Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface   总被引：3，自引：0，他引：3  

John Widdows  Mary D. Brinsley  Peter N. Salkeld  Mike Elliott 《Estuaries and Coasts》1998,21(4):552-559

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m^?2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m^?2 h¹) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m^?2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s^?1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.  相似文献   

Ground-Water Lake Relationships and Ground-Water Quality in the Sand Plain Province of Wisconsin—Nepco Lake     

Robert J. Karnauskas  Mary P. Anderson 《Ground water》1978,16(4):273-281

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Thermal alteration experiments on organic matter in recent marine sediment—II. Isoprenoids     

Raphael Ikan  Mary Jo Baedecker  Isaac R. Kaplan 《Geochimica et cosmochimica acta》1975,39(2):187-194

Several isoprenoid compounds were isolated from a heat-treated marine sediment in the southern California continental shelf (from Tanner Basin) which were not present in the original sediment. Among the compounds identified were: phytol, dihydrophytol, C₁₈-isoprenoid ketone, phytanic and pristanic acids, C₁₉- and C₂₀-monoolefins, and the alkanes 2,6,10-trimethylpentadecane, pristane and phytane. The significance and possible routes leading to these compounds is discussed.  相似文献   

Thermal alteration experiments on organic matter in recent marine sediment—III. Aliphatic and steroidal alcohols     

Raphael Ikan  Mary Jo Baedecker  Isaac R Kaplan 《Geochimica et cosmochimica acta》1975,39(2):195-203

Recent sediments from Tanner Basin (off southern California) and Bandaras Bay (in Gulf of California) have been analyzed for normal, isoprenoid and steroidal alcohols using chromatographic (column, GLC, TLC), and spectroscopic (u.v., i.r., MS) methods, prior to and after heat-treatment (from 65 to 150°C). Normal saturated alcohols (C₁₄-C₂₄) and monounsaturated alcohols (C₂₂-C₂₄) were identified, as well as the isoprenoid alcohols, phytol and dihydrophytol.Two series of sterols (Δ⁵ and Δ⁷) were found in Tanner Basin, and Δ⁵-sterols and triterpenes, in Bandaras Bay sediment. Sterols from both sediments contained the corresponding stanols.  相似文献   

Some thermodynamical and microphysical aspects of monsoon clouds     

A Mary Selvam  A S Ramachandra Murty  R Vijayakumar  S K Paul  G K Manohar  R S Reddy  B K Mukherjee  Bh. V. Ramana Murty 《Journal of Earth System Science》1980,89(2):215-230

The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively. The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment. The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value. The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above. The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand. The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm^?3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona.  相似文献   

Submergence avoidance behavior in the periwinkleLittorina irrorata is not due to threat of drowning     

David F. Bleil  Mary E. Gunn 《Estuaries and Coasts》1978,1(4):267-267

An attempt to establish an LD₅₀ for submergence onLittorina irrorata casts strong doubt on the hypothesis that submergence avoidance behavior is due to the threat of drowning. Predator avoidance is offered as a more plausable hypothesis. Respiration rates of 2.73×10^?3 ml O₂/g body wt./min. for submerged snails and 2.70×10^?2 ml O₂/g body wt./min. for controls were determined.  相似文献   

Archaeomagnetic investigations in Bulgaria: Field-intensity determinations     

Mary Kovachieva 《Physics of the Earth and Planetary Interiors》1977,13(4):355-359

Geomagnetic paleointensity determination have been made by the Thellier method using samples from 27 sites in Bulgaria. The samples include bricks, specimens taken from historic kilns, from prehistoric hearths and the sites of ancient fires. The ages of the samples, which range from about 4500 B.C. to the 19th century A.D., have been determined partly by the ¹⁴C method and partly from archaeological evidence. The (residual NMR)-(induced TRM) diagrams tend to be less linear for the prehistoric samples either due to weathering or because the NRM is not a total TRM.  相似文献   

