Volcanism and archipelagic aprons in the Marquesas and Hawaiian Islands

Geophysical observations demonstrate that the archipelagic apron surrounding the Marquesan hot-spot volcanoes is derived almost entirely from mass wasting processes. Seismic reflection and refraction data constrain the volume of the apron sediments to approximately 200,000 km³, with thicknesses reaching over 2 km in the deep portions of the moat near the edge of the volcanic edifice. Seismic velocities average 4 to 5 km s^–1 in the sediments, and 6 km s^–1 at the top of the underlying basement. Single channel seismic profiles show acoustically chaotic cores in the sediments of the apron, which are interpreted as debris flows from mass wasting events. We deduce that the apron is formed by catastrophic collapses that may involve volumes over 100 km³ tens to hundreds of times during the lifetime of a volcano. Comparison with similar data from the Hawaiian Islands yields the result that the total volume of volcanics and their derived sediments along the strike of the chains is only slightly smaller for the Marquesas, implying comparable eruption rates. However, the ratio of sediment to surface volcanic load is much larger for the latter, leading to an overfilled moat in the Marquesas and an underfilled moat at Hawaii. The much larger size of the Hawaiian islands can be explained as the combined effects of a higher thermal swell, loading a stiffer elastic plate, and proportionately less mass wasting.     

Two sulphur isotope provinces deduced from ores in the Mount Isa Eastern Succession,Australia

The sulphur isotopic characteristics of ore deposits in the Australian Mount Isa Eastern Succession are not well known, unlike those of the Western Succession. In this study new detailed analyses are provided for recently discovered Eastern Succession mineralisation, such as the Starra and Osborne BIF-hosted Cu-Au ores, the Dugald River sediment-hosted Pb-Zn prospect, and four vein-hosted Cloncurry-style Cu±Au deposits (Hampden, Mt Elliot/Swan, Mt Cobalt, and the Answer Mine). All of the deposits of the Eastern Succession have ³⁴S_sulphide between –8 and +9%., regardless of their genesis. Empirically a moderate (³⁴S range averaging close to 0%. characterises Starra-style Cu-Au and Pegmont Pb-Zn BIF ores, whereas shear and vein-style Cu mineralisation populations are tighter and do not average close to 0%. This is a particularly surprising result for Dugald River, where a larger isotopic variation more typical of stratiform sediment-hosted Pb-Zn ores in the region might have been expected. By comparison, Western Succession stratiform Pb-Zn and vein-style Cu deposits span a huge range of-15 to 51%. Large sulphur isotope ranges typify sulphate evaporite or organic sulphur-rich sedimentary successions. The lack of such variation in the Eastern Succession in turn suggests that primary evaporite sequences there were halite-dominated but sulphate-poor, and/or contained only limited volumes of organic-sulphur-rich sediment. Eastern Succession sequences were therefore less likely hosts for giant stratiform Pb-Zn deposits, because of their paucity of sulphur, although local sulphur sources permitted small deposits such as Dugald River to develop. Sedimentary conditions were more favourable for the development of sulphur-poor synsedimentary hydrothermal systems such as Starra, Osborne, and Pegmont, although sulphur isotope evidence is equivocal about the origin of these. Epigenetic deposits close to the Williams Batholith (Mt Dore, Hampden) owe their clustering around 0%. to their granitic fluid source.     

Valuing visitors' economic benefits of public beach access points

An increase in the population of coastal counties and popularity of coastal beaches as tourism destinations create difficulties for management agencies responsible for providing public beach access. The objective of this paper is to determine non-resident visitors to South Carolina beaches economic value for public beach access. Visitors are willing to pay an extra $6.60 per day for additional beach access points and parking or an aggregate of $93 million. Visitors' economic value of public beach access allows decision-makers the ability to better compare management policies in their efforts to provide sufficient public beach access through a target effective strategy.     

Influence of salinity and fish species on PAH uptake from dispersed crude oil

The use of chemical oil dispersants to minimize spill impacts causes a transient increase in hydrocarbon concentrations in water, which increases the risk to aquatic species if toxic components become more bioavailable. The risk of effects depends on the extent to which dispersants enhance the exposure to toxic components, such as polycyclic aromatic hydrocarbons (PAH). Increased salinities can reduce the solubility of PAH and the efficiency of oil dispersants. This study measured changes in the induction of CYP1A enzymes of fish to demonstrate the effect of salinity on PAH availability. Freshwater rainbow trout and euryhaline mummichog were exposed to water accommodated fractions (WAF), and chemically-enhanced water accommodated fractions (CEWAF) at 0 per thousand, 15 per thousand, and 30 per thousand salinity. For both species, PAH exposure decreased as salinity increased whereas dispersant effectiveness decreased only at the highest salinity. Hence, risks to fish of PAH from dispersed oil will be greatest in coastal waters where salinities are low.     

The perceived landfall location of evacuees from Hurricane Gustav

Hurricane evacuations in the United States are costly, chaotic, and sometimes unnecessary. Many coastal residents consider evacuation after viewing a forecasted graphic of where the storm is anticipated to make landfall. During the evacuation process, hurricane tracks commonly deviate from the forecasted landfall track and many evacuees may not pay attention to these track deviations after evacuating. Frequently, a disconnect may occur between the actual landfall track, the official forecasted track, and the perceived track of each individual as they made their evacuation decision. Specifically for evacuees, a shift in track may decrease the hazards associated with a landfalling hurricane since evacuees perceive their threat level to be high at the time of evacuation. Using survey data gathered during the evacuation from Hurricane Gustav (2008) in coastal Louisiana (USA), we calculated a type of Z-score to measure the distance error between each evacuee’s perceived landfall location and the actual landfall location from each evacuee’s home zip code. Results indicate a personal landfall bias in the direction of home zip code for evacuees of three metropolitan regions. Evacuees from the greater New Orleans area displayed the highest error, followed by evacuees from greater Lafayette. Furthermore, we validate the authenticity of the previous results by employing two additional methods of error assessment. A large regional error score might possibly be a predictor of evacuation complacency for a future hurricane of similar magnitude, although there are many other variables that must be considered.     

