The ‘humped’ soil production function: eroding Arnhem Land,Australia

We report erosion rates and processes, determined from in situ‐produced beryllium‐10 (¹⁰Be) and aluminum‐26 (²⁶Al), across a soil‐mantled landscape of Arnhem Land, northern Australia. Soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness. These results thus quantify a well‐defined ‘humped’ soil‐production function, in contrast to functions reported for other landscapes. We compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the Bega Valley, south‐eastern Australia, and found remarkable similarities in rates. The critical difference in this work was that the Arnhem Land landscapes were either bedrock or mantled with soils greater than about 35 cm deep, with peak soil production rates of about 20 m/Ma under 35–40 cm of soil, thus supporting previous theory and modeling results for a humped soil production function. We also show how coupling point‐specific with catchment‐averaged erosion rate measurements lead to a better understanding of landscape denudation. Specifically, we report a nested sampling scheme where we quantify average erosion rates from the first‐order, upland catchments to the main, sixth‐order channel of Tin Camp Creek. The low (～5 m/Ma) rates from the main channel sediments reflect contributions from the slowly eroding stony highlands, while the channels draining our study area reflect local soil production rates (～10 m/Ma off the rocky ridge; ～20 m/Ma from the soil mantled regions). Quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the Earth's soil resource under different erosional regimes. Copyright © 2009 John Wiley & Sons, Ltd.     

Reviewing the uncertainties in climate change science

Summary Climate change science is a highly contentious and politicized field that benefits from open discussion and debate. This paper presents a broadly based up-to-date analysis of the main doubts and uncertainties in climate change science. The primary focus is on the different types and scales of climate change uncertainty including data bases, system complexity, the human fingerprint and climate modelling. The environmental and socio-economic response to climate change is briefly discussed including international agreements on pollution abatement policies.     

Impacts of Drought, Flow Regime, and Fishing on the Fish Assemblage in Southern Australia’s Largest Temperate Estuary

We analysed a 25-year time series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses that under conditions of reduced freshwater inflows and high fishing pressure: (1) the structure of fish assemblages in the lower Murray River system have changed, (2) species diversity of fishes has declined and (3) population age structures of large-bodied, late-maturing, native fish (Macquaria ambigua, Argyrosomus japonicus, Rhombosolea tapirina and Acanthopagrus butcheri) have been reduced. Annual catches and effort in the lower Murray River system were stable for 25 years, but proportional contribution to the total catch from each of freshwater, estuarine and adjacent marine habitats, and the species within them varied. Fish assemblages generally differed between subsequent 5-year periods, with the exception of 1989–1993 when floods occurred in 4 out of 5 years, and the following 5-year period (1994–1998). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H ₂) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches, whilst species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species: golden perch (M. ambigua), black bream (A. butcheri), mulloway (A. japonicus) and a fourth species with an intermediate strategy, greenback flounder (R. tapirina). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand or recover from deteriorated environmental conditions associated with a historically extreme drought in the lower Murray River system. Management of these species should seek to preserve the remnant population age structures and then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries in changeable environments, such as occur in estuaries and other end-river environments, requires a suite of indicators that address changes in fish assemblages and populations.     

Tracer anomaly evolution in the flow field of an isolated eddy

We explore the horizontal stirring of a passive tracer field in the vicinity of an isolated, finite amplitude, quasigeostrophic, β-plane eddy. We consider stirring in the presence of a uniform background gradient of tracer concentration as well as cases in which the tracer anomaly is initially contained within the eddy.This paper reports a survey of phenomenology based upon numerical experiments. We explore the sensitivity of results to physical parameters and to various aspects of the numerical simulation.Under the joint effects of β and of non-linearity, the eddy center migrates. Time dependent effects in a radiated wake provide important stirring mechanisms for the background tracer field. An unexpected, persistent result is a tendency to propel a tendril of tracer westward from near the launch latitude of the eddy. In some cases, the westward penetration of the tendril is even further than the migration of the eddy center.Tracer properties characteristics of the launch site of the eddy tend to be captured and carried with the eddy. However, tracer leaks from the eddy, due to both explicit diffusion-like effects and eddy interaction with background flow features, can result in drawing off of secondary tracer patches.We also calculate trajectories of Lagrangian particles launched in and around the eddy.     

Slow regolith degradation without creep determined by cosmogenic nuclide measurements in Arena Valley, Antarctica

Estimates of regolith degradation in the McMurdo Dry Valleys of Antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces. On the other hand, the existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are younger than the age of surface deposits inferred from stratigraphic relations. This suggests some combination of surface erosion or past ice cover, both of which would reduce the apparent exposure age. This paper quantifies the regolith degradation and/or past ice cover by measuring ¹⁰Be and ²⁶Al from a landslide deposit that contains 11.3 Ma volcanic ash. The surface sample yields an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice, and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit (2 m Ma⁻¹) is taken into account. Soil creep, which is a common degradational process in a wide variety of environments, is non-existent at this field site, which likely reflects the persistent lack of bio- and cryoturbation.     

