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1.
High-resolution (1km) satellite data from the NOAA AVHRR (Advanced Very High Resolution Radiometer) and OrbView-2 SeaWiFS (Sea-viewing Wide Field-of-view Sensor) are used to investigate the upper layer dynamics of the southern Benguela ecosystem in more detailed space and time scales than previously undertaken. A consistent time-series of daily sea surface temperature (SST) and chlorophyll a concentration images is generated for the period July 1998–June 2003, and a quantitative analysis undertaken. The variability in SST, upwelling and phytoplankton biomass is explored for selected biogeographic regions, with particular focus on intra-seasonal time scales. The location and emergence of upwelling cells are clearly identified along the length of the southern Benguela, being distinct on the narrow inner and the mid-continental shelves. Most notable is the rapidly pulsating nature of the upwelling, with intense warm/cold events clearly distinguished. The phytoplankton response to this physical forcing is described. Chlorophyll concentration on the inner shelf largely mirrors the pattern of SST variability, similarly dominated by event-scale processes. Over the mid-shelf, higher chlorophyll is observed throughout all seasons, although low biomass occurs during winter. The variability of the offshore extent of SST and chlorophyll is identified at locations of differing shelf width. Cooler upwelled water is confined primarily to the narrow inner-shelf, with event-scale pulses extending considerable distances offshore. Agulhas Current influences are readily observed, even on the Cape Peninsula inner-shelf. Chlorophyll concentrations vary considerably between the locations of differing shelf width. SST, upwelling and phytoplankton indices are derived for selected locations to quantify the intra-seasonal variations. The SST indices show marked temperature changes associated with rapid pulsation on the event scale. No strong seasonal signal is evident. In contrast, the upwelling indices display a strong seasonal signal, with most intense upwelling occurring in spring/summer in the south. The phytoplankton response to the seasonal upwelling index differs between the selected locations. This study concludes that, although low-resolution SST and chlorophyll data may be useful for investigating general patterns over large scales, higher resolution data are necessary to identify finer scale spatial and temporal variability, especially in the inshore coastal zones.  相似文献   

2.
This work quantifies the role of tropical instability waves (TIWs) in modulating nutrient and chlorophyll distributions in the equatorial Pacific through an analysis of satellite data and a case study of in situ observations. A TIW index is constructed to differentiate periods of strong and weak TIW activity. TIW impacts are first examined in monthly averaged satellite SST and chlorophyll data for three distinct regions north of the equator where TIWs are most active. The chlorophyll data are high-pass filtered to preserve the seasonal cycle and remove long-term trends. Although SST follows a predictable relationship with the TIW index, chlorophyll concentrations do not. Periods of high TIW activity are characterized by cooler SSTs but consistently low chlorophyll. A case study of individual TIW vortices demonstrates that their impact on nutrients and chlorophyll is a function of intensity. Strong TIWs drive reductions in nutrients and chlorophyll due to the subduction of nutrient-replete water north of the equator and the advection of nutrient-poor water toward the equator from adjacent to the upwelling zone. Weak TIWs do not drive these advective processes to the same degree, so retain elevated nutrients that fuel chlorophyll increases. The most positive effect on nutrients and chlorophyll by TIWs was observed during boreal winter, likely owing to thermocline topography. A shallower thermocline in combination with weak TIWs results in elevated nutrients and chlorophyll north of the equator. Given the variability associated with TIW intensity and season, generalizing TIW effects has proven difficult, but targeted Lagrangian studies will better characterize these dynamic features and their impact on elemental fluxes.  相似文献   

