An Evaluation of Publicly Available Global Bathymetry Grids

We evaluate the strengths and weaknesses of six publicly available global bathymetry grids: DBDB2 (Digital Bathymetric Data Base; an ongoing project of the Naval Research Laboratory), ETOPO2 (Earth Topography; National Geophysical Data Center, 2001, ETOPO2 Global 2’ Elevations [CD-ROM]. Boulder, Colorado, USA: U.S. Department of Commerce, National Oceanic and Atmospheric Administration), GEBCO (General Bathymetric Charts of the Oceans; British Oceanographic Data Centre, 2003, Centenary Edition of the GEBCO Digital Atlas [CD-ROM] Published on behalf of the Intergovernmental Oceanographic Commission and the International Hydrographic Organization Liverpool, UK), GINA (Geographic Information Network of Alaska; Lindquist et al., 2004), Smith and Sandwell (1997), and S2004 (Smith, unpublished). The Smith and Sandwell grid, derived from satellite altimetry and ship data combined, provides high resolution mapping of the seafloor, even in remote regions. DBDB2, ETOPO2, GINA, and S2004 merge additional datasets with the Smith and Sandwell grid; but moving from a pixel to grid registration attenuates short wavelengths (<20 km) in the ETOPO2 and DBDB2 solutions. Short wavelengths in the GINA grid are also attenuated, but the cause is not known. ETOPO2 anomalies are offset to the northeast, due to a misregistration in both latitude and longitude. The GEBCO grid is interpolated from 500 m contours that were digitized from paper charts at 1:10 million scale, so it is artificially smooth; yet new efforts have captured additional information from shallow water contours on navigational charts. The S2004 grid merges the Smith and Sandwell grid with GEBCO over shallow depths and polar regions, and so is intended to capture the best of both products. Our evaluation makes the choice of which bathymetry grid to use a more informed one. The U.S. government right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.     

Middle and Late Pleistocene fluvial systems in central Poland

This reconstruction of the fluvial palaeogeography of central Poland is based on an exhaustive and critical review of the published and archival data for the Middle and Late Pleistocene sediments of the area. The Warsaw Basin in central Poland was a major confluence area during the Middle and Late Pleistocene. The fluvial watersheds have been only slightly modified since that time. The past river systems resembled the contemporary one, therefore indicating rebuilding during successive interglacials, at least since the Holsteinian when the sea undoubtedly occupied the southern Baltic Basin. The Weichselian fluvial system was strongly influenced by the Scandinavian ice sheet, especially by meltwater runoff in the extraglacial area and ice-damming in the Warsaw Basin where a large proglacial lake developed. The Weichselian fluvial sediments form up to three terraces in the valleys of the Vistula and its tributaries. The most contentious issue is the mutual relation of the ice-dammed lake and ice marginal spillways in the Warsaw Basin, both being important fragments of a widespread drainage network in the Central European Lowland.     

Composition and origin of rhyolite melt intersected by drilling in the Krafla geothermal field, Iceland

