holocene pedostratigraphic records from the southern chinese loess plateau and their implications for the effects of climate on human civilization abstract the relationship between holocene climate change and the evolution of civilizations both in china and elsewhere is of increasing research interest here we present the results of a study of the particle size caco3 content magnetic susceptibility and soil microstructure of the holocene paleosol and loess sequence at the sites of luochuan and lintong in the southern chinese loess plateau the results reveal that the paleosol in the late stage of the mid holocene is less developed than that in the early stage and that the corresponding average annual precipitation was at least 100 mm higher than today due to the enhancement of the summer monsoon climatic deterioration occurred in the middle stage of the mid holocene during 6000 5000 yr bp which was the coldest and driest stage four stages of monsoon change occurred in the study area during the holocene at 8500 6000 5000 and 3100 yr bp they enable the following climatic subdivision of this interval three cold and dry periods with enhanced winter monsoon and dust storm activity and two warm humid periods with a strong summer monsoon and weak dust storm activity the transformation of the monsoon climate since 3100 yr bp indicates that the modern interglacial period compared with the last interglacial is not typical and possesses some of the characteristics of cold and dry climates the observed pattern of climate change since the mid holocene has substantially affected the development of civilization in the region this is manifested by the frequent migration of ancient capitals caused by the onset of a cold and dry climate the location of capitals shifted from high altitudes in the loess plateau to loess tableland areas on the lower altitude plains including to the first terrace in the low altitude plain and then to the moderately high second terrace of the wei river our results contribute to an improved understanding of the climatic drivers of human civilization in china and provide a basis for predicting future environmental changes in the region

geochemical characterization of the middle and late pleistocene alluvial fan dominated infill of the northern part of the weihe basin central china major reorganizations in climate and tectonic regime occurred in east asia during the pleistocene resulting in large scale environmental changes in this paper a detailed geochemical and mineralogical record of these changes is presented from a distal alluvial fan sedimentary sequence in the northern weihe basin we established that in addition to glacial interglacial variation there are three distinctly different units deposited over the past 1 m y these units are the result of variations in the overall tectonic regime in the northern weihe basin fine grained detrital minerals were predominantly delivered during colder climatic periods whereas evaporative minerals were dominantly deposited during the warmer interglacial periods probably as a result of strong seasonal contrast this compositional variation demonstrates the importance of climate control on hinterland erosion surface runoff chemical weathering and evaporation al normalized ratios of indicative major elements relative to average loess composition indicate important variations in sedimentary processes mostly related to sediment flux si enrichment is an index for past flooding events while fe enrichment just like k and ti reflects influx of clays in contrast ca and mn are strongly enriched throughout the core associated with the authigenic precipitation of carbonates especially during interglacial periods the lower 1000 690 ka and upper 330 0 ka units of the core are characterized by relative intense and frequent flooding which coincided with extensive ponding in the study area in the middle unit 690 330 ka increased salinity levels caused by evaporation as reflected in the high sr ca ratio and dolomite abundance led to increased carbonate precipitation simultaneously the increased influx of fine sediments indicates increased clay production in the source area as a result of a more intense summer monsoon strength after 600 ka 2017 elsevier b v

holocene climatic evolution at the chinese loess plateau testing sensitivity to the global warming cooling events abstract a high resolution petromagnetic analysis demonstrates that pedogenic alterations in holocene loess sand sequences from the regions of the guanzhong basin and the mu us desert on the chinese loess plateau clp were affected by climatic variations in temperature and precipitation three warm humid intervals 8 4 3 7 2 4 1 2 and 0 81 0 48 ka associated with soil formation and relatively high values of petromagnetic parameters occurred during the holocene a substantial paleosol development from 8 4 to 3 7 ka and higher petromagnetic parameter values indicate a generally strong warm humid phase in the mid holocene which can be attributed to the holocene climatic optimum our study demonstrates that the holocene climate in the eastern part of the clp is sensitive to warming and cooling events linked to global changes in temperature and precipitation a complete holocene climate record is constructed correlating well with the other regional climate records along the south to north profile on eastern clp and suggesting that similar climatic changes occurred in eastern monsoonal china during the holocene results are supported by other climate records in different regions of the world and imply that the holocene climatic optimum in the northern hemisphere probably took place at the same time

a record of holocene climate change in the guanzhong basin china based on optical dating of a loess palaeosol sequence optical dating was used to obtain a chronology for a loess palaeosol sequence in the guanzhong basin on the loess plateau in china the sedimentary sequence recorded two dry episodes 3 7 2 4 ka and 1 2 0 8 ka ago in the holocene as shown by the presence of two layers of loess within the holocene deposits these two arid events are consistent with records of global climate change in the holocene and also coincident with major historic events in china this finding suggests that loess paleosol sequences in china can record global climate changes and implies that rapid climate change affected the progress of human civilization in addition changes in the sedimentation rate through the section suggest that agricultural expansion may have accelerated the rate of dust accumulation

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

elemental carbon record of paleofire history on the chinese loess plateau during the last 420 ka and its response to environmental and climate changes an elemental carbon ec record covering the last 420 ka was reconstructed using chemical oxidation method on a loess and paleosol sequence from the lingtai section on the chinese loess plateau the ec record reveals the paleofire history and its relationship with climate and vegetation changes on the chinese loess plateau our results show that the ec abundance is generally higher in the paleosols than in the loess layers showing a glacial interglacial pattern which is coincident with biomass changes this variation pattern indicates that paleofires were intensified when biomass accumulated and climate changed abruptly especially from wet to dry conditions the ec abundance increases sharply at similar to 130 kab p indicating a dramatic change in the vegetation and climate variation patterns the occurrence of a peak value with the highest average ec abundance in the holocene may reflect the occurrence of a major climate event at similar to 6 kab p and may also be partly due to more frequent anthropogenic fire usages c 2007 elsevier b v all rights reserved

a glaciochemical survey of the summit region greenland spatial representativene ss and an understanding of controls on chemical species distribution are essential requirements of any significant ice core investigation snowpit studies provide an essential tool in this process in preparation for the central greenland deep drilling effort a series of snowpits was sampled in detail for oxygen isotopes major anions major cations total acidity and radionuclides the results of this sampling program are used to define 1 the chemical composition of the snow in the region 2 the input timing and spatial distribution of major chemical species 3 the potential dependence of

spatial coherence of the ground motion produced by the 1979 imperial valley earthquake across el centro differential array abstract spatial coherence of digitally recorded acceleration time histories across five elements of the el centro differential array recorded during the october 15 1979 imperial valley california earthquake is studied recorded within a total spacing of 214 m the three component time histories at five stations of this linear array provide a unique set of free field data at sites of similar geology in the near field of a strong earthquake the observed peak ground accelerations vary by as much as 43 13 and 40 on the e w n s and vertical components it is shown that the incoherence of high frequency waves brought about by wave scattering near the receiver is partially responsible for the observed variation this is evident from the frequency dependent reduction of the peak cross correlation amplitudes of the strong phase of ground shaking the observed reductions increase from 1 below 1 hz to 20 30 in the 1 10 hz band and to nearly 80 above 10 hz investigation of the polarization angle of p wave coda indicates that high frequency waves 10 hz approach the recording station randomly from nearly all directions the peak cross correlation of the polarization angle in general is lower than that of amplitudes the successive sampling of this angle in the low frequency band suggest a northwestward propagation of the source during the faulting process

