Hydrocarbon gas in sediment from the shelf,slope, and basin of the Bering Sea

Hydrocarbon gases (methane, ethane, ethene, propane, propene, isobutane and n-butane) are present in low concentrations in the top two meters of sediment from the shelf, slope and basin of the Bering Sea. Methane is most abundant and its concentration increases with depth in the sediment. Average concentrations of methane recovered from these sediments are between about 4000 and 5000 nl per 1 of interstitial water. Ethane, ethene, propane and propene are present in almost all samples, but the concentrations of these gases are about two orders of magnitude lower than the concentration of methane. The average ratios of ethane to ethene are usually greater than one in shelf sediment, about one in slope sediment, and usually less than one in basin sediments. These hydrocarbon gases are probably derived from low-temperature chemical and biochemical processes operating at or near the sea-floor. At one location on the shelf, hydrocarbon gases suggest the possibility of petroleum at depth.     

Behavioural effects of mercury on grass shrimp

Subacute exposure (0.05 ppm) to mercuric chloride significantly impairs the conditioned avoidance responses of grass shrimp Palaemonetes pugio Holthuis, when tested in an aquatic avoidance apparatus. Control animals learn to avoid a shock after the onset of a light which followed a period of dark-adaptation. A third group of shrimp, which establish an avoidance curve similar to the controls, quickly lose its ability to avoid being shocked when exposed to mercury in the final days of the experiment. These experiments demonstrate the value of a simple behavioural index for establishing subacute toxicity standards for organisms in aquatic ecocystems.     

Dynamic interaction of seismic activity along rising and sinking edges of plate boundaries

Cumulative and differential cumulative seismic strain release of shallow earthquakes during 1964 through 1972 show significant time-delayed correlation for many of the rises and/or sinks of tectonic plate boundaries for the Atlantic, Indian and Pacific oceans. For the Pacific, time delays are almost exclusively from areas of higher to areas of lower strain release, and could imply viscous stress relaxation along or near the lithosphere—asthenosphere boundary. Seismically determined slip rates for many of the subduction zones during 1964–1972 are lower than those of the preceding part of the century by a factor of 5. The significant correlation between many rises and sinks suggests worldwide interaction and coupling of plate motion.     

A multivariate analysis of planktonic molluscan distribution in the Middle Atlantic Bight

Faunal structure is described for the planktonic molluscs of the Middle Atlantic Bight based on two years of seasonal data from the continental shelf. Collection and taxa groups are constructed using numerical classification and reciprocal averaging ordination. Discriminant analysis is used to relate surface collection groups to physical variables, then taxa group distribution among these collection groups is analyzed by nodal fidelity analysis. The areal distribution of dominant species is presented by season, as is their surface temperature-salinity distribution.Four communities are recognized on the continental shelf. A subarctic community, including Limacina retroversa, Paedoclione doliiformis, and Clione limacina, is advected down the central shelf region from the northeast. A Gulf Stream community of weak vertical migrators, including Limacina trochiformis, Cavolinia longirostris, Creseis conica, Atlanta peroni, and A. gaudichaudi, is introduced onto the shelf in occasional intrusions across the shelf-edge front. A depth-limited warm-water community of strong vertical migrators, including Limacina inflata, L. bulimoides, L. lesueuri, and Cavolinia inflexa is generally confined offshore of the 100-m isobath since the extent of their daily vertical migration is greater than the bottom depths on the continental shelf. A coastal community, including the larvae of Loligo pealei and of Ensis directus is found in coastal water of local origin and is generally confined within a coastal boundary layer.     

Early diagenesis in sediments from the eastern equatorial Pacific,I. Pore water nutrient and carbonate results

Interstitial waters were extracted from cores at three locations in the eastern equatorial Pacific and analyzed for nutrients, dissolved carbonate species, Mn and Fe. From the depth variation in pore water chemistry, we infer that organic matter oxidation reactions occur with depth in the following sequence: O₂ reduction, NO₃^? and MnO₂ reduction, and then ferric iron reduction. From NO₃^? results we infer that O₂ is largely or totally consumed within the top few centimeters of sediment. NO₃^? is completely reduced at a sediment depth of 20 cm at a site near the crest of the East Pacific Rise, but is preserved at levels of 20–30 μmol/kg at 40 cm depth at a Guatemala Basin site.We have calculated the alkalinity for pore water samples assuming ions diffuse according to relative ionic diffusion coefficients, that the stoichiometry of organic matter oxidation reactions is that of “Redfield” organic matter, and that the pore waters are saturated throughout with respect to CaCO₃. The measured alkalinity increase is only about half of the predicted value. The difference is probably a result of either enhanced mixing of the pore water in the top few centimeters of sediments by biological or physical processes, or the occurrence of an inorganic reaction which consumes alkalinity.At depths of oxygen and nitrate reduction in the sediments, the ion concentration product of CaCO₃ is the same, within the analytical error, as the solubility product of Ingle et al. [34] at 1 atm and 4°C. This result indicates CaCO₃ resaturation on pressure change during coring. Where pore water Mn concentrations become measurable, the ion concentration product increases, indicating either supersaturation with respect to calcite or that another phase is controlling the carbonate solubility.     

Scientific objectives of the Solar Mesosphere Explorer mission

The 1981–82 Solar Mesosphere Explorer (SME) mission is described. The SME experiment will provide a comprehensive study of mesospheric ozone and the processes which form and destroy it. Five instruments will be carried on the spinning spacecraft to measure the ozone density and its altitude distribution from 30 to 80 km, monitor the incoming solar ultraviolet radiation, and measure other atmospheric constituent which affect ozone. The polar-orbiting spacecraft will be placed into a 3pm-3 am Sun-synchronous orbit. The atmospheric measurements will scan the Earth's limb and measure: (1) the mesospheric and stratospheric ozone density distribution by inversion of Rayleigh-scattered ultraviolet limb radiance, and the thermal emission from ozone at 9.6 m; (2) the water vapor density distribution by inversion of thermal emission at 6.3 m; (3) the ozone photolysis rate by inversion of the O₂(¹g) 1.27 m limb radiance; (4) the temperature profile by a combination of narrow-band and wide-band measurements of the 15 m thermal emission by CO₂; and, (5) theNO₂ density distribution by inversion of Rayleighscattered limb radiance at 0.439 m. The solar ultraviolet monitor will measure both the 0.2–0.31 m spectral region and the Lyman-alpha (0.1216 m) contribution to the solar irradiance. This combination of measurements will provide a rigorous test of the photochemical equilibrium theory of the mesospheric oxygen-hydrogen system, will determine what changes occur in the ozone distribution as a result of changes in the incoming solar radiation, and will detect changes that may occur as a result of meteorological disturbances.     

Harmonic splines for geomagnetic modelling

Which features of a geomagnetic field model on the surface of the core are really necessary in order to fit, within observational error, the field observations at and above the Earth's surface? To approach this question, we define ‘roughness’ in various ways as a norm on an appropriate Hilbert space of field models which is small when the field is smooth on the core surface. Then, we calculate the model with least norm (the smoothest model) which fits the data, sources outside the core being treated as noise. Sample calculations illustrate the effects of noise, of the choice of norm and of an uneven distribution of observing stations.