3.
The diel vertical migration(DVM) of zooplankton and the influence of upwelling on zooplankton biomass were examined using water column data of current velocity and mean volume backscattering strength(MVBS)collected by moored acoustic Doppler current profilers(ADCPs) deployed in the southeastern Chukchi Sea during the 5th Chinese National Arctic Research Expedition(CHINARE) in summer 2012, combined with the satellite observational data such as sea surface temperature(SST), wind, and chlorophyll a(Chl a). Hourly acoustic data were continuously collected for 49-d in the mooring site. Spectral analysis indicated that there were different migrating patterns of zooplankton, even though precisely classifying the zooplankton taxa was not available. The prevailing 24-h cycle corresponded to the normal DVM with zooplankton swimming upwards at sunrise and returning to deep waters at sunset. There was a clear DVM in the upper 17 m of the water column during the period with distinct day-night cycles, and no active DVM throughout the water column when the sun above the horizon(polar day), suggesting that light intensity was the trigger for DVM. Also there was a second migrating pattern with 12-h cycle. The upwelling event occurring in the northwest of Alaskan coastal area had important influence on zooplankton biomass at the mooring site. During the upwelling, the SST close to the mooring site dropped significantly from maximal 6.35°C to minimal 1.31°C within five days. Simultaneously, there was a rapid increase in the MVBS and Chl a level, suggesting the aggregation of zooplankton related to upwelling.  相似文献   

4.
根据2011年6月27日至7月4日台湾海峡航次的调查资料,结合6月1日至8月31日海表温度和风场的卫星遥感数据,分析了平潭附近海域、澎湖北部海域、东山附近海域、台湾浅滩东南部海域上升流的变化特征及其与风场的关系.以海表温度差值(SSTd)来反映上升流强度,该值负值越大,上升流强度越强,分析可知:在2011年夏季,平潭附近海域上升流的强度除了7月中、下旬和8月底外,其余时段较为稳定.SSTd值与局地沿岸风速存在滞后3 d左右的相关关系,特别是稳定持续的西南风对其强度有较大的影响.澎湖北部海域上升流的SSTd值在-1℃左右,强度相对较小,且6、7月比8月时强盛,局地风场对澎湖北部海域上升流有一定的影响,但不是主要影响因素,而是由地形和风共同作用.东山附近海域上升流的强度并不稳定,在6、7月变化较剧烈,到8月SSTd值稳定在-3℃左右,SSTd值的变化对于局地沿岸风的响应同样存在一个3 d左右的滞后时间,除此之外还与上升流中心的水平变动有关.而台湾浅滩东南部海域上升流虽有波动,但持续存在,且6、7月比8月时强盛,其变化与局地风场的关系不大,主要受海流和地形等其他因素的影响.  相似文献   

5.
Surface chlorophyll (CHL) measured at the Scripps Pier in the Southern California Bight (SCB) for 18 years (1983–2000) reveals that the spring bloom occurs with irregular timing and intensity each year, unlike sea-surface temperature (SST), which is dominated by a regular seasonal cycle. In the 1990s, the spring bloom occurred earlier in the year and with larger amplitudes compared to those of the 1980s. Seasonal anomalies of the Pier CHL have no significant correlation with local winds, local SST, or upwelling index, which implies that classical coastal upwelling is not directly responsible for driving chlorophyll variations in nearshore SCB.The annual mean Pier CHL exhibits an increasing trend, whereas the Pier SST has no evident concomitant trend during the CHL observation period. The interannual variation of the Pier CHL is not correlated with tropical El Niño or La Niña conditions over the entire observing period. However, the Pier CHL was significantly influenced by El Nino/Southern Oscillation during the 1997/1998 El Niño and 1998/1999 La Niña transition period. The Pier CHL is highly coherent at long periods (3–7 years) with nearby offshore in situ surface CHL at the CalCOFI (California Cooperative Fisheries Investigations) station 93.27.  相似文献   

6.
陈莹  赵辉 《海洋学研究》2021,39(3):84-94
本文使用2003年1月—2019年12月MODIS遥感数据,结合海表温度、风速分析南海中西部叶绿素质量浓度分布特征和影响因素。结果显示南海中西部叶绿素质量浓度分布存在时空变化。EOF分解表明,EOF1可能反映台风等极端天气对叶绿素的影响;而EOF2 和EOF3均反映了夏季沿岸上升流对叶绿素分布的影响。相关分析表明南海中西部叶绿素质量浓度与海面风场呈正相关(r=0.87,p<0.01),与海表温度呈负相关(r=-0.59,p<0.05)。夏季在西南季风影响下越南东南沿海形成上升流,导致该区浮游植物旺发、叶绿素质量浓度升高;冬季受强东北季风影响,研究区海洋上层混合作用强烈,营养盐供应增加,促进了浮游植物生长,叶绿素质量浓度高于其他季节。  相似文献   

