Late Holocene Environmental Reconstructions from Lake Solai,Kenya

Playa lake systems tend to be overlooked archives of paleoenvironmental change due to the likelihood of a short and intermittent record of deposition. Groundwater-fed wetlands associated with these climate-sensitive playas, however, preserve changes in hydrologic budget and are thus valuable archives for semiarid regions. This study examines the paleoecological record of a groundwater-fed wetland from Lake Solai, Kenya. Biological proxies are used to reconstruct paleoenvironmental change and climate impacts over the past millennium. Dry conditions persisted between CE 1115 and 1490, followed by wetter conditions during the Little Ice Age. Near surface sediments indicate increasing anthropogenic impact through pastoralism.     

Stochastic Analysis Method of Sea Environment Simulated by Numerical Models

1 .IntroductionNumericalmodelsmostwidelyusedforseaenvironmentandsedimenttransportfocusonsolvingseriesofdifferentialequations .Theinputandoutputofanumericalmodelareconsideredasdecisivefactors .Butinrealitythecausesofnaturaleventssuchasmeteorological,astronomical,oceanograph ic ,geomorphologicandgeophysicalfactorsarerandom .Therearemanyuncertaintiesinvolvedininputfactorsinnumericalmodels .Correspondinglytheoutputsofnumericalmodelsarealsorandom .There fore ,theoutputparametersofnumericalmodelsca…     

The phytoplankton bloom response to wind events and upwelled nutrients during the CoOP WEST study

In the coastal waters off northern California, seasonal wind-driven upwelling supplies abundant nutrients to be processed by phytoplankton productivity. As part of the Coastal Ocean Processes: Wind Events and Shelf Transport (CoOP WEST) study, nutrients, CO₂, size-fractionated chlorophyll, and phytoplankton community structure were measured in the upwelling region off Bodega Bay, CA, during May–June 2000, 2001 and 2002. The ability of this ecosystem to assimilate nitrate (NO₃) and silicic acid/silicate (Si(OH)₄) and accumulate particulate material (i.e. phytoplankton) was realized in all 3 years, following short events of upwelling-favorable winds, followed by periods of relaxed winds. This was observed as phytoplankton blooms, dominated by chlorophyll in cells greater than 5 μm in diameter, that reduced the ambient nutrients to zero. These communities were located over the near-shore shelf (<100 m depth) and were dominated by diatoms. An optimal window of 3–7 days of relaxed winds, following an upwelling pulse, was required for chlorophyll accumulation. The large-celled phytoplankton that result are likely important players in coastal new production and carbon cycling.     

Plants versus streams: Their groundwater-mediated competition at “El Morro,” a developing catchment in the dry plains of Argentina

Our understanding of how groundwater mediates evapotranspiration/streamflow partitioning is still fragmented and catchment studies under changing vegetation conditions can provide a useful frame for integration. We explored this partition in a flat sedimentary dry catchment in central Argentina in which the replacement of native vegetation with rainfed crops was accompanied by the abrupt formation of groundwater-fed streams by subsurface erosion (i.e., sapping) episodes. Historical records indicated widespread water table rises (~0.3 m y⁻¹ on average). Groundwater level and stream baseflow fluctuated seasonally with minima in the warm rainy season, indicating that evaporative discharge rather than rainfall shapes saturated flows. Diurnal groundwater level fluctuations showed that plant uptake was widespread where water tables are shallow (<3 m) but restricted to deep-rooted Prosopis forests where they are deep (7–10 m). MODIS and LANDSAT NDVI revealed a long-term greening for native vegetation, new wetlands included, but not for croplands, suggesting more limited evapotranspiration-groundwater level regulation under agriculture. Close to the deepest (20 m) and most active incisions, groundwater level and greenness declined and stream baseflow showed no seasonal fluctuations, hinting decoupling from evapotranspiration. Intense ecological and geomorphological transformations in this catchment exposed the interplay of five mechanisms governing evapotranspiration/streamflow partition including (a) unsaturated uptake and both (b) riparian and (c) distributed uptake from the saturated zone by plants, as well as (d) deepening incisions and (e) sediment deposits over riparian zones by streams. Acknowledging the complex interplay of these mechanisms with groundwater is crucial to predict and manage future hydrological changes in the dry plains of South America.     

