Regional circulation around Heard and McDonald Islands and through the Fawn Trough,central Kerguelen Plateau

The fine-scale circulation around the Heard and McDonald Islands and through the Fawn Trough, Kerguelen Plateau, is described using data from three high-resolution CTD sections, Argo floats and satellite maps of chlorophyll a, sea surface temperature (SST) and absolute sea surface height (SSH). We confirm that the Polar Front (PF) is split into two branches over the Kerguelen Plateau, with the NPF crossing the north-eastern limits of our survey carrying 25 Sv to the southeast. The SPF was associated with a strong eastward-flowing jet carrying 12 Sv of baroclinic transport through the deepest part of Fawn Trough (relative to the bottom). As the section was terminated midway through the trough this estimate is very likely to be a lower bound for the total transport. We demonstrate that the SPF contributes to the Fawn Trough Current identified by previous studies. After exiting the Fawn Trough, the SPF crossed Chun Spur and continued as a strong north-westward flowing jet along the eastern flank of the Kerguelen Plateau before turning offshore between 50°S and 51.5°S. Measured bottom water temperatures suggest a deep water connection between the northern and southern parts of the eastern Kerguelen Plateau indicating that the deep western boundary current continues at least as far north as 50.5°S. Analysis of satellite altimetry derived SSH streamlines demonstrates a southward shift of both the northern and southern branches of the Polar Front from 1994 to 2004. In the direct vicinity of the Heard and McDonald islands, cool waters of southern origin flow along the Heard Island slope and through the Eastern Trough bringing cold Winter Water (WW) onto the plateau. Complex topography funnels flow through canyons, deepens the mixed layer and increases productivity, resulting in this area being the preferred foraging region for a number of satellite-tracked land-based predators.     

Monitored Natural Attenuation of Contaminants in the Subsurface: Applications

In recent years there has been increasing interest in the application of passive technologies to reduce or remove contaminants from the subsurface environment including soil and ground water. In most cases, the impetus for this interest lies in a perceived savings compared with more traditional remedial alternatives. In a few cases, the infrastructure at contaminated sites, such as buildings, paved areas, and utilities, makes the use of conventional remedial measures difficult and expensive.
To demonstrate that natural processes are effective in reaching established goals, it is necessary to determine that transformation processes are taking place at a rate that is protective of human health and the environment and that these processes will continue for an acceptable period of time. The basic conditions that must be present to confirm natural attenuation processes arc taking place are discussed along with the behavior of contaminated plumes, monitoring requirements, data analysis, rates of degradation, and mathematical modeling.     

226Ra and222Rn contents of Galapagos Rift hydrothermal waters —the importance of low-temperature interactions with crustal rocks

Hydrothermal waters collected by “Alvin” from the Galapagos Spreading Center are enriched in²²²Rn by factors of 50–200 over bottom waters. The²²⁶Ra in the same samples, however, is enriched by less than a factor of four over bottom waters. Enrichments of²²²Rn result primarily from α-recoil from rock surfaces while²²⁶Ra enrichments are dominantly produced by high-temperature alteration of cooling ridge volcanics. The abundances of both nuclides exhibit positive correlations with temperature. The data extrapolate to bottom water temperatures and compositions, demonstrating the importance of seawater mixing. Different vents, however, have different mixing lines, and vents with high²²²Rn have low²²⁶Ra. We propose these patterns result from variations in the extent of low-temperature crustal interaction with the hydrothermal fluids. Low-temperature crustal waters can maintain high steady state²²²Rn contents due to the α-recoil additions to the fluids. The²²⁶Ra, however, is strongly adsorbed at low-temperatures resulting in low concentrations of this nuclide in low-temperature crustal waters. Thus, physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and²²²Rn/²²⁶Ra values of the hot springs.The²²²Rn/²²⁶Ra value appears to be a sensitive indicator of low-temperature crustal interaction. Values > 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow. Values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust. Values of²²²Rn/²²⁶Ra between 10³ and 10⁴ are indicative of interaction of the hydrothermal fluids with sediments. Such values are observed in water samples from the Galapagos hydrothermal mounds.     

Unravelling the microfacies signatures of parasequences using computer-optimized similarity matrices

The microfacies of a Lower Cretaceous carbonate drillcore from Oman are characterized using optimizing matrices of Jaccard's similarity coefficients of community. Other than systems tract boundaries, there is no obvious evidence of individual parasequences in the core. However, diagnostic patterns in microfossil distribution identify environmental gradients recording changes in water depth. These gradients are used to define individual parasequences, parasequence sets, stacking patterns and key surfaces. The patterns suggest that deposition was controlled by successive fourth‐ to fifth‐order (high‐frequency) relative sea‐level cycles superimposed on an underlying third‐order relative sea‐level rise. Although the correlation of these depositional subunits to systematic changes in water depth and the rate of carbonate accumulation alone is not incontrovertible proof of such a sea‐level control, concurrent multiorder relative sea‐level cyclicity provides by far the most likely explanation. A microfacies deposited when the water depth was shallowing is characterized by a relay of microfossils with affinities that shallow upwards. Conversely, a microfacies that records a gradual increase in water depth has a relay of microfossils with affinities that deepen upwards. Microfacies characterized by an assemblage of microfossils with similar affinities record deposition when the benthic environmental conditions remained stable, either because of an equilibrium between shallow water carbonate deposition and rising sea level, or in deeper water where sediment composition was relatively insensitive to changes of water depth. Microfacies characterized by mixed affinity assemblages record syndepositional reworking. During periods of embedded multiorder sea‐level changes, individual parasequences within systems tracts are shown to record more complex environmental gradients than simply the repetition of successive shallowing‐up units as traditionally represented in carbonate sequence stratigraphic models. The microfacies of an individual parasequence may shallow up, or may record both deepening‐up and shallowing‐up depositional phases, as well as periods of sedimentation when benthic environments remained stable. Individual parasequence boundaries may be submarine or subaerial unconformities, or be conformable, as part of a predictable stratigraphic pattern related to the temporal position of an individual parasequence within the underlying third‐order cycle of relative sea‐level change. The hitherto ubiquitous use of assemblages to describe carbonate microfacies, coupled with the widespread use of the metre‐scale shallowing‐up template to identify parasequences, may have led to such complexities previously being overlooked.     

