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1.
The primary purpose of this paper is to describe the seasonal variation of the various currents which comprise the California Current System—the California Current, the California Undercurrent, the Davidson Current and the Southern California Countercurrent—and to investigate qualitatively the dynamical relationships among these currents. Although the majority of information was derived from existing literature, previously unpublished data are introduced to provide direct evidence for the existence of a jet-like Undercurrent over the continental slope off Washington, to illustrate ‘event’-scale fluctuations in the Undercurrent and to investigate the existence of the Undercurrent during the winter season.The existing literature is thoroughly reviewed and synthesized. In addition, and more important, geostrophic velocities are computed along several sections from the Columbia River to Cape San Lazaro from dynamic heights given by (1966), and (1964), and and (1976). From these data and from long-term monthly wind stress data and vertical component of wind stress curl data (denoted curl τ) given by (1977), interesting new conclusions are made. 1. The flow that has been denoted the California Current generally has both an offshore and a nearshore maximum in its alongshore coponent. 2. The seasonal variation of the nearshore region of strong flow appears to be related to the seasonal variation of the alongshore component of wind stress at the coast, τyN, at all latitudes. Curl τ near the coast may also contribute to the seasonal signal, accounting for the lead of maximum current over maximum wind stress from about 40°N northward. Large-scale flow separation and fall countercurrents that of headlands may account for the sudden occurrence of late summer and fall countercurrents that appear as large anomalies from the wind-driven coastal flow south of 40°N. 3. From Cape Mendocino southward a northward mean is imposed on the nearshore current distribution. The mean is largest where curl τ is locally strongest, in particular, off and south of San Francisco and in the California Bight. It may be responsible for the portion of the Davidson Current that occurs off California, for the San Francisco Eddy and for the Southern California Eddy or Countercurrent. When southward wind stress weakens in these regions, the northward mean dominates the flow. Flow separation in the vicinity of headlands may also be responsible for these northward flows. There is some evidence that during periods of northward flow a mean monthly τyN-driven southward current occurs inshore of the mean northward flow. At all latitudes, wind-driven ‘event’-scale fluctuations are expected to be superimposed on the seasonal nearshore flow. 4. The spatial distribution and seasonal variation oftthe offshore region of southward flow appear to be related to the spatial distribution and seasonal variation of curl τ. The seasonal variation of curl τ in these areas, curl τl, is roughly in phase with the seasonal variation of τy near the coast and roughly 180° out of phase with the seasonal variation of curl τ near the coast. Southward flow lags negative curl τ by from two to four months. The offshore region of southward flow is strongest during the summer and early fall. The mean annual location of the maximum flow is at about 250–350 km from shore off Washington and Oregon, and at 430 km off Cape Mendocino, 270 km off Point Conception and 240 km off northern Baja. The offshore branch of the flow bends shoreward near 30°N, which is consistent with the shoreward extension of the region of negative curl τ, so that by Cape San Lazaro (25°N), a single region of strong flow is observed within 200 km of the coast. 5. A third region of strong southward flow occurs at distances exceeding 500 km from the coast. The spatial distribution of this flow appears to be related to the spatial distribution of curl τ. 6. The mean northward flow known as the Davidson Current consists of two regions in which the forcing may be dynamically different—seaward of the continental slope off Washington and Oregon and between Cape Mendocino and Point Conception, the mean monthly northward currents appear to be related to the occurrence of positive curl τ; along the coast of Oregon and Washington the northward currents are not related to the occurrence of positive curl τ but are consistent with forcing by the mean monthly northward wind stress at the coast. 7. A region of southward flow that is continuous with the California Current to the south is generally maintained off Oregon and parts of Washington during the winter. This southward flow appears to separate the northward-flowing Davidson and Alaskan Currents in some time-dependent region south of Vancouver Island. The banded current structure is consistent with the distribution of curl τ, if southward flow is related to negative curl τ. 8. The seasonal progression of the California Undercurrent may be related both to the seasonal variation of the offshore region of strong flow (hence to curl τl) and to the alongshore component of wind stress at the coast. South of Cape Mendocino a northward mean also seems to be superimposed on the flow. This mean may be related to the occurrence of strong positive curl τ near the coast. Velocities at Undercurrent depths have two maxima, one in late summer and one in winter. The slope Undercurrent is indistinguishable, except by location, from the undercurrent that is observed on the Oregon-Washington continental shelf.  相似文献   