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

holocene sediment accumulation rates in the western loess plateau china and a 2500 year record of agricultural activity revealed by osl dating high resolution optically stimulated luminescence osl dating of a terraced loess section in the western margins of the chinese loess plateau provides evidence of continuous and varying accumulation of dust throughout the holocene from 12030 to 2500 years ago the sediment accumulation rate was approxi mately 0 2 mm year after this time it increased to approximately 0 8 mm year during a historically docu mented period of agricultural expansion in adjacent areas from 680 years ago a further increase in accumu lation rate to approximately 3 4 mm year is evident particle size analysis indicates that this increase in accumulation rate was associated with anthropogenic addition of sandy sediment probably for soil improve ment the osl dating also identifies the period when the terrace was first cut for agricultural use between 2500 and 2070 years ago

the holocene salinity history of bosten lake xinjiang china inferred from ostracod species assemblages and shell chemistry possible palaeoclimatic implications abstract a sediment core from bosten lake the largest freshwater lake in the tianshan mountains and in the northwesternmost province of china provided a high resolution record of environmental change covering the last 8500 cal a bp higher salinity levels of bosten lake were reconstructed from assemblages the stable isotope composition and sr ca and mg ca ratios of ostracod shells between 7800 and 5600 cal a bp a period of low and moderate salinities between 5600 and 4900 cal a bp was followed by the re establishment of higher salinities between 4900 and 4300 cal a bp since then bosten lake has recorded fluctuating conditions with a number of multi centennial phases of low and moderate salinities although the salinity lake level relationship of bosten lake is not fully understood a higher salinity at the core site seems to correspond to periods of higher lake levels this contradictory interpretation is explained tentatively by the changing distance of the core site to the freshwater providing river mouth with changing lake levels and potentially resulting lateral shifts of the salinity distribution pattern within the lake assuming this explanation is correct the record from bosten lake reflects higher moisture availability and a strong climatic influence of the indian monsoon in the early mid holocene until about 4000 cal a bp and more unstable drier conditions susceptible to minor changes in the regional circulation patterns and temperature variations afterwards

the ustic isohumisol chernozem distributed over the chinese loess plateau modern soil or palaeosol abstract the ustic isohumisol chernozem widely distributed over the chinese loess plateau is classified as a modern soil by agricultural pedologists and as a palaeosol by geoscientists high resolution investigations into this soil including field observations element analysis optically simulated luminescence dating and measurements of magnetic susceptibility and particle size distribution were carried out over the plateau uplands the results show that the formation of physico chemical properties and development of the soil profiles has kept pace with the land surface growth because of incessant dust accumulation during the holocene the continuously intensified weathering of accumulated dust from 11 500 a b p had resulted in an increased chemical differentiation through time during the early holocene the development of the ustic isohumisol occurred over the uplands between 8500 and 3100 a b p when the chemical differentiation reached its maximum because of increased precipitation and ample soil moisture in response to the mid holocene climatic optimum the soil formation had sustained for ca 5400 years and ceased at 3100 a b p a major pedogenic regression occurred from 3100 a b p because of climatic aridity and intensified dust accumulation over the loess plateau the newly accumulated loess and topsoil has the ustic isohumisol buried at a depth of ca 50 80 cm in general the pedogenic regression has been intensified by incorporation of the reworked components by increased runoff and erosion redeposition large scale land reclamation extended to the uplands at ca 2170 a b p an agricultural landscape of dry farming has formed since ca 1500 a b p thereafter the present topsoil has accumulated and has been affected by the intensified cultivation and addition of barnyard manure in history the solubles are retained in the topsoil because of dry climate and scant soil moisture

a regional aridity phase and its possible cultural impact during the holocene megathermal in the guanzhong basin china evidence of climatic variations and the impact of past farming was identified in a holocene loess profile near xi an in the guanzhong basin china detailed studies of the profile indicate that crop cultivation began at 7000 yr bp in the neolithic and carried on to present in the area disturbance of the profile by cultivation has not masked evidence of changes in aeolian dust deposition and bio pedogenic processes caused by climatic variations increased dust deposition indicates that a remarkable aridity phase occurred from 6000 to 5000 yr bp during the holocene megathermal 8500 3000 yr bp the aridity and intensified aeolian dust deposition interrupted the formation of the brown soil developing under a warm humid subtropical climate during the megathermal the palaeosol s0 normally associated with the megathermal period is thus separated into two distinct soils namely s01 and s02 this variability in megathermal climate may have been widespread across northwestern china it is also possible that t

anthropocene archaeology of the yellow river china 5000 2000 bp in this paper we use geoarchaeological and paleoenvironmental data from three localities in the yellow river valley china taosi sanyangzhuang and the yiluo valley to argue that human activi

alluvial plains formation in response to 100 ka glacial interglacial cycles since the middle pleistocene in the southern tian shan nw china abstract the tenet of the milankovitch theory is that northern hemisphere solar insolation controlled by earth s orbital is responsible for cyclic climate variations eccentricity in this context is responsible for cyclic variability of 100 ka and may drive periodicity in climate change during the middle and late pleistocene although abundant evidence exists for 100 ka cyclic climatic fluctuations driving glacial interglacial cycles our knowledge about the record of cyclic climatic changes preserved in terrestrial landscapes remains limited especially over multi millennial several glacial interglacial timescales the intermontane yanqi basin in the southeastern tian shan central asia preserves at least seven generations of alluvial surfaces spanning multiple glacial cycles and yields insights into the record of climatic fluctuations that lead to aggradation and incision of river systems we complement existing chronologic data with two new cosmogenic 10be depth profiles and four surface exposure ages of alluvial surface abandonment in the south tian shan piedmont within the yanqi basin new surface exposure dating reveals the successive abandonment of these surfaces with a 100 ka cyclicity between 5 1 0 9 and 550 ka and indicates that there were multiple aggradation incision cycles the superimposed 100 ka cycles of aggradation incision are best explained by eccentricity driven climate change within these cycles sediment is produced during glaciations by glacial and periglacial erosion however due to the dry and cold conditions of the glacial periods in central asia there is little discharge available to transport and evacuate the sediment from the valleys to the piedmont later during the glacial to interglacial transition higher precipitation and high discharge due to glacial melt water resulted in higher transport capacity of the river beyond a threshold to evacuate sediment subsequent rapid incision occurs after the upstream sediment reservoir is depleted and its timing corresponds to the glacial to interglacial transition period in our study area compared with the aggradation and incision of the northern piedmont of the tian shan governed by the westerlies the sedimentary systems of the south tian shan piedmont within the yanqi basin are mainly controlled by eccentricity driven glacial interglacial cycles

long term weakening of the east asian summer and winter monsoons during the mid to late holocene recorded by aeolian deposits at the eastern edge of the mu us desert abstract the east asian summer monsoon easm and east asian winter monsoon eawm are major drivers of environmental conditions in east asia however due to the lack of high resolution eawm records the phase relationship between the easm and eawm during the holocene epoch is still debated here we use magnetic and grain size measurements from a sequence of aeolian sediments from the eastern edge of the mu us desert to track the history of the easm and eawm from 7 5 to 2 5 ka the results show that both the easm and eawm exhibit a similar long term weakening trend during this interval in view of the stable glacial boundary conditions and the significantly decreased rates of atmospheric co 2 rise since the mid holocene we suggest that orbitally induced insolation was the major cause of the weakening of both the easm and eawm decreasing summer insolation and increasing winter insolation reduced the thermal contrast between the ocean and the asian continent in both summer and winter time resulting in the weakening of both monsoon systems during the mid to late holocene

