the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

role of orbital forcing in east asian monsoon climates during the last 350 kyr evidence from terrestrial and marine climate proxies from core rc14 99 proxy records of northeast asian precipitation marine pollen and northwest pacific sea surface temperatures marine fauna contain concentrations of variance frequency peaks coincident with those of orbital variations eccentricity obliquity and precession time series of these monitors of various components of the east asian monsoon system are coherent with changing solar insolation and climate boundary conditions ice volume snow cover albedo at 41 and 23 kyr frequencies winter sea surface temperature wsst maxima are in phase with global ice volume minima at all three milankovitch frequencies 100 41 and 23 kyr periods wsst maxima are also linearly related to summer insolation at 30 n lagging radiation maxima by 55 3 5 kyr across the precessional frequency band 23 kyr period our east asian monsoon rainfall indicator cryptomeria reaches highest values immediately following summer insolation maxima during periods of low ice volume interglacials across the eccentricity frequency band 100 kyr period cryptomeria maxima are in phase with ice volume minima at the higher frequency of orbital precession monsoon rainfall lags both summer radiation maxima 125 8 kyr and ice volume minima 60 3 8 kyr whereas much of the variation in northwest pacific wsst can be attributed to summer radiation forcing and changes in global climate mechanisms driving east asian monsoon precipitation are more complex involving other possibly internal factors

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

is the central arctic ocean a sediment starved basin abstract numerous short sediment cores have been retrieved from the central arctic ocean many of which have been assigned sedimentation rates on the order of mm ka implying that the arctic basin was starved of sediments during plio pleistocene times a review of both shorter term sedimentation rates through analysis of available sediment core data and longer term sedimentation rates through estimates of total sediment thickness and bedrock age suggests that cm ka scale rates are pervasive in the central arctic ocean this is not surprising considering the physiographic setting of the arctic ocean being a small land locked basin since its initial opening during early cretaceous times we thus conclude that the central arctic ocean has not been a sediment starved basin either during plio pleistocene times or during pre pliocene times rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of 2600 km from the northwestern amerasia basin to the northwestern eurasia basin via the lomonosov ridge using paleomagnetic biostratigraphic and cyclostratigraphic data

leaf wax lipids as paleovegetational and paleoenvironmental proxies for the chinese loess plateau over the last 170 kyr abstract high resolution records for long chain n alkane and n alkanol biomarkers have been obtained by extraction of sediments from the profiles of luochan 0 36 ka and xunyi 0 170 ka on the chinese loess plateau clp the two records are similar where they overlap over the last 36 ka at xunyi distributions of the n alkane and n alkanol homologues remain relatively constant over the full 170 kyr the n alkanes are characterized by high odd over even carbon number preference and predominance of the c31 n alkane whereas the n alkanols are dominated by even over odd carbon numbers and by the c28 n alkanol an alkane index a i c3l c29 c31 and an alkanol index alc i c30 c28 c30 are both positively related with magnetic susceptibility of the sediment with higher values during interglacials a lipid index l i averaging the normalized alkane and alkanol indices gives a measure of changing vegetation for palaeo environmental construction a further useful index is provided by the 13 c value of the most abundant n alkane c31 after adjustment for the calculated effect of the estimated atmospheric pco2 and precipitation the record of this index over the last 170 kyr which varies from 36 to 32 indicates that the vegetation on the clp has been mainly c3 plants and became even more so in the glacial periods especially mis 6 and 2 as the minor population of warm season grasses c4 favored in interglacial times declined when temperatures fell the lipid distributions and carbon isotope values are in general accord with the pollen and phytolith evidence recorded for the yuan areas of the clp in indicating steppe or meadow steppe vegetation with abundant cold season grasses c3 and some herbs bushes and trees especially in glacial times

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

late pliocene pleistocene changes in mass accumulation rates of eolian deposits on the central chinese loess plateau 1 late pliocene pleistocene changes in the mass accumulation rates mars of eolian deposits on the central chinese loess plateau clp are reconstructed from measured bulk sediment densities combined with sedimentation rates calculated for two loess red clay sequences the reconstructed mars demonstrate that over the past 3600 kyr distinct aridity humidity fluctuations occurred over glacial interglacial timescales and these were superimposed on a gradual long term drying trend comparisons of the clp mar record with the mar and 18o records for marine sediments suggest that the development of northern hemisphere ice sheets since the late pliocene has played a part in increasing the aridity of central asia in addition the phased uplift of the himalaya tibetan plateau evidently had a profound influence on the aridity of central asia this was mediated by variations in the east asian monsoonal circulation correlations among dust records from ice cores marine sediments and terrestrial loess over the last several glacial cycles provide compelling evidence that glacial periods are characterized by higher and more variable dust fluxes than interglacial intervals synchronous changes in the mar grain size and 18o records reveal dynamic linkages between asian interior aridity paleowind intensity and ice volume after the onset of major northern hemisphere glaciations

