Radium in Arctic surface water

The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8-1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years.

Radionuclides measured in surface water samples from the South Atlantic

In the nutrient-rich Southern Ocean, Fe is a vital constituent controlling the growth of phytoplankton. Despite much effort, the origin and transport of Fe to the oceans are not well understood. In this study we address the issue with geochemical data and Nd isotopic compositions of suspended particle samples collected from 1997 to 1999 in the South Atlantic Sector of the Southern Ocean. Al, Th, and rare earth element (REE) concentrations as well as 143Nd/144Nd isotopic ratios in acetic acid-leached particle samples representing the lithogenic fraction delineate three major sources: (1) Patagonia and the Antarctic Peninsula provide material with eNd > -4 that is transported toward the east with the polar and subpolar front jets, (2) the south African shelf, although its influence is limited by the circumpolar circulation and wind direction, can account for material with eNd of -12 to -14 adjacent to South Africa, and (3) East Antarctica provides material with eNd of -10 to -15 to the eastern Weddell Sea and adjacent Antarctic Circumpolar Current. For this region we interpret the Nd isotopic evidence in combination with oceanographic/atmospheric constraints as evidence for supply of significant amounts of terrigenous detritus by icebergs.

(Table 1) Deuterium ratios, chloride content and hydrate volume of pore water and hydrate meltwater from ODP Site 164-996

Site 996 is located above the Blake Diapir where numerous indications of vertical fluid migration and the presence of hydrate existed prior to Ocean Drilling Program (ODP) Leg 164. Direct sampling of hydrates and visual observations of hydrate-filled veins that could be traced 30-40 cm along cores suggest a connection between fluid migration and hydrate formation. The composition of pore water squeezed from sediment cores showed large variations due to melting of hydrate during core recovery and influence of saline water from the evaporitic diapir below. Analysis of water released during hydrate decomposition experiments showed that the recovered hydrates contained significant amounts of pore water. Solutions of the transport equations for deuterium (d2H) and chloride (Cl-) were used to determine maximum (d2H) and minimum (Cl-) in situ concentrations of these species. Minimum in situ concentrations of hydrate were estimated by combining these results with Cl- and d2H values measured on hydrate meltwaters and pore waters obtained by squeezing of sediments, by the means of a method based on analysis of distances in the two-dimensional Cl- d2H space. The computed Cl- and d2H distribution indicates that the minimum hydrate amount solutions are representative of the actual hydrate amount. The highest and mean hydrate concentrations estimates from our model are 31% and 10% of the pore space, respectively. These concentrations agree well with visual core observations, supporting the validity of the model assumptions. The minimum in situ Cl- concentrations were used to constrain the rates of upward fluid migration. Simulation of all available data gave a mean flow rate of 0.35 m/k.y. (range: 0.125-0.5 m/k.y.).

A numerical model to simulate sediment transport in the vicinity of coastal structures /

Cover title.

Fresh water-salt water density currents : a major cause of siltation in estuaries /

"April 1957."

A method for estimating long-term erosion rates from a long-term rise in water level /

"May 1979."

The SPM energy flux method for predicting longshore transport rate /

"June 1980."

Sand ripple growth in an oscillatory-flow water tunnel /

The development of sand ripples in an oscillatory-flow water tunnel was observed in 104 laboratory experiments approximating conditions at the seabed under steady progressive surface waves. The period, T, and amplitude, a, of the water motion were varied over wide ranges. Three quartz sands were used, with mean grain diameters, D = 0.55, 0.21, and 0.18 millimeter. In 24 experiments, with the bed initially leveled, T was reduced until ripples appeared, and their development to final equilibrium form was observed without further change in T. The remaining 80 experiments investigated the response of previously established bed forms to changes in T or a or both. The ripple length, lambda, and height, eta, were measured from photos, except when bed forms were three dimensional.

Relation between immersed weight and volume rates of longshore transport /

As presently used, the immersed weight rate, I sub l, is the volume rate, Q, of longshore transport, multiplied by a constant. For use in engineering problems, I sub l must be converted back to the equivalent Q. The I sub l formulation may be important where the unit weight of sand differs significantly from the unit weight of sand at the open-coast sites contributing data to the design curve. Increase in void ratio may result in a 10- to 20-percent increase in actual (as compared to predicted) shoaling volumes where sand accumulates in protected water. Void ratio should be measured in field studies of longshore transport.

An in-situ permeable reactive barrier for the treatment of hexavalent chromium and trichloroethylene in ground water /

"Project Officer, Robert W. Puls, Subsurface Protection and Remediation Division."

Soil erosion and sediment transport dynamics in the Blue Creek Watershed, Pike County, Illinois /

"IEPA/WPC/83-004."

Proceedings of the U.S. Nuclear Regulatory Commission Thirteenth Water Reactor Safety Research Information Meeting, held at National Bureau of Standards, Gaithersburg, Maryland, October 22-25, 1985 /

Includes bibliographies.

Importance of water for Archaean granitoid petrology: a comparative study of TTG and potassic granitoids from Barberton Mountain Land, South Africa

A new model for Archaean granitoid magmatism is presented which reconciles the most important geochemical similarities and differences between tonalite-trondhjemite-granodiorite (TTG) and potassic granitoids. Trace element abundances reveal a strong arc magmatism signature in all studied granitoids from Barberton Mountain Land. Characteristic features include HFSE depletion as well as distinct enrichment peaks of fluid-sensitive trace elements such as Pb in N-MORB normalisation, clearly indicating that all studied granitoids are derived from refertilised mantle above subduction zones. We envisage hydrous basaltic (s.l.) melts as parental liquids, which underwent extensive fractional crystallisation. Distinctive residual cumulates evolved depending on initial water content. High-H2O melts crystallised garnet/amphibole together with pyroxenes and minor plagioclase, but no olivine. This fractionation path ultimately led to TTG-like melts. Less hydrous basaltic melts also crystallised garnet/amphibole, but the lower compatible element content indicates that olivine was also a liquidus phase. Pronounced negative Eu-anomalies of the granitic melts, correlating with Na, Ca and Al, indicate plagioclase to be of major importance. In the context of our model, the post-Archaean disappearance of TTG and concomitant preponderance of granites (s.l.), therefore, is explained with secular decrease of aqueous fluid transport into subduction zones and/or efficiency of deep fluid release from slabs.

Performance of hydrophobic and hydrophilic silica membrane reactors for the water gas shift reaction

In this study, a novel molecular sieve silica (MSS) membrane packed bed reactor (PBR) using a Cu/ZnO/Al2O3 catalyst was applied to the low-temperature water gas shift reaction (WGS). Best permeation results were H-2 permeances of 1.5 x 10(-6) mol(.)s(-1) m(-2) Pa-1, H-2/CO2 selectivities of 8 and H-2/N-2 selectivities of 18. It was shown that an operation with a sweep gas flow of 80 cm 3 min(-1), a feed flow rate of 50 cm(3) min(-1) and a H2O/CO molar ratio of one at 280 degreesC reached a 99% CO conversion. This is well above the thermodynamic equilibrium and achievable PBR conversion. Hydrophilic membranes underwent pore widening during the reaction while hydrophobic membranes indicated no such behaviour and also showed increased H-2 permeation with temperature, a characteristic of activated transport. (C) 2003 Elsevier Science B.V. All rights reserved.