a source extent analysis of the imperial valley earthquake of october 15 1979 and the victoria earthquake of june 9 1980 a new method for estimating source extent parameters has been applied to the imperial valley earthquake of october 15 1979 and the victoria earthquake of june 9 1980 from the stations of the world wide standard seismograph network and canadian seismic network estimates of the duration of far field long period sh waves were made by computing the variance or second central moment 2 of instrument corrected attenuation corrected pulses seventeen measurements for the imperial valley event and 25 for the victoria event were made we inverted for the source duration t the fault length l and the directivity parameter d by least squares we find that for the imperial valley t 9 0 0 5 s d 130 43 km s and l 46 13 km and for the victoria event t 10 9 0 6 s and d 251 71 km s l is not well constrained for this second event the inversion gives 23 km the lower bound obtained by constraining 2 to be positive everywhere on the focal sphere although a value as high as 40 km would still be within the uncertainties the positive values of d for both events indicate that rupture propagation was predominantly to the northwest in order to estimate the degree of unilateralness we have computed the rupture mode index defined by r d lt which is 1 for a unilateral rupture and zero for a bilateral rupture we find a value of r 0 31 0 14 for the imperial valley event significantly less than unity which indicates that a southern component of rupture is also present assuming uniform slip we estimate the northern and southern fault segments to be 26 and 20 km respectively the presence of a bilateral component is supported by near field studies which have made use of stations along the southern half of the imperial fault for the victoria event due primarily to the uncertainty in l the value of r can vary from 0 6 to 1 with the value of 1 being most probable assuming that the rupture is unilateral we can obtain an estimate of fault length from the relation l d t which yields l 23 6 km geodetic data and the distribution of aftershocks are consistent with a unilateral rupture mode and the fault length that we have obtained values of seismic moment from measurements of the zeroth moment of the displacement pulse are found to be 5 8 0 4 for imperial valley and 4 8 0 4 for victoria in units of 1018 n m the presence of a southern component of rupture for the imperial valley event would suggest a closer and perhaps causal relationship to the victoria event which occurred 8 months later and about 60 km to the south in a tectonic framework we interpret these two earthquakes as the failure of adjacent transform faults and consider the possibility that a concurrent spreading event may have occurred in the vicinity of cerro prieto

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

greenland ice core signal characteristics an expanded view of climate change the last millenium of earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity we have analyzed the major ions contained in the greenland ice sheet project 2 gisp 2 ice core from the present to 674 a d to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling volcanic emissions sea salt and terrestrial influences we have adapted and extended mathematical procedures for extracting sporadic e g volcanic events secular trends and periodicities found in the data sets finally by not assuming that periodic components signals were stationary and by utilizing evolutionary spectral analysis we were able to reveal periodic processes in the climate system which change in frequency turn on and turn off with other climate transitions such as that between the little ice age and the medieval warm period

an early holocene erosion phase on the loess tablelands in the southern loess plateau of china abstract a holocene loess profile to the west of xi an china was studied multi disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change the proxy data obtained from this aeolian loess and palaeosol sequence indicate large scale variations of climate in the southern loess plateau since the last glaciation a rainwash bed indicative of a wetter climate excessive runoff and erosion on the loess tablelands was identified relating to the early holocene before the onset of the climatic optimum this is synchronous with the early holocene physiographic erosional stage identified in the valleys in north china it means that severe erosion took place when the region was undergoing climatic amelioration during the early holocene the evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern loess plateau during the last glaciation prior to the erosion phase the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation relatively slow dust accumulation and intensive bio pedogenesis responding to the holocene climatic optimum followed the erosion phase the loess tablelands were most vulnerable to erosion during the large scale monsoonal climatic shift from dry cold glacial to humid warm post glacial conditions in the southern loess plateau

direct observation of rupture propagation during the 1979 imperial valley earthquake using a short baseline accelerometer array abstract the 1979 imperial valley california earthquake m s 6 9 was recorded on the el centro differential array a 213 m long linear array of 5 three component digital accelerometers 5 6 km from the nearest tectonic surface rupture although absolute time was not recorded on the array elements a relative time base was established using the main shock hypocentral p wave and the p and s waves from a later aftershock a cross correlation technique was used to measure the difference in arrival times of individual seismic waves in a moving 0 6 to 1 2 sec window at each array element which would then be converted into the wave9s slowness 1 velocity along the array when applied to the main shock vertical and horizontal accelerograms results from both components of motion indicated that the early arriving energy came from a source to the south of the array and the source of the energy moved rapidly to the north of the array during the strong shaking the ground motions at the array elements were well correlated for about the first 11 sec of motion these observations suggest that we have observed the initiation of rupture south of the array and its subsequent propagation along the fault to a position north of the array in about 10 sec and that the energy was radiated from a fairly compact region around the rupture front if the observed vertical and horizontal ground motions are assumed to be caused by p and s waves respectively then the observed slownesses show irregularities which can be interpreted as implying that the observed high frequency ground motions originated at irregularly distributed regions on the fault surface or that the rupture velocity was variable or both one possible interpretation of the data suggests that the rupture proceeded at near p wave velocity over a 7 km long section of fault average rupture velocities of about 2 7 to 3 2 km sec at 8 km depth are consistent with the data and 2 8 km sec is weakly preferred under the assumption that rupture propagates at a fixed fraction of the shear velocity the large vertical pulse which had a peak acceleration of 1 7 g at e06 was emitted from the portion of the fault extending 25 to 30 km northwest of the hypocenter near meloland overpass and not from the point on the fault closest to the differential array nothing can be said about fault behavior southeast of the hypocenter

history and mechanisms for the expansion of the badain jaran desert northern china since 20 ka geological and luminescence chronological evidence desert landscapes are widely distributed in the arid northern china the badain jaran desert bjd is located north west of the tengger desert td and ulan buh desert ubd with the yabrai and ba

late holocene variability of upper north atlantic deep water temperature and salinity 1 magnesium calcium ratios in benthic foraminifera cibicidoides pachyderma from a sediment core on the laurentian slope 1854 m exhibit strong millennial scale fluctuations during the past 4000 years we convert these data to seawater paleotemperatures using a new monospecific linear equation results suggest that the temperature of upper north atlantic deep water dominated by labrador seawater today has varied by at least 2 c during the late holocene millennial scale coolings coincide with previously identified periods of increased drift ice and regional glacier advances including the little ice age paired oxygen isotope measurements indicate that salinity and perhaps density were reduced during the cold periods we discuss possible mechanisms for transmitting this cold fresh signal from surface waters to intermediate depths our reconstructed late holocene ranges in upper north atlantic deep water properties greatly exceed those of the instrumental record and imply that large changes may be yet to come

subdaily earth rotation during the epoch 92 campaign global positioning system gps data were used to estimate earth rotation variations over an 11 day period during the epoch 92 campaign in the summer of 1992 earth orientation was measured simultaneously by several very long baseline interferometry vlbi networks gps and vlbi estimates of ut1 with 3 hour time resolution were then compared and analyzed the high frequency behavior of both data sets is similar although drifts between the two series of 0 1 ms over 2 5 days are evident the geodetic results were also compared with models for ut1 fluctuations at tidal periods and with estimates of atmospheric angular momentum made at 6 hour intervals most of the geodetic signal in the diurnal and semidiurnal frequency bands can be attributed to tidal processes whereas ut1 variations over a few days are mostly atmospheric in origin

evolution of luyang lake since the last 34 000 years climatic changes and anthropogenic impacts abstract a sediment section retrieved from luyang lake shaanxi province china was employed for grain size total organic carbon content toc and carbonates caco 3 analyses based on the optically stimulated luminescence osl chronology the evolution of luyang lake since the last 34 000 years was reconstructed then the historical anthropogenic information like populations and arable lands obtained from literature were incorporated into the environmental sequence to demonstrate the linkage of lake evolution with both climatic and anthropogenic forcings it indicated that the appearance of loessial sediment during ca 33 4 10 7 ka exhibited a much lower lake level associated with a cold and dry climate setting the sediment became finer with increasing toc after ca 10 7 ka implied the enhanced monsoon rainfall and relatively higher lake level until ca 4 6 ka much higher toc and lowest caco 3 at 7 2 4 6 ka suggested the holocene climate optimum in the region the rising caco 3 and declining toc at ca 4 6 2 0 ka revealed the enhanced evaporation precipitation rate and depressed paleoproductivity suggesting a drier climate toc reached its highest after ca 2 ka coinciding with the increasing population and the expanding arable lands since the last 600 years would suggest the anthropogenic impacts like land reclamation and farming rather than climate forcing briefly the evolution of luyang lake was controlled by the monsoon climate through geological times and the intensified anthropogenic interferences since the last 2 ka especially the last 600 years would account for the transformation of freshwater lake to a saline lake and wetland environment

