paleoclimatic significance of magnetic properties on the red clay underlying the loess and paleosols in china abstract the red clay unit of northern china is a widespread miocene pliocene 7 2 2 5 ma aeolian deposit that underlies much of the quaternary loess paleosol sequence in the central loess plateau it comprises a sequence of highly developed soils and interbedded layers of less weathered loess like material here referred to as reddish loess in common with the loess paleosol alternations of the overlying quaternary deposits the soil reddish loess alternations are interpreted to represent climatic fluctuations in this case between warm humid and relatively dry cool conditions however while magnetic susceptibility variations in the quaternary deposits provide a good proxy for pedogenic intensity in the red clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis in an attempt to resolve this issue we have investigated a red clay section and overlying loess paleosol sequence at xifeng and have supplemented these data with samples from the red clay at lingtai our study indicates that the red clay and loess paleosol sequence have a common magnetic mineralogy comprising magnetite maghemite and hematite and possibly goethite and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic sp component this implies that susceptibility enhancement in the red clay is strongly related to the magnitude of the sp content a component that is widely recognised as having a pedogenic origin in quaternary deposits further support for a correlation between pedogenesis and magnetic susceptibility in the red clay is provided by a good correlation between magnetic susceptibility and the rb sr ratio an independent weathering index however differences in the magnetic mineralogy of the two units are also evident the minimum magnetic susceptibility of the red clay is less than half the value of the overlying quaternary deposits at locations such as xifeng and lingtai while the maximum sp content is relatively larger than for the quaternary deposits while we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units climate may also be a contributory factor in explaining these differences precipitation is a major control on magnetic enhancement in paleosols maher and thompson 1995 quat res 44 383 391 liu et al 1995 palaeogeogr palaeoclimatol palaeoecol 113 243 248 but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive central loess plateau china magnetic enhancement negative alaska siberia magnetic destruction or uncertain pakistan argentina new zealand cycles of enhancement and destruction while our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the red clay they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary but independent techniques more work is required to deconvolve the climatic record of the red clay but the reward may be the extension of the record of paleomonsoon evolution back into the pliocene and late miocene

wind effects on estimates of sea level rise 1 variability in sea level at the longest periods observable in modern records has recently been found to be well correlated with local atmospheric pressure at shorter periods however longshore winds are known to be one of the primary mechanisms for forcing sea level variability on the eastern margins of the ocean there is a remarkable 80 mm drop in mean sea level on both the eastern north pacific and north atlantic coasts between the late 1800s and early 1900s it is found here to be in agreement with longshore wind forcing from the equator up to the latitude of the observed tide stations better resolved data beginning in 1960 show that the delay near the annual period between wind forcing and sea level is approximately 1 month the relative high in sea level in the late 1800s on the west coast of europe appears to have propagated westward across the atlantic as a long rossby wave and then to have been seen on the east coast of the united states because many features in long term sea level variability are correlated with wind forcing on time scales from annual to decades it will be prudent to base conclusions about long term sea level rise on the longest records available the results here are based on forcing by longshore winds the related issue of the extent to which open ocean wind curl may also be responsible is not addressed here nor the extent to which coastal sea level observations are representative of the open ocean

enhancement mechanisms of magnetic susceptibility in the chinese red clay sequence 1 little is known about the mechanisms of magnetic susceptibility enhancement for the red clay sequence on the chinese loess plateau clp in comparison to the overlying loess paleosol sequence here we present a rock magnetic study of the red clay sediments from the central clp our results show that frequency dependence of fd lf hf where lf and hf are measured at 470 hz and 4700 hz respectively lf and susceptibility of anhysteretic remanent magnetization arm are linearly correlated within the red clay sequence this linear correlation indicates that the pedogenic magnetic minerals of the red clay have a rather uniform grain size distribution as in the loess paleosol sequence and the grain size is independent of the degree of pedogenesis nevertheless red clay sediments are slightly more enriched in superparamagnetic magnetic particles than the overlying loess paleosol sediments as indicated by the higher slope of the regression line between fd and lf

characterization of the chinese loess paleosol stratigraphy by whiteness measurement abstract changing color is one of the most striking features of loess paleosol sequences in central china the loess is light yellow and the interstratified paleosols are reddish brown until a few years ago conventional color description of loess sediments was made using a qualitative visual method the munsell system to better understand the character of the color changes and to quantify results whiteness and magnetic susceptibility were compared from four loess paleosol sequences results show that the two parameters are highly correlated in the four sequences studied grain size analysis and chemical extraction experiments indicate that the concentration and species of fine grained iron oxides are major factors determining color changes in loess and paleosols whiteness and latitude values from the last glacial interglacial sequence exhibit a linear relationship suggesting that whiteness will be a useful tool for reconstructing past atmospheric circulation especially the east asian summer monsoon whiteness and magnetic susceptibility in the luochuan profile over the past 0 9 myr display a strong correlation indicating that whiteness can be also used to reveal a long climatic history from chinese loess paleosol sequences