2.
A nonlinear theory for the generation of the Ulleung Warm Eddy (UWE) is proposed. Using the nonlinear reduced gravity (shallow water) equations, it is shown analytically that the eddy is established in order to balance the northward momentum flux (i.e., the flow force) exerted by the separating western boundary current (WBC). In this scenario, the presence of β produces a southward (eddy) force balancing the northward momentum flux imparted by the separating East Korean Warm Current (EKWC).It is found that, for a high Rossby number EKWC (i.e., highly nonlinear current), the eddy radius is roughly 2Rd/ε1/6 (here ε≡βRd/f0, where Rd is the Rossby radius), implying that the UWE has a scale larger than that of most eddies (Rd). This solution suggests that, in contrast to the familiar idea attributing the formation of eddies to instabilities (i.e., the breakdown of a known steady solution), the UWE is an integral part of the steady stable solution. The solution also suggests that a weak WBC does not produce an eddy (due to the absence of nonlinearity).A reduced gravity numerical model is used to further analyze the relationship between β, nonlinearity and the eddy formation. First, we show that a high Rossby number WBC which is forced to separate from the wall on an f plane does not produce an eddy near the separation. To balance the northward momentum force imparted by the nonlinear boundary current, the f plane system moves constantly offshore, producing a southward Coriolis force. We then show that, as β is introduced to the problem, an anticyclonic eddy is formed. The numerical balance of forces shows that, as suggested by the analytical reasoning, the southward force produced by the eddy balances the northward flow force imparted by the boundary current. We also found that the observed eddy scale in the Japan/East Sea agrees with the analytical estimate for a nonlinear current.  相似文献   

3.
The structure of the annual-mean shallow meridional overturning circulation(SMOC) in the South China Sea(SCS) and the related water movement are investigated,using simple ocean data assimilation(SODA) outputs.The distinct clockwise SMOC is present above 400 m in the SCS on the climatologically annual-mean scale,which consists of downwelling in the northern SCS,a southward subsurface branch supplying upwelling at around 10°N and a northward surface flow,with a strength of about 1×10~6 m~3/s.The formation mechanisms of its branches are studied separately.The zonal component of the annual-mean wind stress is predominantly westward and causes northward Ekman transport above 50 m.The annual-mean Ekman transport across 18°N is about 1.2×10~6 m~3/s.An annual-mean subduction rate is calculated by estimating the net volume flux entering the thermocline from the mixed layer in a Lagrangian framework.An annual subduction rate of about 0.66×10~6m~3/s is obtained between 17° and 20°N,of which 87% is due to vertical pumping and 13% is due to lateral induction.The subduction rate implies that the subdution contributes significantly to the downwelling branch.The pathways of traced parcels released at the base of the February mixed layer show that after subduction water moves southward to as far as 11°N within the western boundary current before returning northward.The velocity field at the base of mixed layer and a meridional velocity section in winter also confirm that the southward flow in the subsurface layer is mainly by strong western boundary currents.Significant upwelling mainly occurs off the Vietnam coast in the southern SCS.An upper bound for the annual-mean net upwelling rate between 10° and 15°N is 0.7×10~6m~3/s,of which a large portion is contributed by summer upwelling,with both the alongshore component of the southwest wind and its offshore increase causing great upwelling.  相似文献   

