The Last Glacial Maximum in the North Sea Basin: micromorphological evidence of extensive glaciation

Despite a long history of investigation, critical issues regarding the last glacial cycle in northwest Europe remain unresolved. One of these refers to the extent, timing and dynamics of Late Devensian/Weichselian glaciation of the North Sea Basin, and whether the British and Scandinavian ice sheets were confluent at any time during this period. This has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring. This study presents the results of seismic, sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the North Sea Basin. Thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process‐based interpretations from sediment cores. On the basis of micromorphology, critical formations from the basin have been reinterpreted, with consequent stratigraphic implications. Within the current stratigraphic understanding of the North Sea Basin, a complex reconstruction is suggested, with a minimum of three major glacial episodes inferred. On at least two occasions during the Weichselian/Devensian, the British and Scandinavian ice sheets were confluent in the central North Sea. Whilst micromorphology can provide much greater confidence in the interpretation of Late Quaternary offshore stratigraphic sequences, it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records. Copyright © 2006 John Wiley & Sons, Ltd.     

Fossil hyrax dung and evidence of Late Pleistocene and Holocene vegetation types in the Namib Desert

Pollen was derived from fossil dung of herbivorous hyraxes, deposited in a rock shelter on the highest mountain in Namibia, Dâures or Brandberg, situated on the Namib Desert margin. Radiocarbon dating ranging in age between modern times and 30 000 yr BP showed it represents the first empirical pollen evidence of continental palaeovegetation during the Late Pleistocene along the western escarpment of southern Africa. The initial results indicate Last Glacial Maximum vegetation differed totally from the current pattern as vegetation types were dominated by small Asteraceae shrubs, in contrast to those of the Holocene and modern times which show more succulents, grass and woody elements (arboreal pollen). The results suggest that Cape floral communities did not reach into the tropics along the western escarpment of Africa, despite such pollen types occurring in marine cores. Copyright © 2004 John Wiley & Sons, Ltd.     

THE SAND WEDGE AND MIRABILITE OFTHE LAST ICE AGE AND THEIR PALEOCLIMATICSIGNIFICANCE IN HEXI CORRIDOR

Sand wedge is formed under the conditions of coldclimate, and is an important basis for reconstructingpaleoenvironment (LI et al., 1990; WANG, 1991 ). Ithas been reported constantly over the last 20 years inthe Qinghai-Xizang (Tibet) Plateau (GUO, 1979; CUl,1983; XU et al., 1984; LIANG et al.,, 1984; PAN etal., 199 ) and North China (YANG et al., 1983; DONGet al., 1985) and Northeast China (GUO et al.,1981 ). We also found fossil sand wedge groups formedin the end of the Late P…     

秦岭太白山古冰川发育与黄土高原气候变迁

本文通过古冰川遗迹的系统分析,揭示了太白山雪线变化和冰川发育过程,将其与黄土高原晚第四纪气候变化模式对比,阐明了太白山雪线变化和冰川发育的时代和时间序列问题。     

巴颜喀拉山地区第四纪冰期初步探讨

依据地貌、孢粉、岩性沉积特征,划分巴颜喀拉山地区第四纪冰期。并与珠穆朗玛峰、唐古拉山、昆仑山地区进行对比。确定巴颜喀拉山地区第四纪以来有:哈拉滩冰期;巴颜喀拉山冰期;洛曲冰期;汪藏因姆措冰期;折尕考钦新冰期。     

CO<Subscript>2</Subscript> Air–Sea Exchange due to Calcium Carbonate and Organic Matter Storage,and its Implications for the Global Carbon Cycle

Release of CO₂ from surface ocean water owing to precipitation of CaCO₃ and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a quotient θ = (CO₂ flux to the atmosphere)/(CaCO₃ precipitated). θ depends not only on water temperature and atmospheric CO₂ concentration but also on the CaCO₃ and organic carbon masses formed. In CO₂ generation by CaCO₃ precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric CO₂ concentration (195–375 ppmv), and increasing CaCO₃ precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic carbon counteracts the CO₂ production by carbonate precipitation and it results in lower CO₂ emissions from the surface layer. When atmospheric CO₂ increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO₂ transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric CO₂. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon from land, the calculated CO₂ flux to the atmosphere is a function of the CaCO₃ and C_org net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO₂ flux near the Last Glacial Maximum is 17 to 7×10¹² mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time it is 38–42×10¹² mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic emissions of CO₂ to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total alkalinity owing to the CaCO₃ storage and consequent emission of CO₂. These results are in agreement with the conclusions of a number of other investigators. As the CO₂ uptake in mineral weathering is a major flux in the global carbon cycle, the CO₂ weathering pathway that originates in the CO₂ produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large imbalances of the atmosphere and land organic reservoir at 10²–10⁴-year time scales.     

