摘要:

Rates of nitrate uptake in bioassays from the open Gulf of Alaska by Martin et al. (1989) are reinterpreted. During the exponential phase of phytoplankton growth, iron addition affected the rate of nitrate uptake significantly at only one of the three stations (position of the former ocean weather station “Papa”); results from one station (northern) are not interpretable. Appreciable nitrate uptake and algal growth in all controls during the first few days appears to have consumed a few to several times as much dissolved iron as was found initially; this suggests high solubilization (regeneration) rates or uptake of iron moities other than iron measured as dissolved. Exponential increases of biomass at demonstrated reduced grazing made the iron demand in the controls outrun the supply after the first few days, in contrast to the iron treatments. It is suggested that in the field, grazing normally seems to prevent the phytoplankton from reaching concentrations that reduce the iron (and nitrate) to levels that depress division rates drastically. It is unclear whether the flourishing of medium‐sized diatoms in the assays reflects removal of iron limitation on division rates of these rare species or exclusion of grazers from the containers. Although nitrate uptake may be equated with new production, the export to depth of new organic material (and hence of CO2) is not predictable from assays in small (liter) containers, especially so because the role of the large grazers on the size composition of the phytoplankton and the production of large sinking particles is not eval

ISSN:0148-0227    

DOI:10.1029/90JC02371

年代:1991

数据来源: WILEY

摘要:

Complex empirical orthogonal function (CEOF) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial structure function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originating in the equatorial Pacific. The spatial structure function is used to extract the interannual Rossby wave response from observed 300‐m‐depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike features observed in the projection mode are order 1000 km long with most periods ranging between 2 and 4 years. The wave numbers and frequencies found are consistent with Rossby dynamics. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s−1, in agreement with the theoretical Rossby wave phase speed at 40°N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2–4 years was identified by Pares‐Sierra and O'Brien (1989) as poleward propagating Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a majority of their periods ranging between 2 and 4 years, their forcing can be attributed to long‐period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3–4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propagation. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300‐m‐depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300‐m depth t

ISSN:0148-0227    

DOI:10.1029/90JC01973

年代:1991

数据来源: WILEY

摘要:

The steady circulation of the deep Pacific is estimated with a robust diagnostic model, which is internally constrained by hydrographic data. It is shown that the input data should be modified to fit the model in inverse proportion to the Coriolis parameter because a density field inconsistent with the model generates unrealistic geostrophic flows. The model reproduces most of the deep currents previously reported, such as the deep western boundary current east of New Zealand. In addition, as a new feature, the present model diagnoses an anticyclonic circulation around the East Pacific Rise. This circulation is discovered to be associated with a rise of isopycnals at middepth. Tracking of many particles in the diagnosed velocity field reveals that two water masses enter the Southwest Pacific Basin. One is the deep water of the South Indian Basin which enters through a gap to the south of New Zealand. The other is the upper water of the Antarctic Circumpolar Current; this water becomes dense near the Ross Sea and sinks into the deep Southeastern Pacific Basin. The anticyclonic circulation around the East Pacific Rise transports it to the Southwest Pacific Basin. These waters supply comparable volumes to the Southwest Pacific Basin; the residence time is estimated to be 86 years. The deep water in the Southwest Pacific Basin is brought northward rapidly by the deep western boundary current east of New Zealand; it takes only a few decades to move from the east of New Zealand to the North Pacific.

ISSN:0148-0227    

DOI:10.1029/90JC02130

年代:1991

数据来源: WILEY

摘要:

In this note we compare mean seasonal cycles of zonal and meridional velocity in the Pacific South Equatorial Current based on current meter mooring data, drifting buoy data, and ship drift data. Monthly averages of ship drift and drifting buoy data were computed over 2° latitude by 10° longitude rectangles centered at the positions of multiyear current meter moorings near 0°, 110°W, and 0°, 140°W. All three representations of the flow field show the basic character of the annual mean and its variations, provided that the sampling characteristics associated with each measurement technique are taken into account. In particular we find that more than 15 days of drifter data (regardless of year) are required on a 2° latitude by 10° longitude basis to produce monthly mean estimates that agree with moored estimates to within about 5–10 cm s−1rms. We also infer that windage affects climatological monthly mean ship drift velocities, although uncertainties in the data limit a precise determination of the windage magnitude. An upper bound appears to be about 3% of the surface wind speed, though the actual effect of windage may be considera