4.
The sources and fates of metabolizable organic carbon were examined at three sites on the North Carolina slope positioned offshore of Cape Fear, Cape Lookout and Cape Hatteras. The13C/12C compositions (δ13C) of the solid phase organic matter, and the dissolved inorganic carbon (ΣCO2) produced during its oxidation, suggested that the labile fraction was predominantly marine in origin. The ΣCO2 concentration gradient across the sediment-water interface, and by inference the ΣCO2 flux and production rate, increased northward from Cape Fear to Cape Hatteras. Methane distributions and ΣCO2 δ13C values suggest that the rate of anaerobic diagenesis increased northward as well. The differences in sedimentary biogeochemistry are most likely driven by an along-slope gradient of reactive organic carbon flux to the seabed. This trend in reactive organic carbon flux correlates well with macrofaunal densities previously observed at the three sites. Proximity to the shelf and the transport of particulate material by surface boundary currents may control the deposition of metabolizable material on the Carolina slope.Evidence for methanogenesis was found only on the Cape Hatteras slope. The methane, which was produced at a depth of approximately 1 m in the seabed, was consumed nearly quantitatively in the biologically mixed layer as it diffused upward. Irrigation of the sediments by infauna may have provided the necessary oxidant for the consumption of the methane.  相似文献   

5.
In January and February 1998, when an unprecedented fourth repetition of the zonal hydrographic transect at 24.5°N in the Atlantic was undertaken, carbon measurements were obtained for the second time in less than a decade. The field of total carbon along this section is compared to that provided by 1992 cruise which followed a similar path (albeit in a different season). Consistent with the increase in atmospheric carbon levels, an increase in anthropogenic carbon concentrations of 8±3 μmolkg−1 was found in the surface layers. Using an inverse analysis to determine estimates of absolute velocity, the flux of inorganic carbon across 24.5° is estimated to be −0.74±0.91 and −1.31±0.99 PgCyr−1 southward in 1998 and 1992, respectively. Estimates of total inorganic carbon flux depend strongly upon the estimated mass transport, particularly of the Deep Western Boundary Current. The 1998 estimate reduces the large regional divergence in the meridional carbon transport suggested by previous studies and brings into question the idea that the tropical Atlantic constantly outgasses carbon, while the subpolar Atlantic sequesters it. Uncertainty in the carbon transports themselves, dominated by the uncertainty in the total mass transport estimates, are a hindrance to determining the “true” picture.The flux of anthropogenic carbon (CANTH) across the two transects is estimated as northward at 0.20±0.08 and 0.17±0.06 PgCyr−1 for the 1998 and 1992 sections, respectively. The net transport of CANTH across 24.5°N is strongly affected by the difference in concentrations between the northward flowing shallow Florida Current and the mass balancing, interior return flow. The net northward transport of CANTH is opposite the net flow of total carbon and suggests, as has been found by others, that the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today. Combining these flux results with estimates of atmospheric and riverine inorganic carbon input, it is determined that today's oceanic carbon system differs from the pre-industrial system in that today there is an uptake of anthropogenic carbon to the south that is advected northward and stored within the North Atlantic basin.  相似文献   

6.
王毅  崔凤娟 《海洋与湖沼》2015,46(2):241-247
本文通过分析RAMA印度洋观测浮标系统锚系ADCP实测资料,对赤道中印度洋上层海流季节变化进行了研究。研究结果表明,0°,80.5°E纬向流垂向剖面呈现上150m层一致的东向流,而经向流在100m以浅呈现表层向北次表层向南的翻转流结构。赤道中印度洋上层纬向流季节信号被半年周期的东向射流Wyrtki Jets(WJs)所控制。WJs发生于季风方向转换的季节,4—5月份较弱,10—11月份较强。赤道中印度洋上层经向流年周期信号显著。北半球夏季与冬季分别出现风应力旋度驱动的Sverdrup南向流与北向流。本文结论为赤道中印度洋上层环流季节变化特征的研究提供了观测角度的支持。  相似文献   