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

mid holocene climate change and its effect on prehistoric cultural evolution in eastern qinghai province china abstract we studied the mid holocene climate change in eastern qinghai province china and its impact on the evolution of majiayao 3980 2050 bc and qijia 2183 1635 bc cultures near the important neolithic site of changning the investigation focused on analyses of grain size magnetic susceptibility ratios of elemental contents and pollen assemblage from a loess paleosol sequence the results indicate that the climate was wet during 5830 4900 cal yr bp which promoted the development of early mid majiayao culture in eastern qinghai province however 4900 4700 cal yr bp were drought years in the region responsible for the decline and eastward movement of prehistoric culture during the period of transition from early mid to late majiayao culture the climate turned wet again during 4700 3940 cal yr bp which accelerated the spread of qijia culture to the middle reaches of the huangshui river including the changning site

miocene climate change on the chinese loess plateau possible links to the growth of the northern tibetan plateau and global cooling the evolution of the asian monsoon arid environmental system during the cenozoic was closely related to the growth of the himalayan tibetan plateau and global climate change however due to inconsistencies in paleoclimatic reconstructions and to various constraints on the timing of the growth of the tibetan plateau the relative impacts of regional uplift and global cooling on asian climate change remain controversial here we investigate the mineralogical composition of a miocene red clay deposit on the western chinese loess plateau in order to infer changes in chemical weathering and monsoon intensity variations of four mineralogical ratios chlorite quartz illite quartz calcite quartz and protodolomite quartz reveal that the summer monsoon intensity was relatively strong during the early miocene 23 5 18 5 ma weakened gradually until 9 5 ma and strengthened again in the late miocene we synthesized previously published thermochronological data from the northeastern tibetan plateau and surrounding mountains and the results suggest that two phases of the rapid growth of northern tibet occurred around 24 17 and 13 7 ma comparison of paleoclimatic proxies and thermochronological data suggests that the gradual weakening of the summer monsoon intensity from 18 5 to 9 5 ma paralleled global cooling whereas two intervals of strengthened monsoon in the early and late miocene were possibly related to the rapid growth of northern tibet our combination of paleoenvironmental proxies and thermochronological data reveals possible links between miocene asian monsoon evolution phased growth of the tibetan plateau and global climate change and confirms the interconnection of geodynamic and atmospheric processes in the geological past

forcing of coastal sea level rise patterns in the north atlantic and the mediterranean sea sea level trends derived from north atlantic and the mediterranean sea tide gauges have been re evaluated with a common reference period 1960 2000 and with the atmospheric component of the observed sea level variability quantified and removed by means of regional barotropic ocean models forced by wind and atmospheric pressure the atmospherically forced trends are important and have values of 0 2 0 1 mm yr in the north atlantic west coast 0 2 0 2 mm yr in the ne atlantic 0 3 0 4 mm yr in north sea and 0 7 0 1 mm yr in the mediterranean the residual sea level trends corrected for post glacial rebound processes are 0 9 0 4 mm yr in the mediterranean 1 1 0 6 mm yr in the nw atlantic 1 3 1 0 mm yr in the ne atlantic and 1 3 0 8 mm yr in the north sea atmospheric forcing is partly responsible for the observed patterns of sea level rise and for part of the observed sea level acceleration during the 1990s the residual trends have further been corrected for the influence of the steric effects in the mediterranean removing the steric component increases the trends by 40 and makes them consistent with the atlantic trends the remaining sea level rise rates are due to mass addition and their spatial pattern in the region can be related to greenland ice melting rates

