Assimilating altimetric data to control the tropical instability waves: an observing system simulation experiment study

Tropical instability waves (TIWs) are not easily simulated by ocean circulation models primarily because such waves are very sensitive to wind forcing. In this study, we investigate the impact of assimilating sea surface height (SSH) observations on the control of TIWs in an observing system simulation experiment (OSSE) context based on a regional model configuration of the tropical Atlantic. A Kalman filtering method with suitable adaptations is found to be successful when altimetric data are assimilated in conjunction with sea surface temperature and some in situ temperature/salinity profiles. In this rather realistic system, the TIW phase is roughly controlled with a single nadir observing satellite. However, a right correction of the TIW structure and amplitude requires at least two nadir observing satellites or a wide swath observing satellite. The significant impact of orbital parameters is also demonstrated: in particular, the Jason or GFO satellite orbits are found to be more suitable than the ENVISAT orbit. More generally, it is found that as soon as adequate sub-sampling exists (with periods of 5–10?days), the length of the repetitivity cycle of orbits does not have a significant impact.     

Predation by jellyfish on large and emergent zooplankton: Implications for benthic–pelagic coupling

Stable carbon isotopes were used to determine the contribution of emergent demersal zooplankton to the diet of the scyphozoan jellyfish Catostylus mosaicus at Smiths Lake, New South Wales, Australia. A preliminary study in 2004 indicated that there was no difference in the δ¹³C of ectodermal tissue and mesoglea of the medusae. In 2005, medusae and zooplankton present during the day and night were sampled and isotopic signatures were modelled using IsoSource. Modelling indicated that: (1) mollusc veligers and copepods sampled during the day contributed <13% of the carbon to the jellyfish; (2) copepods sampled at night contributed up to 25%; and (3) the large, emergent decapod Lucifer sp. contributed 88–94%. We hypothesised, therefore, that medusae derive most of their carbon from emergent species of zooplankton. In 2006, sampling done in 2005 was repeated three times over a period of 4 weeks to measure short-term temporal variation in isotopic signatures of medusae and zooplankton, and emergent demersal zooplankton was specifically sampled using emergence traps. Short-term temporal variation in isotopic signatures was observed for some taxa, however, actual variations were small (<1.5‰) and the values of medusae and zooplankton remained consistent relative to each other. IsoSource modelling revealed that mysid shrimp and emergent copepods together contributed 79–100% of the carbon to the jellyfish, and that the maximum possible contribution of daytime copepods and molluscs was only 22%. Jellyfish apparently derive most of their carbon from emergent zooplankton and by capturing small numbers of relatively large taxa, such as Lucifer sp. or mysid shrimp. Small but abundantly captured zooplankton (such as mollusc veligers) contribute only minor amounts of carbon. Jellyfish have a major role in the transfer of carbon between benthic and pelagic food webs in coastal systems.     

Impact of seasonal variations in hydrological stresses and spatial variations in geologic conditions on a TCE plume at an industrial complex in Wonju,Korea

Spatial and temporal variations in a trichloroethylene (TCE) plume at an industrial complex in Wonju, Korea, were examined based on hydrogeological data and seven rounds of groundwater quality data collected over a year. The site has considerable vertical heterogeneities; the top layer of soil is covered by impermeable paving material at several locations, followed by a series of reclaimed or residual soil layers, and with weathered rocks to the crystalline biotite granite at the bottom. Areal heterogeneity in the surface conditions plays an important role in controlling groundwater recharge. The heterogeneity structure is influenced by complex surface conditions paved with asphalt and concrete. Owing to the presence of limited recharge area and concentrated summer precipitation events, the effects of seasonal variations on groundwater hydraulics tend to diminish with distance from the recharge area. This result was established by analysing the influence of the contrasting surface recharge conditions between the near‐source zone and the far zone, and the seasonally concentrated precipitation on the transport patterns of a TCE plume. In addition, variations in the plume's downstream contaminant flux levels were also analysed along a transect line near the source zone. The results show that the general tendency of the TCE plume contaminant concentration and mass discharges were reproducible if we account for seasonal recharge variations and the associated changes in the groundwater level. During recharge events, the TCE concentration variations appear to be influenced by leaching of the residual dense non‐aqueous‐phase liquid (DNAPL) TCE trapped in the unsaturated zone. This result shows that seasonal variations in contaminant plume near the source zone is inevitable at this site, and that these variations indicate the presence of residual DNAPL at or above the water table, at least in some isolated locations. Copyright © 2011 John Wiley & Sons, Ltd.     