Refinement Indicators for Optimal Selection of Geostatistical Realizations Using the Gradual Deformation Method

In the analysis of petroleum reservoirs, one of the most challenging problems is to use inverse theory in the search for an optimal parameterization of the reservoir. Generally, scientists approach this problem by computing a sensitivity matrix and then perform a singular value decomposition in order to determine the number of degrees of freedom i.e. the number of independent parameters necessary to specify the configuration of the system. Here we propose a complementary approach: it uses the concept of refinement indicators to select those degrees which have the greatest sensitivity to an objective function quantifying the mismatch between measured and simulated data. We apply this approach to the problem of data integration for petrophysical reservoir charaterization where geoscientists are currently working with multimillion cell geological models. Data integration may be performed by gradually deforming (by a linear combination) a set of these multimillion grid geostatistical realizations during the optimization process. The inversion parameters are then reduced to the number of coefficients of this linear combination. However, there is an infinity of geostatistical realizations to choose from which may not be efficient regarding operational constraints. Following our new approach, we are able through a single objective function evaluation to compute refinement indicators that indicate which realizations might improve the iterative geological model in a significant way. This computation is extremely fast as it implies a single gradient computation through the adjoint state approach and dot products. Using only the most sensitive realizations from a given set, we are able to resolve quicker the optimization problem case. We applied this methodology to the integration of interference test data into 3D geostatistical models.     

Energetics of water dissolution in trachyte glasses and liquids

Enthalpies of dissolution in HF solutions have been measured at 323 K for a series of hydrous trachyte glasses. Enthalpies of mixing between water and molten trachyte have then been calculated from heat capacity data for the same set of samples and available enthalpy for pure water. The moderately negative enthalpies of mixing suggested at 1 bar by the measurements made on glasses almost disappear when trachyte liquids and water are referred to the same temperature, and particularly so when enthalpies of mixing are calculated for a few kbars pressure. As found for albite and phonolite liquids, trachyte melts thus appear to mix nearly ideally as far as enthalpy is concerned. These results imply that the enthalpy of exsolution of water from magmas is very small or negligible under the P-T-X conditions relevant to trachytic volcanism, even for complete degassing of up to 5 wt% H₂O. Furthermore, the viscosity increase associated with exsolution-driven cooling is negligible compared to the decrease caused directly by water exsolution.     

Remote and in situ plume measurements of acid gas release from La Soufrière volcano, Guadeloupe

This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO₂ and H₂S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO₂ and H₂S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit.     

Classifications of retail stores and shopping centres: some methodological issues

This paper reviews current methods used in classifying retail outlets and areas devoted to retailing, in the geographical and town planning literature. For retail outlets, classifications based upon types of goods sold, and types of shopping trip, are discussed. This is followed by an analysis of modern large store development which reflects property developers' and retailers' concerns. Areas devoted to retail uses are subdivided into unplanned ‘retail areas’ and planned ‘shopping centres’. Traditional classifications based upon central place theory are reviewed for both of these types, and found wanting in the light of recent changes in retail development practice and consumer behaviour. Classifications based upon physical development characteristics and type of shopping trip are recommended. Finally, classifications of urban retail location are examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Channel metamorphosis, floodplain disturbance, and vegetation development: Ain River, France

The purpose of this paper is to describe and explain channel metamorphosis of the Ain River in east-central France and the effects of this metamorphosis on floodplain disturbance and vegetation development. The Ain River is a 195 km long stream originating in the Jura Mountains which flows into the Rhône River between Lyon, France, and Geneva, Switzerland. The lower 40 km of the Ain River, beyond the mountain front, are situated in a valley of outwash deposits where the floodplain is 0.2 to 1.2 km wide. A complex mosaic of floodplain landscape units has developed. Maps dating back to 1766 and six sets of aerial photographs dated between 1945 and 1991 were used to document changes in channel pattern. Aerial photos and field surveys were used to compile maps of landscape units based on dominant vegetation life-forms, species, and substrate. Six maps dated between 1945 and 1991 were digitized in ARC/INFO and an overlay was generated to determine the changes in landscape units as related to channel disturbance. Change from a braided to a single-thread meandering channel probably took place in the period 1930–1950. The process of river entrenchment has occurred throughout the Holocene but has accelerated in the present century due to shortening of the river course, construction of lateral embankments, and vegetation encroachment following reservoir construction and cessation of wood-cutting and grazing. The increase in horizontal channel stability coupled with channel entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter. Pioneer and disturbance-dependent landscape units have experienced a more terrestrial-like succession to an alluvial forest. Abandoned channels have also been replaced by alluvial forests. On poorly drained soils, shrub-swamp communities of willow and hydrophytic herbaceous plants have been replaced by mixed forests of ash, alder, black poplar, and oak. On well drained alluvial soils, ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar. All types of vegetation, but particularly dry grasslands-shrublands, have been cleared for mines, campgrounds, agriculture, and other types of development. Using several measures, landscape diversity decreased between 1945 and 1991.