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41.
The rate of zooplankton ammonium regeneration was measured in Great South Bay, Long Island, New York, between July 1982 and May 1984. Ammonium excretion by macrozooplankton (>200 μm) ranged from 7 μg atoms NH4 1+?N m?3 d?1 in winter to 156 μg-atoms NH4 1+?N m?3 d?1 in spring. Ammonium excretion by ctenophores was greater than or equivalent to that of macrozooplankton during the period of ctenophore biomass maximum in summer and fall. The temperature coefficient (Q10) for NH4 1+ excretion was 1.74 from 2.2 to 27.5°C for macrozooplankton and 1.63 between 17 and 26°C for the ctenophores. Ammonium nitrogen excretion by macrozooplankton and ctenophores combined, accounted for 1 to 3% of phytoplankton nitrogen requirements in summer when primary productivity was high and 39% in the spring. *** DIRECT SUPPORT *** A01BY040 00005 相似文献
42.
Associations between polar air cloud vortices (polar lows), as an indicator of intermediate-scale atmospheric activity, and the Antarctic sea ice, are examined for the Southern Hemisphere winter (June–September). Seven consecutive winters, spanning a period of marked interannual variability of the atmospheric circulation and sea ice (1977–83), are analyzed using sets of DMSP (Defense Meteorological Satellite Program) imagery. Relatively high frequencies of polar lows are found in ice-edge and adjacent ocean latitudes. There is some evidence for an equatorward shift in the latitude of maximum monthly polar low occurrence during the June to September period. Polar low incidence over the Southern Hemisphere on interannual time scales shows a close association with positive sea ice anomalies in the longitudes of more frequent cold air outbreaks from higher latitudes. This is particularly apparent for winters of strongly anomalous circulation, such as FGGE (1979) and the major ENSO of 1982–83. However, for individual cases on daily to weekly time scales, the feedback of cold air — sea ice advance — polar low development is not always evident, and implies that additional processes may contribute to polar air cyclogenesis in the marginal ice zone. 相似文献
43.
R. Carpenter M.L. Peterson J.T. Bennett B.L.K. Somayajulu 《Geochimica et cosmochimica acta》1984,48(10):1949-1963
Activity profiles of excess 234Th, excess 210Pb, 232Th, 230Th, 234U and 238U, and 228/232Th ratios determined in eight box cores of sediment from six sites in central Puget Sound provide new insights into the dynamic nature of solid phase mixing in surface sediments, the exchange of 228Ra and other soluble species across the sediment-water interface, and the cycling of U, Th and 210Pb in this coastal zone.Comparison of excess 234Th inventories in sediments with its production rate in the overlying water column indicates a mean residence time of at most 14 days for particles in the central Puget Sound water column.Surface sediment horizons with excess 234Th have no excess 228Th which might be used to ascertain sediment accumulation rates over the past decade. Instead, deficiencies of 228Th due to loss of soluble 228Ra from pore water to the overlying water persist to 20–30 cm, revealing that exchange of soluble chemicals between pore and overlying waters reaches these depths in the extensively bioturbated sediments of Puget Sound.Solid phase U isotope concentrations tend to increase by up to a factor of two with depth in sediments, as a result of dissolved U being biologically pumped down into sediments where it is partially removed when conditions become mildly reducing. 232Th and 230Th activities and 230/232Th ratios are constant with depth in sediments, indicating constant detrital phase compositions and essentially no authigenic 230Th. Steady state 210Pb depositional activities in and fluxes to Puget Sound sediments average only about onehalf those for sediments of the open Washington coast north of the Columbia River mouth, primarily because of a much lower supply of dissolved 210Pb in sea waters adverting into Puget Sound.Excess 234Th profiles in sediments reveal much more detail about the depth dependency, dynamic nature and recent history of solid phase mixing processes than excess 210Pb profiles. At least six of eight 234Th profiles show that mixing within the 210Pb-defined surface mixed layer is depth dependent. In three profiles, 234Th-derived mixing rates are fastest several centimeters below the sediment-water interface, indicating greater macro-benthic activity at these depths. Depth dependent mixing coefficients derived from the best fit of a four layer, advection-diffusion-decay model to the 234Th data are consistent with 210Pb profiles determined for the same sediments, strongly suggesting that 234Th and 210Pb are mixed equivalently and in a multilayered manner. 相似文献
44.
