An eddy-permitting, coupled ecosystem-circulation model of the Arabian Sea: comparison with observations

A nitrogen-based, pelagic ecosystem model has been coupled with an eddy-permitting ocean general circulation model of the Arabian Sea, and the results are compared with observations. The seasonal variability simulated by the model is in good agreement with observations: during the southwest monsoon season, phytoplankton increases in the western Arabian Sea due to upwelling along the coast; during the northeast monsoon season, phytoplankton abundance is large in the northern Arabian Sea because of the enhanced nitrate entrained by relatively deep vertical mixing. Two major differences are, however, found in the basin-wide comparison between model results and observations: an unrealistic nitrate maximum in the subsurface layer of the northern Arabian Sea and too low primary production in oligotrophic regimes. The former may be attributed to the lack of denitrification in the model. Possible causes for the latter include the present model's underestimation of fast nutrient recycling, the neglect of carbon fixation decoupled from nitrogen uptake and of nitrogen fixation, and inadequate nitrate entrainment by mixed layer deepening. The rate at which simulated nitrate increases in the northern Arabian Sea is 11–24 TgN/year, and should correspond to the denitrification rate integrated over the northern Arabian Sea assuming that the loss of nitrogen through denitrification is balanced by advective input. The model does not reproduce the observed phytoplankton bloom in the late southwest monsoon season. Possible causes are that the mixed layer may be too shallow in summer and that the horizontal transport of nitrate from the coast of Oman may be too weak. Sensitivity experiments demonstrate a strong dependence of the simulated primary productivity on the vertical mixing scheme and on the inclusion of a fast recycling loop in the ecosystem model.     

Large-scale physical controls on phytoplankton growth in the Irminger Sea, Part II: Model study of the physical and meteorological preconditioning

The upper water column in the Irminger Sea is characterized by cold fresh arctic and subarctic waters and warm saline North Atlantic waters. In this study the local physical and meteorological preconditioning of the phytoplankton development over an annual cycle in the upper water column in four physical zones of the Irminger Sea is investigated. Data from four cruises of the UK's Marine Productivity programme are combined with results from a coupled biological–physical nitrogen–phytoplankton–zooplankton–detritus model run using realistic forcing. The observations and model predictions are compared and analyzed to identify the key parameters and processes which determine the observed heterogeneity in biological production in the Irminger Sea. The simulations show differences in the onset of the bloom, in the time of the occurrence of the maximum phytoplankton biomass and in the length of the bloom between the zones. The longest phytoplankton bloom of 90 days duration was predicted for the East Greenland Current of Atlantic origin zone. In contrast, for the Central Irminger Sea zone a phytoplankton bloom with a start at the beginning of May and the shortest duration of only 70 days was simulated. The latest onset of the phytoplankton bloom in mid May and the latest occurrence of the maximum biomass (end of July) were predicted for the Northern Irminger Current zone. Here the bloom lasted for 80 days. In contrast the phytoplankton bloom in the Southern Irminger Current zone started at the same time as in Central Irminger Sea, but peaked end of June and lasted for 80 days. For all four zones relatively low daily (0.3–0.5 g C m^− 2d^− 1) and annual primary production was simulated, ranging between 35.6 g C m^− 2y^− 1 in the East Greenland Current of Atlantic origin zone and 45.6 g C m^− 2y^− 1 in the Northern Irminger Current zone. The model successfully simulated the observed regional and spatial differences in terms of the maximum depth of winter mixing, the onset of stratification and the development of the seasonal thermocline, and the differences in biological characteristics between the zones. The initial properties of the water column and the seasonal cycle of physical and meteorological forcing in each of the zones are responsible for the observed differences during the Marine Productivity cruises. The timing of the transition from mixing to stratification regime, and the different prevailing light levels in each zone are identified as the crucial processes/parameters for the understanding of the dynamics of the pelagic ecosystem in the Irminger Sea.     

