摘要:

Attempts are now underway to estimate primary productivity on global scales from a combination of satellite color imagery and manned or unmanned platforms. Regardless of the observing network, productivity over basin scales will be estimated from plankton biomass, estimated in turn from composite (or averaged) satellite images. We show mathematically that the interaction of two‐dimensional horizontal turbulent diffusion with an annual cycle in plankton growth induces an intrinsic large‐scale patchiness in the resulting plankton biomass distributions. We assume, as typical scales, a root‐mean‐square horizontal turbulent velocity of 0.05 m s−1and a turbulent mixing length of 50 km. The corresponding length scale for the resulting patchiness in the annual cycle is of the order of 700 km, or at least 10 times the mixing length. Such patchiness can occur even when the growth rate is spatially uncorrelated; in fact, we show that small‐scale grazing by zooplankton could actually enhance the patchiness at a length scale of 700 km. The existence of the patchiness is not contingent upon assuming a given, finite breadth for the region of fertile water, unlike the earlier “KISS” models, nor upon spatial forcing of any type, but depends only on the existence of an annual cycle in primary productivity. The implication for numerical modeling is obvious. The most plausible physical requirement might be a turbulent quasi‐geostrophic motion field at or approaching statistical stationarity, but the first priority for the biological component embedded in the modeled motion field ought to be a model of the onset of the spring bloom and the subsequent development of

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00823

年代:1989

数据来源: WILEY

摘要:

Nineteen years of wind data over the North Atlantic are used to calculate a field of wind stress curl. An empirical orthogonal function (EOF) analysis is performed on this field, resulting in spatial patterns of wind stress curl and associated time series. A Monte Carlo technique is used to establish the statistical significance of each spatial pattern. The first four statistically significant EOF modes represent more than 50% of the curl variance. The spatial patterns of curl associated with these modes exhibit the major elements of North Atlantic climatology. The associated time series are spectrally analyzed. Most of the variance is contained in annual and semiannual frequencies. Features observed include the individual annual variation of the subtropical high and the subpolar low, the annual oscillation of intensity between the above pressure centers, the influence of localized strong sea surface temperature gradients and associated cyclogenesis regions, and the constant nature of the trades. The EOF curl patterns are in the form of basin‐sized standing wave

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00831

年代:1989

数据来源: WILEY

摘要:

Observations are presented of deep‐water exchange in a large coastal embayment on the south coast of Newfoundland. The bay has several outer sills not unlike those found in fjords. Outside the bay, two submerged channels on the continental shelf are reservoirs for two different deep‐water masses which may flow over separate sills to replace deep water within the bay. The deep water is renewed approximately twice a year. On average, exchange occurs both during the half‐year period centered on midwinter and during the half‐year period centered on late summer, with the water properties of the inflow in each period being dominated by one of the two source water masses in the shelf channels. The system therefore occupies one of two renewal states for much of the year. The transition between states appears to be induced largely by seasonal variations in the wind forcing over th

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00843

年代:1989

数据来源: WILEY

摘要:

CO2evasion within the Atlantic equatorial belt (5°N–5°S) increases from the east to the west [Andrié et al., 1986]. Many factors contribute the variations of pCO2in the equatorial surface waters. To assess their relative importance, a kinematic box model is developed. A 2°×2° box whose depth is defined by the 24.90‰ isopycnal level flows westward from 4°W to 38°W within the Equator‐2°S band with the south equatorial current. Time (zonal) evolution of nitrate, total CO2, total alkalinity and mass, and of the corresponding water pCO2, are simulated taking into account advection, meridional divergence, diffusion, biological activity, and gas exchange. Initial and boundary conditions are taken from the FOCAL 4 (July‐August 1983) data set. The flow field is based on climatology. The ability of the model to reproduce the observed FOCAL data, as well as the correct orders of magnitude of the adjustable parameters KV(vertical mixing coefficient) and Jmax(maximum nitrate uptake rate), as compared with independent estimates, suggests that all major terms controling the equatorial Atlantic CO2values are considered. Advection fluxes dominate the CO2balance. The sinks due to biological consumption approximately balance the inflow from the core of the Equatorial Undercurrent by diapycnal mixing. Calculated new production JCvalues vary from east to west between 17 and 1 mol C/m2/yr, given Kv= 5 × 10−4m2/s. Isopycnal mixing is negligible. Degassing plays a minor role in the total CO2budget. Estimating the biological uptake of nutrients should be a very useful constraint for estimating eq

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00855

年代:1989

数据来源: WILEY

摘要:

Observed eddy heat fluxes, i.e., covariances between heat content and horizontal currents, are analyzed with moored data from the Coastal Ocean Dynamics Experiment. It is demonstrated that much of each sampled covariance arises from the separate correlations of currents and temperature with the upwelling variability, which is attributed to the particular warming and cooling processes present. Thus a large part of the observed eddy heat fluxes is wind driven. The remainder is consistent with being largely statistical noise in the observed covariance between those parts of the flow and temperature which are not correlated with the upwelling. This also suggests that the wind‐driven part alone might be a better estimate of the ensemble average eddy heat flu

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00871

年代:1989

数据来源: WILEY

摘要:

The vertical thermohaline structure in the central Argentine basin is investigated on the basis of high‐resolution hydrographic data. Emphasis is placed on fronts, their horizontal gradients, vertical stability and associated fine structure. Horizontal thermohaline gradients vary strongly with depth, regions of strong gradients alternating with those of weak gradients. The strongest gradients occur often at depths below the upper mixed layer. The salinity gradient maximum occurs above the temperature gradient maximum. Enhanced gradients are found where warm, salty water moves over cooler, fresher water such as between the subtropical water (STW) and antarctic intermediate water (AAIW) and between the North Atlantic deep water (NADW) and the antarctic bottom water (AABW). Temperature, salinity, and density fronts do not always coexist. Density‐compensating temperature and salinity fronts occur in the surface layer of the subantarctic and at abyssal depth below 3500 m. Vertical profiles of the Väisälä frequency indicate much reduced hydrostatic stabilities in the Brazil current and subantarctic frontal zones. Potential vorticity minima indicate the formation of subantarctic mode water just north of the subantarctic front and its subsequent northward and upward spread across isopycnals. The thermohaline fine structure is vertically intermittent. The amplitude variances between the enhanced and quiet regions vary by almost 2 orders of magnitude. Enhanced fine structure amplitudes are found near the STW‐AAIW and NADW‐AABW interfaces, where large horizontal thermohaline gradients occur and the hydrostatic stability is low. The temperature and salinity fine structures are largely density compensating. The coherence between the temperature and salinity fine structure is strongly depth dependent and is highest in regions where warm, salty water moves over cooler, fre

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00877

年代:1989

数据来源: WILEY

摘要:

Altimetric sea level map time series of the tropical Pacific have been produced from the crossover differences generated in the first 17 months of the Geosat mission. To verify the validity of altimetric sea level so produced, they are compared with the dynamic height field derived by expendable bathythermograph (XBT) and island sea level data. Overall, the three fields show statistically significant correlation with each other. At island sea level stations, altimetric sea level, in general, has better correlation with island sea level than the XBT‐derived dynamic height. Complex empirical orthogonal function (CEOF) analysis (which is used to discern coherent structures from data contaminated by random errors) has been conducted on the altimetric sea level and XBT‐derived dynamic height field. The first CEOF modes (which each explain 70% of the variance of the respective field) correlate significantly better with each other than the original fields. The relatively short record is clearly dominated by the annual signal. Major features away from the equator are also observed to propagate to the w

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00897

年代:1989

数据来源: WILEY

摘要:

When wind speed increases and ultimately exceeds a critical value, whitecaps and subsequently sea droplets appear. This is the source of an important increase in the rate of evaporation. Experiments reported here were performed in a large air‐sea interaction simulating facility which allow us to quantify this increased rate. Various wind (10, 12, and 14 m/s) and wave (wind‐generated and mechanically generated) conditions were studied to check this evolution. Profiles of mean wind velocity and humidity are determined at about 35–50 data points across the boundary layer and as close to the air‐water interface as possible. Using the profile method, momentum and water vapor fluxes were evaluated and represented by their dimensionless expressions as friction coefficients Cfand Sherwood number Sh, respectively. When plotted in the conventional manner, i.e., versus Reynolds number based on fetch and free stream velocity, Sherwood numbers show a clear deviation from available results, indicating a large increase of evaporation with increasing Reynolds number. Results were then plotted as a function of a modified Reynolds number based on friction velocity and significant wave height. From this an empirical correlation is p

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00909

年代:1989

数据来源: WILEY

摘要:

Sea ice freeboard, thickness, and snow depth were measured from a series of closely spaced (5 to 10 m) drill hole sites from five free‐floating multiyear ice floes in the Beaufort Sea during the spring of 1986 and 1987. A regression of ice thickness on ice draft was performed on the data from each floe and for the combined data set. Regressions were performed both on nonscreened data and data screened to eliminate pressure ridges. A predictive equation was developed permitting the total ice thickness to be estimated from measured values of ice draft, e.g., from submarine echo sounder traces:t= 1.115d. The keel‐sail height ratio for pressure ridges was found constant at 3.3 to 1, in agreement with past observati

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00919

年代:1989

数据来源: WILEY

摘要:

Continuous measurements of the C band normalized radar cross section (NRCS) at vertical/vertical polarization as a function of wind speed and direction were carried out from a research platform in the North Sea during a period of 11 months in 1984. The NRCSs have been correlated with other environmental data routinely collected at the platform, like air‐water temperature difference, water temperature, and ocean wave slope. The wind speed exponent of the C band NRCS at 45° incidence angle was determined as 1.50, valid in the wind speed range 2–19 m/s. Our data set shows that the C band NRCS depends strongly on the air‐sea temperature difference. For example, when the air‐sea temperature difference decreases from +5°C to −5°C, the NRCS increases by 6 dB at a wind speed of 8–9 m/s and an incidence angle of 45°. For stable air‐sea interfaces and low wind speeds the NRCS increases with increasing root‐mean‐square wave slope. However, no systematic dependence on water tem

ISSN:0148-0227    

DOI:10.1029/JC094iC01p00924

年代:1989

数据来源: WILEY