A hypothesis on the locations of lunar gas venting

Both lunar transient phenomena and ²²²Rn/²¹⁰Po anomalies observed by Apollo-15 and -16 orbital alpha spectrometers display preferences for certain kinds of locations: rims of circular maria and craters with central peaks and/or dark floors. If these classes of observations are due to lunar gas venting, why are these types of locations preferred? The hypothesis offered is that these are locations at which cracks or channels exist extending deep enough into the moon to tap lunar volatile reservoirs. Possible channels include circumferential cracks around circular maria, old lava tubes for dark-floor and volcanic central peak craters, and shattered subsurface rock structure for impact central peak craters.     

The design and testing of small,low-cost GPS-tracked surface drifters

We have designed and constructed drifters appropriate for use in regions characterized by limited horizontal extent. The drifters follow the upper 30 cm of surface currents, but can be modified to follow water at any depth. The drifters store their latitude and longitude internally, and transmit their current latitude and longitude to a handheld Global Positioning System (GPS)-radio receiver, making their location and subsequent retrieval straight forward A field test of six drifters in Hog Island Bay, Virginia, United States, in August 2003 was successful and led to several design improvements. With simple construction and a total materials cost of under U.S.$200 this design will make drifters an accessible part of interdisciplinary experiments, provide a potentially valuable educational tool, and make experiments that require large numbers of drifters more cost-effective.     

Recent changes to conservation of New Zealand's native biodiversity

Abstract: This article examines recent changes to conservation in New Zealand. The argument is influenced by practical experience over the past 15 years, first as conservation planner employed by the Department of Conservation, then as an environmentalist involved in community conservation projects. The development of public‐private partnerships in conservation action over the past 15 years is reviewed. These changes point to the configuration of new landscapes, although the diverse and uncoordinated nature of many contemporary initiatives suggest that future biological communities will comprise a diversity of hybrid mixes from predominantly native to fully non‐native species.     

Late Pleistocene (Last Interglacial) terrace deposits, Bahia Coyote, Baja California Sur, México

Late Pleistocene age terrace deposits are exposed in the narrow cliffed coastal plain of Bahia Coyote, Baja California Sur, resting unconformably on the lagoonal-shallow water volcaniclastics of the early Miocene Cerro Colorado Member of the El Cien Formation. The terrace is dissected by widely spaced arroyos and partically covered by alluvial fans in the inner and central areas. The marine deposits vary in thickness from 0.5 to 10 m and were laid down in pre-existing erosional channels and depressions in the Pleistocene landscape. The sequence begins with a cobble conglomerate with oyster shells, overlain by poorly bedded molluscan-rich bioclastic sands and coral rubble, beds of massive Porites in growth position and coral-rhodolith sands and marls. Beach sands and gravels and coastal dunes cap the sequence.Samples of Porites panamensis selected for U/Th dating are well-preserved aragonite (>95%). Preliminary results yield U/Th ages of 109–209 ka but the corals have initial δ ²³⁴U values in excess of modern seawater values. This indicates open-system behavior and uncertainty associated with the ages. A corrected age for the top of the massive Porites unit suggests that the corals grew during the last interglacial, marine isotope stage (MIS) 5e sea level high stand.Assuming global sea level during MIS 5e was ca. 4–5 m above present-day sea level (McCulloch and Esat, 2000) and the growth position of the corals was 1–5 m below sea level, the terraces have been uplifted between 12 and 25 m (12–15 cm/kyr). This is consistent with other terrace-based uplift rates for the central Baja California peninsula, north of the La Paz fault.     