Modelling Pseudocalanus elongatus stage-structured population dynamics embedded in a water column ecosystem model for the northern North Sea

This paper outlines an approach to couple a structured zooplankton population model with state variables for eggs, nauplii, two copepodites stages and adults adapted to Pseudocalanus elongatus into the complex marine ecosystem model ECOHAM2 with 13 state variables resolving the carbon and nitrogen cycle. Different temperature and food scenarios derived from laboratory culture studies were examined to improve the process parameterisation for copepod stage dependent development processes. To study annual cycles under realistic weather and hydrographic conditions, the coupled ecosystem–zooplankton model is applied to a water column in the northern North Sea. The main ecosystem state variables were validated against observed monthly mean values. Then vertical profiles of selected state variables were compared to the physical forcing to study differences between zooplankton as one biomass state variable or partitioned into five population state variables. Simulated generation times are more affected by temperature than food conditions except during the spring phytoplankton bloom. Up to six generations within the annual cycle can be discerned in the simulation.     

Large-scale physical controls on phytoplankton growth in the Irminger Sea Part I: Hydrographic zones, mixing and stratification

Hydrographic surveys in three consecutive seasons in the Irminger Sea in 2001/2002 have revealed six physical regimes (zones) in which different surface mixing and spring re-stratification processes dominate. They are the South Irminger Current, the North Irminger Current, the Central Irminger Sea, the Polar-origin East Greenland Current, the Atlantic-origin East Greenland Current and the Reykjanes Ridge. The variations in restratification processes in particular have significant implications for the timing of shallow spring mixed layer development and therefore the timing and strength of the spring bloom. The relative roles of heat and freshwater in controlling re-stratification are examined for each hydrographic zone, and it is shown that the simplest concept of solar warming generating spring stratification is appropriate for the Irminger Current and the central Irminger Sea. However in the East Greenland Current and the Reykjanes Ridge zones, the springtime arrival of fresh or saline water at the surface dominates re-stratification and generates the earliest and strongest spring blooms of the region. In the cool fresh centre of the Irminger Sea the relatively low chlorophyll-a throughout the year cannot be wholly explained by stratification or nutrient concentrations. Details of the annual cycle in temperature, salinity, chlorophyll-a and nutrients are presented for each hydrographic zone.     

Monitoring marine plankton ecosystems: Identification of the most relevant indicators of the state of an ecosystem

The number of variables involved in the monitoring of an ecosystem can be high and often one of the first stages in the analysis is to reduce the number of variables. We describe a method developed for geological purposes, using the information theory, that enables selection of the most relevant variables. This technique also allows the examination of the asymmetrical relationships between variables. Applied to a set of physical and biological variables (plankton assemblages in four areas of the North Sea), the method shows that biological variables are more informative than physical variables although the controlling factors are mainly physical (sea surface temperature in winter and spring). Among biological variables, diversity measures and warm-water species assemblages are informative for the state of the North Sea pelagic ecosystems while among physical variables sea surface temperature in late winter and early spring are highly informative. Although often used in bioclimatology, the utilisation of the North Atlantic Oscillation (NAO) index does not seem to provide a lot of information. The method reveals that only the extreme states of this index has an influence on North Sea pelagic ecosystems. The substantial and persistent changes that were detected in the dynamic regime of the North Sea ecosystems and called regime shift are detected by the method and corresponds to the timing of other shifts described in the literature for some European Systems such as the Baltic and the Mediterranean Sea when both physical and biological variables are considered.     

The evolution of the upper water layer in the marginal ice zone, austral spring 1988, Scotia-Weddell Sea

A one-dimensional turbulent erosion model is presented to study the temporal behaviour of the upper layers of the water column in the marginal ice zone during ice retreat. Input parameters in the model are the regular meteorological observations on board, global radiation and ice cover estimates. The model results are validated by comparison with CTD-profiles measured during repeated sections through the marginal ice zone of the Weddell-Scotia Sea sector of the Southern Ocean, over a six week-period in the Austral spring 1988.     