contrasting dust supply patterns across the north western chinese loess plateau during the last glacial interglacial cycle loess grain size distributions of four loess paleosol sequences located on a west to east transect from the north eastern tibetan plateau tp to the north western chinese loess plateau clp are unmixed with the end member modelling algorithm emma the unmixing results indicate that the loess is a mixture of three components representing very fine sandy coarse silty and medium silty loess the proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last glacial interglacial cycle two contrasting dust supply patterns were active over the north eastern tp and the north western clp a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess the variable input of the two coarse dust components is the main cause for the variation in grain size patterns and mass accumulation rates between the studied sites alluvial fans and river floodplains in the intra mountainous basins of the tibetan plateau and the deserts of northern china and inner mongolia are the main dust source areas for loess deposits of the north eastern tp and the clp respectively the sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition in general high dust fluxes are recorded during the last glacial period marine isotope stages mis 2 4 and low dust fluxes during the last interglacial mis 5 the loess sections in the two regions tp clp show contrasting dust flux patterns during mis 3 the records from the clp show a relatively low dust input in this period most likely related to increased humidity in the northern dust sources deserts where an increased vegetation cover minimized dust deflation in contrast to this the tibetan plateau records appear to show increased and highly variable dust fluxes for mis 3 alternating periods of increased humidity and aridity on the tibetan plateau during mis 3 have resulted in an overall increase in fluvial alluvial activity hence the enhanced availability of exposed fine grained fluvial alluvial sediments on the tibetan plateau facilitated dust entrainment which resulted in an increased dust supply towards the tibetan plateau sites during this period

color reflectance of chinese loess and its implications for climate gradient changes during the last two glacial interglacial cycles 1 to examine the relationship between color changes of loess deposits and paleoclimate conditions a north south transect consisting of twelve loess sections were studied color reflectance was measured on loess paleosol samples from the loess transect which accumulated over the last two glacial interglacial cycles the redness value a shows an overall southward increase for both loess and soil units coinciding with the pattern of a southerly increase in pedogenic development and the present north south climatic gradient the redness of loess deposits is linearly correlated with latitude values implying that this parameter is an efficient proxy for the weathering intensity of loess deposits the gradient of weathering intensity is much steeper during interglacials than in glacials by comparison of color records for different time interval

palaeoenvironmental implications of the prehistorical catastrophes in relation to the lajia ruins within the guanting basin along the upper yellow river china archaeological excavations have exposed a shocking picture of the prehistorical catastrophes in the lajia ruins in the upper yellow river the grouped skeletons resting on the dwelling floors show

mineralogic and climatic interpretations of the luochuan loess section china based on diffuse reflectance spectrophotometry we examined the top 135 m that is the entire pleistocene of the classic luochuan section on the chinese loess plateau with a diffuse reflectance spectrophotometer from the near ultraviolet through the visible and into the near infrared from the reflectance data we calculated sample brightness which with some caveats is a reasonable proxy for magnetic susceptibility mineralogic changes were identified by factor analyzing the first derivative of the percent reflectance data and examining samples with high factor scores two factors which explain about 96 of the cumulative variance are distinguished by the relative proportion of hematite and goethite the minerals that are responsible for the color changes in the loess sequence both hematite and goethite are present in both loess and paleosol but goethite dominates in loess whereas hematite dominates in paleosol the goethite factor exhibits an inverse correlation with magnetic susceptibility the hematite factor exhibits a weak positive correlation with susceptibility paleoclimatic interpretations are drawn from comparison of susceptibility to the concentration of spectrally identified hematite based on this comparison paleosols in the early pleistocene wucheng formation are characterized by conditions that are drier than today a dry summer monsoon whereas later pleistocene paleosols are characterized by a wet summer monsoon

changing color of chinese loess geochemical constraint and paleoclimatic significance abstract two loess paleosol sequences on the central chinese loess plateau were investigated to understand spatial and temporal variations in the soil color e g lightness and redness and factors that control those variations color difference between the original samples and pretreated samples suggests that loess lightness is influenced by the pedogenic matter e g iron oxides organic matter and calcium carbonate to varying degrees depending on the concentrations iron oxides and organic matter darken the loess lightness whereas carbonate lightens the loess lightness by contrast the redness is dominantly controlled by the types and concentrations of iron oxides variations in magnetic susceptibility and redness are associated with different magnetic minerals that formed mainly during post depositional processes and therefore both proxies can be employed to reconstruct the history and variability of the east asian summer monsoon since the sensitivity of these two proxies to the summer monsoon variation is different we generate a stacked summer monsoon index by combining these two records and interpret the stacked index as most indicative of precipitation variability the fidelity of this new index is supported by an independent ratio estimated from the first derivative values of the color reflectance spectra our loess based proxies provide a new understanding of the east asian summer monsoon variability as a two phase strengthening of summer monsoon intensity during the penultimate deglaciation

