The impact of anoxia on pelagic macrofauna during the Toarcian Oceanic Anoxic Event (Early Jurassic)     

Bryony A. Caswell  Angela L. Coe 《Proceedings of the Geologists' Association. Geologists' Association》2014

Extreme environmental change during the Toarcian Oceanic Anoxic Event had widespread impacts on marine biota. This study provides new evidence, from the Yorkshire coast sections, UK, that the event was associated with periods of elevated fish and ammonite mortality. Using a synthesis of pelagic macrofaunal changes, benthic macrofaunal data and geochemical proxies we show that there are stratigraphical correlations between: (1) pelagic macrofaunal ranges and abundance, (2) benthic macrofaunal abundance, and (3) geochemical proxies that indicate deoxygenation. We identify eight stratigraphical intervals of differing character. Results suggest two major phases of relatively persistent deoxygenation with photic zone euxinia. The cyclostratigraphic timescale indicates that each phase lasted at least tens of thousands of years. Belemnite migration during the event probably resulted from increased seawater temperatures and low food supply similar to that observed for many marine taxa, including squid, within the present-day oceans.  相似文献   

New evidence of warm early-Holocene summers in subarctic Finland based on an enhanced regional chironomid-based temperature calibration model     

Tomi P. Luoto  Marjut Kaukolehto  Jan Weckström  Atte Korhola  Minna Väliranta 《Quaternary Research》2014

Paleoclimate reconstructions based on biological proxies present methodological challenges, especially during non-analog conditions, such as the early Holocene. Here, two chironomid-based training sets from Finland were amalgamated to create a more accurate transfer function of summer air temperature. The aim was to reconstruct Holocene paleoclimate in northernmost Lapland, in an area that has been either too warm or too cold for reliable reconstructions using the original calibration models. The results showed that the combined calibration model had improved performance statistics. The temperature trends inferred from the downcore chironomid record using the original and combined models were very similar. However, there were major changes in their absolute values with the combined model showing greatly improved accuracy. The chironomid-based temperature reconstruction showed significant correlation with the previous pollen-based reconstructions from northwestern Finnish Lapland. However, differences were observed in the temperature trends of the early Holocene, when the chironomid-inferred temperatures rapidly increased, but the pollen-based reconstructions lagged behind suggesting that a cool climate continued for much longer. However, similar to the chironomid record, new plant macrofossil evidence from northwestern Finland also showed warmer-than-present early Holocene temperatures. Therefore, we conclude that the early Holocene was probably warm in northern Lapland.  相似文献   

A 7000-year record of environmental change,including early farming impact,based on lake-sediment geochemistry and pollen data from County Sligo,western Ireland     

Michael O'Connell  Beatrice Ghilardi  Liam Morrison 《Quaternary Research》2014

Detailed, chronologically tightly constrained, lake-sediment-based geochemical and pollen records have enabled local changes in soil erosion, woodland cover and composition, and prehistoric farming impact to be reconstructed in considerable detail. The profile opens shortly after 7800 BC when tall canopy trees were well-established and presumably in equilibrium with their environment. A distinct perturbation that involved an increase in pine and birch, a decrease in oak and a minor opening-up of the woodland is regarded as the local expression of the 8.2 ka climate anomaly. Lack of response in the geochemical erosional indicators is interpreted as evidence for drier conditions. A short-lived, over-compensation in climate recovery followed the 8.2 ka event. Neolithic farming impact is clearly expressed in both the pollen and geochemical data. Both datasets indicate that Neolithic impact was concentrated in the early Neolithic (3715–3440 BC). In the interval 3000–2700 BC there appears to have been a break in farming activity. The pollen data suggest substantially increased farming impact (both arable and pastoral) in the Bronze Age, with maximum farming and woodland clearances taking place in the late Bronze Age (1155–935 BC). These developments are poorly expressed in the geochemical record, possibly due to within-lake changes.  相似文献   

