210Pb in the ocean: A pilot tracer for modeling particle reactive elements

We discuss the basic requirements for a successful modeling of²¹⁰Pb in the ocean as a test tracer for at least other lead isotopes, but also of other elements that behave similarly to lead. With the aid of realistic models of the oceanic circulation and the major biogeochemical cycles in it, the result is a dynamically consistent model of lead cycling that reproduces observed profiles within 10%.     

The chemical and physical characteristics of heavy metals in humus and till in the vicinity of the base metal smelter at Flin Flon, Manitoba, Canada

 Trace element geochemistry of humus (<0.425 mm) and till (<0.002 mm) collected in the Flin Flon-Snow Lake area, northern Manitoba and Saskatchewan, provides a regional context for assessing smelter contamination in the environment. The area includes a Cu-Zn smelter known to discharge As, Cd, Cu, Fe, Hg, Pb, and Zn. In this study, sequential extraction analyses, scanning electron microscopy and x-ray diffraction analyses were used on a suite of samples to determine: (1) the chemical and physical characteristics of heavy metals in surficial sediments related to distance from the smelter, (2) criteria for assessing the relative contribution of these metals from natural and anthropogenic sources, and (3) the potential of these metals for remobilization in the environment. Humus geochemistry reflects the anthropogenic and natural component of heavy metal concentrations. Smelter-related elements show anomalously high values adjacent to the smelter, decreasing with distance until background values are reached at 70–104 km, depending on the element. In humus, Zn is associated primarily with labile phases; Hg with non-labile phases. Adjacent to the smelter, high proportions and concentrations of Zn and Hg in non-labile phases, indicative of smelter-derived particulates, are confirmed by SEM examination. The particles occur as spheres, irregular grains, and with organics. With increasing distance from the smelter, the geochemical response to bedrock composition is more obvious than the anthropogenic input. Till geochemistry reflects the natural variation imposed by bedrock composition. At highly contaminated sites (<3 km from the smelter), increased percentages of smelter-related elements in labile phases suggests heavy metals are leached from humus to the underlying sediment. Received: 5 November 1996 · Accepted: 31 March 1997     

Paleolimnological features of a mega-lake phase in the Makgadikgadi Basin (Kalahari,Botswana) during Marine Isotope Stage 5 inferred from diatoms

The Makgadikgadi–Okavango–Zambezi basin (MOZB) is a structural depression in the south-western branch of the East African Rift System of the northern and middle Kalahari, central southern Africa. In the present day, the mainly dry subbasins of the MOZB are part of a long-lived lacustrine system that has likely existed since Early Pleistocene and from which an extant freshwater fish radiation emerged seeding all major river systems of southern Africa. During hydrologically favourable periods the subbasins were connected as a single mega-lake termed Lake Palaeo-Makgadikgadi. Previous geomorphological studies and OSL dates have provided evidence for repeated mega-lake periods since approximately 300 ka. The environmental and climatic implications of such large scale late Quaternary lake-level fluctuations are controversial, with the duration of mega-lake phases poorly constrained. Here, we present the first evidence for a Marine Isotope Stage (MIS) 5 mega-lake period (about 935–940 m a.s.l.) reconstructed from a diatom-rich, 30-cm-thick lacustrine sediment section, exposed close to a palaeo-shoreline of the Makgadikgadi Basin. Based upon the environmental setting and in comparison with sedimentation rates of other similar lake environments, we tentatively estimated that the highstand lasted approximately 1 ka during MIS 5d–b. The 30-cm section was sampled in 0.5-cm steps. Diatom species diversity ranges from 19 to 30 through the section. The dominant species are Pseudostaurosira brevistriata, Rhopalodia gibberula, Cyclotella meneghiniana and Epithemia sorex. The total of 60 sediment samples provide us with a record at decadal to bi-decadal resolution. Based on diatom assemblages and their oxygen isotope composition (δ¹⁸O) we infer an alkaline and mostly oligohaline lake with shallow water conditions prevailing in MIS 5, and is potentially analogous to a Heinrich event. The climate over southern Africa during MIS 5 has been considered very arid but the hydromorphological context of our sediment section indicates that we captured a mega-lake period providing evidence that short-term excursions to significantly higher humidity existed. A hydrologically more favourable environment during MIS 5 than formerly presumed is in line with the early human occupation of the Kalahari.     