7.
Spatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore.  相似文献   

8.
The effects of biological heating on the upper-ocean temperature of the global ocean are investigated using two ocean-only experiments forced by prescribed atmospheric fields during 1990–2007, on with fixed constant chlorophyll concentration, and the other with seasonally varying chlorophyll concentration. Although the existence of high chlorophyll concentrations can trap solar radiation in the upper layer and warm the surface, cooling sea surface temperature (SST) can be seen in some regions and seasons. Seventeen regions are selected and classified according to their dynamic processes, and the cooling mechanisms are investigated through heat budget analysis. The chlorophyll-induced SST variation is dependent on the variation in chlorophyll concentration and net surface heat flux and on such dynamic ocean processes as mixing, upwelling and advection. The mixed layer depth is also an important factor determining the effect. The chlorophyll-induced SST warming appears in most regions during the local spring to autumn when the mixed layer is shallow, e.g., low latitudes without upwelling and the mid-latitudes. Chlorophyll-induced SST cooling appears in regions experiencing strong upwelling, e.g., the western Arabian Sea, west coast of North Africa, South Africa and South America, the eastern tropical Pacific Ocean and the Atlantic Ocean, and strong mixing (with deep mixed layer depth), e.g., the mid-latitudes in winter.  相似文献   

9.
The El Ni?o Southern Oscillation(ENSO) is a natural phenomenon that relates to the fluctuation of temperatures over the Pacific Ocean. The ENSO significantly affects the ocean dynamics including upwelling event and coastal front. A recent study discovered the seasonal upwelling in the east coast of Peninsular Malaysia(ECPM), which is significant to the fishery industry in this region. Thus, it is vital to have a better understanding of the influence of ENSO towards the coastal upwelling and thermal front in the ECPM. The sea surface temperature(SST) data achieved from moderate resolution imaging spectroradiometer(MODIS) aboard Aqua satellite are used in this study to observe the SST changes from 2005 to 2015. However, due to cloud cover issue, a reconstruction of data set is applied to MODIS data using the data interpolating empirical orthogonal function(DINEOF) to fill in the missing gap in the dataset based on spatial and temporal available data. Besides, a wavelet transformation analysis is done to determine the temperature fluctuation throughout the time series. The DINEOF results show the coastal upwelling in the ECPM develops in July and reaches its peak in August with a clear cold water patch off the coast. There is also a significant change of SST distribution during the El Ni?o years which weaken the coastal upwelling event along the ECPM. The wavelet transformation analysis shows the highest temperature fluctuation is in 2009–2010 which indicates the strongest El Ni?o throughout the time period. It is suggested that the El Ni?o is favourable for the stratification in water column thus it is weakening the upwelling and thermal frontal zone formation in ECPM waters.  相似文献   

10.
This study attempts to explain the variability in recruitment of sardine in the northern Benguela and to develop potential models by including environmental information to predict recruitment. Two different recruitment and spawner number datasets were available: a VPA-developed dataset, for the period 1952-1987, and data from a simple age-structured model for 1992-2007. In all, four environmental indices were used: the degree of the intrusion of the warm Angola Current into northern Namibia, termed the Angola-Benguela front index; the extent of the upwelling area off central Namibia; average sea surface temperature (SST) over the northern and central Namibian shelf; and wind stress anomalies at Luderitz as an indicator of upwelling strength. Contrary to general belief, it was found that extremely high recruitment can happen at low spawner levels. This occurred in years in which a large upwelling area existed in association with the minimum southward intrusion of the Angola Current. These effects override the normal negative linear relationships with SST and the positive linear relationship with wind. However, when the area of upwelling is average or small, the effects of spawner biomass, SST and wind become important factors in the variability of recruitment. To estimate exceptional recruitment, the upwelling and front indices were included in the model. To measure medium and weak recruitment, spawner numbers and the SST and wind anomaly formed part of the model. These models can be used simultaneously to predict recruitment before annual acoustic surveys take place and thus aid management decisions.  相似文献   

