the anthropocene and the landscape of confucius a historical ecology of landscape changes in northern and eastern china during the middle to late holocene the yellow river catchment of northern china was central to the rise of complex societies from the first neolithic farmers through to early states and empires these cultural developments brought with them rising populations and increasing intensity of land use this region provides an important record of landscape changes that mark the development of the anthropocene in china geoarchaeological research in the middle reaches of the yellow river catchment of henan province and eastward to the si river drainage of shandong province illustrates human impact on vegetation and hydrological systems dating back at least until the middle neolithic yangshao period in the mid holocene ca 7000 yr bp this research provides geomorphological evidence that early human impact began in the yangshao period with deforestation soil erosion and increased alluviation in the upper catchment of the yiluo river the increased alluviation allowed small scale neolithic farmers to intensify and supplement their production with

the impact of environmental change and human land use on alluvial valleys in the loess plateau of china during the middle holocene abstract in recent years a growing number of studies have reported proxy evidence for holocene climatic and environmental change on the loess plateau of north central china pollen from lake cores and sediment analyses from loess sections firmly point to a warm moist mid holocene climatic optimum archaeological evidence indicates that at the same time human agricultural settlements expanded into this area during the middle neolithic period a geoarchaeological study of sediment sections from several valleys within the catchment of the yiluo river henan province indicates a sequence beginning with a stable landscape soil development and high water tables in the early mid holocene which was exploited by early neolithic millet farmers in the peiligang period subsequently there was a rapid shift to episodes of hillslope erosion and increased valley alluviation in the later mid holocene the resulting alluvial sediments dating from 5300 5010 cal bc through 2130 1870 cal bc represent clay rich water logged deposits that contain sediment and phytolith evidence for the first rice paddy farming in this region this coincides with the first migration of neolithic rice farmers to the area in the yangshao period ca 5500 cal bc these fills temporally and stratigraphically linked to archaeological sites and human land use practices suggest that they originated as a direct result of human impact on the landscape after ca 2000 cal bc holocene valley incision in this catchment led to narrowing floodplains the disappearance of the valley wetland deposits and a reduction in land available for paddy farming

paleocene planktonic foraminifera from dsdp site 356 south atlantic paleoceanographic inferences abstract in the present study the planktonic foraminiferal distribution in a core section representing an interval between the cretaceous paleogene k pg boundary and the end of the paleocene danian selandian from dsdp site 356 sao paulo plateau south atlantic was analyzed the results point towards a gradual recovery of the marine pelagic ecosystem in the aftermath of the k pg mass extinction event the changes in distribution patterns and composition of the danian planktonic foraminiferal assemblages are primarily related to the instability and changing conditions of oceanic surface waters the quantitative analyses of the planktonic foraminifera showed that a series of speciation events took place in the danian immediately after the k pg boundary marking three distinct main intervals i in the p zone evidenced by the predominance of specimens that likely inhabited the most superficial portions of the water column mixed layer represented mainly by microperforated taxa globoconusa guembelitria parvularugoglobigerina and woodringina the occurrence of this group suggests poorly stratified water masses and a water column with meso eutrophic conditions in this interval the first appearance of spines in the planktonic foraminifera eoglobigerina of the family globigerinidae evidences the development of a carnivorous habit ii between zones p1a and p2 there is a continuous increase of species that inhabited the lower portion of the water column in the thermocline and sub thermocline suggesting the recovery of the pelagic ecosystem with the development of a more stratified water column in mesotrophic to oligotrophic conditions iii from zone p3 onwards most of the planktonic foraminifera inhabited the lowest portions of the water column together with the first occurrences of mixed layer endosymbiont bearing species such as morozovella acarinina and igorina