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

high resolution paleoclimatic information from chinese eolian sediments based on grayscale intensity profiles abstract grayscale intensity profiles from photographic images offer a rapid means of obtaining paleoclimate proxy records from chinese loess dune sand and paleosols although the data can be obtained using conventional 35 mm film images a digital camera and laptop computer will produce a high resolution grayscale profile at a field site within minutes comparison of grayscale profiles with profiles of magnetic susceptibility measured down loess and dune sand sections at sites on the loess plateau and tibetan plateau in a range of altitudes and climatic regimes shows that the two parameters are highly correlated therefore grayscale intensity is a convenient alternative to magnetic susceptibility for generating paleoclimatic data in the loess and desert margin regions of china the resolution of both grayscale and susceptibility profiles ultimately is limited by bioturbation which is most pronounced in paleosols

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

ocean circulation and iceberg discharge in the glacial north atlantic inferences from unmixing of sediment size distributions variability in iceberg discharge and deep ocean circulation in the north atlantic during the last glacial period is inferred from the grain size distribution and trace elemental composition of terrigenous sediments in a deep sea core taken on reykjanes ridge south of iceland end member modeling of the grain size distributions is used to unmix the signals of varying bottom current speed and iceberg discharge the size distribution within the silt fraction appears to be influenced by both factors based on th sc la relationship we established that during the ice rafted detritus events continental material of likely greenlandic origin increased to 87 and that bottom current derived material contains to 40 mid oceanic ridge fines probably of icelandic origin our results have important implications for the use of silt grain size as an indicator for paleocurrent speed in the glacial north atlantic we show that reconstructions of variations in bottom current speed based on the raw grain size data are opposite to inferences from the unmixed record the latter indicates that deep water convection decreased during periods of enhanced iceberg discharge which is in general agreement with paleoceanographic reconstructions of the north atlantic

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

mid late holocene temperature and precipitation variations in the guanting basin upper reaches of the yellow river abstract the reconstruction of prehistoric temperature and precipitation variations in the upper reaches of the yellow river is essential for understanding the cultural evolution of the region but related information is sparse due to the limitations of the available proxies recent studies have shown that microbial glycerol dialkyl glycerol tetraethers gdgts are promising tools for reconstructing mean annual temperature mat and mean annual precipitation map in terrestrial deposits in this study we reconstructed mid late holocene climatic changes using gdgt distributions in a loess paleosol sequence in the lajia ruins of the neolithic qijia culture guanting basin in the southwestern end of the chinese loess plateau our gdgt records show that map decreased from ca 600 mm to 430 mm while mat decreased from 11 9 c to 8 0 c during the past ca 7000 yr and a drastic decline in map 70 mm accompanied by a 0 8 c decline in mat occurred at 3800 3400 yr bp our results provide direct evidence supporting a hypothesis that the flourishing 4200 4000 yr bp and decline 4000 3600 yr bp of the qijia culture mainly based on millets cultivation and subsequent rise of the xindian kayue culture 3600 2600 yr bp based on mixed agriculture of sheep husbandry and millets cultivation were triggered by climate change

extraordinary floods of 4100 4000 a bp recorded at the late neolithic ruins in the jinghe river gorges middle reach of the yellow river china abstract holocene palaeohydrological investigations were carried out in the middle reach of the jinghe river that drains the central part of the loess plateau a set of palaeoflood slackwater deposits was found interbedded in the holocene loess soil sequence within the cliff riverbanks both the sedimentary criteria and the analytical results show that this sediment was sourced from a suspended sediment load of floodwater the major cultural layer of a late neolithic settlement 4300 4000 a bp occurring at the same site is blanketed by this flood deposit directly slopewash with pottery shards charcoal and burnt earth occurs in between the palaeoflood slackwater deposit beds it indicates that each of the slackwater deposit beds has recorded one individual flood event and that these extraordinary floods occurred when the late neolithic people occupied the riverbank terrace land this pre historical settlement was abandoned after the floods eventually due presumably to repeated inundation by overbank floodwater the flood events were osl dated to between 4100 and 4000 a bp and checked by archaeological dating of the anthropogenic remains retrieved from the sequences peak discharges of the floods were estimated to between 19 500 and 22 000 m3 s 1 which is several times gauged maximum floods during the 4200 4000 a bp climatic event severe droughts were documented in china s monsoonal regions and great floods were known from an ancient legend this study provides a well dated sediment record of pre historical floods which occurred at the transition from the neolithic to the bronze age in the yellow river basin it shows that extraordinary floods were part of the abrupt climatic variability during the 4200 4000 a bp climatic event the highly variable unstable and catastrophic climate typified by both droughts and floods resulted in settlement abandonment and possibly the decline of the highly developed late neolithic civilizations in china s monsoonal regions

