Sensitivity of the Australian summer monsoon to tilt and precession forcing

The response of the Australian summer monsoon to orbital forcing is studied using a coupled General Circulation Model (GCM) with the focus on the relative roles of tilt and precession on the forcing of the northern Australian summer monsoon. It was found that unlike the Northern Hemisphere monsoons, which are dominated by precession forcing, the Australian monsoon can be enhanced significantly not only by precession forcing, but also by tilt forcing coupled to oceanic feedback. The new insights obtained from a series of experiments with differing tilt-precession configurations allow an interpretation of the Australian Late Quaternary monsoon record in which insolation forcing plays a significant role.     

Effects of topographic–isostatic masses on gravitational functionals at the Earth’s surface and at airborne and satellite altitudes

Topographic–isostatic masses represent an important source of gravity field information, especially in the high-frequency band, even if the detailed mass-density distribution inside the topographic masses is unknown. If this information is used within a remove-restore procedure, then the instability problems in downward continuation of gravity observations from aircraft or satellite altitudes can be reduced. In this article, integral formulae are derived for determination of gravitational effects of topographic–isostatic masses on the first- and second-order derivatives of the gravitational potential for three topographic–isostatic models. The application of these formulas is useful for airborne gravimetry/gradiometry and satellite gravity gradiometry. The formulas are presented in spherical approximation by separating the 3D integration in an analytical integration in the radial direction and 2D integration over the mean sphere. Therefore, spherical volume elements can be considered as being approximated by mass-lines located at the centre of the discretization compartments (the mass of the tesseroid is condensed mathematically along its vertical axis). The errors of this approximation are investigated for the second-order derivatives of the topographic–isostatic gravitational potential in the vicinity of the Earth’s surface. The formulas are then applied to various scenarios of airborne gravimetry/gradiometry and satellite gradiometry. The components of the gravitational vector at aircraft altitudes of 4 and 10 km have been determined, as well as the gravitational tensor components at a satellite altitude of 250 km envisaged for the forthcoming GOCE (gravity field and steady-state ocean-circulation explorer) mission. The numerical computations are based on digital elevation models with a 5-arc-minute resolution for satellite gravity gradiometry and 1-arc-minute resolution for airborne gravity/gradiometry.     

Bedload entrainment,travel lengths,step lengths,rest periods—studied with passive (iron,magnetic) and active (radio) tracer techniques

This paper reports results from bedload transport investigations with active (radio) and passive (iron, magnetic) tracers in the Lainbach, a step-pool mountain river, in Bavaria, Southern Germany. The spatial distributions of the iron tracers after flood events can be best described by exponential or Gamma distributions. There is some indication of a tendency of size-selective transport of the iron tracers, but there is also a considerable amount of scatter in the correlations between weight (size) and travel length owing to the masking influence of other variables, such as the shape of the particles and different positions in the river bed. The experiments with artificial magnetic tracers showed that elongated pebbles (rods) had the longest mean transport distance, platy ones (discs) remained relatively close to the starting points. The particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded. The Pebble Transmitter System (PETSY) consists of transmitters implanted into individual pebbles, a computerized receiver, a stationary antenna system with an antenna switchboard, and a data logging system. The particles do not move continuously but in a series of transport steps and non-movement intervals. A single value for a given size-class is not adequate to describe the critical conditions of entrainment under natural circumstances. A probability approach is much more suitable. The critical unit discharges (total discharge divided by active channel width) along the measuring reach are dependent on river bed morphology. In the steps bedload needs higher unit discharges to be entrained. Once entrained, the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods. The distributions of both parameters can be approximated by exponential functions. Applying the stochastic concept proposed by Einstein the mean values of the random variables [step length] and [duration of rest period] measured with the PETSY technique were used for the simulation of spatial distributions of bedload particles from point sources. More field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics.     

Zur zeitlichen Variation des Metallgehaltes in der Galaxis

The two oldest known open clusters, NGC 188 and M67, are observed to have a higher heavy-element abundance than the sun and the stars in the Hyades. This observation might be explained by assuming that these clusters were formed from unusually dusty and hence metal-rich interstellar clouds. Alternatively it may be supposed that the radiation pressure produced by stars in the spiral arms of the Galaxy ejected dust from high-latitude clouds. The calculations presented in this paper show that the loss of dust from such clouds might just be sufficient to produce a significant decrease in the mean heavy-element abundance of the interstellar gas. According to this picture, the first burst of star formation in the Galaxy led to a rapid increase in the interstellar heavy-element abundance. Subsequently, the metal abundance of the interstellar gas decreased due to the radiation pressure by young stars. The present rate of change of the heavy-element abundance in the Galaxy depends on the ratio of heavy-element production by stars to ejection of these elements by radiation pressure on dust grains. Since noble gases do not condense on grains, the neon abundance in the interstellar gas should be a monotonously increasing function of time. The observation that the neon abundance in the sun is much lower than that in young stars and nebulae lends some support to the suggestion that ejection of grains from the Galaxy effects the heavy-element abundance in the interstellar gas.     