sedimentation rates in the lower yellow river over the past 2300 years as influenced by human activities and climate change analysis of the sedimentary record has been used to determine the historical sedimentation rate in the lower yellow river and the historical literature has been studied to obtain information on climate change and human activities based on the data obtained the temporal variation in the sedimentation rate in the lower yellow river over the past 2300 years has been studied in relation to climate change and the impact of human activities the results indicate that the response of the sedimentation zone of yellow river system to changes in the erosion zone are consistent with existing understanding changes in vegetation and land use both related to climate change and human activities are two major controls responsible for the increase in sedimentation rates additionally the changing strategies for harnessing of the lower yellow river are also responsible for such acceleration with the trend of accelerated sedimentation in the past 2300 years the period from the 7th to 10th centuries and the period since the mid 19th century have been identified as two periods in which abrupt changes occurred copyright c 2003 john wiley sons ltd

river floodplain aggradation history and cultural activities geoarchaeological investigation at the yuezhuang site lower yellow river china abstract archaeobotanical research at the yuezhuang and xihe sites of the houli culture in the lower yellow river has found abundant carbonised plant remains including rice millet weed seeds and many other plants 7800 7000 cal bp although studies of the diverse economic practices of the houli people have begun issues such as ecological diversity and relationships between site formation processes with environmental changes are still poorly understood applying soil micromorphology and related methods such as particle size distribution and loss on ignition at yuezhuang this paper presents results of the geoarchaeological investigation and the implications for the reconstruction of site formation processes in relation to river alluvial history a long alluvial sequence is reconstructed consisting of frequent alternations of short periods surface stabilities and succeeding alluviations human occupations corresponded to those short term surface stabilities and are evidenced by the presence of anthropogenic inclusions in thin sections including burned bone fragments and pottery sherds the significances of this study to an ecological approach focusing on environmental changes and cultural adaption are discussed

holocene colluviation and its implications for tracing human induced soil erosion and redeposition on the piedmont loess lands of the qinling mountains northern china abstract colluvial components incorporated in loess soil sequences have preserved evidence of soil erosion and redeposition in the middle reaches of the yellow river drainage basin holocene loess soil sequences on the gentle sloped lands were studied by measuring magnetic susceptibility particle size distribution caco3 and extraction and identification of the non dust materials the analytical results indicate that in the early holocene soil erosion and redeposition by overland flow occurred even on the loess lands with small ground gradient in response to climatic amelioration linked to global climatic change no obvious soil erosion and redeposition events were found to correspond with the climatic fluctuations recorded in the loess soil sequence during the holocene climatic optimum the primary neolithic farming did not cause apparent erosion and redeposition because the loess landscape was mantled by well developed ustic luvisols and probably by forest vegetation both provided adequate resistance to sheet erosion by overland flow enhanced soil erosion and redeposition are traceable back to ca 4000 a b p it is attributed to intensified land use of arable farming and human settlement from the early bronze age onward a major event of sheet erosion and redeposition by overland flow occurred in the loess landscape during 4000 3600 a b p in the xia dynasty soil degradation and reduced resistance caused by climatic aridity and intensified dust accumulation may have played a secondary role in promoting soil erosion since 3100 a b p these results provide new insights into the history of soil erosion in the semi arid and semi humid loess regions and into the evaluation of human induced accelerated soil erosion against the background of the holocene natural erosion forced by monsoonal climatic fluctuation

environmental and archaeological implications of a late quaternary palynological sequence poyang lake southern china paleoecological data from poyang lake southern china indicate that significant natural and human induced vegetational changes have occurred during the late quaternary in the middle yangtze river valley the likely location of rice oryza sativa l domestication during the late pleistocene from ca 12 830 to ca 10 500 yr b p the climate was cooler and drier than today s the subtropical mixed deciduous evergreen broad leaved forest which constitutes the modern potential vegetation was reduced and herbaceous vegetative cover expanded a hiatus in sedimentation occurred in poyang lake beginning sometime after ca 10 500 yr b p and lasting until the middle holocene ca 4000 yr b p at ca 4000 yr b p the regional vegetation was a diverse broad leaved forest dominated by many of the same arboreal elements e g quercus castanopsis liquidambar that grow in the area today a significant reduction of arboreal pollen and an increase of herbaceous pollen at ca 2000 yr b p probably reflect human influence on the vegetation and the expansion of intensive rice agriculture into the dryland forests near the river valleys