7.
In this paper, the characteristics of the bottom boundary layer flow induced by nonlinear, asymmetric shoaling waves, propagating over a smooth bed of 1/15 uniform slope, is experimentally investigated. Flow visualization technique with thin-layered fluorescent dye was first used to observe the variation of the flow structure, and a laser Doppler velocimeter was then employed to measure the horizontal velocity, U.The bottom boundary layer flow is found to be laminar except within a small region near the breaking point. The vertical distribution of the phase-averaged velocity U at each phase is non-uniform, which is directly affected by the mean velocity, . The magnitude of increases from zero at the bottom to a local positive maximum at about z/δ2.02.5 (where z is the height above the sloping bottom and δ is the Stokes layer thickness), then decreases gradually to zero at z/δ6.07.0 approximately, and finally becomes negative as z/δ increases further. Moreover, as waves propagate towards shallower water, the rate of increase in the maximum onshore oscillating velocity component is greater than that of the offshore counterpart except near the breaking point. The free stream velocities in the profiles of the maximum onshore and offshore oscillating velocity components, and are found to appear at z/δ≥6.0. This implies that, if the Stokes layer thickness is used as a length scale, the non-dimensionalized boundary layer thickness remains constant in the pre-breaking zone. Although is greater than and the asymmetry of the maximum free stream velocities (i.e. ) increases with decrease of water depth, a universal similar profile can be established by plotting z/δ versus ( ) or ( ). The final non-dimensional profile is symmetric and unique for the distributions of the maximum onshore and offshore oscillating velocity components within the bottom boundary layer, which are induced by nonlinear, asymmetric shoaling waves crossing the pre-breaking zone.  相似文献   

8.
The western boundary layer (WBL) plays a fundamental role in basin-scale wind-driven ocean circulations. In idealized ocean models with flat bottom topography, this layer is required not only to balance the interior Sverdrup transport to close the gyre circulation, but also to dissipate the vorticity imposed by the wind-stress curl. The width of the WBL in Munk-type models is estimated to be δM(AH/β)1/3, where AH and β are horizontal eddy viscosity and the meridional derivative of the Coriolis parameter respectively. For commonly used values of AH, the boundary-layer width δM ranges from 30 to less than 200 km in the mid-latitude ocean. This scale is often poorly resolved in large-scale climate models.This paper intends to demonstrate some consequences when the western boundary layer is not adequately resolved. It is found that coarse resolution models reach equilibrium states by distorting some important dynamics in order to dissipate wind-imposed vorticity. In three-dimensional models, for instance, very strong spurious upwelling and downwelling can occur along the WBL. In models of two-dimensional flow, however, spurious recirculations may develop near the boundary. These false features can be removed when the boundary layer is better resolved. We propose a method in which a spatially varying AH is used to broaden the WBL without affecting mixing in the interior. The method improves the model results considerably.  相似文献   

9.
The antagonistic effects of Kepone (chlordecone) and o,p'-DDD on maturation-inducing steroid (17α,20β,21-trihydroxy-4-pregnen-3-one, 20β-S) induced final maturation of Atlantic croaker (Micropogonias undulatus). Oocytes were investigated in an in vitro germinal vesicle breakdown (GVBD) bioassay. Exposure to Kepone or o,p'-DDD (100 nM-100 μM) prevented the majority of the oocytes from completing GVBD in response to 20β-S; many of them were arrested at the lipid coalescence or germinal vesicle migration stages when exposed to high xenobiotic concentrations (100 μM). In addition, clearing of the ooplasm, oil droplet formation and hydration were incomplete in xenobiotic-exposed oocytes that underwent GVBD. The xenobiotics inhibited GVBD in a concentration-dependent manner. One minute exposure to either of the xenobiotics was sufficient to block GVBD. Washing the follicle-enclosed oocytes after xenobiotic exposure restored their ability to undergo GVBD in response to 20β-S. These results suggest that o,p'-DDD and Kepone exert antagonistic effects on 20β-S action, possibly by competing for the ovarian 20β-S membrane receptor.  相似文献   