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

near source attenuation of peak horizontal acceleration strong motion data recorded within 50 km of the rupture zone were used to study near source attenuation characteristics of horizontal peak ground acceleration for worldwide earthquakes of magnitudes 5 0 to 7 7 the data base consisted of 229 horizontal components of peak acceleration recorded from 27 earthquakes including the 15 october 1979 imperial valley earthquake these data were found to be adequately represented by the functional relationship pga a exp b m r c m d where pga represents the mean of the peak values scaled from the two horizontal components of each recording m is richter magnitude and r is distance from the fault rupture zone peak acceleration was found to be lognormally distributed with a standard error representing a 45 per cent increase in the median estimate the regression analysis statistically confirmed the results of earthquake simulation studies that have predicted peak acceleration to become independent of magnitude and distance in the near field an extensive sensitivity study showed that predictions based on our attenuation relationships are stable with respect to reasonable model and parameter variations an analysis of residuals was used to investigate the behavior of peak acceleration with respect to various earthquake site and recording parameters the more significant findings being 1 a similarity in the level of acceleration recorded on soil or rock 2 larger than average accelerations recorded at sites located on shallow soils or in areas of steep topography 3 larger than average accelerations associated with earthquakes having reverse fault mechanisms and 4 lower than average accelerations recorded in large embedded structures

analysis of the el centro differential array for the 1979 imperial valley earthquake two methods of analysis have been applied to the el centro differential array data from the 1979 imperial valley earthquake spectral ratios of array averages were developed as one way of estimating the spatial averaging of ground motion this spatial averaging will result in a reduction in the high frequency motion experienced by a large rigid foundation that is assumed to move as a single unit as an alternative covariance measurements in several frequency bands were made to illustrate how the fraction of the power propagating as single traveling wave decreases with increasing distance between stations base averaging reduction factors determined from these analyses show that reductions of 10 to 30 per cent would be expected for this particular earthquake for foundations of about 50 m in dimension and for frequencies above 20 hz the effect is frequency dependent and does not show any significant reduction at frequencies below 5 hz for this particular situation at a distance from the rupture surface of about 5 km the reduction is more pronounced for horizontal components than for vertical components

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

holocene erosion triggered by climate change in the central loess plateau of china abstract understanding changes in holocene erosion is essential for predicting soil erosion in the future however the quantitative response of natural erosion to holocene climate change is limited for the loess plateau of china in this study two soil profiles were investigated on the luochuan and yanchang sites in the central loess plateau of china and four climate indicators i e magnetic susceptibility calcium carbonate content total organic carbon content and clay content

mineralogical and pedogenetic evidence for palaeoenvironmental variations during the holocene on the loess plateau china abstract clay minerals in soils reflect successive stages of mineralogical evolution which depend on the environmental conditions that have prevailed during pedogenesis the objective of this research was to document the mineralogy of the clay fractions

high resolution alkenone sea surface temperature variability on the north icelandic shelf implications for nordic seas palaeoclimatic development during the holocene the palaeoceanography of the northern icelandic shelf for the holocene period was reconstructed from alkenone indices measured in core jr51 gc35 this contains a continuous record of holocene sedimentation spanning 0 10 2 cal kyr bp with a resolution of 20 yr cm we have identified a general holocene cooling trend that has superimposed millennial scale oscillations of 28c their timing is in close agreement with the timing of glacier advances in northern iceland for the later half of the holocene the alkenone sea surface temperature sst record from jr51 gc35 correlates with proxy data for the strength of nadw formation recorded in cores south of iceland this is interpreted as evidence of a close connection existing between north icelandic sea surface temperatures and the north atlantic meridonal overturning circulation the timing of the millennial scale sst variability in our core off north iceland is found to be out of phase or anti phased with the sst variability of a record in the eastern nordic seas md952011 this suggests that the evolution of holocene climate in the nordic seas was more complex than previously proposed and it is likely to be caused by differential responses of the irminger and norwegian currents and modulated by changes in atmospheric circulation analogous to the north atlantic oscillation

high resolution studies of the oldest cultivated soils in the southern loess plateau of china abstract the holocene loess soil sequence on the chinese loess plateau constitutes an excellent record of evolution of soil formation monsoonal climate eolian dust accumulation and influences of arable farming of over 8000 years a high resolution soil profile on the zhouyuan loess tableland to the west of xi an was studied using particle size analysis measurement of magnetic susceptibility total fe toc and caco3 the results provide new insights into the roles of eolian dust deposition and human impact of cultivation on soil development in this environmentally sensitive zone several loess layers are found interbedded with cinnamon soils in the profile this has been caused by changes in rainfall and intensity of dust deposition that is forced by changes in balance between the northwest continental monsoon and southeast maritime monsoon of east asia during the holocene the processes of soil formation were interrupted several times by intensified dust fall and climatic aridity in the last 11 500 years the initial clearance of forest for arable farming occurred at ca 7500 years bp on the loess tableland it was contemporaneous with the arrival of the wetter and warmer climate of the holocene megathermal 8500 3100 years bp thereafter arable farming has been maintained during both the time of soil formation and that of intensified dust accumulation though there could be temporary cessation or reduced intensity of cultivation in the drier intervals because of lack of rainfall and soil moisture increased intensity of dust accumulation has been ongoing since ca 3100 years bp in the loess plateau a loess deposit of 40 80 cm has overlaid the multiple or single welded cinnamon soils on the flat land over the plateau

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

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

loess and early land use geoarchaeological investigation at the early neolithic site of guobei southern chinese loess plateau abstract prehistoric land use at the guobei site and its relationship with the local environment are examined by applying osl dating micromorphological examination and geo physical analysis the majority of the osl dates are of early to middle holocene ages and are thus comparable to many osl dates derived from other studies in the same region according to the particle size analysis silt sized particles 2 60 m were predominant throughout the profiles examined however there are spatial and temporal variations of different size groups of particles throughout the profiles which provide complementary information for the micromorphological interpretation the total organic component of the samples examined through loi is relatively high all 2 with those of the overlying holocene deposits higher than those of the underlying malan loess by about 0 2 moreover in all three profiles the highest organic contents appear in the palaeosols confirming that there was greater organic accumulation during soil formation periods the groundmass of most slides collected from the early to middle holocene horizons displays a very homogeneous pattern while the abundance and distribution of different kinds of pedo features mainly including clay textural calcitic iron mn and crustal features vary greatly temporally and spatially these different lines of information demonstrate diversified pedo sedimentary processes due to variations in micro environmental conditions and cultural activities we discuss the importance of a palaeo ecological perspective allowed by the geoarchaeological study to an improved understanding of the relationship between loess changing hydrology prehistoric farming practice and land use and long term landscape change in the chinese loess area this will thus contribute to a comparison on the dynamic relationship between loess and prehistoric farming in other regions of the world such as europe and north america

tropospheric rivers a one year record and a possible application to ice core data the morphology of tropospheric rivers has been examined for the period june 1991 may 1992 from atmospheric specific humidity and wind velocity data vertically integrated water vapor flux vectors are subjected to harmonic analysis and the high frequency components periods less than 3 days show large amplitude values in the north atlantic north pacific south atlantic south indian ocean and south pacific plus small amplitude occurrences in the red sea arabian sea region in the december february season in june august the latter is replaced with a large amplitude monsoon related region over south east asia maximum intensities increase slightly in altitude with latitude the correspondence between rivers frontal boundaries and storm tracks is noted sometimes rivers originating over the north pacific cross north america and reach greenland while at other times they pass polewards over the north atlantic raising the possibility that water vapor involved in ice core formation may have evaporated from surface water bodies with different temperature and salinity characteristics changes in oxygen isotope variations at a point may therefore reflect changes in the dynamics of tropospheric rivers in addition to local temperature changes

