a jokulhlaup near sondre stromfjord west greenland and some effects on the ice sheet margin description de la vidange d un lac marginal par un tunnel sous glaciaire les 19 et 20 aout 1984

observations of thermospheric horizontal neutral winds at watson lake yukon territory λ 65 n fabry perot interferometer observations of the thermospheric o i 6300 a emission have been conducted from an airglow observatory at a dark field site in the southeastern yukon territory canada for the period november 1991 to april 1993 the experiment operated in an unattended remote fashion has resulted in a substantial data set from which mean neutral winds have been determined dependent upon geomagnetic activity the nocturnal location of the site is either equatorward of the auroral oval or within the oval boundaries the data set is rich enough to permit hourly binning of neutral winds based upon the kp geomagnetic disturbance index as well as the season for cases of low geomagnetic activity the averaged vector horizontal neutral wind exhibits the characteristics of a midlatitude site displaying antisunward pressure gradient driven winds as the geomagnetic activity rises the late afternoon and evening winds slowly rotate sunward in an anticlockwise direction initially remaining near 100 m s in speed but eventually increasing to 300 m s for kp 5 for the higher levels of activity the observed neutral wind flow pattern resembles a higher latitude polar cap pattern characterized by ion drag forcing of thermospheric neutral gases in addition rotational coriolis forcing on the dusk side enhances the ion drag forcing resulting in dusk winds which trace out the clockwise dusk cell plasma flow on the dawn side the neutral winds also rotate in an anticlockwise direction as the strength of geomagnetic disturbances increase since the site is located at a transition latitude between the midlatitude and the polar cap the data set provides a sensitive test for general circulation models which attempt to parameterize the contribution of magnetospheric processes a comparison with the vector spherical harmonic vsh model indicates several regions of poor correspondence for december solstice conditions but reasonable agreement for the vernal equinox

results of paleoecological studies in the loess region of szeged othalom se hungary abstract new results of sedimentological magnetic susceptibility geochemical radiocarbon and malacological analysis from a typical and an infusion loess section are presented from se hungary the geologic and geomorphologic value of the area is that aeolian typical loess accumulated on sand dunes that formed during mis3 while in the interdune depressions on the top of lacustrine deposit series infusion loess developed as the two types of loess interfinger it is the first demonstration that the two types of loess formed during the same time period isochron in different environments heterotype at the end of mis3 and during mis 2 between 33 000 13 000 cal bp a temperate steppe forest steppe environment characterized the loess surface of the se great hungarian plain during the first interstadial phase of mis2 a pinus sylvestris charcoal rich paleosol layer developed on the loess covered surface of a wind blown sand hummock while in the interdune depressions a pond phase developed after the formation of the paleosol layer on the surface of the loess covered wind blown sand hummock during the heinrich 2 event vertigo modesta vallonia tenuilabris indicate a cold steppe forest steppe environment and a deeper and colder lake phase in the interdune depressions after that a short microinterstadial phase developed and a pupilla triplicata chondrula tridens dominated temperate steppe forest steppe environment evolved on the terrestrial surface between 23 000 21 000 cal bp after 21 000 cal bp in the last glacial maximum lgm the environment completely changed the average dust accumulation accelerated and coarse silt 0 02 0 06 mm became dominant as a result the lake stage transformed to a marshy environment while on the land area shade loving including closed forest environment preferring mollusca taxa appeared such as vestia turgida vitrina pellucida and mastus venerabilis based on the mollusca fauna composition humidity increased during the cooling of the lgm horizon forestation started and a boreal forest steppe evolved at the study site during the post lgm the interdune depressions filled and aeolian loess layers developed formation of the infusion loess occurred between 24 000 17 000 cal bp loess formation lasted until the beginning of the late glacial maximum last permafrost maximum and ended in a forest steppe environment with boreal central european holarctic palearctic and continental mollusc fauna elements

assessing the utility of visible to shortwave infrared reflectance spectroscopy for analysis of soil weathering intensity and paleoclimate reconstruction abstract visible to shortwave infrared reflectance vswir spectroscopy is a fast and efficient approach for estimation of soil properties in order to test whether soil weathering intensity can be predicted using reflectance spectra in the vswir range 350 2500 nm and to examine the efficacy of this methodology to supplement or substitute for traditional mineralogical and geochemical techniques of paleoclimate reconstruction we investigated a quaternary soil sequence at shengli in the sichuan basin of southwestern china vswir absorption bands can be characterized by geometrical parameters including position p depth d width w asymmetry as and full width at half maximum f our results indicate that spectral features in the visible to near infrared vnir 350 1000 nm range can be interpreted in terms of the presence and or concentration of individual fe oxide phases spectrally detected water is mostly bound in clay minerals and this single dominant water source facilitates interpretation of shortwave infrared swir 1000 2500 nm parameters soil spectral parameters were compared with the fe oxide mineralogy major element composition and clay mineralogy of soil samples obtained from conventional laboratory analyses strong correlations are found between vnir parameters and fe oxide mineralogy with d 900 serving as the best proxy for total ferric iron concentration p 900 and d 700 d 500 exhibit similar variation trends and relationships to the hematite hematite goethite h h g ratio of soil samples confirming their value as monsoonal weathering intensity proxies lower values of p 900 and d 700 d 500 indicate warmer and seasonally drier pedoenvironments reflecting a stronger east asian summer monsoon the utility of some swir parameters for assessment of weathering intensity declines in inhomogeneous soils e g those having vermiform structure thus spectral evaluation of weathering intensity is most effective in soils that are relatively homogeneous for which weathering degree is highly correlated to as 2200 d 2200 d 1900 and as 1400 the utility of these spectral proxies depends mainly on the mineral composition of soils and the application type i e laboratory versus field studies the application of vswir in the field e g imaging spectroscopy or is shows promise for rapid in situ mapping of weathering intensity thus providing a convenient approach to paleoclimate reconstruction in remote and inaccessible regions

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

cool la nina during the warmth of the pliocene the role of el nino southern oscillation enso in greenhouse warming and climate change remains controversial during the warmth of the early mid pliocene we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial pacific consistent with the prevalence of a la nina like state rather than the proposed persistent warm el nino like conditions our pliocene paleothermometer supports the idea of a dynamic ocean thermostat in which heating of the tropical pacific leads to a cooling of the east equatorial pacific and a la nina like state analogous to observations of a transient increasing east west sea surface temperature gradient in the 20th century tropical pacific

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

dolomite abundance in chinese loess deposits a new proxy of monsoon precipitation intensity dolomite of detrital origin in carbonate rich soil can help indicate the intensity of carbonate dissolution and leaching processes using fourier transform infrared spectroscopy we generated a high resolution record of dolomite and calcite contents from eight sections on the chinese loess plateau spanning the last 130 kyr based on the relative abundance of calcite and dolomite four dissolution phases of carbonate minerals related to summer monsoon sm variations are identified as follows 1 coexistence of dolomite and calcite indicating a very weak sm with a mean annual precipitation map 725 mm

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind water erosion crisscross region of the chinese loess plateau abstract sediment sources in catchments under the control of check dams in the wind water erosion crisscross region are more complicated compared to other regions on the chinese loess plateau this is due to their general complexity which mainly results from variation in soil landform vegetation and erosion agents accordingly we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region the aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam sediment sources were classified into three source paleosol loess and sand and four source paleosol gully loess gully slope bare of sand and slope covered by sand groups on the basis of soil and landform types respectively sediment sources throughout the whole trapping history of the check dam 1978 2010 could be classified into three stages according to variation in sedimentation rate results showed that depositional sediment in the check dam was primarily from gullies averaging 80 1 especially the paleosol gully 54 1 the large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity coal mining also had a significant impact on contribution of sediment sources especially for slopes since 1987 mining began to change the structure of hills in this region leading to slope fissures collapse and landslides at junctions where gullies meet slopes which increased the risk of slope erosion this has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures which converted sloping cropland into grassland or forest further studies are necessary to gain better insight into sediment transport and deposition within such complex environments as well as to distinguish between the effects of multiple erosion agents

