Geology of the Atlantis Massif (Mid-Atlantic Ridge, 30° N): Implications for the evolution of an ultramafic oceanic core complex

Marine Geophysical Research - The oceanic core complex comprising Atlantis Massif was formed within the past 1.5–2 Myr at the intersection of the Mid-Atlantic Ridge, 30° N, and the...     

Brown trout (Salmo trutta) removal by rotenone alters zooplankton and phytoplankton community composition in a shallow mesotrophic reservoir

Brown trout (Salmo trutta) are known to have effects on multiple trophic levels in New Zealand streams, but their impacts on lower trophic levels are less well understood within lentic systems. We examined the effects of brown trout removal using rotenone on zooplankton and phytoplankton community composition in the Upper Karori Reservoir, New Zealand. Significant shifts were observed in zooplankton and phytoplankton composition following removal of brown trout from the reservoir. Shifts in zooplankton community composition did not occur immediately following trout removal (February), but instead followed the likely timing of galaxiid spawning (July). The removal of brown trout likely resulted in reduced predation pressure on galaxiids. A major change occurred in the zooplankton community with the dominance shifting from larger crustaceans to smaller rotifers, indicating an increased predation pressure from the larval native galaxiid. A delayed response in zooplankton community composition change indicates rotenone was not the direct cause of this. A major shift in phytoplankton community composition occurred immediately following trout removal. This was not consistent with the trophic cascade hypothesis of reduced grazing pressure from larger zooplankton due to increased galaxiid predation as a result of brown trout removal.     

Decadal flood trends in Bangladesh from extensive hydrographic data

Bangladesh is a country that comprises much of the world’s largest delta, formed from the Ganges, Brahmaputra, and Meghna (GBM) rivers and their tributaries. Flooding is a fact of life in Bangladesh where up to two-thirds of the country is flooded annually from combined monsoonal rains and Himalayan snowmelt. For this reason, understanding flood dynamics on both local and regional scales is critical. However, flood hazard studies to date typically rely on single flooding events to create flood maps and to evaluate flood hazards using satellite imagery. Here we use geographic information systems to analyze weekly water level data from 304 river gauges and over 1200 groundwater gauges from the Bangladesh Water Development Board to determine the spatial and temporal changes in flood depth and extent. These data cover an eight year period from 2002 to 2010 and provide a temporal resolution that match or are better than that of available satellite imagery. Country-wide ground and surface water levels and corresponding annual flooding events were determined along with groundwater level, flooding, and precipitation trends in Bangladesh at multiple scales. We find that while precipitation within the GBM basin has steadily increased through the time series, the average country-wide inundation depth and absolute water level has been decreasing. These respective trends could be attributed to improved flood management strategies in Bangladesh and surrounding countries that are within the GBM basin, as well as fluctuating weather patterns, declining volume of Himalayan snowmelt runoff, dam construction upriver from the GBD both within and outside the Bangladesh border, and increased groundwater abstraction of shallow groundwater aquifers for sustaining life in the eighth most populous country in the world.     

Socioeconomic dynamics of the Ghanaian tuna industry: a value-chain approach to understanding aspects of global fisheries

This study investigated how an industrial tuna fishery functions in terms of procedures, practices, governance and finance in the context of Ghana, West Africa. Tuna is Ghana’s biggest seafood export, contributing significantly to the domestic fisheries sector. A case-study approach was used to analyse relevant social and economic factors at the local scale to better understand how the global seafood industry operates in a low-income country. A value-chain framework was adopted to assess market structures, sales pathways and revenue distribution. We also investigated the role of actors engaged in the industry using secondary data, interviews, questionnaires and participant observations. The results revealed a changing organisational structure in tuna production, moving from bait-boat fishing with smaller companies to large-scale purse-seine fishing backed by consolidated Asian seafood companies. Production was found to depend significantly on local female intermediaries for access to funds through prefinancing arrangements. Considerable illegalities were identified within the value chain, highlighting the need for improved partnership and licensing negotiations, and for low-cost marine control and surveillance tools. As vertical integration increases within the industry, the influence of corporations as keystone actors becomes evident for the future social and ecological sustainability of the industry.     

岩浆侵入体对有机质生烃(成熟)作用的影响及数值模拟

火山作用带来的热源对有机质的成烃进程和成烃量产生了重要影响,这种热效应一方面可以加速烃源岩的成熟和成烃作用,另一方面可以破坏先期形成的油藏。目前国内外对火山作用的生烃热效应方面的研究主要在热成熟度参数变化描述及岩浆侵入体引起的围岩热蚀变程度的讨论。火山作用对成烃/成藏的利弊,影响的时/空范围、程度的定量研究尚未报道。本次在前人研究基础上,建立了描述岩浆侵入体散热的热传导模型,进一步结合EasyRo%模型和前人报道的实测Ro数据进行了模型检验。通过调整模型的参数和岩浆侵入体厚度、位置及个数等进行了火山作用对有机质成熟作用及生烃影响的研究。模拟结果表明:岩浆侵入体的热作用范围是有限的,但是不同地质情况,影响的范围广度也不相同,对于相同厚度的侵入体,初始温度越高,作用范围越广,但是一般X/D3(X/D代表离接触面的距离与侵入体厚度的比值)。对于不同厚度侵入体而言,在侵入体热作用影响的范围内,侵入体越厚,热作用的范围越广。同时数值模拟结果也表明岩浆侵入体的存在可以改变烃源岩生烃期。     

Closed system Fischer-Tropsch synthesis over meteoritic iron,iron ore and nickel-iron alloy

Meteoritic iron, iron ore and nickel-iron alloy (either alone or in some cases mixed with alumina, carbonaceous chondrite, potassium carbonate or sodium carbonate) were used to catalyze the reaction of deuterium and carbon monoxide in a closed reaction vessel. The mole ratio of deuterium to carbon monoxide ranged from 1/2:1 to 10:1, the reaction temperature from 195 to 370°C, and the reaction time from 6 to 480 hr. Analysis of the reaction products showed that normal alkanes and alkenes (C₁₁-C₂₅), their monomethyl substituted isomers and aromatic hydrocarbons (e.g. naphthalene, acenaphthene, fluorene, phenanthrene and the methyl derivatives of these hydrocarbons) were synthesized. In addition to the aforementioned hydrocarbons, one reaction product was shown to contain perdeutero normal fatty acids (10:0–16:0).     

Predominance of isoprenoids among the alkanes in the Irati oil shale,Permian of Brazil

An alkane distribution in which isoprenoid alkanes are present in excess of n-paraffins and pristane, phytane, and norpristane (in this order) are the major components, has been found in two different beds of the Irati oil shale, Brazilian Permian formation of São Mateus do Sul, Paranã.