The Iceland Deep Drilling Project Well 1 was designed as a 4- to 5-km-deep exploration well with the goal of intercepting supercritical hydrothermal fluids in the Krafla geothermal field, Iceland. The well unexpectedly drilled into a high-silica (76.5 % SiO₂) rhyolite melt at approximately 2.1 km. Some of the melt vesiculated while extruding into the drill hole, but most of the recovered cuttings are quenched sparsely phyric, vesicle-poor glass. The phenocryst assemblage is comprised of titanomagnetite, plagioclase, augite, and pigeonite. Compositional zoning in plagioclase and exsolution lamellae in augite and pigeonite record changing crystallization conditions as the melt migrated to its present depth of emplacement. The in situ temperature of the melt is estimated to be between 850 and 920 °C based on two-pyroxene geothermometry and modeling of the crystallization sequence. Volatile content of the glass indicated partial degassing at an in situ pressure that is above hydrostatic (~16 MPa) and below lithostatic (~55 MPa). The major element and minor element composition of the melt are consistent with an origin by partial melting of hydrothermally altered basaltic crust at depth, similar to rhyolite erupted within the Krafla Caldera. Chondrite-normalized REE concentrations show strong light REE enrichment and relative flat patterns with negative Eu anomaly. Strontium isotope values (0.70328) are consistent with mantle-derived melt, but oxygen and hydrogen isotope values are depleted (3.1 and ?118 ‰, respectively) relative to mantle values. The hydrogen isotope values overlap those of hydrothermal epidote from rocks altered by the meteoric-water-recharged Krafla geothermal system. The rhyolite melt was emplaced into and has reacted with a felsic intrusive suite that has nearly identical composition. The felsite is composed of quartz, alkali feldspar, plagioclase, titanomagnetite, and augite. Emplacement of the rhyolite magma has resulted in partial melting of the felsite, accompanied locally by partial assimilation. The interstitial melt in the felsite has similar normalized SiO₂ content as the rhyolite melt but is distinguished by higher K₂O and lower CaO and plots near the minimum melt composition in the granite system. Augite in the partially melted felsite has re-equilibrated to more calcic metamorphic compositions. Rare quenched glass fragments containing glomeroporphyritic crystals derived from the felsite show textural evidence for resorption of alkali feldspar and quartz. The glass in these fragments is enriched in SiO₂ relative to the rhyolite melt or the interstitial felsite melt, consistent with the textural evidence for quartz dissolution. The quenching of these melts by drilling fluids at in situ conditions preserves details of the melt–wall rock interaction that would not be readily observed in rocks that had completely crystallized. However, these processes may be recognizable by a combination of textural analysis and in situ analytical techniques that document compositional heterogeneity due to partial melting and local assimilation.     

Interactions between geomorphology and ecosystem processes in travertine streams: Implications for decommissioning a dam on Fossil Creek, Arizona

Travertine deposits of calcium carbonate can dominate channel geomorphology in streams where travertine deposition creates a distinct morphology characterized by travertine terraces, steep waterfalls, and large pools. Algae and microorganisms can facilitate travertine deposition, but how travertine affects material and energy flow in stream ecosystems is less well understood. Nearly a century of flow diversion for hydropower production has decimated the natural travertine formations in Fossil Creek, Arizona. The dam will be decommissioned in 2005. Returning carbonate-rich spring water to the natural stream channel should promote travertine deposition. How will the recovery of travertine affect the ecology of the creek? To address this question, we compared primary production, decomposition, and the abundance and diversity of invertebrates and fish in travertine and riffle/run reaches of Fossil Creek, Arizona. We found that travertine supports higher primary productivity, faster rates of leaf litter decomposition, and higher species richness of the native invertebrate assemblage. Observations from snorkeling in the stream indicate that fish density is also higher in the travertine reach. We postulate that restoring travertine to Fossil Creek will increase stream productivity, rates of litter processing, and energy flow up the food web. Higher aquatic productivity could fundamentally shift the nature of the stream from a sink to a source of energy for the surrounding terrestrial landscape.     

Integrated microfossil biostratigraphy,Mid-Cretaceous (Albian to Saronian)

An attempt is made to integrate biozones based on planktic Foraminifera with those on calcareous nannofossils, mainly on first order correlation. An approximate correlation with ammonite zones, magnetic events and radiometric age values, partly on first-order data, partly from the literature, is added.     

Simulated soil water storage effects on streamflow generation in a mountainous snowmelt environment,Idaho, USA

Although soil processes affect the timing and amount of streamflow generated from snowmelt, they are often overlooked in estimations of snowmelt‐generated streamflow in the western USA. The use of a soil water balance modelling approach to incorporate the effects of soil processes, in particular soil water storage, on the timing and amount of snowmelt generated streamflow, was investigated. The study was conducted in the Reynolds Mountain East (RME) watershed, a 38 ha, snowmelt‐dominated watershed in southwest Idaho. Snowmelt or rainfall inputs to the soil were determined using a well established snow accumulation and melt model (Isnobal). The soil water balance model was first evaluated at a point scale, using periodic soil water content measurements made over two years at 14 sites. In general, the simulated soil water profiles were in agreement with measurements (P < 0·05) as further indicated by high R² values (mostly > 0·85), y‐intercept values near 0, slopes near 1 and low average differences between measured and modelled values. In addition, observed soil water dynamics were generally consistent with critical model assumptions. Spatially distributed simulations over the watershed for the same two years indicate that streamflow initiation and cessation are closely linked to the overall watershed soil water storage capacity, which acts as a threshold. When soil water storage was below the threshold, streamflow was insensitive to snowmelt inputs, but once the threshold was crossed, the streamflow response was very rapid. At these times there was a relatively high degree of spatial continuity of satiated soils within the watershed. Incorporation of soil water storage effects may improve estimation of the timing and amount of streamflow generated from mountainous watersheds dominated by snowmelt. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultramafic blocks from the ocean floor southwest of Australia