Public support for carbon dioxide removal strategies: the role of tampering with nature perceptions

Climatic Change - Carbon dioxide removal (CDR) describes a suite of controversial approaches to mitigating climate change that involve removing existing carbon dioxide from the atmosphere. Through...     

Decentring poverty studies: Middle class alliances and the social construction of poverty

Editors' Note: The following is the tenth in the Singapore Journal of Tropical Geography Lecture Series. It is based on the plenary presentation of 13 April at the AAG held in Seattle in 2011. In this essay I explore relational poverty analysis to take seriously the spatially varied intersections of political‐economic, social ordering and cultural‐political processes in shaping understandings of poverty. My work as part of the Middle Class Poverty Politics Research Group employs a relational comparative methodology to theorize where, when and under what circumstances those framed as ‘middle class’ act in opposition to or in solidarity with those named as ‘poor’. Our approach focuses on the exploitative effects of capital accumulation, processes of unequal sociospatial categorization and political and discursive systems that limit or exclude the poor. Our research focuses on places experiencing capitalist crisis because intense periods of restructuring highlight material and discursive struggles over poverty. We conclude by identifying a research agenda focused on the ways in which poverty politics are constituted by the nonpoor through place and in the articulation of places with processes of political economy, governance and cultural politics.     

Estimates of UK CO2 emissions from aviation using air traffic data

The allocation of CO₂ emissions to specific sources is a major policy issue for international aviation, especially for determining allocations for emissions trading schemes. This paper addresses the problem by recommending a possible methodology to allocate emissions to specific sources using detailed air traffic data. The basis for the calculations is an air traffic sample for one full-day of traffic from the UK. In order to analyse aircraft fuel burn use and hence CO₂ emissions, the Reorganized Air Traffic Control Mathematical Simulator (RAMS Plus) and the Advanced Emission Model (AEM III) are used. The results from these detailed simulations are compared with two of the most widely-used aviation CO₂ emission estimates to have been made for the UK: the SERAS study and NETCEN estimate. Their estimates for the year 2000 are 26.1 and 31.4 Mt, respectively. In addition, the most recent NETCEN estimate for the year 2003 is 34.1 Mt of CO₂. Our estimate of total aviation CO₂ emissions, using detailed simulations and real air traffic data, is 34.7 Mt for the year 2004. In addition, emission estimates are compared with two global aviation emission inventories: AERO2K and SAGE. Contributions of the highest-emitting flights and aircraft types are identified. International departures dominate; 6% of flights account for 50% of total emissions. The largest aircraft emit the most per flight-km, although not per passenger-km. Different methodologies and their implications are also discussed.     

Temporal characteristics and fog water collection during summer in Tenerife (Canary Islands, Spain)

The study of fog dynamics in the island of Tenerife began in 1993 at six sites. The analysis of the relationship between fog and several meteorological parameters was conducted at the site located at Anaga. Anaga is located at the summit of a mountain range, at an altitude of 842 m and 3.5 km away from the north-western coastline of the island. The study uses hourly data of the three summer months (June, July and August) that were collected over a period of nine years — from 1996 to 2005. The mean summer (June–August) rainfall was found to be 21.2 mm whilst the total volume of fog water collected was 879.9 l m^− 2; the daily average fog water collection was 9.5 l m^− 2 day^− 1, and the hourly average about 0.4 l m^− 2 h^− 1. Although these amounts were recorded with wind speeds of between 8 and 12 m s^− 1, the correlation between water collected and wind speed is not statistically significant. In spite of this, the volume of fog water collected and wind speed showed a very distinct daily behavioural pattern, their frequency and speed reaching their minimum at 12 a.m. and their maximum from 7 p.m. to 8 a.m. GMT. The importance of this research is that it shows that the fog in the Canary Islands occurs more frequently and makes a more significant contribution to the growth of vegetation in the summer (the dry season) than in the winter, when fog accompanies rainfall.     

