Evidence for a regime shift after the 1997–1998 El Niño, based on 1995, 1998, and 2001 acoustic surveys in the Pacific Eastern Boundary Current

Increasing physical oceanographic evidence suggests that a regime shift, which featured increased equatoward surface winds and upwelling in the Eastern Pacific Boundary Current region, occurred following the 1997–1998 El Niño. We expect the signal of this change in biota to be stronger in euphausiids than in pelagic fishes such as Pacific hake (Merluccius productus) because lower trophic levels are more responsive to changes in upwelling and primary production. We used acoustic backscatter data from acoustic surveys in summer 1995, 1998, and 2001 to explore whether significant changes in abundance and distribution of euphausiids and fishes have occurred between 1995 and 2001. Graphical and statistical results show that the density of fish schools and euphausiid patches increased significantly south of Cape Blanco between 1995 and both 1998 and 2001. North of Cape Blanco there was no consistent change in euphausiid abundance, although both fish and euphausiid distributions in 2001 appear to be significantly higher nearshore than in the other years. Pelagic fish abundance distributions appeared more closely linked to El Niño than to regime shifts, with abundance shifted much farther north in 1998, an El Niño year, than in the other years, while 1995 and 2001 fish abundance distributions are similar to each other. The regime shift appears so far to have had a stronger effect on euphausiids than on pelagic fishes. The change in euphausiid abundance and distribution between the survey years was linked, through a conceptual model, to the relative strength of the poleward flowing California undercurrent and equatorward flowing California current and to the distribution and abundance of hake.     

The Influence of Geomorphologic Heritage on Present Nival Erosion: Peñalara, Spain

This article examines how snow plays a role in current erosive processes in a high mountain area (1800—2400 m a.s.l.) known as Peñalara, located in Spain's Central Range (40°50' N; 3°58' W). The hypothesis maintains that snow becomes an important erosive factor when it accumulates over sedimentary or weathered materials, therefore geomorphological heritage is a key factor in nival erosion. To test this hypothesis, the authors identified the landforms in the study area and determined their relative ages by weathering and lichenometry ( Rizocarpon geographicum ag. ), differentiating between preglacial, glacial (Recent Pleistocene) and postglacial (Holocene) forms. The information was used to plot a reticulate pattern of observation sites for the study area. Snow depth and the movement of selected blocks at each site were recorded from October 1991 to June 1995. The relationship between late-lying snowpatches, geomorphological heritage and current erosive processes was determined. Between 1800 and 2000 m a.s.l., there is an indirect relationship between snowpatches and predominant processes (stream incision and gelifluction) on terminal moraines. Between 2000 and 2200 m, direct action is present where there are late-laying snowpatches on lateral moraines and some glacial steps. Between 2200 and 2400 m, gelifraction and gravity processes are also in direct relation to snowpatches.     

Converting Radial Distortions Due to Geopotential Models to Geopotential Stokes Coefficients

A methodology for improving geopotential models has been developed. Theoretical relations have been derived converting coefficients in harmonic expansions for radial distortions due to geopotential models into geopotential Stokes coefficients. Terms of the order of 10 ^–10 in magnitude have been retained.     

GRASS GIS-embedded Decision Support Framework for Flood Simulation and Forecasting

This study presents a spatiotemporal analysis tool, called Shyska. This tool allows the simulation and prediction of flash floods in semiarid basins. Shyska has been developed by Geographical Information System (GIS)‐embedded functions, allowing the integration of hydrometeorological information from modern technologies of data acquisition in real time. A Digital Elevation Model (DEM) is used in order to obtain the relevant parameters from the integrated rainfall‐runoff models. Some of its most relevant modules and methodology employed for its development are described. Case studies in basins of south‐east Spain illustrate the applicability of the proposed techniques.     