Normalized gas chromatograms of the normal alkane fraction extracted from 22 surface sediment samples from a salt marsh near Georgetown, South Carolina were submitted to an unmixing algorithm. This algorithm identified four end-number contributors, three of which very closely resemble n-alkane patterns from dominant plant species. The fourth end-member is apparently a mixture. Proportioning of the n-alkane patterns of the sediments suggests that the patterns reflect contributions from living surface plant material and dead plant material brought in by tides. The successful unmixing of complex patterns of alkanes from marsh sediments suggests a valuable new technique for the interpretation of chromatographic data. 相似文献
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The aim of this paper is to evaluate the results of a survey of the availability and uptake of port reception facilities within the North Sea area. The evaluation is based primarily on original survey data from the autumn of 2002 which followed on from a similar survey conducted in the summer of 2000. The EU Directive on port reception facilities for ship-generated waste etc. (Directive 2000/59/EC) was due to enter into force in December 2002, and required all EU ports to provide reception facilities to meet the needs of the vessels normally calling in at them. This paper examines the readiness of North Sea ports to meet that requirement and also considers the actual uptake levels of facilities, where ports were able to provide such information. 相似文献
48.
Geophysical response of slackwater and sandy terrace deposits near Savanna, Northwestern Illinois 总被引:1,自引:1,他引:0
Low-permeability clayey and silty river terrace deposits are an important component in protecting underlying aquifers from contamination by agrochemicals and other contaminants. Such deposits also record deglaciation dynamics, meltwater drainage and local climatic variations. In this study, conducted over Mississippi River terraces near Savanna, Illinois, clayey slackwater terrace deposits and sandy terrace deposits are examined using resistivity soundings, ground-penetrating radar (GPR) profiles and direct-push conductivity logs. The clayey terrace deposits are characterized by low resistivity (10–35 ohm-m) and slow GPR wave velocity (0.07 m/ns), whereas non-clayey terrace deposits exhibit much higher resistivity (169–1,762 ohm-m) and faster GPR wave velocities (0.15 m/ns). Sandy and clayey terrace deposits may thus be differentiated and mapped on the basis of their geophysical response. Models based on resistivity soundings provide reasonably accurate estimates of the thickness of clayey slackwater deposits, but fail to reveal thin sands embedded in the clayey deposits. In some cases, the full thickness of the slackwater deposits was also not revealed. GPR profiles, however, imaged these embedded shallow sands and possibly imaged deeper sands below the base of the slackwater deposits, giving more accurate estimates of thickness. GPR also accurately resolved the thickness and character of sandy terrace deposits. Direct-push conductivity logs provide both accurate estimates of the thickness of clayey slackwater terrace deposits and a means of identifying thin embedded sands. In summary, resistivity soundings image these deposits at the lowest resolution with one-dimensional models, whereas GPR provides much higher resolution showing detailed layering within the upper several meters. Direct-push conductivity logs provide the highest resolution, but are invasive and only reveal stratigraphy at one location. 相似文献
49.
A. C. Becker E. Agol N. M. Silvestri J. J. Bochanski C. Laws A. A. West G. Basri V. Belokurov D. M. Bramich J. M. Carpenter P. Challis K. R. Covey R. M. Cutri N. W. Evans M. Fellhauer A. Garg G. Gilmore P. Hewett P. Plavchan D. P. Schneider C. L. Slesnick S. Vidrih L. M. Walkowicz D. B. Zucker 《Monthly notices of the Royal Astronomical Society》2008,386(1):416-424
We report on Two-Micron All-Sky Survey (2MASS) J01542930+0053266, a faint eclipsing system composed of two M dwarfs. The variability of this system was originally discovered during a pilot study of the 2MASS Calibration Point Source Working Data base. Additional photometry from the Sloan Digital Sky Survey yields an eight-passband light curve from which we derive an orbital period of 2.639 0157 ± 0.000 0016 d. Spectroscopic followup confirms our photometric classification of the system, which is likely composed of M0 and M1 dwarfs. Radial velocity measurements allow us to derive the masses (M1 = 0.66 ± 0.03 M⊙ ; M2 = 0.62 ± 0.03 M⊙ ) and radii (R1 = 0.64 ± 0.08 R⊙ ; R2 = 0.61 ± 0.09 R⊙ ) of the components, which are consistent with empirical mass–radius relationships for low-mass stars in binary systems. We perform Monte Carlo simulations of the light curves which allow us to uncover complicated degeneracies between the system parameters. Both stars show evidence of Hα emission, something not common in early-type M dwarfs. This suggests that binarity may influence the magnetic activity properties of low-mass stars; activity in the binary may persist long after the dynamos in their isolated counterparts have decayed, yielding a new potential foreground of flaring activity for next generation variability surveys. 相似文献
50.
Four adult specimens of the pycnogonid Ammothea magniceps were observed swimming at the sea surface at night at Kaikoura. Even after capture the animals continued to swim at the surface of the water for over an hour. Such swimming behaviour is considered important in explaining the presence of “benthic” animals in plankton samples. 相似文献