Samples dredged from the ocean floor near the junction of the Naturaliste Fracture Zone and the Diamantina Zone, 300 km southwest of Cape Leeuwin, Western Australia, contain 3- to 10-cm blocks of Cr-spinel lherzolites and Al-spinel-olivine clinopyroxenites. Both assemblages show textural evidence for deformation and recrystallization, with extensive development of kaersutite in one clinopyroxenite. The blocks are enclosed by clay and Fe-Mn oxide-rich fragmental material, which also contains a diverse detrital mineral suite and microfossils.Diopsides in the lherzolites are Na- and Cr-rich, with marked similarities to those of lherzolite nodules in alkaline basaltic suites. The Al- and Ti-rich diopsides of the clinopyroxenites are more magnesium than those of common pyroxene-rich nodules. The lherzolites are interpreted as upper mantle residues, while the clinopyroxenites probably represent partly recrystallized cumulates from high-temperature basaltic magmas traversing the lherzolite mantle. Both are thought to have been derived from an ultramafic body emplaced into the shallow crust near the Cretaceous/early Tertiary continent-ocean boundary off Australia.     

Characterizing the distribution of observed precipitation and runoff over the continental United States

This paper describes the development of a comprehensive geographic database of historical precipitation and runoff measurements for the conterminous U.S. The database is used in a spatial analysis to characterize large scale precipitation and runoff patterns and to assess the utility and limitations of using historical hydro-meteorological data for providing spatially distributed precipitation estimates at regional and continental scales. Long-term annual average precipitation (P) and runoff (Q) surfaces (geographically referenced, digital representations of a continuous spatial distribution) generated from interpolation of point measurements are used in a distributed water balance calculation to check the reliability of precipitation estimates. The resulting input-output values (P- Q) illustrate the deficiency (sparse distribution and low elevation bias) of historical precipitation measurements in the mountainous western U.S. where snowmelt is an important component of the annual runoff. The incorporation of high elevation snow measurements into the precipitation record significantly improves the water balance estimates in some areas and enhances the utility of historical data for providing spatially distributed precipitation estimates in topographically diverse regions. Regions where the use of historical precipitation data may be most limited for precipitation estimation are identified and alternatives to the use of interpolated historical data for precipitation estimation across large heterogenous regions are suggested. The research establishes a database for continental scale studies and provides direction for the successful development of spatially distributed regional scale water balance models.     

Interpreting geology at Portreath, Cornwall: a resource for geological education

The geology of Portreath preserved both in the natural outcrop and as building stones is assessed as a potential resource for visiting educational groups. Portreath is a former mining port, its expansion and historical development being closely associated with local and regional geology. A fieldwork programme and complementary literature search revealed that this location contains a wide range of accessible rock types suitable for student analysis.     

Determination of EC50 Values for Cu,Zn, and Cr on Microorganisms Activity in a Mediterranean Sandy Soil

Ecotoxicity of three potentially toxic metals (PTM) (Cu, Zn, and Cr) in a slightly acidic sandy soil is tested using the soil respiration test (OECD‐217) in order to determine EC₅₀ values for the carbon transformation activity of microorganisms. Addition of an organic amendment of Populus leaves is also crossed with metal spiking in order to investigate possible interaction with metal toxicity. Soil respiration is measured at day 1 and 28 after the soil spiking with the PTM to assess short‐term effects on soil microbial activity. Of the three metals tested, Cu shows the highest toxicity at the longest exposure times (day 28) and Zn shows a strong inhibitory effect in the short‐term (day 1), even though later toxicity diminish significantly. Cr is the least toxic studied PTM. Organic amendment outweighs any adverse effects of these metals, increasing soil respiration, even in the treatments with high doses of metals.