high resolution hematite goethite records from chinese loess sequences for the last glacial interglacial cycle rapid climatic response of the east asian monsoon to the tropical pacific 1 in order to study the variability of dry versus humid conditions resulting from the east asian monsoon eam we analyzed hematite and goethite from two high resolution chinese loess sections by diffuse reflectance spectroscopy the hematite and goethite concentrations are higher in interglacial paleosols than in glacial loess sediments whereas the hematite goethite hm gt ratios are lower in paleosols than in loess such changes are consistent with higher precipitation and temperature and increased pedogenesis during interglaciation and lower precipitation and temperature and decreased pedogenesis during glaciation the hm gt ratio can be employed as a tool to assess short term variations in humidity and aridity of the eam the hm gt ratios of the last glacial loess displays millennial scale abrupt climate oscillations revealing a pattern of significantly reduced and enhanced summer monsoon moisture our results indicate that the eam responded to tropical pacific climate by millennial scale changes in precipitation during the last glaciation

extraordinary floods related to the climatic event at 4200 a bp on the qishuihe river middle reaches of the yellow river china abstract palaeo hydrological study was carried out in the qishuihe river valley in the middle reaches of the yellow river several bedsets of flood slackwater deposit were identified in the holocene loess soil sequences on the riverbanks they were differentiated from aeolian loess and soils by the parallel and waving beddings and the distinctive stratigraphic breaks separating individual palaeoflood events chronology of the flood events was established by osl dating checked by archaeological identification of the anthropogenic remains retrieved from the sequences the results show that successive floods occurred between 4300 and 4000 a bp in association with the abrupt climatic event of 4200 a bp these overbank floods had the riverbank settlement inundated repeatedly another series of extraordinary floods occurred between 3200 and 3000 a bp when monsoonal climate shifted from the mid holocene climatic optimum toward late holocene dry conditions the climatic event of 4200 a bp and the climatic decline at 3100 a bp were believed to be characterized by droughts previously this work provides solid evidence that both severe droughts and extreme floods were parts of the climatic variability during abrupt climatic event and climatic decline in the semi arid to sub humid zones over the world

new magnetochronology of late miocene mammal fauna ne tibetan plateau china mammal migration and paleoenvironments abstract lanzhou basin lies on the northeastern margin of the tibetan plateau in western china and is a rich source of oligocene miocene mammalian fossils obtaining precise age determinations for these fossils is important to address key questions concerning mammalian and environmental evolution in asia associated with stepwise tibetan plateau uplift here we report a new magnetostratigraphic record for the xingjiawan fluvio lacustrine section from the northwestern margin of lanzhou basin that can be correlated to the geomagnetic polarity timescale with two options the late miocene xingjiawan fauna is located either at the boundary between reversed polarity chron c4r 1r and normal polarity chron c4n 2n or at the boundary between subchrons c5r 1r and c5n 2n with an estimated age of at least 8 ma or perhaps as early as 11 ma both age estimations imply that the fossil stegodon in the lanzhou basin is the oldest known record of stegodon worldwide it predates the formerly oldest stegodon find from africa by at least one million years and perhaps by as many as four million years this provides new evidence for an asian origin of stegodon together with other faunal components a mixed woodland grassland setting existed in the lanzhou basin during the late miocene in contrast to its modern arid environment