10.
In the context of a multidisciplinary study to determine current and past ecosystem health and the relative contributions of sources of organic matter (marine vs. terrestrial and natural vs. anthropogenic input), sterols were determined in plankton, settling particles and sediments from Trinity Bay, Newfoundland, a sub-polar Atlantic Ocean ecosystem. The centric diatoms Chaetoceros spp., Thalassiosira spp. and Leptocylindrus danicus were all prominent in the plankton samples, and centric diatoms predominated in the settling particles. Plankton samples contained 0.4±0.4 mg/g dw (1995) or 1.4±1.3 mg/g dw (1996) total sterols, with cholesta-5,24-dien-3β-ol (mean 26% of total sterols), cholest-5-en-3β-ol (24%) and cholesta-5,22(E)-dien-3β-ol (13%) chief among these, denoting diatom and zooplankton sources. In settling particles, the prominence of cholesta-5,24-dien-3β-ol (24%), cholest-5-en-3β-ol (24%), cholesta-5,22(E)-dien-3β-ol (13%) and 24-methylcholesta-5,22(E)-dien-3β-ol (9%) again suggested mainly marine sources. The sterol composition of plankton and settling particles from different sampling periods showed a high degree of consistency. Higher plant C29 sterols (notably 24-ethylcholest-5-en-3β-ol, 9–26%) were prominent in sediments from both inshore and offshore sites. No decreasing trend in total or individual sterols was observed down the 30-cm sediment cores, suggesting good overall preservation. No 5β-stanols such as 5β-cholestan-3β-ol (coprostanol) were detected in offshore sediments, plankton or settling particles, with only low levels (5β-cholestan-3β-ol max. 4.4%, 5β-cholestan-3α-ol max. 5.1%) in certain inshore sediments. This suggests that raw sewage discharges in rural Newfoundland are being efficiently degraded or dispersed, or that inputs are highly localized. Source apportionation of organic matter in the sediment samples based on sterol composition was attempted. This highlighted the large terrestrial contribution to the sterols in marine sediments (up to 58% of sterols inshore, 24% offshore) and suggests either degradation or effective recycling of marine sterols.  相似文献   

11.
A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward.  相似文献   

12.
We examined stable carbon and nitrogen isotopic signatures of 17 fish and 16 invertebrate taxa common to the Newfoundland and Labrador (NL) continental shelf food web. Particular sampling emphasis was placed on Atlantic cod (Gadus morhua) and related prey species (e.g. shrimp, Pandalus borealis, and capelin, Mallotus villosus). We found highly significant (p < 0.0001) differences between near-shore (bays) and offshore (shelf edge) δ15N signatures for cod, ‘other fish’ (pooled) and invertebrates (pooled). In contrast, there were only minor differences in δ13C signatures of ‘other fish’ (p < 0.05) and no difference for cod and invertebrates among the two habitats. We sampled at two times of the year (January and June) and found no systematic effect of season on both δ13C and δ15N in cod, ‘other fish’ and invertebrates. We calculated isotopic fractionation factors for cod from the entire shelf (mixed diet) and for cod with diets composed mainly of capelin or shrimp. These values ranged between 2.2‰ and 3.9‰ for δ15N and −0.4‰ and 0.8‰ for δ13C and, for δ15N, may reflect diet-related differences in bioenergetic status. We discuss potential mechanisms for near-shore versus offshore enrichment of δ15N signatures, and demonstrate the implications of this spatial variation on δ15N-derived trophic position estimates.  相似文献   

