Sailfish (Istiophorus platypterus) spawning and larval environment in a Florida Current frontal eddy     

David E. Richardson  Joel K. Llopiz  Kevin D. Leaman  Peter S. Vertes  Frank E. Muller-Karger  Robert K. Cowen 《Progress in Oceanography》2009,(4):252-264

Fronts and eddies are widely hypothesized to be critical spawning habitat for large pelagic fishes, due to increased larval and/or adult feeding opportunities at these features. We examined sailfish (Istiophorus platypterus) spawning around a cyclonic, submesoscale (∼13 × 7 km) Florida Current frontal eddy. The temporal progression of eddy dynamics over a 65 h period was determined using ocean color satellite imagery, continuous surface measurements along the cruise track, and non-linear least-squares fitting of the positions of three drifters deployed within the eddy. A peak in larval sailfish densities (n = 2435, stations = 49), composed primarily of yolk-sac and first-feeding larvae, occurred at the eddy frontal zone. A majority of these larvae were estimated to have been spawned during the formation of the eddy. A comparison between the distribution of similar-age sailfish and scombrid larvae indicated that the peak in larval sailfish density likely resulted from spawning directly at the front, rather than transport by convergent flow. The first-feeding prey items of larval sailfish (Farranula and Corycaeus copepods) were most abundant at the frontal zone and to a lesser extent inside the eddy. Egg distributions were used to indirectly assess the distribution of adult sailfish prey items. Euthynnus alleteratus and Auxis spp. eggs were in highest abundance outside the eddy, while the eggs of small carangids were in highest abundance at the eddy frontal zone. Overall, this study indicates that sailfish spawn at small-scale oceanographic features that provide a favorable feeding environment for their larvae and potentially also for the adults.  相似文献   

An Examination of Scale-Dependent Dispersion Coefficients   总被引：1，自引：0，他引：1  

Fred J. Molz  Oktay Güven  Joel G. Melville 《Ground water》1983,21(6):715-725

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A scheme for computing surface fluxes from mean flow observations   总被引：3，自引：0，他引：3  

Martin I. Hoffert  Joel Storch 《Boundary-Layer Meteorology》1979,17(4):429-442

A computational scheme is developed for estimating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at a single height in the atmospheric surface layer; conditions at this reference level are presumed known from observations or from a numerical atmospheric circulation model. The method is based on coupling a Monin-Obukhov similarity profile to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant flux at the surface.In addition to reference-level mean flow properties, the parameters needed to implement the scheme are thermal heat capacity of the soil, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity.Sample calculations are presented for (a), constant atmospheric forcing at the reference level, and (b) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert in California. The latter case simulated the observed diurnal variations resonably well for the parameters used.Consultant, Atmospheric Sciences Division, Department of Energy and Environment, Brookhaven National Laboratory, Upton, N.Y., pc11973, U.S.A.  相似文献   

Uranium series dating of stalagmites from Blanchard Springs Caverns,U.S.A.     

Glenn M. Thompson  David N. Lumsden  Raymond L. Walker  Joel A. Carter 《Geochimica et cosmochimica acta》1975,39(9):1211-1218

Because stalagmites are enriched in ²³⁴U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, ²³⁴U/²³⁸U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP.  相似文献   

Uranium deposition and Th-234 alpha-recoil: An explanation for extreme U-234/U-238 fractionation within the trinity aquifer     

Joel Kronfeld 《Earth and Planetary Science Letters》1974,21(3):327-330

²³⁴Th alpha-recoil appears to be a valid mechanism for explaining the generation of extreme²³⁴U/²³⁸U disequilibria found in the waters of the Trinity aquifer.  相似文献   

Isotope Dilution MC-ICP-MS Rare Earth Element Analysis of Geochemical Reference Materials NIST SRM 610, NIST SRM 612, NIST SRM 614, BHVO-2G, BHVO-2, BCR-2G, JB-2, WS-E, W-2, AGV-1 and AGV-2     

Adam J.R. Kent  Benjamin Jacobsen  David W. Peate  Tod E. Waight  Joel A. Baker 《Geostandards and Geoanalytical Research》2004,28(3):417-429

