High-temperature emplacement of the Cerro Galán and Toconquis Group ignimbrites (Puna plateau,NW Argentina) determined by TRM analyses

Estimates of pyroclastic flow emplacement temperatures in the Cerro Galán ignimbrite and Toconquis Group ignimbrites were determined using thermal remanent magnetization of lithic clasts embedded within the deposits. These ignimbrites belong to the Cerro Galán volcanic system, one of the largest calderas in the world, in the Puna plateau, NW Argentina. Temperature estimates for the 2.08-Ma Cerro Galán ignimbrite are retrieved from 40 sites in 14 localities (176 measured clasts), distributed at different distances from the caldera and different stratigraphic heights. Additionally, temperature estimates were obtained from 27 sample sites (125 measured clasts) from seven ignimbrite units forming the older Toconquis Group (5.60–4.51 Ma), mainly outcropping along a type section at Rio Las Pitas, Vega Real Grande. The paleomagnetic data obtained by progressive thermal demagnetization show that the clasts of the Cerro Galán ignimbrite have one single magnetic component, oriented close to the expected geomagnetic field at the time of emplacement. Results show therefore that most of the clasts acquired a new magnetization oriented parallel to the magnetic field at the moment of the ignimbrite deposition, suggesting that the clasts were heated up to or above the highest blocking temperature (T _b) of the magnetic minerals (T _b = 580°C for magnetite; T _b = 600–630°C for hematite). We obtained similar emplacement temperature estimations for six out of the seven volcanic units belonging to the Toconquis Group, with the exception of one unit (Lower Merihuaca), where we found two distinct magnetic components. The estimation of emplacement temperatures in this latter case is constrained at 580–610°C, which are lower than the other ignimbrites. These estimations are also in agreement with the lowest pre-eruptive magma temperatures calculated for the same unit (i.e., 790°C; hornblende–plagioclase thermometer; Folkes et al. 2011b). We conclude that the Cerro Galán ignimbrite and Toconquis Group ignimbrites were emplaced at temperatures equal to or higher than 620°C, except for Lower Merihuaca unit emplaced at lower temperatures. The homogeneity of high temperatures from proximal to distal facies in the Cerro Galán ignimbrite provides constraints for the emplacement model, marked by a relatively low eruption column, low levels of turbulence, air entrainment, surface–water interaction, and a high level of topographic confinement, all ensuring minimal heat loss.     

The coupled δC-radiocarbon systematics of three Late Glacial/early Holocene speleothems; insights into soil and cave processes at climatic transitions

The coupled δ¹³C-radiocarbon systematics of three European stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ¹³C and ¹⁴C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher δ¹³C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ¹³C and initial ¹⁴C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ¹³C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial ¹⁴C activities of all three stalagmites broadly follow the contemporaneous atmospheric ¹⁴C trends (the Younger Dryas atmospheric ¹⁴C anomaly can be clearly discerned), subtle changes in speleothem initial ¹⁴C activities are linked to climate-driven changes in soil carbon turnover at a climate transition.     

Biocalcification in the Eastern Oyster (<Emphasis Type="Italic">Crassostrea virginica)</Emphasis> in Relation to Long-term Trends in Chesapeake Bay pH

Anthropogenic carbon dioxide (CO₂) emissions reduce pH of marine waters due to the absorption of atmospheric CO₂ and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed 23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures. Biocalcification declined significantly with a reduction of ∼0.5 pH units and higher temperature and salinity mitigated the decrease in biocalcification.     

Hydrothermal models of the Perth metropolitan area, Western Australia: implications for geothermal energy

Hydrothermal simulations are used to provide insight into the subsurface thermal regime of the Perth metropolitan area (PMA) in Western Australia. High average permeabilities and estimated fluid flow rates in shallow aquifers of the PMA suggest that advection and convection may occur in these aquifers. These processes are simulated, using a new geological model of the PMA to constrain the geometry of aquifers, aquitards and faults. The results show that advection has a strong influence on subsurface temperature, especially in the north of the PMA, where aquifer recharge creates an area of anomalously low temperature. Convection may be important, depending on the permeability of the Yarragadee Aquifer. If convection occurs, it creates thermal highs and lows with a spacing of approximately 5 km. Some of these thermal anomalies migrate over geological time due to coupling between advection and convection, but they are stationary on human timescales. Fault permeability influences the pattern of convection. Advection and convection cause variations in the geothermal gradient which cannot be predicted by conductive models; therefore, these processes should be considered in any model that is used for assessment of geothermal resources in the PMA.     

Next stop: the Moon

Andrew J Ball, Sarah K Dunkin and David J Heather report on optimistic and innovative ideas raised at the Fourth International Conference on Exploration and Utilisation of the Moon, which resulted in a declaration reviewing the current state of lunar exploration and setting targets for future work.     

Principles Of Radiometry

In the first part of this tutorial paper, we survey the physical basis of radiometry – the measurement of electromagnetic energy, and the physical quantities needed to quantify it and to describe reflected and emitted radiation The second part considers what a radiometer is, how it works and on what the signal depends. The third part addresses radiometry inthe context of Earth Observations, with an emphasis on the solar reflected region (visible near infrared) and thermal infrared region. The role of the atmosphere, the ambient radiation, and how to extract information from the signal at the satellite are also discussed briefly.     

Photographic monitoring of soiling and decay of roadside walls in central Oxford, England

As part of the Environmental Monitoring of Integrated Transport Strategies (EMITS) project, which examined the impact of the Oxford Transport Strategy (OTS) on the soiling and decay of buildings and structures in central Oxford, England, a simple photographic survey of a sample of roadside walls was carried out in 1997, with re-surveys in 1999 and 2003. Thirty photographs were taken each time, covering an area of stonework approximately 30 × 30 cm in dimensions at 1–1.3 m above pavement level. The resulting images have been used to investigate, both qualitatively as well as quantitatively, the progression of soiling and decay. Comparison of images by eye reveals a number of minor changes in soiling and decay patterns, but generally indicates stability except at one site where dramatic, superficial damage occurred over 2 years. Quantitative analysis of decay features (concavities resulting from surface blistering, flaking, and scaling), using simple techniques in Adobe Photoshop, shows variable pixel-based size proportions of concavities across 6 years of survey. Colour images (in Lab Color) generally have a reduced proportion of pixels, representing decay features in comparison to black and white (Grayscale) images. The study conveys that colour images provide more information both for general observations of soiling and decay patterns and for segmentation of decay-produced concavities. The study indicates that simple repeat photography can reveal useful information about changing patterns of both soiling and decay, although unavoidable variation in external lighting conditions between re-surveys is a factor limiting the accuracy of change detection.     

Confronting Power and Environmental Injustice: Legacy Pollution and the Timber Industry in Southern Mississippi

Research has documented how grass-roots activists deploy the environmental justice frame to convey their grievances and demand their right to health and safety. While scholars have highlighted the widespread success of this frame, little attention has been paid to instances where the environmental justice frame fails to resonate. Drawing from social movements and environmental justice literatures, we examine how local discursive and cultural contexts can pose barriers to environmental justice claims. Our case is based on legacy pollution from a decommissioned creosote facility in Southern Mississippi. When black residents discovered the pollution in their neighborhood, they made repeated appeals to authorities for remediation and compensation. After being denied inclusion in a lawsuit filed by white residents, they formed an environmental justice organization to mobilize support for their campaign. Findings reveal the importance of both historical contextualization and the social situation of frame deployers in analyses of the environmental justice frame.