The Tilia decline: vegetation change in lowland Britain during the mid and late Holocene

Pollen data indicate Tilia was an important component of the primary woodland cover of many lowland areas in northern and central Europe. High values recorded in mid-Holocene pollen diagrams are generally followed by well-defined declines. In this study the palynological, spatial and temporal trends associated with declines in Tilia pollen at sites from lowland Britain are assessed to evaluate the nature and relative importance of the processes responsible. Processes primarily related to the depositional environment (paludification, marine inundation, breaks in sedimentation) and percentage representation of pollen data play the dominant role in 44% of the 164 declines included in the study. Anthropogenic activity can account for the remainder. Tilia rarely recovers from low values after anthropogenic declines, suggesting such declines have the potential to elucidate patterns in the destruction of primary woodland across lowland Britain. Other than declines associated with the mid-Holocene Ulmus decline event, few anthropogenic Tilia declines have been reliably dated prior to c. 5000 cal. BP. Tilia largely disappeared from areas with calcareous and loamy soils as a result of clearance activity in the period 5000–3000 cal. BP (Late Neolithic to Late Bronze Age). Between 3000 and 2500 cal. BP few declines are recorded suggesting a link between clearance activity and climate change. Later declines are concentrated on the sandier lithologies and often associated with heathland formation. The scarcity of declines after 2000 cal. BP is likely to be related to the exhaustion of primary woodland.     

Sulphide oxidation under partially anoxic conditions at the bed of the Haut Glacier d'Arolla,Switzerland

Oxygen isotopic data are presented for bulk glacial meltwaters draining the Haut Glacier d'Arolla, Valais, Switzerland and for the sulphate contained within them in an attempt to assess the redox status of the subglacial chemical weathering environment. The sulphate derived from subglacial chemical weathering is so depleted in ¹⁸O that it must have formed, at least partially, in an anoxic environment. Under these conditions, Fe³⁺ can act as an oxidizing agent and oxygen atoms incorporated into sulphate are derived from ¹⁸O‐depleted water molecules (by contrast, dissolved O₂ is strongly enriched in ¹⁸O). These data therefore support the hypothesis that sectors of the glacier bed are anoxic and that Fe³⁺ may act as a significant oxidizing agent under these conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Ensuring appropriate and proportionate responses to environmental threats: A response to Caras and Pasternak

The ecological consequences of coral mining can be severe, with immediate reduction in reef-associated biodiversity and longer term implications for linked habitats such as mangrove forests and seagrass meadows. However, research into the effects of coral mining must take into account other environmental processes which may affect reef communities and the socio-economic context within which coral mining takes place if appropriate and proportionate management responses are to be identified. This article builds upon recently published research detailing the adverse effects of coral mining in Indonesia to illustrate the significance of these points. We use the previous paper to demonstrate that accurate identification of the ecological impacts of coral mining requires the use of appropriate control sites and recognizing natural stresses which may account for short-term variability in ecological parameters. We also underline the need to appreciate that government institutions can directly or indirectly facilitate coral mining, whilst proposed alternative income-generating activities intended to reduce coral mining should be tailored to the local economic, cultural and environmental context if they are to gain community support. This demonstrates the value of an integrated approach to analyzing marine resource usage which combines information from the natural and social sciences to address environmental problems such as coral mining.     

复杂介质有限元法2.5维可控源音频大地电磁法数值模拟

利用有限元2.5维可控源音频大地电磁法（简称CSAMT）数值模拟方法,对100Ωm均匀半空间介质中有限长度的电偶极源产生的电场、磁场及视电阻率、相位特征进行了数值模拟,研究了场的空间变化规律. 在一个象限中,场的特征存在双叶现象,当收发距大于4个趋肤深度时,电阻率较接近介质真实的电阻率,这些结果为观测系统和收发距的选择提供了依据. 波数域场的特征表明,低波数对源的贡献占较大的比例. 有限元法2.5维CSAMT数值模拟的优势在于能较准确地获得复杂介质结构的波场特征. 本文结合直立异常体、倾斜异常体及断陷模型对CSAMT电阻率、相位剖面特征及频率曲线特征的可靠性进行了研究. 数值模拟结果直观地给出了异常体的剖面异常形态. 通过对比研究异常体的剖面异常形态和半空间场的特征进一步说明本文方法和软件在模拟复杂介质结构场特征时是可靠的. 这为认识观测数据,指导反演解释提供了较好的依据.     