contributions to sea level variability along the norwegian coast for 1960 2010 1 global sea level has been rising by about 20 cm during the last century and is expected to continue to rise in the 21st century the rise and variability is not spatially uniform to be able to project local changes in relative sea level rsl it is important to identify the processes that govern regional rsl variability in this study we assess the importance of different contributions to rsl variability along the coast of norway in the period 1960 2010 by using hydrographic station data at the coast sea level pressure and observed vertical land uplift we compute rsl changes due to thermal expansion haline contraction the inverted barometer effect and land uplift caused by glacial isostatic adjustment the combination of these contributions is compared to rsl variability observed with tide gauges for all but the two southernmost stations the reconstructed rsl explains 70 85 of the observed variability of the monthly sampled time series the inverted barometer effect is responsible for more than half of the explained variability while thermosteric height represents the largest contribution to the linear trend due to land uplift the local rsl rise is weaker and partly negative along the norwegian coast the residual observed minus reconstructed shows a positive trend ranging from 1 3 mm yr 1 to 2 3 mm yr 1 it is speculated that the reason for this is an increase of mass in the ocean due to melting of land based ice and to a lesser degree the combined thermohaline expansion in the deep nordic seas

iron oxide characteristics of mid miocene red clay deposits on the western chinese loess plateau and their paleoclimatic implications abstract the middle miocene climate optimum mmco 14 3 16 3 ma was a warm climatic interval that may provide an analog for future climates in the context of ongoing global warming in continental regions however reconstruction of the mmco remains controversial due to the lack of robust proxies from continuous sedimentary sequences in this study we investigated the composition and relative abundance of pedogenic iron oxides in the zhuanglang red clay deposits from the western chinese loess plateau using rock magnetic color reflectance and geochemical analyses our aim was to assess the climatic sensitivity of iron oxides in order to produce robust proxies for reconstructing regional temperature and moisture relationships during the mmco our results indicate that the mmco in the study region was characterized by high effective precipitation relatively high temperature and strong pedogenesis suggesting a strong east asian summer monsoon easm the strengthening of the easm intensity during the mmco is consistent with records of enhanced terrigenous chemical weathering in the south china sea and the occurrence of a relatively warm and humid climate on a global scale implying the strong coupling between asian monsoon evolution and global climate change during the middle miocene in addition the magnetic susceptibility record of the zhuanglang red clay demonstrates that eccentricity played the dominant role in controlling the easm during the mmco

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

sea level dependence on the nao over the nw european continental shelf 1 the connection between changes in the north atlantic oscillation nao and the sea level over the northwest european continental shelf is investigated for the period 1955 2000 using a two dimensional model of tides and storm surges there is a clear spatial pattern in the correlation between sea level and the nao on a winter mean timescale correlations are positive 0 8 in the northeast and negative 0 7 in the south the sensitivity of the sea level to the nao is strongest in the southern north sea up to 96 mm per unit nao index where most of the sensitivity is present also in the non hydrostatic component of sea level the relationships are validated using observed data recorded at coastal tide gauges

sea surface height variability in the north east atlantic from satellite altimetry data from 21 years of satellite altimeter measurements are used to identify and understand the major contributing components of sea surface height variability ssv on monthly time scales in the north east atlantic a number of ssv drivers is considered which are categorised into two groups local wind and sea surface temperature and remote sea level pressure and the north atlantic oscillation index a multiple linear regression model is constructed to model the ssv for a specific target area in the north sea basin cross correlations between candidate regressors potentially lead to ambiguity in the interpretation of the results we therefore use an objective hierarchical selection method based on variance inflation factors to select the optimal number of regressors for the target area and accept these into the regression model if they can be associated to ssv through a direct underlying physical forcing mechanism results show that a region of high ssv exists off the west coast of denmark and that it can be represented well with a regression model that uses local wind sea surface temperature and sea level pressure as primary regressors the regression model developed here helps to understand sea level change in the north east atlantic the methodology is generalised and easily applied to other regions

new evidence for the catastrophic demise of a prehistoric settlement the lajia ruins in the guanting basin upper yellow river nw china abstract the lajia ruins in the guanting basin nw china are a product of the prehistoric qijia culture like pompeii they are a rare example of an archaeological site preserved by a natural disaster and are therefore important in archaeology anthropology and geology however the nature of the disaster s responsible for the destruction of the site remains controversial most studies have focused on an earthquake and a red clay layer directly overlying the site and a detailed stratigraphic study of the mid holocene sedimentary strata combined with other intervals of red clay deposition hence possible disasters is lacking we identified a mid holocene paleosol sequence the shanglajia section at the site which contains two layers of red clay dated to 3950 a bp and 3500 a bp intercalated within the mid holocene paleosol s0 subsequent multi proxy analysis indicated that the characteristics of the two red clay layers resemble those of typical tertiary red clay deposits and the modern gully deposit at the foot of the great red hills but are distinctly different from those of the slackwater deposits of the yellow river and the mid holocene paleosol our results suggest that at 3950 a bp and 3500 a bp two large scale rainstorm induced mudflow events originating from the gullies to the north flooded the lajia area on the second terrace of the yellow river devastating and burying the human settlements we infer that the intensified erosion and mass wasting were caused by human activity in addition natural factors such as rainstorms and earthquakes may also have played an important role in triggering catastrophic mudflow events in the tertiary red clay deposits overall our results provide further insights into prehistoric man land relationships in this environmentally sensitive region which may have implications for modern land use in this region of china and elsewhere