11.
We used Sea-viewing Wide Field-of-view Sensor (SeaWiFS) to document the seasonal cycle of surface chlorophyll in the western tropical Pacific. Surface waters in this region can be divided into two ecosystems. The western end of the cold, salty waters of the cold tongue with high nutrient low chlorophyll (HNLC) characteristics occupies most of the eastern part of the region, while warm, fresh, and oligotrophic waters of the warm pool stand in the western part. Nevertheless, disruption of the oligotrophy may show up at different locations. We reconstructed the seasonal cycle of chlorophyll, sea surface temperature (SST), winds, and surface currents from satellite data and satellite-derived products by extracting the annual and semi-annual harmonics of the time series at each grid point. The calculation was done for the 1999–2004 years in order to exclude the consequences of the major 1997–1998 El Niño Southern Oscillation event. The variance explained by the seasonal cycle for this period highlights three regions with high seasonality: (1) The oligotrophy/HNLC transition zone undergoes meridional seasonal displacements. The cold tongue is at its northernmost (southernmost) position during boreal spring (fall). These displacements can be explained in terms of meridional advection of chlorophyll-rich waters and are consistent with the seasonal cycle of the north and south equatorial countercurrents that transport phytoplankton-poor waters. (2) Ocean-color images show seasonal enrichments in the far western north equatorial countercurrent (NECC) area, especially during boreal spring. The chlorophyll maximum coincides with the maximum NECC velocity, follows a SST minimum, and occurs during the upwelling-favorable phase of the wind stress curl. We attribute these enrichments to local upwelling associated with current meandering, horizontal advection from further west, and transport of nutrient-rich waters by the New Guinea coastal undercurrent. (3) Near the Solomon Archipelago, we observe enhancements of chlorophyll concentration southwest of the islands in austral winter, when both the southwestward surface currents and the southeasterly wind stress are strongest. This may be a combination of an island-mass effect and wind-driven upwelling. Horizontal advection from the Solomon area leads to an almost concurrent seasonal chlorophyll enrichment in the northern Coral Sea. In the Gulf of Papua, high chlorophyll concentrations at the same time can be explained by the presence of a strong cyclonic circulation. This study highlights the richness of the response of surface chlorophyll to physical processes at the seasonal time scale in a region usually acknowledged as oligotrophic.  相似文献   

12.
High primary productivity on the Pacific coast of the Baja California Peninsula is usually related to coastal upwelling activity that injects nutrients into the euphotic zone in response to prevailing longshore winds (from the northwest to north). The upwelling process has maximum intensity from April to June, with the coastal upwelling index varying from 50 to 300 m3/s per 100 m of coastline. Along the entire coast of the peninsula, the upwelling intensity changes in accordance with local wind conditions and bottom topography. Spatial variability can also be modulated by the influence of mesoscale meanders of the California Current. We have identified the seasonal and synoptic variability of upwelling signatures on the Baja California shelf, using averaged monthly and weekly sea surface temperature (SST) distributions obtained from remote sensing imagery from the Advanced Very High Resolution Radiometer in the period from 1996 to 2001. Analysis of SST distribution and direct experimental data on temperature and nutrient concentration shows that the areas with the coldest SST anomalies were closely related to the bottom slope, shelf width, and coastline orientation relating to wind direction. We also assume that the nutrient transport into the coastal lagoons may be forced by the coupling of coastal upwelling and tidal pumping of surface waters into the lagoon system. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

13.
1998年8月台湾海峡表层叶绿素a含量的分布特征   总被引：2，自引：0，他引：2  
根据1998年8月台湾海峡表层温度、盐度、叶绿素a的走航式观测结果 ,讨论了调查期间叶绿素a的分布特征。结果表明 ,夏季台湾海峡存在明显的上升流现象 ,表层较高的叶绿素a含量均位于低水温区。表层叶绿素a最大值出现在上升流区的边缘。作者认为这是上升流中心区与边缘区浮游植物的大量繁殖具有一定的“时间差”的缘故。台湾海峡24°N以南及以北海域 ,由于上升流强度的差异 ,表层叶绿素a的分布变化也明显不同。夏季 ,台湾海峡表层叶绿素a含量呈南高北低的趋势。  相似文献   

14.
以往对上升流的研究更多的是关注其年际或季节变化, 高时间分辨率遥感产品的出现使得研究上升流的高频特征成为可能。本文基于融合的逐日海表温度数据, 结合多尺度分割方法, 提出了一种探测上升流冷信号异质性的新算法, 通过上升流面积和强度指数展示了一个完整的琼东上升流过程。分析SST(Sea Surface Temperature)图像的结果表明, 夏季琼东涌升到海面的上升流存在间断期, 平均间隔为6d。每年夏季(6—9月)平均有98d在海表面识别到上升流, 其平均面积为7698km2, 平均强度为1.0℃, 两者存在较高的相关性。琼东上升流发生频率与离岸距离成反比, 琼东北海域为高发区。不同上升流的影响因子可能不同, 离岸风、风应力旋度、热带气旋均与上升流短期变化密切相关。  相似文献   

15.
基于2002年夏季开展的"中国近海环流形成变异机理、数值预测方法及对环境的影响"观测项目获得的往复走航温盐流资料,结合同期的卫星观测(风、SST、海表动力高度)数据,初步探讨了粤东陆架边缘上升流区的内潮现象及其局地反馈特征.研究结果表明:粤东陆架边缘海域存在显著的、间歇性的相对低温海水的沿陆坡涌升现象,其中A航段的低温(18～23℃)海水涌升发生在约50～150m深度,B航段的低温(<18℃)海水涌升则主要位于150 m以深.由于观测期间海表风变化很小,而海洋涡旋在几周至几个月内相对稳定,并且研究海域涡旋对流场的影响似乎局限于75 m以浅的上层海洋,因而A、B航段的差异显然不能用海表风或海表动力高度变化来解释.进一步的分析表明粤东陆架边缘上升流区存在显著的内潮现象,尽管资料所限使得我们无法准确判定该内潮性质,往复走航海流剖面的确揭示了1阶和5阶内潮模的存在.内潮的不同模态极大地改变了上层海洋的热力和环流结构;低阶内潮模导致沿最大温度水平梯度处水温的剧烈垂向起伏(>30 m)以及跃层两侧的海流反向现象;高阶内潮模导致垂直陆坡方向水平流速的多次反向,强烈的流剪切可能与增强的混合联系在一起.导致低阶内潮模(A航段)向高阶内潮模(B航段)转变的原因可能是由于内潮特征线倾角与地形坡度比较接近而激发的"临界反射"效应.分析结果还表明,不同内潮模态导致的环流结构变异叠加在背景环流场之上,会显著影响粤东陆架边缘上升流的空间结构及强度.  相似文献   

16.
采用福建沿海4个站点(包括浮标)2016年的实测水文气象数据,初步分析了不同天气系统影响情况下海表温度的变化特征。研究结果表明:福建沿海月均海温日变化和气温日变化有一定关系,二者都有明显的日变化周期,海温的日变化的峰值略滞后于气温日变化的峰值;无明显天气系统影响时,海温和气温的变化趋势比较一致,有冷空气或台风系统影响时海温和气温的变化趋势不再一致;冷空气系统影响时气温下降的时间从北到南依次滞后,而海温的下降从北到南延迟不明显;7月上升流的作用使得古雷浮标附近海表温度降低,并且周期发生明显改变。  相似文献   

17.
Phytoplankton samples were collected from the equatorial Pacific (10°S to 10°N along 155°E) in June 1992 as part of the Australian contribution to the JGOFS program. Chlorophyll and carotenoid pigments were measured by HPLC, and a PC-based computer program (CHEMTAX) was used to estimate the contribution of 9 algal classes to the total chlorophyll a concentration in 9 separate depth bands at each location. This cruise occurred in the middle of the prolonged 1991/1993 El Niño, and the results are compared with similar data from a cruise in October 1990 which occurred before this El Niño but after the 1988/1989 La Niña.Changes in the pigment : chlorophyll a ratios appeared consistent across algal classes and, apart from some minor exceptions, consistent between cruises. Pigments involved in light-harvesting generally increased relative to chlorophyll a with increasing depth, whereas the ratio for photoprotective pigments (e.g. diadinoxanthin) usually decreased with depth. The zeaxanthin concentration per cell for cyanobacteria decreased with depth in the surface 75 m during 1992 as would be expected for a photoprotective pigment.Based on their contribution to the total chlorophyll a concentration, haptophytes, prochlorophytes, cyanobacteria (Synechococcus) and chlorophytes were the dominant algal classes in 1992. The chlorophyte contribution to chlorophyll a in 1992 (14.8%) was almost double that in 1990 (7.8%). This increase was largely at the expense of the cyanobacteria and haptophytes, which both decreased significantly. The increase in chlorophytes in 1992 was particularly noticeable in the surface waters south of the equator at about 4°S, where there was evidence of upwelling.  相似文献   

