Coherent Emission in Astrophysics: A Critique

The applications of 'coherent emission' to radioastronomical sources is discussed critically. The applications considered are electron cyclotron maser emission applied to certain solar and stellar radio emissions, pulsar radio emission, and suggested coherent emission from active galactic nuclei. This revised version was published online in July 2006 with corrections to the Cover Date.     

Data collection methodology for dynamic temperature model testing and corroboration

This article describes a data collection approach for determining the significance of individual heat fluxes within streams with an emphasis on testing (i.e. identification of possible missing heat fluxes), development, calibration and corroboration of a dynamic temperature model. The basis for developing this approach was a preliminary temperature modelling effort on the Virgin River in southwestern Utah during a low‐flow period that suggested important components of the energy balance might be missing in the original standard surface‐flux temperature model. Possible missing heat fluxes were identified as bed conduction, hyporheic exchange, dead zone warming and exchange and poor representation of the amount of solar radiation entering the water column. To identify and estimate the relative importance of the missing components, a comprehensive data collection effort was developed and implemented. In particular, a method for measuring shortwave radiation behaviour in the water column and an in situ method for separating out bed conduction and hyporheic influences were established. The resulting data and subsequent modelling effort indicate that hyporheic and dead zone heat fluxes are important, whereas solar radiation reflection at the water surface was found to be insignificant. Although bed conduction can be significant in certain rivers, it was found to have little effect on the overall heat budget for this section of the Virgin River. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of connectivity theory to model the impact of terrace failure on runoff in semi‐arid catchments

Terraces are a common feature of Mediterranean landscapes. In many places they are no longer maintained so that the number of intact terraces is in prolonged decline. The aim of this paper is to examine the effect of terrace removal and failure on hydrological connectivity and peak discharge in an agricultural catchment (475 ha) in south‐east Spain. The situation of 2006 is compared to that in 1956 and to a scenario without terraces (S2). The spatial distribution of concentrated flow was mapped after four storms in 2006. The degree of connectivity was quantified by means of connectivity functions and related to storm characteristics, land use and topography. For 1956, 2006 and scenario S2, connectivity functions and peak discharge to the river were determined for a storm with a return period of 8·2 years. The results show that the decrease in intact terraces has led to a strong increase in connectivity and discharge. The contributing area to the river system has increased by a factor 3·2 between 1956 and 2006. If all terraces were to be removed (scenario S2), the contributing area may further increase by a factor 6·0 compared to 2006. The spatial extent of concentrated flow and the degree of connectivity are related to storm magnitude as expressed by the erosivity index (EI₃₀). Although a large part of the concentrated flow (25–50%) occurs on dirt roads, it appears that croplands become a major source of runoff with increasing rainfall. The results suggest that connectivity theory can be used to improve rainfall–runoff models in semi‐arid areas. Copyright © 2009 John Wiley & Sons, Ltd.     

Low-salinity plumes in the oceanic region of the Basque Country

Low-salinity waters, within the upper layers of the water column, have been observed in the oceanic region of the southeastern limit of the Bay of Biscay (in March, 2007). This contribution assesses the potential role of large surface freshwater discharges from the Adour (France), Nervión, Oria, Deba, Urola, Urumea and Bidasoa (Basque Country) rivers, to explain the presence of these low-salinity waters. Such discharges, within the offshore waters, reached to at least 50 m in depth; likewise, extending over 15–20 km, in the horizontal. This pattern is confirmed by field data collected by offshore buoys, model results, and the analysis of satellite images. The presence of the low-salinity waters is corroborated by numerical simulations, performed by the ROMS (Regional Ocean Modeling System) hydrodynamic model, with the incorporation of river discharges. In order to simulate the freshwater movements and to identify their origin, particles were released at the river mouths and dispersed (by a Lagrangian particle-tracking model, LPTM), supplied by 3-hourly current fields derived from the ROMS model. The plumes of the Nervión, Oria, Urola and Urumea rivers appear to be the main factors contributing to the low-salinity field, at the offshore locations of the buoys. This pattern is related mainly to the prevailing oceano-meteorological conditions, over the period of analysis.     