Measuring Historical Coastal Change using GIS and the Change Polygon Approach

This study compares two automated approaches, the transect‐from‐baseline technique and a new change polygon method, for quantifying historical coastal change over time. The study shows that the transect‐from‐baseline technique is complicated by choice of a proper baseline as well as generating transects that intersect with each other rather than with the nearest shoreline. The change polygon method captures the full spatial difference between the positions of the two shorelines and average coastal change is the defined as the ratio of the net area divided by the shoreline length. Although then change polygon method is sensitive to the definition and measurement of shoreline length, the results are more invariant to parameter changes than the transect‐from‐baseline method, suggesting that the change polygon technique may be a more robust coastal change method.     

Contributions from glacially derived sediment to the global iron (oxyhydr)oxide cycle: Implications for iron delivery to the oceans

Estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving, and their sediment loads. The combined total (2900 Tg yr⁻¹) of the suspended sediment load in meltwaters (1400 Tg yr⁻¹) and the sediment delivered by icebergs (1500 Tg yr⁻¹) are within the range of earlier estimates. High-resolution microscopic observations show that suspended sediments from glacial meltwaters, supraglacial, and proglacial sediments, and sediments in basal ice, from Arctic, Alpine, and Antarctic locations all contain iron (oxyhydr)oxide nanoparticles, which are poorly crystalline, typically ∼5 nm in diameter, and which occur as single grains or aggregates that may be isolated or attached to sediment grains. Nanoparticles with these characteristics are potentially bioavailable. A global model comparing the sources and sinks of iron present as (oxyhydr)oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans, beyond the continental shelf. Iceberg delivery of sediment containing iron as (oxyhydr)oxides during the Last Glacial Maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric CO₂ to the levels observed in ice cores.     

An 11 000-year record of vegetation and environment from Lago di Martignano,Latium, Italy

A pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000-year record of vegetation and environment change. The earliest pollen spectra are dominated by Artemisia and Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad-leaved forests were established by ca. 11 000 yr BP. Although Quercus initially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (<10%). After ca. 7000 yr BP, however, they begin to increase and rise to a peak of >40% of total land pollen at ca. 6700 yr BP, with Olea europaea the single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities. Castanea sativa and luglans regia pollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this period.     

Geophysical images of the creeping segment of the San Andreas fault: implications for the role of crustal fluids in the earthquake process

High-resolution magnetotelluric (MT) studies of the San Andreas fault (SAF) near Hollister, CA have imaged a zone of high fluid content flanking the San Andreas fault and extending to midcrustal depths. This zone, extending northeastward to the Calaveras fault, is imaged as several focused regions of high conductivity, believed to be the expression of tectonically bound fluid pockets separated by northeast dipping, impermeable fault seals. Furthermore, the spatial relationship between this zone and local seismicity suggests that where present, fluids inhibit seismicity within the upper crust (0–4 km). The correlation of coincident seismic and electromagnetic tomography models is used to sharply delineate geologic and tectonic boundaries. These studies show that the San Andreas fault plane is vertical below 2 km depth, bounding the southwest edge of the imaged fault-zone conductor (FZC). Thus, in the region of study, the San Andreas fault acts both as a conduit for along-strike fluid flow and a barrier for fluid flow across the fault. Combined with previous work, these results suggest that the geologic setting of the San Andreas fault gives rise to the observed distribution of fluids in and surrounding the fault, as well as the observed along-strike variation in seismicity.     

Stratospheric ozone reduction,solar UV-B radiation and terrestrial ecosystems

Stratospheric ozone reduction is occurring and will continue to increase in magnitude into the next century. Yet, the consequences for terrestrial ecosystems of the increased solar UV-B (280–320 nm) radiation resulting from total column ozone reduction are not understood. Based on studies of higher plant response to UV-B, several possible consequences for ecosystems include decreased primary production, altered plant species composition, and altered secondary chemistry with implications for herbivory, litter decomposition and biogeochemical cycles. However, like the assessment of increased atmospheric CO₂, extrapolation from studies with isolated plants to ecosystem function is very tenuous at best. Very few UV-B studies have dealt with multispecies systems. Most of the UV-B research in the past two decades (since the first suggestions of ozone reduction) has been conducted as short-term experiments in growth chambers and greenhouses where the unnatural spectral balance of radiation can lead to unrealistic conclusions. Technical difficulties in suitable measurement and manipulation of UV-B radiation also complicate the conduct of reliable experiments. This essay surveys and categorizes some 300 papers from the past 20 years on this subject, draws general conclusions from the research and offers some recommendations with respect to ecosystem consequences.     

Lack of effect of ingested Forties field crude oil on avian growth

The reported cessation of growth by young herring gulls dosed with Kuwait and Louisiana crude oil was not observed when chicks of herring gull and other birds were dosed with Forties crude oil from the North Sea. One reason for this discrepancy is thought to be that the former birds may already have completed their growth at the time of the experiments.