The Old Woman,California, IIAB iron meteorite

Abstract– The Old Woman meteorite, discovered in March 1976 by two prospectors searching for a fabled lost Spanish gold mine in mountains ～270 km east of Los Angeles, has achieved the status of a legend among meteorite hunters and collectors. The question of the ownership of the 2753 kg group IIAB meteorite, the second largest ever found in the United States (34°28′N, 115°14′W), gave rise to disputes involving the finders, the Bureau of Land Management, the Secretary of the Department of the Interior, the State of California, the California members of the U.S. Congress, various museums in California, the Smithsonian Institution, and the Department of Justice. Ultimately, ownership of the meteorite was transferred to the Smithsonian under the powers of the 1906 Antiquities Act, a ruling upheld in a U.S. District Court and a U.S. Court of Appeals. After additional debate, the Smithsonian removed a large cut for study and curation, and for disbursement of specimens to qualified researchers. The main mass was then returned to California on long‐term loan to the Bureau of Land Management’s Desert Discovery Center in Barstow. The Old Woman meteorite litigation served as an important test case for the ownership and control of meteorites found on federal lands. The Old Woman meteorite appears to be structurally unique in containing both hexahedral and coarsest octahedral structures in the same mass, unique oriented schreibersites within hexahedral areas, and polycrystalline parent austenite crystals. These structures suggest that different portions of the meteorite may have transformed via different mechanisms upon subsolidus cooling, making the large slices of Old Woman promising targets for future research.     

Co‐seismic deformation and post‐glacial slip rate along the Magallanes‐Fagnano fault,Tierra Del Fuego,Argentina

Across the extreme south of Patagonia, the Magallanes‐Fagnano Fault (MFF) accommodates the left‐lateral relative motion between South America and Scotia plates. In this paper, we present an updated view of the geometry of the eastern portion of the MFF outcropping in Tierra del Fuego. We subdivide the MFF in eight segments on the basis of their deformation styles, using field mapping and interpretation of high‐resolution imagery. We quantify coseismic ruptures of the strongest recorded 1949, M_w7.5 earthquake, and determine its eastern termination. We recognize several co‐seismic offsets in man‐made features showing a sinistral shift up to 6.5 m, greater than previously estimated. Using ¹⁰Be cosmogenic nuclides depth profiles, we date a cumulated offset in post‐glacial morphologies and estimate the long‐term slip rate of the eastern MFF. We quantify a 6.4 ± 0.9 mm/a left‐lateral fault slip rate, which overlaps geodetic velocity and suggests stable fault behaviour since Pleistocene.     

Implicit structural inversion of gravity data using linear programming,a validation study*

In this study, a regional scale gravity data set has been inverted to infer the structure (topography) of the top of the basement underlying sub‐horizontal strata. We apply our method to this real data set for further proof of concept, validation and benchmarking against results from an earlier forward modelling done elsewhere. Our aim is to carry out implicit structural inversion, i.e., to obtain a geologically reasonable model, without specifically solving for structure. The 2.5D volume of interest is parametrized with homogeneous horizontal prisms and a two‐lithology medium is assumed. A possible regional linear trend and a general floating reference are also inverted for. Using a gridded parametrization, linear programming is used to minimize the L₁ ‐norm of the data misfit, relative to a floating reference. Given a known density contrast between the lithologies, an inversion using linear programming has the intrinsic advantage that a relatively sharp image of the sub‐surface is retrieved instead of a smooth one. The model recovered is almost bi‐modal and its general features seem to be robust with respect to several parametrization scenarios investigated. The floating reference and a linear trend in the data were also retrieved simultaneously. The inversion results, indicating two depressions in the basement, are robust and agree with those obtained earlier based upon detailed 2D forward modelling using many narrow, near‐vertical prisms.     

Chlorobiphenyls in the blubber of harbour porpoises (Phocoena phocoena) from the UK: Levels and trends 1991-2005

Harbour porpoises sampled within the UK Cetacean Strandings Investigation Programme have been analysed for 25 chlorobiphenyl congeners. In all, 440 porpoises stranded or bycaught during the period 1991-2005 were studied. There are regional differences in the trend in summed congener concentrations over time but, despite controls on PCBs having been in place for decades, they are declining only slowly. Their toxic impacts in UK porpoises - increased susceptibility to infectious disease mortality in the most contaminated individuals - looks likely to continue for some time yet. Further efforts to limit or eliminate PCB discharges to the marine environment are still needed.     

