摘要:

An ocean model has been developed which, for prescribed physics, deals with interrelationships between chemical distributions, biogeochemical sinks and sources, chemical reactions at redox fronts, and transports across the air‐sea and sediment‐water interfaces. In its first application here, the model focuses on biogeochemical cycling of phosphorus, nitrogen, oxygen, and sulphur in an ocean forced by river input of nutrients. This is a natural starting point for a global climate model since ocean circulation and biology determine atmospheric CO2concentrations for a given inventory of inorganic C and oceanic production is controlled mainly by the availability of inorganic P and/or N. A general approach is taken to look at oxic versus anoxic conditions, P versus N limitation of primary production, with or without inorganic removal of phosphate to the sediments. As demanded by this approach, the model is nonlinear and continuous in a vertical coordinate. To focus on the biogeochemical aspects, ocean physics are kept as simple as possible. Cold, oxygen‐rich water sinks at high latitudes and is upwelled with a constant velocity. Turbulent mixing is parameterized with a constant, vertical diffusion coefficient. The biogeochemical processes considered are new production, burial, nitrogen fixation, phosphorite formation, and three types of organic decomposition: oxidation with O2, denitrification, and sulphate reduction. Organic matter is taken to consist of a high‐ and a low‐reactive fraction. The chemical species considered explicitly are PO43−‐P, NO3−‐N, O2, NH4+‐N and H2S‐S. Results indicate that a change from oxic to weakly anoxic conditions at middepths in a P‐limited ocean would lead to strong local denitrification and low nitrate concentrations throughout the water column. New production would also become dominated by nitrogen fixers. Geological evidence implies that anoxic conditions in the water column have been rare in the Phanerozoic ocean. Both phosphorite formation (for P limitation) and denitrification (for N limitation) can strongly constrain primary production and the development of anoxia. N limitation, i.e., negligable nitrogen fixation, practically precludes anoxia but is unlikely for very long times scales. For P limitation and no phosphorite formation the model indicates that the redox state of the ocean may be most sensitive to changes in ocean biology followed by changes in ocean circulation and mixing and finally by chang

ISSN:0148-0227    

DOI:10.1029/JC094iC02p01979

年代:1989

数据来源: WILEY

摘要:

Twelve days of microstructure measurements at the equator (140°W) in November 1984 showed a surprisingly strong effect of both the daily cycle of solar heating and wind on mixing in the upper ocean. Because of limited variations in atmospheric forcing and currents during the experiment, processes in the daily mixing cycle were similar from day to day. Only the intensity of mixing varied. The lower boundary of the diurnal surface layer separated two distinct mixing regimes, the diurnal surface layer and the thermocline. Within the diurnal surface layer (which extended to 10‐ to 35‐m depth), turbulent kinetic energy dissipation rates ε varied relatively little. Although variations in surface layer depth coincided with the daily change in direction of air‐sea surface buoyancy production of turbulent kinetic energy (or simply, the surface buoyancy flux), ε was significantly greater relative to the buoyancy flux than was expected for a simple convective layer. In the thermocline below the diurnal surface layer, ε was highly intermittent; the day‐night cycle was stronger, and variability was enhanced by turbulent “bursts” of 2–3 hours duration, which may be related to internal wave breaking events. The turbulent heat flux crossing 20‐m depth was almost equal to the surface heat flux less the irradiance penetrating below 20 m. Seventy percent of the surface heat flux was transported vertically to the water below 30 m by turbulent mixing. Only a negligible amount penetrated to the core of the Equatorial Undercurrent. The gradient Richardson numberRidistinguishes between statistically different mixing environments. However, ε cannot be predicted from the value ofRi, since the intensity of mixing depends on the intensity of forcing in a way not specified by

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02005

年代:1989

数据来源: WILEY

摘要:

Recent current measurements have shown that the subthermocline equatorial circulation in the central Pacific is considerably more complicated than had been thought. Below 1500 m depth on 159°W there are three currents south of the equator that appear to be permanent. Eastward currents are found at 1700 m and 3100 m, and a westward current is found at 4000 m. The 1700‐m current is at the southern edge of the 3°S to 3°N range of current measurements, so its meridional extent and its transport are unknown. The 3100‐m and 4000‐m currents have 16‐month mean transports of about 6 − 7 × 106m3s−1. All three of these currents may be important components of the gene

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02023

年代:1989

数据来源: WILEY

摘要:

Two subsurface current meter moorings were deployed for 20 months along 70°W in a low‐energy portion of the western North Atlantic. The resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies. Currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations, usually more than 500 km away from the mooring and generally to the east. Coherences generally decrease with increasing frequency. The current response is surface intensified. A linear stratified model for stochastically wind‐forced Rossby waves in a flat‐bottomed ocean is presented as an attempt to rationalize the results. The effort was not entirely successful, so that it appears that a more realistic model, perhaps including bottom topography and mean currents, will be needed to rationalize these observations

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02029

年代:1989

数据来源: WILEY

摘要:

Wind generation of mixed layer near‐inertial frequency oscillations has been observed and successfully modeled many times. Modeling of the decay of these currents by linear wave theory has been more difficult because the necessary horizontal scales are much smaller than the typical horizontal scales of the wind. A new, and highly effective, mechanism for generating such scales by the β effect is proposed here. An asymptotic analysis of the linear equations is presented which suppresses high‐frequency gravity waves and thus simplifies the near‐inertial frequency dynamics. The computed residence time for inertial motions in the mixed layer depends both on the scales of the wind and on β, with β imposing an upper limit of 1–2 weeks. The relative importance of the wind and β is estimated using realistic wind stress fields, generated by advecting Seasat scatterometer data over the simulated ocean. The predicted horizontal scales and decay times of mixed layer inertial motions are similar to those observed. The subsynoptic scales of the wind, the advection speed, and β are all important in determining the decay time of the simulated mixed layer inert

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02045

年代:1989

数据来源: WILEY

摘要:

A cruise was conducted on the NOAA shipOceanographerin August and September 1986 in the Chukchi Sea. Four short‐term moorings were instrumented with sediment traps and Aanderaa RCM4 current meters. The currents at the three moorings near the Alaskan coast indicate a reversal of the normal northeastward flow to southwestward. This reversal was produced by wind, which had begun to blow from the east‐northeast at up to 4.2 m s−1. The temperature time series indicated that upwelling colder water was moving upward near the coast. The nearshore mooring had the largest amplitude variation of currents and the largest temperature variation. The amplitude of the reversal decreased offshore. The station farthest from the coast was near the ice edge and on the other side of Barrow Canyon and a subsea bank. The flow there was consistently toward the east and is only poorly related to the wind. Water mass analysis was conducted using two techniques; the first was a traditional TS diagram method, and the second was a cluster analysis on TS pairs for the surface and near‐bottom waters. Based on the shapes of the TS curves and their positions on the TS diagrams, a map of the water masses was constructed. A cluster analysis was performed on the surface TS pairs from each station and separately for the bottom TS pairs. For both of these techniques, the line separating the groupings follows the temperature contours (5° at the surface and 4° at the bottom) and the bottom salinity contours (

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02057

年代:1989

数据来源: WILEY

摘要:

A coupled ice‐ocean model has been developed for use in the short‐term (order of days) prediction of the ice and water movement on the shallow Arctic continental shelf. Our interest in partially ice‐covered conditions allows the neglect of ice‐ice interactions. Thermodynamic effects are also assumed negligible over the short time scale of interest. The intended application to shallow‐water regions permits the use of the vertically integrated water momentum equations but necessitates the inclusion of finite depth effects. Model comparison with actual measurements of ice floe movement in the Beaufort Sea are extremely encouraging, especially when compared with predictions afforded by uncoupled or ice‐only formulations. The use of the depth‐averaged circulation model has been found to weaken the algorithm's ability to simulate ice floe movement in a wind field rapidly varying in time. Recommendations for future improvements include refinement of wind forecasting methods for inclusion in a coupled air‐

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02065

年代:1989

数据来源: WILEY

摘要:

Four 19‐month time series of indirect measurements of dynamic height were obtained in the tropical Atlantic along 28°W at 0°, 3°, 6°, and 9°N with three inverted echo sounders and one current meter mooring. The series were analyzed to study the time‐latitude variability of the North Equatorial Countercurrent (NECC). The eastward flow associated with the NECC was present at 28°W from 3° to 9°N during most of the observed period except in March‐April 1983 and April‐May 1984, periods that coincided with the onset of the wind at the equator. The amplitude of the NECC's annual cycle was maximum at 6°N and was larger in 1983 than in 1984. The analysis of the time‐latitude variability of differences in dynamic height shows a long‐period meridional shift of the NECC. The core of the current attains its northernmost location during August‐September in both years and its southernmost location during March‐April in 1983 and March in 1984. The location of the core is directly related to the position of the intertropical convergence zone. From the time series of dynamic height obtained from the indirect measurements, geostrophic velocities and transports were estimated and compared with direct observations of currents and values obtained

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02079

年代:1989

数据来源: WILEY

摘要:

Spectra of sea level and current taken from the central Pacific during the NORPAX experiment contain broad peaks centered around 10‐day periods. Zonal dispersion shows these peaks to be caused by Rossby‐gravity waves. An empirical orthogonal function (EOF) analysis indicates that 44% of the variance can be attributed to these Rossby‐gravity waves, and they show clear temporal modulation in amplitude. There is no evidence that the Rossby‐gravity waves are generated locally, but coherence between the EOF and a modeled response to winds from Kapingamarangi Island, allowing for dispersion, suggests that these waves are generated by meridional wind stress in the west

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02091

年代:1989

数据来源: WILEY

摘要:

A compact array of four bottom‐mounted pressure sensors arranged in a square, a slope array, is frequently used to obtain estimates of the wave radiation stresses in shallow water. For wavelengths long in comparison with the array dimension (L), existing processing methods (Higgins et al., 1981) have bias errors ofO(kL)2, withkthe wavenumber. An estimator for wave radiation stresses and energy fluxes is derived here that reduces the bias toO(kL)4, thus considerably extending the frequency range of accurate estimates of a slope array. The stability of the new estimator to statistical fluctuations in the cross spectra is similar to the method of Higgins et al. [1981

ISSN:0148-0227    

DOI:10.1029/JC094iC02p02099

年代:1989

数据来源: WILEY