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Abrupt vegetation shifts caused by gradual climate changes in central Asia during the holocene

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Science China Earth Sciences 2017年第7期60卷 1317-1327页

作者： ZHAO Yan LIU YaoLiang GUO ZhengTang FANG KeYan LI Quan CAO XianYong Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences Beijing 100101 China University of Chinese Academy of Sciences Beijing 100049 China Key Laboratory of Cenozoic Geology and Environment Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences Beijing 100101 China College of Geographical Sciences Fujian Normal University Fuzhou 350007 China Alfred Wegener Institute Helmholtz Center for Polar and Marine Research 14473 Potsdam Germany

Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the holocene gradual climate changes has been well documented for the Sahara-Sahel ecosystem. Whether such a non-linear response is of universal significance remains to be further addressed. Here,we examine the vegetation-climate relationships in central Asia based on a compilation of 38 high-quality pollen records. The results show that the holocene vegetation experienced two major abrupt shifts, one in the early holocene(Shift I, establishing shift) and another in the late holocene(Shift II, collapsing shift), while the mid-holocene vegetation remained rather stable. The timings of these shifts in different regions are asynchronous, which are not readily linkable with any known abrupt climate shifts,but are highly correlated with the local rainfalls. These new findings suggest that the observed vegetation shifts are attributable to the threshold effects of the orbital-induced gradual climate changes. During the early holocene, the orbital-induced precipitation increase would have first reached the threshold for vegetation "establishment" for moister areas, but significantly later for drier areas. In contrast, the orbital-induced precipitation decrease during the late holocene would have first reached the threshold, and led to the vegetation "collapse" for drier areas, but delayed for moister areas. The well-known 4.2 kyr BP drought event and human intervention would have also helped the vegetation collapses at some sites. These interpretations are strongly supported by our surface pollen-climate analyses and ecosystem simulations. These results also imply that future climate changes may cause abrupt changes in the dry ecosystem once the threshold is reached.

关键词： Fossil pollen Vegetation response Threshold effects holocene climate Central Asia

Evolution of a holocene banner bank controlled by morphodynamics and structural setting of a macrotidal coast: Saint-Brieuc Bay (NW-Europe)

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Geoscience Frontiers 2021年第5期12卷 166-181页

作者： Kalil Traoréa David Menier Erwan Gensac Pascal Le Roy Clément Lambert Paul Bessin Kevin Pedoja Anne Duperret Romain Le Gall Laboratoire Géoscience Océan UMR 6538CNRSUniversitéBretagne SudCampus de Tohannic56000 VannesFrance Laboratoire Géoscience Océan UMR 6538CNRSIUEMUniversitéBretagne Occidentale29280 PlouzanéFrance Laboratoire de Planétologie et Géodynamique UMR 6112CNRSLe Mans UniversitéAvenue Olivier Messiaen72085 Le Mans CEDEX 9France Laboratoire Morphodynamique Continentale et Côtière UMR 6143CNRSUniversitéCaen Normandiecampus 12-4Rue des Tilleuls14000 Caen cedexFrance Laboratoire Ondes et Milieux Complexes UMR 6294CNRSUniversitéLe Havre Normandie53 rue de PronyCS8054076058 Le Havre cedexFrance

The morphology and internal structure of the Horaine Bank(Bay of Saint-Brieuc,NW France)are described based on multibeam echosounder and high-resolution seismic datasets coupled with vibro-core *** Horaine Bank shows large-scale bedforms in the lee of a submerged rocky shoal,which allowed defining it as a Banner *** internal structure of the sandbank reveals four seismic units(U1-U4)on a Cambrian basement(U0).The basal unit U1 is interpreted as reworked lowstand fluvial sediments those infilled micro incised valleys during a rise in sea *** unit is overlain by paleo-coastal barrier sand-spit(U2)whose development was controlled by swell in the context of a rapid rise in sea *** successive prograding unit(U3)is interpreted as flooding deposits in continuity with unit *** unit U4 is characterized by oblique reflectors oriented in two opposite *** last unit,dated post 3500 yr BP,corresponds to migrating dunes superimposed on the bank and observable in the high-resolution bathymetric *** strong correlation between tidal currents and the apparent clockwise migration of dune crests suggests the presence of a tidal gyre controlling the present-day dynamics of most of the Horaine bank *** study proposes a new model for the construction of banner banks characterized by the gradual transition of a sand spit to a banner bank during marine transgression and ensuing hydrodynamic variability.