ISSN:0148-0227    

DOI:10.1029/90JC02136

年代:1991

数据来源: WILEY

摘要:

234Th activity profiles in Puget Sound have been studied using a model that incorporates reversible exchanges between dissolved, fine particulate, and macroaggregate Th reservoirs. Macroaggregate settling is made responsible for the downward flux of Th and the vertical gradients of activity in measured profiles. Least squares fits of model to data yield rates/time scales for the exchange processes involved. Fine‐particle scavenging by macroaggregates is found to occur with a time scale of 4–6 days over a large range of macroaggregate settling speeds,ws. Macroaggregate‐disaggregation time scales are 1–4 days whenwsis 100 m/d. Rates of sorption and remobilization characterizing the exchange between dissolved and fine‐particulate forms of the isotope cannot be individually identified from these data, but acceptable model values include those measured in the laboratory. Rates of sorption that depend on particulate concentrations which increase to the seafloor result in profiles of dissolved Th having above‐bottom maxima. Based on inferred exchange rates, the residence time for fine particles introduced at the surface of this deep (∼200 m) estuary is estimated to be 11–16 days

ISSN:0148-0227    

DOI:10.1029/90JC02197

年代:1991

数据来源: WILEY

摘要:

Detailed glaciological studies have been completed at 28 sites lying on an approximate flow line, extending 760 km across Ronne Ice Shelf. Parameters measured at each location include ice velocity, thickness, principal strain rates, surface elevation, temperature, and accumulation rate. The data have been used in a steady state model to derive the basal mass flux and the temperature profile with depth at each site, from the principles of mass and energy conservation. These calculations indicate basal melting in excess of 1 m yr−1over the first 100 km of the flow line downstream of the grounding line, where the ice shelf is between 1200 m and 1600 m thick. The maximum melt rates in this region occur near the inland margin and exceed 4 m yr−1. Melting continues at a lesser rate over the next 200 km before freezing commences. Freezing then dominates up to the final 100 km before the ice front, resulting in the accumulation of a layer of basal sea ice up to 50 m thick. This is rapidly removed as melt rates increase to over 6 m yr−1at the ice front. The cumulative effect of this pattern of basal accumulation and ablation is the wastage by melting of 85% of the mass discharged across the grounding line before it reaches the ice front. Supporting evidence for a layer of saline ice underlying the ice shelf is provided by the strength of basal radar reflections, observed during radio echo sounding of ice thickness. In the region where mass balance calculations suggest an accretion of basal sea ice, reflection coefficients are consistently low, ranging from −6 dB to −38 dB. Most of these weak reflections are believed to originate from the true base of the ice shelf, the additional energy loss being the result of increased attenuation of the radar signal within the saline layer. The derived pattern of basal melting and freezing is consistent with a simple model of sub‐ice‐shelf oceanic circulation, involving a deep thermohaline convection cell. Dense, saline water, which is formed over the continental shelf during winter when the sea surface freezes, drains into the deepest parts of the sub‐ice‐shelf cavity. At the inland margin, where this water mass comes into contact with the ice shelf, its temperature is 1°C above the local pressure freezing point. Melting of ice results, producing a buoyant outflow of cold, relatively fresh water, along the ice shelf base. Basal freezing occurs towards the ice front, where the ascending water becomes supercooled. This circulation has important implications for the production of Antarctic Bottom Water and for the response of the ice shelf to driving stresses, through the temperature dependen

ISSN:0148-0227    

DOI:10.1029/90JC01952

年代:1991

数据来源: WILEY

摘要:

The variation with time in the oxygen isotope ratio of the oceans is of prime interest in a variety of research fields. An excellent correlation between oxygen isotope ratios of cetacean (whales, dolphins, and porpoises) bone phosphate and their environmental water is found in this study. Bone phosphate samples of dolphins living in fresh waters are more depleted in oxygen 18 than those of cetaceans living in the oceans, reflecting the clear difference in the isotope composition of water. Cetaceans distributed in the higher latitudes in the oceans are more depleted in oxygen 18 than those distributed in the lower latitudes where seawater is slightly enriched in oxygen 18 relative to that in the higher latitudes. The present results provide a promising tool for estimating the oxygen isotope ratio of the oceanic water of the past without assuming water temperature.

ISSN:0148-0227    

DOI:10.1029/90JC01580

年代:1991

数据来源: WILEY

摘要:

The seasonal variation of the intrusion of the Philippine Sea Water into the South China Sea was studied by analyzing the historical hydrographic station data in the northern South China Sea and the Philippine Sea. Water masses at 150, 200, and 250 m were classified by discriminant analysis according to their temperature‐salinity characteristics. At each depth, most water in the study region was classified into two groups representing the Philippine Sea Water and the South China Sea Water, respectively. The geographic distribution of water masses in the South China Sea shows that the Philippine Sea Water was present along the continental margin south of China between October and January. A westward current in the northern South China Sea in winter was inferred from the distribution of the intrusion wate

ISSN:0148-0227    

DOI:10.1029/90JC02367

年代:1991

数据来源: WILEY

摘要:

The effect of the degree of wave development on the sea state bias (SSB) in Geosat altimeter height measurement is evaluated. Theoretical considerations suggest that the altimetric SSB is generally not a linear function of significant wave height but depends also on other factors of wave development. Of particular interest is its dependence on wave age, defined as the ratio of the phase speed of the dominant ocean waves to ocean wind speed. We estimate wave age rather crudely, on the basis of the significant wave height (H⅓) and wind speed measured by the altimeter. Under general conditions when the sea is not in equilibrium with the wind, this estimate may not correspond to the wave age in a strict sense and hence is called “pseudo wave age” in this paper. Nevertheless, the pseudo wave age is a rough indicator for the degree of wave development. The general trend in the dependence of the SSB on pseudo wave age, as found by analyzing 2.7 years' worth of Geosat data, agrees well with the theoretical prediction: for a givenH⅓, the SSB decreases as the degree of the wave development (measured by the pseudo wave age) increases. This empirical trend is modeled as SSB= A(ξ/ξm)MH⅓, where ξ and ξmare the pseudo wave age and its average value, respectively;A= 0.013 ± 0.005, andM= −0.88 ± 0.37. Statistically, this model performs slightly better than a standard model (i.e., SSB = β H⅓with β being a constant). In terms of the global rms error the improvement is by 1.6 cm. However, because the degree of wave development varies with the season and geographical location, this small improvement could become important for more accurate altimetric missions in the future when the centimetric, basin‐scale signals are

ISSN:0148-0227    

DOI:10.1029/90JC02319

年代:1991

数据来源: WILEY

摘要:

Surface wind stresses associated with the Madden‐Julian oscillation transfer angular momentum between the atmosphere and the underlying ocean. The resulting anomalies in oceanic angular momentum (related to either changes in zonal currents or latitudinal redistribution of mass) and the torques coupling the ocean and the solid Earth are examined for simple zonal stress patterns representing idealized 40‐ to 50‐day fluctuations of Pacific winds. Because the contribution of baroclinic variability to the angular momentum budget is in general small when vertically integrated quantities are considered (Ponte, 1990), only the barotropic response is studied. Numerical solutions of the shallow water equations with linear bottom friction are found for a constant depth basin centered on the equator and extending over 140° in longitude. The angular momentum exchanges between the ocean and solid Earth in the model involve the continental torque (i.e., body forces on eastern and western walls due to coastal sea level anomalies) and the bottom friction torque. Solutions yield a dominant balance between the wind and continental torques, with the bottom friction torque being negligible. The amplitude of the total torque acting on the ocean and the corresponding angular momentum fluctuations are very small compared with the amplitude of the applied wind torque. The ocean delivers to the solid Earth, with no significant time delays, the angular momentum anomalies received from the atmosphere. In general, sea level anomalies are nearly uniform along the eastern boundary, and the respective meridionally integrated torque is much larger than the one exerted on the western wall. Solutions also suggest that coastal (barotropic) sea level fluctuations as small as 0.5–1.5 cm are sufficient to cause variations in the length of day comparable to observed values in the 40‐ to 5

ISSN:0148-0227    

DOI:10.1029/90JC02277

年代:1991

数据来源: WILEY