摘要:

The role of physical oceanographical, geochemical, and sedimentological data in the problem of estimating ocean primary productivity is analyzed using geostatistical and algebraic multivariate spatial methods. The available maps mirror difficulties in measuring productivity directly and quantifying biological observations, which result in a very spotty survey coverage of the world's oceans. This paper takes an approach of estimating the target productivity from related sedimentological, physical oceanographical, and marine geochemical variables. The variables are considered as a multivariate spatial system. Geostatistical estimation is applied to fill in the survey gaps, and the individual data sets are then integrated into a multivariate spatial model using algebraic map comparison. Results are used in the quality assessment and calibration of transform models between the proxy variables and primary productivity. For the Atlantic Ocean, case studies are carried out for phosphate distribution at the 100 m level, foraminifera abundance in sediments, and sea surface temperature. The utility of each proxy variable in the prediction of productivity is discussed. A new map of phosphate concentration at the 100 m level with full coverage of the Atlantic Ocean is compiled by application of geostatistics to an enlarged data base containing new observations. Primary productivity can be predicted from this phosphate map, using transforms that involve also distance from the coastline, and latitude (photosynthesis restriction). Foraminifera abundance is in principle closely related to productivity and is of importance in view of a paleoceanographic reconstruction, but difficulties in measuring and quantifying reflected in the quality of the data set prohibit a direct estimation. The relationship between higher fertility and lower temperature known from upwelling areas does not provide a simple global predictor; instead, sea surface temperature seasonality is an indicator of primary productivity under the constraint of regional availability of nutrients.

ISSN:0148-0227    

DOI:10.1029/91JC02448

年代:1992

数据来源: WILEY

摘要:

Interannual changes in the strength and seasonal evolution of the 1979 through 1982 surface level southwest monsoon winds have been related to variations in the summer phytoplankton bloom of the northwestern Arabian Sea by synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets. The 1979–1981 southwest monsoon phytoplankton blooms in the northwest Arabian Sea peaked during August‐September, extended from the Omani coast to about 65°E, and appeared to lag the development of open‐sea upwelling by at least 1 month. In all 3 years the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore Ekman pumping. Coastal upwelling was evident from May through September, yielded the most extreme concentrations of phytoplankton biomass, and along the Omani coast was limited in its impact on upper ocean biological variability to the continental shelf. Ekman pumping stimulated the development of a broad open‐ocean component of the southwest monsoon phytoplankton bloom oceanward of the Omani shelf. Phytoplankton biomass on the Omani continental shelf was increased during both the early and late phases of the 1980 southwest monsoon due to stronger coastal upwelling under the most intense southwesterly winds of the four summers investigated. Diminished coastal upwelling during the early phase of the weak 1982 southwest monsoon resulted in a coastal bloom that reached a mean phytoplankton pigment concentration that was 28% of that seen in 1980. The lack of a strong regional northwestern Arabian Sea bloom in late summer 1982 is attributed to the development of persistent, shallow temperature stratification that rendered Ekman pumping less effective in driving upward nutrien

ISSN:0148-0227    

DOI:10.1029/91JC02225

年代:1992

数据来源: WILEY

摘要:

The conventional two‐layered, alongshore independent, wind‐driven upwelling model is extended to incorporate an initial subsurface current, through the advective term involving cross‐stream shear. Under the condition that the thickness of the upper layer and the equilibrium displacement of the interface are both much smaller than the thickness of the second layer, explicit solutions are obtainable for cases of exponential and parabolic profiles of the initial interface. In the presence of the initial current in the lower layer, the upwelling is reduced near the coast, and increased offshore compared to a case without the initial current. The modification is achieved through an abatement and an enhancement in divergence near the coast and offshore, respectively, as a result of the net effect from the continuity condition and the advection of the offshore velocity in terms of the cross‐stream shear. The mechanism provides one of the possible explanations for an exceptionally wide cold water zone observed in an upwelling system influenced by an ambient large‐scale ocea

ISSN:0148-0227    

DOI:10.1029/91JC02496

年代:1992

数据来源: WILEY

摘要:

A bottom‐mounted, circularly scanning sonar operating at 40 kHz has been used to map changes in water sound speed over a circular region 150 m in diameter. If it is assumed that the salinity remains constant, the change in sound speed can be converted to a change in temperature. For the present system, the spatial resolution is 7.5 m and the temperature resolution is 0.05°C. The technique is based on comparison of successive sonar scans by means of a correlation algorithm. The algorithm is illustrated using data from the Sediment Transport Events on Slopes and Shelves (STRESS) experime

ISSN:0148-0227    

DOI:10.1029/91JC02166

年代:1992

数据来源: WILEY

摘要:

A simple method is developed to analyze current measurements obtained from a moving platform. The need for this is motivated by the now common use of the ship‐mounted acoustic Doppler current profiler (ADCP) to acquire absolute velocity data during an oceanographic survey of a given region. The full potential of this new measurement technique is severely hindered when the presence of high‐frequency phenomena (e.g., tidal or inertial motions) prevents a clear visualization of the lower‐frequency current structure of interest. Our analysis method is based on a spatial interpolation scheme, using arbitrary functions, that allows for the tidal current time variability, which then permits the tide‐induced motions to be subtracted from the ADCP data to yield the subtidal current field. The method also allows nearby moored and drifter current measurements (if available) to be combined with the shipboard ADCP observations in a single analysis to obtain the best description of the tidal and subtidal currents. To illustrate this method, we present results from the analysis of ADCP data taken during oceanographic surveys in two different continental shelf regions, the East China Sea and the Amazon shelf. A 5‐day conductivity‐temperature‐depth (CTD) and ADCP survey was made in the East China Sea near the mouth of the Yellow Sea during January 1986. There the currents were essentially barotropic and dominated by the semidiurnal tide. The ADCP‐derived cotidal chart for theM2(12.42 hours) component agrees well with existing charts derived empirically from sea level observations or from regional numerical models. The ADCP‐derived steady flow is also consistent with the observed density field and indicates little flow in or out of the Yellow Sea and a transport of about 1 Sv toward the Tsushima Strait. Two CTD‐ADCP surveys lasting 21 and 23 days were conducted over the Amazon shelf during March and May, 1990. Simultaneously moored current observations were also obtained at three locations along a cross‐shelf array 200 km north of the Amazon River mouth, for a common period of at least 2 months (February 12 to April 13). Over the shelf, tidal and subtidal currents were comparable in magnitude. Our analysis indicates that the tidal currents were essentially barotropic, semidiurnal, and polarized in the cross‐shelf direction, increasing in magnitude toward the inner shelf where current values of more than 2 m/s are common. The ADCP‐derived steady currents were aligned in the along‐shelf direction and strongly influenced by the North Brazil Current (NBC). During both ADCP surveys, the northwestward flowing NBC was transporting more than 2 Sv over the shelf at

ISSN:0148-0227    

DOI:10.1029/91JC02569

年代:1992

数据来源: WILEY

摘要:

The exchange between the water column and the sediment bed and the transport inside the permeable sediment layer are important processes in the cycles of chemical elements. In this paper we examine quantitatively the effects of modulations in the profile of the water‐sediment interface on this exchange and on the advective transport inside the sediment bed. The flow field inside a sediment layer bounded between spatially periodic ripples on top and an impermeable bottom surface is modeled using Darcy's law. The forcing is due to progressive gravity waves in the water above. The results of two different models for the pressure variation imposed on the upper boundary are compared. The two pressure profiles are derived from potential flow theory and from a numerical solution to the Navier‐Stokes equations for the oscillatory flow over a rippled bed. From an analytic solution to the two‐dimensional model, the trajectories of pore water particles immediately below the ripple profile are found to be quite different from the simple elliptical pattern found below a flat bed. The shapes of these trajectories can be quite complicated and vary considerably both along the length of the ripple and over the depth of the sediment layer close to its surface. The total exchange across the water‐sediment interface, averaged over one wave period, is significantly higher across a rippled interface than across a flat bed. This difference increases with increasing ripple slope and the strength of the wave motion, and it decreases with increasing thickness of the sediment layer relative to the length of the gravity wave. Since rippled bed forms are commonly found in coastal waters, the increase in the total exchange across a rippled water‐sediment boundary can enhance the exchange of solutes due to “wave pumping.” Immediately below the water‐sediment interface, circulation cells with net advective transport over a wave period are found. Such net advection patterns can lead to spatial (in the horizontal direction) inhomogeneities of the vertical concentration (or temperature) profiles if the overlying water column and/or the sediment bed act(s) as source or sink. This gives a plausible physical mechanism to explain the spatial variations in vertical concentration profiles found in fie

ISSN:0148-0227    

DOI:10.1029/91JC02101

年代:1992

数据来源: WILEY

摘要:

The wind speeds and the significant wave heights derived from the Geosat altimeter are validated by comparing with the data obtained at Japanese ocean data buoy stations. A systematic error is found in the altimeter wind speeds at high winds. An experimental equation is derived in order to correct this error for the present study. By using the corrected wind speeds and the wave heights, growth of wind waves with fetch in the Japan Sea under winter monsoon is investigated. The altimeter‐derived nondimensional significant wave height and nondimensional fetch show good agreement with the empirical fetch graph formulas. Fetch variation of the wind speeds is also discussed in relation to the evolution of the turbulent boundary layer over wind waves by using the altimeter dat

ISSN:0148-0227    

DOI:10.1029/91JC02452

年代:1992

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/91JC02892

年代:1992

数据来源: WILEY