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

obstacle marks produced by flow around stranded ice blocks during a glacier outburst flood jokulhlaup in west greenland the effects of glacier ice block grounding on the morphology and sedimentology of proglacial fluvial outwash were examined during a glacier outburst flood or jokulhlaup near sondre stromfjord west greenland observations made during and after the 1987 jokulhlaup both on the surface of an ice contact delta and within a confined valley sandur plain provided information about the formation of ice block obstacle marks and the significance of these bedforms for sandur morphology and sedimentology flow directions determined from obstacle mark morphology have been used successfully to chart flow direction changes on the falling limb of the jokulhlaup maximum flow depths for scour around stranded ice blocks may be given by 0 5 0 9 times the diameter of the ice block as estimated from the depth of scour the height of the obstacle shadow or the extent of ice block meltout sediments minimum flow depths can be represented by the height of the obstacle shadow above the mean bed level the internal composition of the shadow indicates the ability of the flow to transport various sizes of material into the lee of obstacles ice block obstacle marks within the distal portion of the sandur initiated waning stage channel change proximal and lateral erosion around stranded ice blocks extended downstream from the ice block forming chute channels which then captured waning stage flows resulting in significant bar incision with associated deposition of lobate or deltaic deposits it is suggested that ice block obstacle marks are important in terms of channel morphology channel morphological change and their usefulness as palaeohydrological indicators

paleosol carbonate multiple isotopologue signature of active east asian summer monsoons during the late miocene and pliocene east asian summer monsoon precipitation has a globally unique 18 o signature characterized by low 18 o values related to the precipitation amount effect we explore the history of this signature using carbonate clumped isotope thermometry and 18 o of paleosol carbonates from northern china we find that soil water 18 o throughout the late miocene and pliocene was indistinguishable from present day summer meteoric water 18 o additionally soil temperatures were similar to present day summer temperatures as were latitudinal gradients in temperature paleosol carbonate 13 c values document a pattern of northward increasing c 4 vegetation during 7 3 ma interpreted as marking a paleobiome transition from forest to steppe the present day summer monsoons give rise to a similar transition owing to latitudinal gradients in precipitation amount and seasonal duration taken together these lines of evidence point to active east asian summer monsoons during the warm climates of the late miocene and pliocene

spatial evolution of frictional heating and the predicted thermospheric wind effects in the vicinity of an auroral arc measured with the sondrestrom incoherent scatter radar and the reimei satellite 1 simultaneous observation with the sondrestrom incoherent scatter is radar and the reimei satellite was conducted on 3 october 2007 the objective was to measure horizontal patterns of the ionospheric structure in the vicinity of an auroral arc the is radar was scanned azimuthally with a fixed elevation angle and the satellite narrow view camera 557 7 nm was directed downward taking pictures every 0 12 s a stationary auroral arc was captured at 05 17 ut 02 54 mlt with both instruments simultaneously gross ionospheric features measured with the is radar around the arc were in good agreement with the expected magnetosphere ionosphere current system of particular interest was the horizontal pattern in the ion speed and temperature in the f region the ion speed within the arc was close to zero by contrast the larger ion speed 350 400 m s 1 on the poleward side was parallel to the arc and almost no horizontal shear within about 20 km width perpendicular to the arc this area was separated into two parts by the ion temperature one was associated with clear enhancements in excess of 1200 k and another was with more moderate enhancements less than 1000 k the widths of the two areas were approximately 10 km each the horizontal shear seen in the ion temperature suggested the presence of a narrow thermospheric wind shear of about 10 km width this paper suggests that the possible cause for the thermospheric wind shear was ion drag associated with localized soft particle precipitation or f region ionization

spatial pattern of grain size in the late pliocene red clay deposits north china indicates transport by low level northerly winds abstract the confirmation of an eolian origin of the tertiary red clay from north china would make it a valuable terrestrial paleoclimatic record however it is still controversial as to which wind primarily transported the dust forming the red clay onto the loess plateau careful consideration of this question is a prerequisite for better understanding the history of atmospheric circulation in central and east asia during the miocene and pliocene epochs in this paper the grain size distributions of bulk samples and chemically isolated quartz grains of the late tertiary red clay were investigated to explore the potential transportation mechanisms of the dust as well as the atmospheric circulation at the time of deposition the samples were taken from six localities spanning across 550 km on the loess plateau the results show that the mean grain size of both bulk and quartz samples decreases southward as does the coarse fraction content 42 m these data not only give new evidence for the eolian origin of the red clay but also indicate that the red clay was probably transported mainly by northerly low level winds or the winds at least had a strong northerly component therefore the spatial distribution of grain size of the red clay is comparable to that of the overlying quaternary eolian loess which demonstrates a remarkable northwest southeast decrease in grain size sedimentation rate and thickness during the last glacial coinciding with the dominant wind direction of the northwesterly east asian winter monsoon however the grain size of the red clay is generally finer than the corresponding loess this indicates that the red clay may have been transported by a weaker winter monsoon associated with stronger pedogenic modification and or the dust source area was not extensive compared to that during the quaternary moreover the high content of grains coarser than 19 m transported mainly by energetic low level winds over short distances suggests that the dusts were not transported by upper level westerly

the geochemistry of loess asian and north american deposits compared abstract loess is widely distributed over asia and north america and constitutes one of the most important surficial deposits that serve as terrestrial records of the quaternary the oldest pleistocene loess in china is likely 2 6 ma thus spanning much or all of the pleistocene in north america most loess is no older than the penultimate glacial period with the exception of alaska where the record may go back to 3 0 ma on both continents loess deposits date primarily to glacial periods and interglacial or interstadial periods are represented by paleosols both glacial and non glacial sources of silts that comprise the bulk of loess deposits are found on both continents although loess has been considered to be representative of the average upper continental crust there are regionally distinctive compositions of loess in both asia and north america loess deposits in asia from yakutia tajikistan and china have compositionally distinct major element compositions due to varying abundances of silicate minerals carbonate minerals and clay minerals in north america loess in the mississippi river valley the great plains and alaska are also distinguishable with regard to major element composition that reflects highly diverse source sediments trace element geochemistry sc th zr and the rare earth elements also shows regional diversity of loess bodies in both asia and north america on both continents most loess bodies show significant contributions from later cycle altered sedimentary rocks as opposed to direct derivation from igneous rocks further some loess bodies have detectable contributions from mafic igneous rocks as well as major contributions from average upper crustal felsic rocks intercalated paleosols in loess sections show geochemical compositions that differ significantly from the underlying loess parent materials ratios of soluble to insoluble elements show depletions in paleosols due to chemical weathering losses of calcite dolomite plagioclase mica apatite and smectite in asia and north america the last interglacial paleosol is more weathered than equivalent modern soils which could be due either to a climate that was warmer and more humid a longer period of pedogenesis or both in asia early pleistocene loess and paleosols are both more weathered than those from the middle and late pleistocene forming prior to a mid pleistocene aridification of asia from uplift of the tibetan plateau understanding the geochemistry of loess and paleosols can tell us much about past atmospheric circulation past temperature and moisture regimes and even tectonic processes