lower temperature as the main cause of c4 plant declines during the glacial periods on the chinese loess plateau abstract the distribution of c3 and c4 plants changed in regionally contrasting ways during the last glacial period c4 plant expansion in low latitude africa and america coincided with c4 plant decreases in mesoamerica and the us great plains this c4 plant expansion has been attributed to lower pco2 and increased aridity and the decline in c4 plants is believed to have been caused by increased winter precipitation and lower temperatures however it is still difficult to generalize whether pco2 temperature or aridity was mainly responsible for c3 vs c4 vegetation changes during glacial periods paleoclimate conditions on the chinese loess plateau clp offer opportunities to further evaluate the role of temperature in the c3 vs c4 competition detailed climate records have shown that the clp region was drier and colder during glacial periods with aridity favoring c4 expansion and lower temperatures favoring c3 expansion here we present two high resolution compound specific carbon isotope records of n alkanes from the clp as vegetation biomarkers to estimate the relative abundance of c4 plants during the last two glacial interglacial transitions more negative 13c values during the glacial periods from two clp sites clearly show that in contrast with low latitude sites c4 plants declined this decrease in c4 abundance was caused by lower temperature despite the lower pco2 and increased aridity on the clp during glacial time

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

the effect of ocean tides on the earth s rotation as predicted by the results of an ocean tide model the published ocean tidal angular momentum results of seiler 1991 are used to predict the effects of the most important semidiurnal m2 s2 n2 diurnal k1 o1 p1 and long period mf mf mm and ssa ocean tides on the earth s rotation the separate as well as combined effects of ocean tidal currents and sea level height changes on the length of day ut1 and polar motion are computed the predicted polar motion results reported here account for the presence of the free core nutation and are given in terms of the motion within the rotating body fixed terrestrial reference frame of the celestial ephemeris pole so that they can be compared directly to the results of observations outside the retrograde diurnal tidal band the summed effect of the semidiurnal and diurnal ocean tides studied here predict peak to peak polar motion amplitudes as large as 2 mas within the retrograde diurnal tidal band the resonant enhancement caused by the free core nutation leads to predicted polar motion or equivalently nutation amplitudes as large as 9 mas at the unobservable retrograde k1 tidal frequency

lateglacial and holocene variation in aeolian sediment flux over the northeastern tibetan plateau recorded by laminated sediments of a saline meromictic lake predominantly laminated lake sediments from a saline closed basin lake on the northeastern tibetan plateau were investigated using a multi proxy approach 14c accelerator mass spectrometry dating smear slide analysis loss on ignition grain size x ray diffraction elemental concentration ostracod assemblages stable isotopes of ostracod shells to trace the regional environmental and climatic history in the lateglacial and holocene before about 15 cal ka bp small saline water bodies probably filled the basin under unstable cold and harsh environmental conditions soon after about 14 9 cal ka bp a relatively deep saline lake was established probably as a result of runoff from melting snow ice and frozen ground in the lake s catchment large changes in flux of aeolian material to the lake were recorded during this initial period of formation of lake kuhai highest lake levels a low sediment accumulation rate and less saline conditions were maintained between about 12 8 and 7 1 cal ka bp when the aeolian influx diminished significantly after about 7 1 cal ka bp the aeolian influx remained at a moderate level apart from a strongly increased dust delivery to the lake between about 6 1 and 5 4 cal ka bp and a minor short lived period of slightly enhanced aeolian influx at about 2 7 cal ka bp the strongly enhanced dust input to the lake between 6 1 and 5 4 cal ka bp represented the largest influx of aeolian material to lake kuhai during the entire holocene however evidence for climatic deterioration during this period is not seen at most other palaeoclimate sites on the tibetan plateau but instead a significant increase in aridity has been recorded at numerous sites in the northern foreland of the tibetan plateau and on the chinese loess plateau the large dust input to lake kuhai between 6 1 and 5 4 cal ka bp probably did not result from a severe climate deterioration on the tibetan plateau itself but from the pronounced aridity in its northern and eastern foreland in contrast the increase in dust influx about 2 7 cal ka bp seems to correspond to a brief warming spell recorded at other sites on the tibetan plateau too a slight increase in lake level and decrease in salinity after about 0 6 cal ka bp suggests a slightly higher effective moisture during the final lake stage accompanied by a somewhat larger dust influx this apparent contradiction possibly results from enhanced human activities on the northeastern tibetan plateau during the last 600 years copyright 2009 john wiley sons ltd

a holocene sedimentary record from bosten lake china abstract a 9 24 m long sediment record from the kaidu river delta margin of bosten lake northwestern china provides evidence for changes in water balance of the lake during the past 8600 calendar years quantitative and qualitative analyses of detrital components authigenic calcite toc and sr ca molar ratios as well as comparisons with selected ostracod assemblages show that lake level fluctuations at minimum 5 6 m display changes in effective moisture supply mainly driven by the west wind system distinct periods of negative water balances and thus dry conditions are dated to 8 5 8 1 7 3 7 1 around 6 0 at 5 4 5 0 4 6 4 3 3 9 3 6 3 4 3 2 2 6 2 5 1 9 1 1 0 5 0 3 and 0 18 0 05 cal ky bp and match the regional and global pattern of climate shifts during the holocene temporal shifts of moisture availability during mid holocene time were recognised as well and may be attributed to regionally different airflow conditions the last 150 years of rising lake levels are accompanied by strong eutrophication as a result of increased human impact

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

analysis of near source static and dynamic measurements from the 1979 imperial valley earthquake gross features of the rupture mechanism of the 1979 imperial valley earthquake ml 6 6 are inferred from qualitative analysis of near source ground motion data and observed surface rupture a lower bound on the event s seismic moment of 2 5 1025 dyne cm is obtained by assuming that the average slip over the whole fault plane equals the average surface rupture 40 5 cm far field estimates of moment suggest an average slip over the fault plane of 105 cm from which a static stress drop of 11 bars is obtained an alternative slip model consistent with the far field moment has 40 5 cm of slip in the upper 5 km of the fault and 120 cm of slip in the lower 5 km this model suggests a static stress drop of 39 bars from the lower estimate of 11 bars an average strain drop of 32 strain is derived this strain drop is four times greater than the strain that could have accumulated since the 1940 el centro earthquake based on measured strain rates for the region hence a major portion of the strain released in the 1979 main shock had been accumulated prior to 1940 unusually large amplitude 500 to 600 cm sec2 vertical accelerations were recorded at stations e05 e06 e07 e08 eda of the ei centro array and the five stations of the differential array near eda although the peak acceleration of 1705 cm sec2 at e06 is probably amplified by a factor of 3 due to local site conditions these large amplitude vertical accelerations are unusual in that they are evident on only a few stations all of which are near the fault trace and at about the same epicentral range two possible explanations are considered first that they are due to a direct p wave generated from a region about 17 km north of the hypocenter or second that they are due to a pp phase that is unusually strong in the imperial valley due to the large p wave velocity gradient in the upper 5 km of the imperial valley based on the distribution of both the horizontal and vertical offsets it is likely that the rupture went beyond stations e06 and e07 during the main shock by exploiting the antisymmetry of the parallel components of particle velocity between e06 and e07 and by examining polarization diagrams of the particle velocity at e06 and e07 an average rupture velocity in the basement of 2 5 to 2 6 km sec between the hypocenter and station e06 is obtained in addition several lines of evidence suggest that the imperial fault dips about 75 to the ne

semidiurnal variations in the budget of angular momentum in a general circulation model and in the real atmosphere abstract diurnal and semidiurnal variations in the budget of atmospheric angular momentum are evident in a simulation by the ncar community climate model ccm2 these variations depicted with 20 min time resolution each time step are used as guides to study similar variations determined from 6 hourly ncep ncar reanalysis data a semidiurnal variation in relative angular momentum and in angular momentum related to solid body rotation of the atmosphere is found in the reanalysis although there is evidence that both frictional and gravity wave drag torques play roles the effects of semidiurnal variations in mountain torque resulting from the migrating semidiurnal pressure wave are most thoroughly documented