Ventilation of bottom water in the North Sea–Baltic Sea transition zone

The transition zone between the North Sea and the Baltic Sea is a highly dynamic region where a general estuarine circulation forms a regional scale frontal system from northern Kattegat to the Arkona Sea. This system is characterized by an upper low saline out?owing Baltic water mass from the in?owing saline Skagerrak bottom water to the Kattegat and Belt Sea area. Large and rapid ?uctuations of the frontal system are caused by barotropic transports, forced by changing sea level difference between northern Kattegat and the western Baltic Sea, and this results in high variability of the hydrographic conditions and also in frequent in- and out?ow events to the Baltic. The dynamics in the region are here analyzed by a regional model of the transition zone, covering the area from the northern Kattegat to the Arkona Sea. The model is validated against water level, temperature and salinity measurements from the region, and the transports through the Danish straits are related to previous estimates and empirical relations. A sensitivity study quantify the role of bathymetry, the tidally induced mixing and the in?owing Skagerrak bottom water for ventilating the bottom water with Skagerrak water or surface water.Furthermore, the dynamics in the region is analyzed with tracers representing the age of the water. The distribution of age tracers with different boundary conditions are analyzed, and the role of advection and mixing for ventilating the bottom water is quanti?ed in terms of the water age. It is shown that the Great Belt area is a very dynamical area where bottom water is ventilated with surface water. The interannual variation of the ventilation of bottom water in the period 2001–2003 is analyzed by various age tracers and related to observed oxygen conditions, and it is shown that the extreme hypoxic event in the autumn 2002 in the southern Kattegat, the Great Belt and in the western Baltic Sea coincide with an unusual low vertical ventilation rate in the Great Belt area, but normal advection rates of bottom water from the northern Kattegat. This indicates that during this particular event, and probably in general, ventilation of bottom water in the Great Belt has signi?cant in?uence on oxygen conditions in the southern part of the region and for ventilation of bottom waters in the western Baltic Sea. In contrast, the central Kattegat is primarily ventilated by advection of bottom water from the Skagerrak. An age tracer representing the ventilation rate of bottom water with either Skagerrak water or surface water is shown to be inversely correlated to the observed oxygen distribution in the region.     

Study of the seasonal cycle of the biogeochemical processes in the Ligurian Sea using a 1D interdisciplinary model

A one-dimensional coupled physical–biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version 1D) developed at the GeoHydrodynamics and Environmental Laboratory (GHER) of the University of Liège. The ecosystem model contains 19 state variables describing the carbon and nitrogen cycles of the pelagic food web. Phytoplankton and zooplankton are both divided in three size-based compartments and the model includes an explicit representation of the microbial loop including bacteria, dissolved organic matter, nano-, and microzooplankton. The internal carbon/nitrogen ratio is assumed variable for phytoplankton and detritus, and constant for zooplankton and bacteria. Silicate is considered as a potential limiting nutrient of phytoplankton's growth. The aggregation model described by Kriest and Evans in (Proc. Ind. Acad. Sci., Earth Planet. Sci. 109 (4) (2000) 453) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air–sea interface by meteorological data coming from the “Côte d'Azur” Meteorological Buoy. The dynamics of atmospheric fluxes in the Mediterranean Sea (DYFAMED) time-series data obtained during the year 2000 are used to calibrate and validate the biological model. The comparison of model results within in situ DYFAMED data shows that although some processes are not represented by the model, such as horizontal and vertical advections, model results are overall in agreement with observations and differences observed can be explained with environmental conditions.     

Description of a flexible and extendable physical–biogeochemical model system for the water column

A modelling system for coupled physical–biogeochemical simulations in the water column is presented here. The physical model component allows for a number of different statistical turbulence closure schemes, ranging from simple algebraic closures to two-equation turbulence models with algebraic second-moment closures. The biogeochemical module consists of models which are based on a number of state variables represented by their ensemble averaged concentrations. Specific biogeochemical models may range from simple NPZ (nutrient–phytoplankton–zooplankton) to complex ecosystem models. Recently developed modified Patankar solvers for ordinary differential equations allow for stable discretisations of the production and destruction terms guaranteeing conservative and non-negative solutions. The increased stability of these new solvers over explicit solvers is demonstrated for a plankton spring bloom simulation. The model system is applied to marine ecosystem dynamics the Northern North Sea and the Central Gotland Sea. Two different biogeochemical models are applied, a conservative nitrogen-based model to the North Sea, and a more complex model including an oxygen equation to the Baltic Sea, allowing for the reproduction of chemical processes under anoxic conditions. For both applications, earlier model results obtained with slightly different model setups could be basically reproduced. It became however clear that the choice for ecosystem model parameters such as maximum phytoplankton growth rates does strongly depend on the physical model parameters (such as turbulence closure models or external forcing).     

