摘要:

The potential for greater air‐sea exchange rates in the northern Atlantic to decrease atmospheric CO2during the ice ages is examined using a simple model of the solubility pump. This potential is shown to depend on whether the modern ocean's region of sinking cold water is reequilibrating with atmospheric CO2at a rate comparable to the poleward transport of warm surface water. If this is the case, it is possible that greater ice age polar ventilation may have produced as much as 60% of the decrease observed in ice cores. In this scenario, the cold surface water CO2partial pressure does not covary with the atmosphere but instead would remain approximately constan

ISSN:0148-0227    

DOI:10.1029/92JC02323

年代:1993

数据来源: WILEY

摘要:

Profiles of210Pb,210Po, and nutrients were measured within a cold, chlorophyll‐rich filament observed in satellite images off Point Arena, California. The most striking observation was the large excess of210Po in the surface water of near‐shore filament stations. This excess210Po, typically associated with the breakdown of particles in the upper thermocline, is indicative of the transport of recently upwelled water seaward within the filament. Its large inventory and association with NO2within the filament surface is consistent with the filament being part of a continuous, meandering, southward flowing jet within the California Current. Nutrients and biomass are “pumped” along the meander path by the interaction of biological processes (production, grazing) and vertical motion (upwelling, downwelling). Products of particle breakdown, such as NO2and210Po, are continuously recycled and accumulate along the meander path. The implication is that within the coastal transition zone, some portion of the nutrients incorporated into new production has also been regenerated along the meandering flow. The excess210Po is removed from the chlorophyll‐rich filament at a rate which is approximately an order of magnitude greater than210Po removal from open ocean surface water. This suggests that the scavenging rate of210Po, like that of234Th, varies with the rate of primary p

ISSN:0148-0227    

DOI:10.1029/92JC01932

年代:1993

数据来源: WILEY

摘要:

The seasonal variability of bio‐optical and physical properties within the upper ocean at a site in the Sargasso Sea (34°N, 70°W) has been observed using multivariable moored systems (MVMS) during a 9‐month period (March through November 1987). In addition, complementary meteorological data, sea surface height (Geosat) and sea surface temperature maps, and expendable bathythermograph (XBT) and shipboard profile data (physical and bio‐optical) have been utilized for interpretation. The observations during March are characteristic of late wintertime conditions of a deep isothermal layer (∼18–19°C), but with intervening periods of warming due to the advection of warm outbreak waters associated with Gulf Stream meanders. The mixed layer depth shoals from greater than 160 m to about 25 m in late March (spring transition). Phytoplankton blooms follow the mixed layer shoaling. A succession of phytoplankton populations occurs during this transitional interval. Mesoscale variability associated with cold core rings and warm outbreak waters associated with the Gulf Stream are evident at various times. The mixed layer remains near 25 m for the summer and deepens in mid‐September. A relatively intense subsurface maximum in chlorophyll develops at ∼75 m following the spring transition. The maximum persists, but weakens in mid‐summer. The present study clearly indicates that important processes associated with and contributing to the seasonal cycle occur on short time and space scales and that integrated data sets obtained from moorings, ships, and satellites can be used to effectively study bio‐optical and physical phenomena on time scales fro

ISSN:0148-0227    

DOI:10.1029/92JC01830

年代:1993

数据来源: WILEY

摘要:

Estuarine measurements of suspended sediments over sand waves have been taken with the objective of clarifying the role of turbulence in suspension transport, sand waves development, and migration. To discern the mechanisms of transport, observations of the turbulent flow were taken and records of the response of the suspended sediment concentration were obtained using acoustic backscattering (ABS). As an intermediate goal of the overall objective an analysis of the ABS data has been conducted with the aim of assessing and quantifying the acoustic technique. Recent theoretical descriptions of the interaction of sound with suspensions are presented, and predictions are compared with a laboratory study on suspensions of spheres and noncohesive sediments. The laboratory data show the theoretical approach to be broadly correct, and it has been implemented to interpret the estuarine observations. Acoustic estimates of the suspended sediment concentration have been compared with pumped sample data and shown to be similar. Comparison of the laboratory and estuarine estimates for the form function and total scattering cross section for the estuarine sediments is presented, and some unresolved differences are considered. The effects of the sediment attenuation and the random amplitude of the backscattered signal are also highlighted, and their implications regarding acoustic estimates of the suspended sediment concentration are addressed. Finally, after assessing the accuracy of the acoustic approach, high‐resolution estimates of the suspended concentration are presented with some speculation on the origins of the concentration variability observe

ISSN:0148-0227    

DOI:10.1029/92JC01855

年代:1993

数据来源: WILEY

摘要:

Data from synthetic aperture radars (SAR's) can be used to measure the surface height spectrum of the ocean. Traditionally, only the real SAR image is used; we show, both theoretically and with SAR data, that the complex image contains more information about the ocean scene. We derive an expression for the ambiguity function of the complex image, which is an extension of the concept of a power spectrum, but generalized to phenomena with time‐dependent properties. The ambiguity function of the complex image is derived as an integral of the surface height spectrum; this allows us to calculate the statistics of the complex SAR image directly, without having to generate individual realizations of the surface. In the derivation of the ambiguity function, we find that a simple assumption about the complex reflectivity of the surface leads to a formulation of the SAR imaging process that circumvents many traditional problems. By using ambiguity functions, we can remove some of the smearing that is otherwise seen in the images of time‐dependent scenes. One result of this analysis is that we can explain SAR focusing in a simple way, and extend it to range‐traveling waves as well as azimuth‐traveling waves. Also, we can calculate the correlation length and time of the surface directly from the surface height spectrum. While the correlation length seems to play only a minor role in this theory, the correlation time determines the minimum wavelength for azimuth waves that can be imaged. This paper shows how the ambiguity function of the image is related to the surface height spectrum and presents an example using S

