Sediment size variation in a braided reach of the Sunwapta River,Alberta, Canada

The downstream diminution in sediment size in a braided reach of the proglacial Sunwapta River, Alberta, Canada, was examined statistically to identify the sources of the observed variation about an expected exponential relationship between clast size and distance. Major deviations from this hypothetical relationship, such as a relative increase in grainsize, may be attributed to the effects of tributary sediment inputs and downstream changes in channel behaviour, whilst local variation is associated with complex patterns of sediment deposition observed at a bar scale. A comparison of diminution coefficients, calculated for separate lithologies and for subreaches along the river, with those obtained from previous studies, is used as an indicator of river behaviour and sediment transport processes. It is shown that rates of diminution vary within the reach in response to differing rates of aggradation and to the backwater effects created by tributary alluvial fans. The relatively high values for the calculated diminution coefficients indicate that processes of differential transport are the main cause of the grain size decrease.     

Volume flux and fresh water transport associated with the East Icelandic Current

The importance of the circulation of fresh water within the Nordic Seas has frequently been pointed out, especially its effect on deep water formation and therefore possibly on the thermohaline circulation. The main source of fresh water is the East Greenland Current entering the Nordic Seas through Fram Strait. The Jan Mayen Polar Current and the East Icelandic Current (EIC) carry a part of the fresh water into the Greenland and Iceland Seas respectively. As a part of the EU project VEINS, Aanderaa current meters were deployed on two moorings within the EIC from June 1997 to June 1998 on a standard CTD section from Langanes, Northeast Iceland, to the central Iceland Sea in the direction towards Jan Mayen. The current was mainly concentrated along the slope where it was baroclinic, while over the deeper part a weak barotropic flow was observed. Geostrophic calculations, referenced to the current meter data, were used for estimating the volume flux and fresh water transport with the current. The total transport over the section towards the east was found to be 2.5 Sv. The fresh water transport relative to a salinity of 34.93, above 170 m, amounted to 5.5 mSv. This is roughly 4% of the fresh water transport through Fram Strait. This transport is put into a long-term perspective using hydrographic data from the Langanes section.     

Signals of tree volume and temperature in a high‐resolution record of pollen accumulation rates in northern Finland

Pollen accumulation rates (PARs) provide a potential proxy for quantitative tree volume (m³ ha^?1) reconstruction with reliable absolute pollen productivity estimates (APPEs). We obtained APPEs for pine, spruce and birch at their range limits in northern Finland under two temperature periods (‘warm’ and ‘cold’) based on long‐term pollen trap and tree volume records within a 14‐km radius of each trap. APPEs (mean ± SE; × 10⁸ grains m^?3 a^?1) tend to be higher for the ‘warm’ periods (pine 123.8 ± 24.4, birch 528.0 ± 398.4, spruce 434.3 ± 113.7) compared with the ‘cold’ periods (pine 95.5 ± 37.3, birch 317.3 ± 282.6, spruce 119.6 ± 37.6), although the difference is only significant for spruce. Using an independent temperature record and the APPEs obtained, we reconstruct a low‐frequency record of pine volume changes over the last 1000 years at Palomaa mire, where a high‐resolution record of Pinus PARs is available. Five phases are distinguished in the reconstruction: moderate pine volume, AD 1080–1170; high volume, AD 1170–1340; low volume, AD 1340–1630; very low volume, AD 1630–1810; and rising pine volume, AD 1810–1950. These phases do not coincide with periods of high or low June–July–August temperatures, and thus appear to reflect regional variations in tree volume, while high‐frequency changes within each time‐period block show variations in PARs in response to temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

印、澳板块边界分布与GPS资料用于对2004年Sumatra-Andaman岛地壳破裂测地学机制的再讨论

基于作者此前对印度尼西亚苏门答腊-安达曼岛地震测地学机制的讨论，进一步根据McCloskey等人应用的INDI板块与AUST板块之间大致呈SW（≈S5）-NE（≈N2）走向的板块边界划分模型，利用GPS站速度资料，估计了沿整个苏门答腊-尼科巴岛地壳破裂带INDI板块与Burma／SEEURA板块之间的板块聚敛率，并与基于NUVEL-1A模型的INDI、AUST板块边界的分布所估计的AUST板块与Burma／SEEURA板块问聚敛率结果作了比较；根据2004年印尼苏门答腊-安达曼岛地壳破裂特征，对该地壳破裂的测地学机制作了进一步讨论，认为基于NUVEL-1A模型的INDI、AUST板块边界分布条件下地壳破裂的测地学机制讨论和2004年主震由AUST板块运动触发的结论可能更符合2004年地壳破裂事件的观测结论。目前的Burma微板块的欧拉旋转参数可能不适合用于对该次地壳破裂事件的测地学估计和机制的讨论；INDI、AUST板块间的相对运动是这两者板块间造山带的主要动力源。     

2013年1月安徽持续性霾天气成因分析

2013年1月安徽霾天气具有范围广、持续时间长、能见度低等特点。利用合肥、安庆、阜阳2009~2013年1月地面常规资料、高分辨率探空资料,结合轨迹分析和聚类分析,讨论了2013年1月安徽霾天气频发的原因。结果表明:低风速、高湿度不能解释2013年1月霾天气增多、增强的现象。大气层结稳定、接地逆温偏多、偏厚,可部分解释这次霾天气增多现象。边界层中上部输送条件的变化也不能解释2013年1月霾天气增多现象,但近地层输送条件的变化能较好地解释2013年1月霾天气增多现象,如偏东北来向的轨迹组对应着最低的能见度,且2013年1月各地最低能见度对应的轨迹组所占比例(或与次低能见度的轨迹组所占比例之和)在历年中最高。因此,大气层结稳定、近地层偏东北来向气团较多是2013年1月安徽各地能见度偏低、霾天气偏多的主要原因。     