The role of porous matrix in water flow regulation within a karst unsaturated zone: an integrated hydrogeophysical approach

Some portions of the porous rock matrix in the karst unsaturated zone (UZ) can contain large volumes of water and play a major role in water flow regulation. The essential results are presented of a local-scale study conducted in 2011 and 2012 above the Low Noise Underground Laboratory (LSBB – Laboratoire Souterrain à Bas Bruit) at Rustrel, southeastern France. Previous research revealed the geological structure and water-related features of the study site and illustrated the feasibility of specific hydrogeophysical measurements. In this study, the focus is on hydrodynamics at the seasonal and event timescales. Magnetic resonance sounding (MRS) measured a high water content (more than 10 %) in a large volume of rock. This large volume of water cannot be stored in fractures and conduits within the UZ. MRS was also used to measure the seasonal variation of water stored in the karst UZ. A process-based model was developed to simulate the effect of vegetation on groundwater recharge dynamics. In addition, electrical resistivity tomography (ERT) monitoring was used to assess preferential water pathways during a rain event. This study demonstrates the major influence of water flow within the porous rock matrix on the UZ hydrogeological functioning at both the local (LSBB) and regional (Fontaine de Vaucluse) scales. By taking into account the role of the porous matrix in water flow regulation, these findings may significantly improve karst groundwater hydrodynamic modelling, exploitation, and sustainable management.     

Re-specifying disaster risk: concepts,methods, and models

The discussion on the social-ecological dimensions of hazards is constantly evolving. This paper explores the trajectory of research relating to hazards and their impact on vulnerable human populations. Interpretations of disaster risk have included estimating losses in terms of human life and property, and analyzing the social mechanisms in place that exacerbate or mitigate a population’s sensitivity to hazard events. In keeping with recent trends in research relating to disaster risk, the paper focuses on the social dimension of vulnerability and the contribution of social structures and relationships in building community resilience. Institutional frameworks and policies in particular determine the quantity and quality of resources and services available to people that contribute to resilience over time. The hazard-risk-location-model (HRLM) is proposed that is based on re-specifying disaster risk in terms of exposure and coping ability to capture the focus on social vulnerability and resilience. The framework of the HRLM incorporates the following components: (1) linkages within existing social capital; (2) spatial variation in social and institutional frameworks; (3) positive and negative feedbacks; and (4) characteristics of the hazard event. The model contributes to the range of place-based assessments designed to address the human-environmental impacts of hazards and disasters.     

Facies in a Devonian‐Carboniferous volcanic fore‐arc succession,Campwyn Volcanics,Mackay district,central Queensland∗

The Middle Devonian to Early Carboniferous Campwyn Volcanics of coastal central Queensland form part of the fore‐arc basin and eastern flank of the volcanic arc of the northern New England Fold Belt. They consist of a complex association of pyroclastic, hyaloclastic and resedimented, texturally immature volcaniclastic facies associated with shallow intrusions, lavas and minor limestone, non‐volcanic siliciclastics and ignimbrite. Primary igneous rocks indicate a predominantly mafic‐intermediate parentage. Mafic to intermediate pyroclastic rocks within the unit formed from both subaerial and ?submarine to emergent strombolian and phreatomagmatic eruptions. Quench‐fragmented hyaloclastite breccias are widespread and abundant. Shallow marine conditions for much of the succession are indicated by fossil assemblages and intercalated limestone and epiclastic sandstone and conglomerate facies. Volcanism and associated intrusions were widely dispersed in the Campwyn depositional basin in both space and time. The minor component of silicic volcanic products is thought to have been less proximal and derived from eruptive centres to the west, inboard of the basin.     

