Late Holocene linkages between decade–century scale climate variability and productivity at Lake Tanganyika, Africa

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between ∼∼2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals.Time series analyses of laminae thickness patterns demonstrate significant periodicities at interannual–centennial time scales. Longer time scale periodicities (multidecadal to centennial scale) of light and dark half couplet thicknesses are coherent and in some cases are similar to solar cycle periods on these time scales. Although laminae thickness cycles do not strongly covary with the actual Δ¹⁴C record for this same time period, two large Δ¹⁴C anomalies are associated with substantial decreases in both light and dark laminae thickness. In contrast to the multidecadal– centennial time scale, significant annual to decadal periodicities, which are broadly consistent with ENSO/PDO forcing and their impact on East African climate, are not coherent between light and dark half couplets. The coherency of light–dark couplets at decadal–centennial time scales, but not at shorter time scales, is consistent with a model of a long-term relationship between precipitation (recorded in wet season dark laminae thickness) and productivity (light laminae thickness), which is not manifest at shorter time scales. We hypothesize that this coupling results from long-term recharging of internal nutrient loading during wet periods (higher erosion of soil P) and reduced loading during drought intervals. The relationship is not expressed on short time scales during which the dominant control on productivity is wind-driven, dry season upwelling, which is uncorrelated with wet-season precipitation. Our record greatly extends the temporal record of this quasi-periodic behavior throughout the late Holocene and provides the first evidence linking decade- to century-scale episodes of enhanced productivity to enhanced precipitation levels and nutrient recharge in a productive tropical lake.     

The (re)making of the western 'geographical tradition': some missing links

Summary A brief investigation of certain missing links in the narration of the history of geography focuses on the need to consider the contribution of non-western geographical and scientific knowledges to the making of 'European discovery' and therefore to the development of a putatively western geographical tradition.     

Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes

Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 10⁹ pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.     

Discussion: Structural and stratigraphic problems of the Argylla Formation near Mary Kathleen,Queensland

Circumstantial evidence indicates that Gaussberg, an isolated, 370 m high volcanic cone on the Antarctic coast at 57°S, 89°E, is the product of subglacial eruption. The vesicular, highly potassic leucitite, of which Gaussberg is composed, has been dated by K‐Ar and fission‐track methods, the former being applied to leucite concentrates, the latter to glassy leucitite from the ropy‐textured, outer rind of a pillow‐like structure. The K‐Ar geochronology yields an average date of 56 000 ± 5000 years, jwhich is interpreted as defining the time of Gaussberg's formation. The fission‐track work yields a less precise date, which supports the K‐Ar age estimate. These new age determinations indicate that previously published K‐Ar age determinations of 20 Ma and 9 Ma for Gaussberg should be rejected.     

SOCIAL AND ENVIRONMENTAL IMPACTS OF WORLD BANK/IMF-FUNDED ECONOMIC RESTRUCTURING IN BOLIVIA: AN ANALYSIS OF ENRON AND SHELL'S HYDROCARBONS PROJECTS

With the spectacular financial collapse of Enron in 2001, Enron and Shell's Rio San Miguel‐Cuiabá gas pipeline gained international notoriety for degrading the last, most intact dry tropical forest in the world, Bolivia's Chiquitano forest. The paper uses specific case studies, including the case of the Cuiabá pipeline, to examine how economic restructuring sponsored by the World Bank, International Monetary Fund (IMF) and Inter‐American Development Bank (IDB) facilitated the entrance of multinational oil corporations that have caused significant social and environmental impacts in Bolivia. The paper explores the influence of international financial institutions and multinational oil corporations on Bolivian state institutions, particularly their ability to regulate and address impacts caused by developments in the hydrocarbons sector. It concludes that neoliberal policies, which resulted in partial privatisation of the state oil company and in expanded control over natural resources by multinational corporations (MNCs), were detrimental to sensitive ecosystems and indigenous inhabitants.     

Effect of fault reactivation on deformation of off-fault fractures near a generic deep geological repository in crystalline rock in Canada

Journal of Seismology - In this study, fault rupture and its effect on the deformation of the off-fault fractures are numerically simulated. The purpose of the analysis is to determine the distance...     

