Late Quaternary tephra layers around Raoul and Macauley Islands,Kermadec Arc: implications for volcanic sources,explosive volcanism and tephrochronology

A suite of deep‐sea cores were collected along transects up to 100 km across the fore‐arc and back‐arc regions of the predominantly submarine Kermadec arc near Raoul and Macauley islands, southwest Pacific. The cores reveal a macroscopic tephra record extending back >50 ka. This is a significant addition to the dated record of volcanism, previously restricted to fragmented late Holocene records exposed on the two islands. The 27 macroscopic tephra layers display a wide compositional diversity in glass (～50–78 wt% SiO₂). Many tephra layers comprise silicic shards with a subordinate mafic shard population. This could arise from magma mingling and may reflect mafic triggering of the silicic eruptions. Broadly, the glass compositions can be distinguished on diverging high‐K and low‐K trends, most likely arising from different source volcanoes. This distinction is also reflected in the tephra records exposed on Raoul (low‐K) and Macauley (high‐K) islands, the likely source areas. Heterogeneous tephra comprising shards of both high‐ and low‐K affinity, silicic and mafic compositions, and more homogeneous tephra with subordinate outlier shard compositions, are best explained by post‐depositional mixing of separate eruption deposits or contemporaneous eruptions. Evidently, the slow sedimentation rates of the calcareous oozes (～10¹–10² mm ka^?1) were insufficient to adequately separate and preserve closely spaced eruption deposits. This exemplifies the difficulty in assessing eruption frequencies and magmatic trends, and erecting a tephrostratigraphy, using geochemical fingerprinting in such environments. Despite these difficulties, the ca. 5.7 ka Sandy Bay Tephra erupted from Macauley Island can be correlated over a distance of >100 km, extending east and west of the island, showing that the mostly submerged volcanoes are capable of wide tephra dispersal. Hence there is potential for developing chronostratigraphies for the southwest Pacific beyond the region covered by the extensive rhyolite marker beds from the Taupo Volcanic Zone. Copyright © 2011 John Wiley & Sons, Ltd.     

Mid-infrared polarisation and inferred magnetic field direction toward YSOs with outflow

The position angle of mid-infrared polarisation can be directly related to the magnetic field direction projected onto the plane of the sky. Such observations, from both ground and space-based platforms, have been used to investigate the relation between the magnetic field and other “symmetry axes” associated with embedded young stars, such as the interstellar magnetic field, bipolar outflow and disk/toroid axes. Interpretation of the results in terms of hydromagnetic driving mechanisms of bipolar outflow is discussed.     

Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range

Recent sediments of eight small lakes in the northern winter range of Yellowstone National Park were cored to examine stratigraphic records of past changes in limnology and local environment that might be attributed to grazing and other activities of elk, bison, and other large ungulates. Cores of undisturbed sediment were analyzed at close intervals to depths covering the last 100–150 years according to chronologies established by lead-210 dating. Pollen analyses were made to show change in regional vegetation, and diatom and geochemical analyses were made to reveal possible limnological changes resulting from soil erosion and nutrient input from the lake catchments.Variations in sedimentary components prior to establishment of the Park in 1872 indicate some natural variability in environmental factors e.g., erosional inputs in landslide areas west of Gardiner. All lakes had abundant nutrient inputs.After the Park was founded, fire suppression may have been responsible for small increases in pollen percentages of various conifers and Artemisia tridentata (big sagebrush) at different times in different lakes. Perceptible decreases in pollen of willow, aspen, alder, and birch at different times may reflect local ungulate browsing, although drier climatic conditions may have been a factor as well.The most striking manifestation of accelerated erosion in a catchment was found at a lake located beside a road constructed in the 1930s. In contrast to changes at this site, the record of erosion at other lakes is hardly perceptible. Changes in sediment-accumulation rates seen at most sites result from redistribution of sediment within the lake after initial deposition.In the century following Park establishment, the abundance of planktonic diatoms relative to benthic taxa varies among lakes and may reflect differential nutrient inputs or changes in lake level. Four of the five lakes analyzed for diatoms show in the last few decades an increase in planktonic relative to benthic species, implying elevated nutrient inputs. The recent flora, however, is similar to that in pre-Park levels which suggests that these lakes have not been perturbed outside their normal range. Increased nutrient supply in recent decades for at least two of the lakes is supported by the geochemical data, which show an increase in biogenic silica and in organic matter.As a whole, our investigation of the sedimentary record does not support the hypothesis that ungulate grazing has had a strong direct or indirect effect on the vegetation and soil stability in the lake catchments or on the water quality of the lakes.     

