Laterites and paleoclimates. Weathering processes and anthropogenic impact

The European Union of Geosciences held its 9th biannual meeting in Strasbourg, March 23–27, 1997. During this meeting, Symposium No. 63, Weathering Processes: Mineral deposits and soil formation in tropical enÍironments, was merged with Symposium No. 78, Anthropogenic Impact on Weathering processesco-sponsored by IGCP Project 405. The resulting symposium No. 63, Weathering processes and Anthropogenic Impact, was held under the sponsorship of EUROLAT1 and attracted 36 oral and poster presentations and about 100 participants, reflecting the interest of the Earth Sciences community in weathering processes and anthropogenic impact

Production of 21 Ne in depth-profiled olivine from a 54 Ma basalt sequence, Eastern Highlands (37° S), Australia

In this study we investigate the cosmogenic neon component in olivine samples from a vertical profile in order to quantify muogenic 21Ne production in this mineral. Samples were collected from an 11 m thick Eocene basalt profile in the Eastern Highlands of southeastern Australia. An eruption age of 54.15 ± 0.36 Ma (2σ) was determined from 40Ar/39Ar step-heating experiments (n = 6) on three whole-rock samples. A 36Cl profile on the section indicated an apparent steady state erosion rate of 4.7 ± 0.5 m Ma−1. The eruption age was used to calculate in situ produced radiogenic 4He and nucleogenic 3He and 21Ne concentrations in olivine. Olivine mineral separates (n = 4), extracted from the upper two metres of the studied profile, reveal cosmogenic 21Ne concentrations that attenuate exponentially with depth. However, olivine (Fo68) extracted from below 2 m does not contain discernible 21Ne aside from magmatic and nucleogenic components, with the exception of one sample that apparently contained equal proportions of nucleogenic and muogenic neon. Modelling results suggest a muogenic neon sea-level high-latitude production rate of 0.02 ± 0.04 to 0.9 ± 1.3 atoms g−1 a−1 (1σ), or <2.5% of spallogenic cosmogenic 21Ne production at Earth’s surface. These data support a key implicit assumption in the literature that accumulation of muogenic 21Ne in olivine in surface samples is likely to be negligible/minimal compared to spallogenic 21Ne

Distribution of ostracods in west-central Argentina related to host-water chemistry and climate : Implications for paleolimnology

Ecological and biogeographical studies of Neotropical non-marine ostracods are rare, although such information is needed to develop reliable paleoecological and paleoclimatic reconstructions for the region. An extensive, yet little explored South American area of paleoclimatic interest, is the arid-semiarid ecotone (Arid Diagonal) that separates arid Patagonia from subtropical/tropical northern South America, and lies at the intersection of the Pacific and Atlantic atmospheric circulation systems. This study focused on the Laguna Llancanelo basin, Argentina, a Ramsar site located within the Arid Diagonal, and was designed to build a modern dataset using ostracods (diversity, spatial distribution, seasonality, habitat preferences) and water chemistry. Cluster and multivariate analysis of the data indicated that salinity is the most significant variable segregating two ostracod groups. Limnocythere aff. staplini is the only species that develops abundant populations in the saline ephemeral Laguna Llancanelo during almost all seasons, and is accompanied by scarce Cypridopsis vidua in summer. The latter species is abundant in freshwater lotic sites, where Ilyocypris ramirezi, Herpetocypris helenae, and Cyprididae indet. are also found in large numbers. Darwinula stevensoni, Penthesilenula incae, Heterocypris incongruens, Chlamydotheca arcuata, Chlamydotheca sp., Herpetocypris helenae, and Potamocypris smaragdina prefer freshwater lentic conditions (springs), with C. arcuata and Chlamydotheca sp. found only in the Carapacho warm spring, which has a year-round constant temperature of ~20 °C. Seasonal sampling was necessary because some taxa display a highly seasonal distribution. Species that were recorded have either subtropical or Patagonian affinities, although a few taxa are endemic or common to both regions. These data can serve as modern analogues for reconstructing the late Quaternary history of the area, and to investigate the extent and position of the arid/semiarid ecotone (Arid Diagonal) during past glacial/interglacial cycles.Instituto de Limnología "Dr. Raúl A. Ringuelet

Fluctuations in productivity and denitrification in the Southeastern Arabian Sea during the Late Quaternary

Sedimentological and stable isotopic characteristics of sediments have been studied in a core from the southeastern Arabian Sea containing records of the past 70 ka. Palaeoproductivity proxies such as organic carbon (Corg), total nitrogen (TN) and calcium carbonate (CaCO3) contents, show high values at the core top and during the Last Glacial Maximum (LGM) and marine isotope stage (MIS) 4, suggesting high productivity, whereas low Corg and CaCO3 contents are associated with the MIS ½ and mid-MIS 3, indicating reduced productivity. The δ18O values in planktonic foraminifera range between - 2.7% and - 0.1%, with a large glacial-interglacial amplitude Δδ18O of ∼2.6%, suggesting changes related to monsoonal precipitation/ runoff. The δ15N values fluctuate between 5.4% and 7.3%, signifying variation in denitrification intensity. The δ15N indicates an overall increase in denitrification intensity during MIS 1 and MIS 3 and, reduced intensity during MIS ½, LGM and mid-MIS 3. Higher primary productivity and reduced denitrification intensity during LGM and MIS 4 might be due to convective winter mixing and more oxygenated subsurface waters. Reduced primary productivity during MIS ½ and mid-MIS 3 might be the effect of enhanced precipitation associated with the intensified southwest monsoon fortifying near-surface stratification

Climate change and freshwater zooplankton: what does it boil down to?

