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1.
Louis W. Botsford Cathryn A. Lawrence Edward P. Dever Alan Hastings John Largier 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):3116
The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction. 相似文献
2.
In this paper, the authors study the influence of the wind on the dynamics of the continental shelf and margin, in particular the formation of a secondary upwelling (or downwelling) front along the shelf break.Observations during the MOUTON2007 campaign at sea along the Portuguese coast in summer 2007 reveal the presence of several upwelling fronts, one being located near the shelf break. All upwellings are characterized by deep cold waters close to or reaching the surface and with high chlorophyll concentrations. Simplified numerical models are built in order to study a possible physical mechanism behind this observation. First, a simple shallow water model with three distinct layers is used to study the formation of secondary upwelling fronts. We show that the physical mechanism behind this process is associated with onshore transport of high potential vorticity anomalies of the shelf for upwelling favorable conditions. Sensitivity studies to bottom friction, shelf width, continental slope steepness, shelf “length” are analysed in terms of potential vorticity dynamics. In particular bottom friction is analyzed in detail and we find that, even though bottom friction limits the barotropic velocity field, it enhances the cross-shore circulation, so that no steady state is possible when stratification is taken into account. Bottom friction accelerates the onshore advection of high potential vorticity, but also drastically reduces its amplitude because of diabatic effects. The net effect of bottom friction is to reduce the secondary upwelling development. Based on similar mechanisms, previous results are then extended to downwelling favorable conditions. Finally a more realistic configuration, with bottom topography, wind forcing and stratification set up from observations, is then developed and the results confronted to the observations. Simulations overestimate the velocity amplitude but exhibit good agreement in terms of density ranges brought over the shelf and general isopycnal patterns.The application and extension of the results to more general oceanic regions is discussed and we conclude on the influence of such process on the dynamics of wind driven circulation over a shelf. 相似文献
3.
B.T. Kuebel Cervantes J.S. Allen 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):2956
The three-dimensional circulation on the continental shelf off northern California in the wind events and shelf transport (WEST) experiment region during summer 2001 is studied using the primitive equation regional ocean modeling system (ROMS). The simulations are performed with realistic topography and initial stratification in a limited-area domain with a high-resolution grid. Forcing consists of measured wind-stress and heat flux values obtained from a WEST surface buoy. The general response shows a southward coastal upwelling jet of up to and a weakening or reversal of currents inshore of the jet when upwelling winds relax. Model results are compared to WEST moored velocity and temperature measurements at five locations, to CODAR surface current observations between Pt. Reyes and Bodega Bay, and to hydrographic measurements along shipboard survey lines. The model performs reasonably well, with the highest depth-averaged velocity correlation (0.81) at the inshore mooring (40 m water depth) and lowest correlation (0.68) at the mid-depth mooring (90 m depth). The model shows generally stronger velocities than those observed, especially at the inshore moorings, and a lack in complete reversal of southward velocities observed when upwelling winds relax. The comparison of surface velocities with CODAR measurements shows good agreement of the mean and the dominant mode of variability. The hydrography compares closely at the southern and northern edges of the survey region (correlation coefficients between 0.90 and 0.97), with weaker correlations at the three interior survey lines (correlation coefficients between 0.44 and 0.76). Mean model fields over the summer upwelling period show slight coastal jet separation off Pt. Arena and significant separation off Pt. Reyes. The cape regions also experience relatively strong bottom velocities and nonlinearity in the surface flow. Across-shelf velocity sections examined along the shelf reveal a double jet structure that appears just north of Bodega Bay and shows the offshore jet strengthening to the south. We examine the dynamics during an upwelling and subsequent relaxation event in May 2001 in which the WEST measurements show evidence of a strong flow response. The alongshelf variability in the upwelling and relaxation response introduced by Pt. Reyes is evident. Analysis of term balances from the depth-averaged momentum equations helps to clarify the event dynamics in different regions over the shelf. A clear pattern in the nonlinear advection term is due to the spatial acceleration of the southward jet around the capes of Pt. Arena and Pt. Reyes during upwelling. Results from a three-dimensional Lagrangian analysis of water parcel displacement show significant southward displacement in the coastal jet region, including a strong signal from the double jet. Alongshelf variability in parcel displacements and upwelling source waters due to the presence of Pt. Arena and Pt. Reyes is also apparent from the Lagrangian fields. A cyclonic eddy-like recirculation feature offshore of Pt. Arena prior to the upwelling event causes large patches of onshore-displaced parcels. Additionally, across-shelf variability in the response of water parcels along the D line includes decreased vertical displacement and increased alongshelf displacement in the offshore direction. 相似文献
4.
