Spatial and temporal variations of hydrogen peroxide in Gulf of Mexico waters

Hydrogen peroxide concentrations in the Gulf of Mexico were measured on two cruises in May and August, 1982, in a variety of locations ranging from oligotrophic oceanic stations to highly productive coastal sites. Measurements were made using a fluorescence decay technique. Depth profiles of H₂O₂ exhibit surface maxima of 1?2 × 10^?7 mol L^?1 and decreasing concentrations with depth. Peroxide concentrations decreased only slightly or were invariant with depth in the mixed layer but decreased sharply to below the limit of detection (5 × 10^?9 mol L^?1) in the region of the pycnocline at the base of the mixed layer. Surface concentrations were generally highest in coastal regions but did not vary by more than a factor of three among all stations studied. There was a marked diel variation in peroxide profiles, with the highest values occurring during the late afternoon, and the lowest values occurring at dawn. Diel variations were more pronounced in coastal surface waters than in oligotrophic waters. The observations are consistent with photochemical formation of H₂O₂ by photooxidation of dissolved organic matter. However, other formation pathways, such as biological formation or atmospheric deposition, cannot be ruled out at this point.     

Rare earth element abundances in rocks and minerals from the Fiskenaesset Complex,West Greenland

Rare earth element (REE) abundances determined by activation analysis in rocks, plagioclase and mafic separates from the Fiskenaesset Complex are presented together with data on major and trace elements in the minerals. The REE data for the rocks and plagioclases are distinct from those of many other anorthositic complexes and the abundances are some of the lowest recorded for plagioclase from terrestrial anorthosites. The bulk and trace element compositions of the Fiskenaesset plagioclases show a number of similarities to those of lunar plagioclases. The plagioclases show a positive Eu anomaly of about 10 and a depletion in the heavy REE relative to the light ones. The mafic separates are enriched in the heavy REE relative to the light ones, and show no Eu anomaly except in one sample with a positive anomaly not attributable to plagioclase contamination. It is estimated, from experimental partition coefficient data, that the REE pattern in the magma at an early stage of fractionation was La (17×) to Lu (0.7× chondrites) with a possible positive Eu anomaly. This highly fractionated REE pattern may be attributed to partial melting of a garnet-bearing source.     

Anelastic damping of acoustic and seismic pulses

The basic question of the linearity or non-linearity of the seismic attenuation mechanism has not yet been conclusively answered. Alternative linear theories are compared with recent measurements of the degeneration of pulse shape in attenuating media. Only a theory due to Azimiet al., (1968) survives the test. The assumption of linearity conflicts with observations of stress-strain hysteresis loops which always have cusped (pointed) ends, but no successful hysteretic model of pulse attenuation has emerged. Observations of the independence of attenuations of superimposed waves are critical to the linearity assumption, but all superposition observations so far are defective in that they have considered the superposition of phase-uncorrelated waves, whereas only the superposition of phase-correlated waves is a true test of superposition.     

Approximation of terrestrial lead isotope evolution by a two-stage model

Parameters on which models for terrestrial lead isotope evolution are based have recently been revised. These parameters are the isotopic composition of troilite lead, the age of the meteorite system and the decay constants of uranium and thorium. As a result, the normal single-stage model in which the age of the earth is taken to be that of the meteorite system is now untenable.A two-stage model has been constructed which permits the age of the earth to be that of the meteorite system and which also yields good model ages for samples of all ages. The new model postulates that lead developed initially from a primordial composition assumed to be that of troilite lead beginning at 4.57 b.y. ago. The average values of ²³⁸U/²⁰⁴Pb and ²³²Th/²⁰⁴Pb for this first stage were 7.19 and 32.21 respectively. At approximately 3.7 b.y. ago differentiation processes brought about the conditions of a second stage, in which ²³⁸U/²⁰⁴Pb ≈ 9.74 and ²³²Th/²⁰⁴Pb ≈ 37.19 in those portions of the earth which took part in mixing events, giving rise to average lead.     

Heavy metals in organic phases of river and estuarine sediment

Analysis of sediments taken from various levels in the lightly polluted River Blyth in Northumberland shows that quite high concentrations of metals can be accumulated in sediments.     

Some considerations in management of computer-processable files of geological data

Many sets of data in the natural sciences have a hierarchical structure that is either inherent in the data or that is imposed on them during collection. These data structures can be defined using mathematical set-theory notation. If data from two or more computer-processable files are accessed simultaneously, the application of operations of set union and intersection leads to emergence of certain criteria which must be adhered to when managing data files using a generalized, database management system. One of the situations in which these principles come into play is illustrated by the merging of two computer-processable files of geotechnical data, the data for both files having been derived from the same source but structured differently.     

An inexpensive sampler for obtaining bulk sediment cores

A large-volume core sampler for sediment—muck substrates is described. The sampler can acquire a discrete sediment core of 10 cm in diameter and up to 1.5 m long. Such samplers are needed to collect the volume necessary for analysis of sediments for contaminants, bulk density, or radioactive dating. The sampler consists of a 1- to 2-m length of PVC pipe mounted below a threaded metal pipe air exhaust—intake assembly. This assembly is quick-connected to standard threaded lengths (300 cm) of water pipe (2 cm diam) or electrical conduit so that bottom sediments in water depths of up to 10 m can be sampled. The core sampler is hand-operated and pushed into bottom sediments from a boat. It does not have to be triggered remotely because of the one-way modified check valve in the air exhaust—intake assembly. After the sampler is extracted from the sediment, the extension handle can be quickly removed for ease of sampler handling, and the core can be extruded from the PVC tube by air pressure.Contribution of the National Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Oxford, Mississippi 38655, U.S.A.     

Sediment accumulation and its effects on a Mississippi River oxbow lake

Recent sediment accumulation rates were measured in Moon Lake, a large (10.1 km²) Mississippi River oxbow lake in northwestern Mississippi. Moon Lake, which receives channeled inflow from an intensively cultivated soybean, rice, and cotton watershed (166 km²) and limited overland flow from surrounding lands, exhibited depositional patterns that were associated with (1) points of inflow, (2) flow patterns, and (3) lake morphology. From 1954 to 1965, 70 percent of the lake bottom experienced accumulation rates greater than 2 cm/yr. Accumulation rates exceeded 4 cm/yr in areas of delta formation. Changes in cropping systems during the 1960s, from cotton to soybeans and rice which require less cultivation, resulted in significantly (a = 0.01) less sediment accumulation during the period 1965- 1982 when 86 percent of the lake averaged less than 2 cm/yr sediment deposition. If current sediment accumulation rates continue, open water habitat in the lake will be reduced by only 3 to 7 percent during the next 50 years.Contribution of the Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Oxford, MS 38655     

The distribution of rare phenolic type compounds in wild and cultivated wheats

In 14 species of Aegilops, four species of Triticum and two species of Hordeum, a complex of rare phenolic compounds was found and showed quantitative differences between the wild and domestic species. There was a dramatic reduction in the cultivars to about 5% of the amount of these phenolic constituents. In the wild species these phenolic compounds may act as important germination regulators, such as water-dissolving germination inhibitors which may act as 'rain gauges'. This is especially important for the germination at the appropriate time in species inhabiting arid regions or deserts.