A new methodology for building local climate change scenarios: A case study of monthly temperature projections for Mexico City     

《Atmósfera》2014,27(4):429-449

This paper proposes a new methodology for generating climate change scenarios at the local scale based on multivariate time series models and restricted forecasting techniques. This methodology offers considerable advantages over the current statistical downscaling techniques such as: (i) it provides a better representation of climate at the local scale; (ii) it avoids the occurrence of spurious relationships between the large and local scale variables; (iii) it offers a more appropriate representation of variability in the downscaled scenarios; and (iv) it allows for compatibility assessment and combination of the information contained in both observed and simulated climate variables. Furthermore, this methodology is useful for integrating scenarios of local scale factors that affect local climate. As such, the convenience of different public policies regarding, for example, land use change or atmospheric pollution control can be evaluated in terms of their effects for amplifying or reducing climate change impacts.  相似文献   

近40年来气候变化对青海盐湖及其矿产资源开发的影响——以小柴旦湖为例   总被引：2，自引：0，他引：2  

闫立娟  郑绵平  袁志洁 《矿床地质》2014,33(5):921-929

青海是中国盐湖主要分布区之一,蕴藏着丰富的矿产资源。文章以RS和GIS技术为基础,从20世纪70年代、90年代、2000年前后、2008~2009年和2013~2014年五期Landsat遥感影像中提取了青海面积大于10 km2的所有盐湖(不包括干盐湖),分析了其近40年来的变化趋势:总体上,盐湖总面积除在2000年前后有所减少外,基本上呈现增加的趋势;具体而言,2000年前后,萎缩的盐湖主要分布在柴达木盆地;其他时期均呈现全面扩张的趋势。在全球气候变暖的大背景下,通过分析青海地区11个气象台站的年平均气温、年降雨量和蒸发量数据,可知青海地区气候呈现了向暖湿方向转型的趋势,且2002年之后更为明显。最后,以青海省小柴旦湖为例,分析了湖泊淡化、矿产资源贫化对盐湖资源开发的影响,具体为:1资源开发成本升高、难度加大,甚至使一些处于工业开发临界品位的盐湖失去开发价值;2盐湖淡化条件下,锂等矿产资源有效提取技术亟待研发;3政府制定矿产资源开发政策时,需要对气候及盐湖的动态变化过程综合考虑。以上说明,青海地区的暖湿气候使盐湖大幅度淡化,给盐湖矿产资源开发带来了新的挑战。  相似文献   

Remote sensing-based analysis of the planform changes in the Upper Amazon River over the period 1986–2006     

《Journal of South American Earth Sciences》2014

An analysis of the planform changes of the Colombian reach of the Amazon River was carried out over a period of 19.9 years. Remote sensing image processing techniques were applied to Landsat images acquired in 1986, 1994, 2001 and, 2006. These images were selected based on minimal daily water level variations, while providing the widest temporal span. Plan view river changes and geomorphologic characteristics were examined to identify which channel pattern classification best represents this large tropical river system. Discharge was also analyzed to determine whether changes in the river's plan view are a direct response to variations in discharge. The system had a depositional tendency between 1986 and 2006, with a period where erosion was more intense than deposition between 1994 and 2001. Percent change in the plan view area of the system (1.4% yr⁻¹) and the maximum migration rates (125 m yr⁻¹) suggest that this reach of the Amazon is less active than reaches upstream and the downstream reach between the confluences of the Jutaí and Japurá Rivers. Variations in discharge appear to be responsible for deposition and erosion dynamics observed after this remote sensing analysis in the Colombian reach of the Amazon River. Characteristics including multiple channels with vegetated islands developed from within-channel deposition, meandering planform, lateral activity of channel margins, and the absence of islands with saucer-like morphology suggest a multichannel, meandering pattern for this reach of the Amazon, that corresponds to a laterally active anabranching river.  相似文献   

