parameters compared include tidal elevation, intra-tidal and residual velocities, salinity, temperature, stratification, and flux calculated through the Bay mouth.After validation, the model was applied to simulate bay hydrodynamics for the 10 years of 1985–94. These results were used to drive the three-dimensional water quality model of Chesapeake Bay, which is discussed in a companion paper. 相似文献
19.
A total of 95 surface water samples (6 m depth) was collected during a transect from the Bothnian Bay to Kiel between 28 August and 5 September 1982. This report presents the dissolved trace metal (<0.4 μm) and the associated hydrographic and nutrient data. Except for aluminium, all other metals determined (Zn, Cd, Cu, Ni, Fe, Mn) showed a rather homogeneous distribution within the subregions, with highest values in the Bothnian Bay (except for Mn) and net variations of the individual samples of about 20%. Cadmium, copper and nickel reveal conservative behaviour when values from this study and literature data from the Kattegat and North Sea area are plotted against salinity. 相似文献
20.
Numerical study on the summer upwelling system in the northern continental shelf of the South China Sea 总被引：7，自引：0，他引：7
A three-dimensional baroclinic nonlinear numerical model is employed to investigate the summer upwelling in the northern continental shelf of the South China Sea (NCSCS) and the mechanisms of the local winds inducing the coastal upwelling, associated with the QuikSCAT wind data. First, the persistent signals of the summer upwelling are illustrated by the climatological the Advanced Very High-Resolution Radiometer (AVHRR) Sea Surface Temperature (SST) image over 1985–2006 and field observations in 2006 summer. Then, after the successful simulation of the summer upwelling in the NCSCS, four numerical experiments are conducted to explore the different effects of local winds, including the wind stress and wind stress curl, on the coastal upwelling in two typical strong summer upwelling regions of the NCSCS. The modeled results indicate that the summer upwelling is a seasonal common phenomenon during June–September in the NCSCS with the spatial extent of a basin-scale. Typical continental shelf upwelling characteristics are clearly shown in the coastal surface and subsurface water, such as low temperature, high salinity and high potential density in the east of the Hainan Island, the east of the Leizhou Peninsula and the southeast of the Zhanjiang Bay (noted as the Qiongdong-QD), and the inshore areas from the Shantou Coast to the Nanri Islands of the Fujian Coast (noted as the Yuedong-YD). The analysis of the QuikSCAT wind data and modeled upwelling index suggests that the local winds play significant roles in causing the coastal upwelling, but the alongshore wind stress and wind stress curl have different contributions to the upwelling in the Qiongdong (QDU) and the coastal upwelling in the Yuedong (YDU), respectively. Furthermore, model results from the numerical experiments show that in the YD the stable alongshore wind stress is a very important dynamic factor to induce the coastal upwelling but the wind stress curl has little contribution and even unfavorable to the YDU. However, in the QD the coastal upwelling is strongly linked to the local wind stress curl. It is also found that not only the offshore Ekman transport driven by the alongshore wind stress, the wind stress curl-induced Ekman pumping also plays a crucial effect on the QDU. Generally, the wind stress curl even has more contributions to the QDU than the alongshore wind stress. 相似文献