Using geochemistry as a tool for correlating proximal andesitic tephra: case studies from Mt Rainier (USA) and Mt Ruapehu (New Zealand)

Volcanic hazards assessments at andesite stratovolcanoes rely on the assessment of frequency and magnitude of past events. The identification and correlation of proximal and distal andesitic tephra, which record the explosive eruptive history, are integral to such assessments. These tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and age dating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they are interbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recent volcanic record remains unresolved because of the difficulty in identifying proximal tephra. This study investigates the value of geochemical methods in discriminating andesitic tephra. Our dataset comprises petrological and geochemical analyses of tephra that span the late Quaternary eruptive record of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous in composition. Tephra compositions fluctuate widely over short time intervals, and there are no simple or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra geochemistry limits the application of geochemical approaches to tephrostratigraphic studies, beyond a general characterisation useful to provenance assignation. Petrological and geochemical data suggest that the products of andesite systems are inherently variable and therefore intractable to discrimination by simple geochemical methods alone. Copyright © 2006 John Wiley & Sons, Ltd.     

Cluster Observations of the Magnetospheric Low-Latitude Boundary Layer and Cusp during Extreme Solar Wind and Interplanetary Magnetic Field Conditions: II. 7 November 2004 ICME and Statistical Survey

We present a study of the plasma properties inside and dynamics of the low-latitude boundary layer (LLBL)/cusp during the ICME event on 7 November 2004 based on data from the four Cluster spacecraft. The interplanetary magnetic field (IMF) is predominantly strongly northward, up to 50 nT, with some short-duration rotations. The observed LLBL/cusp is very thick (∼6 – 7° invariant latitude (ILAT)) and migrates equatorward with rates of 0.55° and 0.04° ILAT per minute during quick southward IMF rotations and stable northward IMF, respectively. The LLBL/cusp observed by Cluster 1 and Cluster 4 is in a fast transition between different states and is populated by different types of plasma injection, presumably coming from multiple reconnection sites. During a period of extremely northward IMF, signatures of pulsed dual reconnection inside the LLBL/cusp are observed by Cluster 3, suggesting that at least part of the LLBL/cusp is on closed field lines. However, analysis of the ion data implies that the boundary layer is formed in the dawn sector of the magnetosphere and does not slowly convect from the dayside as has been suggested previously. A statistical study of the location of the LLBL/cusp equatorward boundary during the ICME events on 28 – 29 October 2003 and 7 – 10 November 2004 is performed. During extreme conditions the LLBL/cusp position is offset by −7° ILAT from the location under normal conditions, which might be explained by the influence of the high solar wind dynamic pressure. The LLBL/cusp moves equatorward with increasing southward and northward IMF. However, the LLBL/cusp position under strong southward IMF is more poleward than expected from previous studies, which could indicate some saturation in the dayside reconnection process or enhancement of the nightside reconnection rate. The LLBL/cusp position under strong northward IMF is extremely low and does not agree with the location predicted in previous studies. For the events with solar wind dynamic pressure >10 nPa, the LLBL/cusp position does not depend on the solar wind dynamic pressure. This might indicate some saturation in the mechanism of how the LLBL/cusp location depends on the solar wind dynamic pressure.     

The H i opacity of the intergalactic medium at redshifts 1.6 < z < 3.2

We use high-quality echelle spectra of 24 quasi-stellar objects to provide a calibrated measurement of the total amount of Lyα forest absorption (DA) over the redshift range  2.2 < z < 3.2  . Our measurement of DA excludes absorption from metal lines or the Lyα lines of Lyman-limit systems and damped Lyα systems. We use artificial spectra with realistic flux calibration errors to show that we are able to place continuum levels that are accurate to better than 1 per cent. When we combine our results with our previous results between  1.6 < z < 2.2  , we find that the redshift evolution of DA is well described over  1.6 < z < 3.2  as   A (1 + z )^γ  , where   A = 0.0062  and  γ= 2.75  . We detect no significant deviations from a smooth power-law evolution over the redshift range studied. We find less H  i absorption than expected at   z = 3  , implying that the ultraviolet background is  ∼40  per cent higher than expected. Our data appears to be consistent with an H  i ionization rate of  Γ∼ 1.4 × 10⁻¹² s⁻¹  .     