A Review of Sampling Effects and Response Bias in Internet Participatory Mapping (PPGIS/PGIS/VGI)

Global interest in participatory mapping described as public participation GIS (PPGIS), participatory GIS (PGIS), and volunteered geographic information (VGI) continues to grow, but systematic study of spatial data quality and sampling effects is limited. This article provides a review and meta‐analysis of Internet‐based PPGIS studies conducted during the period 2006–2015 (n=26) to answer the following research questions: (1) How does mapping effort, as a proxy measure for spatial data quality, differ by sampling group? (2) Does the purpose and context of PPGIS influence mapping results? (3) What is the potential for mapping bias through sampling design? (4) Given the results, what should be the focus of future PPGIS research? Mapping effort was highest in sampling groups whose livelihoods were closely related to the purpose of the study, there was greater mapping effort in household sampling groups compared to volunteer groups, and participant domicile had strong effects on mapped results through spatial discounting. The use of online Internet panels provides higher response rates but lower spatial data quality. Future research should focus on increasing sampling response rates, assessing social trade‐offs using alternative spatial weighting schemes, and examining the capacity of the public to select land use alternatives as a complement to traditional expert‐driven planning systems.     

Beyond the boundaries: social place in a protected space

Tourism is increasingly promoted worldwide by public and private agencies as a means of achieving sustainable community development. Rare are the economic windfalls that come without social costs, however, and marketing rural communities as tourist 'products' inevitably forces upon their residents a social transfiguration. Yet, concerns about local places have largely been marginalized in the regionalization and commodification of tourist spaces. As a result, important questions remain unanswered. In response, this study uses the cognitive images of visitors and residents of the twin Alaska 'ghost' towns of Kennicott and McCarthy to describe the evolving landscape of tourism in a protected wilderness community. Specifically, it poses two questions. First, how might disparate perceptions of the tourism landscape serve to define the boundaries of 'place' experience for those who live in or visit Kennicott-McCarthy? Second, can this geographic perspective encourage a proactive planning process more cognizant of the effects on – and responsive to the concerns of – the destination community? A preliminary analysis of the results is presented with a focus on tourism as both agent and process in the structure, identity, and meaning of local places, embedded within larger regions and economies.     

The International Radiation Symposium 2016

正1.Overview The 2016 International Radiation Symposium,a joint venture between the IRC(International Radiation Commission)and IAMAS(International Association of Meteorology and Atmospheric Sciences),took place at the University of Auckland from April 16th to 22nd.The wide scope of atmospheric radiation research was apparent,with focuses rang-     

A merine seismic refraction study of the Santa Barbara Channel,California

Seismic data from a 186 km-long refraction profile in the Santa Barbara Channel have been interpreted using several velocity inversion techniques. Data were obtained during two cruises in 1978 and 1979. Seismic arrivals from fifty explosions of between 1 and 300 lbs. of TNT were recorded by two ocean bottom seismometers, four permanent ocean bottom stations (University of Southern California), and much of the United States Geological Survey/California Institute of Technology southern California seismic network. Travel-time inversion gives a V _p of 6.3 km sec^-1 at 7.2 km depth above 7.2 km sec^-1 at 14.4 km depth at the western end of the channel. At the eastern end, solutions suggest three sediment refractors overlying V _p of 6.4 km sec^-1 at 7.3 km depth, above 7.0 km sec^-1 at 11.6 km depth, above mantle arrivals with V _p of 8.3 km sec^-1 at 21.8 km depth. The velocity structure determined by these methods suggests that the channel has a sedimentary fill of from 4 to 7 km and a layer of mafic plus ultramafic rock 14 to 17 km thick. The greatest thicknesses of sediments are restricted to east of Point Conception. The velocity data also suggest that the Franciscan formation may not be present beneath the channel. Rather, the crust here may represent a thickened portion of the Coast Range ophiolite.     

A relation between magnetic field strength and temperature in sunspots

We present Stokes I Zeeman splitting measurements of sunspots using the highly sensitive (g = 3) Fe i line at = 1.5649 m. The splittings are compared with simultaneous intensity measurements in the adjacent continuum. The relation between magnetic field strength and temperature has a characteristic, nonlinear shape in all the spots studied. In the umbra, there is an approximately linear relation between B ² and T _b, consistent with magnetohydrostatic equilibrium in a nearly vertical field. A distinct flattening of the B ² vs T _brelationship in the inner penumbra may be due to changes in the lateral pressure balance as the magnetic field becomes more horizontal; spatially unresolved intensity inhomogeneities may also influence the observed relation.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.