The expansion of the giant filamentary shell, DEM 171, in the Magellanic Bridge

The giant filamentary shell, DEM 171, is found to be expanding at approximately 37 km s⁻¹. A supernova and stellar wind origin are both explored as possible causes for the expanding shell. A stellar wind origin would imply a mass-loss rate of the order of 10⁻⁵ M_⊙ yr⁻¹, indicating that it could be caused by a Wolf–Rayet star. A number of blue stars are found to lie within the shell and one is identified as a Wolf–Rayet candidate.     

A demographic approach to monitoring the health of coral reefs

Inshore coral reefs adjacent to the wet tropics in North Queensland, Australia, are regularly exposed to flood plumes from coastal river systems. Changes in the nature of these plumes have been linked to the declining health of coral reefs in the region. The effect of flood plumes on the health of inshore corals was investigated by quantifying aspects of the demography of populations of corymbose and digitate Acropora at three groups of Island reefs along a gradient of exposure and decreasing water quality (High Island >Frankland's >Fitzroy). The size-structures of colonies, the rates of sexual recruitment, and the growth and survival of juveniles, all varied among the Island reefs. Juvenile and adult sized colonies were far more abundant at the Fitzroy Island reefs, than at the High or Frankland Island reefs that were more exposed to flood plumes. Additionally, there were up to eight times as many sexual recruits at the Fitzroy Island reefs, compared with the High Island reefs. However, the rates of growth and survival of the juvenile sized corals at the Fitzroy Island reefs were lower than at the more exposed reefs. The comparatively low abundance of adult corals at the exposed reefs is most likely due to their histories of disturbance from crown-of-thorns and coral bleaching, but the lack of subsequent recovery due to their low levels of larval recruitment. If a stock-recruitment relationship is typical for these groups of reefs, then the low rates of recruitment may be linked to the low density of adult colonies. Alternately, direct or indirect effects of chronic exposure to poor water quality may have resulted in less suitable substrata for larval settlement. We discuss these results and provide examples of how information about population structure and dynamics can be used in simple matrix models to quantify the current and future health of populations of corals under various scenarios.     

Full-glacial paleosols in perennially frozen loess sequences, Klondike goldfields, Yukon Territory, Canada

Perennially frozen loess deposits in the Klondike goldfields include paleosols formed in full-glacial environments, correlated by Alaskan distal tephra with Marine Isotope Stages (MIS) 2 and 4. Patterns of organic and inorganic carbon and clay distribution, microstructures, and profile morphologies indicate that soil formation occurred in a base-rich environment in which organic matter accreted predominantly as root detritus. At sites approximately 20 km apart, the expression of cryoturbation and ice wedge development decreases in strength upward in loess-paleosol sequences correlated with MIS 4, suggesting increasing aridity. Configurations of cryoturbation features and ice-wedge thaw unconformities, the presence of numerous ground squirrel burrows, and an absence of peat accumulation suggest that these substrates were predominantly well-drained, with active layers of equal or greater thickness than in modern soils on similar sites in the west-central Yukon. Some characteristics of these paleosols are similar to those of modern steppe and tundra soils, consistent with plant macrofossil evidence for local ecological diversity during full-glacial conditions in eastern Beringia.     

Fluorescence spectra of Titan tholins: in-situ detection of astrobiologically interesting areas on Titan's surface

We report the three-dimensional fluorescence spectra of Titan tholins in water and acetonitrile, and separate some of the fluorescent components of tholins using two-dimensional thin layer chromatography. In acetonitrile, tholins exhibit a broad fluorescence with a maximum at 471 nm, and an excitation maximum at 410 nm. The fluorescence spectrum of a water extraction displays a more complicated spectrum with multiple peaks. TLC results indicate the presence of at least three distinct fluorescent species. In addition, we obtained the two-dimensional fluorescence spectrum of tholins in water ice at 77 K, close to the surface temperature of Titan. The fluorescence of tholins in a 77 K ice matrix is red-shifted in comparison to a water solution, and undergoes a further red-shift when the water solution is heated prior to freezing. These results suggest that a simple fluorescence probe could be used on the surface of Titan to identify sites where tholins have been mixed with water, and possibly reveal information about the extent of heating the tholin-water mixture has undergone. This would be useful for a future mission with the goal of examining the organic chemistry of Titan.     

Stable carbon and oxygen isotopic evidence for late Pleistocene to middle Holocene climatic fluctuations in the interior of southern Africa

Stable carbon and oxygen isotope analyses of ungulate grazers from four archaeological sites located in different environs within the Caledon River Valley have provided a relatively well‐dated proxy palaeoenvironmental and palaeoclimatic sequence for the period between 16 000 and 6000 calendar (cal.) yr BP. Within the overall trend towards hot mid‐Holocene temperatures and a summer rainfall pattern, stable carbon isotope results show that there were three periods when growth season temperatures were cool enough for C₃ grasses to be present: 16 000–14 000; 10 200–9600, and 8400–8000 cal. yr BP. Similar trends were recorded in stable oxygen isotope values, reflecting shifts in either temperature or available moisture. Although having a similar pattern to that of the lower altitude site, sites situated in foothills and montane portions of the valley consistently maintained lower temperatures until the mid‐Holocene altithermal. At this time growth season temperatures warmed sufficiently for a 100% C₄ grassland to expand in altitude from the warmer low lying localities. In relation to present understanding of synoptic and global climatic patterning, these findings suggest that the early to middle Holocene transition was not a gradual warming trend, but rather it was marked by a series of climatic fluctuations. Of particular note is the possible global, rather than regional, occurrence of the 8200 cal. yr BP ‘event’. Copyright © 2002 John Wiley & Sons, Ltd.