芦山地震同震和震后地表形变及重力变化的理论模拟          下载免费PDF全文

邓明莉  孙和平  徐建桥  祝意青 《地球科学》2014,39(9):1373-1382

为了研究芦山地震的孕震过程和震源区的长期构造过程以及解释实测的震后形变和重力资料, 采用分层介质模型, 利用数值模拟的方法, 考虑区域流变系数, 计算了地震引起的地表同震、震后的形变和重力变化以及区域内部分GPS与重力连续观测台站的震后形变和重力变化的时间序列.结果表明: 芦山地震的地表同震形变显示出发震断层明显的逆冲特性; 粘弹性松弛效应引起的震后地表形变和重力变化比同震形变和重力变化的范围明显扩大, 但随着粘滞系数的增加, 变化量明显减小; 观测台站的震后变化时变曲线显示震后形变和重力变化在震后50 a间变化显著, 100 a后基本平缓, 趋于稳定; 模拟计算的GPS台站中除了MEIG台和MYAN台以外, 其余台站的震后观测必须考虑粘弹性松弛的影响.   相似文献   

Research on quantitative assessment of climate change risk at an urban scale: Review of recent progress and outlook of future direction     

《Chemie der Erde / Geochemistry》2014

Cities are not only major contributors to global climate change but also stand at the forefront of climate change impact. Quantifying and assessing the risk potentially induced by climate change has great significance for cities to undertake positive climate adaptation and risk prevention. However, most of the previous studies focus on global, national or regional dimensions, only a few have attempted to examine climate change risk at an urban scale and even less in the case of a recent literature review. As a result, a quantitative assessment of climate change risk for cities remains highly challenging. To fill this gap, the article makes a critical review of the recent literature on urban-scale climate change risk assessment, and classifies them into four major categories of studies which jointly constitute a stepwise modelling chain from global climate change towards urban-scale risk assessment. On this basis, the study summarizes the updated research progresses and discusses the major challenges to be overcome for the seamless coupling of climate simulation between different scales, the reproduction of compound climate events, the incorporation of non-market and long-lasting impacts and the representation of risk transmission insides or beyond a city. Furthermore, future directions to advance quantitative assessment of urban-scale climate change risk are highlighted, with fresh insights into improving study methodology, enriching knowledge of climate change impact on city, enhancing abundance and accessibility to data, and exploring the best practice to provide city-specific climate risk service.  相似文献   

不同压实度荆门弱膨胀土的一维膨胀-压缩特性   总被引：1，自引：0，他引：1  

周葆春  张彦钧  汤致松 《岩土力学》2014,35(5):1275-1283

为探讨压实膨胀土的体变行为,以荆门弱膨胀土为研究对象,借助高压固结仪对6种制样压实度下的膨胀土试样进行了一维无荷载膨胀和含一次卸载-再加载循环的压缩试验。基于膨胀试验结果,构建了膨胀时程方程,通过参数分析,明确了方程参数的物理意义,并建议了膨胀时程曲线3阶段的划分方法。基于压缩试验结果,探讨了固结屈服应力、压缩指数Cc、回弹指数Cs、膨胀力与制样压实度、土体结构性、膨胀势、孔隙比的相关关系。试验结果及其分析表明,膨胀土体积变化是膨胀势与外部荷载、湿度变化的耦合作用结果,且具有强烈的水-力路径依赖性。  相似文献   

Climate Change and Geochemistry May Explain the Finding of Marine Cyanobacteria in a Continental Saline Lake     

Zorigto NAMSARAEV  Vladimir GORLENKO  Boris KUZNETSOV  Bair NAMSARAEV 《《地质学报》英文版》2014,88(Z1):158-159

正1 Introduction Alkaline Lake Khilganta located in a steppe zone of South Siberia(N 50°42'535,E 115°06'086)is unique among adjacent lakes because of a development of a thick(up to 3 cm)cyanobacterial mat dominated by  相似文献