high resolution evidence from southern china of an early holocene optimum and a mid holocene dry event during the past 18 000 years abstract computer models suggest that the holocene optimum for east asian summer monsoon precipitation occurred at different times in different regions of china previous studies indicate that this time transgressive holocene optimum should have been experienced about 3000 yr ago in southern china in this study we describe a section which allows us to test this timing directly we have closely examined high resolution eutrophic peat mud sequences covering the past 18 000 cal yr at dahu jiangxi on the southern boundary of the mid subtropical zone in china late pleistocene successions in the dahu record indicate cooler and much wetter conditions relative to synchronous events in north central china our results indicate that the holocene optimum occurred between ca 10 000 and 6000 cal yr ago in southern china consistent with the global pattern conditions were relatively dry and cold from 6000 to 4000 cal yr ago our data also support the conclusion that the last deglaciation to early holocene in the south was much wetter resulting in the formation of dense broad leaved forests which could have acted to moderate land temperature 10 000 to 6000 cal yr ago yielding a stable early holocene climate after 6000 cal yr forest reduction led to unstable land temperatures and possibly to a northerly shift of the subtropical high pressure system whatever the mechanism these changes resulted in decreased precipitation between 6000 and 4000 cal yr b p in southern china

prehistoric and historic overbank floods in the luoyang basin along the luohe river middle yellow river basin china abstract paleohydrological investigations were carried out in the luoyang basin along the luohe river in the middle reaches of the yellow river basin three units of overbank flood deposits ofd were identified in a holocene aeolian loess soil profile on the south cliffy river bank at taixuecun site txc analytical results including magnetic susceptibility grain size distribution and geochemical elements indicate that these well sorted overbank flood deposits were deposited from the suspended sediment load in floodwaters we identified two episodes of prehistoric extraordinary overbank flooding that were dated to 6000 5500 and 4000 3800 yr bp using ams 14c and osl dating techniques with references to the already known ages of the archaeological remains among of the two episodes the overbank episode at 4000 3800 yr bp likely had a profound impact on the cultural development from the late longshan culture 4500 4000 yr bp to the erlitou culture 3700 3500 yr bp in the alluvial plain of the luo river within the luoyang basin providing geological evidence for the legends of ancient floods and their social impacts at ca 4000 yr bp in addition an episode of historic overbank flood event was dated to 1800 1700 yr bp i e from the han to wei dynasties during which the ancient capital luoyang city was subjected to frequent flooding these aforementioned hydro climatic events are considered to be regional expressions of known climatic events the study adds our knowledge of the holocene extraordinary overbank floods and their relationship with monsoonal climate change and human land use practices and the social impact of prehistoric environmental changes on human cultural development

organic geochemical changes in pliocene sediments of odp site 1083 benguela upwelling system the intensification of the northern hemisphere glaciation inhg was a major event in the development of the current climate state and as one of the most productive regions in the world s oceans the behaviour of the benguela upwelling system bus following the inhg is of wide interest to investigate post inhg changes in productivity and organic matter accumulation total organic carbon and biomarker accumulation rates were determined for sediments from cop site 1083 and compared to alkenone derived sea surface temperatures and nitrogen isotopic compositions these data indicate that the interval between 2 6 and 2 4 ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern bus the upwelling is reflected by significant changes in alkenone derived sst estimates between glacial and interglacial intervals with a total variability of 16 degrees c the studied interval is also characterized by large changes in organic matter export as reflected by changes in toc and biomarker accumulation rates which show maxima during ois 98 and during the transition from ois 97 to 96 intervals of elevated toc are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower caco 3 suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released co 2 being consumed by caco 3 dissolution however in apparent contrast to recent pleistocene sediments at the same site organic matter export after the inhg was not solely driven by upwelling intensity of the three pliocene glacial interglacial cycles examined ois 101 to 96 each is unique with respect to the timing and magnitude of changes in organic matter accumulation each is also characterized by different algal assemblages as inferred from biomarker distributions with ois 97 and 96 particularly dominated by diatoms we suggest that these differences reflect the important but evolving role of southern ocean waters in the pliocene bus nutrient depletion of so waters occurred during parts of pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates c 2009 elsevier b v all rights reserved

