Cape Lyot Hα-heliograph results

The Lyot H-heliograph at the Royal Observatory, Cape of Good Hope was in almost daily operation from March 12, 1958 to December 31, 1965. From the records obtained, a definitive list of 2907 flares was compiled, their properties analyzed, and the results presented herein.The data on East-West distribution of activity, although inconclusive, shows an asymmetry of flare activity with 56.5% of the flares West of the central meridian; this is partially due, however, to an inhomogeneous density distribution in the filtergrams.Flare distribution with respect to heliographic longitude, association with spot types and number of spots in the group are also discussed. The frequency of flare areas, rise times, and durations are examined as is their relationship to distance from the disk centre.     

Comparison of benthic invertebrate assemblages at Spartina alterniflora marshes reestablished after an oil spill and existing marshes in the Arthur Kill (NY/NJ)

In January 1990, an oil spill damaged salt marshes along the banks of the Arthur Kill (New York and New Jersey, USA). In the years following the spill, Spartina alterniflora seedlings were planted at a number of the oil damaged sites and successfully reestablished at these sites. In 1996, the National Marine Fisheries Service began a study to compare the benthic invertebrate assemblages at the reestablished S. alterniflora marshes to those at nearby existing marshes in the Arthur Kill. Oligochaetes, nematodes, and the small tube-building polychaete, Manayunkia aestuarina were the dominant taxa in the study. Significant differences were found in the abundances of all invertebrate individuals, oligochaetes, and nematodes between the September and May sampling times but not between reestablished and existing marshes. Although benthic invertebrate community structure was similar at reestablished and existing marshes three to four years after planting, the functional similarity of these marshes was not assessed in this study.     

A milliarcsecond-resolution image of the OH masers in G34.3+0.2

We present measurements of the distribution of the OH masers at 1665 and 1667 MHz towards the cometary ultracompact H  ii region in the complex G34.3+0.2. The results are based on observations made in both senses of circular polarization with a very long baseline interferometry (VLBI) array having an angular resolution of 5×20 mas². 38 maser features are identified in the region. 33 of these lie on an arc at the edge of the cometary H  ii region. Five are located in a cluster offset toward the north-east by 3 arcsec, and are probably associated with an independent ultracompact H  ii region. There is a velocity gradient of 30 km s⁻¹ pc⁻¹ across the arc. We identify five Zeeman pairs and determine that the magnetic field varies between 1 and 7 mG, but is always directed away from the Earth.
The OH masers may arise in clumps in a shell of gas in a bow shock caused by the motion of the exciting star through the molecular cloud. The stand-off distance and the thickness of the shocked shell are roughly consistent with those predicted by such a bow-shock model. Also, the position of the exciting star(s), as estimated from the focus of the parabolic bow shock, closely matches that of the peak emission from the cometary H  ii region. However, the north–south velocity gradient in the ionized material remains difficult to explain in the context of the bow-shock model.     

Zircon-scale insights into the history of a Supervolcano,Bishop Tuff,Long Valley,California, with implications for the Ti-in-zircon geothermometer

Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE³⁺:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720°C for zircon rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage in its evolution. There is also no compelling evidence for punctuated heat ± chemical influxes during the intermediate stages of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir by—or zircon entrainment in—a less evolved melt from the one in which the zircons had previously resided.     

The influence of flood frequency, geomorphic setting and grazing on plant communities and plant biomass on a large dryland floodplain

Plant communities on semi-arid floodplains are ecologically important and support a diverse local and regional fauna and often pastoral economies. Water resource development may affect these communities and economies by decreasing water supply; determining the nature of these relationships is not straightforward because of the complex nature of plant responses to wetting and possible interactions with other drivers. We investigate the effects of reduced wetting on vegetation by examining spatial patterns in plant communities and above-ground herbaceous plant biomass across a flood frequency gradient, geomorphic settings and grazing exclosures. Community and biomass changes were also examined over time in relation to wetting events. The results demonstrate the importance of wetting on plant communities across timescales. At longer timescales, flood frequency influences community composition; at shorter timescales, wetting increase plant biomass and has a secondary influence on community composition. Plant biomass is also influenced in the short-term by grazing, but there is little influence of grazing on community composition. Soil nutrients do not vary systematically across the floodplain and have little influence on species distributions. We conclude that reduced water availability due to water resource development will result in reduced productivity in the short-term and community composition changes in the long-term.