关键词： Sand banks Banner bank holocene climate Geomorphology Sea level rise Tidal gyre

OSL chronology and paleoclimatic implications of paleodunes in the middle and southwestern Qaidam Basin, Qinghai-Tibetan Plateau

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Research in Cold and Arid Regions 2013年第2期5卷 211-219页

作者： LuPeng Yu ZhongPing Lai Ping An Qinghai Geological Survey Institute State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences State Key Laboratory of Cryospheric Sciences Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences CAS Key Laboratory of Salt Lake Resources and Chemistry Qinghai Institute of Salt Lakes Chinese Academy of Sciences

Aeolian sediments are widely distributed in the Qaidam Basin, northeastern Qinghai-Ti^tan Plateau （QTP）. The pale（xiunes are mainly located at the southeastern, middle and southwestem Qaidam Basin. However, ages ofpaleodunes in the middle and southwestern Qaidam Basin have not been well studied, although they are close to and might connect to the evolution of salt lakes in the cenWal basin. In this study, we use single aliquot regeneration （SAR） protocol of Optically Stimulated Luminescence （OSL） to date the dune sand in these two regions. The results show that：（1） Sand accumulation in these regions started at ca. 4-3 ka and lasted to ca. 0.5 ka when they were stabilized, due to the arid climate in the late holocene. （2） The underlying fluvial sand was fomaed during deghcialion at 12.6±0.8 ka. （3） The stabilization pe- riods of the paleodunes correspond to stages of glacier advance in the northeastem QTP, during which lower temperatures caused the decrease of evapomlion and increase of the effective moisttwe, leading to an increase of vegetation cover and stabilizalion of the dunes.

关键词： Qaidam Basin aeolian sediments paleodunes Luminescence dating holocene climate

Periglacial Lake Environments in Eastern Siberia

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Periglacial Lake Environments in Eastern Siberia

中国东部南北方过渡带淮河半湿润区全新世气候变化

Asian Conference on Permafrost

作者： Diekmann,B. Andreev,A.A. Gerasimova,M. Liipfert,H. Nazarova,L. Pestryakova,L. Popp,S. Siegert,C. Subetto,D.A. Alfred Wegener Institute for Polar and Marine Research Research Station Potsdam Department of Ecology Yakutsk State University Institute of Limnology Russian Academy of Sciences

Research work during the last decades highlighted the role of the northern high-latitude regions for global climate *** climatic influence arising from the vast periglacial regions of eastern Eurasia is poorly *** regions were only affected by regional mountain glaciations,are covered by Taiga and Tundra vegetation and are characterized by deep-reaching frozen *** particular,Yakutia in the northeastern part of Eurasia represents one of Earth’s most extreme climate regions with semiarid continental climate and coldest winter temperatures on the northern *** landscape of Yakutia is occupied by widespread lake *** sediment records of these lakes provide the basis for palaeolimnological reconstructions of former environmental and climate conditions of the periglacial realm in eastern *** using sedimentological,geochemical,and micropalaeontological proxy records,including the application of ecological transfer functions,an interdisciplinary approach is followed to characterize the dynamics of lacustrine systems related to holocene climate *** lakes of tectonic-glacial origin are located at the Verkhoyansk Mountain *** mostly oligotrophic lakes are dominated by siliciclastic muds with low abundances of organic *** in grain-size characteristics indicate variations in fluvial sediment runoff,possibly related to spring snow *** majority of Yakutian lakes are eutrophic and occur in shallow closed to semiclosed thermokarst depressions and in deep alass *** of the semiarid climate setting,the lakes respond very sensitively to perturbations in the hydrological balance,driven by summer precipitation and *** longer time scale,pollen and chironomid records in the lacustrine sediments document an early holocene climate optimum between 8.0 and 4.5 ka BP with generally warm and wet summer *** the same time,a marked variability in the proportions of pe

关键词： East Siberia holocene climate limnogeology thermokarst alass lake status

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中国东部南北方过渡带淮河半湿润区全新世气候变化