a holocene east asian winter monsoon record at the southern edge of the gobi desert and its comparison with a transient simulation the east asian winter monsoon eawm exhibits significant variability on intraseasonal interannual and interdecadal time scales and the variability can be extended to holocene centennial and millennial scales previous holocene eawm proxy data records which were mostly located in central eastern and southern china did not show a consistent holocene eawm history therefore it is difficult to provide insights into mechanisms of the long term winter monsoon variability on the basis of the records eolian sediments at the southern edge of the gobi desert western china are sensitive to the eawm changes and less affected by the east asian summer monsoon due to an obstruction of the qinghai tibet plateau this paper presents a comparison between a well dated holocene eawm record and coupled climate model simulations so as to explore physical processes and influencing factors of the holocene eawm sediment samples from two holocene eolian sedimentary sections huangyanghe a and huangyanghe b were acquired at the southern edge of the gobi desert chronologies were established based on twenty bulk organic matter ams 14c ages and five pollen concentrates ams 14c ages proxy data including grain size total organic carbon magnetic susceptibility and carbonate content were obtained from the two eolian sections the grain size standard deviation model was applied to determine components sensitive to variability of the holocene eawm after a comparison of environmentally sensitive grain size components and proxy data the 20 200 m component at the huangyanghe a and the 20 159 m component at the huangyanghe b section were selected as indicators of the holocene eawm which show a strong early holocene winter monsoon and a decline of the winter monsoon since the mid holocene we also present equilibrium and transient simulations of the climate evolution for the holocene using a state of art coupled climate model the community climate system model version 3 ccsm3 indices for the holocene eawm were calculated and are consistent with the reconstructed holocene eawm intensity the simulations indicate that orbital forcing effects on the land sea temperature and sea level pressure contrast can account for the observed eawm trends other forcings that were present in the early holocene including the remnant laurentide ice sheet and meltwater forcing in the north atlantic were not responsible for the holocene trends

late neogene evolution of the east asian monsoon revealed by terrestrial mollusk record in western chinese loess plateau from winter to summer dominated sub regime article i nfo more and more evidence indicates that the onset of the east asian ea monsoon can be traced back to the oligocene miocene boundary at about 23 ma however the process of its evolution is still less well known until now here we investigate its late neogene evolution by analyzing a terrestrial mollusk sequence from the chinese loess plateau clp covering the period between 7 1 and 3 5 ma considering the modern ecological requirements of these organisms we were able to define two groups of cold aridiphilous ca and thermo humidiphilous th species representing the ea winter and summer monsoon variations respectively as previously defined in the quaternary glacial interglacial cycles variations in these two groups indicate two different monsoon dominated periods during 7 1 3 5 ma first between 7 1 and 5 5 ma the ea winter monsoon with a 100 kyr periodicity was dominant second between 5 1 and 4 ma the ea summer monsoon dominated with a 41 kyr periodicity furthermore our mollusk record yields valuable evidence for a late miocene pliocene transition of about 400 kyr from winter monsoon dominated towards summer monsoon dominated associated with a periodicity transition from weak 100 kyr to 41 kyr the strengthened winter monsoon interval with a 100 kyr periodicity is coeval with orbital scale global ice volume changes in conjunction with the uplift of the tibetan plateau which probably reinforced the winter monsoon sub regime conversely closures of the panama and indonesian seaways associated with changes in obliquity between 5 1 and 4 ma are probably major forcing factors for the observed dominant summer monsoon with 41 kyr frequency favoring heat and moisture transports between low and high latitudes to allow th mollusks to grow and develop in the clp

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

jokulhlaup ice dammed lake outburst flood impact within a valley confined sandur subject to backwater conditions kangerlussuaq west greenland abstract this paper examines the controls on the morphology and sedimentology of a valley confined proglacial outwash plain or sandur in west greenland subject to glacial outburst floods jokulhlaups jokulhlaup flow conditions observed during a recent 1987 flood are linked to sandur sedimentology and morphological change backwater effects over the distal sandur resulted in a reduction of stream power despite increasing discharge bar units were typically large bar front advance of 60 m during 1987 jokulhlaup occurred prior to waning stage bar dissection by chute channels channel change was confined to the distal sandur due to the greater erodibility of the finer grained bars a temporary zone of sediment storage prevailed at the transition between free flowing and ponded flood waters until flood powers increased during waning flood stage as backwater effects were removed extension of pre existing high relief amplitude bars within the distal sandur records sedimentation related to at least eight jokulhlaups whilst lower relief amplitude proximal sandur sediments provide a composite record of the last high stage jokulhlaup flows backwater conditions during jokulhlaups have increased the rapidity of spatial variation of grain sizes and fluvial facies types complex within event sediment reworking and routing is generated by the onset and break up of backwater effects the role of local topography is therefore crucial when interpreting the sedimentary record of former proglacial channels potentially subject to jokulhlaups this study may prove useful in identifying the presence of flood cycles within palaeo fluvial systems in both formerly glaciated and non glaciated areas

intrusion of ice into porous media by regelation a mechanism of sediment entrainment by glaciers unlithified sediment at glacier beds should be entrained in ice as a result of melting above individual grains and refreezing below grains regelation to test this hypothesis a device that simulates subglacial conditions was used to push ice downward through idealized and natural porous media in contact with a flat bed ice regelated toward the bed at speeds proportional to the gradient in ice pressure across the thickness of particles ice temperatures responded predictably to changes in driving stress and demonstrated that the ice particle mixtures were at or very near the pressure melting temperature a theory of pore ice motion by regelation predicted the measured speed usually to within a factor of two although at low driving stresses the speed was less than the predicted value by as much as a factor of five the low speeds were probably caused by imperfect temperature control that resulted either in heat loss from the ice particle mixtures or in slightly subfreezing pore ice temperatures that were not detected by thermistors ice should intrude the pores of underlying sediment to a steady depth at which the downward regelation speed equals the rate of basal melting departures from the steady state should cause release of debris from ice or further entrainment an approximate calculation of the steady intrusion depth yields values comparable to typical thicknesses of debris in basal ice a few centimeters to more than a meter intrusion of sediment by regelation is consistent with the isotopic composition of debris bearing ice if melting exceeds refreezing

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

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

spatial structure in the thermospheric horizontal wind above poker flat alaska during solar minimum a new all sky imaging wavelength scanning fabry perot spectrometer was used to record high resolution r 200 000 spectra of the 630 nm thermospheric optical emission above poker flat alaska these spectra were used to derive spatially resolved maps of the horizontal wind vector at approximately 250 km altitude we describe the procedure used to infer vector winds from line of sight doppler shifts along with its limitations we present the time evolution of the vector wind fields obtained from this method for 6 nights of observation five of the 6 nights contained periods when we inferred the existence of significant curvature divergence or shear in the thermospheric wind across our instrument s 1000 km diameter field of view the sixth night exhibited little spatial structure and is shown for comparison we compare these results with a generic solar minimum winter time run of the national center for atmospheric research s thermosphere ionosphere and electrodynamics general circulation model while agreement was good at the start and end of the night considerable differences were found in the late evening and midnight sectors some possible origins for these discrepancies are proposed in particular we suggest that the f region horizontal wind may be deflected by upwelling vertical winds which are in turn driven by e region heating in the auroral zone we note that both the instrument used and our high latitude implementation of the analysis procedure are new experimental techniques thus the data presented here should be regarded as preliminary and if possible be validated by comparison with results from other techniques

