Shear-wave splitting and implications for mantle flow beneath the MELT region of the east pacific rise

Shear-wave splitting across the fast-spreading East Pacific Rise has been measured from records of SKS and SKKS phases on the ocean-bottom seismometers of the Mantle Electromagnetic and Tomography (MELT) Experiment. The direction of fast shear-wave polarization is aligned parallel to the spreading direction. Delay times between fast and slow shear waves are asymmetric across the rise, and off-axis values on the Pacific Plate are twice those on the Nazca Plate. Splitting on the Pacific Plate may reflect anisotropy associated with spreading-induced flow above a depth of about 100 km, as well as a deeper contribution from warm asthenospheric return flow from the Pacific Superswell region.     

Sensitivity of boreal forest carbon balance to soil thaw

We used eddy covariance; gas-exchange chambers; radiocarbon analysis; wood, moss, and soil inventories; and laboratory incubations to measure the carbon balance of a 120-year-old black spruce forest in Manitoba, Canada. The site lost 0.3 +/- 0.5 metric ton of carbon per hectare per year (ton C ha-1 year-1) from 1994 to 1997, with a gain of 0.6 +/- 0.2 ton C ha-1 year-1 in moss and wood offset by a loss of 0.8 +/- 0.5 ton C ha-1 year-1 from the soil. The soil remained frozen most of the year, and the decomposition of organic matter in the soil increased 10-fold upon thawing. The stability of the soil carbon pool ( approximately 150 tons C ha-1) appears sensitive to the depth and duration of thaw, and climatic changes that promote thaw are likely to cause a net efflux of carbon dioxide from the site.     

The brown dog tick (Rhipicephalus sanguineus) on an imported dog

Abstract

Extract

Sir, — We wish to record the presence of the tick Rhipicephalus sanguineus on a dog imported from Australia. This tick is mainly parasitic on dogs although on rare occasions it has been collected from non-canine hosts (Roberts, 1965 Roberts, F. H. S. 1965. The taxonomie status of the species of the genera Rhipicephalus (Koch) and Boophilus (Curtice) occurring in Australia. Aust. J. Zool., 13: 491–523.  [Google Scholar]). Experimentally it has been shown capable of transmitting a wide variety of serious diseases but its role as a natural vector of many of them is unknown. In Australia it has been demostrated as being naturally infected with Coxiella burnetii (Smith, 1942 Smith, D. J. W. 1942. Studies on the epidemiology of Q Fever. Aust. J. exp. Biol. med. Sci., 20: 295–296.  [Google Scholar]) and is recorded from all continents and some oceanic islands lying between latitudes 50°N and 36°S (Roberts, 1970 Roberts, F. H. S. 1970. Australian ticks, 87–87. CSIRO.  [Google Scholar]). Auckland falls within this boundaries and therefore it is not unreasonable to suggest that R. sanguineus could become established in New Zealand.     

Demonstration of a herpesvirus from piglets with lesions of Aujeszky's disease in New Zealand

Extract

Sir, — Four suckling piglets have been examined at this laboratory from a Taranaki herd in which sudden death, chorea and convulsions were the clinical features.     

Breeding for tolerance to beet-cyst eelworm Heterodera schachtii Schm. in sugarbeet

Summary Successive mass selections were made in sugarbeet varieties (Beta vulgaris L.) and in B. vulgaris × B. maritima L. hybrids for tolerance to wilting caused by beet-cyst eelworm attack. The selected lines showed improved tolerance to wilting, but no evidence of resistance to eelworm infection was demonstrated. By repeated back-crossing of the selected lines with the commercial varieties and concurrent selection root yield could be improved without substantially decreasing the tolerance to eelworm attack. These results indicate that tolerance is partly conditioned by complete and incomplete dominant genes.