The characteristics and source of laminated mud at Lake Barrine, Northeast Australia

In a small (1 km²) crater lake in the Australian upland tropics (17°15′S, 145°38′E, 721 m a.s.l.), laminated mud has accumulated throughout the past 5 ka. It is limited to a central region below 50–67 m of water where it is protected by a monimolimnion. The contents of the laminae (e.g., total lake products, organic detritus, diatoms, pollen grains, vivianite crystals) distinguish two contrasting types, namely detritus-rich and detritus-poor. Judged against radiocarbon dates over long sequences, these couplets are not annual. Gravimetric, mineralogical and chemical observations on the mud, and on suspended organic and inorganic matter caught through several periods, indicate some diagenetic changes across the mud–water interface. Diatom analyses do not assist in relating mud type to source or period of origin. The most likely mechanism of lamination is that continuous deposition of clay, with small and varied detrital accompaniment, is periodically enhanced by greater detrital input. This occurs in some, but not all, periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights. This leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone. Fine variations in, e.g., diatom content, partly independent of lamination type, probably contain a wealth of detail about the lake’s environmental history.     

Multi-Spacecraft Study of the 21 January 2005 ICME

We examine the near-Earth Interplanetary Coronal Mass Ejection (ICME) apparently related to the intense Solar Energetic Particle (SEP) event of 20 January 2005. Our purpose is to contribute to the understanding of the macroscopic structure, evolution and dynamics of the solar corona and heliosphere. Using Cluster, ACE and Wind data in the solar wind, and Geotail data in the magnetosheath, we perform a multi-spacecraft analysis of the ICME-driven shock, post-shock magnetic discontinuities and ejecta. Traversals by the well-separated near-Earth spacecraft provide a coherent picture of the ICME geometry. Following the shock, the ICME sequence starts with a hot pileup, i.e.,? a sheath, followed by a fast ejecta characterised by a non-compressive density enhancement (NCDE), which is caused essentially by an enrichment in helium. The plasma and magnetic observations of the ejecta are consistent with the outskirts of a structure in strong expansion, consisting of nested magnetic loops still connected to the Sun. Within the leading edge of the ejecta, we establish the presence of a tilted current sheet substructure. An analysis of the observations suggests that the tilted current sheet is draped within the overlying cloud canopy, ahead of a magnetic cloud-like structure. The flux rope interpretation of this structure near L1, confirmed by observations of the corresponding magnetic cloud, provided by Ulysses at 5.3 AU and away from the Sun?–?Earth line, indicates that the bulk of the cloud is in the northwest sector as seen from the Earth, with its axis nearly perpendicular to the ecliptic. This is consistent with the primary direction of travel of the fast halo CME observed at the Sun. Moreover, the NCDE and helium enrichment are consistent with the position near the streamer belt of the flaring active region NOAA 10720 associated with the CME. However, differences between interplanetary and solar observations indicate a large rotation of the erupting filament and overlying arcade, which can be attributed to the flux rope being subject to the helical kink instability.     

Red spruce canopy response to acid fog exposure

The health of red spruce is adversely affected by exposure to acid fog. Epicuticular wax structure over epistomatal chambers, mesophyll membrane calcium and changes in redox state of glutathione are affected in both chamber and field studies and are correlated with leaf exposure to acid fog, but not with soil or total leaf calcium concentrations. Experiments tracking fog deposition under conditions of illumination or darkness, with or without a metabolic inhibitor, support the mechanism of diffusiophoresis linked with photosynthetic gas exchange. Based on deposition pattern and leaf morphology, a stomatal pathway for water and hydrogen ion penetration to leaf interior is proposed. Ecophysiological parameters are discussed in relation to differential sensitivities of red spruce and white pine to ozone and acid fog.