Adriana Huyer 《Progress in Oceanography》1983,12(3):259-284
Coastal upwelling in the California Current system has been the subject of large scale studies off California and Baja California, and of small scale studies off Oregon. Recent studies of the winds along the entire coast from 25°N to 50°N indicate that there are significant along-shore variations in the strength of coastal upwelling, which are reflected in the observed temperature distribution. Active upwelling appears to be restricted to a narrow coastal band (about 10–25 km wide) along the entire coast, but the region influenced by coastal upwelling may be much wider. Intensive observations of the upwelling zone during summer off Oregon show the presence of a southward coastal jet at the surface, a mean vertical shear, a poleward undercurrent along the bottom, and persistently sloping isopycnals over the continental shelf; most of the upwelling there occurs during relatively short periods (several days long) of upwelling-favorable winds. During the upwelling season off Oregon, the offshore Ekman transport is carried by the surface Ekman layer, and the onshore return flow occurs through a quasi-geostrophic interior. It is not known whether the structure and dynamics observed off Oregon are typical of the upwelling zone along the entire coast, though some of the same features have been observed off Baja California. Current and future research will eventually show whether the Oregon results are also applicable in the region of persistently strong upwelling-favorable winds off northern California, and in the region of complex bathymetry off central and southern California. 相似文献
5.
Moninya Roughan Newell Garfield John Largier Edward Dever Clive Dorman Dwight Peterson Jeff Dorman 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):2931
The paradox of upwelling is the relationship between strong wind forcing, nutrient enrichment, and shelf productivity. Here we investigate how across-shelf structure in velocity and hydrography plays a role in the retention (inshore) and export (offshore) of particles such as nutrients, plankton and larvae. We examine the spatial structure of the coastal currents during wind-driven upwelling and relaxation on the northern Californian Shelf. The field work was conducted as part of the Wind Events and Shelf Transport (WEST) project, a 5-year NSF/CoOP-funded study of the role of wind-driven transport in shelf productivity off Bodega Bay (northern California) from 2000 to 2003. We combine shipboard velocity profiles (ADCP) and water properties from hydrographic surveys during the upwelling season to examine the mean across-shelf structure of the hydrography and velocity fields during three contrasting upwelling seasons, and throughout the upwelling-relaxation cycle. We also present results from two winter seasons that serve as contrast to the upwelling seasons.During all three upwelling seasons clear spatial structure is evident in velocity and hydrography across the shelf, exemplified by current reversals inshore and the presence of a persistent upwelling jet at the shelf break. This jet feature changes in structure and distance from the coast under different wind forcing regimes. The jet also changes from the north of our region, where it is a single narrow jet, adjacent to the coast, and to the south of our region, where it broadens and at times two jets become evident. We present observations of the California Under Current, which was observed at the outer edge of our domain during all three upwelling seasons. The observed across-shelf structure could aid both in the retention of plankton inshore during periods of upwelling followed by relaxation and in the export of plankton offshore in the upwelling jet. 相似文献
6.