Messing with nature? Exploring public perceptions of geoengineering in the UK

Anthropogenic influence on the climate – and possible societal responses to it – offers a unique window through which to examine the way people think about and relate to the natural world. This paper reports data from four, one-day deliberative workshops conducted with members of the UK public during early 2012. The workshops focused on geoengineering – the deliberate, large-scale manipulation of the planetary environment – as one of three possible responses to climate change (alongside mitigation and adaptation). Here, we explore one of the most pervasive and wide-ranging themes to emerge from the workshops: whether geoengineering represented an unprecedented human intervention into ‘nature’, and what the moral consequences of this might be. Using the concept of ‘messing with nature’ as an analytical lens, we explore public perceptions of geoengineering. We also reflect on why ‘messing with nature’ was such a focal point for debate and disagreement, and whether the prospect of geoengineering may reveal new dimensions to the way that people think about the natural world, and their relationship to it.     

Radiocarbon Ages Constraints on the Origin and Shedding of Bank-Top Sediment in the Bahamas during the Holocene

Great quantities of fine-sized aragonite needles are produced in the shallow waters that cover the tops of the Bahama Banks and then exported to the bank margins where they accumulate with shells of pelagic organisms. To better understand these processes, we investigated Holocene-aged sediments in a core from the southwestern margin of Little Bahama Bank. The aragonite content of the sediments, ??¹⁸O of planktonic foraminifera shells, and radiocarbon ages of aragonite-rich <63 ??m sediments and coexisting planktonic foraminifera shells were determined. Sediment deposition was rapid overall, and a significant increase in deposition rate occurred 3,500?C4,000 years ago, shortly after rising sea level flooded the bank top with seawater and caused a dramatic increase in the shallow water area where aragonite production occurred. During the latest Holocene when high deposition rates minimize effects of bioturbation, aragonite-rich <63 ??m sediments are 400?C600 years older than coexisting foraminifera. This difference indicates the net age of aragonite when it was exported from the bank top. It is consistent with expectations of the ??hip-hop??n?? model (Morse et al. in Geochimica et Cosmochimica Acta 67: 2819?C2826, 2003) whereby aragonite needles on the bank top, formed initially by biologic or other processes, continue to grow for hundreds of years via precipitation of epitaxial carbonate cement from seawater. Earlier in the Holocene, when sea level was lower and the top of Little Bahama Bank was subaerially exposed, the deposition rate and aragonite content of the sediments were less, and the aragonite-rich <63 ??m sediments are about 1,000 years younger than coexisting foraminifera. This age difference can be explained by downward mixing of latest-Holocene <63 ??m material into older early-Holocene sediments.     

Ten guiding principles for the delineation of priority habitat for endangered small cetaceans

The adoption of endangered species laws in various nations has intensified efforts to better understand, and protect, at-risk species or populations, and their habitats. In many countries, delineating a portion of a species' habitat as particularly worthy of protection has become a mantra of these laws. Unfortunately, the laws themselves often provide scientists and managers with few, if any, guidelines for how to define such habitat. Conservationists and scientists may view protecting part of the habitat of an endangered species as an ineffectual compromise, while managers may be under pressure to allow a range of human activities within the species' habitat. In the case of small cetaceans, establishing boundaries for such areas can also be complicated by their mobility, the fluid nature of their environment, and the often ephemeral nature of their habitat features. The convergence of multiple human impacts in coastal waters around the world is impacting many small cetaceans (and other species) that rely on these areas for feeding, reproducing, and resting. The ten guiding principles presented here provide a means to characterize the habitat needs of small, at-risk cetaceans, and serve as a basis for the delineation of ‘priority habitat’ boundaries. This conceptual approach should facilitate a constructive discourse between scientists and managers engaged in efforts to recover endangered species. The degree to which the recovery of an at-risk species can be reconciled with sustainable economic activity will depend in part on how well these principles are incorporated into the delineation of priority habitat.