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

a detailed comparison of asian monsoon intensity and greenland temperature during the allerod and younger dryas events abstract an annual layer counted and 230th dated stalagmite oxygen isotope record from qingtian cave in hubei province central china provides an asian monsoon am history across the allerod to younger dryas yd transition with an average 2 5 year resolution seasonal 18o profiles indicate that the calcite 18o is a sensitive proxy for am changes and the close similarity between the qingtian and other cave records from eastern china suggests a large scale regional coherence of monsoonal precipitation 18o variations associated with the temperature changes in high northern latitudes the annually resolved chronology with a u th age uncertainty of less than 100 yr defines the timing duration and transition of the early allerod the intra allerod cold period iacp the late allerod and the start of the yd the 160 yr long iacp with two brief reversals is clearly shown in both 18o and lamina thickness records the early and late allerod separated by the iacp are characterized by several decadal to centennial cycles of 18o variations each punctuated by sub cycles these decadal to centennial monsoon variations correlate with the greenland temperature changes supporting a model simulation that the decadal north atlantic oscillation nao and north pacific oscillation npo are coupled via atmospheric circulation under glacial boundary conditions perhaps affecting tropical subtropical monsoon changes however the monsoon transition between the late allerod and yd lasted 380 yr longer than the analogous greenland temperature shift by at least 130 yr stuiver m grootes p m gisp2 oxygen isotope ratios quat res 53 2000 277 284 this implicates other links besides the direct link between greenland and the am which is now well documented one possibility is the influence by southern hemisphere climate via cross equatorial air flow an z s the history and variability of the east asian paleomonsoon climate quat sci rev 19 2000 171 187

late quaternary environmental change of yellow river basin an organic geochemical record in bohai sea north china abstract bulk geochemical characterization total organic carbon grain size distribution carbon isotope composition and molecular biomarkers lignin phenols straight chain aliphatic hydrocarbons glycerol dialkyl glycerol tetraethers were analyzed for a 21 m core from the bohai sea north china spanning ca 21 ka bp these paleo proxies presented remarkable differences between the late glacial period and the holocene reflecting continental and coastal environments respectively two peat layers were deposited during the period of ca 9000 8460 yr bp thereafter the core site has been consistently covered by seawater until recent reclamation of land from the sea the occurrence of a total organic carbon maximum from ca 6000 3800 yr bp was attributed to delivery of organic carbon enriched sediments via the yellow river consistent with increased vegetation density and higher development of soil under warm and humid mid holocene climate conditions the distributions of lignin phenol compositions and c 31 c 29 n alkane ratio suggested the largest expansion of woody plants between ca 5300 and 4000 yr bp corresponding to the extremely favorable climatic conditions since ca 3800 yr bp an abrupt increase in the c 31 c 29 n alkane ratio suggested higher abundance of grasses consistent with a drying climate trend after the mid holocene since our coastal sediments close to the yellow river outflow contain catchment integrated environmental signals of the river basin molecular proxies demonstrate that the variability of vegetation distributions in the holocene is a widespread phenomenon in those areas adjacent to yellow river basin

