The fate of subducted continental margins: Two-stage exhumation of the high-pressure to ultrahigh-pressure Western Gneiss Region, Norway

Thermobarometry suggests that ultrahigh‐pressure (UHP) to high‐pressure (HP) rocks across the Western Gneiss Region ponded at the Moho following as much as 100 km of exhumation through the mantle and before exhumation to the upper crust. Eclogite across the c. 22 000 km² study area records minimum pressures of c. 8–18 kbar and temperatures of c. 650–780 °C. One orthopyroxene eclogite yields an UHP of c. 28.5 kbar, and evidence of former coesite has been found c. 50 km farther east than previously known. Despite this widespread evidence of UHP to HP, thermobarometry of metapelite and garnet amphibolite samples reveals a surprisingly uniform ‘supra‐Barrovian’ amphibolite‐facies overprint at c. 11 kbar and c. 650–750 °C across the entire area. Chemical zoning analysis suggests that garnet in these samples grew during heating and decompression, presumably during the amphibolite‐facies event. These data indicate that the Norwegian UHP/HP province was exhumed from mantle depths of c. 150 km to lower crustal depths, where it stalled and underwent a profound high‐temperature overprint. The ubiquity of late‐stage supra‐Barrovian metamorphic overprints suggests that large‐scale, collisional UHP terranes routinely stall at the continental Moho where diminishing body forces are exceeded by boundary forces. Significant portions of the middle or lower crust worldwide may be formed from UHP terranes that were arrested at the Moho and never underwent their final stage of exhumation.     

OBC signal fidelity

A suite of three tests was performed to characterize the signal fidelity of OBC 4C acquisition systems. The test methodology was to evaluate individual sensor stations by acquiring source lines that were parallel to the in‐line and cross‐line horizontal sensors and source lines that were at 45° to the in‐line and cross‐line sensors. This technique provides constant azimuth gathers with a uniform offset range and removes issues associated with source array directivity. Characterization of the test data identified the frequency content of the geophone signals and the correlation between the vertical and cross‐line geophones as the most sensitive indicators of signal infidelity. In the former case, stations with questionable signal fidelity exhibited a very reverberatory signal. This signal was most evident on the cross‐line sensor. In the latter case, when normalized cross‐correlation coefficients are computed in a moving window, the cross‐line sensor and the vertical sensor are highly correlated, beginning several hundred milliseconds after the first arrivals. These characteristics can be exploited to allow stations with questionable signal fidelity to be programmatically identified. One means of identifying questionable stations is to compute the histogram of the instantaneous frequency. The frequency distributions from questionable stations are unambiguously distinguishable from stations that exhibit better signal fidelity. It was noted that signal fidelity appeared as a range, between acceptable and poor. To characterize the signal fidelity of an acquisition system adequately, the number of test samples must be statistically significant.     

Public pharmaceutical expenditure: identification of spatial effects

The aim of the present study is to analyse the spatio-temporal dynamics underlying Spanish pharmaceutical expenditure increases. We suggest alternative ways to resolve the problem of identifying exogenous and endogenous spatial spillover in a seemingly unrelated regression framework, while parametric instability is captured using linear time trends in the coefficients. The results highlight the need of considering these dynamic aspects in the pharmaceutical expenditure analysis.     

Stylized environments and ABMs: educational tools for examining the causes and consequences of land use/land cover change

A challenge in land change science is to assess the causes and consequences of LULC change and associated pattern–process relations. Increasingly, land change organizations are examining land use at local to global scales for historical, contemporary and future periods through scenarios that assess population–environment interactions. Spatial analytical tools in GIScience are being used to link people and environment and to search for the distal and proximate factors that affect local to global land use patterns. Spatial simulation models that rely upon complexity theory as the framework and agent-based models as the analytical approach offer the capability to inform through experimentation about land issues important to science and society. Using a stylized landscape where a selected set of key social, geographical and ecological elements are spatially organized, we describe how land dynamics can be examined through agent-based models as educational tools that are useful in the classroom, boardroom and public forums.     

Hurricane Overwash and Decadal-Scale Evolution of a Narrowing Barrier Island,Ocracoke Island,NC

Barrier islands are found around the world and are important environmentally and economically. With accelerated sea level rise and relentless storms, their evolution is complex but important to understand, especially from a coastal planning and managing perspective. In this study, shoreline change estimates from aerial photography (1949, 1974, 2006), sedimentological and stratigraphic investigation, and analysis of geomorphic character were used to evaluate the hurricane response and decadal evolution of Ocracoke Island, NC. Between 1949 and 2006, the majority (>?65% of transects) of the entire island eroded at an average rate of ??0.54 m/year. Cross-island width decreased by as much as 40% (180 m) over the period. Hurricane Isabel (2003) represented up to 23% of the long-term net change in some regions of the island. The rate of narrowing of Ocracoke Island appears to have increased in the last half century and is due to a combination of natural and anthropogenic factors. Isabel overwashed a total of 9% of the island based on aerial photographic analysis with an average deposit thickness of 0.24 m based on trench investigation. Assessment with the Storm Impact Scale showed a direct relationship between overwash and the pre-existing dune conditions, which had been affected by long-term erosion. Sedimentological signatures interpreted from cores show up to four distinct stacked overwash deposits, potentially dating back as far as 1944. This multi-pronged analysis shows the complexity of barrier island evolution and highlights the necessity to examine and model a system response in four dimensions (i.e., spatially and with time).     