Assimilation of buoy and satellite data in wave forecasts with integral control variables

The quality of numerical wave forecasts can be improved significantly by assimilating wave observations prior to the forecast. In the present study a technique for such assimilation is developed that exploits (a) the efficiency of a limited number of integral control variables, and (b) the effectiveness of variational (model-consistent) assimilation. The formal procedure is independent of the type of control variables and of the wave model (moreover, no adjoint wave model is required). In the present study, integral control variables are chosen to represent large-scale errors in the driving wind fields and uncertainties in the wave model. The assimilation technique is validated with observations of the ERS-1 satellite altimeter and two waverider buoys in two consecutive storms in the Norwegian Sea. The assimilation of the observations reduced the errors in the forecasted significant wave height at the buoy locations typically from 25% to 12%. For low-frequency waves the effect of the assimilation is similarly significant at one buoy location but marginal at the other buoy location.     

Bathymetric influences on the lower Chesapeake Bay hydrography

Observations of salinity and density in the lower Chesapeake Bay are used to describe the bathymetric influence on the transverse hydrographic structure in the area. Current velocity observations of high spatial resolution are also used to relate the flow structure to the hydrographic structure. Tidal flow characteristics in the lower bay are affected by the combination of bathymetry and hydrography. Increased stratification over channels relative to shoals may increase M₂ ellipticity with depth over channels but not over shoals. It is found that three consistent hydrographie features can be related to the transverse structure of the longitudinal flow: (1) persistent stratification over channels due to differential tidal advection of density gradients, (2) development of bottom front separating net inflows from net outflows at the region south of Chesapeake Channel, and (3) outflow of low salinity water at the northern end of a lower bay section. Based on these hydrographie features, two basic hydrographic regimes are proposed to exist throughout the year in the lower Chesapeake Bay: (1) a low buoyancy-high mixing energy regime of stratification restricted to channels, a northward monotonical increase in salinity, and a weak bottom front, and (2) a high buoyancy-weak mixing energy regime of stratified conditions everywhere, a large region of northward salinity decrease at the northern half of the section, and a robust bottom front. The dynamics in the transverse direction for the former regime is ageostrophic, and in the latter regime the contribution by geostrophy is approximately 50% as bathymetric influences become less evident.     

A reduced-gravity model of the Catalan Sea

A reduced-gravity model is used to study the effects of the wind on the upper layer circulation in the Catalan Sea. The model parameters were set by observed features of the circulation in the basin. It is shown that the results are particularly sensitive to the open sea boundary conditions. Simulations were done using the following boundary fluxes: (i) mean values estimated by Bethoux (1980) and (ii) more recent geostrophic transports computed from hydrographic data by Font et al. (1988). The latter seem to lead to more realistic circulation patterns. The influence of seasonal winds (climatological data) on the dynamics is clear, especially during the winter.     

Optimal interpolation of sea surface temperature for the North Sea and Baltic Sea

Sea surface temperature fields of the North Sea and Baltic Sea have been constructed for the year 2001 using a multiplatform Optimal Interpolation scheme. The analyzed fields are constructed every 12 h on a 10 km spatial grid. The product is based upon observations from the three NOAA satellites 12, 14 and 16 together with a large amount of in situ observations. Space dependent covariance functions are estimated from the satellite observations and account for spatial and temporal lags. Several independent methods have been used to assess the error on the sea surface temperature product. Compared against independent in situ observations, the mean RMS difference for the year 2001 is 0.78 °C. The spatial distribution of the errors reveals that the Baltic Sea in general show higher errors than the North Sea. The error statistics throughout the year show a temporal variation of the errors with maximum during summer and winter. Tests with a varying number of satellite observations show that the accuracy of the satellite observations is the most important parameter in terms of reducing the errors on the interpolated sea surface temperature product.     

