Projective ordination by SIMCA: A dynamic strategy for cost-efficient environmental monitoring around offshore installations

A method for environmental monitoring using benthic species profiles as input is developed in this work. The method, referred to as projective ordination, utilises local principal component modelling (SIMCA) to obtain a cross-validated model which spans the natural variation in a region around offshore oil-producing installations. The borderline between regions with disturbed and non-disturbed species communities is subsequently decided from the residual distribution. This distribution is used to design an approximate F-test for assessing whether a community at a particular sampling location is disturbed or not. If so, the nature of the disturbance is determined by projecting the data on the PC model.Projective ordination utilises information from previous surveys to define the permissible variation in species communities, i.e. the limit of the natural variation. In addition, the method is dynamic, in a sense that the sampling locations may vary from survey to survey.Furthermore, our analysis shows that the customary number of replicate samples per station can be reduced. Modelling with only four randomly chosen replicates out of the complete set of five for each sampling location, does not affect the model significantly. On the other hand, taking only 3 replicates into account leads to significant divergences.A model based on the 1990 and 1993 surveys at the Statfjord field is presented as an example of the technique.     

A Sample-Freezing Drive Shoe for a Wire Line Piston Core Sampler

Loss of fluids and samples during retrieval of cores of saturated, noncohesive sediments results in incorrect measures of fluid distributions and an inaccurate measure of the stratigraphic position of the sample. To reduce these errors, we developed a hollow drive shoe that freezes in place the lowest 3 inches (75 mm) of a 1.88-inch-diameter (48 mm), 5-foot-long (1.5 m) sediment sample taken using a commercial wire line piston core smapler. The end of the core is frozen by piping liquid carbon dioxide at ambient temperature through a steel tube from a bottle at the land surface to the drive shoe where it evaporates and expands, cooling the interior surface of the shoe to about - 109°F (- 78°C). Freezing a core end takes about 10 minutes. The device was used to collect samples for a study of oil-water-air distributions, and for studies of water chemistry and microbial activity in unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota. Before freezing was employed, samples of sandy sediments from near the water table sometimes flowed out of the core barrel as the sampler was withdrawn. Freezing the bottom of the core allowed for the retention of all material that entered the core barrel and lessened the redistribution of fluids within the core. The device is useful in the unsaturated and shallow saturated zones, but does not freeze cores well at depths greater than about 20 feet (6 m) below water, possibly because the feed tube plugs with dry ice with increased exhaust back-pressure, or because sediment enters the annulus between the core barrel and the core barrel liner and blocks the exhaust.     

Chemical constraints on the petrogenesis of mildly alkaline lavas from Vestmannaeyjar,Iceland: the Eldfell (1973) and Surtsey (1963–1967) eruptions

The Vestmannaeyjar archipelago is composed of alkalic lavas erupted at the southern end of the active, southward propagating, Eastern Volcanic Zone. Recent eruptions include the most primitive (Surtsey) and most evolved (Eldfell) compositions found in this area. We studied time-stratigraphic sample suites from both eruptions to characterize the magmatic environment of Vestmannacyjar. All samples are nearly homogeneous in radiogenic isotopic ratios (⁸⁷Sr/⁸⁶Sr 0.70304 to 0.70327;¹⁴³Nd/¹⁴⁴Nd 0.51301 to 0.50307;²⁰⁶Pb/²⁰⁴Pb 18.96 to 19.18;²⁰⁷Pb/²⁰⁴Pb 15.50 to 15.53;²⁰⁸Pb/²⁰⁴Pb 38.47 to 38.76; KH Park and A Zindler, in preparation). Compositional trends of lavas from the two eruptions are not consistent with fractionation in a near-surface environment, but indicate rather moderate pressure evolution of small magma batches. At Eldfell, mugearite lavas can be modeled by 30% closed-system fractional crystallization of olivine+plagioclase+clinopyroxene+Fe–Ti oxides from parental hawaiite. The phase proportions are consistent with an experimentally determined moderate pressure (8 kbar) cotectic in mildly alkaline systems (Mahood and Baker 1986). Compositional variations of Surtsey lavas can be modeled by crystallization of clinopyroxene+olivine+plagioclase+minor Fe–Ti oxides. The presence of sodic plagioclase megacrysts and clinopyroxene with 8 wt% Al₂O₃ in xenoliths from Surtsey lavas are consistent with a moderate pressure fractionation event. Based on major-element and REE data the most primitive Surtsey lavas formed by small degrees of melting of a lherzolite source. The alkaline nature of Vestmannaeyjar lavas is not the result of assimilation of lower crustal melts (cf. Oskarsson et al. 1985; Steinthorsson et al. 1985).     