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

process of paleofloods in guanting basin qinghai province china and possible relation to monsoon strength during the mid holocene abstract prehistoric disasters including paleofloods and earthquakes in guanting basin qinghai province china and their impact on neolithic cultures have attracted academic attention over the last decade however the process and mechanism of paleofloods in the basin remain unsolved this paper describes studies of the periodicity and process of paleofloods in guanting basin during the mid holocene and their relations to monsoon strength based on geological and archaeological investigations including analysis of magnetic susceptibility and color reflectance application of radiocarbon dating and comparison with the stalagmite oxygen isotope record in dongge cave during the mid holocene paleofloods in guanting basin began between 7550 cal a bp and 6510 cal a bp and lasted to 2220 cal a bp at least four cycles of frequent followed by infrequent paleofloods have been detected three periods of infrequent paleofloods occurred during 4380 3970 cal a bp 2850 2720 cal a bp and 2310 2140 cal a bp respectively the other one took place around 5000 cal a bp coinciding well with periods of weak asian monsoon events the process of paleofloods in guanting basin during the mid holocene was possibly dominated by the precipitation changes responding to asian monsoon strength

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

a luminescence dating study of the sediment stratigraphy of the lajia ruins in the upper yellow river valley china abstract pedo sedimentological fieldwork were carried out in the lajia ruins within the guanting basin along the upper yellow river valley in the eolian loess soil sections on the second river terrace in the lajia ruins we find that the land of the qijia culture 4 20 3 95 ka bp are fractured by several sets of earthquake fissures a conglomerated red clay covers the ground of the qijia culture and also fills in the earthquake fissures the clay was deposited by enormous mudflows in association with catastrophic earthquakes and rainstorms the aim of this study is to provide a luminescence chronology of the sediment stratigraphy of the lajia ruins eight samples were taken from an eolian loess soil section xialajia section in the ruins for optically stimulated luminescence osl dating the osl ages are in stratigraphic order and range from 31 94 1 99 ka to 0 76 0 02 ka combined osl and 14c ages with additional stratigraphic correlations a chronological framework is established we conclude that 1 the second terrace of the upper part of yellow river formed 35 00 ka ago which was followed by the accumulation of the eolian loess soil section and 2 the eolian loess soil section is composed of the malan loess of the late last glacial mis 2 and holocene loess soil sequences

inter annual to decadal sea level variability in the coastal zones of the norwegian and siberian seas the role of atmospheric forcing inter annual to decadal sea level variations from tide gauge records in the coastal zones of the norwegian and siberian seas are examined for the period 1950 2010 using a combination of hydrographic observations wind data and theory we identify two large areas of highly coherent sea level variability one that includes the norwegian barents and kara seas and another one that includes the laptev east siberian and chukchi seas we provide evidence of a new contribution to the sea level variability along the norwegian coast associated with the poleward propagation of sea level fluctuations along the eastern boundary of the north atlantic when this propagating signal is combined with the local wind we are able to explain over 70 of the variance along the norwegian coast the steric component explains 61 of the sea level corrected for the inverse barometer variability along the norwegian coast the high coherency between the sea level along the norwegian coast and that in the barents and kara seas suggests that part of the norwegian signal propagates further north into these regions we introduce an atmospheric vorticity index that explains much of the sea level variability in the laptev east siberian and chukchi seas with correlations ranging from 0 73 to 0 81 in the east siberian sea we identify a sea level increase of 22 cm between 2000 and 2003 which is partly explained by the vorticity index and a decline of 15 cm after 2003 which we relate to the strengthening of the beaufort gyre