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

a review of glacier outburst floods in iceland and greenland with a megafloods perspective the very largest glacier outburst floods have been termed megafloods given their volume and peak discharge that definition might be revised because those floods have become understood due to their distinctive and pervasive landscape impacts at least three floods in iceland can be categorized as megafloods since they produced impressive bedrock canyons and giant fluvially transported boulders glacier lake outburst floods glofs in greenland might also have megaflood type attributes given the enormous lake volumes drained we therefore here present the first review of glacier outburst floods in greenland sites isvand russell glacier kuannersuit glacier lake tininnilik two unnamed lakes near amitsulooq ice cap and iluliallup tasersua base camp lake lake hullett qorlortorssup tasia imaersartoq tordenso north midternaes and an outlet glacier of the a p olsen ice cap overall megaflood type landscape impacts in iceland tend to be best preserved and most easily identified inland although there has also been extensive offshore sedimentation there are very few reported impacts of glacier outburst floods in greenland in greenland ice dam failure causes frequent flooding compared to the volcanically triggered floods in iceland and this combined with the proximity of the greenland glacier lakes to the coast means that most proglacial channels in greenland are flood hardened and most landscape impact is likely to be offshore in estuaries and fjords future floods with megaflood type attributes will occur in iceland induced by volcanic activity in greenland they will be induced by extreme weather and rapid ice melt any potential landscape impact of these future floods remains open to question

glacial geomorphology modeling processes and landforms abstract the primary goal of glacial geomorphology is to provide physically based explanations of the past present and future impacts of glaciers and ice sheets on landform and landscape development to achieve this requires the integration of studies of landform with studies of the processes responsible for form development over a wide range of spatial and temporal scales during the twentieth century significant improvements in approaches to recognizing and describing glacial landforms have been matched by impressive advances in understanding and modeling ice flow and glacial erosion and deposition processes at present process models are being tested explicitly in terms of predicting the development of known forms which also provides new insight into the controls on form development evaluations of the implications of deformable beds for process and form development are also being attempted finally we are reassessing long held beliefs about the significance of glacial action in landform development and sediment production as we head towards the twenty first century glacial geomorphology will advance through the use of three dimensional numerical models that include ice flow basal sliding with explicit consideration of deformable beds erosion and deposition processes and underlying material characteristics these models will be used to address form evolution and test process models and will include both the temporal and spatial aspects of form development space based landform recognition as well as the challenges presented by the concerns of global change will place heightened emphasis on large scale problems which will include reexamination of the basic significance of glacial versus nonglacial action in landform development and sediment production

linking coarse silt production in asian sand deserts and quaternary accretion of the chinese loess plateau the chinese loess plateau clp is a large spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the east asian monsoon many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions although spatial and temporal variations in the grain sizes of clp sediments are fundamental to this effort controversy over the origin of the dominant coarse quartz silt has limited interpretations reexamination of the spatial pattern of grain size distribution across the clp and a field scale experiment conducted in the gobi desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal mu us tengger and badain jaran sandy deserts our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in central asia and identify this process as the most consistent with the well recognized systematic northwest southeast depositional pattern of the clp we suggest that only abraded coarse quartz grains transported short distances by long term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau these results decouple the production and transport of coarse silt and finer silt and clay particles which have a more distant and wider provenance changing the constraints on previous paleoclimatic reconstructions

variation of soil magnetism across the russian steppe its significance for use of soil magnetism as a palaeorainfall proxy abstract modern soils across the chinese loess plateau exhibit strong but disputed correlation between their pedogenic magnetic content and annual rainfall a soil magnetism rainfall transfer function could provide a quantitative proxy of quaternary rainfall for this region however some argue that magnetic dilution through spatially varying fluxes of weakly magnetic dust controls the soil magnetic properties here we test the soil magnetism rainfall couple by examining 22 russian steppe soils free of present dust accumulation across a climatic transect from the semi arid caspian region to the more humid caucasus the soils display systematic increases in topsoil ferrimagnetic concentrations with the exception of climate and its co variant vegetation soil forming factors are essentially constant across this stable area hence the soil magnetic variations dominantly reflect climate and from statistical analysis principally rainfall further the russian steppe magnetic rainfall relationship matches that observed for the chinese loess plateau these independent data thus substantiate the soil magnetism rainfall climofunction and by inference eliminate dust dilution as a significant magnetic factor

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

rainfall dependent transformations of iron oxides in a tropical saprolite transect of hainan island south china spectral and magnetic measurements 1 the iron oxide content of soils and sediments controlled by weathering and pedogenesis is generally considered a reasonable indicator of climate previous studies in temperate zones have established a positive correlation in aerobic soils between ferrimagnets and low to moderate rainfall the correlation seems to be reversed under extreme climates with high rainfall here we present a transect of saprolitic soils from hainan island south china with high rainfall 1440 2020 mm yr little temperature variation 23 24 c and extreme weathering along this transect we observed that both hematite concentration and magnetic susceptibility decrease with increasing rainfall whereas goethite concentration displays a large increase however there is no systematic trend in the total amount of iron oxides related to chemical weathering intensity along the transect goethite is the favored mineral phase of iron oxide with increasing rainfall and accumulates at the expense of hematite and maghemite through the dominance of rainfall driven processes these pedogenic processes coincide with the fundamentals of previous nonmonotonic models of hematite magnetic susceptibility and rainfall control of an inflection point this study also verifies a common genetic relationship between hematite and pedogenic ferrimagnets across a wide climate range a conceptual model considering both rainfall and temperature is proposed to help interpret the mechanism of ferrimagnet formation and changes in the rainfall inflection point

from dust to dust quaternary wind erosion of the mu us desert and loess plateau china the ordos basin of china encompasses the mu us desert in the northwest and the chinese loess plateau to the south and east the boundary between the mostly internally drained mu us desert and fluvially incised loess plateau is an erosional escarpment up to 400 m in relief composed of quaternary loess linear ridges with lengths of 10 2 10 3 m are formed in cretaceous quaternary strata throughout the basin ridge orientations are generally parallel to near surface wind vectors in the ordos basin during modern winter and spring dust storms our observations suggest that the loess plateau previously extended farther to the north and west of its modern windward escarpment margin and has been partially reworked by eolian processes the linear topography mu us desert internal drainage and escarpment retreat are all attributed to wind erosion the aerial extent of which expanded southeastward in china in response to quaternary amplification of northern hemisphere glaciation

isotopic record of palaeodiet of a 7 4 ma hipparionine fauna from the central loess plateau northern china palaeo ecological and palaeo climatic implications abstract ecological shifts from c3 to c4 vegetation took place in many parts of the world around 7 5 5 ma in response to global climate change previous evidences from pollen paleosol isotope and faunal have suggested that the expansion of c4 vegetation also occurred in the central chinese loess plateau clp at 7 4 ma which however is incompatible with palaeoclimate evidence from the clp of cold and dry conditions during the late miocene in this study stable oxygen 18o and carbon 13c isotope ratios preserved in tooth enamel from hipparionine were analyzed to elucidate the late miocene 7 4 ma palaeoecology of the central clp the enamel 13c values indicated a diet comprised entirely of c3 plants consistent with the c3 steppe inferred from the faunal composition for the western district of the neogene palaeozoogeographical boundary of northern china the 18o values were indicative of a mild continental climate with late miocene seasonality that is not as pronounced as the modern steppe environment of mongolia the local landscape was most likely dominated by c3 steppe which belonged to the western district of the neogene palaeozoogeographical boundary of northern china comparison of results presented here and with published records from other localities in this region such as the linxia basin yushe and central inner mongolia suggests a veer of the east asian summer monsoon easm since 7 5 ma

stable carbon and oxygen isotopic evidence for late cenozoic environmental change in northern china abstract stable carbon and oxygen isotope ratios of 311 enamel samples from a diverse group of herbivorous mammals including equidae rhinocerotidae bovidae rodentia and ochotonidaewere were analyzed in order to reconstruct the late cenozoic history of vegetation and environmental change in the yushe basin in north china the 13c values of bulk and serial enamel samples from large mammals show a wide range of variation from 13 3 to 1 4 with a mean of 7 4 3 5 n 294 this indicates that large herbivorous mammals in the area had a variety of diets since 6 5 ma ranging from pure c3 to mixed c3 c4 and pure c4 diets in contrast the 13c values of small mammals vary from 11 9 to 7 6 with a mean of 9 7 1 1 n 17 indicating that rodents and ochotonids were feeding mostly on c3 plants variations in 13c values within and between species reflect the variations in the habitat and the vegetation consumed by the animals in general horses had higher amounts of c4 grasses in their diets than other contemporary taxa such as bovids rhinos rodents and deer suggesting that horses exploited more open habitats such as grasslands while deer rhinos and rodents may have preferred more c3 vegetation which is more indicative of forested environments the carbon isotope data show that c4 grasses have been an important component of horses diets and of local ecosystems since 6 5 ma confirming that the late miocene c4 expansion occurred in north china as it did in africa indian subcontinent and the americas this supports a global factor as a main driver of the late miocene c4 expansion the combined carbon and oxygen isotope data reveal major shifts in climate to drier and or warmer conditions after 5 8 4 1 3 3 and 2 5 ma and significant shifts to relatively wetter and or cooler conditions after 6 4 5 3 5 ma the shifts to drier and or warmer climate after 5 8 ma and 2 5 ma coincide with two major fauna turnover events intra tooth 13c and 18o values are negatively correlated within individual modern teeth and some fossil teeth displaying the characteristic pattern of the summer monsoon regime and confirming a strong monsoon influence in the area since at least the early pliocene the data also suggest that the c4 abundance in the area has fluctuated over the past 6 5 ma in response to changes in climate with more c4 grasses during warmer and or drier periods and a reduced c4 component at cooler and or wetter times

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

rate of solar insolation change and the glacial interglacial transition 1 climate changes are driven largely by variations in the distribution of solar insolation associated with changes in the earth s orbital parameters here we define the rate of solar insolation change rsic as a parameter to evaluate and quantify solar heating changes through time we propose that rsic may control the timing of transitions between warm and cold periods through its control on the rate of climate changes specifically the glacial interglacial transitions took place when the 65 n july insolation experienced the most rapid changes interglacials start with a maximum positive rsic and end with a maximum negative risc the rsic curve thus provides a new astronomically tuned method for dating interglacials the 65 n july risc curves average a 4 7 ky lead compared to ice sheet changes as indicated by bassinot et al 1994 for the last 0 9 ma possibly implying a more rapid response of monsoonal climate to the insolation heating

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

new insights into magnetic enhancement mechanism in chinese paleosols article i nfo magneticsusceptibilityof chineseloess paleosolsequenceshasbeenextensivelyusedasareliablepaleoclimatic proxy for reconstruction of the asian summer monsoon system and its enhancement is usually attributed to neoformation of fine grained ferrimagnetic particles via pedogenesis but there is little understanding of either the formation process of such magnetic particles or their actual form and grain sizes to investigate these problems scanning electron microscope observations were conducted on magnetic extracts from pristine loess and strongly pedogenicpaleosol samples from xifeng onthe chineseloess plateau both magneticextracts commonly contained coarse grained detrital magnetite with grain size ranging from a few mt o several tens of m however the magnetic extract from the mature paleosol sample additionally included coarse silicate parti cles with ultrafine ferrimagnetic inclusions while that from the pristine loess sample did not the size of the ferrimagnetic inclusions mainly ranged from tens to hundreds of nanometers the temperature dependent susceptibility and hysteresis loops of the paleosol sample combined with the stratigraphic variations of rock magnetic parameters showed that the pedogenic maghemite inclusions should be a potential contributor to magnetic enhancements in chinese paleosols the fine grained ferrimagnetic inclusions have been pedogenically formed by weathering of coarse grained fe bearing silicate minerals our proposed magnetic enhancement mechanism is consistent with the accepted rock magnetic result that magnetic enhancement in chinese paleosols is caused by pedogenic maghemite grains in superparamagnetic and single domain size regions the presence of ultrafine ferrimagnetic grains as inclusions within coarse silicate particles is also consis tent with han and jiang s 1999 significant experimental result that magnetic enhancement in chinese paleosols is mainly contributed by the 0 5 m sediment fractions

the verification of millennial scale monsoon water vapor transport channel in northwest china summary long term changes of the asian summer monsoon water vapor transport play a pivotal role in the variability of monsoon precipitation paleo climate simulations have shown that there is an important monsoon vapor transport channel in western china previous studies mostly focused on the correlation between monsoon precipitation and intensity little research has been done on the verification of the water vapor channel compared with speleothem and lacustrine systems the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor in this study we used carbonate 18 o and organic matter 13 c of the surface eolian sediments from the piedmont of the northern qilian mountains to verify the monsoon water vapor on the holocene millennial scale two surface sedimentary sections were selected to study paleo monsoon water vapor transport proxy data including carbonate 18 o and organic matter 13 c of surface eolian sediments as well as total organic matter and carbonate content were obtained from the two eolian sections we also synthesized transient simulations of the ccsm3 and the kiel climate models the pmip 3 0 project and trace isotopic simulations were also compared with the reconstructed monsoon water vapor transport our findings indicate that the strength of the holocene asian summer monsoon is consistent with the water vapor transport in western china that has significant impacts to long term monsoon precipitation in northern china this study verifies a significant millennial scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern qinghai tibet plateau

a new cycle of jokulhlaups at russell glacier kangerlussuaq west greenland jokulhlaups in 2007 and 2008 from an ice dammed lake at the northern margin of russell glacier west greenland marked the onset of a renewed jokulhlaup cycle after 20 years of stability we present a record of successive ice dammed lake drainage events and associated ice margin dynamics spanning 25 years robust calculations of lake volumes and peak discharges are made based on intensive field surveys and utilizing high spatial resolution orthophotographs of the lake basin and ice margin these data enable identification of controls on the behaviour of the ice dammed lake and provide the first field based examination of controls on jokulhlaup magnitude and frequency for this system we find that russell glacier jokulhlaups have a much higher peak discharge than predicted by the clague mathews relationship which we attribute to an unusually short englacial subglacial routeway and the presence of a thin ice dam that permits incomplete sealing of jokulhlaup conduits between lake drainage events additionally we demonstrate that the passage of jokulhlaups through an interlinked system of proglacial bedrock basins produces significant attenuation of peak discharge downstream we highlight that improved understanding of jokulhlaup dynamics requires accurate information about ice dammed lake volume and ice proximal jokulhlaup discharge

