Age constraints on Pleistocene megafauna at Tight Entrance Cave in southwestern Australia

A well-stratified succession of fossiliferous sediments occurs in Tight Entrance Cave, southwestern Australia. These infill deposits contain the remains of megafauna and have accumulated intermittently since the Middle Pleistocene: >137, 137–119 and 50–29 ka, according to the results of ¹⁴C, U–Th, ESR and OSL dating techniques. Megafaunal species richness was highest in the latest part of the penultimate glacial maximum and during the subsequent last interglacial (137–119 ka), but remains are less abundant following an apparent 70 ka depositional hiatus in the sequence. Most megafaunal specimens from the upper (<44 ka) units are fragmentary, and reworking from older strata cannot yet be ruled out. However, one specimen of Simosthenurus occidentalis (a large extinct kangaroo), a pair of articulated dentaries showing no signs of secondary transportation, was found within a sedimentary layer deposited between 48 and 50 ka. This represents one of the youngest demonstrably in situ occurrences of an Australian megafaunal taxon.     

Defining a Digital Earth System

In a 1998 speech before the California Science Center in Los Angeles, then US Vice‐President Al Gore called for a global undertaking to build a multi‐faceted computing system for education and research, which he termed “Digital Earth.” The vision was that of a system providing access to what is known about the planet and its inhabitants’ activities – currently and for any time in history – via responses to queries and exploratory tools. Furthermore, it would accommodate modeling extensions for predicting future conditions. Organized efforts towards realizing that vision have diminished significantly since 2001, but progress on key requisites has been made. As the 10 year anniversary of that influential speech approaches, we re‐examine it from the perspective of a systematic software design process and find the envisioned system to be in many respects inclusive of concepts of distributed geolibraries and digital atlases. A preliminary definition for a particular digital earth system as: “a comprehensive, distributed geographic information and knowledge organization system,” is offered and discussed. We suggest that resumption of earlier design and focused research efforts can and should be undertaken, and may prove a worthwhile “Grand Challenge” for the GIScience community.     

Exploring uncertainties in terrain feature extraction across multi-scale,multi-feature,and multi-method approaches for variable terrain

Terrain analysis uses different workflows to extract features from terrain models for the purpose of understanding topographic patterns and processes. However, the results of different workflows often conflict, leading to uncertainties about feature locations. Instead of relying upon a single workflow, we suggest that a fusion of information from multiple workflows better informs terrain analysis. From terrain data with different degrees of variability, we extracted terrain features related to the set of topographic surface network feature classes {peaks, pits, saddles, ridges, courses} using workflows from free, open-source, and commercial software. A multi-scale analysis produced terrain features with fuzzy membership values for various feature classes and revealed that terrain locations can exhibit characteristics of all classes. Multi-feature maps were created by determining at each location the dominant and second-ranked features, and an uncertainty value. Our multi-method approach incorporated all of the workflows’ multi-scale results and again produced multi-feature maps that increased the confidence of some features and reduced the signal of dissimilar results. We also found that high variability terrain produced crisper features in both spatial extent and membership strength. Our overall conclusion is that multi-scale, multi-feature, and multi-method analyses clarify terrain feature uncertainty.     

Measuring and modeling the speed of human navigation

Navigation, the goal-related movement through space and time to reach a destination, is a fundamental human activity. Geographers, physiologists, anthropologists, and psychologists have long been interested in the spatial and temporal aspects of navigation speed. Hikers, search and rescue teams, firefighters, the military, and others navigate on foot, and their success depends on understanding how the dynamics of foot-based navigation affect individual capabilities. This research modeled the speed of movement of humans engaged in navigation in wooded environments with varied terrain. Movement models were developed using spatiotemporal analysis of multiple subjects’ trajectories. Speed estimates were collected via satellite positioning from 200 subjects engaged in foot-based navigation. Trajectory data were merged with land-cover data to analyze human navigation over varying slopes and terrain. Generalizing these characteristics provided a model of navigational speed of movement from an origin to a destination along an unknown route. Tobler’s hiking function and Naismith’s rule were used in an analysis of the trajectory data. The model created from this study was shown to outperform those classic human movement speed estimators by predicting route completion time within 10% accuracy (M = 11.1min, 95% CI [9.8, 12.4] min). These models help explain the human dynamics of navigation.]     