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

climatic interpretation of the luochuan and lingtai loess sections china based on changing iron oxide mineralogy and magnetic susceptibility abstract hematite and goethite estimated from diffuse reflectance spectra and magnetic susceptibility ms have been determined from both the luochuan and lingtai loess sections of the loess plateau of central china changing concentrations of these iron oxides and ms were used to determine paleoclimatic change based on a model that relates pedogenic production of hematite and magnetite to precipitation we propose two precipitation phases on the loess plateau during the last 2 6 ma from the wucheng red clay boundary up to paleosol s5 mis 13 precipitation on the loess plateau was moderate probably not frequently exceeding 450 mm yr and highly seasonal from s5 to the present precipitation during interglacial times has gradually increased to the present levels of 600 650 mm yr for the localities examined throughout the pleistocene spanning both glacial and interglacial conditions hematite to goethite ratios display a consistent decrease this decrease suggests that precipitation on the loess plateau has been getting less seasonal and or has been occurring during times when temperature was lower in addition to these long term changes it also appears that iron oxide records from the loess plateau exhibit 400 500 ka cycles from the wucheng red clay boundary to s5 these 400 500 ka cycles may be analogous to similar length cycles recorded in 13 c marine records in the south china sea and may be linked through weathering and silica production as a result of the asian monsoon

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

asian summer monsoon instability during the past 60 000 years magnetic susceptibility and pedogenic evidence from the western chinese loess plateau abstract the 28 m high resolution shajinping loess section in lanzhou on the western chinese loess plateau records a 60 ka millennial summer monsoon variation the record shows that asian summer monsoons have rapid episodic pulse enhancements spanning only ca 1 2 ka in high frequency domain and having sub milankovitch cycles of progressive weakening in low frequency domain in the last glaciation soil formation seems to occur with a surprisingly fast response to these summer monsoon enhancements resulting in weakly or moderately developed paleosol sequences both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm dansgaard oeschger episodes and long term cooling bond cycles of the north atlantic climatic records indicating a possible teleconnection between tropic oceanic air masses and the north atlantic climatic system but differences exist for the transition of mis 2 3 and the holocene where extraordinarily heavy dust input events and fairly variable climatic fluctuations occur for the former and latter respectively a westerlies swing model is proposed to interpret this link

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

can the magnetic susceptibility record of chinese red clay sequence be used for palaeomonsoon reconstructions red clay underlying the loess palaeosol sequences on the chinese loess plateau is an eolian deposit there is a controversy over whether magnetic susceptibility chi variations in red clay sequence can be used as an indicator of summer palaeomonsoon intensity this study investigates the magnetic mineralogy magnetic concentration and magnetic grain size distribution of jiaxian red clay with multimagnetic methods our results indicate that the magnetic properties of jiaxian red clay are similar to those of the quaternary loess palaeosol sequences and ultrafine ferrimagnetic grains produced during pedogenesis are responsible for an increase in susceptibility therefore the chi enhancement mechanism of red clay is similar to that of the overlying loess palaeosol sequences this paper explores chi variations in the red clay sequence through spatial and temporal analysis the susceptibility variation of six sites along a nne to ssw transect correlate to palaeoclimatic cycles so chi can be used to trace the summer palaeomonsoon intensity from a spatial perspective however a simple loess derived calibration function cannot be used to quantitative reconstruct the palaeomonsoon intensity variations thought time an adjusted calibration function for palaeosols from red clay sequence needs to be developed so that chi can be used to quantitative reconstruct palaeomonsoon intensity further study is necessary to develop such a transfer function

u pb ages of detrital zircon and provenances of red clay in the chinese loess plateau abstract the chinese loess plateau clp which is located in the central part of china mainly contains two sequences the quaternary loess paleosol sequence and the late miocene pliocene red clay sequence u pb ages of detrital zircon from the quaternary loess paleosol sequences indicate that the current spatial pattern of central asian aridification was largely established during the early quaternary u pb ages of detrital zircon from the underlying red clay sequences demonstrate that the northern source regions were important contributors for the dust since the late miocene except for the periods of 8 ma and 5 5 to 4 ma these two periods correspond to increased and decreased dust deposition in the north pacific respectively ascribed to the late miocene aridification of the qaidam basin in the west of the clp and the early pliocene aridification of the tarim basin in the west of the clp we attribute the increase of the qaidam basin derived north pacific dust fluxes to the uplift of the ne tibetan plateau such uplift also controlled the climatic and environmental changes in central asian during the late miocene this study highlights the dynamical process of the central asian aridification during the late miocene pliocene