Feldspathic clast populations in polymict ureilites: Stalking the missing basalts from the ureilite parent body

Polymict ureilites DaG 164/165, DaG 319, DaG 665, and EET 83309 are regolith breccias composed mainly of monomict ureilite-like material, but containing ∼2 vol% of feldspathic components. We characterized 171 feldspathic clasts in these meteorites in terms of texture, mineralogy, and mineral compositions. Based on this characterization we identified three populations of clasts, each of which appears to represent a common igneous (generally basaltic) lithology and whose mafic minerals show a normal igneous fractionation trend of near-constant Fe/Mn ratio over a range of Fe/Mg ratios that extend to much higher values than those in monomict ureilites. The melts represented by these populations are unlikely to be impact melts, because the ubiquitous presence of carbon in polymict ureilites (the regolith of the ureilite parent body) implies that impact melts would have crystallized under conditions of carbon redox control and therefore have highly magnesian mafic mineral compositions with constant Mn/Mg ratio. Therefore, these melts appear to be indigenous products of igneous differentiation on the ureilite parent body (UPB), complementary to the olivine-pigeonite residues represented by the majority of monomict ureilites.The most abundant population is characterized by albitic plagioclase in association with pyroxenes, phosphates, ilmenite, silica, and incompatible-element enriched glass. Model calculations suggest that it formed by extensive fractional crystallization of the earliest melt(s) of precursor materials from which the most magnesian (shallowest) olivine-pigeonite ureilites formed. A less abundant population, characterized by labradoritic plagioclase, may have formed from melts complementary to more ferroan olivine-pigeonite ureilites, and derived from deeper in the UPB. The third population, characterized by the presence of olivine and augite, could only have formed from melts produced at greater depths in the UPB than the olivine-pigeonite ureilites. Many other feldspathic clasts cannot be positively associated with any of these three populations, because their mafic mineral compositions exhibit carbon redox control. However, they may be products of early crystallization of basaltic melts produced on the UPB, before carbon was exhausted by reduction.Partial melting on the ureilite parent body was a fractional (or incremental) process. Melts were produced early in UPB history, and most likely extracted rapidly, thus preserving primitive chemical and oxygen isotopic signatures in the residues.     

Seismic studies of the Brasília fold belt at the western border of the São Francisco Craton, Central Brazil, using receiver function, surface-wave dispersion and teleseismic tomography

The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate.     

An approach for quantifying geomorphological impacts for EIA of transportation infrastructures: a case study in northern Spain

A methodological proposal for the assessment of impacts due to linear infrastructures such as motorways, railways, etc. is presented. The approach proposed includes a series of specific issues to be addressed for each geomorphological feature analysed—both ‘static’ and ‘dynamic’—as well as a series of steps to be followed in the process.Geomorphic characteristics potentially affected were initially identified on the basis of a conceptual activities/impacts model that helps to single out geomorphic impacts related to environmental concerns for the area. The following issues were addressed for each individual impact: nature of potential effects; indicators that can be used to measure impacts; criteria of ‘geomorphologic performance’; procedure for measurement/prediction of changes; translation of geomorphologic impacts into significant terms from the viewpoint of human concerns; possible mitigation and/or compensation measures.The procedure has been applied to a case study corresponding to a new motorway in the Basque Country, northern Spain. Geomorphological impacts considered in this analysis included: (1) consumable resources; (2) sites of geomorphological interest; (3) land units with high potential for use, high productivity or value for conservation; (4) visual landscape; (5) slope instability processes. The procedure has been designed for implementation in a Geographic Information System (GIS) environment. Details are given on the application of the method to each individual impact analysed and results are presented in both numerical and map form.Impacts assessed were initially expressed by means of heterogeneous magnitudes, depending on the geomorphological feature considered. Those geomorphological impacts were then translated into significant terms and homogeneous magnitudes. Integration was carried out on the basis of impact values thus obtained. Final integrated results were also expressed in numerical and map form.The method proposed enables comparison of alternatives as well as ‘prediction’ and assessment of impacts in terms directly related to geomorphic characteristics. It also facilitates the expression of those impacts in terms that allow integration with other types of environmental impacts.