Interactions between dam‐regulated river flow and riparian groundwater: a case study from the Yellow River,China

The Xiaolangdi Dam, completed in 2000, is second in scale in China to the Three Gorges Project. It has generated remarkable economic and social benefits but with profound impacts to the riverine and regional environments. This paper reports field monitoring of riparian groundwater in the Kouma section of the Yellow River to illustrate the interactions between dam‐regulated river flow and riparian groundwater. The results show that the hydrological condition in riparian zones downstream from the dam has changed from a typical wet–dry cycle to a condition of semi‐permanent dryness, resulting in degradation of the typical attributes and functions of the wetland ecosystem. Hydrological processes in the riparian zone have changed from a complex multiple flooding regime to a simple regime of dominant groundwater drainage towards the river, which only reverses temporarily during the water and sediment regulation period of the dam. Data on groundwater level and groundwater quality show that there are two key points, at ca 200 and 400 m from the river bank, which distinguish zones with different sensitivity to changes of river flow and indicate different interactions between river water and groundwater. The shallow groundwater quality also is negatively affected by the intensive agricultural development that has occurred since the dam was completed. Ecological restoration needs to be carried out to construct a protective natural riparian zone within ca 200 m from the river, this being an ecotone, which is key to the protection of both riparian groundwater and the river. The riparian zone from 200 to 400 m also should be treated as a transitional zone. In addition, ecologically sensitive agriculture and ecotourism organized by local communities would be beneficial in the area beyond 400 m. Copyright © 2011 John Wiley & Sons, Ltd.     

A hillslope forest floor (duff) water budget and the transition to local control

The partially decomposed organic layer (duff: F and H layers) of the forest floor is an important boundary between the soil and atmospheric processes. Here we use both empirical data and a three‐dimensional coupled heat and water budget model to explain the duff hydrological hillslope shift between very brief wet periods when lateral flow in the duff and infiltration into the mineral soil occur and dry periods when evaporative flow dominates and both lateral and mineral soil flow are not important. The duff moisture transitions from wet to dry periods were the result of low lateral flow which moves liquid and water vapour only centimetres to metres, very rapidly and mostly in the H layer immediately after precipitation. During wet periods, the net lateral fluxes were negative on divergent areas and positive on convergent areas of the hillslope, leading to a net moisture loss in divergent areas and a net gain in convergent areas. The response to lateral flow in the H layer was more rapid than in the F layer. The transition from the lateral downwards flow to mineral soil to evaporative control was within approximately 48 h of precipitation. Canopy species and aspect were important with lodgepole pine, southwest aspect and 4‐cm deep duff controlled by evaporative processes while Engelmann spruce, northeast aspect and 30‐cm duff were more controlled by hillslope redistribution processes. Copyright © 2010 John Wiley & Sons, Ltd.     

Sediment-transport modeling on Southern Californian shelves: A ROMS case study

Suspended sediment-transport processes in Santa Monica and San Pedro Bay are analyzed using the sediment-transport capabilities of the Regional Oceanic Modeling System (roms). A one-month simulation for December 2001 has been carried out with a set of nested domains. The model inputs include tides, winds, surface waves, and idealized initial sediment conditions for sand and non-cohesive silt. Apart from the control run, the sensitivity of the results to surface waves, ripple roughness and bed armoring has been analyzed. From the control experiment, the horizontal transport of sand turns out to be limited to within a few km of the nearshore erosion zones. During high wave events, silt is transported over further distances and also partly offshelf in distinct plumes. The effectiveness of horizontal silt transport depends strongly on vertical mixing due to both surface wind stress and wave-enhanced bottom stress. High wave events coincident with strong winds (hence strong vertical mixing) are the most optimal conditions for sediment-transport. Excluding wave effects in the simulation shows that surface waves are the dominant factor in resuspending bed material on the Southern Californian shelves. The sensitivity experiments also show that the direct influence of additional ripple roughness on erosion and deposition is relatively weak. Switching off bed armoring locally results in increases of near-bottom concentrations by a factor of 20 for silt and a factor of 5 for sand as well as stronger spatial gradients in grain size.     

On YORP-induced spin deformations of asteroids

The alteration of the spin states of small Solar-System bodies by the YORP thermal effect has recently become a plausible and, for some, the favorite candidate for the formation of binary asteroids. The idea is that if an asteroid is slowly spun up to a state where some strength measure is exceeded; it can no longer remain rigid and adjusts to a new configuration. Such a process might involve global fission, global shape changes without fission, or gradual surface mass loss with subsequent mass re-accumulations forming a secondary body.Here I analyze the changes in the shape, spin, and state during slowly increasing angular momentum of rubble-pile, self-gravitating, homogeneous ellipsoidal bodies undergoing homogeneous motions. I use, as appropriate for rubble-pile asteroids, the strength models of granular materials with zero tensile strength (cohesionless but arbitrary dilatancy); those are characterized by the “angle of friction” material constant. There are distinct limit spins depending on that angle of friction and the shape, which were previously presented [Holsapple, K.A., 2001. Icarus 154, 432-448; Holsapple, K.A., 2004. Icarus 172, 272-303]. Here the deformations and state changes when the angular momentum is slowly increased from that of a limit spin state are determined, to study the YORP processes. When a body is at its limit spin and the angular momentum increases further, the body deforms in a unique way along definite paths in the ellipsoidal shape space: it evolves as an elongating shape with an increasing rotational inertia, which in most cases produces a decreasing spin. I give exact analytical solutions for those shape and spin histories, as well as the histories of the mass density, angular momentum and energy. Comparison to other approaches is made.