Spatial variation of early season surface water chemistry in Kärkevagge, Swedish Lapland

This study examines the spatial variability of early season water chemistry in the arctic-alpine valley of Kärkevagge, Sweden. The data demonstrate the spatially heterogeneous nature of water chemistry and the general patterns of chemical weathering in the valley. Water chemistry in this valley is dominated by two anions, bicarbonate and sulfate. Bicarbonate is derived from the dissolution of atmospheric CO₂ and the weathering of carbonate units in the local metamorphic rocks, while the sulfate is derived from the oxidation of pyrite in the Seve-Koli tectonic nappe. Spatial patterns of chemical constituents reflect the broad effects of local geology on surface water chemistry. In particular, they demonstrate the effects that mineral species present in minor amounts have on basin-wide water chemistry. However, solute flux rates derived from water chemistry and discharge demonstrate less variability.     

Integrated land-use systems: Assessment of promising agroforest and alternative land-use practices to enhance carbon conservation and sequestration

Degraded or sub-standard soils and marginal lands occupy a significant proportion of boreal, temperate and tropical biomes. Management of these lands with a wide range of existing, site-specific, integrated, agroforest systems represents a significant global opportunity to reduce the accumulation of greenhouse gases in the atmosphere. Establishment of extensive agricultural, agroforest, and alternative land-use systems on marginal or degraded lands could sequester 0.82–2.2 Pg carbon (C) per year, globally, over a 50-year time-frame. Moreover, slowing soil degradation by alternative grassland management and by impeding desertification could conserve up to 0.5–1.5 Pg C annually. A global analysis of biologic and economic data from 94 nations representing diverse climatic and edaphic conditions reveals a range of integrated land-use systems which could be used to establish and manage vegetation on marginal or degraded lands. Promising land-use systems and practices identified to conserve and temporarily store C include agroforestry systems, fuelwood and fiber plantations, bioreserves, intercropping systems, and shelterbelts/windbreaks. For example, successful establishment of low-intensity agroforestry systems can store up to 70 Mg C/ha in boreal, temperate and tropical ecoregions. The mean initial cost of soil rehabilitation and revegetation ranges from $500–3,000/ha for the 94 nations surveyed. Natural regeneration of woody vegetation or agro-afforestation establishment costs were less than $1000/ha in temperate and tropical regions. The costs of C sequestration in soil and vegetation systems range from $1-69/Mg C, which compares favorably with other options to reduce greenhouse gas emissions to the atmosphere. Although agroforestry system projects were recently established to conserve and sequester C in Guatemala and Malaysia, constraints to wide-spread implementation include social conditions (demographic factors, land tenure issues, market conditions, lack of infrastructure), economic obstacles (difficulty of demonstrating benefits of alternative systems, capital requirements, lack of financial incentives) and, ecologic considerations (limited knowledge of impacts and sustainability of some systems).The information in this document has been funded by the U.S. Environmental Protection Agency. It has been subject to the Agency's peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement for use.     

Mercury concentrations in stomach contents and muscle of five fish species from the north east coast of England

Mercury concentrations in stomach contents and muscle tissue are reported for five fish species: herring (Clupea harengus), whiting (Merlangius merlangus), roker (Raja clavata), plaice (Pleuronectes platessa) and dab (Limanda limanda) collected in summer 1992 off the mouth of the River Tyne, North East England. Median muscle mercury concentrations in the area increase in the order plaice < herring < roker < dab < whiting. Absolute mercury concentrations and muscle mercury-length relationships indicate that the environmental availability of mercury in the study area is low. Stomach contents were recovered from dab, plaice and roker only. Median mercury concentrations in stomach contents increased in the order plaice < roker < dab. The variability of the ratio (muscle mercury/stomach content mercury) has been examined for these three species. In dab the variation is relatively low (39.7% RSD), whereas in plaice and roker it is considerably higher (128.4% and 184.6%, respectively). If stomach content mercury concentrations accurately reflect local mercury availability then dab muscle tissue would make a more reliable availability index than muscle tissue of plaice or roker.     

Gebel Dahanib,Egypt: A late Precambrian layered sill of komatiitic composition

Gebel Dahanib is a well preserved, late Precambrian layered mafic-ultramafic sill about 1.5 km thick, forming a prominent peak in the Southeastern Desert of Egypt. Dunites, harzburgites and thin chromite layers at the base grade upward through pyroxenites to layered gabbros and rare anorthosite at the top. Peridotitic dykes from the main body, unsheared margins, and ubiquitous cumulate textures all suggest magmatic rather than tectonic emplacement.Olivine ranges from Fo₉₄ to Fo₇₆, orthopyroxene from En₉₀ to En₇₉, and abundant clinopyroxene is typically low Cr diopside or diopsidic augite. Plagioclase is exceptionally calcic (An₉₄-An₈₃) and typically is 10% more calcic at a given coexisting olivine composition than plagioclase in the Skaergaard and Stillwater intrusions. Assimilation of the country rock is common along the borders, and chilled margins are not developed. The bulk composition of the sill, estimated from whole rock analyses weighted according to outcrop areas, is SiO₂=50.1%, A1₂O₃= 8.9%, MgO=19.9%, CaO=12.1%, K₂O=0.06%, TiO₂=0.2%. REE contents in the original magma were less than four times chondritic abundances. The chemical and mineralogical characteristics of the Dahanib sill suggest comparisons with basaltic or pyroxenitic komatiites.