Robert S. Pickart Michael A. Spall G.W.K. Moore Thomas J. Weingartner Rebecca A. Woodgate Knut Aagaard Koji Shimada 《Progress in Oceanography》2011,88(1-4):78-100
The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea. 相似文献
7.
Summer upwelling on the continental shelf north of Cape Canaveral, Florida, has been previously observed to result from wind forcing. A two-layer, finite element model reproduces reasonably well the characteristics of the wind-driven upwelling in respect to location and magnitude. Model investigation also shows that upwelling results from offshore current forcing which is imposed through an along-shelf sea level slope. This sea level slope, which has been found to be of the order of −10−7, represents a mean Gulf Stream effect. The results suggest that the strongest upwelling events near Cape Canaveral occur when the wind and Gulf Stream forcings act together. 相似文献
8.
A two-dimensional numerical model is constructed to study the interaction between the coastal upwelling and the coastal front off Zhejiang coast in summer. In the f-plane model, the shelf topography, continuous stratification, and Richardson number-dependent eddy coefficients are considered. The results show that the coastal up-welling off Zhejiang in summer can be divided into two regions, the nearshore one (Region A) and the offshore one (Region B). In Region A, the alongshore wind stress has more important effect on the coastal upwelling while in Region B, the upwelling is mainly induced by the Taiwan Warm Current. The results also suggest that the formation of coastal front off Zhejiang in summer is closely related to the strength of the coastal upwelling in Region A. 相似文献
9.
10.
To address the mechanisms controlling halocline variability in the Beaufort Sea, the relationship between halocline shoaling/deepening and surface wind fields on seasonal to decadal timescales was investigated in a numerical experiment. Results from a pan-Arctic coupled sea ice-ocean model demonstrate reasonable performances for interannual and decadal variations in summer sea ice extent in the entire Arctic and in freshwater content in the Canada Basin. Shelf-basin interaction associated with Pacific summer and winter transport depends on basin-scale wind patterns and can have a significant influence on halocline variability in the southern Beaufort Sea. The eastward transport of fresh Pacific summer water along the northern Alaskan coast and Ekman downwelling north of the shelf break are commonly enhanced by cyclonic wind in the Canada Basin. On the other hand, basin-wide anti-cyclonic wind induces Ekman upwelling and blocks the eastward current in the Beaufort shelf-break region. Halocline shoaling/deepening due to shelf-water transport and surface Ekman forcing consequently occur in the same direction. North of the Barrow Canyon mouth, the springtime down-canyon transport of Pacific winter water, which forms by sea ice production in the Alaskan coastal polynya, thickens the halocline layer. The model result indicates that the penetration of Pacific winter water prevents the local upwelling of underlying basin water to the surface layer, especially in basin-scale anti-cyclonic wind periods. 相似文献
11.
Nobuo Suginohara 《Journal of Oceanography》1974,30(1):23-33
On the assumption that motions of the barotropic mode are horizontally nondivergent, action of the wind stress with longshore variation on a two-layer ocean adjacent to the meridional east coast is studied. Only the equatorward wind stress is considered. Along the east coast, upwelling is induced by the direct effect of the coast and is confined in a narrow strip with the width of the order of the internal radius of deformation. The upwelling propagates poleward with the internal gravity wave speed. Coastal upwelling induced by the wind stress with longshore variation may be interpreted as the generation and propagation of internal Kelvin waves. Associated with the coastal upwelling, the equatorward flow in the upper layer and the poleward flow in the lower layer are formed as an internal mode of motions. When the bottom topography with the continental shelf and slope is taken into account, occurrence of the poleward undercurrent is delayed by a few days because of the generation of continental shelf waves. And, after the forcing is stopped, the shelf waves propagate poleward away from the upwelling region and the poleward undercurrent fully develops. At the margin of the continental shelf, another upwelling region is induced and propagates poleward. 相似文献
12.
利用三维斜压流体动力学模型 ,通过对东海沿岸海区冬、夏季的斜压环流及其温盐结构的数值研究 ,揭示研究海区垂直环流及其温盐结构的动力过程及其成因。垂直环流的模拟结果表明 :冬季 ,沿岸海区的垂直环流以逆时针流动 ,近表层为向岸流 ,沿岸为下降流 ,近表层以下为离岸流 ,其在外海有明显的上升趋势 ,沿岸下降流自表层至底层逐渐由强变弱 ;夏季 ,沿岸海区的垂直环流以顺时针流动 ,近表层以下为向岸流 ,沿岸为上升流 ,近表层为离岸流 ,其在外海有明显的下降趋势 ,沿岸上升流自底层至表层逐渐由弱变强。就整个沿岸海区而论 ,冬季沿岸下降流和夏季沿岸上升流的强度都随着岸界地形坡度、风速及风向与岸线偏角的变化而变化。沿岸下降流形成的主要原因是由于冬季东北风与岸界地形的耦合效应及海区温盐分布不均匀所致 ,而沿岸上升流形成的主要原因则是由于夏季西南风与岸界地形的耦合效应及海区温盐分布不均匀所致。 相似文献
13.
《African Journal of Marine Science》2013,35(2):157-170
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
14.
Manganese and iron distributions off central California influenced by upwelling and shelf width 总被引：4，自引：1，他引：4
Zanna Chase Kenneth S. Johnson Virginia A. Elrod Joshua N. Plant Steve E. Fitzwater Lisa Pickell Carol M. Sakamoto 《Marine Chemistry》2005,95(3-4):235-254
In July 2002, a combination of underway mapping and discrete profiles revealed significant along-shore variability in the concentrations of manganese and iron in the vicinity of Monterey Bay, California. Both metals had lower concentrations in surface waters south of Monterey Bay, where the shelf is about 2.5 km wide, than north of Monterey Bay, where the shelf is about 10 km wide. During non-upwelling conditions over the northern broad shelf, dissolvable iron concentrations measured underway in surface waters reached 3.5 nmol L−1 and dissolved manganese reached 25 nmol L−1. In contrast, during non-upwelling conditions over the southern narrow shelf, dissolvable iron concentrations in surface waters were less than 1 nmol L−1 and dissolved manganese concentrations were less than 5 nmol L−1. A pair of vertical profiles at 1000 m water depth collected during an upwelling event showed dissolved manganese concentrations of 10 decreasing to 2 nmol L−1, and dissolvable iron concentrations of 12–20 nmol L−1 in the upper 100 m in the north, compared to 3.5–2 nmol L−1 Mn and 0.6 nmol L−1 Fe in the upper 100 m in the south, suggesting the effect of shelf width influences the chemistry of waters beyond the shelf.These observations are consistent with current understanding of the mechanism of iron supply to coastal upwelling systems: Iron from shelf sediments, predominantly associated with particles greater than 20 μm, is brought to the surface during upwelling conditions. We hypothesize that manganese oxides are brought to the surface with upwelling and are then reduced to dissolved manganese, perhaps by photoreduction, following a lag after upwelling.Greater phytoplankton biomass, primary productivity, and nutrient drawdown were observed over the broad shelf, consistent with the greater supply of iron. Incubation experiments conducted 20 km offshore in both regions, during a period of wind relaxation, confirm the potential of these sites to become limited by iron. There was no additional growth response when copper, manganese or cobalt was added in addition to iron. The growth response of surface water incubated with bottom sediment (4 nmol L−1 dissolvable Fe) was slightly greater than in control incubations, but less than in the presence of 4 nmol L−1 dissolved iron. This may indicate that dissolvable iron is not as bioavailable as dissolved iron, although the influence of additional inhibitory elements in the sediment cannot be ruled out. 相似文献
15.
