摘要:

The Indonesian throughflow is analyzed in an extended simulation with a coupled ocean‐atmosphere model. The model, developed by the Max‐Planck‐Institut für Meteorologie, Hamburg, Germany, combines an atmospheric general circulation model at T42 resolution (2.8° latitude by 2.8° longitude) and a primitive equation ocean model with zonal resolution of 2.8° and a meridional resolution of 0.5° in the tropics and is coupled without flux correction equatorward of a latitude of 60°. The onset and strength of the monsoon in the Indonesian waters agree well with climatology, and many aspects of the observed temperature fields in the eastern Indian Ocean and Timor Seas are found in simulation. Differences between simulation and observations of temperature occur in mean and seasonal cycles in the far western Pacific. The annual cycles of sea level along the coast of Sumatra and Java are simulated satisfactorily. The simulated throughflow transports on average 13.8 Sv (106m3S−1) from the Pacific to the Indian Ocean. The vertically averaged (barotropic) component of the throughflow has a seasonal range of 13.1 Sv and is weakest in February and strongest in July. In contrast, deviations from the vertical average of the throughflow (baroclinic) are strongest in March and September. The average and seasonal cycle of the barotropic component of the throughflow are forced by winds over the Pacific and along the western coasts of Australia and South America, as described by the island rule. For closed Torres Strait, the contribution of the average bottom pressure torque is small, and friction closes the vorticity balance. For annual timescales, baroclinic flows affect the throughflow transport through the bottom pressure torque. The annual cycle of the baroclinic component of the throughflow is forced predominantly by winds over the Indonesian Seas. The throughflow exports 0.9 PW of heat from the Pacific into the Indian Ocean and is an important heat sink for the western Pacific. The throughflow is a major heat source for the Indian Ocean and is associated with reversal of the divergence of the meridional transport of heat south of 10°S that is balanced by heat fluxes from the ocean to

ISSN:0148-0227    

DOI:10.1029/97JC00022

年代:1997

数据来源: WILEY

摘要:

Radiocarbon variability inPoritesspp. corals from Guam and the Makassar Strait (Indonesian Seaway) was used to identify the source waters contributing to the Indonesian throughflow. Time series with bimonthly resolution were constructed using accelerator mass spectrometry. The seasonal variability ranges from 15 to 60‰, with large interannual variability. Δ14C values from Indonesia and Guam have a nearly identical range. Annual mean Δ14C values from Indonesia are 50 to 60‰ higher than in corals from Canton in the South Equatorial Current [Druffel,1987 ]. These observations support a year‐round North Pacific source for the Indonesian throughflow and imply negligible contribution by South Equatorial Current water. The large seasonality in Δ14C values from both sites emphasizes the dynamic behavior of radiocarbon in the surface ocean and suggests that Δ14C time series of similar resolution can help constrain seasonal and interannual changes in ocean circulation in the Pacific over the last severa

ISSN:0148-0227    

DOI:10.1029/97JC00590

年代:1997

数据来源: WILEY

摘要:

We have compared vertical transport of temperature, anthropogenic CO2, natural radiocarbon (14C), and bomb14C in a global box‐diffusion model (B‐D) and a three‐dimensional (3‐D) ocean general circulation model from the Geophysical Fluid Dynamics Laboratory. Our main objectives were (1) to test the eddy diffusion parameterization of large‐scale vertical transport in ocean box models and (2) to assess the utility of bomb‐produced and natural14C observations to validate ocean models used to estimate anthropogenic CO2uptake. Prom the 3‐D model's distributions and fluxes of natural14C, bomb14C, and anthropogenic CO2, we have calculated apparent diffusivities (Kap) vertically over the global ocean that range mostly between 4000 and 8000m2yr−1. TheseKapagree quantitatively with diffusivities found by fitting B‐D models to observed distributions of natural and bomb14C We then used these sets ofKapin different runs of a global B‐D model. Results from all B‐D models runs matched to within 13% those from the 3‐D model for global uptake of anthropogenic CO2and bomb‐14C penetration depth. AlthoughKapfrom 3‐D simulations for bomb14C vary with time, those from 3‐D runs for anthropogenic CO2are essentially constant. Still, we found nearly the same results with the B‐D model whenKapfrom 3‐D bomb14C simulations are approximated as time invariant. The best agreement (within 3%) between 3‐D CO2simulations and B‐D model runs was found when applyingKapderived from bomb14C in the surface and from natural14C in the deep. Agreement was worse when usingKapfrom 3‐D simulations for anthropogenic CO2itself, mostly because in this case deeperKapcould only be extrapolated from higher surface values. We have found it appropriate to study global oceanic uptake of anthropogenic CO2with B‐D model and to validate anthropogenic carbon uptake models using natural and bomb14C observations. For bomb14C in the 3‐D model, convective transport was most important during 1955–1964 while atmospheric levels were rising; afterward, atmospheric levels drop, and advective overturning dominates as for natural14C. Thus14C seems less than ideal to validate the co

