末次冰期低纬度西太平洋硅藻席沉积与生态特征

硅藻在全球碳循环中发挥着重要的作用。"树荫种"硅藻在次表层水体中的勃发成席,并迅速埋藏成为硅藻席沉积,使人们逐渐意识到次表层生产在整个生产力及输出生产中起着重要作用。介绍了首次在低纬度西太平洋区域发现的硅藻席沉积的分布特征,硅藻席发现站位呈带状分布,大致呈北西-南东向展布,大部分散布在17.5°～20°N之间。采集到硅藻席沉积物的站位其水深在碳酸钙补偿深度(CCD)以下4837～6150m的深水区,多分布在较平坦的海底,且受风力和陆源物质输入影响相对较强的区域。该区域硅藻席的形成可能是由于末次冰期时该海区有大洋锋面的形成所致。该区域的成席硅藻Ethmodiscus rex(Wallich)Hendey为典型的"树荫种"硅藻,可以通过自身调节浮力的作用,在水体相对稳定的贫氧大洋中生存并勃发成席。末次冰期低纬度西太平洋硅藻席沉积的发生,可能使该区成为CO2的汇。     

Formation and evolution of the modem warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDPI02, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modem Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modem warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BE and synchronously the modem TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus,the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC,indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BE caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.     

Agriculture development-induced surface albedo changes and climatic implications across northeastern China

To improve the understandings on regional climatic effects of past human-induced land cover changes,the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years,and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains.As a consequence,in the Northeast China Plain,the surface net radiation increased by 4-8 W/m 2,2-5 W/m 2,and 1-3 W/m 2,and the climate was therefore warmed by 0.1℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ in the spring,autumn and winter,respectively.In the surrounding mountain area,the net radiation decreased by less than 1.5 W/m 2,and the climate was therefore cooled too slight to be detected.In summer,effects of surface albedo changes on climate were closely associated with moisture dynamics,such as evapotranspiration and cloud,instead of being merely determined by surface radiation budget.The simulated summer climatic effects have large uncertainties.These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.     

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.     

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。     

对青藏高原末次冰盛期降温值、平衡线下降值与模拟结果的讨论

1999年 5期《第四纪研究》刊登的“青藏高原冰期环境与冰期全球降温”论文 ,内容丰富 ,提出了许多重大问题和新鲜讯息 ,发人深思。本文就部分内容进行讨论 ,认为根据新近若干冰期降温值较大的信息 ,就得出冰期降温幅度为过去认识的两倍的普遍性推断 ,还为时过早。青藏高原新近研究表明夏季降温值是较小的 ;冰川平衡线高度取决于以夏季温度为标志所提供的消融热量与全年降雪积累量的平衡 ,单纯就降温值 ,不能决定平衡线下降值 ;全球各地气候、地形差别很大 ,冰期变化也很悬殊 ,不存在全球均一的 1 0 0 0m左右平衡线下降值 ,干旱区的下降值多低于此数。青藏高原末次冰盛期 (LGM)冰川堆积 (终碛、侧碛 )和侵蚀形态(冰斗、槽谷 )一般保存良好、形态鲜明 ,较易识别 ,近年已获取测年资料 ,证明过去地貌法判别的LGM冰川规模 ,并以此决定的LGM平衡线位置基本恰当 ,当然也有误判者。从 2 0世纪 2 0年代起 ,研究者逐渐认识高原内部主要是中西部LGM平衡线下降值较小 ,经过多次改进的LGM平衡线高度分布图显示约有 1 /3左右地区 ,平衡线下降值不足 30 0m ,实为世所罕见。其原因可能主要在高原西北部是全球惟一高海拔寒旱核心区域 ,为极大陆型或极地型冰川分布区 ,以现代西昆仑山崇测冰川、古里雅冰帽为例 ,平衡线高度