H2 in molecular shocks: observations from 2 to 12 microns

We present spectroscopy of the molecular shock in the supernova remnant IC 443. The H₂ level populations in IC 443 are nearly identical to Orion Peak 1 (Brand et al. 1988; Parmar et al. 1994) and are consistent with a partially dissociative J-shock. The similarity with Orion suggests the shock processes which dominate the emission in both regions are essentially identical.     

Spaceborne visible and thermal infrared lithologic mapping of impact‐exposed subsurface lithologies at the Haughton impact structure,Devon Island,Canadian High Arctic: Applications to Mars

Abstract— This study serves as a proof‐of‐concept for the technique of using visible‐near infrared (VNIR), short‐wavelength infrared (SWIR), and thermal infrared (TIR) spectroscopic observations to map impact‐exposed subsurface lithologies and stratigraphy on Earth or Mars. The topmost layer, three subsurface layers and undisturbed outcrops of the target sequence exposed just 10 km to the northeast of the 23 km diameter Haughton impact structure (Devon Island, Nunavut, Canada) were mapped as distinct spectral units using Landsat 7 ETM+ (VNIR/SWIR) and ASTER (VNIR/SWIR/TIR) multispectral images. Spectral mapping was accomplished by using standard image contrast‐stretching algorithms. Both spectral matching and deconvolution algorithms were applied to image‐derived ASTER TIR emissivity spectra using spectra from a library of laboratory‐measured spectra of minerals (Arizona State University) and whole‐rocks (Ward's). These identifications were made without the use of a priori knowledge from the field (i.e., a “blind” analysis). The results from this analysis suggest a sequence of dolomitic rock (in the crater rim), limestone (wall), gypsum‐rich carbonate (floor), and limestone again (central uplift). These matched compositions agree with the lithologic units and the pre‐impact stratigraphic sequence as mapped during recent field studies of the Haughton impact structure by Osinski et al. (2005a). Further conformation of the identity of image‐derived spectra was confirmed by matching these spectra with laboratory‐measured spectra of samples collected from Haughton. The results from the “blind” remote sensing methods used here suggest that these techniques can also be used to understand subsurface lithologies on Mars, where ground truth knowledge may not be generally available.     

Coring tips

This commentary is intended as a practical guide for the non-motorized use of piston corers to obtain undisturbed sections of lake sediments. Good recovery is essential for accurate reconstruction of environmental and limnological history. Emphasis is placed on the square-rod piston corer, which is widely used for acquisition of sediment cores in meter-long sections from lakes as much as 30 m deep. Coring platforms for open water can be easily prepared on pairs of boats or canoes or (in water depth up to 15 m) even a single small rubber raft, but firm anchoring is essenial to maintain the vertical position of the casing and to assure re-entry into a single hole. Incomplete recovery on individual drives is not a result of sediment compaction but rather the build-up of friction on the tube interior, by which the core forms a plug that prevents further recovery.Short cores of soft sediment for the study of recent changes in lakes are also best acquired with a piston corer, for a gravity corer without a piston may be subject to the same type of plug formation. In cases in which the structure of the sediment must be preserved (e.g. annual laminations), freezing the sediment in place with a dry-ice solution is the best procedure.