Coupling mechanisms in double sandbar systems. Part 1: patterns and physical explanation

Crescentic sandbars and rip channels along wave‐dominated sandy beaches are relevant to understand localized beach and dune erosion during storms. In recent years, a paradigm shift from hydrodynamic template models to self‐organization mechanisms occurred to explain the formation of these rhythmic features. In double sandbar systems, both the inner‐ and outer‐bar rip channels and crescentic planshapes are now believed to be free instabilities of the nearshore system arising through self‐organization mechanisms alone. However, the occasional occurrence of one or two inner‐bar rip channels within one outer‐bar crescent suggests a forced, morphologically coupled origin. Here we use a nonlinear morphodynamic model to show that alongshore variability in outer‐bar depth, and the relative importance of wave breaking versus wave focussing by refraction across the outer bar, is crucial to the inner‐bar rip channel development. The coupling patterns simulated by our model are similar to those observed in the field. Morphological coupling requires a template in the morphology (outer‐bar geometry) which, through the positive feedback between flow, sediment transport and the evolving morphology (that is, self‐organization) enforces the development of coupling patterns. We therefore introduce a novel mechanism that blurs the distinction between self‐organization and template mechanisms. This mechanism may also be extended to explain the dynamics of other nearshore patterns, such as beach cusps. The impact of this novel mechanism on the alongshore variability of inner‐bar rip channels is investigated in the companion paper. Copyright © 2010 John Wiley and Sons, Ltd.     

A numerical study of island wake generated by an elliptical tidal flow

An idealized numerical study of the influence of a tidal flow around an island has been undertaken with ROMS. The study focusses on coastal island wakes which are mainly controlled by elliptical tidal current flows on shallow shelves. This model is typical of some isolated continental shelf islands. The model is forced by a semi-diurnal barotropic inertia gravity wave imposed on the four open boundaries of a rectangular domain and its propagation results in an elliptical tidal flow within the domain in which the circular island lies. The influence of the surrounding island bathymetry and of the ellipse shape has been studied both in two and three dimensions. In the island vicinity, the residual circulation patterns over a tidal period show alongshore flow divergence along the major axis and convergence along the minor axis. A thin tidal ellipse (i.e. with a large ratio between major and minor axes) leads to strong eddy activity periods in the lee of the island during the flood and ebb phases, with eddy dissipation phases in between. By contrast, an almost round ellipse (axis ratio nearly 1) leads to vorticity filaments which continuously progress around the island without eddy shedding. The presence of a topographic slope in the vicinity of the island strengthens the eddy activity. This study suggests that the tidal current rotation favors the development of the eddy rotating in the same direction and weakens the development of the second eddy. In three dimensions with a surrounding bathymetry, an intense upwelling occurs in a large area in the lee of the island and the vertical velocities are stronger with thinner ellipses. With a flat bottom the vertical motions are almost fully generated by convergence and divergence of the secondary flow. With a varying bottom topography, the vertical motions come from a combination of this mechanism with convergence and divergence of the depth averaged flow.     

Contaminants in cetaceans from UK waters: status as assessed within the Cetacean Strandings Investigation Programme from 1990 to 2008

Since 1990, tissue samples from UK-stranded and -bycaught cetaceans have been available for study of contaminant burdens. These have been used to study spatial and temporal trends in concentrations in UK waters, and to investigate potential associations between contaminants and health status. We describe the current status of cetaceans (primarily harbour porpoises, Phocoena phocoena) in UK waters in relation to pollution. Concentrations of BDEs, HBCD, and the organochlorine pesticides are declining. In contrast, concentrations of CBs have plateaued following earlier reductions due to regulation of use, and further reductions are likely to take decades. Blubber PCB concentrations are still at toxicologically significant levels in many harbour porpoises and regularly occur at even higher levels in bottlenose dolphins and killer whales due to their higher trophic level in marine food chains. Further reductions in PCB inputs into the marine environment are needed to mitigate risk from PCB exposure in these species.