The densest meteorite collection area in hot deserts: The San Juan meteorite field (Atacama Desert,Chile)

Abstract– We describe the geological, morphological, and climatic setting of the San Juan meteorite collection area in the Central Depression of the Atacama Desert (Chile). Our recovery activities yielded 48 meteorites corresponding to a minimum of 36 different falls within a 3.88 km² area. The recovery density is in the range 9–12 falls km^?2 depending on pairing, making it the densest among meteorite collection areas in hot deserts. This high meteorite concentration is linked to the long‐standing hyperaridity of the area, the stability of the surface pebbles (> Ma), and very low erosion rates of surface pebbles (approximately 30 cm Ma^?1 maximum). The San Juan meteorite population is characterized by old terrestrial ages that range from zero to beyond 40 ka, and limited weathering compared with other dense collection areas in hot desert. Chemical weathering in San Juan is slow and mainly controlled by the initial porosity of meteorites. As in the Antarctic and other hot deserts, there is an overabundance of H chondrites and a shortage of LL chondrites compared with the modern falls population, suggesting a recent (< few ka) change in the composition of the meteorite flux to Earth.     

http://www.sciencedirect.com/science/article/pii/S1674987113000327

The Panzhihua intrusion in southwest China is part of the Emeishan large igneous province and host of a large Fe-Ti-V ore deposit.In previous interpretations it was considered to be a layered,differentiated sill with the ore deposits at its base.New structural and petrological data suggest instead that the intrusion has an open S-shape,with two near-concordant segments joined by a discordant dyke-like segment. During emplacement of the main intrusion,multiple generations of mafic dykes invaded carbonate wall rocks,producing a large contact aureole.In the central segment,magmatic layering is oriented oblique to the walls of the intrusion.This layering cannot have formed by crystal settling or in-situ growth on the floor of the intrusion;instead we propose that it resulted from inward solidification of multiple,individually operating,convection cells.Ore formation was triggered by interaction of magma with carbonate wall rocks.     

Stratigraphy and depositional environments of the Mamfe Formation and its implication on the tectonosedimentary evolution of the Ikom-Mamfe Embayment, West Africa

A 42 m thick outcropping portion of the Mamfe Formation is subdivided into Manyu (31 m thick) and Kesham (11m thick) Members on the basis of textural, mineralogical and structural differences. The Manyu Member (Albian) consists of folded and indurated, medium to coarse grained arkosic sandstones and thickly laminated organic-rich shales deposited in a lacustrine environment. The Kesham Member (Cenomanian) consists of subarkoses intercalated with massive green shale and mudstone deposited in a fluvial environment. The change in depositional environment was tectonically controlled. The mid Cretaceous paleogeography of the embayment was governed by the NE-SW trending “Ikom ridge” which prevented marine incursion from adjacent the Benue Sea. Evaporites found within the basin were precipitated from ocean water that was periodically spilled by strong tides and storms across the ridge into the embayment. The filling-up of the embayment to base level in the Cenomanian resulted in a shift in the depositional center downstream to adjoining lower Benue Trough. Similarity in heavy mineral composition and maturity of the Cenomanian sandstones with recent clastics in the embayment indicates their derivation from the same source terrain and relatively stable tectonic and climatic conditions at the source area since the Cenomanian time.     

Understanding Effectiveness in its Broader Context: Assessing Case Study Methodologies for Evaluating Collaborative Conservation Governance

Abstract

Collaborative forms of governance are increasingly favored in conservation and potentially offer a range of practical and outcome-based benefits. However, tools for critically assessing whether and how collaboration enhances the attainment of conservation objectives are lagging behind the enthusiasm. We use a framework that considers effectiveness in relation to capacity of key actors and institutions to achieve outcomes and respond to emergent problems, robustness over time (i.e. adapting to changes while still achieving objectives), context-specific drivers of change, and the structure of networks and institutions to assess common approaches for evaluating effectiveness. Network analysis performs well in terms of structure, while action research and the diagnostic method offer deep insights into capacity and context. Scenario planning performs well in understanding robustness and context but performs better when combined with a diagnostic. The evaluation reveals important insights for approaching and standardizing investigations of collaborative governance regimes and their effectiveness.     

Role of dynamic vegetation in regional climate predictions over western Africa

This study examines the role of vegetation dynamics in regional predictions of future climate change in western Africa using a dynamic vegetation model asynchronously coupled to a regional climate model. Two experiments, one for present day and one for future, are conducted with the linked regional climate-vegetation model, and the third with the regional climate model standing alone that predicts future climate based on present-day vegetation. These simulations are so designed in order to tease out the impact of structural vegetation feedback on simulated climate and hydrological processes. According to future predictions by the regional climate-vegetation model, increase in LAI is widespread, with significant shift in vegetation type. Over the Guinean Coast in 2084–2093, evergreen tree coverage decreases by 49% compared to 1984–1993, while drought deciduous tree coverage increases by 56%. Over the Sahel region in the same period, grass cover increases by 31%. Such vegetation changes are accompanied by a decrease of JJA rainfall by 2% over the Guinean Coast and an increase by 23% over the Sahel. This rather small decrease or large increase of precipitation is largely attributable to the role of vegetation feedback. Without the feedback effect from vegetation, the regional climate model would have predicted a 5% decrease of JJA rainfall in both the Guinean Coast and the Sahel as a result of the radiative and physiological effects of higher atmospheric CO₂ concentration. These results demonstrate that climate- and CO₂-induced changes in vegetation structure modify hydrological processes and climate at magnitudes comparable to or even higher than the radiative and physiological effects, thus evincing the importance of including vegetation feedback in future climate predictions.     

Scaling of adsorption reactions: U(VI) experiments and modeling

Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate–adsorbent systems as well.