13.
The western equatorial Atlantic is characterized by the formation and shedding of 3–4 large anticyclonic rings per year. These rings originate from the North Brazil Current which, in response to the vanishing wind stress curl (over the ocean interior), retroflects and turns eastward at around 4°N. After their formation and shedding the rings propagate toward the northwest along the South American coast carrying an annual average of about 4Sv. As such, the rings constitute an important part of the meridional heat flux in the Atlantic.The same cannot be said, however, of the western equatorial Pacific. Here, the situation is entirely different even though the South Equatorial Current retroflects at roughly the same latitude as its Atlantic counterpart, the North Brazil Current. Although the South Equatorial Current retroflection is flanked by two quasi-permanent eddies (the so-called Halmahera and the Mindanao eddies), these eddies are an integral part of the current itself and are not shed. Consequently, they are not associated with any meridional heat flux. An important question is, then, why the two oceans behave in such a fundamentally different way even though the source of the rings, the retroflected currents, are very similar in the two oceans.To answer this question, the two oceans are compared using recently developed analytical and numerical models for the western equatorial oceans. It is first pointed out that, according to recent developments in the modelling of the western equatorial Atlantic, the North Brazil Current retroflection rings are formed, shed and drift to the west because, in the Atlantic, this is the only way by which the momentum flux of the approaching and retroflecting current can be balanced. In this scenario, the northwestward flow force exerted by the approaching and retroflecting North Brazil Current (analogous to the force created by a rocket) is balanced by the southwestward force exerted by the rings as they are formed (analogous in some sense to the kickback associated with a firing gun).On the other hand, in the western equatorial Pacific, the formation and shedding of rings is unnecessary because the southward flowing Mindanao Current provides an alternative mechanism for balancing the northward momentum flux of the South Equatorial Current. This implies that it is the absence of a counter current (such as the Mindanao) in the western Atlantic that causes the formation and shedding of North Brazil Current rings. A remaining difficulty with the above scenario is that most colliding and retroflecting currents (i.e. the Mindanao and South Equatorial currents) are not “balanced” in the sense that they cannot be stationary but rather must drift along the coast. It is shown that, in the case of the western Pacific, the long-shore migration is arrested by the Indonesian Throughflow which allows the “unbalanced” fraction of the approaching currents to leak out into the Indian Ocean. This resolves the above difficulty and allows the retroflection to be approximately steady.  相似文献   

14.
Dissolved organic carbon (DOC), stable carbon isotopic (δ13C) compositions of DOC and particulate organic carbon (POC), and elemental C/N ratios of POC were measured for samples collected from the lower Mississippi and Atchafalaya rivers and adjacent coastal waters in the northern Gulf of Mexico during the low flow season in June 2000 and high flow season in April 2001. These isotopic and C/N results combined with DOC measurements were used to assess the sources and transport of terrestrial organic matter from the Mississippi and Atchafalaya rivers to the coastal region in the northern Gulf of Mexico. δ13C values of both POC (−23.8‰ to −26.8‰) and DOC (−25.0‰ to −29.0‰) carried by the two rivers were more depleted than the values measured for the samples collected in the offshore waters. Strong seasonal variations in δ13C distributions were observed for both POC and DOC in the surface waters of the region. Fresh water discharge and horizontal mixing played important roles in the distribution and transport of terrestrial POC and DOC offshore. Our results indicate that both POC and DOC exhibited non-conservative behavior during the mixing especially in the mid-salinity range. Based on a simple two end-member mixing model, the comparison of the measured DOC-δ13C with the calculated conservative isotopic mixing curve indicated that there was a significant in situ production of marine-derived DOC in the mid- to high-salinity waters consistent with our in situ chlorophyll-a measurements. Our DOC-δ13C data suggest that a removal of terrestrial DOC mainly occurred in the high-salinity (>25) waters during the mixing. Our study indicates that the mid- to high- (10–30) salinity range was the most dynamic zone for organic carbon transport and cycling in the Mississippi River estuary. Variability in isotopic and elemental compositions along with variability in DOC and POC concentrations suggest that autochthonous production, bacterial utilization, and photo-oxidation could all play important roles in regulating and removing terrestrial DOC in the northern Gulf of Mexico and further study of these individual processes is warranted.  相似文献   

15.
Studies of mixing were done at the northern flank of Georges Bank in the summer and autumn of 1988. Two time-series of the evolution and intensity of microstructure were examined over a tidal period in the context of tidal forcing and the evolution of the density and velocity field at the site. From the CTD, ADCP and microstructure observations (EPSONDE) on Georges Bank, several interesting features of the mixing processes were found. High dissipation and diffusivity regions appear near the bottom of the Bank. Turbulence near the bottom is highest in intensity and reaches farthest from the bottom at peak tidal flow and diminishes in intensity and vertical extent as the flow decreases. The thickness of the bottom turbulent layer has its maximum value when the flow is strongest and the stratification is weakest. Characterization of the dissipation rate and turbulent diffusivities in respect to buoyancy frequency N, current shear S, Richardson Number Ri and ε/νN2 was done. Dissipation and χT showed little dependence on shear or N2 but decreased at larger Ri. χt was found to be higher in regions of higher N2 and increased as ε/νN2 increased. KT, K and Kν, were all highest near the bottom in excess of 10−2m2s−1 and decreased towards the surface. There was little suggestion of a dependence of mixing efficiency on S2, Ri or ε/νN2, but some indication that Γ decreases with decreasing N2.  相似文献   

