40Ar39Ar dating of glauconites: Measured 39Ar recoil loss from well-crystallized specimens

Nine glauconite samples with relatively high K concentrations and which appear to be well crystallized using normal X-ray diffraction techniques have been studied using the ${}^{40}\text{Ar}{}^{39}\text{Ar}$ method. The glauconite ${}^{40}\text{Ar}{}^{39}\text{Ar}$ apparent ages exceed their KAr, RbSr and, in most cases, stratigraphic ages by substantial amounts. ${}^{40}\text{Ar}{}^{39}\text{Ar}$ release spectra sometimes yield plateaus but these apparent ages have no geological significance. The results indicate that ³⁹Ar is lost by recoil from mineral grains during neutron irradiation, consistent with previously reported observations. The amount of ³⁹Ar loss was measured by isotope dilution for four samples and varied from 29% to 17%. In contrast, radiogenic ⁴⁰Ar is quantitatively retained during irradiation. The very fine blades which make up glauconite grains yield the mineral susceptible to large amounts of ³⁹Ar loss and unsuitable for ${}^{40}\text{Ar}{}^{39}\text{Ar}$ dating.     

Faecal indicators and pathogens in selected New Zealand waterfowl

Freshly excreted droppings from Canada geese (n=80), black swans (n=80), ducks (n=80) and gulls (n=80) were collected from sites around New Zealand. The droppings were enumerated for Escherichia coli, enterococci and Salmonella spp., and for the presence/absence of Cryptosporidium spp. Overall prevalence of E. coli and enterococci in samples was 95% and 94%, respectively. Cryptosporidium spp. was detected in 2% of the samples, whereas no Salmonella spp. were detected in the survey. Preliminary estimates of daily microbial outputs suggest that ducks will produce the highest loadings of E. coli and enterococci per bird, whereas Canada geese will produce the highest loadings of Campylobacter spp. per bird. This study provides the first set of indicator and pathogen counts for one of the largest sources of diffuse faecal contamination of natural waters in New Zealand.     

The other 93%: trophic cascades,stressors and managing coastlines in non-marine protected areas

Abstract

This paper reviews interactions involving stands of macroalgae on rocky reefs, and presents new data on changing sea surface temperatures (SSTs), as a contribution to the celebration of the fiftieth anniversary of the Leigh Marine Laboratory (LML) of the University of Auckland. The focus is on trophic interactions involving predators, sea urchins and large brown algae, particularly trophic cascades. Of the 369 publications arising from work at LML, 40 have been on key aspects of these trophic interactions. Quantitative investigations of the structure of kelp bed communities and mechanistic studies involving manipulative field-based experiments, essentially a bottom-up perspective based on habitats and key species, dominated the research through the 1980s. From the mid-1990s onwards, the focus was more on marine reserves and a hierarchical, top-down perspective of community structure, with a particular focus on the role of predatory fish, and marine reserves as a tool of management. I discuss these models of community structure of kelp beds within the wider context of the New Zealand nearshore zone, the varying biogeographic regimes around the coastline, diffuse stressors and the changing nearshore climate. I show there appears to have been a significant warming trend in SST in northeast and northwest New Zealand over the past 30 years. I conclude that a trophic effects model is unlikely to apply to much of the coastline of New Zealand, and that a model involving multiple effects, including bottom-up forces, environmental and climatic influences, species' demographics, and catchment-derived sedimentation is more appropriate for kelp communities over most of the country. New management models are needed to safeguard marine resources and the services they provide.     

Ionospheric plasma acceleration at Mars: ASPERA-3 results

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on-board the Mars Express spacecraft (MEX) measured penetrating solar wind plasma and escaping/accelerated ionospheric plasma at very low altitudes (250 km) in the dayside subsolar region. This implies a direct exposure of the martian topside atmosphere to solar wind plasma forcing leading to energization of ionospheric plasma. The ion and electron energization and the ion outflow from Mars is surprisingly similar to that over the magnetized Earth. Narrow “monoenergetic” cold ion beams, ion beams with broad energy distributions, sharply peaked electron energy spectra, and bidirectional streaming electrons are particle features also observed near Mars. Energized martian ionospheric ions (O⁺, O⁺₂, CO⁺₂, etc.) flow in essentially the same direction as the external sheath flow. This suggests that the planetary ion energization couples directly to processes in the magnetosheath/solar wind. On the other hand, the beam-like distribution of the energized plasma implies more indirect energization processes like those near the Earth, i.e., energization in a magnetized environment by waves and/or parallel (to B) electric fields. The general conditions for martian plasma energization are, however, different from those in the Earth's magnetosphere. Mars has a weak intrinsic magnetic field and solar wind plasma may therefore penetrate deep into the dense ionospheric plasma. Local crustal magnetization, discovered by Acuña et al. [Acuña, M.J., Connerey, J., Ness, N., Lin, R., Mitchell, D., Carlsson, C., McFadden, J., Anderson, K., Rème, H., Mazelle, C., Vignes, D., Wasilewski, P., Cloutier, P., 1999. Science 284, 790-793], provide some dayside shielding against the solar wind. On the other hand, multiple magnetic anomalies may also lead to “hot spots” facilitating ionospheric plasma energization. We discuss the ASPERA-3 findings of martian ionospheric ion energization and present evidences for two types of plasma energization processes responsible for the low- and mid-altitude plasma energization near Mars: magnetic field-aligned acceleration by parallel electric fields and plasma energization by low frequency waves.