A Strain Rate Dependent Constitutive Model for the Lower Silurian Longmaxi Formation Shale in the Fuling Gas Field of the Sichuan Basin,China

Shale, as a kind of brittle rock, often exhibits different nonlinear stress-strain behavior, failure and time-dependent behavior under different strain rates. To capture these features, this work conducted triaxial compression tests under axial strain rates ranging from 5×10?6 s?1 to 1×10?3 s?1. The results show that both elastic modulus and peak strength have a positive correlation relationship with strain rates. These strain rate-dependent mechanical behaviors of shale are originated from damage growth, which is described by a damage parameter. When axial strain is the same, the damage parameter is positively correlated with strain rate. When strain rate is the same, with an increase of axial strain, the damage parameter decreases firstly from an initial value (about 0.1 to 0.2), soon reaches its minimum (about 0.1), and then increases to an asymptotic value of 0.8. Based on the experimental results, taking yield stress as the cut-off point and considering damage variable evolution, a new measure of micro-mechanical strength is proposed. Based on the Lemaitre’s equivalent strain assumption and the new measure of micro-mechanical strength, a statistical strain-rate dependent damage constitutive model for shale that couples physically meaningful model parameters was established. Numerical back-calculations of these triaxial compression tests results demonstrate the ability of the model to reproduce the primary features of the strain rate dependent mechanical behavior of shale.     

Assessing Soil Remobilisation in Catchments using a 137Cs-sediment Hillslope Model

Soil redistribution studies are important, especially in water supply catchments, because the rate at which denudation is occurring has implications for offsite water quality. However, the extent to which soil is redistributed within the landscape can be difficult to determine. This challenge can be overcome using fallout caesium-137 (¹³⁷Cs). This paper describes the rates of soil loss and remobilisation in two sub-catchments within the Sydney Basin region, namely Kembla and Kentish Creeks, which drain to the Cordeaux reservoir. The total inventories of ¹³⁷Cs in catchment soils were determined, a ¹³⁷Cs-regression equation and a theoretical diffusion and migration model were used to established relationships between ¹³⁷Cs inventories and the rates of soil loss. These relationships revealed relatively low occurrence of soil loss in Kentish Creek, but two slopes in the Kembla Creek sub-catchment had losses that appear to be moderate. However, there was no clear evidence to suggest whether slopes in upper and lower reaches of catchments had specific patterns of soil remobilisation. Qualitative categorisation of the slope elements using a ¹³⁷Cs-sediment hillslope model can be a useful sentinel for land users and decision makers even if absolute rates of soil loss or gain are not certain. The findings suggest that sediments mobilised in the study sub-catchments are not likely to impact significantly on the water quality in the Cordeaux reservoir.     

Empirical models for describing recent sedimentation rates in lakes distributed across broad spatial scales

Over the last 20 years there has been a surge of interest in paleolimnology and as a result a large accumulation of lake sedimentation records. This emerging archive has allowed us to develop empirical models to describe which variables explain significant variation in sedimentation rates over the past ∼150 years across large spatial scales. We hypothesized that latitude would be a significant explanatory variable of profundal zone lake sedimentation rates across a temperate to polar gradient. We further hypothesized that along a more longitudinally-constrained dataset (i.e. east coast of North America), latitude would explain a greater proportion of the variance. To test these hypotheses, we collated data from 125 natural, average-sized lakes (with surface area <500 km²) by recording authors’ estimates of sedimentation rates (measured as mm/year) or by digitizing recent sediment profiles and calculating sedimentation rates over the past ∼150 years. We found that, at both scales, latitude was the strongest predictor of lake sedimentation rates (full dataset: r ² = 0.28, P = 0.001, n = 125; east coast dataset: r ² = 0.58, P < 0.001, n = 43). By conducting a multiple linear regression analysis, we found that 70% of the variance in sedimentation rates from the east coast transect was explained by latitude and elevation alone. This latter model is of sufficient strength that it is a robust predictive tool. Given that climate and land-use strongly co-vary with latitude and that both of these factors have previously been shown to influence lake sedimentation rates, it appears that latitude is a surrogate measure for climate and land-use changes. We also show support for land-use as an important variable influencing sedimentation rates by demonstrating large increases in recent versus Holocene accumulation rates. These results indicate that it is possible to make generalizations about sedimentation rates across broad spatial scales with even limited geographic data.     

古尔班通古特沙漠季节性冻土入渗特性试验研究

以古尔班通古特沙漠南缘融雪期冻结土壤入渗试验为依据,分析了沙漠地区季节性冻土水分入渗特性及主要影响因素.结果表明:沙漠地区季节性冻土具有较高的入渗能力,沙漠冻结风沙土的稳渗率为0.26～0.30 mm/min,是田间冻结壤土的10～20倍,可以保证融雪水及时入渗进入土壤,为融雪水的高效储存创造了有利条件.入渗能力随着土壤含水率的升高而减小.沙地土壤初始的低含水率、土壤大孔隙结构特征是沙地冻结土壤具有较高入渗能力的主要原因.研究结果为进一步研究春季融雪水在沙地的再分配过程奠定了基础.