The causes and environmental effects of land use conversion during agricultural restructuring in Northeast China

1IntroductionLand use change has received lots of attention internationally (Turner etal., 1994). Understanding of the mechanism of land use change and its adverse effect on the environment is conducive to understanding of population, resources, environment and sustainable economic development on the global, national and regional scales. With the rapid rise in human population, human-induced changes in land use form an important component of regional environmental change. In China, to emphasi…     

Mobility of arsenic in a Bangladesh aquifer: Inferences from geochemical profiles, leaching data, and mineralogical characterization

Aquifer geochemistry was characterized at a field site in the Munshiganj district of Bangladesh where the groundwater is severely contaminated by As. Vertical profiles of aqueous and solid phase parameters were measured in a sandy deep aquifer (depth >150 m) below a thick confining clay (119 to 150 m), a sandy upper aquifer (3.5 to 119 m) above this confining layer, and a surficial clay layer (<3.5 m). In the deep aquifer and near the top of the upper aquifer, aqueous As levels are low (<10 μg/L), but aqueous As approaches a maximum of 640 μg/L at a depth of 30 to 40 m and falls to 58 μg/L near the base (107 m) of the upper aquifer. In contrast, solid phase As concentrations are uniformly low, rarely exceeding 2 μg/g in the two sandy aquifers and never exceeding 10 μg/g in the clay layers. Solid phase As is also similarly distributed among a variety of reservoirs in the deep and upper aquifer, including adsorbed As, As coprecipitated in solids leachable by mild acids and reductants, and As incorporated in silicates and other more recalcitrant phases. One notable difference among depths is that sorbed As loads, considered with respect to solid phase Fe extractable with 1 N HCl, 0.2 M oxalic acid, and a 0.5 M Ti(III)-citrate-EDTA solution, appear to be at capacity at depths where aqueous As is highest; this suggests that sorption limitations may, in part, explain the aqueous As depth profile at this site. Competition for sorption sites by silicate, phosphate, and carbonate oxyanions appear to sustain elevated aqueous As levels in the upper aquifer. Furthermore, geochemical profiles are consistent with the hypothesis that past or ongoing reductive dissolution of Fe(III) oxyhydroxides acts synergistically with competitive sorption to maintain elevated dissolved As levels in the upper aquifer. Microprobe data indicate substantial spatial comapping between As and Fe in both the upper and deep aquifer sediments, and microscopic observations reveal ubiquitous Fe coatings on most solid phases, including quartz, feldspars, and aluminosilicates. Extraction results and XRD analysis of density/magnetic separates suggest that these coatings may comprise predominantly Fe(II) and mixed valence Fe solids, although the presence of Fe(III) oxyhydroxides can not be ruled out. These data suggest As release may continue to be linked to dissolution processes targeting Fe, or Fe-rich, phases in these aquifers.     

Simple models of coupled fluid infiltration and redox reactions in the crust

Simple one-dimensional numerical models are presented for coupled advection-hydrodynamic dispersion and kinetically controlled oxidatioin-reduction reactions in graphite-free porous media containing magnetite coexisting with silicate assemblages. Fluid-solid interactions involving either OH (O₂-H₂O-H₂) or COH (O₂-H₂O-H₂-CO₂-CO-CH₄) fluids are considered at ∼500 ^∘C and 5 kbar. The major implications of the modeling are as follows: (1) Regional (km scale) reduction of typical magnetite-bearing rocks originally at f _O2 near NNO may be possible during long-term metamorphic fluid flow if the infiltrating fluids have sufficiently low f _O2 and sufficiently large concentrations of CH₄ and/or H₂. Regional oxidation of such rocks by highly oxidized OH or COH fluids appears to be difficult to achieve. (2) Nearly identical mineral assemblages and modes may be produced by very different kinetic reaction pathways. The model implies that “equilibrium” assemblages preserved in rocks may not always reflect the true kinetic reaction path that evolved during fluid flow, and highlights the need for quantitative measurements of metamorphic reaction rates. (3) Preservation of sharp lithologic contacts between rocks of very different redox states containing accessory amounts of oxides may be unlikely if fluid-rock interaction times exceed 10³10⁴ years. Substantial contact disruption over these times scales is predicted even for oxide-rich rocks if redox contrasts between layers are large. Flow across lithologic contacts may produce asymmetric patterns of metasomatic mineral zonation that may prove useful for mapping flow directions in metamorphic sequences. (4) For fluid flow in typical T gradients through originally homogeneous rock, significant major element metasomatism (e.g., K, Na, Ca) may be possible without producing large changes in oxide abundances. Received:12 November 1997 / Accepted: 9 March 1998