Recently, major advances in the climate–zooplankton interface have been made some of which appeared to receive much attention in a broader audience of ecologists as well. In contrast to the marine realm, however, we still lack a more holistic summary of recent knowledge in freshwater. We discuss climate change-related variation in physical and biological attributes of lakes and running waters, high-order ecological functions, and subsequent alteration in zooplankton abundance, phenology, distribution, body size, community structure, life history parameters, and behavior by focusing on community level responses. The adequacy of large-scale climatic indices in ecology has received considerable support and provided a framework for the interpretation of community and species level responses in freshwater zooplankton. Modeling perspectives deserve particular consideration, since this promising stream of ecology is of particular applicability in climate change research owing to the inherently predictive nature of this field. In the future, ecologists should expand their research on species beyond daphnids, should address questions as to how different intrinsic and extrinsic drivers interact, should move beyond correlative approaches toward more mechanistic explanations, and last but not least, should facilitate transfer of biological data both across space and time

Chemical cleaning effects on properties and separation efficiency of an RO membrane

This study aims to investigate the impacts of chemical cleaning on the performance of a reverse osmosis membrane. Chemicals used for simulating membrane cleaning include a surfactant (sodium dodecyl sulfate, SDS), a chelating agent (ethylenediaminetetraacetic acid, EDTA), and two proprietary cleaning formulations namely MC3 and MC11. The impact of sequential exposure to multiple membrane cleaning solutions was also examined. Water permeability and the rejection of boron and sodium were investigated under various water fluxes, temperatures and feedwater pH. Changes in the membrane performance were systematically explained based on the changes in the charge density, hydrophobicity and chemical structure of the membrane surface. The experimental results show that membrane cleaning can significantly alter the hydrophobicity and water permeability of the membrane; however, its impacts on the rejections of boron and sodium are marginal. Although the presence of surfactant or chelating agent may cause decreases in the rejection, solution pH is the key factor responsible for the loss of membrane separation and changes in the surface properties. The impact of solution pH on the water permeability can be reversed by applying a subsequent cleaning with the opposite pH condition. Nevertheless, the impacts of solution pH on boron and sodium rejections are irreversible in most cases

Enhanced boron rejection by NF/RO membranes by complexation with polyols: measurement and mechanisms

Boron rejection by nanofiltration (NF) and reverse osmosis (RO) membranes in the presence of glycerol, mannitol and sorbitol was investigated as a function of feed solution pH and boron:polyol molar ratio. In the presence of polyols, significant boron rejection improvement was obtained and the extent of the impact was directly related to the stability constant of the boron-polyol complex. Polyols could complex with boron in either the boric acid or borate anion forms; however the complexation between polyol and boric acid appeared to be incomplete. With and without the presence of polyols, boron rejection was strongly pH dependent. The increase in boron rejection due to polyol addition was higher for the NF membrane compared to the RO membrane. A boron:polyol molar ratio of 1:1 appeared to be adequate. The presence of polyols did not cause any observable membrane fouling. Results reported here suggest that the addition of polyols could allow NF membranes to be effectively used for boron removal

Diversité et écologie des charophytes (Charales) actuelles et du Quaternaire d'Australie

La distribution biogéographique des charophytes d\u27Australie (62 espèces inventoriées) montre une grande proportion de taxons endémiques (62 ) et dioïques (45 ), ainsi que des espèces qui ne développent pas de gyrogonites (84 ). La présente étude s\u27appuie sur la récolte de charophytes (Charophyta, Charales) de cent cinquante-deux localités et quarante-deux taxons ont été identifiés. Des facteurs écologiques, en particulier la salinité et la profondeur d\u27eau, sont indiqués parce que ce sont les principaux facteurs pour la distribution des charophytes et qu\u27ils sont indicateurs d\u27une augmentation de la salinité dans certaines pièces d\u27eau en Australie. Les différentes espèces ont été rencontrées à des salinités entre 0 g L-1 et 58 g L-1 et à des profondeurs allant de quelques cm d\u27eau à 12 m. Les données sur la salinité et la profondeur d\u27eau sont résumées par des graphiques montrant les relations Salinité/Espèce et Profondeur/Espèce qui pourront être utiles pour modéliser des changements dans les pièces d\u27eau et pour retracer des séries paléo-écologiques à l\u27aide de matériel fossile. Pour comprendre la distribution et l\u27écologie de l\u27espèce actuelle, il nous paraît important d\u27inclure les données disponibles pour le Quaternaire australien qui se limitent à deux références sur le Pléistocène et une sur l\u27Holocène. La méthodologie paléolimnologique utilise les données de l\u27écologie actuelle pour en déduire les changements environnementaux.The Australian charophyte flora (62 species recorded) is characterized by a high proportion of taxa which are endemic (62), dioecious (45), and that do not develop gyrogonites (84). In this study, charophytes (Charophyta, Charales) were collected from one hundred and fifty two localities and forty two species identified. Ecological factors were recorded, in particular, salinity and water depth because these are the main factors affecting charophyte distribution, and pertinent to increasing salinisation of some Australian water-bodies. The different species were recorded at salinities ranging between 0 g L-1 and 58 g L-1 and at depths between few cm of water up to 12 m. Data on salinity and water depth are summarized by salinity/species and water depth/species graphs. A temporal perspective is important to understand the modern species distribution and ecology, so available data from the Australian Quaternary record are incorporated, being two from the Late Pleistocene and one from the Holocene. The palaeolimnological methodology uses the modern environmental data to infer environmental changes.</p