The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton,Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203–2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323–354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0–1.4 Ga Namaqua Province, 1.7–2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu–Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. εHf(t) signatures range between ?24 and +14.8, which relate to T_DM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from magmas generated from Mesoproterozoic crustal material show more juvenile εHf(t) signatures of +14, +8 to +4 with T_DM model ages of 1.05–1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show εHf(t) signatures of ?3 to ?5.5 with T_DM model ages of 2.4–2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without any evidence for a passive margin. All of this can be explained by the erosion of rocks related to the Namaqua Belt, which represents one of the two major peaks of zircon U–Pb ages in all analysed samples. Therefore, the Namaqua Belt was well exposed during the Cryogenian, available to erosion and apart from the also well-exposed Palaeoproterozoic basement of the Kalahari Craton one potential source area for the sedimentary rocks in the investigated areas.     

Using embodied HANPP to analyze teleconnections in the global land system: Conceptual considerations

Geografisk Tidsskrift—Danish Journal of Geography 109(2):119–130, 2009

In our rapidly globalizing world economy activities in one region have increasingly important effects on ecological, economic or social processes elsewhere, an effect which we here denote as ‘teleconnections’ between different regions. Biomass trade, one of the causes behind such teleconnections, is currently growing exponentially. Integrated analyses of changes in the global land system are high on the agenda of sustainability science, but a methodological framework for a consistent allocation of environmental burdens related to the consumption and production of biomass between regions has not been put forth to date. The concept of the ‘embodied human appropriation of net primary production’ (abbreviated ‘embodied HANPP’ or ‘eHANPP’) allows for the assessment of the ‘upstream’ effects on ecosystem energetics associated with a particular level of biomass consumption or with a given biomass-based product. This concept is based on HANPP and its two components: (1) productivity changes resulting from land conversion (ΔNPP_LC), and (2) harvest of biomass in ecosystems (NPP_h). HANPP, defined as the sum of ΔANPP_LC and NPP_h in any given territory, is indicative of the intensity with which humans use the land for their purposes. eHANPP is defined as the NPP appropriated in the course of biomass production, encompassing losses along the production chain as well as productivity changes induced through land conversion or harvest. By making the pressure exerted on ecosystems associated with imports and exports visible, eHANPP allows for the analysis of teleconnections between producing and consuming regions. This article puts forward the eHANPP concept, illustrates its utility for integrated socioecological land-change research based on top-down data on global HANPP and biomass consumption, and discusses the possibilities and challenges related to its quantification in bottom-up approaches.     

Determination of the cleat angle distribution of the RECOPOL coal seams, using CT-scans and image analysis on drilling cuttings and coal blocks

Cleat orientation, cleat frequency and cleat angle distribution of deep coal seams are only available by the use of drilling cores and from coal mine samples. Coal drilling cuttings are a cheap and fast alternative to measure cleat angle distributions with the use of image analysis techniques. In this study oriented coal samples and drilling cuttings of the RECOPOL field experiment are compared and used to explain and validate the proposed method. In other words, cleat angle distributions from drilling cuttings are measured by image analysis. The geological framework of the polish coals is described. The image analysis methodologies for the measurement of fracture faces of cuttings and from CT-scan images, derived from these coals, are explained. The results of the methods on the cuttings are compared with cleat orientation distributions from CT-scans and artificial fragments from coal blocks of the same seams. These evaluations show high agreements between the methods. The cleat angle distributions of drilling cuttings of four seams are compared with the cleat orientation distributions of a regional structural geological study. The high correlation in this study shows that cleat angle distributions of coal seams can be used as input parameters for reservoir modelling.     

Climate variability and the Peruvian scallop fishery: the role of formal institutions in resilience building

Peru experiences recurrent ENSO (El Niño Southern Oscillation) events during which the Peruvian bay scallop (Argopecten purpuratus) undergoes substantial changes in its stock size. In the North of the country strong warm ENSO events are synonymous with floods and river discharges that negatively affect scallop biomass, while in the South increased sea surface temperatures lead to an increase in stock size. This paper explores how formal institutions respond to climate variability and resource fluctuations in the scallop fishery, and what role they play in the maintenance or erosion of resilience. The research shows that formal institutions are slow to learn, self-reorganize and respond to climate variability while fishermen’s responses are spontaneous, ensuring a rapid process of individual adaptation. Institutional responses are mostly ex-post, and are not strongly shaped by past experience, thus eroding the resilience of the system. However, fishermen’s responses sometimes lead to negative outcomes such as local stock overexploitation or ‘invasion’ of natural scallop habitats for scallop grow-out, and formal institutions play an important role in resilience building through the control of effort and entry in the fishery. In this paper causal loop diagrams are used to conceptualize the fishery system to highlight key variables and processes. The study thus provides the opportunity to explore the usefulness of causal loop diagrams and conceptual models combined with participatory approaches in the exploration of the resilience of a system. The case study also illustrates that individual adaptation, a feature of resilience, is occurring and will occur spontaneously, changing property right regimes and responding not only to climate variability but also market forces. In order to maintain and build resilience and engender positive management outcomes, formal institutions not only need to shape fishermen decision-making, they must also contribute to knowledge building as well as the adoption of innovative approaches.