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   

The physical structure of a cold filament in a Chilean upwelling zone (Península de Mejillones, Chile, 23°S)     

Marcus Sobarzo  Dante Figueroa 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12)

Cold filaments associated with Eastern Boundary Currents are typically narrower than 100 km but can be several hundred kilometers long, extending from the coast to the open ocean in upwelling areas. One such structure, observed off Península de Mejillones (23°S, Chile), was studied with both satellite images and two 5-days hydrographic cruises carried out during January 1997. The study used a coastal grid of 31 stations in an area of 165 ×155 km², approximately. The spatial distribution of the filament and its change between cruises are described from the horizontal distributions of dynamic height, temperature, salinity and dissolved oxygen. The filament was a shallow feature (thickness <100 m) and extended at least 165 km toward the open ocean. A meandering northward current flowed at the borders of the filament, separating oceanic and coastal waters of different physical properties. Comparisons of cross sections of the filament near the coast and in the oceanic zone show the ascent of the shallow salinity minimum (SSM), and its extension toward the ocean, bound to the filament. It is concluded that Subantarctic Water ((SAAW) distinguish by low salinity, high dissolved oxygen) and Equatorial Subsurface Water ((ESSW) high salinity, low dissolved oxygen, high nutrient content) form this filament, and that their relative proportions depend on the strength of the coastal upwelling. Thus, the knowledge of the dynamics of these structures is fundamental to better understanding of the spatial distribution of important biological variables, such as nutrients and chlorophyll, in the coastal ecosystem.  相似文献   

闽南-台湾浅滩表层沉积物中底栖有孔虫分布及其环境特征     

方惠瑛 《热带海洋学报》1992,(2)

本文分析了闽南-台湾浅滩表层沉积物样品中的底栖有孔虫计有132属、328种。根据种类组成及分布特征,可将海区划分为6个动物群区,每个动物群区各有自己的环境特点。文中分析了动物群种类组成特征与其所赋存的环境之间的关系,并讨论了浅滩西南303站底栖有孔虫的分布与上升流的关系。  相似文献   

Diatom Assemblage and Productivity Changes during the Last 340,000 Years in the Subarctic Pacific     

Kota Katsuki  Kozo Takahashi  Makoto Okada 《Journal of Oceanography》2003,59(5):695-707

Diatoms represent the major part of the microfossils preserved in the subarctic Pacific sediments. During the warm climate intervals the diatom accumulation rate (DAR) tended to increase, whereas it tended to decrease during the cold intervals. Principal component (PC) analysis of the fossil diatom assemblages in Piston Core KH99-3 ES samples from the subarctic Pacific was carried out to investigate the paleoceanographic conditions of the area. PC1 (59.9% of the total variance) was represented by Neodenticula seminae, a characteristic species representing the high nutrient concentrations, which dominated during the interglacial periods. The DAR and PC changes can be attributed to a global origin that is influenced by the nutrient change due to intermediate water change and to a local one that is explained by the change of upwelling region. The analysis of PC2 (17.1% of the total variance) indicates the change of water mass in the western subarctic Pacific. During Marine Isotope Stages (MIS) 2 and 3, the western subarctic Pacific region was significantly influenced by the sea-ice, which may have been derived from the coastal region or a proximal marginal sea. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities   总被引：1，自引：0，他引：1  

J.L. Largier  C.A. Lawrence  M. Roughan  D.M. Kaplan  E.P. Dever  C.E. Dorman  R.M. Kudela  S.M. Bollens  F.P. Wilkerson  R.C. Dugdale  L.W. Botsford  N. Garfield  B. Kuebel Cervantes  D. Kora in 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):2833

The “Wind Events and Shelf Transport” (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000–03. WEST was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling-favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms. Observations of winds, ocean circulation, nutrients, phytoplankton and zooplankton off Bodega Bay and Point Reyes (38°N) were combined with model studies of winds, circulation and productivity. This overview of the WEST program provides an introduction to the WEST special issue of Deep-Sea Research, including the motivation for WEST, a summary of study components, an integrative synthesis of major research results to-date, and background on conditions during field studies in May–June 2001 (the upwelling period on which this special issue is focused).  相似文献   