Creep in geodynamic processes     

U.R. Vetter  R.O. Meissner 《Tectonophysics》1977,42(1):37-54

From the connnection between the homologous temperature T/T_m and the viscosity a stabilization effect at viscosities of about 10²³ poise is achieved for T/T_m = 0.6–0.7. This most probably is the steady-state temperature in the upper mantles of terrestrial planets of similar composition and should be a function of pressure only. Solid-state convection in the (larger) planets is connected with deviations of temperature and viscosity from their steady-state values. Viscosity values are obtained from the uplift data of deglaciated shield areas and from the temperature and strain-rate values of oceanic plate movements. Differences in the homologous temperature of 0.1 between both regions result in differences in viscosity by two orders of magnitude, assuming the crystal size of the material to be equal. The lower viscosity values for oceanic regions may explain the absence of seismicity and the generally faster spreading rates of purely oceanic plates. From the analysis of the uplift data two creep laws are indicated. Also the temperature (T = 0.7 T_m) and the crystal size in the upper mantle (0.1–1 cm) has been obtained from these data. Diffusion creep with a linear relationship between stress and strain rate seems to be important for small stresses, below one bar. This kind of creep apparently exists during the final stage of isostatic uplift and in most parts of the oceanic asthenospheric flow. Dislocation or power-law creep prefers larger stresses like those found in regions of fast uplift, in descending oceanic plates, active plate marginsand perhaps in the depth range of reverse flow.  相似文献   

Currents and sediment transport in the Mississippi Canyon and effects of Hurricane Georges     

Cheryl Burden Ross  Wilford D. Gardner  Mary Jo Richardson  Vernon L. Asper 《Continental Shelf Research》2009,29(11-12):1384-1396

The temporal variability in currents, temperature, and particulate matter concentration were measured in the Mississippi Canyon axis where the thalweg was 300 m deep from May–July and August–November 1998 using current meters, thermographs, a light-scattering sensor, and sediment traps. Canyon sediments were sampled by coring and observed using an ROV video camera. Currents in the upper Mississippi Canyon generally oscillated up/down canyon with diurnal periodicity and were bottom-intensified. Mean current speed at 3.5 mab was approximately 8 cm s^?1 during both deployments, reaching maximum speeds of over 50 cm s^?1 under normal conditions. Based on current velocities, critical bed shear stress for resuspension of canyon-floor sediments was exceeded about 30% of the time during both deployments. In late September, Hurricane Georges passed 150 km NE of the study site, significantly intensifying current velocities, bed shear stress, resuspension, trap fluxes and temperature fluctuations. As the hurricane passed, maximum current speed reached 68 cm^?s and temperature decreased ～7 °C in less than two hours. Critical bed shear stress for sediment resuspension was exceeded approximately 50% of the time during the five days of hurricane influence. Further evidence for sediment resuspension was the five-fold (and perhaps 70–130 fold) increase in trap fluxes and compositional similarities between canyon surface sediment and material collected by traps.  相似文献   

Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories     

Joshua Kurek  Les C. Cwynar  Thomas A. Ager  Mark B. Abbott  Mary E. Edwards 《Quaternary Science Reviews》2009,28(9-10):799-811

Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (～39,000–34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination. Paleotemperature trends reveal substantial differences in the timing of climatic warming following the late Wisconsin at each site, although chronological uncertainty exists. Zagoskin Lake shows early warming beginning at about 21,000 cal yr B.P., whereas warming at Burial Lake begins ～4000 years later. Summer climates during the last glacial maximum (LGM) were on average ～3.5 °C below the modern temperatures at each site. Major shifts in vegetation occurred from ～19,000 to 10,000 cal yr B.P. at Zagoskin Lake and from ～17,000 to 10,000 cal yr B.P. at Burial Lake. Vegetation shifts followed climatic warming, when temperatures neared modern values. Both sites provide evidence of an early postglacial thermal maximum at ～12,300 cal yr B.P. These chironomid records, combined with other insect-based climatic reconstructions from Beringia, indicate that during the LGM: (1) greater continentality likely influenced regions adjacent to the Bering Land Bridge and (2) summer climates were, at times, not dominated by severe cold.  相似文献