Multicomponent reactive transport modeling of uranium bioremediation field experiments

A reaction network integrating abiotic and microbially mediated reactions has been developed to simulate biostimulation field experiments at a former Uranium Mill Tailings Remedial Action (UMTRA) site in Rifle, Colorado. The reaction network was calibrated using data from the 2002 field experiment, after which it was applied without additional calibration to field experiments performed in 2003 and 2007. The robustness of the model specification is significant in that (1) the 2003 biostimulation field experiment was performed with 3 times higher acetate concentrations than the previous biostimulation in the same field plot (i.e., the 2002 experiment), and (2) the 2007 field experiment was performed in a new unperturbed plot on the same site. The biogeochemical reactive transport simulations accounted for four terminal electron-accepting processes (TEAPs), two distinct functional microbial populations, two pools of bioavailable Fe(III) minerals (iron oxides and phyllosilicate iron), uranium aqueous and surface complexation, mineral precipitation and dissolution. The conceptual model for bioavailable iron reflects recent laboratory studies with sediments from the UMTRA site that demonstrated that the bulk (∼90%) of initial Fe(III) bioreduction is associated with phyllosilicate rather than oxide forms of iron. The uranium reaction network includes a U(VI) surface complexation model based on laboratory studies with Rifle site sediments and aqueous complexation reactions that include ternary complexes (e.g., calcium-uranyl-carbonate). The bioreduced U(IV), Fe(II), and sulfide components produced during the experiments are strongly associated with the solid phases and may play an important role in long-term uranium immobilization.     

Drainage beneath ice sheets: groundwater–channel coupling,and the origin of esker systems from former ice sheets

The nature of the drainage system beneath ice sheets is crucial to their dynamic behaviour but remains problematic. An experimentally based theory of coupling between groundwater and major channel systems is applied to the esker systems in the area occupied the last ice sheet in Europe, which we regard as a fossil imprint of major longitudinal drainage channels. We conclude that the large-scale distribution and spacing of major eskers is consistent with the theory of groundwater control, in which esker spacing is partly controlled by the transmissivity of the bed.It is concluded that esker patterns reflect the large-scale organisation of the subglacial drainage pattern in which channel development is coupled to groundwater flow and to the ice sheet's dynamic regime. The theory is then used to deduce: basal meltwater recharge rates and their spatial variability from esker spacing in an area in which the ice sheet was actively streaming during its final retreat; patterns of palaeo-groundwater flow and head distribution; and the seasonally varying magnitude of discharge from stream tunnels at the retreating ice sheet margin. Major channel/esker systems appear to have been stable at least over several hundred of years during the retreat of the ice sheet, although major dynamic events are demonstrably associated with major shifts in the hydraulic regime.Modelling suggests: that glaciation can stimulate deep groundwater circulation cells that are spatially linked to channel locations, with groundwater flow predominantly transverse to ice flow; that the circulation pattern has the potential to create large-scale anomalies in groundwater chemistry; and that the spacing of channels will change through the glacial cycle, influencing water pressures in stream tunnels, subglacial hydraulic gradients and effective pressure. If the latter is reduced sufficiently, it could trigger enhanced bed deformation, thus coupling drainage to ice sheet movement. It suggests the possibility of distinctive phases of sediment deformation and drumlin mobilisation during a glacial cycle.     

Relict sand wedges in southern Patagonia and their stratigraphic and paleo-environmental significance

Relict sand wedges are ubiquitous in southern Patagonia. At six sites we conducted detailed investigations of stratigraphy, soils, and wedge frequency and characteristics. Some sections contain four or more buried horizons with casts. The cryogenic features are dominantly relict sand wedges with an average depth, maximum apparent width, minimum apparent width, and H/W of 78, 39, 3.8, and 2.9 cm, respectively. The host materials are fine-textured (silt loam, silty clay loam, clay loam) till and the infillings are aeolian sand. The soils are primarily Calciargidic Argixerolls that bear a legacy of climate change. Whereas the sand wedges formed during very cold (?4 to ?8 °C or colder) and dry (ca. ≤100 mm precipitation/yr) glacial periods, petrocalcic horizons from calcium carbonate contributed by dustfall formed during warmer (7 °C or warmer) and moister (≥250 mm/yr) interglacial periods. The paleo-argillic (Bt) horizons reflect unusually moist interglacial events where the mean annual precipitation may have been 400 mm/yr. Permafrost was nearly continuous in southern Patagonia during the Illinoian glacial stage (ca. 200 ka), the early to mid-Pleistocene (ca. 800–500 ka), and on two occasions during the early Pleistocene (ca. 1.0–1.1 Ma).     

Digital mapping of coastal boulders – high-resolution data acquisition to infer past and recent transport dynamics

Coastal boulder fields provide clues to long-term frequency-magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour-intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub-metre resolution (from Pléiades and WorldView-3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon-generated waves. During the investigated events, boulders with a-axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a-axes and b-axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra-high-resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a-axes and b-axes including their orientation, while precise values for c-axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder-specific Structure from Motion-based three-dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre-scale, or documentation of fine-grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre-scale and to better understand the hydrodynamics of extreme-wave events on a fringing reef coastline.     

‘PALEOVAN’, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives

Lake Van is the fourth largest terminal lake in the world (volume 607 km³, area 3570 km², maximum depth 460 m), extending for 130 km WSW–ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial–interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East (‘PALEOVAN’). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of ～850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of ‘PALEOVAN’ to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities.