Genetic and meristic variation in black and smooth oreos in the New Zealand exclusive economic zone

Meristic and genetic methods were used to determine the stock relationships of black Allocytus niger (James, Inada & Nakamura, 1988) and smooth oreo Pseudocyttus maculatus (Gilchrist, 1906) in the New Zealand Exclusive Economic Zone (EEZ). Samples were collected from four management areas—OEO 1 (south‐west), OEO 3A (Chatham Rise west), OEO 4 (Chatham Rise east), and OEO 6 (subantarctic) during the 1998 October‐December spawning period. Lateral line scale counts and pyloric caeca counts revealed differences between black oreo samples from OEO 6 and the other three OEO management areas. Lateral line scale counts in smooth oreo showed no significant differences between areas. Genetic analyses of four non‐coding regions of nuclear DNA and mitochondrial (mt) DNA haplotypes in black oreo showed no significant differentiation among the four management areas. Likewise for smooth oreo, genetic analyses of five non‐coding regions of nuclear DNA and mtDNA haplotypes showed no overall regional differentiation, although there was weak evidence at one locus for a difference between OEO 3A and OEO 6. The data do not reject the null hypothesis of a single genetic stock in New Zealand waters, and are typical of marine species with long pelagic juvenile stages.     

Seasonal and topographic variations in porewaters of a southeastern USA salt marsh as revealed by voltammetric profiling†

We report electrochemical profiles from unvegetated surficial sediments of a Georgia salt marsh. In creek bank sediments, the absence of ΣH₂S or FeS_aq and the presence of Fe(III)–organic complexes suggest that Mn and Fe reduction dominates over at least the top ca. 5 cm of the sediment column, consistent with other recent results. In unvegetated flats, accumulation of ΣH₂S indicates that SO₄ ^2- reduction dominates over the same depth. A summer release of dissolved organic species from the dominant tall form Spartina alterniflora, together with elevated temperatures, appears to result in increased SO₄ ^2- reduction intensity and hence high summer concentrations of ΣH₂S in flat sediments. However, increased bioturbation and/or bioirrigation seem to prevent this from happening in bank sediments. Studies of biogeochemical processes in salt marshes need to take such spatial and temporal variations into account if we are to develop a good understanding of these highly productive ecosystems. Furthermore, multidimensional analyses are necessary to obtain adequate quantitative pictures of such heterogeneous sediments.     

Buried scour marks as indicators of palaeo-current direction at the Mary Rose wreck site

A 3-dimensional seismic reflection survey (using a Chirp source) of the excavated Mary Rose wreck site (King Henry VIII's flagship, wrecked in 1545) was conducted in the East Solent, off the south coast of England. The high resolution geophysical survey identified two ‘brightspot' anomalies, buried to a depth of 4–5 m, trending east–west adjacent to the western margin of the excavation hole. These anomalous reflectors are interpreted as infilled palaeo-scour features associated with the wrecking and subsequent degradation of the Mary Rose. The features were previously unrecognized on the site, and to the authors' knowledge this is the first time that such preserved longitudinal palaeo-scour marks have been recognized in the sedimentary record. Implications associated with the preservation and identification of the scour features are discussed.     

Cosmic ray tracks in the Shalka meteorite

Track densities of heavy cosmic rays have been studied in hypersthene crystals taken from seven known depths below a fusion crust in the Shalka meteorite. By comparing these with a theoretical model, a preatmospheric radius of 20 ± 2cm has been estimated for the meteorite, assuming it to have been originally spherical. The fossil track-length distributions show a prominent peak in the region of 12–15 μm; and this has been attributed, on the basis of accelerated-ion calibration experiments, to cosmic ray Fe ions. The value (≥0.38 ± 0.04) of relative abundance of Fe ions to the total Fe-group ions (20 ≤ Z. ≤ 28) found in the cosmic ray flux averaged over the last ～19 m.y. is shown to be broadly similar to those given by present-day measurements.     

Subaqueous,rhyolitic dome-top tuff cones: a model based on the Devonian Bunga Beds,southeastern Australia and a modern analogue

The relics of two Late Devonian subaqueous rhyolitic dome-top tuff and pumice cone successions are preserved in the Bunga Beds outlier of the Boyd Volcanic Complex, southeastern Australia. These cone successions and other rhyolitic volcanics of the Bunga Beds are associated with turbidite and other deep-water massflow sedimentary rocks. The two cone successions have a generally similar stratigraphy. At the base, flow-banded, variably autobrecciated and quench-fragmented rhyolite, representing an intrusive to extrusive dome, is overlain by rhyolitesediment breccia, representing extrusion of the dome through the deep-water sediment pile and resedimentation down its flanks. In the northern cone succession an overlying, succession of bedded pumiceous crystal-rich to crystal-poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone. An overyling debris flow deposit represents degradation of part of the cone. The topmost unit, a stratified pumice succession, is thought to represent another cone-building eruptive phase, and is separated from the underlying strata by a major slide surface. The southern cone succession contains less tuff and abundant pumice, and is also terminated by a debris-flow deposit, indicating cone degradation. A modern analogue for the inferred eruptive style and sequence is the 1953–1957 rhyolite eruption that formed the Tuluman Island lava-tuff cone complex in the Bismarck Sea. The eruptions were often cyclical consisting of an initial inferred submarine-lava-forming stage, passing into a pumicecone-forming stage, in some cases a subaeriallava-forming stage, and a final stage, following the cessation of volcanism, during which the cones collapsed gravitationally or were destroyed by wave erosion. Using observations from both the Tuluman Island eruptions and the preserved stratigraphies of the Devonian tuff cones, a dynamic model is proposed for the formation of subaqueous rhyolitic dome-top tuff and pumice cones.     

The fission track records of the Estherville,Nakhla and Odessa meteorites

Investigation of fossil charged-particle track densities in various mineral phases of three meteorites—Estherville, Nakhla and Odessa—coupled with U content determination, has led to the evaluation of various contributions to the total fossil track density, including those due to the spontaneous fission of ²³⁸U and ²⁴⁴Pu. A fission-track age for Estherville of around 4 × 10⁹ yr is found, which is thought to reflect slow cooling of the parent body. A Pu track excess of (106 ± 9): 1 over the spontaneous fission of ²³⁸U is found in Odessa diopside, which is larger than may be allówed on a simple ‘continuous synthesis’ model for the production of heavy elements prior to solar system formation. Possible explanations for this value are discussed, including fractionation of Pu relative to U. No detectable U was found in Nakhla diopside, and a measurable contribution of track densities from the fission of superheavy elements is ruled out on the basis of track-length measurements and laboratory calibration with Fe ions.