16.
CTD, vessel-mounted ADCP and LADCP measurements in the Caribbean passages south of Guadeloupe (three repeats) and along 16°N (five repeats) were carried out between December 2000 and July 2004. The CTD data were used to calculate the contribution of South Atlantic water (SAW) in the upper 1200 m between the isopycnals σθ=24.5 and 27.6. Northern and southern source water masses are defined and an isopycnal mixing approach is applied. The SAW fractions are then combined with the ADCP flow field to calculate the transport of SAW into the Caribbean and across 16°N. The SAW inflow into the Caribbean through the passages south of Guadeloupe ranges from 7.6 to 11.6 Sv, which is 50–75% of the total inflow. The mean (9.1±2.2 Sv) is in the range of previous estimates. Ambiguities in the northern and southern source water masses of the salinity maximum water permitted us only to calculate the contribution of SAW from the eastern source in this water mass. We estimated the additional SAW transport by the western source to be of the order of 1.9±0.7 Sv. The calculation of the SAW transport across 16°N was hampered by the presence of several anticyclonic rings from the North Brazil Current (NBC) retroflection region, some of the rings were subsurface intensified. Provided that the rings observed at 16°N are typical rings and that all rings which are annually produced in the NBC retroflection area (6.5–8.5 per year) reach 16°N, the SAW ring transport across 16°N is calculated to 5.3±0.7 Sv. From the 5 repeats at 16°N, only two showed a net northward flow, suggesting that the mean northward SAW transport is dominated by ring advection. The joint SAW transports of the Caribbean inflow (9.1 Sv) and the flow across 16°N (5.3 Sv) sum up to 14.4 Sv. The transport increases to 16.3 Sv if the additional SAW transport from the western source of SMW (1.9±0.7 Sv) is included. These transport estimates and the following implications depend strongly on the assumption that the surface water in the Caribbean inflow is of South Atlantic origin. The transport estimates are, however, in the range of the inverse model calculations for the net cross-hemispheric flow. About 30–40% of this transport is intermediate water from the South Atlantic, presumably supporting studies which found the contributions of intermediate and upper warm water to be of a comparable magnitude. For the upper warm water (σθ<27.1), the Caribbean inflow seems to be the major path (7.9±1.6 Sv), the ring induced transport across 16°N is about 30% of that value. The intermediate water transport across 16°N was calculated to be 2.3–3.6 Sv, the inflow into the Caribbean is slightly smaller (1.5–2.4 Sv).  相似文献   

17.
The determination of heme b in marine phyto- and bacterioplankton   总被引：1，自引：0，他引：1  
Martha Gledhill   《Marine Chemistry》2007,103(3-4):393-403
A method for the quantification of heme b in marine phyto- and bacterioplankton is described. Heme b was extracted from filtered cells using a solution of 2.5% octyl β-glucopyranoside in 0.02 M ammonium hydroxide. The extract was analysed by high performance liquid chromatography diode array spectrophotometry. Maximum absorbance for heme b was at 400 nm. Heme b was separated from other pigments using a polystyrene divinyl benzene stationary phase and a gradient elution programme with 0.1% (v:v) nonafluoropentanoic acid in water and 50:50 (v:v) isopropanol:acetonitrile as the mobile phases. Heme b was quantified using Fe (III) protoporphyrin IX chloride (hemin) standards. The detection limit, calculated from 3 × s.d. of the lowest standard was 0.08 pmol or 1.57 nM with a 50 μL injection volume. The first data for heme b in marine phyto- and bacterioplankton are reported. Heme b contents are reported for the eukaryotes Thalassiosira weissflogii, Thalassiosira oceanica, Dunaliella tertiolecta and Emiliania huxleyi, and the prokaryotes Synechococcus WH8102, WH7803, RCC307, Erythrobacter litoralis, Roseobacter denitrificans and Vibrio natriegens. For T. weissflogii, T. oceanica, D. tertiolecta and E. huxleyi cellular heme b concentrations varied between 12 and 60 μmol L− 1 and chlorophyll a to heme b ratios varied between 216 and 309.  相似文献   

