Congo River sand and the equatorial quartz factory

A never solved problem in sedimentary petrology is the origin of sandstone consisting exclusively of quartz and most durable heavy minerals. The Congo River offers an excellent test case to investigate under which tectonic, geomorphological, climatic, and geochemical conditions pure quartzose sand is generated today. In both upper and lowermost parts of the catchment, tributaries contain significant amounts of feldspars, rock fragments, or moderately stable heavy minerals pointing at the central basin as the main location of the "quartz factory". In Congo sand, quartz is enriched relatively to all other minerals including zircon, as indicated by Si/Zr ratios much higher than in the upper continental crust. Selective elimination of old zircons that accumulated radiation damage through time is suggested by low percentages of grains yielding Archean U-Pb ages despite the basin being surrounded by Archean cratonic blocks. Intense weathering is documented by the lack of carbonate grains in sand and by dominant kaolinite and geochemical signatures in mud. In sand, composed almost entirely of SiO2, the weathering effect is masked by massive addition of quartz grains recycled during multiple events of basin inversion since the Proterozoic. Changes in mineralogical, geochemical, and geochronological signatures across Bas-Congo concur to suggest that approximately 10% of the sand supplied to the Atlantic Ocean is generated by rapid fluvial incision into the recently uplifted Atlantic Rise. The Congo River connects with a huge canyon similar to 30 km upstream of the mouth, and pure quartzose sand is thus funnelled directly toward the deep-sea to feed a huge turbidite fan. Offshore sediments on both sides of the canyon are not derived from the Congo River. They reflect mixed provenance, including illite-rich dust wind-blown from the arid Sahel and augite, hypersthene, and smectite ejected from volcanic centres probably situated along the Cameroon Line in the north. Because mixing of detritus from diverse sources and supply of polycyclic grains almost invariably occurs in the terminal lowland tract of a sediment-routing-system, no ancient sandstone can be safely considered as entirely first-cycle. Moreover, the abundance of pure quartzarenite in the rock record can hardly be explained by chemical weathering or physical recycling alone. The final cleansing of minerals other than quartz, zircon, tourmaline, and rutile requires one or more cycles of chemical dissolution during diagenesis, which operates at higher temperatures and over longer periods than weathering at the Earth's surface

On not knowing one’s place

Ethnographers have described many cultural worlds of the Pacific with subtlety and energy, but those worlds were and are always more complex than most standard forms of ethnography have recognized. The ASAO model for the presentation of expertise, while an impressive vehicle for demonstrating ethnographic skills and thoroughness, has yet to reform the accepted boundaries of the discipline or the tradition of Pacific societies seen as "social wholes." It has depended on a division of labor that allocates theory and field-work to different roles, it has recognized ethnographic authority as accruing to those with a concretely territorial claim to represent others, and it has encour-aged a static, monocultural sense of its audiences. I hasten to add that ASAO is not unique in this regard; these strictures apply to academic anthropology in general. Moreover, change is always possible as ethnographers strive to reinvent their discipline beyond the boundaries of the possible. But the historically closed and compartmentalized nature of academic knowledge means that challenges to its perceptual boundaries tend to result from the serendipitous recognition of moments where one does not "know one's place.

Identifying anthropogenic features at Seoke (Botswana) using pXRF: Expanding the record of southern African Stone Walled Sites.

Numerous and extensive 'Stone Walled Sites' have been identified in southern African Iron Age landscapes. Appearing from around 1200 CE, and showing considerable variability in size and form, these settlements are named after the dry-stone wall structures that characterize them. Stone Walled Sites were occupied by various Bantu-speaking agropastoral communities. In this paper we test the use of pXRF (portable X-ray fluorescence analysis) to generate a 'supplementary' archaeological record where evident stratigraphy is lacking, survey conditions may be uneven, and excavations limited, due to the overall site size. We propose herein the application of portable X-ray fluorescence analysis (pXRF) coupled with multivariate exploratory analysis and geostatistical modelling at Seoke, a southern African SWS of historical age (18th century CE). The aim of the paper is twofold: to explore the potential of the application of a low cost, quick, and minimally invasive technique to detect chemical markers in anthropogenic sediments from a Stone Walled Site, and to propose a way to analyse the results in order to improve our understanding of the use of space at non-generalized scales in such sites

Fine-Tuning Climate Resilience in Marine Socio-Ecological Systems: The Need for Accurate Space-Time Representativeness to Identify Relevant Consequences and Responses

Climate change triggers a wide mosaic of regional and local responses, often different to the large-scale variability in magnitude and direction. Because of the psychological connections (cognitive and emotional) with the frequency, intensity and age of a climatic event, people may have the capacity to recognize key variations at lower scales, especially those from which they perceive risk. Yet, the anticipatory actions and social engagement to respond or adapt to climate change are difficult to achieve, mostly when there exists a long psychological distance to climatic phenomena. Research about climate change communication provides clues about the relevance of place-based discussion to gauge risk perception and improve response protocols, their design and prioritization. It argues that strategies and actions required to face climate risks may widely differ depending on the scale and accuracy of the local representations displayed during discussions of climate impacts. This work examines how local attributes (from climate to social) operate and control place-specific risks and priorities, by comparing coastal communities in two locations, Cabo Pulmo, Mexico and Zanzibar, Tanzania, which are subject to different climate dynamics. This paper discusses the need to identify relevant climate risks/responses at the local level and how psycho-social factors (e.g., psychological distance, collective memory, and social engagement) may operate positively for building climate resilience. We also illustrate a workflow to increase and enhance collaboration between researchers and local people by promoting dialogue, participation and narratives that rigorously consider the local knowledge

PICES Press, Vol. 7, No. 2, July 1999

Improving PICES CO2 measurement quality The status of the Bering Sea: July - December 1998 The state of the eastern North Pacific since October 1998 The state of the western North Pacific in the second half of 1998 Paul Henry LeBlond Report on the ICES/SCOR Symposium on Ecosystem Effects of Fishing What is the carrying capacity of the North Pacific Ocean for salmonids? Southeast Bering Sea Carrying Capacity (SEBSCC) The Whole Earth System: The role of regional programs Sub-Arctic Gyre Experiment in the North Pacific Ocean (SAGE) The Alaska Predator Ecosystem Experiment (APEX): An integrated seabird and forage fish investigation sponsored by the Exxon Valdez Oil Spill Trustee Council ICES and GOOS: A progress report Report on GOOS Living Marine Resource Panel Meetin

Chemical leaching from polyethylene mulching films to soil in strawberry farming

Mulching is a widely practiced agricultural technique able to boost crop productivity and to reduce weed growth and water evaporation. One of the most common materials used for mulching is polyethylene. Polyethylene films are known to contain phthalates, plasticizers recognized as endocrine disruptors, thus able to endanger the hormonal system. Only few data exist on the possible transfer of plasticizers from polyethylene mulching films to agricultural soil, especially in Europe, or on the potential implications for the environment and human health. In this study, we analyzed the occurrence of plasticizers such as phthalates and acetyl tributyl citrate from polyethylene mulching films and soil samples collected from strawberry fields where polyethylene films have been used. The samples were analyzed with a gas chromatograph-mass spectrometer and the results indicated that the soil exposed to polyethylene mulches contained a significantly higher concentration, compared to the control soil, of some of the most common plasticizers, including dibuthyl phthalate, benzylbutyl phthalate and acetyl tributyl citrate. These outcomes highlight the need to carry out further research to understand the potential risks that mulching practices can cause for the environment and human health.Peer reviewe