Insights into silicic melt generation using plagioclase, quartz and melt inclusions from the caldera-forming Rotoiti eruption, Taupo volcanic zone, New Zealand

The Rotoiti (~120 km³) and Earthquake Flat (~10 km³) eruptions occurred in close succession from the Okataina Volcanic Centre at ~50 ka. While accessory mineral geochronology points to long periods of crystallization prior to eruption (10⁴–10⁵ years) and separate thermal histories for the magmas, little was known about the rates and processes of the final melt production and eruption. Crystal zoning patterns in plagioclase and quartz reveal the thermal and compositional history of the magmatic system leading up to the eruption. The dominant modal phase, plagioclase, displays considerable within-crystal zonation: An_37–74, ~40–227 ppm MgO, 45–227 ppm TiO₂, 416–910 ppm Sr and 168–1164 ppm Ba. Resorption horizons in the crystals are marked by sharp increases (10–30%) in Sr, MgO and X_An that reflect changes in melt composition and are consistent with open system processes. Melt inclusions display further evidence for open system behaviour, some are depleted in Sr and Ba relative to accompanying matrix glass not consistent with crystallization of modal assemblage. MI also display a wide range in XH₂O that is consistent with volatile fluxing. Quartz CL images reveal zoning that is truncated by resorption, and accompanied by abrupt increases in Ti concentration (30–80 ppm) that reflect temperature increases ~50–110°C. Diffusion across these resorption horizons is restricted to zones of <20 μm, suggesting most crystallization within the magma occurred in <2000 years. These episodes are brief compared to the longevity (10⁴–10⁵ year) of the crystal mush zones. All textural and compositional features observed within the quartz and plagioclase crystals are best explained by periodic mafic intrusions repeatedly melting parts of a crystal-rich zone and recharging the system with silicic melt. These periodic influxes of silicic melt would have accumulated to form the large volume of magma that fed the caldera-forming Rotoiti eruption.     

Palaeomagnetic investigations of the tertiary and quaternary igneous rocks: IV The tertiary volcanic rocks of the Tokaji mountains,Hungary

Measurements are reported from samples collected at twenty three sites in the Tokaj mountains of north-eastern Hungary. The simplest interpretation of the results is in terms of geomagnetic field reversals, for there is no petrological or magnetic evidence of self reversal or of correlation of oxidation state and magnetic sign. Four magnetic zones satisfy the minimum stratigraphic requirements, speculative use of these zones against theHeirtzler et al. magnetic time scale as a control suggests locating the Miocene-Pliocene boundary at 11.75 my. However it seems probable that much of the lower Sarmatian is not represented in the Tokaj samples, although the scatter of individual readings suggest secular variation is averaged out. The virtual pole position at 70.4 W, 82.8 N is not significantly different from the theoretical dipole field.

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Zusammenfassung Es wird über paläomagnetische Messungen an ungarischen Gesteinen berichtet, die von 23 Punkten in den Tokajer Bergen stammen.Die Ergebnisse werden als magnetische Feldumkehrungen gedeutet, da sich weder für Selbstumkehrungen noch für Beziehungen zwischen den jeweiligen Oxidationszuständen der Ilmenite und Titanomagnetite und den magnetischen Daten Anhaltspunkte ergeben haben.Vier magnetische Zonen entsprechen dieser stratigraphischen Abfolge; ein möglicher Vergleich dieser Zonen mit der magnetischen Zeitskala vonHeirtzler u. a. als Kontrolle legt die Vermutung nahe, die Miozän-Pliozän-Grenze mit 11,75 Millionen Jahren anzugeben.Einerseits ist es wahrscheinlich, daß das Untere Sarmat durch die Tokajer Vulkanite nicht vollständig erfaßt wird, andererseits kann eine Säkular-Variation als Deutungsmöglichkeit wahrscheinlich ausgeschlossen werden.Die virtuelle Pol-Position mit 70.4 W, 82.8 N weicht nicht bedeutend vom theoretischen Dipol-Feld ab.

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Résumé Des mesures paléomagnetiques ont été effectuées sur des roches hongroises qui proviennent de 23 endroits des montagnes TokaÏ.Les résultats sont interprétés comme des inversions du champ magnétique car il n'y a pas de raisons d'admettre ni d'auto-inversion ni de rapports entre les états d'oxidation des ilménites et des titanomagnétites et les données magnétiques.Quatre zones magnétiques correspondent à cette suite stratigraphique; une comparaison possible de ces zones avec l'échelle du temps deHeirtzler et al. comme contrÔle laisse supposer que la limite Miocène-Pliocène se situe à 11.75 millions années.Il est probable d'une part qu'une grande partie du Sarmatien inférieur n'est pas représentée par ces roches volcaniques de TokaÏ, d'autre part qu'une variation séculaire comme un interprétation possible peut Être exclue avec grande probabilité.La position virtuelle du pÔle avec 70.4 ouest, 82.8 nord n'est pas très différente du champ théorique du dipole.

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