Mass balance of trace metals in the Adriatic Sea

A first order mass balance of six different trace metals (Mn, Fe, Pb, Zn, Cu, Ni) was presented for a 1-year period for the different compartments of the Adriatic Sea: compartment 1 (northern Adriatic Sea), compartment 2 (central Adriatic Sea and surface layer of the southern Adriatic Sea) and compartment 3 (deep water of the southern Adriatic Sea). The Adriatic Sea appeared to be a source of dissolved Cu, Mn and Fe for the Mediterranean Sea through the Strait of Otranto whereas for dissolved Zn and Pb the Adriatic Sea appeared to be a net sink. For dissolved Ni, inputs and outputs through the Strait of Otranto balanced each other. The residence times of all metals in compartment 1 were significantly shorter than that of water indicating significant removal. In compartments 2 and 3, residence times of Mn and Fe were relatively short suggesting removal from the water column whereas for the other metals their residence times were similar to that of water. Calculations of turnover times of metals with respect to different processes showed that in compartments 1 and 2, sedimentation was the main process that affected the content of the reservoirs whereas in compartment 3, the water flux exchanges played an important role for Zn, Cu and Ni.Most of the metals clearly undergo a very dynamic cycle of sedimentation/remobilization particularly in the Northern Adriatic Sea. In the northern Adriatic Sea, most of the Mn and Fe in deposited sediment were remobilized. This was related to diagenetic processes involving the utilisation and solubilisation of Mn and Fe oxides, which occur in the surface of the sediment in the northern Adriatic Sea. In the central Adriatic Sea, remobilization of Mn and Fe was less than in the northern Adriatic Sea, suggesting that diagenesis processes appear deeper in the sediment. Advective transport of sediment was a major source of metals for the deep basin. As much as 80% of the sediments in the South Adriatic Pit might be advected from the shelf. Remobilization fluxes in the South Adriatic Pit were significantly less than in the Northern and Central Adriatic Sea reflecting hemi-pelagic sediments.     

Variability of the Bohai Sea circulation based on model calculations

The circulation and the hydrography of the Bohai Sea are simulated with the Hamburg Shelf Ocean Model (HAMSOM). The model is three-dimensional, prognostic baroclinic and has a resolution of 5 min in latitude and longitude and 10 layers in the vertical. It is initialised and forced with the five main tidal constituents, temperature and salinity distributions taken from the Levitus database, monthly mean river run-off values and European Centre for Medium Range Weather Forecast (ECMWF) re-analysed data of air pressure, wind stress and of those parameters relevant for the calculation of heat fluxes. The simulation period covers 14 years from 1980 to 1993 due to the availability of the time-dependent ECMWF forcing.The results are analysed by means of time series and EOFs focussing on the interpretation of fluctuations with periods above the tidal cycle. Furthermore, tracer simulations are carried out and turnover times are calculated in order to evaluate the importance of these fluctuations on the renewal and transport of water masses in the Bohai Sea.One of the major outcomes of the investigation is the overall dominance of the annual cycle in all hydrographic parameters and the importance of stochastic weather fluctuations on the transport of water masses in the Bohai Sea.     

Short time-scale analysis of the NW Mediterranean ecosystem during summer–autumn transition: A 1D modelling approach

Modelling was used as a tool to better understand the physical and biological processes observed during the multidisciplinary cruise DYNAPROC 2 (DYNAmic of rapid PROCesses in the water column), which took place in the Ligurian Sea in September–October 2004. The aim of the cruise was to study the short time-scale physical and biological processes that occur when the ecosystem switches from summer oligotrophy to autumnal mesotrophy. In this study, we have tested two 1D physical–biological coupled models. The first was a classical model in which surface layer dynamics were obtained using the turbulent kinetic energy model of Gaspar [Gaspar et al., 1990]. The simulated food-web took into account ten state variables: three nutrients, three classes of phytoplankton, two classes of zooplankton and two types of detritus. The second model (called IDA, Isopycnals Depth Adjustment) was based on the initial one but it took into account the measured variations of isopycnals depths. The results showed that the IDA model most efficiently reproduced the observed ecosystem dynamics. We have therefore used the IDA model to show that physical processes observed during the cruise had a major effect on biological compartment, mainly on nano- and picophytoplankton.     

在他国专属经济区内的海军活动——专用术语在法律制度中的作用

在海洋法的应用方面,专用术语的定义是非常关键的。一个词的定义可由他的普通特征和个别差异来决定。利用这个方法,与水文地理有关的军事调查不算是一种使用武力的威胁。     

A Mean Dynamic Topography of the Mediterranean Sea computed from altimetric data, in-situ measurements and a general circulation model