The early history of the earth—moon system

The study of the Earth—Moon system provides the connecting link between purely astronomical studies of the origin of the solar system and its planets, and geophysical and biological studies of the evolution of the Earth's geology, its surface features, atmosphere and hydrosphere, and of terrestrial life.A coherent account is presented here, based on the hypothesis that the Moon formed separately and was later captured by the Earth. The adoption of this hypothesis, together with the observed depletion of iron in the Moon, sets some important constraints on the development of condensation and agglomeration phenomena in the primeval solar nebula, which led to the formation of planetesimals, and ultimately to planets.Capture of the Moon also defines a severe heating event within the Earth, whereby its kinetic energy of rotation is largely dissipated internally by the mechanism of tidal friction. From this melting event dates the geologic, atmospheric, and oceanic history of the Earth. An attempt is made to account for the unique development of the Earth, especially in relation to Mars and Venus, its neighboring planets.     

Why image Uranus?

A review of visual and photographic data on the appearance of Uranus indicates that markings frequently occur on the planet. The featureless images obtained by the Stratoscope II balloon telescope are possibly the result of the broad spectral band that was used. Difference, or ratio, picture techniques which enhance color or polarization contrasts are proposed as the basis for Uranus imagery on the '79 MJU Mission. An attempt is made to predict the aspect of Uranus at high resolution on the basis of what is currently known about the Uranus atmosphere. The planet should have no visible surface, the tops of a thick NH₃ cloud layer should exist near the 3–4 bar level and there is a very uncertain possibility of a thin, broken CH₄ cloud layer near 300 mbar. It is proposed that if the choice of an MJU imaging system rests on Uranus objectives alone (i.e., excluding the satellites) then the system should emphasize photo-polarimetric observations between 5500 and 10 000 Å. If, however, the total mission objectives are the basis of choice then a high resolution imaging system, based on the Mariner Jupiter-Saturn system, but including a solid state silicon array would be a more suitable choice. The performance of such a system at Uranus is analyzed.     

Comets,ice ages,and ecological catastrophes

A total mass 10¹⁴ g added to the Earth's upper atmosphere in the form of small particles of high albedo for visual wavelengths would produce an inverse greenhouse effect, shielding ground level from sunlight but permitting infrared radiation from the ground to escape into space. Such a mass of small particles might be acquired by the Earth in a close approach to a cometary nucleus. Ice ages and ecodisasters, such as that which occurred 6.5×10⁷ years ago, could arise from the effects of such an addition of small particles.Supported in part by the National Science Foundation [PHY76-83685] at Caltech.     

Near-infrared spectra of the Galilean satellites: Observations and compositional implications

