Tephra layers in the Byrd Station ice core and the Dome C ice core, Antarctica and their climatic importance

Volcanic glass shards from tephra layers in the Byrd Station ice core were chemically analyzed by electron microprobe. Tephra in seven layers have similar peralkaline trachyte compositions. The tephra are believed to originate from Mt. Takahe, on the basis of their chemical similarity to analyzed rocks from Mt. Takahe and because dated rock samples from the volcano are younger than 250,000 years old. Glass shards from 726 m deep in the Dome C ice core, which is 2400 km from Byrd Station, are composed of peralkaline trachyte and may have also been derived from Mt. Takahe. The tephra could have resulted from eruptions which were triggered by increased ice loading during the late Wisconsin glaciation. Preliminary grain size data suggest the eruptions were only minor and they were unlikely to have instantaneously altered global climate as have explosive eruptions in the tropics. Nevertheless, the effect of this localized volcanic activity upon the Antarctic energy budget warrants further investigation.     

The Rio Grande fracture zone in the western South Atlantic and its tectonic implications

A broad zone of linear, mappable basement structures is observed north and northeast of the Rio Grande Rise in the South Atlantic Ocean. These structures lie along the same flow line as the Sa?o Paulo Ridge, the Florianopolis High, and onshore lineaments, suggesting that they all comprise the same tectonic trend: the Rio Grande fracture zone. The morphology developed along this fracture zone during the early opening of the South Atlantic Ocean formed a barrier to open ocean circulation during the Aptian and allowed the formation of extensive evaporite deposits to the north of it.     

Bioaccumulation and histopathological effects of oil on a stony coral

Colonies of the shallow-water Caribbean coral Manicina areolata incorporated petroleum hydrocarbons into their tissues during exposure to water accommodated fractions of No. 2 fuel oil for three months. This contamination was not removed after depuration periods of up to two weeks. Although these corals remained alive, evidence of pathological responses was found which included impaired development of reproductive tissues, degeneration and loss of symbiotic zooxanthellae, and atrophy of mucous secretory cells and muscle bundles.     

Geometry and pressure-temperature significance of the kyanite-sillimanite isograd in the Mica Creek area,British Columbia

Late Precambrian and Lower Paleozoic metapelitic rocks near Mica Creek, British Columbia, range in metamorphic grade from biotite zone to sillimanite zone. The kyanite-sillimanite isograd was established after phase 2 folding but was deformed by phase 3 folding. Topographic relief of about 2 km, combined with phase 3 folding, permits reasonably precise determination of the geometry of the isogradic surfaces. The effects of phase 3 folding have been accounted for and the isobaric surfaces at the time of metamorphism are inferred to have been dipping gently. Using the kyanite-sillimanite experimental phase diagram, intersection of the isobars and the isograd permits estimates of differences in temperature and pressure along a cross section. These estimates are about 400 bars and 20° C. Mineral geothermometry (garnet-biotite) and geobarometry (garnetplagioclase-Al ₂SiO₅-quartz) does not provide a fine enough resolution to detect these predicted differences.     

Origin of Archean migmatites from the Gwenoro Dam area,Zimbabwe-Rhodesia

Archean migmatites in the vicinity of Gwenoro Dam in Zimbabwe-Rhodesia are composed chiefly of trondhjemite gneiss (TR), mafic tonalite (MT), amphibolite (AM), leuco-trondhjemite veins (LTR), and pegmatites. The gneiss is intruded in nearby areas with small tonalite plutons (TN). Geochemical model studies together with field relationships are consistent with the following model for migmatite production: AM is produced by partial melting of a partly depleted ultramafic parent in which neither garnet nor amphibole remain in the residue; TR and TN are produced by partial melting of undepleted to variably depleted amphibolite in which garnet does not remain in the residue; MT is produced by mixing of plagioclase-rich TR with AM; and LTR represents the solid residue after fractional crystallization of TR.     

Coupled substitutions in the tourmaline group

Statistical analysis of 136 natural tourmaline compositions from the literature reveals the presence and extent of coupled substitutions involving several cations and structural sites. In schorls and dravites these are a dehydroxylation type substitution (1) (OH)^–+R²⁺ = R³⁺+O^2– and an alkali-defect type substitution (2) R⁺+R²⁺ = R³⁺+, Al³⁺ being the predominant R³⁺ action. Substitution (1) which represents solid solution towards a proton-deficient end-member, R⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃ Si₆O₁₈O₃(OH), accounts for three times as much of the observed compositional variability as does (2) which represents substitution toward a hypothetical alkali-free end-member, (R ₂ ²⁺ R³⁺) R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄. The occurrence of both of these substituions produces intermediates between end-member schorl/ dravite, R⁺ R ₃ ²⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈(OH)₄, and a new series within the tourmaline group, R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x (OH)_1+x.In addition to dehydroxylation type, 2(OH)^–+Li⁺ = R³⁺+20^2–, and possibly alkali-defect type, 2R⁺+Li⁺ = R³⁺+2, substitutions, a third type Li⁺+O^2– = (OH)^–+, occurs in the elbaites giving rise to Li-poor, proton-rich species. All three substitutions serve to reduce the Li-content of natural elbaite which, as a result, does not attain the composition of the ideal end-member, Na(Li_1.5Al_1.5)Al₆(BO₃)₃Si₆O₁₈(OH)₄. Substitution from elbaite and schorl/dravite toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x is very extensive and may be complete.Substitution toward R _1–x ⁺ R ₃ ³⁺ R ₆ ³⁺ (BO₃)₃Si₆O₁₈O_3–x(OH)_1+x results in improved local charge balance. The mean deviation from oxygen charge saturation is at a maximum in end-member schorl, dravite and elbaite. Substitutions (1) and (2) progressively decrease but substitution (1) does so more effectively, which may explain its predominance in nature. However, alkali-defective end-members appear to be unstable regardless of . Substitution (3) in the elbaites cannot be discussed on the basis of charge balance considerations at present due to the lack of structural information on proton-rich species.     

Fe2+ -F avoidance in silicates

Fe²⁺-F avoidance, reported in the literature in micas and amphiboles, can be accounted for by crystal field theory. The crystal field splitting parameter, Δ_O, of Fe²⁺ octahedrally coordinated to F^? is significantly smaller than its value when (OH)^? is the coordinating anion. Thus, the presence of Fe²⁺ is not favored at sites where F^? substitutes for (OH)^? due to smaller crystal field stabilization energy.     

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.     

Toxic dinoflagellates and tidal power generation in the Bay of Fundy,Canada

The incidence of Paralytic Shellfish Poisoning along the eastern seaboard of America has increased and spread during the last decade. One of the core areas for Paralytic Shellfish Poison (PSP), a poison that is derived from toxic dinoflagellates, is centred on the Bay of Fundy. It is in the upper reaches of the Bay of Fundy that a proposal has been made to construct a tidal power generation plant; this project would have a considerable effect on the water circulation, tidal regime and sedimentation characteristics of the Bay of Fundy and Gulf of Maine. Alterations such as these to the hydrography of this area may lead to changes in the occurrence of toxic dinoflagellates and the associated patterns and intensity of PSP.     

Estimating the Surface Wind Speed Over Drifting Pack Ice from Surface Weather Charts

Routine surface wind speed data, vital for the study of drifting pack ice, are not available for the polar oceans. Over sea, it has been demonstrated by Hasse that estimates of surface wind speed may be obtained from the geostrophic wind speed using linear formulae. Comparing estimated with observed data for six sites in Canada, it is found that the formulae may also be applied to obtain estimates of surface wind speed over pack ice.