摘要:

This issue of theJournal of Geophysical Researchcontains seven papers that describe results from a cruise of R/VWecoma, which worked in the equatorial Pacific in February and March 1988. The name of the cruise was WEC88. The research plan for this cruise was based on the evolving understanding of the regulation of biological productivity in equatorial waters. When the eastern and central equatorial Pacific was originally found to be richer than waters to the north and south, the first question oceanographers asked was, “Why is the tropical region so rich?” Early work established that a zonal band straddling the equator and extending across the entire Pacific basin has enhanced nutrient concentrations, increased phytoplankton productivity, and increased abundance of Zooplankton and fish [Sette, 19

ISSN:0148-0227    

DOI:10.1029/91JC02425

年代:1992

数据来源: WILEY

摘要:

The WEC88 cruise sampled along a meridional transect from 15°N to 15°S along 150°W from February 17 to March 18, 1988, with a 6‐day time series at the equator. The large‐scale hydrographic patterns were typical for boreal spring. Equatorial maxima in dissipation of turbulent kinetic energy ∈, and of thermal variance χ, were found between 2°N and 2°S for the top 60 m. The equatorial time series coincided with a shift from southward to northward velocity, which returned the zonal current system to the equator. This led to a decrease in temperature, and increases in salinity, nutrient, and chlorophyll concentrations in the surface layer. Vertical diffusivity as well as ∈ and χ increased with the observed intensification of the Equatorial Undercurrent. Maximum values of ∈ and χ were observed at around 55 m, and the temporal trends occurred first at depth. Turbulent heat flux out of the mixed layer was the same order of magnitude as the penetrative irradiance at that depth. Maximum vertical heat flux occurred at depth in response to large diffusivity coefficients. The Richardson number was useful in predicting the regions of enhanced mixing in the meridional transect. However, for the equatorial time series, where theRiwas less than 0.45, intensity of dissipation was not proportional to

ISSN:0148-0227    

DOI:10.1029/91JC02479

年代:1992

数据来源: WILEY

摘要:

Biological, optical, and hydrographical data were collected on the WEC88 cruise along 150°W and during a 6‐day time series station on the equator during February/March 1988. This area was characterized by a subsurface chlorophyll maximum (SCM), located at 50–70 m depth at the equator and descending down to 120–125 m at the north and south end of the transect. Highest primary production rates were near‐surface and confined to the equatorial region and stations between 7° and 11°N. To determine the relationship between solar‐stimulated fluorescence (centered at 683 nm wavelength) and primary production, a production‐fluorescence model based on phytoplankton physiology and marine optics is described. Results of model calculations predict that there is a linear relation between production and fluorescence. A comparison between morning and midday measurements of the production‐fluorescence relation showed that there was some difference between the two, whereas evening measurements, on the other hand, were distinctly different from the morning/midday ones. This seems to suggest that diurnal variations contribute significantly to variability in the quantum yield of photochemical processes. The ratio of the quantum yield of photosynthesis to the quantum yield of fluorescence (Φc/Φƒ), the parameter which will determine how well production can be estimated from optical recordings, ranged between 0.24 and 0.44 molC Ein−1(an Einstein equals a mole of photons) for all stations. The highest value for this ratio occurred at the equatorial stations, indicating that interstation (i.e., latitudinal) variability could have an effect on the production‐fluorescence relation. Measured (with14C incubations) and predicted production compared quite well, although high measured production rates for near‐surface samples were underestimated in most cases. Since both production and fluorescence were nonlinear at high irradiance intensities, we recommend in the future that a nonlinear component be incorporated into our model to take this effect into account and thus allow us to refine our es

ISSN:0148-0227    

DOI:10.1029/91JC02014

年代:1992

数据来源: WILEY

摘要:

Macronutrients persist in the surface layer of the equatorial Pacific Ocean because the production of phytoplankton is limited; the nature of this limitation has yet to be resolved. Measurements of photosynthesis as a function of irradiance (P‐I) provide information on the control of primary productivity, a question of great biogeochemical importance. Accordingly, P‐I was measured in the equatorial Pacific along 150°W, during February‐March 1988. Diel variability of P‐I showed a pattern consistent with nocturnal vertical mixing in the upper 20 m followed by diurnal stratification, causing photoinhibition near the surface at midday. Otherwise, the distribution of photosynthetic parameters with depth and the stability of P‐I during simulated in situ incubations over 2 days demonstrated that photoadaptation was nearly complete at the time of sampling: photoadaptation had not been effectively countered by upwelling or vertical mixing. Measurements of P‐I and chlorophyll during manipulations of trace elements showed that simple precautions to minimize contamination were sufficient to obtain valid rate measurements and that the specific growth rates of phytoplankton were fairly high in situ, a minimum of 0.6 d−1. Diel variability of beam attenuation also indicated high specific growth rates of phytoplankton and a strong coupling of production with grazing. It appears that grazing is the proximate control on the standing crop of phytoplankton. Nonetheless, the supply of a trace nutrient such as iron might ultimately regulate productivity by influencing species composition and food

ISSN:0148-0227    

DOI:10.1029/91JC01320

年代:1992

数据来源: WILEY

摘要:

In March 1988 a north‐south transect at longitude 150°W was carried out in the equatorial Pacific between latitude 15°N and 15°S. Observations of suspended particulate matter in the euphotic zone included particulate carbon, nitrogen, and chlorophyll, with a few samples taken for counting picoplankton and nanoplankton. Nearly all the particulate nitrogen is accounted for by bacteria and phytoplankton. The standing stock of bacterial C and N exceeded that of phytoplankton. The residence time of particulate organic carbon in the surface water was only 4–5 days in the equatorial upwelling, but 10–15 days to the north and south, suggesting relatively rapid removal by recycling and lateral a

ISSN:0148-0227    

DOI:10.1029/91JC01386

年代:1992

数据来源: WILEY

摘要:

Rates of nitrate utilization were measured in March 1988, from 6°N to 8°S on longitude 150°W in the Pacific Ocean. Surface waters in the equatorial upwelling contained about 5‐μMnitrate. Samples of seawater incubated on deck, as in primary production experiments, lost about 150‐nMnitrate during the day and an equal amount at night at the equator. These rates exceeded by several fold the rates of nitrate incorporation into particulate matter. The carbon equivalent of the 24‐hour nitrate consumption also exceeded the rate of14C primary production. The large nitrate consumption is not readily explained in terms of phytoplankton physiology but may serve to fuel speculation on the possible production of dissolved organic nitrogen and on the role of bacteria in processing nitrate in the equatorial Pacific upwelli

ISSN:0148-0227    

DOI:10.1029/91JC01271

年代:1992

数据来源: WILEY

摘要:

During the R/VWecomaWEC88 cruise that sampled a meridional transect along 150°W from 15°N to 15°S, uptake of nitrate and ammonium by phytoplankton was measured using the stable isotope15N with simulated in situ bottle incubations and shipboard mass spectrometry. A set of 25 daily productivity stations showed the influence of equatorial upwelling on nitrate distribution and15N uptake in a band from 6°N to 7.5°S compared with the oligotrophic waters to the north and south, with the highest values of nitrate uptake occurring at the equator (0.14 mg‐at. m−2h−1). During a 5‐day time series at the equator, there was an increase in nitrate accompanied by increased nitrate uptake. Interestingly, nitrate uptake rates (equivalent to new production rates) at the equator were lower than those predicted by previous investigators. Holdover experiments and uptake versus irradiance curves showed that the phytoplankton there were in an early stage of metabolic adaptation and that may have been a contrib

ISSN:0148-0227    

DOI:10.1029/91JC01534

年代:1992

数据来源: WILEY

摘要:

A major goal of the WEC88 cruise of the R/VWecomato the equatorial Pacific (made in February‐March 1988), was to establish rates of new production along a meridional section at 150°W and to compare these measured rates with the relatively high values for the equatorial Pacific that had been reported previously using indirect methods and models. New production values were obtained from the traditional approach (in the sense of Dugdale and Goering (1967)) using15N labelled nitrate uptake, and by using14C fixation values multiplied by ƒ (proportion of new production) from various sources: from15N data, from a14C fixation versus ƒ relationship (Eppley and Peterson, 1979) or from a nitrate versus ƒ relationship (Platt and Harrison, 1985). The ratios of directly measured nitrate and carbon uptake and the ratios of nitrate to nitrate plus ammonium uptake, i.e., values of ƒ, agree well; values of ƒ calculated from carbon uptake or from nitrate concentration are overestimates for the equatorial upwelling region. Carbon to nitrogen uptake ratios measured with14C and15N, respectively, approximate the Redfield molar ratio, 6.6 C:N. The overall mean value of ƒ (0.17) helps confirm the view that the low primary production in the enriched eastern equatorial Pacific is due to failure of the nitrate uptak

ISSN:0148-0227    

DOI:10.1029/91JC01533

年代:1992

数据来源: WILEY

摘要:

As part of the World Ocean Circulation Experiment community modelling effort, a realistic primitive equation model of the North Atlantic Ocean has been implemented with a resolution high enough to allow the generation of eddies. In the present paper, the kinetic energy of the model ocean circulation is analyzed. The eddy kinetic energy distribution in the model shows a good agreement with data in the western Atlantic but a deficit in the eastern Atlantic, especially at periods of about 100 days. Kinetic energy balances are computed to allow comparison between the primitive equation model and previous quasi‐geostrophic eddy resolving models. Essential instability mechanisms are present in both cases, but they are not efficient enough in the primitive equation model, which is too viscous and lacks the inertial character of quasi‐geostrophic solutions. Our study therefore emphasizes the need for even higher resolution mod

ISSN:0148-0227    

DOI:10.1029/91JC02350

年代:1992

数据来源: WILEY

摘要:

The Guinea Dome is a permanent, quasi‐stationary feature on the eastern side of the thermal ridge extending zonally across the tropical North Atlantic. The dome is a part of the large‐scale near‐surface flow fields associated with the North Equatorial Current, the North Equatorial Countercurrent and the North Equatorial Undercurrent. In the present study, historical and recently obtained hydrographic data are combined to investigate the thermohaline structure and geostrophic flow field in the vicinity of the dome. It is shown that the Guinea Dome exists throughout the year both in subthermocline and thermocline layers, that it has a corresponding cyclonic geostrophic flow, and that seasonal changes occur with respect to its vertical structure, horizontal extent, and position. The observational results are then compared with simulations from a general circulation model of the tropical Atlantic. A seven‐year simulation forced by observed monthly winds is run to compute a monthly climatology. The model adequately simulates the Guinea Dome with respect to its structure, flow field, and seasonal vari

ISSN:0148-0227    

DOI:10.1029/91JC02501

年代:1992

数据来源: WILEY