A multivariate assessment of the coral ecosystem health of two embayments on the lee of the island of Hawai'i

Four coral-dominated coastal sites within two embayments (Kealakekua Bay and Honokōhau Bay) on the lee of the island of Hawai'i were studied to assess evidence of anthropogenic impacts in these relatively pristine locales. Nutrient-loading parameters were analyzed in relation to benthic composition data. Statistically, there were significant positive relationships between nitrate+nitrite, silicate, and ammonium with the abundance of macroalgae, coralline algae, and dead coral, and between delta(15)N and dead coral abundance. The north outside site of Kealakekua Bay and the south outside site of Honokōhau Bay appear to be most impacted by nutrient-loading factors in each bay, respectively. Comparisons with past nutrient data indicate that nutrient inputs have increased to the two bays, and that early impacts of these increased loadings are evident. It is predicted that at current nutrient-loading rates, the north sites of Kealakekua Bay and the south sites of Honokōhau Bay will exhibit evidence of further degradation in future years.     

On the Development of a Second-Order Bistatic Radar Cross Section of the Ocean Surface: A High-Frequency Result for a Finite Scattering Patch

The development of a model for the second-order bistatic high-frequency (HF) radar cross section on an ocean surface patch remote from the transmitter and receiver is addressed. A new approach is taken that allows a direct comparison with existing monostatic cross sections for finite regions of the ocean surface. The derivation starts with a general expression for the bistatically received second-order electric field in which the scattering surface is assumed to be of small height and slope. The source field is taken to be that of a vertically polarized dipole, and it is assumed that the ocean surface can be described, as is usually done, by a Fourier series in which the coefficients are zero-mean Gaussian random variables. Subsequently, a bistatic cross section of the surface, normalized to patch area, is derived. The result is verified by the following two means: 1) the complete form of the bistatic HF radar cross section in backscattering case is shown to contain an earlier monostatic result that has, itself, been used extensively in radio oceanography applications; and 2) the bistatic electromagnetic coupling coefficient is shown to reduce exactly to the monostatic result when backscattering geometry is imposed. The model is also depicted and discussed based on simulated data     

Photographic evidence of rate of development of plant cover on the emergent island Anak Krakatau from 1971 to 1991 and implications for the effect of volcanism

Photographs of the vegetated North and East Forelands of Anak Krakatau, which emerged from the sea in 1930 and was totally devastated by volcanic activity in 1952/53 provide some evidence of rate of change of plant cover from grassland to woodland between 1971 and 1991. The series of photographs demostrate that vegetational stages of the two forelands have not been synchronous and suggest that the North Foreland is lagging the East Foreland by about 12 years.A recent hypothesis that Anak Krakatau's vegetation was destroyed, totally or almost so, by eruptions in 1972/73 and the island's vegetation has regenerated since that time is not easily accommodated by the photographic evidence, nor by the relative rates of change on Rakata (Krakatau's post-1883 remnant) and Anak Krakatau. The photographic evidence accords more closely with a hypothesis that the 1972/73 eruptions affected the North Foreland's vegetation only, or affected it to a much greater degree than that of the East Foreland, allowing the latter's post-1952/53 succession to proceed relatively unhampered.     

A fine-scale point process model of rainfall with dependent pulse depths within cells

Abstract

A cluster point process model is considered for the analysis of fine-scale rainfall time series. The model is based on three Poisson processes. The first is a Poisson process of storm origins, where each storm has a random (exponential) lifetime. The second is a Poisson process of cell origins that occur during the storm lifetime, terminating when the storm finishes. Each cell has a random lifetime that follows an exponential distribution (or terminates when the storm terminates, whichever occurs first). During cell lifetimes, a third Poisson process of instantaneous pulses occurs. The model is essentially an extension of the well-known Bartlett-Lewis rectangular pulses model, with the rectangular profiles replaced with a Poisson process of instantaneous pulse depths to ensure more realistic rainfall profiles for fine-scale series. Model equations, derived in Cowpertwait et al. (2007 Cowpertwait, P., Isham, V. and Onof, C. 2007. Point process models of rainfall: developments for fine-scale structure. Proceedings of the Royal Society of London, Series A, 463: 2569–2587. [Crossref], [Web of Science ®] , [Google Scholar]), are used to fit different sets of properties to a 60 year record of 5-min data taken from Kelburn, New Zealand. As in the previous work, two superposed processes are used to account for two main and distinct precipitation types (convective and stratiform). By treating the within-cell pulses as dependent random variables, it is found, by simulation, that improved fits to extreme values and the proportion of dry intervals are obtained.

Citation Cowpertwait, P. S. P., Xie, G., Isham, V., Onof, C. & Walsh, D. C. I. (2011) A fine-scale point process model of rainfall with dependent pulse depths within cells. Hydrol. Sci. J. 56(7), 1110–1117.     

Evaluation of LPM permafrost distribution in NE Asia reconstructed and downscaled from GCM simulations

A high‐resolution map of potential frozen ground distribution in NE Asia (90–150°E, 25–60°N) at the period of the Last Permafrost Maximum (LPM, c. 21 000 years ago) was dually reconstructed by means of a statistical classification using air freezing and thawing indices and a topographical downscaling using a digital relief model (ETOPO1). Background LPM climate data were derived from global climate model simulations of the Paleoclimate Model Intercomparison Project, Phase II (PMIP2). The reconstructed LPM map shows the southward shift of the southern limit of climate‐driven permafrost by 400–1500 km, with the greatest advance in the western sector (90–110°E), encompassing an area from central Siberia to most of the Altai area. The advance of environmentally conditional permafrost and seasonally frozen ground was greatest in the eastern sector (110–150°E), with an average shift of about 450 km. The descent of the lower limit of LPM alpine permafrost was in the range of 400–800 m. A comparison of the reconstructed map with published literature shows that this method, simplistically constructed yet effectively recognizing seasonality, continentality and topography, captures local features better than more elaborate methods. The sensitivity examination of a constant atmospheric lapse rate shows that altitudes of 2000–5000 m a.s.l. were most sensitive, though with only a limited effect on overall LPM distribution.