Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.     

First Mass-resolved Measurement of High-Energy Cosmic-Ray Antiprotons

We report new results for the cosmic-ray antiproton-to-proton ratio from 3 to 50 GeV at the top of the atmosphere. These results represent the first measurements, on an event-by-event basis, of mass-resolved antiprotons above 18 GeV. The results were obtained with the NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas-RICH (Ring-Imaging Cerenkov) counter and a silicon-tungsten imaging calorimeter. The RICH detector was the first ever flown that is capable of identifying charge-one particles at energies above 5 GeV. The spectrometer was flown on 1998 May 28-29 from Fort Sumner, New Mexico. The measured p&d1;/p ratio is in agreement with a pure secondary interstellar production.     

Bacterial mineralization patterns in basaltic aquifers: implications for possible life in martian meteorite ALH84001

To explore the formation and preservation of biogenic features in igneous rocks, we have examined the organisms in experimental basaltic microcosms using scanning and transmission electron microscopy. Four types of microorganisms were recognized on the basis of size, morphology, and chemical composition. Some of the organisms mineralized rapidly, whereas others show no evidence of mineralization. Many mineralized cells are hollow and do not contain evidence of microstructure. Filaments, either attached or no longer attached to organisms, are common. Unattached filaments are mineralized and are most likely bacterial appendages (e.g., prosthecae). Features similar in size and morphology to unattached, mineralized filaments are recognized in martian meteorite ALH84001.     

与海侵面有关的白云石化作用——白垩纪中期的一个实例

许多碳酸盐地台都有着不同程度的白云石化作用，白云石化作用的机理至今仍有争议、在许多例子中，白云石出现于沉积物成岩历史的早期阶段，但在埋藏过程中常有重结晶作用，因此，许多化学标志如同位素、痕量元素和有序度发生重排，不再反映形成白云石的原始孔隙流体的成分（Hardie，1987）。Urgonian地台位于法国Subal…ne山脉北部，这条山脉是一个位于法国东南部的NE─SW向这山带，部分为西阿尔卑斯的延伸带。Subalpine山脉包括了所有在Daupinois／Helvetlc盆地、Jura／BasDauphine他台和Provencal他台沉积的沉积物。该地区是被动边…     

氢氧同位素在岩石研究中的应用

近二十年来稳定同位素地球化学发展相当快。国内也逐渐地发展起来了,在地质系统中,先后请外国专家讲学,派人出去学习,现已有20多个单位建立或正在筹建稳定同位素实验室,有十多台较先进的仪器设备,有几百人的专业队伍。1975年以前只开展了硫同位素研究,近几年已建成了一批氢、氧、铅等同位素实验室,并开展了工作,取得了初步成果。主     

选矿中金矿物学平衡的意义

本文研讨了在详细地设计冶炼实验和处理难选金矿石的最佳条件中,金矿物学平衡的意义。通过对32个金矿石和含金矿石的实验而得到了一个完整的定量化的矿物学平衡程序。这个平衡程序是以特殊的氧化作用用鉴定可见金的百分比和用光学显微镜及电子探针测定金矿物的特征为基础提出的。不可见金即胶体粒级金和固体中的金,这两者直接用氧化作用选剔测定效果不佳,用定量的离子探针微区分析(SIMS)可直接测定。这样就直接测定了所有的载金矿物,鉴定结果准确无误。本文选择五个例子作了介绍。目的之一是提供一个体系——通过鉴定金的赋存形式来研究金的矿物学程序,并有助于设计和优化选矿工艺过程。     

Evidence for Differential Unroofing in the Adirondack Mountains, New York State, Determined by Apatite Fission-Track Thermochronology

Apatite fission-track ages of 168-83 Ma for 39 samples of Proterozoic crystalline rocks, three samples of Cambrian Potsdam sandstone, and one Cretaceous lamprophyre dike from the Adirondack Mountains in New York State indicate that unroofing in this region occurred from Late Jurassic through Early Cretaceous. Samples from the High Peaks section of the Adirondack massif yielded the oldest apatite fission-track ages (168-135 Ma), indicating that it was exhumed first. Unroofing along the northern, northwestern, and southwestern margins of the Adirondacks began slightly later, as shown by younger apatite fission-track ages (146-114 Ma) determined for these rocks. This delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the High Peaks. Apatite fission-track ages for samples from the southeastern Adirondacks are distinctly younger (112-83 Ma) than those determined for the rest of the Adirondack region. These younger apatite fission-track ages are from a section of the Adirondacks dissected by shear zones and post-Ordovician north-northeast-trending normal faults. Differential unroofing may have been accommodated by reactivation of the faults in a reverse sense of motion with maximum compressive stress, sigma1, oriented west-northwest. A change in the orientation of the post-Early Cretaceous paleostress field is supported by a change in the trend of Cretaceous lamprophyre dikes from east-west to west-northwest.