In the Mediterranean Sea, where the mean circulation is largely unknown and characterized by smaller scales and less intensity than in the open ocean, the interpretation of altimetric Sea Level Anomalies (SLA) is rather difficult. In the context of operational systems such as MFS (Mediterranean Forecasting System) or MERCATOR, that assimilate the altimetric information, the estimation of a realistic Mean Dynamic Topography (MDT) consistent with altimetric SLA to be used to reconstruct absolute sea level is a crucial issue. A method is developed here to estimate the required MDT combining oceanic observations as altimetric and in-situ measurements and outputs from an ocean general circulation model (OGCM).In a first step, the average over the 1993–1999 period of dynamic topography outputs from MFS OGCM provides a first guess for the computation of the MDT. Then, in a second step, drifting buoy velocities and altimetric data are combined using a synthetic method to obtain local estimates of the mean geostrophic circulation which are then used to improve the first guess through an inverse technique and map the MDT field (hereafter the Synthetic Mean Dynamic Topography or SMDT) on a 1/8° resolution grid.Many interesting current patterns and cyclonic/anticyclonic structures are visible on the SMDT obtained. The main Mediterranean coastal currents are well marked (as the Algerian Current or the Liguro–Provenço–Catalan Current). East of the Sicily channel, the Atlantic Ionian Stream divides into several main branches crossing the Ionian Sea at various latitudes before joining at 19°E into a unique Mid-Mediterranean Jet. Also, strong signatures of the main Mediterranean eddies are obtained (as for instance the Alboran gyre, the Pelops, Ierapetra, Mersa-Matruh or Shikmona anticyclones and the Cretan, Rhodes or West Cyprius cyclones). Independent in-situ measurements from Sea Campaigns NORBAL in the North Balearic Sea and the North Tyrrhenian Sea and SYMPLEX in the Sicily channel are used to validate locally the SMDT: deduced absolute altimetric dynamic topography compares well with in-situ observations. Finally, the SMDT is used to compute absolute altimetric maps in the Alboran Sea and the Algerian Current. The use of absolute altimetric signal allows to accurately follow the formation and propagation of cyclonic and anticyclonic eddies in both areas.     

Carbon flux in ice–ocean–plankton systems of the Bellingshausen Sea during a period of ice retreat

Most analyses of marine microbial systems in the seasonally ice covered areas of the Southern Ocean have been based on data from the major embayment areas of the Ross and Weddell Seas. In this study data were collected at stations covering a range of regimes from full ice cover through to open water in the Bellingshausen Sea. A major feature of the production system was a rapid retreat of the ice-edge, which uncoupled the marginal ice zone from a phytoplankton bloom which remained associated with a frontal system. This bloom was maintained, and probably initiated, in an unusual environment generated by the interaction between the marginal ice zone and the front. Size-based analyses of the microbial system were derived for ice-covered, recently ice-covered and open water sites. Estimates of standing stocks and key rate processes were combined to produce a single food web network for each station. The under-ice system was one of low production and low recycling but apparently high retention. As the ice retreated the microbial systems to the north began to develop, but these were constrained by grazing pressure. The bloom in the area appeared to be sustained even though estimated losses were far higher than production, although the high sedimentation losses expected were not observed. The carbon flow networks are discussed in relation to the environmental changes and the interaction of the marginal ice zone and the frontal system appears crucial to the phytoplankton. Microzooplankton grazing is implicated as a major controlling factor. The local microbial dynamics are strongly influenced by material which was produced at an earlier time and somewhere else in the Southern Ocean.     

Upwelling mechanisms in the northwestern Alboran Sea

From April 1996 to July 1997, a series of hydrographic surveys were carried out in the Northwestern part of the Alboran Sea to investigate the upwelling that is an almost permanent feature in this area. Simultaneously a mooring line was deployed in the north part of the eastern section of the Strait of Gibraltar to monitor the variability of the Atlantic Jet (AJ). Two mechanisms are shown to be relevant for the upwelling dynamic in the region: the southward drifting of the AJ and wind stress. A linear relation between the angle under which the Jet enters the Alboran Sea and the distance from the coastline to the front associated with the Jet has been found. This angle that has been estimated from the low passed time series of current velocity measured by the uppermost instrument of the moored line has been then used to identify the onshore–offshore excursions of the Jet. Both upwelling mechanisms are identified from hydrographic data, because each of them has associated a different type of water mass, and they take place in different locations. Wind-driven upwelling dominates in coastal zones, on the shelf, while upwelling associated with southward drifting of the AJ prevails further offshore. The amount of sub-surface water brought up to the surface by each one is of the same order. However, wind-driven upwelling contributes to the fertilization of this region in a major extent because water upwelled by wind is richer in nutrient concentration.