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

extreme flooding of the lower yellow river near the northgrippian meghalayan boundary evidence from the shilipu archaeological site in southwestern shandong province china abstract understanding the societal impacts of past climate changes may deepen our insight into human adaptation and resilience against potential climate changes in the future however the degree and nature of climate civilization link are still a matter of debate fluvial deposits preserved within a cultural stratigraphical context at archaeological sites in the lower yellow river area may offer an exceptional framework for evaluating the role of climate changes in the rise and fall of ancient civilizations here we show evidence for great lower yellow river floods during the neolithic bronze age transition about 4000 3500 years ago comparing with existing terrestrial and marine records suggests that they were a downstream manifestation of flooding in the middle reaches of the yellow river most likely triggered by excessive summer precipitation while a weak el nino condition prevailed the floods substantially modified the preexisting landscape and altered the agricultural conditions thereby driving people dwelling on the higher mounds to move upward our results provide a past analogue of the linked climatic environmental and societal changes at a time when large and rapid climate changes occurred

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

charcoal records of fire history in the holocene loess soil sequences over the southern loess plateau of china abstract charcoal preserved in accretionary loess soil profiles within the southern part of the loess plateau has recorded fire history and landscape evolution connected with climatic variations and human activities local wildfires occurred frequently during the late last glacial period and the early holocene before 8500 years bp when steppe vegetation expanded from the inner mongolian plateau southerly over the loess plateau during the holocene climatic optimum between 8500 years bp and 3100 years bp natural wildfires were largely reduced pedogenesis of the luvisols and isohumisols was intensified because of the increased monsoonal precipitation and soil moisture localized fires in connection with human activities occurred in different patterns at the study sites fire seems to have been applied to vegetation clearance for land reclamation for millet cultivation at many places during the neolithic and early bronze age levels of biomass burning were very high during the late holocene when the climate became drier and historical land use became more intensive at some sites the intensity of human disturbance by fire and cultivation increased continuously during the last 3100 years at the other sites local fires occurred most frequently between 3100 years bp and 1500 years bp during the major period of land reclamation for cereal cultivation human burning of the landscape has been reduced since then

geology of mankind for the past three centuries the effects of humans on the global environment have escalated because of these anthro pogenic emissions of carbon dioxide global climate may depart significantly from natural behaviour for many millennia to come it seems appropriate to assign the term anthropocene to the present in many ways human dominated geological epoch supplementing the holocene the warm period of the past 10 12 millennia

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

aging of marine organic matter during cross shelf lateral transport in the benguela upwelling system revealed by compound specific radiocarbon dating organic matter accumulation and burial on the namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers much of the material deposited in depo centers on the slope ultimately derives from the shelf supply of organic matter from the shelf involves selective transport of organic matter we studied these selective transport processes by analyzing the radiocarbon content of co occurring sediment fractions here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity phytoplankton derived alkenones membrane lipids of pelagic crenarchaeota crenarchaeol and calcareous microfossils of planktic foraminifera in core top and near surface sediment samples the samples were collected on the namibian margin along a shelf slope transect 85 to 1040 m at 24 s and from the upper slope depo center at 25 5 s in core top sediments alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth crenarchaeol while younger than alkenones also increased in age with distance offshore it was concluded that the observed ages were a consequence of cross shelf transport and associated aging of organic matter radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied pre aged material present in a sample highlighting the importance of nepheloid transport for the sedimentation of organic matter over the namibian margin