We have obtained reflectivity spectra of the trailing and leading sides of all four Galilean satellites with circular variable filter wheel spectrometers operating in the 0.7- to 5.5-μm spectral interval. These observations were obtained at an altitude of 41,000 ft from the Kuiper Airborne Observatory. Features seen in these data include a 2.9-μm band present in the spectra of both sides of Callisto; the well-known 1.5-μm and 2.0-μm combination bands and the previously more poorly defined 3.1-μm fundamental of water ice observed in the spectra of both sides of Europa and Ganymede; and features centered at 1.35 ± 0.1, 2.55 ± 0.1, and 4.05 ± 0.05 μm noted in the spectra of both sides of Io. In an effort to interpret these data, we have compared them with laboratory spectra as well as synthetic spectra constructed with a simple multiple-scattering theory. We attribute the 2.9-μm feature of Callisto's spectra primarily to bound water, with the product of fractional abundance of bound water and mean grain radius in micrometers equaling approximately 3.5 × 10^?1 for both sides of the satellite. The fractional amounts of water ice cover on the trailing side of Ganymede, its leading side, and the leading side of Europa were found to be 50 ± 15, 65 ± 15, and 85% or greater, respectively. The bare ground areas on Ganymede have reflectivity properties in the 0.7- to 2.5-μm spectral region comparable to those of Callisto's surface and also have significant quantities of bound water, as does Callisto. Interpretation of the spectrum for the trailing side of Europa is complicated by magnetospheric particle bombardment which causes a perceptible broadening of strong bands, but the ice cover on this side is probably comparable to that on the leading side. These irradiation effects may be responsible for much of the difference in the visual geometric albedos of the two sides of Europa. Minor, but significant, amounts of ferrous-bearing material (either ferrous salts or alkali feldspars but not olivines or pyroxenes) account for the 1.35-μm feature of Io. The two longer wavelength bands are most likely attributable to nitrate salts. Ferrous salts and nitrates can jointly also account for much of the spectral variation in Io's visible reflectivity, thereby eliminating the need to postulate large quantities of sulfur. The absence of noticeable features near 3-μm wavelength in Io's spectra leads to upper bounds of 10% on the fractional cover of water and ammonia ice and 10^?3 on the relative abundance of bound water and hydroxylated material on Io. The two sides of Io have similar compositions. We suggest that the systematic increase in fractional water ice cover from Callisto to Ganymede to Europa is bought about by variations in efficiencies of recoating the satellite's surface by interior water brought to the surface, and by the deposition of extrinsic dust. The most important component of the latter is debris, derived from the outer irregular satellites of Jupiter, which impacts the Galilean satellites at relatively low velocities. Europa has the largest water ice cover because its crust is thinnest and thus the frequency of water recoating is the greatest, and because it is farthest from the sources of low-velocity dust. While models which depict Io's surface as consisting primarily of very fine-grained ice are no longer viable, we are unable to definitively distinguish between the salt assemblage and alkali feldspar models. The salt model can better account for Io's reflectivity spectrum from 0.3 to 5 μm, but the absence of appreciable quantities of bound water and hydroxylated material may not be readily understood within the context of that model.     

Cometary brightness variation and nucleus structure

The Bobrovnikoff and Beyer photometric data for more than 100 comets have been analyzed for intrinsic brightness variations,before andafter perihelion, according to ther ^–n law, wherer is solar distance. The Oort and Schmidt classification of comet age has been extended and applied with Marsden's new determinations of inverse semi-major axis, 1/a, original. All classes of comets withP>25 yr show statistically the same value ofn after perihelion. New comets approach perihelion with smaller values ofn and older comets with increasingly larger values (Table II). For comets ofP<25 yr,n is larger and erratic.A physical interpretation involves the quick loss of a frosting of super-volatile materials from new comets; then, for all comets, the development of an insulating crust after perihelion. The crust also includes globs of meteoroidal and icy material. The crust tends to be purged near perihelion but generally to grow in a spotty fashion with cometary age. The orientation of the axes of rotating comets is shown to be an important unknown factor in cometary brightness variations. A speculation is made concerning the axis of rotation for C/Kohoutek, 1973 XII.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May 1978.This research has been supported by Grant No. NSG 7082 from the U.S. National Aeronautics and Space Administration.     

Comparative studies on the dispersal of the Great Ramshorn (Planorbarius corneus L.): A modelling approach

The Great Ramshorn (Planorbarius corneus L.) is a frequent inhabitat of central European wetlands and floodplains. The dispersal capacity of P. corneus, as a key factor to survival, was analysed using different computer model approaches: a general equation-based model and an individual-based model. Both models came to different conclusions on the maximum covered distances of P. corneus-individuals. The parametrisation of the models were based on detailed laboratory measurements and field experiments performed with specimen of the fen wetland system of Rhin-Havelluch (Brandenburg, North-East Germany). Based on the results of the statistical analysis, the dispersal behaviour could be depicted in the equation-based model as a random walk which implied a relatively regular resource utilisation in long-term simulations.Depicting the dispersal qualities of P. corneus with a highly resolved individual-based model showed distinct local aggregations clusters of the snail-individuals. As a consequence, the resource utilisation was less regularly in the long-term simulations for the individual-based model than it was in the equation-based model. Another characteristic of the individual-based representation was that in the case of several consecutive move steps and based on the autocorrelation of the data the P. corneus-individuals could use a wider area of space.The data from the empirical measurements of short-term dispersal observations of single individuals were integrated within the different model extrapolations. This made it possible to discuss the long-term consequences, like the large dispersal range of the individuals and the spatial distribution of the population in the plane, for the persistence of P. corneus in a real landscape.