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

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

controls on the sedimentology of an ice contact jokulhlaup dominated delta kangerlussuaq west greenland abstract this paper characterises the sedimentary impact of a glacial outburst flood or jokulhlaup on an ice contact delta topset at russell glacier kangerlussuaq west greenland rapid drainage of an ice dammed lake in july 1987 generated a jokulhlaup with a peak discharge of 1300 m3 s 1 which drained across a 500 m wide 200 m long delta top into a proglacial lake the delta topset comprises boulder clusters ice block obstacle marks with relief of up to 4 m and is graded to lake levels up to 6 m higher than those during typical non jokulhlaup conditions the delta top was dissected by the 1987 jokulhlaup causing a fan shaped extension of the delta front by 30 m surface grain size on the delta decreases rapidly away from the main flood flow direction reflecting rapid downstream reduction in sediment transport capacity the 1987 jokulhlaup was predominantly fluidal and turbulent and had peak stream powers of 2846 w m 2 proximally and

investigating soil magnetic properties with pedogenic variation along a precipitation gradient in loess derived soils of the golestan province northern iran abstract in the golestan province in northern iran extensive loess deposits and widespread loess derived soils crop out while a strong precipitation gradient 200 700 mm per year from north to south is characteristic temperature differences are negligible 17 18 c per year recently many studies on loess derived palaeosols and modern soils from this region were published however in these publications only limited information on the magnetic properties of loess and loess derived soils is given nor the potential of these properties to be applied as proxies for palaeoclimate reconstruction in order to study soil magnetic properties along the precipitation gradient in the golestan province six pedons of modern soils were selected the physicochemical properties the clay mineralogy and magnetic parameters of soil samples were analysed susceptibility measurements 20 2 130 77 10 8 m3kg 1 arm susceptibility values 0 00489 0 068 m3kg 1 irm values 0 0027 0 0105 am2kg 1 and hysteresis measurements provide significant evidences for an increase of the content of fine grained ferromagnetic minerals with increasing mean annual precipitation simultaneously the amount of sp sized particles increase magnetite maghemite and hematite are the major magnetic minerals in the studied samples whereby magnetite seems to be dominant in the soils of the loess plateau of northern iran by presenting data from this region of the northern iran for the first time another example is provided for the application of magnetic properties as proxies for the reconstruction of the paleoclimate the results are compared to data of the chinese loess plateau the russian steppe and loessic soils from the midwestern united state with similar relations of pedogenic susceptibility and map

rapid identification of dolomite using a fourier transform infrared spectrophotometer ftir a fast method for identifying heinrich events in iodp site u1308 this study demonstrates that fourier transform infrared spectrophotometry ftir provides a quick and relatively inexpensive method for identifying and quantifying dolomite in deep marine sediments ftir is used to determine concentrations of dolomite in the top 29 m of sediments recovered at iodp site u1308 some of these dolomite peaks can be reliably correlated with heinrich events h1 through h6 thus ftir appears to provide a fast and reliable method for identifying heinrich events in deep sea sediments

the hex experiment determination of the neutral wind field from 120 to 185 km altitude near a stable premidnight auroral arc by triangulating the drift of rocket deployed chemical trails 1 on 25 march 2003 horizontal e region experiment hex released trimethyl aluminum trails from two rockets launched northward from poker flat research range near fairbanks to map the vertical wind field near a stable premidnight auroral arc system they deployed three trails of trimethyl aluminum chemical puffs whose subsequent motion traced the prevailing wind field this motion was determined using triangulation from four ground observation sites position and speed accuracies were estimated to be 1 km and a few meters per second respectively the first rocket followed a novel flat trajectory it released a nearly horizontal trail of length 200 km at an average altitude of 145 km the second rocket was launched 19 min later and released two trails between 125 and 175 km altitude along a conventional steep trajectory all puffs between 130 and 175 km altitude drifted geomagnetic westward almost exactly parallel to the aurora from prior observations and modeling we had expected to observe convective upwelling near the arcs we did not vertical winds were essentially downward throughout the horizontal trail with speeds between 0 and 20 m s 1 although an abatement of downward flow was observed 40 km equatorward of the arcs these data alone do not establish a causal relationship between the abatement and the arcs vertical speeds of 20 m s 1 are relatively modest however because the observed wind field would entrain air parcels in flow parallel to the arc system even vertical speeds around 15 m s 1 could displace individual air parcels by several scale heights if they occurred all along the arcs

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

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

a comparison of two recent jokulhlaups from an ice dammed lake sondre stromfjord west greenland the hydro graphs of two jokulhl aups resulting from the sudden drainage of an ice d ammed lake in west greenland in 1984 and 1987 are compared the first flood had a similar peak discharge to the second but drained only two thi rds of the total volume of the 1987 event which amounted to 32 36 x 106 m3 in 36 h calcula tions based on the lake refill time suggest that it drains every 2 3 years but that peak flows may be variable from flood to flood the timing of the joku lhlaups in relation to the melt season may reflect variations of water pressure within the subglacial drainage networks and changes in the

winds in the high latitude lower thermosphere dependence on the interplanetary magnetic field 1 wind observations in the summertime lower thermosphere at high southern latitudes measured by the wind imaging interferometer windii on the upper atmosphere research satellite are statistically analyzed in magnetic coordinates and correlated with the interplanetary magnetic field imf to determine influences of imf dependent ionospheric convection on the winds effects are clearly detectable down to 105 km altitude above 125 km the wind patterns show considerable similarity with ionospheric convection patterns and the speed of the averaged neutral wind in the polar cap often exceeds 300 m s the correlation between the imf bz component and the diurnal harmonic of the winds is generally best when the imf is averaged over the preceding 1 4 5 hours the magnetic zonal mean zonal wind below 120 km correlates best with the imf by component when the latter is averaged over approximately the preceding 20 hours the wind has a significantly stronger rotational than divergent component around and above 120 km a dusk side anticyclonic wind vortex is prominent consistent with earlier findings around 140 km and higher the dusk side vortex intensifies for negative bz but around 120 km it is the dawn side cyclonic vortex that responds more strongly to bz variations the dependence of the wind on the imf is nonlinear especially with respect to imf bz for positive bz the difference winds are largely confined to the polar cap while for negative bz the difference winds extend to subauroral latitudes a significant correlation between the diurnal bz dependent neutral and convection velocity components exists above 108 km when the convection velocity is suitably rotated in magnetic local time mlt with respect to the wind the rotation that maximizes the correlation ranges from 1 5 hours at 130 km wind preceding convection to nearly 6 hours at 108 km wind lagging convection the rotated diurnal bz dependent wind pattern projects onto the diurnal bz dependent ionospheric convection pattern with about 60 the amplitude of the latter above 125 km decreasing to about 17 at 108 km on timescales of 20 hours a by dependent magnetic zonal mean zonal wind generally exists with maximum wind speeds at 80 magnetic latitude typically 10 m s at 105 km increasing to about 60 m s at 123 km and 80 m s at 200 km in the southern hemisphere the wind is cyclonic when the time averaged by is positive and anticyclonic when by is negative the wind direction is expected to be opposite in the northern hemisphere

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

a strengthened east asian summer monsoon during pliocene warmth evidence from red clay sediments at pianguan northern china abstract the pliocene epoch 5 3 2 6 ma is the most recent geological interval in which atmospheric co2 levels were similar to those of the present day 400 ppmv this epoch is therefore considered to be the best ancient analog for predicting a future anthropogenic greenhouse world in order to determine the response of the east asian summer monsoon easm rainbelt during pliocene warmth a 71 9 m thick aeolian red clay sequence at pianguan was investigated rock magnetic experiments suggest that magnetite of pseudo single domain size is the dominant remanence carrier in the red clay sequence magnetostratigraphic data constrained by lithostratigraphy show that the polarity zones of the red clay section correlate with those between subchrons c2an 2r and c3an 2n of the geomagnetic polarity time scale gpts yielding an age range of 6 9 2 9 ma the red clay deposits exhibit enhanced weathering intensity over two time intervals namely 5 23 4 3 ma and 3 7 2 9 ma as evidenced by their well developed pedogenic characteristics as well as their high free to total fe2o3 ratios and high redness a values which in turn indicate an increased summer monsoon intensity during most of the pliocene furthermore the pedogenic characteristics of the well weathered pliocene soils were compared with those of paleosol unit s5 one of the best developed soil units found in pleistocene loess from the yulin luochuan and lantian sections which constitute a north south transect across the chinese loess plateau clp the pliocene soils at pianguan show a pedogenic development similar to the s5 0 5 ma at luochuan in the central plateau which is located some 3 7 latitude south of pianguan but this development is much stronger than that observed at yulin in the north and weaker than that seen at lantian in the south this may imply a more northerly penetration 400 km of the monsoon rainbelt during pliocene warmth compared with the pleistocene interglacial period 0 5 ma ago supporting the prediction that the easm rainbelt shifts northward in a warmer world in addition our results show that pliocene warmth was unlikely to have been characterized by a permanent el nino like state but was possibly influenced by a la nina like state

