Radium and lead-210 in marine barite

Measurements of ²²⁶Ra and ²¹⁰Pb in barite samples separated from different depths of a piston core from the eastern equatorial Pacific are reported. ²²⁶Ra is enriched in the barite as would be expected from the chemistries of Ra and Ba; the ${}^{226}\text{Ra}\text{Ba}$ ratio centers around 1.5 · 10¹⁴ atoms/mole. The results suggest that barite is concentrating Ra at a rate comparable to its decay rate, viz. 5.78 · 10^?3 yr^?1. The gross ²¹⁰Pb depletion with respect to ²²⁶Ra is indicative of ²²²Rn loss due to the smallness of the barite crystals.     

Extreme value estimates for arbitrary bandwidth Gaussian processes using the analytic envelope

A procedure is presented for the estimation of extreme values of stationary Gaussian random processes with arbitrary bandwidths. This approach is based on the analytic envelope defined by the Hilbert Transform; this envelope is Rayleigh distributed regardless of bandwidth. For experimentally derived data that has been converted into digital form, the Hilbert Transform is approximated using algorithms implemented on a digital computer to produce samples of the envelope's time history. Next, the degree of correlation between these envelope samples is taken into account using a method developed from simulation studies of a series of synthetic Gaussian time histories with varying bandwidths. Once this correlation effect has been estimated, the standard methods of order statistics are applied to these samples using the Rayleigh probability density function. Examples of applying this procedure to experimentally derived data are presented.     

Marine mammals from northeast Atlantic: relationship between their trophic status as determined by delta13C and delta15N measurements and their trace metal concentrations

The relationship between trophic position through delta13C and delta15N and trace metal concentrations (Zn, Cd, Cu and Hg) was investigated in the tissues of six marine mammal species from the Northeast Atlantic: striped dolphin Stenella coeruleoalba, common dolphin, Delphinus delphis, Atlantic white-sided dolphin Lagenorhynchus acutus, harbour porpoise Phocoena phocoena, white beaked-dolphin Lagenorhynchus albirostris, grey seal Halichoerus grypus stranded on French Channel and Irish coasts. White-beaked dolphins, harbour porpoises, white-sided dolphins, common and striped dolphins display the same relative and decreasing trophic position, as measured by delta15N values, along both the Irish and French channel coasts, reflecting conservative trophic habits between these two places. Hepatic and renal Cd concentrations were significantly correlated to muscle delta13C and delta15N values while Hg, Zn and Cu did not. These results suggest that Cd accumulation is partly linked to the diet while other factors such as age or body condition might explain Hg, Zn or Cu variability in marine mammals. Combined stable isotope and trace metal analyses appear to be useful tools for the study of marine mammal ecology.     

In situ and satellite observations of the eastward migration of the Western Alboran Sea Gyre

During October 2003 an intensive oceanographic survey (BIOMEGA) was carried out in the Alboran Sea, coinciding with a migration event of the Western Alboran Sea Gyre (WAG). The observations gathered during that cruise constitute the first field evidence of a migrated stage of the WAG. In this work we present the main differences between the 3D hydrodynamic fields observed during BIOMEGA and those corresponding to a WAG located at its usual position. The migration of the gyre was followed by satellite (altimetry and sea surface temperature) imagery. The causes of the gyre migration are explored in terms of the quasi-geostrophic tendency equation, in particular of the dynamics governing scales larger than the Rossby radius of deformation. It is shown that the steady state gyre must be almost equivalent barotropic and that the key process to break down the stationarity would be a density advection at gyre scale. The mechanisms to explain the migration of the WAG proposed by previous authors are discussed in light of the explanation proposed in this work.     

Coping with disaster: Rehabilitating coastal livelihoods and communities

This paper examines lessons from past approaches to natural disasters, as well as early lessons from the post-2004 Asian tsunami rehabilitation, to draw out general principles for rehabilitating livelihoods in poor coastal communities. We contend that avoiding the mistakes of the past requires: (1) a framework for understanding the diversity of coastal people's livelihood strategies and the sources of their vulnerability, (2) a process for designing interventions that build on this understanding in order to strengthen and revitalize coastal communities, including a means of assessing and selecting the most promising livelihood options, and (3) a focus on the longer-term challenge of building future resilience and sustainability in the communities by addressing the root causes of vulnerability.     

Effects of crab–halophytic plant interactions on creek growth in a S.W. Atlantic salt marsh: A Cellular Automata model

The Bahía Blanca Estuary (38° 50′ S, and 62° 30′ W) presents salt marshes where interactions between the local flora (Sarcocornia perennis) and fauna (Chasmagnathus granulatus) generate some kind of salt pans that alter the normal water circulation and condition its flow and course towards tidal creeks. The crab–vegetation dynamics in the salt marsh presents variations that cannot be quantified in a reasonable period of time. The interaction between S. perennis plant and C. granulatus crab is based on simple laws, but its result is a complex biological mechanism that causes an erosive process on the salt marsh and favors the formation of tidal creeks. To study it, a Cellular Automata model is proposed, based on the laws deduced from the observation of these phenomena in the field, and then verified with measurable data within macroscale time units. Therefore, the objective of this article is to model how the interaction between C. granulatus and S. perennis modifies the landscape of the salt marsh and influences the path of tidal creeks. The model copies the basic laws that rule the problem based on purely biological factors.The Cellular Automata model proved capable of reproducing the effects of the interaction between plants and crabs in the salt marsh. A study of the water drainage of the basins showed that this interaction does indeed modify the development of tidal creeks. Model dynamics would likewise follow different laws, which would provide a different formula for the probability of patch dilation. The patch shape can be obtained changing the pattern that dilates.     

The U.S. National 8 m telescope project

The National Optical Astronomy Observatories (NOAO) are planning to buld two 8 m telescopes, one for Mauna Kea, Hawaii, the other for a site in Chile. Optical configurations, primary mirror systems, and the telescope mounting are discussed. A new optical testing method is outlined. The system imaging goal is 0.25 FWHM. Construction could begin in the early 1990's.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation.     

Radiometry of near-earth asteroids

We report 10 micrometers infrared photometry for 22 Aten, Apollo, and Amor asteroids. Thermal models are used to derive the corresponding radiometric albedos and diameters. Several of these asteroids appear to have surfaces of relatively high thermal inertia due to the exposure of bare rock or a coarse regolith. The Apollo asteroid 3103, 1982 BB, is recognized as class E. The Jupiter-crossing Amor asteroid 3552, 1983 SA, is confirmed as class D, but low albedos remain rare for near-Earth asteroids.