late quaternary climate change loess sedimentation and soil profile development in the central great plains a pedosedimentary model research on soil genesis often assumes a top down model in which the soil profi le develops downward from a stable land surface this model is inapplicable to upland landscapes affected by frequent dust deposition where soils grow upward as they develop on the central great plains late quaternary loess sections proximal to immediate source areas contain the brady soil a prominent marker separating late pleistocene peoria loess from holocene bignell loess farther from immediate dust source areas the brady soil and bignell loess are not recognizable in the fi eld on loess tablelands in these distal regions surface soils typically contain a prominent clay rich b horizon below a thick silty a horizon assuming top down pedogenesis this could be interpreted as a postglacial soil profi le formed in peoria loess with the b horizon produced by weathering and clay illuviation we propose a strikingly different interpretation in which the upper b horizon at distal sites is the brady soil a horizon that has been transformed by burial organic matter loss and modern subsoil structure formation processes the overlying modern a horizon represents bignell loess properties of the brady soil at proximal sites a distinctive burrowed zone high clay content and tio 2 zro 2 and low volcanic glass content can be traced to the b horizon in distal soils a decrease in smectite abundance above the brady soil at proximal sites is identifi able at the top of the clay rich b horizon in distal soils the spatial variation of clay content in loess and soil horizons is best explained by eolian sedimentation patterns the higher clay content in the brady soil and distal b horizons defi nes a fi ne grained zone that represents a late phase of peoria loess accumulation evidence of chemical weathering is minimal and illuvial clay is rare to absent in the clay rich b horizons illuvial clay does often occur deep in the solum and is related to the depth below the top of the brady soil the depth of occurrence of illuvial clay is not related to modern climate parameters although depth to secondary carbonate appears to be in equilibrium with modern climate upland soils in the central great plains are composite soils their properties are the result of a pedosedimentary history linked to regional climate change that has infl uenced sedimentation and pedogenesis since the late pleistocene

a high resolution record of holocene rainfall variations from the western chinese loess plateau antiphase behaviour of the african indian and east asian summer monsoons tropical monsoons are key mechanisms for transfer of heat and moisture to higher latitudes here we present a high resolution terrestrial proxy summer monsoon record for the southeast asian monsoon from a rapidly accumulating holocene loess soil sequence in the western chinese loess plateau we use magnetic and clastic grain size proxies to make quantitative estimates of holocene rainfall and identify variations in winter monsoon intensity our record reveals cyclical millennial and multimillennial rainfall changes as with the northwest african southwest asian monsoon records a short arid interval at 12 5 to 11 5 ka bp the younger dryas and subsequent summer monsoon intensification are recorded however at 6 ka bp the southeast asian summer monsoon weakened when the northwest african southwest asian monsoons strengthened and then from 5 ka bp intensified when northwest africa southwest asia became dry these antiphase monsoonal relationships may reflect competition between sea surface temperature changes and solar forcing the intensity of the southeast asian winter monsoon intensified from 9 ka bp onwards varying in its phase relationships with summer monsoon intensity after 2 25 ka bp extreme climatic instability is indicated by both climate proxies

timing and duration of the east asian summer monsoon maximum during the holocene based on stalagmite data from north china we present a continuous c o isotope series that shows the detailed variability of east asian summer monsoon easm since 11 0 ka bp the series is based on two stalagmites namely dsy1 and lm2 wh

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

deterministic frequency wavenumber methods and direct measurements of rupture propagation during earthquakes using a dense array data analysis data recorded by the smart 1 array in taiwan are used to make the first direct measurements of two dimensional earthquake rupture propagation using frequency wavenumber techniques and ray theory we obtain estimates of the spatial extent duration and directions of rupture propagation during two earthquakes located offshore taiwan our estimates include uncertainties due to errors in fault plane location and orientation velocity structure and slowness ray parameter measured at the array we find that the january 29 1981 ml 6 3 taiwan earthquake ruptured unilaterally updip and toward the west on a 60 dipping 109 striking reverse fault using p waves we find its fault length and duration to be 25 18 km and 7 4 3 4 s respectively s waves indicate a fault length and duration of 27 15 km and 9 4 3 6 s respectively we suggest that the november 14 1986 ml 7 0 hualien taiwan earthquake was triggered by a shallow h 14 km foreshock ml 5 4 which occurred on a subparallel or splay fault approximately 5 s before the mainshock based on p waves rupture propagation during the foreshock is unilateral towards the northeast and slightly downdip on a 58 dipping 38 striking reverse fault its spatial extent and duration are approximately 23 km and 5 4 s the mainshock initiated at greater depth h 34 km than the foreshock with its primary direction of rupture unilateral toward the northeast and slightly updip on a 57 dipping 43 striking reverse fault using p waves we found a spatial extent and duration of 68 15 km and 12 4 2 2 s s waves indicate a similar extent duration and direction of propagation for the mainshock however we found it difficult to distinguish the foreshock and mainshock 5 waves we show by example that these results represent an improvement over what can be obtained using long period t 5 s teleseismic methods comparison of our results with those obtained using teleseismic data suggests either a short duration slip time function or that most slip occurs near the rupture front our results indicate that much of the complexity in the seismograms recorded during these events by the smart 1 array is due to spatial and temporal variations of the source this suggests that at least in some cases predictions of both the phase and amplitude of strong ground motion as a function of time would require a priori knowledge of source properties finally we recommend siting small 10 station dense arrays on land above offshore subduction zones which are considered seismic gaps because they can provide more detailed measurements of rupture propagation than is presently possible

pollen records from southern taiwan implications for east asian summer monsoon variation during the holocene pollen records from two cores retrieved from a valley basin in southern taiwan show major changes in vegetation and climate occurring during the holocene between 11 400 and 8200 cal yr bp the up

holocene dust accumulation and the formation of polycyclic cinnamon soils luvisols in the chinese loess plateau chinese loess palaeosol sequences are well known for their records of monsoonal climatic variations however the modern processes of dust accumulation and soil formation remain poorly understood a high resolution investigation on modern soils including the measurement of magnetic susceptibility particle size distribution total fe total organic carbon caco3 content and optical stimulated luminescence osl dating was carried out on the zhouyuan loess tableland in the southern loess plateau the results indicate that modern cinnamon soils luvisols have developed on contemporarily accumulated aeolian dust during the holocene the aeolian loess accumulated during the younger dryas was identi ed in the top part of the malan loess that underlay the modern soil by osl dating and proxy climatic data it indicates that the malan loess accumulated during the last glaciation marine isotope stages 2 4 does not serve as the parent material for the modern soils pedogenesis of the soils started with the increased precipitation and soil moisture that have occurred on the loess tableland since the early holocene precipitation driven pedogenesis and organic activities are responsible for the leaching of caco3 decomposition of mineral dust and the production of clay and ferromagnetic minerals drier intervals have interrupted soil formation several times and therefore pro les with multiple soils have been developed at many sites on the loess tableland at places where soil erosion was relatively strong either a single soil or welded soils are preserved in the holocene pro les this does not necessarily mean however that modern soils over the plateau have been developed without interruption under a constantly warmer moister climate this is signi cant for understanding the surface processes and climatic variation during the formation of the numerous palaeosols over the loess plateau in the quaternary copyright 2003 john wiley sons ltd

east asian monsoon evolution during the eemian as recorded in the western chinese loess plateau abstract we present a high resolution environmental magnetic record of the east asian summer monsoon spanning paleosol s1 corresponding to marine oxygen isotope mis 5 from the jiuzhoutai jzt loess section in lanzhou on the northwestern edge of the chinese loess plateau we use a chronology based on a sediment grain size age model frequently used for chinese loess the eemian is dated to 127 37 121 31 ka bp and can be divided into three sub stages based on variations in summer monsoon intensity early eemian 127 37 125 67 ka bp with an intermediate summer monsoon intensity mid eemian 125 67 124 24 ka bp with weakest summer monsoon intensity and late eemian 124 24 121 31 ka bp with the strongest summer monsoon intensity contrasting the winter monsoon weakened at the beginning of mis5e reached its weakest intensity during the late eemian 121 ka bp and then commenced an irreversible strengthening trend furthermore the eemian exhibits a similar climatic trend to the holocene optimum since both are divided into two parts by an intervening arid interval and the most humid period occurs in the secondary pedogenic stage therefore we suggest that the climate evolution during eemian and later may provide useful information about climate forecast in the future