ISSN:0148-0227    

DOI:10.1029/92JC02069

年代:1993

数据来源: WILEY

摘要:

Estimates of any given flux (momentum, heat, or moisture) that use the full set of diabatic profile relations applicable to the marine atmospheric surface layer require an accurate representation of flux coefficients, diabatic parameters, roughness lengths, and mean values for all meteorological quantities. Calculation of the momentum flux, for example, requires that the stratification function include both temperature and humidity effects and that the solution to the equation set be based on full set iteration. We find that over warm water, particularly during cases of low humidity, the momentum flux and stratification estimates are very sensitive to the reported relative humidity. Similarly, we find that the ERS 1 radar cross section, when treated as a function of the wind stress (or momentum flux), varies significantly with relative humidity, particularly when surface temperatures are warm. This study suggests that any calibration/validation campaign using remote‐sensing observations, in particular the ERS 1 scatterometer, should utilize high‐quality ground truth relative humidity measurements in addition to the traditional suite of high‐quality wind and temperature gradient measure

ISSN:0148-0227    

DOI:10.1029/92JC02220

年代:1993

数据来源: WILEY

摘要:

Large off‐nadir attitude deviations and high surface wave heights cause an alteration in the ocean return signal from a satellite radar altimeter. This leads to an error in the on‐board calculation of the height measurement. The error can be removed by reprocessing the full radar return signal on the ground. In the ground processing, the correct tracking point in the return signal is recomputed through a procedure called retracking. There has been a controversy over whether or not all altimeter data would be retracked. This study analyzes retracked southern ocean data from the first 34 repeat cycles of the Geosat Exact Repeat Mission (ERM), covering November 1986 through April 1988. The final data set consists of over 2.5 million smoothed one‐per‐second measurements of the ocean surface. The significant wave height (SWH) distribution as given on the NOAA geophysical data records (GDRs) for these measurements peaks at around 2.1 m (19% of the measurements) and drops down almost linearly to 2% of the measurements at 5.8 m. There are over 1100 observations with SWH greater than 15 m. The difference between the surface heights calculated from the retracked data and the original on‐board estimates is less than 10 cm for SWH less than 10 m but increases to approximately 1.0 m at a SWH of 18 m. In general, the electromagnetic (EM) bias coefficient calculated using the retracked data is slightly less than that using the unretracked data and does not decrease as much with SWH as do the EM bias coefficients calculated from the unretracked data. A map of the sea surface height variability of the southern ocean created using the retracked data shows differences from variability maps created using the unretracked data in regions of high wave heights. Retracking can be done efficiently on modern UNIX work stations at 0.064 times real‐time acquisition. This study shows that retracking will improve altimete

ISSN:0148-0227    

DOI:10.1029/92JC02271

年代:1993

数据来源: WILEY

摘要:

Hydrographic data collected during March–April 1991 show the presence of a poleward current along the western boundary of the Bay of Bengal north of about 10° N carrying warmer waters of southern origin. The inshore side of the current was marked by cooler, more saline waters brought to the surface due to the presence of the current which transported approximately 10 × 106m3/s. The hydrography is suggestive of many of the features that have been associated with the western boundary currents of the subtropical gyres of the world oceans: a recirculation zone, waves, eddies, etc. These features, however, were not satisfactorily resolved in the data. Using available climatologies of monthly mean ship drifts, seasonal hydrography, and monthly mean wind stress, we propose that the poleward current is the western boundary current of a seasonal anticyclonic subtropical gyre which forms in the Bay during January, is best developed during March‐April, and decays by June. The gyre and the western boundary current are unique because of their seasonal character. The pattern of circulation leading to formation and decay of the gyre is reproduced reasonably well in the computation of the monthly mean barotropic transport induced by the curl of wind stress, which has a well‐defined annual cycle due to the monsoons and which is conducive to the formation of an anticyclonic gyre only during the months of January‐May. The pattern of circulation due to baroclinic transport induced by the wind stress curl, however, is not known at present, and this makes it difficult to conclude unequivocally that the wind stress curl over the bay is the sole mechanism to force

ISSN:0148-0227    

DOI:10.1029/92JC02070

年代:1993

数据来源: WILEY

摘要:

Field measurements of tidal flow around a headland indicate secondary circulation induced by flow curvature. The secondary flow, defined to be the flow in the plane normal to the direction of the vertically averaged current, is directed toward the headland near the bottom and seaward near the surface, consistent with theoretical predictions. The strength of the secondary flow varies from 5 to 15% of the streamwise flow. It is strongest when the water column is stratified because of both the enhanced shear of the streamwise flow and the reduced frictional damping of the secondary flow. The transverse exchange accomplished by the secondary flow significantly influences the structure of the streamwise flow, causing a broadening of the transverse shear and changing the horizontal and vertical distributions of momentum. It may also have a significant influence on horizontal dispersion in the vicinity of headlands.

ISSN:0148-0227    

DOI:10.1029/92JC02270

年代:1993

数据来源: WILEY

摘要:

Analysis of the hydrographic data taken in the northern North Pacific has revealed a water‐mass front defined as the abrupt change of mixing rates between the two typical water masses. Typical water masses are situated above the main thermocline in the subtropical and subpolar gyres. This front, termed Water‐Mass Front in the present study, can be regarded as the boundary between the subtropical gyre and the subpolar gyre. The index for detecting the frontal position from the temperature field is given as the 5°C isotherm at the 300‐m level. Comparisons with data from previous studies are also made, and this front appears to correspond to the Subarctic Front in almost every in

ISSN:0148-0227    

DOI:10.1029/92JC01854

年代:1993

数据来源: WILEY