Palaeoflood activity and climate change over the last 1400 years recorded by lake sediments in the north‐west European Alps

A high‐resolution sedimentological and geochemical study of a high‐altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352 m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800–1300) and the current period of global warming. On a multi‐decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi‐centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi‐decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright © 2013 John Wiley & Sons, Ltd.     

The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains,northern Spain)

A sedimentological and geochemical study of the Lago Enol sequence (Cantabrian Mountains, northern Spain), together with detailed geomorphological mapping, provides a first record of glacier evolution and climate change over the last 40 ka in the Picos de Europa National Park. The Enol glacier retreated from its maximum extent prior to 40 ka BP as demonstrated by the onset of proglacial lacustrine sedimentation in two glaciated depressions: the Comella hollow to the north (before 40 ka BP) and the Lago Enol (before 38 ka BP). These results support previous evidence that the maximum extent of southern European glaciers occurred earlier than in northern Europe. Alternation of homogeneous and laminated proglacial sediments during the glacier retreat illustrate a dynamic glacial evolution during the Marine Isotope Stage (MIS) 3 (40–26 ka BP). A slight warming is detected at 26 ka ago with the change from proglacial sediments (in a lake located in contact to the glacier) to glaciolacustrine sedimentation (in a non‐contact or distal lake). Finally, the onset of organic‐rich sediments took place at 18 ka ago. This last transition occurred in two phases, similarly to the North Atlantic Last Termination, suggesting a link between North Atlantic Deep Water formation oscillations and palaeohydrological variability in the Cantabrian Mountains. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of snow and soil frost melting on the concentrations of suspended solids and phosphorus in two rural watersheds in Western Finland

Hydrological processes are known to have a considerable effect on nutrient transport from agricultural land to watercourses. In cold temperate regions peak discharges are caused not only by storm conditions but also by melting of snow and frost. The objective of this work was to investigate the effects of snow and frost melt on concentrations of phosphorus and suspended solids. The samples were taken using flowweighted automatic sampling techniques from two agricultural drainage basins. During the beginning of the snowmelt period the concentration of suspended solids was rather low by comparison with the total phosphorus concentration and the discharge. The different behaviour compared with the relationships found during storm conditions was probably caused by continuous extraction of the soil surface by low ionic concentration melt water, and to some extent by leaching from plant residues. The gradual decrease of total phosphorus concentration during the frost thawing period could be attributed to the gradually increasing proportion of the subsurface and ground water discharge in the runoff.     

湖北省钟祥第四纪冰缘融冻构造的发现及其意义

笔者于1986年在钟祥首次发现了第四纪地层间的冰缘融冻构造——古冰楔与揉皱,其时代为早更新世末期—中更新世初期。它的发现不仅为建立本区第四纪地层层序,而且为确定更新世北方冰缘冻土的南界和研究长江中下游更新世古气候环境的演变提供了重要的科学依据。     

Some aspects on the variations in depositional flux of excess Thorium-230 in the Central Indian basin during Late Quaternary

Examined in this paper is the tentative history of the depositional flux of²³⁰Th_xs (the unsupported fraction of²³⁰Th scavenged from the overlying water column), for the Late Quaternary period from a sediment core of the Central Indian Basin (CIB). The measured depositional flux of²³⁰Th_xs is found substantially higher than that of the possible theoretical flux from the overlying water column. Historical records, reconstructed from the²³⁰Th_xs chronology suggests that the depositional flux has varied considerably with time, reflecting an enhanced scavenging during the Holocene and the preceding interglacial periods whereas, comparatively lower flux than the predicted one occurred during the Last Glacial Maximum (LGM) period. The average ratio of the measured depositional flux to that of the predicted flux from the overlying water column, indicates that the core site acts as a sink for²³⁰Th_xs and based on the existence of bottom current activity; the²³⁰Th_xs could be the result of focusing of younger sediments. The depositional index (Di) has also been calculated to quantify the extent of lateral supply throughout the core with time. The estimated (Di) suggests that bottom focusing and feeble deposition and/or winnowing processes had occurred and that the former was most prevalent during the Holocene and the preceding interglacials, whereas the latter was observed at the LGM period.     

近百年长江中游旱涝的变化

利用史料和器测雨量记录重建的近百年长江中游区域平均逐年旱涝等级指数序列研究了旱涝变化特征，发现：（１）２０世纪前涝后旱，（２）２２年、５－６年和２－３年的准周期振动，（３）６个交替出现的旱涝阶段。     

末次冰期东亚季风快速波动的模式与成因

通过对位于东亚季风区中东部与西部边缘的两个高分辨率黄土剖面记录的对比研究，发现它们不仅捕捉到了20个Dansgaard Oeschger事件与6个Heinrich事件，而且黄土记录与GRIP冰芯记录的这些快速气候波动基本上是同步的。暗示在整个末次冰期，东亚季风气候同样存在千年—百年尺度上的快速波动。所不同的是，西面的沙沟剖面对这些快速气候波动的反应比东面的王官剖面敏感。结合末次冰期中国黄土记录的先前研究结果，我们发现，自西向东Dansgaard Oeschger旋回的幅度逐渐变小，推测这主要是由西风与东亚夏季风共同作用所造成的。