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

archaeology of the anthropocene in the yellow river region china 8000 2000 cal bp although archaeological analysis emphasizes the importance of climatic events as a driver of historical processes we use a variety of environmental and archaeological data to show that human modif

sub daily resolution of earth rotation variations wtth global positioning system measurements data from a worldwide global positioning system gps tracking experiment have been used to determine variations in earth rotation ut1 utc over a time period of three weeks kalman filtering and smoothing enabled changes in ut1 utc over intervals of 2 to 24 hrs to be detected with the gps data internal consistency checks and comparisons with other solutions from very long baseline interferometry vlbi and satellite laser ranging slr indicate that the gps ut1 utc estimates are accurate to about 2 cm comparison of gps estimated variations in ut1 utc with 2 hr time resolution over 4 days with predicted variations computed from diurnal and semi diurnal oceanic tidal contributions strongly suggests that the observed periodic sub daily variations 0 1 msec 5 cm are largely of tidal origin

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

spatial temporal distribution and geographic context of neolithic cultural sites in the hanjiang river basin southern shaanxi china abstract understanding how to live successfully within our environment is among the most pressing challenges facing contemporary society this paper probes the problem based on comparative analysis and discusses the relationship between the spatial temporal distribution of the neolithic cultural sites and the geographic context in the hanjiang river basin in the south of shaanxi province china archaeological studies have identified 175 neolithic cultural sites in the study area with a sequence of laoguantai 14 c age 8 7 ka bp yangshao 14 c age 7 5 ka bp and the late period of the neolithic age 14 c age 5 4 ka bp the total number of archaeological sites the distribution area and the density all showed an early ascending and later descending trend but the proportion of the number of archaeological sites in the study area to the corresponding value of the entire shaanxi province declined sharply spatially these sites were concentrated on the terraces of the hanjiang river and its main tributaries with an altitude of 400 800 m multiple data were integrated to clarify the critical effects of tectonic and geomorphologic conditions on the distribution of the neolithic sites further comparisons revealed the correlation of holocene climate change and environmental evolution with the neolithic cultural succession in the study area that ameliorated conditions to generally promote the development of the primitive culture while degeneration coincided with the culture s transition or interruption the discussion on the origin of the primitive culture and the temporal spatial distribution corresponding to the regional culture differentiation sheds light on the complex and dynamic human nature interaction system during the neolithic age thus emphasising the wider field based investigation and high resolution reconstruction works of the palaeoclimate and palaeoenvironment in the future

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

reconstructing holocene shore displacement and stone age palaeogeography from a foredune sequence on ruhnu island gulf of riga baltic sea abstract holocene shore displacement and the palaeogeography of late mesolithic and late neolithic settlements on ruhnu island gulf of riga were reconstructed using foredune sequence luminescence dating sedimentological data supported by ground penetrating radar analysis and gis based landscape modelling the foredune ridges consist of very well to well sorted fine to medium grained aeolian sand and are underlain by seaward dipping foreshore sediments the studied sequence of 38 ridges was formed between 6 91 0 58 ka and 2 54 0 19 ka ago and represents a period of falling relative sea level foredune plain progradation with average rates of 0 3 0 6 m per year was controlled by isostatic land uplift which caused a continuous withdrawal of shorelines to lower elevations the dated foredune succession was used to reconstruct the coastal palaeogeography of the island palaeogeographical reconstructions show that during two phases of late mesolithic habitation at ca 7 2 cal ka bp and 6 2 cal ka bp seal hunters settled the coastal zone of ruhnu island based on tool material and pottery type they could have originated from saaremaa island which according to palaeoreconstruction of the gulf of riga was located approximately 70 km northwest of ruhnu island during the late mesolithic later signs of human occupation radiocarbon dated to ca 4 7 cal ka bp were from the centre of the island hundreds of metres away from the shore at about 8 m above its contemporary sea level this late neolithic habitation shows a clearly different pattern than earlier coastal settlement and suggests a shift in subsistence strategy towards agriculture and animal husbandry

source complexity of the 1980 southern italian earthquake from the analysis of strong motion s wave polarization strong motion records from 23 november 1980 earthquake in irpinia basilicata southern italy recorded less than 59 km to the source show strong s wave phases coherent up to 10 hz at more distant stations the signal is only coherent up to 5 hz even when recordings contain signal up to 10 hz hodogram plots of the coherent signal in the 5 to 10 hz range show lissajous figures of sh and sv waves radiated by the nearest point with strong seismic radiation by the terminations of the rupture or by other relatively compact features the largest acceleration recorded at the sturno station is due to high frequency pulses radiated by a source south of the station and 25 km from the epicenter hodogram plots of low frequencies show polarizations due to the propagation of the large scale rupture along the fault lissajous figures help to discriminate p and s arrivals and reveal their direction of propagation on the basis of this kind of analysis it is confirmed that the 1980 irpinia basilicata earthquake ml 6 5 was composed of three main sub events at 0 sec 19 sec and 39 sec in relative time the first and second events broke the same structure striking nw there is also evidence of bilateral propagation the third event broke a second smaller structure also striking nw and placed very close to the alignment of the previous ones

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

holocene climatic change revealed by aeolian deposits from the gonghe basin northeastern qinghai tibetan plateau a climate record for the gonghe basin in the northeastern qinghai tibetan plateau during the holocene period was determined from a 3 90 m aeolian deposit as revealed by the variation of proxies including sedimentary facies magnetic susceptibility the total organic carbon toc content grain size and geochemical parameters the regional climatic evolution during this period can be divided into the following stages there was a cold and dry phase in 11 8 10 1 ka probably related to the younger dryas yd event prior to the holocene an optimum stage with relatively warmer and wetter climate dominated the region between 10 1 ka and 8 7 ka the climate tended to relatively dry condition from 8 7 ka to 4 7 ka although weak paleosol weakly developed paleosol developed during this period this is inconsistent with the megathermal maximum in the holocene or holocene optimum a relatively warm and wet climate emerged in 4 7 0 7 ka and an obviously cold and dry stage emerged since 0 7 ka thereafter the regional climate became warmer in addition eight cold events were recorded including the yd event around 11 8 ka 9 8 9 5 ka 9 2 8 7 ka 8 1 7 6 ka 7 0 6 1 ka 5 3 4 7 ka 3 1 1 5 ka and since 0 7 ka these events are coincident with cold phases revealed by aeolian depositions and lake records in the northeastern qinghai tibetan plateau and also with the evidence of deteriorated climate phases in the high and low latitudes of the northern hemisphere on a millennial scale such as in hongyuan peat and drift ice tracers in the north atlantic ocean in the holocene

history of moisture change indicated by aeolian deposit in the horqin sandy land northeastern china since the last glacial maximum abstract the horqin sandy land located in the monsoonal boundary of northeastern china is sensitive to the vicissitudes of the asian monsoon am the aeolian sand paleosol sequences in this area especially since the last glacial maximum lgm have preserved valuable geological archives indicating the history of humidity changes in the region however existing studies on the local humidity rhythms have not been sufficient to reach a consensus in a relatively in depth study of the forcing mechanism we present the results of a systematic optically stimulated luminescence osl chronology and detailed multi proxy analyses of the grain size geochemical elements magnetic susceptibility and organic matter since the lgm the results demonstrate that the humidity gradually increased from the lgm to the middle holocene reaching optimum humidity around 9 3 ka despite intense oscillations occurring during 6 5 ka that is largely consistent with other paleoenvironmental records from ne china it is suggested that the variation in the humidity is basically controlled by the solar driven monsoonal precipitation which is the most dominant moisture source the coupled atmosphere pacific ocean system and the westerlies could have both disturbed the monsoon precipitation thus indirectly affecting the humidity of the sandy land during the late holocene human occupation also played a significant role in the re activation of dunes