wetland geomorphology and paleoecology near akab muclil rio bravo floodplain of the belize coastal plain abstract to understand wetland geomorphology and paleoecology we collected a 2 6 m sediment core from a flooded swamp adjacent to the maya archaeological site of akab muclil in the maya lowlands of northwestern belize the site of akab muclil has a known occupation that persisted from early maya classic 1700 1350 bp through the terminal maya classic 1180 1050 bp and into the postclassic 1050 450 bp and lies near a vast network of ancient maya canal and field systems we analyzed this core using a combination of paleoecological and geochemical techniques to determine the history of land use and natural change over time within this wetland accelerator mass spectrometry dating pollen charcoal analysis micropaleontology geochemical analysis and magnetic susceptibility provide a suite of methods from which we interpret the geomorphic and ecological history of this wetland system four ams dates from the length of the core provide us with an age model that runs from 1675 cal bp through the maya classic onward to the present at the base of this system soil composition and chemistry provide evidence that the system changed from a seasonally wet terrestrial soil to a perennially wet swamp as the basal mollisol soil lies buried by peats and calcareous sediments this shift to a perennial wetland could be related to ancient maya water management or a natural geomorphic change though we suspect the former because of nearby ancient maya large scale geomorphic and hydrological manipulation in the form of intensive canalization and agriculture evidence of ancient maya uses and impacts including sedimentation zea mays pollen and high charcoal counts occur from the lowest levels of the sequence through the classic and into the postclassic period above this level the strata change to stable peats laminated deposits of light gray dark gray gypsum authigenic carbonate and layers of fibrist peat with little evidence of human impact until recent increases in charcoal and phosphorous this study compared with other regional studies indicates a later transition from terrestrial to wetland later human impacts in the postclassic and a geomorphic impact record closely tied to the history of the adjacent site rather than broader land use trends

the huanghe yellow river and changjiang yangtze river deltas a review on their characteristics evolution and sediment discharge during the holocene abstract today asian rivers play an important role in delivering sediment from the land to the oceans however past sediment discharge before human activities modified the landscape is not well known and is estimated to have been roughly one third to one half of the present level chinese rivers have been strongly influenced by human activities and their sediment discharge has changed over the last 6000 years for the study of the long term human impact on rivers and catchment basins chinese rivers provide excellent examples because continuous historical records are available here the characteristics evolution and sediment discharge during the holocene of the deltas of two large chinese rivers huanghe yellow river and changjiang yangtze river are summarized the huanghe and changjiang deltas are different with respect to coastal environments water and sediment discharge the pattern of development of the delta lobe thickness of holocene sediments and basal topography of the incised valleys formed during the last glacial period the huanghe delta is characterized by a high concentration of sediment huge sediment discharge thin holocene deltaic sediments a lateral delta lobe shift and a steep longitudinal profile in its lower reaches the changjiang delta is characterized by a large water discharge a large interseasonal water level change a tide dominated coastal environment continuous seaward progradation with isolated river mouth sand bodies thick holocene sediments and a deep incised valley formed during the last glacial period based on the sediment volume of prograding deltaic sediments over the last 6000 years the sediment discharge of huanghe 1000 years ago is estimated to have been 1 10 8 tons year 1 10 of the present level an abrupt increase occurred at ca 1000 years ago as a consequence of human activities on the loess plateau especially involving cultivation and deforestation moreover the estimated sediment load of huanghe at sanmenxia station prior to 1000 years was 2 7 4 0 10 8 tons year or about 20 15 25 of the present level our recent study estimated that the sediment discharge of changjiang before 2000 years bp was ca 2 4 10 8 tons year total sediment discharge of both rivers before 2000 years bp is estimated to have been 3 4 10 8 tons year or only about 20 of the present level moreover the total sediment load to the lower reaches is estimated to have been 5 6 10 8 tons year or one fourth the present level

dry or humid mid holocene humidity changes in arid and semi arid china abstract spatial changes of effective moisture during the mid holocene have been reconstructed based on the compilation of recently published paleoclimate records including ice core lake level pollen assemblage and loess paleosol records both geological data and the spatial pattern indicate that it was dry in deserts during the mid holocene but the timing of the beginning and end of dry intervals differs from place to place deserts having higher aridity index values remain dry longer dry intervals during the mid holocene are more possibly asynchronous than synchronous in arid and semi arid china in the xinjiang region except in sites located in deserts the climate is generally wet during 7000 5000 a bp in the northern qinghai tibetan plateau effective moisture in most sites began to decrease after 5000 a bp the climate became dry after 4000 a bp except in the deserts in the loess plateau and the inner mongolia plateau