18.
In this paper, we use a coupled biological/physical model to synthesize and understand observations taken during the US JGOFS Arabian Sea Process Study (ASPS). Its physical component is a variable-density, -layer model; its biological component consists of a set of advective–diffusive equations in each layer that determine nitrogen concentrations in four compartments, namely, nutrients, phytoplankton, zooplankton, and detritus. Solutions are compared to time series and cruise sections from the ASPS data set, including observations of mixed-layer thickness, chlorophyll concentrations, inorganic nitrogen concentrations, particulate nitrogen export flux, zooplankton biomass, and primary production. Through these comparisons, we adjust model parameters to obtain a “best-fit” main-run solution, identify key biological and physical processes, and assess model strengths and weaknesses.Substantial improvements in the model/data comparison are obtained by: (1) adjusting the turbulence-production coefficients in the mixed-layer model to thin the mixed layer; (2) increasing the detrital sinking and remineralization rates to improve the timing and amplitude of the model's export flux; and (3) introducing a parameterization of particle aggregation to lower phytoplankton concentrations in coastal upwelling regions.With these adjustments, the model captures many key aspects of the observed physical and biogeochemical variability in offshore waters, including the near-surface DIN and phytoplankton P concentrations, mesozooplankton biomass, and primary production. Nevertheless, there are still significant model/data discrepancies of P for most of the cruises. Most of them can be attributed to forcing or process errors in the physical model: inaccurate mixed-layer thicknesses, lack of mesoscale eddies and filaments, and differences in the timing and spatial extent of coastal upwelling. Relatively few are clearly related to the simplicity of the biological model, the model's overestimation of coastal P being the most obvious example. Overall, we conclude that future efforts to improve biogeochemical models of the Arabian Sea should focus on improving their physical component, ensuring that it represents the ocean's physical state as closely as possible. We believe that this conclusion applies to coupled biogeochemical modeling efforts in other regions as well.  相似文献   

19.
渤海海温与叶绿素季节空间变化特征分析   总被引：4，自引：0，他引：4  
以2003年MODIS数据为数据源，在图像处理、空间插值的基础上作海温与叶绿素浓度的空间相关分析。结果表明，整个海域的叶绿素浓度和海温的分布具有明显的区域和季节变化特征。基本规律是叶绿素浓度从近岸向渤海中央递减；温度则随季节发生变化，随着温度升高，近海叶绿素浓度增高，而渤海中央区域叶绿素浓度降低。渤海叶绿素浓度的分布与河口径流、季节等因素有关。从空间关系看，海温与叶绿素浓度不存在很明显的空间分布相关性，但不同季节有不同的相关性。上述研究可用于估算海洋初级生产力。  相似文献   

20.
A coastal upwelling event in the southern Taiwan Strait (STWS) was investigated using intensive cruise surveys (four repeated transects in a month) and satellite data in July and early August 2004.The extensive upwelling-associated surface cold water was first observed in early July (～2.0×10 4 km 2) along the STWS coast.Then,the cold surface water reduced in size by ～50% with decreased chlorophyll concentrations after 15 days,indicating the weakening of the upwelling event.At the end of July,the cold surface water disappeared.The temporal variations of the surface cold water and the 3-D hydrography around Dongshan Island are thought to be mainly attributed to the weakened upwelling-favorable southwestern wind,the asymmetric spatial structure of the wind field and the intrusion of warm water from the northern South China Sea.  相似文献   

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