simulating magnetic susceptibility profiles in loess as an aid in quantifying rates of dust deposition and pedogenic development abstract magnetic susceptibility profiles z in loess sequences reflect a combination of two climatically modulated processes dust deposition and pedogenic development prominent soils with high values for example likely reflect periods of slow dust deposition and warm wet conditions favorable for rapid chemical weathering to refine our understanding of the climate records contained in loess we develop a numerical model as a tool for exploring quantitatively the integrated record of the temporal variation in rates of loess aggradation and soil development contained in profiles in our model the aggrading loess is pedogenically altered in a reactive zone near the ground surface the strength of the signal is dictated by both the depth dependent intensity of pedogenic processes and the rate of dust accumulation which dictates the total time a loess parcel spends in the near surface reactive zone the model can accommodate both pedogenic production of magnetically susceptible minerals and arrival of magnetically susceptible grains as eolian dust to explore the model performance and develop a sense of time and length scales implicit in profiles we first examine simple synthetic cases with idealized steady and cyclic climatic forcing reported profiles in three chinese loess sequences at varying distances from the western china dust source are then modeled in two illustrative ways i by imposing a specific dust deposition rate history that is proportional to the dust accumulation rate history reported from western pacific deep sea cores allowing the time variation of pedogenic rates to be calculated directly from profiles and ii by imposing both dust accumulation and pedogenic rate histories that are independently scaled by the deep sea 18 o history which reflects global climate cycles to which regional climate forcing is linked we find that the zone of pedogenic activity is roughly 0 5 1 0 m thick both deposition rate and pedogenic intensity have varied dramatically over the last 140 000 yr the age structure of the luochuan loess sequence is best fit by driving the model with the 18 o record and environmental conditions must have been anomalously favorable for pedogenesis during isotope stage 3 at all three sites finally we advocate the assembly of a variety of data types at a suite of sites within any loess field that taken together will better constrain the temporal and spatial patterns of climatically modulated deposition and pedogenic processes

characterising chinese loess stratigraphy and past monsoon variation using field spectroscopy abstract the loess record in china constitutes one of the most important archives of past environmental change and specifically the east asian monsoon system changes in summer monsoon driven pedogenesis are commonly inferred from magnetic susceptibility of loess however there is still controversy as to the signal s origin and the uncertain effects of sediment accumulation rates this is linked to a wider problem that is emerging from recent work that of the relative importance on proxy records such as magnetic susceptibility of both regional climate patterns i e the monsoon and local site specific influences particularly modulated through site specific sedimentation rate at present this is poorly constrained and significantly increases the degree of uncertainty over the wider scale applicability of climate reconstructions from individual sites to resolve this issue for sub orbital timescales a rapidly deployable technique is needed that can be used to test multiple sites and differentiate between local and regional signals this research develops the first use of full spectrum reflectance spectroscopy in studying loess in the field at one site on the south of the loess plateau and utilises statistical analyses to compare such data with magnetic susceptibility records establishment of loess reflectance as a proxy for climate variability will potentially allow extension of the technique from point measurements to an imaging system and so enable the compilation of large data sets in order to investigate lateral facies variations in loess profiles this may allow the extraction of a broad scale climate record field spectra were obtained from 350 to 1100 nm with red edge reflectance spectra indicating the presence of iron oxides previously demonstrated to be indicators of pedogenesis through laboratory measurements an off the shelf camera was also tested with visible wavelength spectra being useful for rapid but general profile characterisation in order to mitigate the effects of bidirectional reflectance distribution function a potential problem in field measurements further laboratory measurement was made of powdered samples 400 2400 nm absorption features indicative of montmorillonite and illite muscovite were noted and stepwise regression modelling utilising absolute reflectance first derivative spectra and continuum removed spectra indicated strong predictive relationships with magnetic susceptibility particularly against the presence of montmorillonite the abundance of such clay minerals could be used to infer weathering rates and hence be used as a proxy for pedogensis reconstructions for the studied site are presented and demonstrate the potential power of loess reflectance environmental reconstruction

sediment magnetic signature of climate in modern loessic soils from the great plains our magnetic analysis of 40 modern loessic soil profiles from the midwestern united states shows that the upper soil horizons of all sites are characterized by an increase in the concentration of fine grained do0 1mm ferrimagnetic minerals magnetite and or maghemite our sites were selected from stable upland positions along a precipitation gradient extending from sw nebraska mean ann precip o500 mm yr to central missouri mean ann precip 41000 mm yr changes in magnetic remanence parameters irm arm and magnetic susceptibility w between soil and parent material vary systematically along the transect and are likely to reflect changes in source area and transport distance magnetic enhancement is calculated for several magnetic parameters by taking the ratio menhanced mparent material where m stands for either arm irm or w our analyses show that magnetic enhancement of modern soils based on irm and w correlates with changes in mean annual precipitation the best correlation however is observed when arm is used as a proxy of magnetic enhancement which might reflect the bias of arm towards small single domain grains of likely pedogenic origin our study shows that magnetic soil properties in combination with non magnetic proxies such as solum depth b horizon color depth to carbonates or other weathering indices have the potential to yield reliable reconstructions of paleoclimate in parts of the great plains where well preserved loessic paleosols exist

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

glacier advance ice marginal lakes and routing of meltwater and sediment russell glacier greenland the ice sheet margin at russell glacier west greenland advanced 7 m a 1 between 1968 and 1999 as the ice advanced over moraine ridges small changes in position caused major changes in the routing of proglacial water and sediment these included changes in the distribution of ice marginal lakes in the periodic drainage of ice dammed lakes in the routing and sediment content of meltwater draining into the proglacial zone and in the release of sediment from the moraines by erosion and mass movements proglacial hydrology and sediment flux appear to be controlled not simply by glacier mass balance but by evolving ice marginal geomorphology which must be accounted for in palaeoenvironmental interpretation of proglacial sediments

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

dwm07 global empirical model of upper thermospheric storm induced disturbance winds 1 we present a global empirical disturbance wind model dwm07 that represents average geospace storm induced perturbations of upper thermospheric 200 600 km altitude neutral winds dwm07 depends on the following three parameters magnetic latitude magnetic local time and the 3 h kp geomagnetic activity index the latitude and local time dependences are represented by vector spherical harmonic functions up to degree 10 in latitude and order 3 in local time and the kp dependence is represented by quadratic b splines dwm07 is the storm time thermospheric component of the new horizontal wind model hwm07 which is described in a companion paper dwm07 is based on data from the wind imaging interferometer on board the upper atmosphere research satellite the wind and temperature spectrometer on board dynamics explorer 2 and seven ground based fabry perot interferometers the perturbation winds derived from the three data sets are in good mutual agreement under most conditions and the model captures most of the climatological variations evident in the data