A distinct, coastal upwelling cell inshore of the southern limb of the East Madagascar Current is described. The upwelling cell has cold surface water, with high concentrations of chlorophyll-a. It is located where this current moves from a bathymetry characterised by a narrow continental shelf and a steep slope to one characterised by a wider shelf and a less steep slope. There seems to be no correlation between the local winds and the presence of upwelled water, suggesting current-induced upwelling. Advection of upwelling filaments is consistent with the concept of an East Madagascar retroflection. 相似文献
16.
南海上升流研究概述 总被引：39，自引：3，他引：39
本文对近40a来南海上升流研究结果进行了概述，重点介绍了南海北部陆架区上升流的时空分布特征，及其消长和形成机制等研究成果．这些研究成果揭示上升沈是整个南海北部陆架区夏季的普遍现象，具有南海海盆的空间尺度．引起南海北部陆架区夏季上升流存在的动力因素是盛行的西南季风．该上升流在空间和时间上的分布是不均一的，海南岛东北和闽、粤边界海域是上升流中心区；台湾浅滩周围的上升流呈多元结构，各上升流区海水的理化性质存在看明显差异；在粤东，上升流的影响可达沿海港湾内部，并支配看这些港湾的夏季水文条件．南海除了在其北部陆架区存在看夏季上升流外，夏季在越南东部沿岸和冬季在吕宋岛沿岸均存在看上升流。 相似文献
17.
This paper examines the simplification strategy of retaining only the nonhydrostatic effect of local acceleration in a three-dimensional fully nonhydrostatic model regarding the submesoscale wave phenomenon in the ocean.Elaborate scale analysis of the vertical component of the Reynold-averaged Navier–Stokes(RANS) equation was performed, confirming the rationalization of this simplification. Then, the simplification was implemented in a RANS equation-based nonhydrostatic model NHWAVE(nonhydrostat... 相似文献
18.
Frontal upwelling is an important phenomenon in summer in the Yellow Sea (YS) and plays an essential role in the distribution of nutrients and biological species. In this paper, a three-dimensional hydrodynamic model is applied to investigate the characteristics and influencing factors of frontal upwelling in the YS. The results show that the strength and distribution of frontal upwelling are largely dependent on the topography and bottom temperature fronts. The frontal upwelling in the YS is stronger and narrower near the eastern coast than near the western coast due to the steeper shelf slope. Moreover, external forcings, such as the meridional wind speed and air temperature in summer and the air temperature in the preceding winter and spring, have certain influences on the strength of frontal upwelling. An increase in air temperature in the previous winter and spring weakens the frontal upwelling in summer; in contrast, an increase in air temperature in summer strengthens the frontal upwelling. When the southerly wind in summer increases, the upwelling intensifies in the western YS and weakens in the eastern YS. The air temperature influences the strength of upwelling by changing the baroclinicity in the frontal region. Furthermore, the meridional wind speed in summer affects frontal upwelling via Ekman pumping. 相似文献
19.
2007 年长江口邻近海域夏季上升流演变机制研究 总被引：3，自引：0，他引：3
研究长江口邻近海域夏季上升流强度和空间分布的变化,对渔业生产和赤潮的防治具有重要的指导意义.采用2007年6~10月高分辨率卫星遥感资料 NGSST 海表温度和 CCMP 风场,通过经验正交函数(EOF)分解和区域海洋数值模式(ROMS)研究了该海域夏季上升流的短期演变机制及其与 SST 异常的关系.结果表明,夏季上升流强度和范围存在明显变化,是引起该海域 SST 异常的重要原因;风场对上升流短期演变起着关键作用,风应力旋度对局地上升流变化的影响与沿岸风应力同等重要;地形变化影响着上升流中心的分布,陡而窄的海底凸起容易在顺流侧形成较强的上升流中心,并在逆流侧诱发下降流. 相似文献
20.
Oleg Zaytsev Rafael Cervantes-Duarte Orzo Montante Artemio Gallegos-Garcia 《Journal of Oceanography》2003,59(4):489-502
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