We present data for the concentrations of eleven rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in eleven international geochemical reference materials obtained by isotope dilution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We have analysed both rock powders and synthetic silicate glasses, and the latter provide precise data to support the use of these as reference materials for in situ trace element determination techniques. Our data also provide precise measurements of the abundance of mono-isotopic Pr in both glasses and powders, which allows more accurate constraints on the anomalous redox-related behaviour of Ce during geochemical processes. All materials were analysed in replicate providing data that typically reproduce to better than one percent. Sm/Nd ratios in all these materials also reproduce to better than 0.2% and are accurate to < 0.2% and can thus be used as calibrants for Sm-Nd geochronology. Our analyses agree well with existing data on these reference materials. In particular, for NIST SRM 610, USGS BHVO-2, AGV-1 and AGV-2, our measured REE abundances are typically within < 2% (and mostly 1%) of REE concentrations previously determined by isotope dilution analysis and thermal ionisation mass spectrometry, consistent with the higher degree of precision and accuracy obtained from isotope dilution techniques. Close agreement of results between basaltic glass reference materials USGS BHVO-2G and BCR-2G and the BHVO-2 and BCR-2 powders from which they were created suggests that little fractionation, concentration or dilution of REE contents occurred during glass manufacture.  相似文献   

Capybara (<Emphasis Type="Italic">Hydrochaeris hydrochaeris</Emphasis> rodentia: Hydrochaeridae): A mammalian seagrass herbivore     

Joel C. Creed 《Estuaries and Coasts》2004,27(2):197-200

This note reports an unknown trophic interaction between a mammalian herbivore, the capybara (Hydrochaeris hydrochaeris), and the seagrassRuppia maritima (wigeongrass) and compares the feeding behavior of capybaras to other seagrass grazers. Observations were made in Spring 2002 in the Barra Grande, a small, shallow, moderately stratified, bar-built estuary at Ilha Grande, Rio de Janeiro State, southeast Brazil. The activities of the capybaras were investigated and grazing impacts were quantified in situ. The capybaras were observed feeding onR. maritima during the day and aquatic feeding alternated with periods of feeding on land.R. maritima was the only submerged aquatic vegetation to be consumed by the capybaras. The feeding activity of the capybaras on wige ongrass consisted of alternately diving down to theR. maritima then surfacing; the capybaras spent a significantly greater amount of time under water. In the area where the capybaras foraged 18.1% of the seagrass meadow showed recent grazing scars. Vegetation of recently and not recently grazed areas were compared. Grazing scars, which were slightly elongated, were not completely devoid ofR. maritima but presented reduced standing crop: canopy height, shoot density, and shoot, rhizome, and root biomass were reduced in grazed areas. The grazing patterns observed in capybaras resembled those previously reported in the sirenia, mammals that include two seagrass-eating species.  相似文献   

The impact of urban areas on the deposition of air toxics to adjacent surface waters: A mass budget of PCBs in Lake Michigan in 1994     

John Offenberg  Matt Simcik  Joel Baker  Steven J. Eisenreich 《Aquatic Sciences - Research Across Boundaries》2005,67(1):79-85

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The role of Pan-African structures in intraplate seismicity near the termination of the Romanche fracture zone, West Africa     

Kodjopa Attoh  Larry Brown  Joel Haenlein 《Journal of African Earth Sciences》2005,43(5):111

The distribution of epicenters of both historic earthquakes and recent seismic events in southeastern Ghana, compiled from local and teleseismic networks, show strong correlation with the Pan-African structures onshore and indicate an alignment with disruptions on seismic sections offshore. The seismic reflection sections reveal basement structures of the external zone of the Pan-African Dahomeyide orogen and these structures can be traced to offsets of shelf strata and seabottom reflectors, providing direct evidence, for the first time, for neotectonic activity that may be responsible for seismicity in the area. The deep structure of the external zone consists of moderately-dipping reflectors inferred to represent high-strain zones in the variably deformed margin of the West African craton. Taken together, the available data suggest that active tectonics in this intraplate environment may involve inversion of the Pan-African thrust structures but that this activity is apparently not related to reactivation of the nearby Romanche Fracture Zone.  相似文献   

Setting seagrass depth, coverage, and light targets for the Indian River Lagoon system, Florida     

Joel S. Steward  Robert W. Virnstein  Lori J. Morris  Edgar F. Lowe 《Estuaries and Coasts》2005,28(6):923-935

Seagrass protection and restoration in Florida’s Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs. These programs require, the establishment of management targets indicative of seagrass recovery and health. We used three metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the IRLS’s spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments. Our method consisted of two steps: mapping the union of seagrass coverages from all availabe mapping years (1943, 1986, 1989, 1992, 1994, 1996, and 1999) to delineate wherever seagrass had been mapped and determining the distribution of depth limits based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively.Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using a 10-yr record of light data (1990–1999) and the union coverage depth limit distributions from the most temporally stable seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 ± 17% of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions, is 20 ± 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 ± 13%). Variation in depth limits and light requirements, is probably due to factors other than light that influence the depth limit of seagrasses (e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data sets and can be applied to other estuaries where grass beds are routinely monitored and mapped.  相似文献