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

carbon reservoir changes preceded major ice sheet expansion at the mid brunhes event the beginning of the mid brunhes event ca 430 ka coincided with the largest amplitude change in d 18 o in the global ocean over the past 6 m y this large d 18 o change recorded a major ice sheet expansion that cannot be explained by small changes in orbital forcing our recent studies at ocean drilling program site 1143 from the south china sea show that this large d 18 o change was preceded by a significant negative d 13 c shift a global survey of long deep sea records has revealed periodic d 13 cmax episodes i e maximum positive values of d 13 c and both major ice sheet expansion events in the pleistocene the mid brunhes event and the middle pleistocene revolution were preceded by d 13 cmax ep isodes followed by negative d 13 c shifts this new finding suggests that disturbance in carbon reservoirs leads to major growth of ice sheet size and challenges the prevalent concept of arctic control of glacial cycles because earth is now passing again through a d 13 cmax episode it is crucial to understand the causal relationship between the successive d 13 c changes and ice sheet growth events

auroral zone thermospheric dynamics 1 averages forty four nights of thermospheric neutral wind and temperature measurements were obtained with a ground based fabry perot spectrometer at college alaska 65 invariant latitude mostly during high to moderate levels of solar activity the spectrometer scanned the o i 15 867 k 6300 a emission line yielding line profile measurements that originate from an altitude range between 170 and 280 km the observed average wind direction is to the northwest in the early evening changing to the south near midnight and then to the southeast in the morning the overall wind pattern generally persists but the wind speed increases with increasing geomagnetic activity a change in the zonal wind direction occurs earlier in magnetic local time with increasing magnetic activity the meridional wind pattern also shifts equatorward with the auroral oval during increasing magnetic activity consequently the average wind pattern in the north during low geomagnetic activity is rather similar to the moderate activity average in the south and the moderate geomagnetic activity average wind pattern in the north is similar to the high geomagnetic activity average in the south the observed average thermospheric temperature is found to be governed by geomagnetic activity and the previous day s 10 7 cm solar flux

dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle

quantitative relationships between magnetic enhancement of modern soils and climatic variables over the chinese loess plateau environmental magnetism has been widely employed to reconstruct past climate changes on the chinese loess plateau clp and several climofunctions based on the magnetic properties of loess have been developed however systematic investigation of the quantitative relationship between topsoil magnetic enhancement and modern climate remains uncommon in this study we obtained surface soil samples from 257 sites over the clp and adjacent regions from this set we used 180 samples from sites unaffected by potential contamination to investigate the relationship between the commonly measured magnetic properties of magnetic susceptibility and magnetic remanence and modern climatic variables the spatial distribution of the results demonstrates a strong nw se gradient of the magnetic enhancement of surface soils the results of more detailed magnetic parameters indicate that pedogenic viscous superparamagnetic and stable single domain particles are mainly responsible for the magnetic enhancement of the soils in the studied region and that the magnetic grain size distribution of the ferrimagnetic components of pedogenic origin remains almost constant independent of pedogenic intensity the uniform mechanism of magnetic enhancement mainly linked with the concentration of the pedogenic components rather than with variations in magnetic grain size decreases the level of ambiguity in climate reconstructions based on magnetic measurements of chinese loess statistical analyses including correlation principal component analysis pca and multiple regression analysis suggest that annual rainfall rather than temperature exerts the dominant effect on soil magnetic enhancement finally we used the results to develop several transfer functions to reconstruct mean annual precipitation map transfer functions based on frequency dependent susceptibility fd and anhysteretic remanent magnetization arm provide the most reliable estimates of map this study significantly improves the understanding of the relationship between soil magnetic properties and climate

carbonate leaching processes in the red clay formation chinese loess plateau fingerprinting east asian summer monsoon variability during the late miocene and pliocene 1 high resolution variations in carbonate minerals from the jiaxian red clay section located at the northern limit of the present east asian summer monsoon easm on chinese loess plateau were quantified using fourier transform infrared spectroscopy we analyzed a large quantity of sediments dated from the late miocene to pliocene 8 2 2 6 ma the carbonates in this interval show high frequency variations alternating between leached and calcareous horizons the low carbonate contents and high values of magnetic susceptibility and high rb sr ratios were found in the leached zones a pattern that is consistent with that observed in the overlying quaternary loess paleosol sequences this pattern suggests that east asian monsoon eam rainwater enhanced leaching and accumulation processes of carbonate minerals in the red clay formation in a way similar to the loess paleosol sequence seven alternating leached and calcareous zones are identified suggesting oscillations of the easm and east asian winter monsoon intervals the calcareous zones were also found to have high zr rb ratio these indications of shifts from a strong easm to east asian winter monsoon dominance correlate well with the cooling transition indicated by deep sea 18o isotopes this evidence suggests that the eam was active during the late miocene and pliocene and was similar to the quaternary monsoon the presence of a strong eam during the pliocene warm period also raises questions about the hypothesis that past and future warm climate conditions could produce a permanent el nino like state

seasonal dependence of northern high latitude upper thermospheric winds a quiet time climatological study based on ground based and space based measurements this paper investigates the large scale seasonal dependence of geomagnetically quiet time northern high latitude f region thermospheric winds by combining extensive observations from eight ground based optical remote sensing and three space based optical remote sensing and in situ instruments to provide a comprehensive picture of the wind morphology data are assimilated into a seasonal empirical vector wind model as a function of season latitude and local time in magnetic coordinates the model accurately represents the behavior of the constituent data sets there is good general agreement among the various data sets but there are some major offsets between goce and the other data sets especially on the duskside the assimilated wind patterns exhibit a strong and large duskside anticyclonic circulation cell sharp latitudinal gradients in the duskside auroral zone strong antisunward winds in the polar cap and a weaker tendency toward a dawnside cyclonic circulation cell the high latitude wind system shows a progressive intensification of wind patterns from winter to equinox to summer the latitudinal extent of the duskside circulation cell does not depend strongly on season zonal winds show a mainly diurnal variation two extrema around polar and middle latitudes and semidiurnal variation four extrema at auroral latitudes meridional winds are primarily diurnal at all high latitudes the strength of zonal winds channeling through the auroral zone on the duskside is strongest in the summer season the vorticity of the wind pattern increases from winter to summer whereas divergence is maximum in equinox in all three seasons divergence is weaker than vorticity

strengthened east asian summer monsoons during a period of high latitude warmth isotopic evidence from mio pliocene fossil mammals and soil carbonates from northern china the east asian monsoons have fluctuated in concert with high latitude warmth during the past several hundred thousand years with humid summer monsoon dominant climates characterizing warm intervals including interglacials and interstadials and arid winter monsoon dominant climates characterizing cool intervals including glacials and stadials of the states comprising the mid pleistocene to recent climatic regime interglacials are most similar in terms of high latitude ice volumes and temperatures to those extant during the late miocene and early pliocene thus an important question is whether mio pliocene climates in northern china were analogous to a hypothetical prolonged interglacial state with increased summer monsoon precipitation and expansion of forest and steppe environments at the expense of desert environments we utilize new and previously published carbon isotopic data from fossil teeth and soil carbonates to place constraints on paleovegetation distributions and to help infer the behavior of the monsoon system between 7 and 4 ma we find that plants using the c 4 photosynthetic pathway which today are largely grasses found in regions with warm season precipitation were present in northern china by late miocene time demonstrating that the c 4 expansion in china was not significantly delayed compared to the global c4 event during the late miocene early pliocene interval soil carbonate and tooth enamel 13 c data indicate 1 that nearly pure c 3 plant ecosystems existed in the southern chinese loess plateau clp and therefore ecosystems there were dominated by woody dicot herbaceous dicot or cool season grass vegetation or a combination of these and 2 that the clp was characterized by a pattern of northward increasing c 4 vegetation and aridity utilizing a broadened conceptual model for interpreting 13 c data and citing independent faunal floral and lithostratgraphic data we suggest that these patterns reflect northward expansion of forest and steppe ecosystems and relatively humid monsoon climates during the late miocene and early pliocene an important implication of this interpretation is that the forcing mechanism illuminated by the temporal correlation during the pleistocene between warm high latitudes and strong east asian summer monsoons is a robust feature of the eurasian tectonic climatic system that predates the plio pleistocene climatic reorganization