18.
The eddy viscosities for the steady and the periodic components of combined wave-current flows have been studied quantitatively from the presently available experimental data. It has been found that inside the boundary interaction layer [z < δ] the eddy viscosity εc for the steady flow is increased in the presence of waves while outside the boundary interaction layer [z >δ] it is affected little by the wave motion, and that the eddy viscosity εw for the wave motion in the boundary layer is independent of the current strength U*. On the other hand, a new eddy viscosity model is presented to give a good prediction of the velocity distributions of the waves and currents in comparison with experimental data.  相似文献   

19.
The C/N and stable C and N isotope ratios (δ13C, δ15N) of sedimentary and suspended particulate matter were determined in the Schelde Estuary. Suspended matter was divided into 2 to 5 size fractions by centrifugation. Four major pools of organic matter were recognized: riverine, estuarine, marine and terrestrial materials. Terrestrial organic matter (δ13C≈−26‰, δ15N≈3.5‰, C/N≈21) is important for the sedimentary pool, but suspended matter is dominated by the marine (δ13C≈−18‰, δ15N≈9‰, C/N≈8), riverine (δ13C≈−30‰, δ15N≈9‰, C/N≈7.5) and estuarine (δ13C≈−29‰, δ15N≈15‰, C/N≈8) end-members. In the upper estuary, the suspended matter size fractions vary systematically in their carbon and nitrogen biogeochemistry, with the small particles having low C/N ratios, depleted δ13C and enriched δ15N values relative to large particles. Moreover, sedimentary and suspended matter differ significantly in terms of C/N ratios (17 vs. 8.9), δ13C (−26.3 vs. −28.9‰) and δ15N (+6.9 vs. 12.0‰). In the lower estuary, suspended matter fractions are similar and sedimentary and suspended organic matter differ only in terms of δ13C (−23.5 vs. −20.1‰). Our data indicate that autochthonous organic matter contributes significantly to the total suspended matter and that the suspended organic matter composition cannot be explained in terms of conservative mixing of riverine and terrestrial sources on the one hand and marine sources on the other hand.  相似文献   

20.
We analysed the alkenone unsaturation ratio (UK′37) in 87 surface sediment samples from the western South Atlantic (5°N–50°S) in order to evaluate its applicability as a paleotemperature tool for this part of the ocean. The measured UK′37 ratios were converted into temperature using the global core-top calibration of Müller et al. (1998) and compared with annual mean atlas sea-surface temperatures (SSTs) of overlying surface waters. The results reveal a close correspondence (<1.5°C) between atlas and alkenone temperatures for the Western Tropical Atlantic and the Brazil Current region north of 32°S, but deviating low alkenone temperatures by −2° to −6°C are found in the regions of the Brazil–Malvinas Confluence (35–39°S) and the Malvinas Current (41–48°S). From the oceanographic evidence these low UK′37 values cannot be explained by preferential alkenone production below the mixed layer or during the cold season. Higher nutrient availability and algal growth rates are also unlikely causes. Instead, our results imply that lateral displacement of suspended particles and sediments, caused by strong surface and bottom currents, benthic storms, and downslope processes is responsible for the deviating UK′37 temperatures. In this way, particles and sediments carrying a cold water UK′37 signal of coastal or southern origin are transported northward and offshore into areas with warmer surface waters. In the northern Argentine Basin the depth between displaced and unaffected sediments appears to coincide with the boundary between the northward flowing Lower Circumpolar Deep Water (LCDW) and the southward flowing North Atlantic Deep Water (NADW) at about 4000 m.  相似文献   

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