ISSN:0148-0227    

DOI:10.1029/97JC00470

年代:1997

数据来源: WILEY

摘要:

The coastal zone color scanner (CZCS) that operated aboard the Nimbus 7 satellite provided extensive coverage of phytoplankton pigment concentrations in the surface waters of the eastern tropical Atlantic (ETA) from March 1979 to February 1980 and coincided with four major research cruises to this region. Total primary production within the ETA (5°N–10°S, 25°W–10°E) was determined from CZCS pigment estimates and an empirical algorithm derived from concurrent in situ data taken along 4°W that relates near‐surface chlorophyll concentration and integrated primary production. We estimated an average annual production for the ETA of 2.3 Gt C yr−1with an associated 3.5‐fold seasonal variation in the magnitude of this production. We describe the principal physical mechanisms controlling seasonal phytoplankton dynamics within the ETA and propose that in addition to seasonal change in the thermocline depth, one must also consider changes in the depth of the equatorial undercurrent. An extensive validation effort indicates that the standard CZCS global products are a conservative estimate of pigment concentrations in ETA surface waters. Significant underestimates by the CZCS global products were observed in June and July which we attributed, in part, to aerosol correction errors and, more importantly, to errors caused by a significant reduction in the concentration of near‐surface dissolved organic matter that resulted from strong equa

ISSN:0148-0227    

DOI:10.1029/96JC03982

年代:1997

数据来源: WILEY

摘要:

Chlorophyll‐specific absorption coefficients of particles,a*p(λ), and of phytoplankton,a*ph(λ), were determined using the glass‐fiber filter technique along 150°W in the equatorial Pacific (13°S–1°N). A site‐specific algorithm for correcting the path length amplification effect was derived from field measurements. Then a decomposition technique using the high‐performance liquid chromatography pigment information and taking into account the package effect was used to partitiona*phinto the contributions of photosynthetic pigments (a*ps) and nonphotosynthetic pigments (a*nps). Botha*phanda*npsvalues were observed to decrease from the oligotrophic waters of the subequatorial area (13°–1°S) to the mesotrophic waters of the equatorial area (1°S‐1°N) and from the surface to deep waters. Thea*phvariations were primarily, but not exclusively, caused by changes in the concentrations of nonphotosynthetic pigments. The level of pigment packaging was also variable both horizontally and vertically, as a result of changes in populations and photoacclimation. In comparison witha*ph,a*psexhibited a reduced range of variation with depth and along the latitudinal gradient. The variations ina*psoriginating from the package effect were partly compensated by variations in the concentrations of photosynthetic pigments. We extended this analysis to include data collected in other areas with different trophic states. Thea*psvalues varied over a factor of 4 at 440 nm, instead of 8 fora*ph, for chlorophyllaconcentrations covering 2 orders of magnitude (0.02–2 mg m−3). In agreement with a previous study performed off California with a different method [Sosik and Mitchell,1995], we conclude thata*psis less dependent on environmental parameters thana*ph. In addition, our results provide evidence that the variability ina*pscannot be neglected. The use ofa*psinstead ofa*phin light‐photosynthesis models (in conjunction with a quantum yield for carbon fixation defined with respect to the photosynthetically active absorbed amount of quanta) presents the advantage of removing the variability associated wit

ISSN:0148-0227    

DOI:10.1029/97JC00380

年代:1997

数据来源: WILEY

摘要:

A multiparameter analysis is applied on zonal and meridional hydrographic sections obtained for the South Atlantic Ventilation Experiment (SAVE) to determine the spreading and mixing of water masses in the South Atlantic Ocean, focusing our interest on the large‐scale flow of intermediate and deep waters. The method utilizes all information from the hydrographic data set including temperature, salinity, dissolved oxygen, and nutrient fields. Mixing proportions are quantified and plotted along the eight sections considered. Results show no evidence of a primary route of Antarctic Intermediate Water along the western boundary of the South Atlantic. In the eastern basin the eastward extension of the Upper North Atlantic Deep Water (NADW) in the Guinea Basin following the cyclonic subequatorial gyre is confirmed. In the Angola Basin a weak but thick NADW core layer is observed in conjunction with very little presence of Lower Circumpolar Deep Water (LCDW). High LCDW concentrations in Cape Basin are indicative of the communication of this basin to cold water sources in the south. The method is sensitive enough to detect for instance the presence of the Congo River Plume in the Angola Basin or the influence of the Weddell Sea Deep Water in the vicinity of the Romanche and Chain Fracture Zones in the equatorial region. In conjunction with the multiparameter analyses along SAVE sections, an analysis of components of the residual vectorRindicates a middepth minimum in theRN/Putilization ratio. Both a suitable explanation for the minimum and the potential consequences for the multiparameter analyses of South Atlantic water mass circulation are still to be foun

ISSN:0148-0227    

DOI:10.1029/97JC00629

年代:1997

数据来源: WILEY

摘要:

Satellite‐tracked drifters were used to examine eddy activity in the vicinity of the Emperor Seamount Chain (ESC) in the North Pacific during 1991–1993. The trajectories of two drifters drogued at a depth of 120 m revealed a pair of counterrotating mesoscale eddies attached to the leeside of Ojin/Jingu Seamount in the summer of 1992. The eddies had diameters of 75–100 km and rotational speeds of 20–40 cm/s at 120 m. Sea surface height anomalies derived from blended TOPEX/ERS‐1 satellite altimetry revealed that the eddies had a surface manifestation as well. One of the drifters made five loops within the cyclonic eddy over a period of 62 days, during which time the eddy translated westward, toward the seamount, at 2.9 cm/s. This is one of the first observations demonstrating an extended attachment of a topographically generated eddy to a seamount. Drifters drogued at a depth of 15 m which crossed the ESC in the summer of 1991 and winter of 1993 revealed no eddy activity, most likely because of a decoupling of the topographic influence to the 15 m flow at their crossing latitude over the Nintoku Seamount (summit depth at 1000 m). The implication is that eddy formation within the mixed layer near the ESC is confined to the region around the taller Ojin/Jingu and Kinmei Seamounts (summit depths at 800 m and 100 m, respectively). It is suggested that long‐lived eddies attached to the leeside of the ESC can profoundly influence local biological production and water exchange between the western and eastern basins of the No

ISSN:0148-0227    

DOI:10.1029/97JC00585

年代:1997

数据来源: WILEY

摘要:

Time‐dependent wind‐driven circulation in the subarctic region in the North Pacific is investigated by using TOPEX/POSEIDON (T/P) altimeter data and European Centre for Medium‐Range Weather Forecasts (ECMWF) wind data for about 2 years. The first empirical orthogonal function (EOF) of the sea level anomaly (SLA) without the variation related to the steric height change (SLA*) represents a basin‐sized oscillation, which is associated with the spin‐up and spin‐down of the subarctic gyre. Moreover, the time series of the first EOF corresponds to the Oyashio current variation measured by the moored current meter at about 1250‐m depth. The first and third EOFs of the wind stress curl fields represent basin‐sized south‐north oscillations being associated with changes in intensity and the latitudinal position of the Aleutian low. Time series of both the dominant EOFs of the SLA* and the wind stress curl anomaly are correlated well, which suggests that dominant variation of the SLA* is mainly controlled by the wind stress curl fields represented by the first and third EOFs. The time series of the first EOF of the SLA* is in agreement with that of Sverdrup transport estimated by the wind stress curl near 40°N with a correlation of 0.70. Both standard deviations of the T/P SLA‐derived transports in the interior and the western boundary regions are consistent with that of the Sverdrup transport in the same order of magnitude. These results suggest that sea surface height variation in the subarctic North Pacific is approximately explained by the time‐dependent w

ISSN:0148-0227    

DOI:10.1029/97JC00447

年代:1997

数据来源: WILEY

摘要:

Generation of large‐scale internal waves by a hurricane traveling over the ocean with a uniform velocity is investigated by using a three‐dimensional, multilevel numerical model. It is found that two distinctive kinds of internal waves are excited in the wake of the hurricane, namely, near‐inertial waves, which can be explained based on the linear theory, and superinertial waves with frequencies 2ƒ0and 3ƒ0(ƒ0is the inertial frequency at the latitude of the hurricane track), which are generated through nonlinear effects. Our special attention is directed to the superinertial waves with frequencies 2ƒ0and 3ƒ0because these internal waves are considered to be efficient energy sources for small‐scale mixing in the deep ocean. These superinertial waves predominantly have low‐vertical‐mode structures and satisfy the dispersion relation for lee waves. In areas away from the hurricane track, in particular, the double‐inertial frequency waves become larger than the near‐inertial waves. The nonlinear resonant triads causing the generation of such superinertial waves are examined by calculating the bispectrum, which clearly shows that the lowest‐vertical‐mode double‐inertial frequency wave is generated efficiently through the nonlinear interaction between the high‐verti

ISSN:0148-0227    

DOI:10.1029/97JC00588

年代:1997

数据来源: WILEY

摘要:

A weak constraint variational formulation is used for inverse calculations and parameter estimation in a one‐dimensional Ekman model. When parameters in the model are allowed to contain errors, the inverse problem becomes nonlinear even if the model itself is linear. It is shown that a convergent iteration can be defined for the nonlinear system of Euler‐Lagrange equations and that improved estimates of the poorly known parameters can be calculated by solving the inverse problem for each of the linear iterates using the representer method. The formulation of the variational problem and the solution methods are illustrated using a simple example. The use of a simple dynamical model makes it possible to give an instructive presentation of the representer method. The method is finally used in an example using real current meter data. It is shown that the weak constraint formulation results in smooth solutions in good agreement with the data all through the water column and that it is superior to the traditional strong constraint inverse estim

ISSN:0148-0227    

DOI:10.1029/96JC03454

年代:1997

数据来源: WILEY