Climate during the last glacial maximum in the Wasatch and southern Uinta Mountains inferred from glacier modeling

Recent improvements in understanding glacial extents and chronologies in the Wasatch and Uinta Mountains and other mountain ranges in the western U.S. call for a more detailed approach to using glacier reconstructions to infer paleoclimates than commonly applied AAR-ELA-ÄT methods. A coupled 2-D mass balance and ice-flow numerical modeling approach developed by [Plummer, M.A., Phillips, F.M., 2003. A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. Quaternary Science Reviews 22, 1389–1406] allows exploration of the combined effects of temperature, precipitation, shortwave radiation and many secondary parameters on past ice extents in alpine settings. We apply this approach to the Little Cottonwood Canyon in the Wasatch Mountains and the Lake Fork and Yellowstone Canyons in the south-central Uinta Mountains. Results of modeling experiments indicate that the Little Cottonwood glacier required more precipitation during the local Last Glacial Maximum (LGM) than glaciers in the Uinta Mountains, assuming lapse rates were similar to modern. Model results suggest that if temperatures in the Wasatch Mountains and Uinta Mountains were  6 °C to 7 °C colder than modern, corresponding precipitation changes were  3 to 2× modern in Little Cottonwood Canyon and  2 to 1× modern in Lake Fork and Yellowstone Canyons. Greater amounts of precipitation in the Little Cottonwood Canyon likely reflect moisture derived from the surface of Lake Bonneville, and the lake may have also affected the mass balance of glaciers in the Uinta Mountains.     

Past,present and future vegetation-cloud feedbacks in the Amazon Basin

To begin exploring the underlying mechanisms that couple vegetation to cloud formation processes, we derive the lifting condensation level (LCL) to estimate cumulus cloud base height. Using a fully coupled land–ocean–atmosphere general circulation model (HadCM3LC), we investigate Amazonian forest feedbacks on cloud formation over three geological periods; modern-day (a.d. 1970–1990), the last glacial maximum (LGM; 21 kya), and under a future climate scenario (IS92a; a.d. 2070–2090). Results indicate that for both past and future climate scenarios, LCL is higher relative to modern-day. Statistical analyses indicate that the 800 m increase in LCL during the LGM is related primarily to the drier atmosphere promoted by lower tropical sea surface temperatures. In contrast, the predicted 1,000 m increase in LCL in the future scenario is the result of a large increase in surface temperature and reduced vegetation cover.     

城市化对华北地区最高, 最低气温和日较差变化趋势的影响

利用华北地区255个一般站和国家基本、 基准站1961\_2000年的实测资料, 经过质量检验和均一性订正后, 将所有台站根据人口和台站地理位置分为5个类别, 分析了这5个类别台站和国家基本、 基准站地面平均气温、 最高、 最低气温的年和季节变化趋势以及城市化影响。结果表明： 华北全部台站的年平均气温、 最高、 最低气温均呈增加趋势, 且以最低气温上升最为明显, 导致年平均日较差呈现明显下降。就城市化影响而言, 平均气温、 最低气温变化趋势中城市热岛效应加强因素的影响明显, 但城市化对最高气温趋势影响微弱, 个别台站和季节甚至可能造成降温。在国家基本、 基准站观测的年平均气温和年平均最低气温上升趋势中, 城市化造成的增温分别为0.11℃·(10a)-1和0.20℃·(10a)-1, 对全部增温的贡献率分别达39.3%和52.6%。各类台站的四季平均气温和最低气温序列中城市化影响均造成增温。城市化增温以冬季为最大, 夏季最小。城市化还导致乡村站以外的各类台站日较差减小, 近40年华北地区国家基本、 基准站年平均和秋、 冬季平均气温日较差明显下降均由城市化影响造成的。     

北京夏季日最大电力负荷预报模型建立方法探讨

为了探索夏季(6～8月)日气象负荷的最佳分离方式和引起日最大电力负荷波动的主要因子,以及建立预报模型最佳个数,基于北京市2005～2010年逐日最大电力负荷和同期的气象资料,分析了北京地区日最大电力负荷的变化规律,采用不同方法将气象负荷从夏季日最大电力负荷中分离出来,分析北京夏季气象负荷与气温、相对湿度、降水及炎热指数、高温持续日数、炎热日数持续时间、前一日气象负荷等因子之间的关系,并基于2005～2009年夏季逐日气象负荷和其主要影响因子采用逐步回归方法建立日最大电力负荷的预报模型,将2010年夏季北京日最大电力负荷作为预报效果的独立样本检验。结果显示:2005～2010年,北京逐日最大电力负荷具有明显的线性增长趋势,夏季日最大电力负荷具有显著的星期效应;与去掉逐年夏季日最大电力负荷趋势和夏季平均日最大电力负荷趋势相比,去掉全年逐日最大电力负荷变化趋势的夏季日气象负荷预报模型的拟合能力更优;北京夏季日气象负荷与当日气温的相关系数最高,与前一日气象负荷也关系密切;利用前一日相对气象负荷和当日气象要素一周逐日分别建立预报模型的拟合和预测效果较好。