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

tidal variations of earth rotation we have rederived the periodic variations of the earth s rotation due to the tidal deformation of the earth by the sun and moon and included all terms with amplitudes 0 002 milliseconds 1 mm this series applies to the mantle plus crust and oceans which rotate together for characteristic tidal periods the parameter which scales the rotational series is k c where k is that fraction of the love number which causes the tidal variation in the moment of inertia of the coupled mantle and oceans while c is the dimensionless polar moment of inertia of the coupled units if the whole earth minus oceans were coupled rotationally then k 0 30 and c 0 33 ocean tides increase k by 0 04 decoupling of the fluid core from the mantle decreases k by 0 06 while c cmantle 0 29 since neither pressure viscous nor hydromagnetic coupling locks the fluid to the mantle for periods less than 5 to 25 years from the analysis of lunar laser ranging data we find that k c at monthly and fortnightly frequencies equals 0 99 0 15 and 0 99 0 20 as compared with a theoretical value of 0 94 0 04 in addition we have estimated theoretically the effects of ocean tides on earth rotation nutation and polar motion using models based on the laplace tidal equations

impacts of human activity on the late holocene development of the subaqueous yangtze delta china as shown by magnetic properties and sediment accumulation rates development of the yangtze delta during the late holocene and its relationship to human activities in the drainage basin was analyzed using data from 16 cores collected from distributaries to the

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

changes in atmospheric circulation and ocean ice cover over the north atlantic during the last 41 000 years high resolution continuous multivariate chemical records from a central greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41 000 years these chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to greenland defined here as the polar circulation index pci and in the extent of ocean ice cover massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in pci during stadials without discharge events ocean ice cover appears to reach some common maximum level the massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling

holocene environmental change inferred from a high resolution pollen record lake zhuyeze arid china a high resolution pollen record c 50 yr sample from terminal lake sediments in the shiyang river drainage basin on the present margin of the summer monsoon was used to reconstruct vegetation and climate history during the holocene forest trees from mountainous areas of the drainage including sabina picea and pinus dominated pollen assemblages in the early holocene 11 6 7 1 cal ka in the mid holocene 7 1 3 8 cal ka desert and steppe shrubs and herbs around the lake including nitraria poaceae compositae and artemisia were dominant the late holocene 3 8 0 cal ka was again dominated by alternation of pinus sabina tree pollen and desert steppe pollen the early holocene forest expansion in the mountains and subsequent increase in the river transport of tree pollen corresponds with maximum precipitation during the east asian summer monsoon maximum the timing of these changes in our record from arid china is different from that of east china where the holocene monsoon maximum appeared in

source dynamics of the 1979 imperial valley earthquake from near source observations of ground acceleration and velocity two sets of observations obtained during the 15 october 1979 imperial valley earthquake ms 6 9 are presented the data suggest different dynamic characteristics of the source when viewed in different frequency bands the first data set consists of the observed residuals of the horizontal peak ground accelerations and particle velocity from predicted values within 50 km of the fault surface the residuals are calculated from a nonlinear regression analysis of the data campbell 1981 to the following empirical relationships pga a 1 r c 1 d 1 pgv a 2 r c 2 d 2 in which r is the closest distance to the plane of rupture the so calculated residuals are correlated with a positive scalar factor signifying the focusing potential at each observation point the focusing potential is determined on the basis of the geometrical relation of the station relative to the rupture front on the fault plane the second data set consists of the acceleration directions derived from the windowed time histories of the horizontal ground acceleration across the el centro differential array ecda the horizontal peak velocity residuals and the low pass particle acceleration directions across ecda require the fault rupture to propagate northwestward the horizontal peak ground acceleration residuals and the high frequency particle acceleration directions however are either inconclusive or suggest an opposite direction for rupture propagation the inconsistency can best be explained to have resulted from the incoherence of the high frequency radiation which contributes most effectively to the registration of pga a test for the sensitivity of the correlation procedure to the souce location is conducted by ascribing the observed strong ground shaking to a single asperity located 12 km northwest of the hypocenter the resulting inconsistency between the peak acceleration and velocity observations in relation to the focusing potential is accentuated the particle velocity of delta station mexico in either case appears abnormally high and disagrees with other observations near the southeastern end of the fault trace from the observation of a nearly continuous counterclockwise rotation of the plane of p wave particle motion at ecda the average rupture velocity during the first several seconds of source activation is estimated to be 2 0 to 3 0 km sec a 3 km upper bound estimate of barrier dimensions is tentatively made on the basis of the observed quasiperiodic variation of the polarization angles

palaeosol development in the chinese loess plateau as an indicator of the strength of the east asian summer monsoon evidence for a mid holocene maximum the interpretation of the stalagmite delta o 18 record from southern china as an indicator of east asian summer monsoon easm rainfall amount or intensity is strongly debated soil development in the chinese loess plateau clp situated in the modern summer monsoon domain has long been treated as a direct and reliable easm proxy in this study we compiled 81 loess and 229 palaeosol dates from 77 profiles across the clp and synthesized the data statistically in order to investigate the easm history during the holocene the resulting history of holocene loess deposition and palaeosol development demonstrates that 1 loess deposition decreased and palaeosol formation increased across the clp after 11 5 ka 1 ka 1000 cal yr bp revealing a gradually intensified easm during the early holocene 2 numerous palaeosols developed in the clp between 8 8 ka and 3 4 ka indicating a generally strong easm during the mid holocene 3 the number of palaeosol dates decreased rapidly at around 3 ka suggesting a sudden retreat of the easm in the late holocene these trends of easm evolution are broadly consistent with variations in aeolian sand activity in the four main sandlands the mu us otindag horqin and hulun buir sandlands along the modern monsoon fringe in northern china and are supported by a wide range of independent evidence in addition we also found that high loess deposition and stronger aeolian activity occurred at similar to 5 ka representing a weak easm event within the context of an overall strong mid holocene easm the strong mid holocene easm revealed by palaeosol development in the clp and aeolian sand activity in the sandlands in northern china contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china our results are compatible with the proposal that the stalagmite delta o 18 variations in china do not result from changes in easm rainfall amount or intensity but instead reflect changes in moisture source driven by variations in atmospheric oceanic circulation c 2014 elsevier ltd and inqua all rights reserved

mid late holocene climatic changes recorded by loess deposits in the eastern margin of the tibetan plateau implication for human migrations abstract the climatic fluctuations during the mid late holocene in northern sichuan southwest china were inferred from loess deposits using multi proxies of total organic carbon toc carbonates magnetic susceptibility stable isotopic composition of organic carbon 13 corg and grain size distribution in combination with the dates determined by the accelerator mass spectrometry ams 14 c and optically stimulated luminescence osl methods from 6300 to 5500 a bp the regional climate presented gradually increased warmth and humidity subsequently characterized by reduced precipitation but with relatively high air temperature between 5500 and 4800 a bp demonstrating that the east asian monsoon weakened a warmer and wetter climate prevailed since 4800 a bp and was interrupted by a sharp cold reversal at approximately 3300 a bp that was likely caused by solar irradiance forcing which resulted in a global cold climatic change and glacier advance large scale human migrations into the eastern margin of the tibetan plateau occurred in the cold and dry events that developed at 6000 2500 and 1200 a bp indicating a critical stimulus effect of climatic change on human migration