Experimental Study of the Effects of DNAPL Distribution on Mass Rebound

The release of stored dissolved contaminants from low permeability zones contributes to plume persistence beyond the time when dense nonaqueous phase liquid (DNAPL) has completely dissolved. This is fundamental to successfully meeting acceptable low concentrations in groundwater that are driven by site‐specific cleanup goals. The study goals were to assess the role of DNAPL entrapment morphology on mass storage and plume longevity. As controlled field studies are not feasible, two‐dimensional (2D) test tanks were used to quantify the significance of mass loading processes from source dissolution and stored mass rebound. A simple two‐layer soil domain representing a high permeable formation sand overlying a zone of lower permeability sand was used in the tests. DNAPL mass depletion through dissolution was monitored via X‐ray photon attenuation, and effluent samples were used to monitor the plume. These data enabled analysis of the DNAPL distribution, the dissolved plume, and the dissolved phase distribution within the low permeability layer. Tests in an intermediate tank showed that mass storage contributes substantially to plume longevity. Detectable effluent concentrations persisted long after DNAPL depletion. The small tank results indicated that the DNAPL morphology influenced the flow field and caused distinctive transport mechanisms contributing to mass storage. Zones of high DNAPL saturation at the interface between the low and high permeability layers exhibited flow bypassing and diffusion dominated transport into the low permeability layer. In the absence of a highly saturated DNAPL zone near the soil interface the contaminant penetrated deeper into the low permeability layer caused by a combination of advection and diffusion.     

The pre-Colombian footprint on terrestrial nutrient cycling in Costa Rica: insights from phosphorus in a lake sediment record

The impact of pre-Columbian subsistence agriculture on soil nutrient cycling in the American tropics is poorly quantified. Paleolimnological research can address this deficit by documenting the temporal evolution of nutrient cycling in lake watersheds over different time scales. Here we describe our use of a chemical sequential extraction technique adapted from soil fertility research to discern geochemical fractions of phosphorus (P) in lake sediments that serve as proxies for landscape-scale soil nutrient status. These P fractions are mineral P (the original lithic source of bioavailable P), occluded P (mainly bound to soil oxides), and organic P (remains of organic matter production by plants). We applied the P fractionation technique to a lake sediment core from a small lake in southern Costa Rica, Laguna Zoncho. Prior analyses of microfossils and stable carbon isotopes in this core documented an approximately 3,000 year history of human occupation and agricultural activity in the Zoncho watershed, and shifts in diatom communities in the lake associated both with human impacts and with climate-driven changes in lake level. Our P analyses revealed relatively constant P geochemistry during the first approximately 2,500 years of the record, when other sedimentary proxies reveal forest clearance and maize agriculture of varying intensity. However, the period from approximately 500 to 100 years BP is marked by a drastic shift toward a P geochemistry dominated by occluded forms, with a concomitant decrease in the relative content of both the organic and mineral P forms. This interval coincides with post-Conquest depopulation and forest regeneration at the site, and with an apparent deepening of the lake caused by a shift toward a wetter climate. The dominance of the occluded P fraction during this interval is the opposite of the trend expected with such a climate shift, implicating human dynamics as the principal driver of the changes in soil nutrient status indicated by the P fractions in the Zoncho core. We propose that the entire P geochemical record is dominated by human-induced alteration of the soil nutrient cycles via agriculture and occupation, and that the only interval that reveals the “natural” nutrient status in the region is the short interval when the site is abandoned and surrounding forests regrow. These results for Laguna Zoncho reveal the close connection between even relatively low-technology human activities and soil nutrient status.     

Numerical modeling of contaminant transport in a stratified heterogeneous aquifer with dipping anisotropy

The combined influence of dip angle and adsorption heterogeneity on solute transport mechanisms in heterogeneous media can be understood by performing simulations of steady-state flow and transient transport in a heterogeneous aquifer with dipping anisotropy. Reactive and non-reactive contaminant transport in various types of heterogeneous aquifer is studied by simulations. The hydraulic conductivity (K) of the heterogeneous aquifer is generated by HYDRO_GEN with a Gaussian correlation spectrum. By considering the heterogeneity of the adsorption distribution coefficient (K _d), a perfect negative correlation between lnK and lnK _d is obtained by using the spherical grains model. The generated K and K _d are used as input to groundwater flow and transport models to investigate the effects of dipping sedimentary heterogeneity on contaminant plume evolution. Simulation results showed that the magnitude of the dip angle strongly controls the plume evolution in the studied anisotropic and heterogeneous aquifer. The retarded average pore-water velocity (v/R) of the adsorption model significantly controls the horizontal spreading of the plume. The bottom plume is intensively retarded in the zones between the dipping lenses of lower hydraulic conductivity and the no-flow bottom boundary. The implications of these findings are very important for the management of contaminated heterogeneous aquifers.