Improved dithiocarbamate/oxine solvent extraction method for the preconcentration of trace metals from seawater using metal exchange back-extraction

A rapid single extraction procedure using dithiocarbamate complexing agent, a di-isobutyl ketone (DIBK) organic phase and Hg exchange back-extraction is described for the simultaneous quantitative preconcentration of Cd, Co, Cu, Fe, Ni, Pb and Zn in seawater. An 8-hydroxyquinoline (oxine) extraction technique is also presented for the subsequent determination of Mn using the same reagents and operating system. The proposed method gave quantitative spike recoveries for all metals and was in excellent agreement with the certified results for CASS-3 marine reference seawater. Blanks and detection limits are in the low ppt range. The method gives a preconcentration factor of 72 for an 80-ml sample, facilitating the analysis of pristine seawater samples.     

Sensitivity of direct global warming potentials to key uncertainties

The concept of global warming potential was developed as a relative measure of the potential effects on climate of a greenhouse gas as compared to CO₂. In this paper a series of sensitivity studies examines several uncertainties in determination of Global Warming Potentials (GWPs). For example, the original evaluation of GWPs for the Intergovernmental Panel on Climate Change (IPCC, 1990) did not attempt to account for the possible sinks of carbon dioxide (CO₂) that could balance the carbon cycle and produce atmospheric concentrations of CO₂ that match observations. In this study, a balanced carbon cycle model is applied in calculation of the radiative forcing from CO₂. Use of the balanced model produces up to 21% enhancement of the GWPs for most trace gases compared with the IPCC (1990) values for time horizons up to 100 years, but a decreasing enhancement with longer time horizons. Uncertainty limits of the fertilization feedback parameter contribute a 20% range in GWP values. Another systematic uncertainty in GWPs is the assumption of an equilibrium atmosphere (one in which the concentration of trace gases remains constant) versus a disequilibrium atmosphere (one in which the concentration of trace gases varies with time). The latter gives GWPs that are 19 to 32% greater than the former for a 100 year time horizons, depending upon the carbon dioxide emission scenario chosen. Five scenarios are employed: constant-concentration, constant-emission past 1990 and the three IPCC (1992) emission scenarios. For the analysis of uncertainties in atmospheric lifetime (τ) the GWP changes in direct proportion toτ for short-lived gases, but to a lesser extent for gases withτ greater than the time horizontal for the GWP calculation.     

Comparison of physical and chemical properties of maceral groups separated by density dradient centrifugation

Eight coals have been selected for study of the physical and chemical properties of the maceral group . The density-gradient centrifugation technique was employed to affect maceral group separation. The maximum reflectance method of Ting and Lo was used for estimating the reflectance of very small coal particles. The reflectograms were used to characterize the separated maceral fractions. The density, elemental composition, reflectance, NMR parameters of aromaticity, protonated aromatic carbon content and ƒ_stuggereda^stuggeredH of the maceral groups were compared. Variations in the aromatic structure of the maceral groups are discussed as well as the observation that ƒ_stuggereda and ƒ_stuggereda^stuggeredH change with particle density.     

Suspended sediment discharge of the Susquehanna river to Northern Chesapeake Bay, 1966 to 1976

Between 1966 and 1976, the Susquehanna River at Conowingo, Maryland, discharged approximately 50 million metric tons of suspended sediment to Northern Chesapeake Bay. About 40 million metric tons were discharged in two floods associated with hurricanes: Agnes (24–30 June 1972) and Eloise (26–30 September 1975). In the six years with complete records and no major floods, the Susquehanna River discharged 0.9±0.3 million metric tons of suspended sediment per year at Conowingo Dam. Aout 50 to 60 percent of the annual sediment discharge is usually floods, suspended sediment transport at Harrisburg, Pennsylvania, exceeds sediment discharge at Conowingo, Maryland, probably due to sediment deposition in the lower river and behind three hydroelectric dams.     

Degrees of melting in mantle diapirs and the origin of ultrabasic liquids

The temperature and degree of melting in an upwelling diapir in the mantle may be considerably less than that anticipated from an adiabatic cooling curve. Several geological and thermodynamic parameters may be incorporated to produce a more realistic melting model in diapirs. The latent heat of fusion of mantle material is the greatest buffer on degrees of melting. Models are presented which suggest that an uprising diapir intersecting the anhydrous solidus of mantle material at 50 kbars may be only 29% melted on reaching the surface. A diapir initiated at 100 kbars may be 69% melted. These are maximum values. These calculations imply that the generation of komatiitic liquids by diapiric uprise alone demands that the diapir originate at depths in excess of 300 km. Melting of mantle with an irregular geotherm is preferred for the origin of these liquids.     

Cluster analysis of marine sediments and waste deposits in New York bight

Cluster analysis of some chemical characteristics of marine sediments and associated waste deposits in the New York Bight reveals the existence of four cluster facies. Cluster facies I is the sediment containing dredged wastes from New York Harbor. Cluster facies II is the widespread sand and gravel deposit of the continental shelf. Cluster facies III is the finergrained material in the Hudson Channel and the material accumulated in the sewage sludge disposal area. Cluster facies IV is not easily identified; it may correspond to some relict sedimentary feature in the area. Editor's Note: Ali is now with the Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543; Gross is now with Chesapeake Bay Institute. The Johns Hopkins University, Baltimore, Maryland 21218.     

Geology of the platanares geothermal area, Departamento de Copán, Honduras

The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids.     

Abundance of larval rainbow smelt (Osmerus mordax) in relation to the maximum turbidity zone and associated macroplanktonic fauna of the middle St. Lawrence estuary

We tested the hypothesis that the distribution and retention of larval smelt (Osmerus mordax) in the middle estuary of the St. Lawrence River is related to the maintenance of other planktonic organisms in the maximum turbidity zone (MTZ). We documented the horizontal and vertical distribution of larval smelt, macrozooplankton, and suspended particulate matter over four tidal cycles at each of three stations located along the major axis of the turbid upstream portion of the middle estuary. During summer, the turbid, warm, and low salinity waters of the two upstream stations were characterized byNeomysis americana, Gammarus sp. (principallyG. tigrinus), larval smelt,Mysis stenolepsis, andCrangon septemspinosus. The more stratified and less turbid waters of the downstream station were characterized by a coastal marine macrozooplanktonic community and the almost total absence of smelt larvae. Within the MTZ, the distribution ofN. americana coincided with the zone of longest average advective replacement times (null zone). Smelt larvae were distributed further upstream within the MTZ thanN. americana. Overall, larger larvae were distributed further upstream than smaller larvae. The relationship between turbidity and larval density at a specific time was weak (due to resuspension of sediments but not larvae), but the mechanism responsible for producing higher residence times for both sediment and larvae on a longer term basis appears the same. The daily movement and skewed nature of the null zone (due to the general cyclonic circulation of the middle estuary) defines a geographic zone over which the larval smelt population oscillates and remains despite the mean downstream velocities over the water column.