Larval fish assemblages in nearshore coastal waters off central Chile: temporal and spatial patterns   总被引：1，自引：0，他引：1  

E. Hernndez-Miranda  A. T. Palma  F. P. Ojeda 《Estuarine, Coastal and Shelf Science》2003,56(5-6):1075-1092

In this study we identified spatial and temporal patterns in the distribution and abundance of larval stages of several fish species in nearshore waters off central Chile. Larvae were sampled monthly at two close (20 km apart) but contrasting localities, El Quisco and Las Cruces. Surveys corresponded to standard plankton tows stratified according to bathymetry and distance from shore. Our results indicate that at both localities: (1) there is a seasonal reproductive pattern for most of the species studied; (2) there is a seasonal-related change in larval species composition and abundance, with austral Winter–Spring being the time of greatest diversity; (3) larval stages of several species that, as adults occupy intertidal, estuarine–riverine, subtidal, benthic-demersal, epipelagic or mesopelagic habitats, are found within these coastal environments; (4) there is a distinctive cross-shelf pattern of larval distribution, which seems to correspond, at least for the intertidal species, with the shallower (<30 m depth) portion of area surveyed; and (5) there is a coupling between the patterns of distribution and abundance of the entire ichthyoplankton assemblage with short-term physical features such as wind forcing, Ekman transport, and local currents. Our findings suggest that both the specific composition as well as the abundance of larval fish species varies spatially and temporally and that this variability may result from the interaction of physical and biological factors at different scales.  相似文献   

2014年与2015年夏季琼东上升流的年际变化及其成因分析   总被引：1，自引：1，他引：0  

李凯  高璐  董旭  潘爱军  王维波  万小芳 《海洋学报》2019,41(1):1-10

本文通过2014年与2015年7月琼东海域的现场调查资料，结合卫星遥感数据，对ENSO影响下琼东上升流的变化进行研究分析，结果表明:2015年为强厄尔尼诺年，2015年7月低温高盐水总体上离表层较深，大约为20~30 m（24.5℃等温线和34等盐线），但在近岸处（离岸20 km以内）却相对较浅，24.5℃等温线和34等盐线在整个断面抬升15~25 m，上升流的爬升现象更为明显；受西南季风影响，表层海水离岸运动，低温高盐水沿地形爬升进行补充，是典型的风生上升流。2014年为正常年份，2014年7月，整个断面低温高盐水更接近表层（近岸例外），大约为10~20 m，同等深度低温高盐现象比2015年明显，但上升流爬升现象不明显，24.5℃等温线和34等盐线在整个断面抬升不到10 m；盛行风为东南风、向岸风，对上升流的形成起抑制作用，低温高盐水使整个断面的抬升，不符合风生上升流的特征规律，表明该年琼东上升流的形成可能与外海环流变化导致的温跃层抬升有关。  相似文献   

Relationships between primary productivity and bottom‐water oxygenation off northwest Africa during the last deglaciation     

Helena L. Filipsson  Oscar E. Romero  Jan‐Berend W. Stuut  Barbara Donner 《第四纪科学杂志》2011,26(4):448-456

The upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface‐ and deep‐water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bølling–Allerød (15.5–13.5 ka BP) and Younger Dryas (13.5–11.5 ka BP). A high accumulation rate gravity core GeoB7926‐2, recovered at ～20° N, 18° W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bølling–Allerød with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low‐oxygen‐tolerant foraminiferal species Bulimina exilis. This is surprising since low‐oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present‐day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep‐sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Flow separation and vertical motions in a tidal flow interacting with a shallow-water island     

Laurent White  Eric Wolanski 《Estuarine, Coastal and Shelf Science》2008

This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia), lying perpendicular to tidal flow in shallow waters. At ebb and flood, attached (stable) eddies develop in the wake where swirls of turbidity suggest that sediment-laden waters are brought to the surface as a result of vertical transport. Both eddy and tip upwellings are encountered in the tidal flow around Rattray Island but there is currently no clear-cut answer as to which secondary flow generates upwelling with the largest intensity. This paper addresses this specific issue through idealized and realistic high-resolution numerical experiments. The analysis is supported by physical arguments based on the theory of flow separation. Given Rattray's geometry and surrounding bathymetry, the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity. The results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at Rattray Island.  相似文献