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

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

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

atmospheric dust loadings and their relationship to rapid oscillations of the asian winter monsoon climate two 250 kyr loess records abstract similar to records extracted from marine sediments paleoceanography 6 1991 349 rev geophys 32 1994 159 and ice cores nature 399 1999 429 estimates of dust inputs to the chinese loess plateau indicate that the dust fluxes during periods of extensive glaciation were higher than those in interglacial times catena 18 1991 125 quat res 41 1994 35 prior studies nature 375 1995 305 quat sci rev 18 1999 811 indicating that millennial scale oscillations of asian dust occurred during glacial times have raised questions about the conditions that govern the generation and transport of dust particularly those operating during the winter monsoon we present here atmospheric dust loadings reconstructed from two central loess plateau sections these extended our present day observations to cover the last two glacial cycles and thus provided a unique perspective on the relationships between asian dust and climate the reconstructed loadings indicate that higher and more variable dust concentrations occurred during glacials compared with interglacials and the high dust loadings frequently preceded decreases in winter sea surface temperature of the north pacific ocean during glacials a mechanism was proposed to explain how the thermal contrasts between the eurasian continent and the surrounding oceans induced by the high dust loadings could either trigger or modulate millennial scale variations in the winter monsoon climate and thus rapid transitions of glacial dust loadings

constraints on the pleistocene chronology of sediments from the lomonosov ridge 1 despite its importance in the global climate system age calibrated marine geologic records reflecting the evolution of glacial cycles through the pleistocene are largely absent from the central arctic ocean this is especially true for sediments older than 200 ka three sites cored during the integrated ocean drilling program s expedition 302 the arctic coring expedition acex provide a 27 m continuous sedimentary section from the lomonosov ridge in the central arctic ocean two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the cobb mountain subchron 1215 ka beyond 1215 ka two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted milankovitch frequencies these cyclic variations record glacial and interglacial modes of sediment deposition on the lomonosov ridge as evident in studies of ice rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model potential errors which largely arise from uncertainties in the nature of downhole paleomagnetic variability and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

paleomagnetic constraints on sedimentation ratesin the eastern arctic ocean abstract deep sea sediments recovered from six sites visited during the international arctic ocean expedition of 1991 were examined to determine sedimentation rates in the eastern arctic ocean basin the dearth of age diagnostic biogenic material in these sediments precludes the application of biostratigraphic methods but ages can be deduced using paleomagnetism in conjunction with measurements of radiocarbon and carbonate concentration although no one of these techniques gives an unambiguous determination of age the interpretation most consistent with these diverse data implies that sedimentation rates in the eastern arctic are in general a few centimeters per thousand years such estimates of sedimentation rate are an order of magnitude greater than those previously determined from many sediment cores taken from the canada basin however one site examined on the morris jesup rise shows a relatively low rate of sediment accumulation less than 0 6 cm 103yr suggesting that although higher than in the canada basin sedimentation rates in the eastern arctic can be highly variable

a shift in heavy and clay mineral provenance indicates a middle miocene onset of a perennial sea ice cover in the arctic ocean during the arctic coring expedition acex a 428 m thick sequence of upper cretaceous to quaternary sediments was penetrated the mineralogical composition of the upper 300 m of this sequence is presented here for the first time heavy and clay mineral associations indicate a major and consistent shift in provenance from the barents kara western laptev sea region characterized by presence of common clinopyroxene to the eastern laptev east siberian seas in the upper part of the section characterized by common hornblende amphibole sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the acex drill site if considering modern sea ice trajectories and velocities this shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the arctic ocean which occurred at about 13 ma thus suggesting a coeval freeze in the arctic and antarctic regions

optically stimulated luminescence dating supports central arctic ocean cm scale sedimentation rates 1 this paper presents new results from optically stimulated luminescence osl dating on a sediment core raised from the crest of the lomonosov ridge in the central arctic ocean there has been much debate about dating sediment cores from the central arctic ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast cm scale ka sedimentation rates were typical of arctic s pleistocene depositional mode on the basis of mainly paleomagnetic reversal stratigraphy many previous studies suggest mm scale ka sedimentation rates a common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the brunhes matuyama boundary at about 780 ka our osl dating results indicate that this assumption is not generally valid and that the first encountered negative inclination represents younger age excursions within the brunhes chron implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central arctic ocean our dating results furthermore corroborates a correlation of the uppermost 2 3 m of the lomonosov ridge cores to a well dated core located off the barents kara sea margin that in turn is correlated to cores in the fram strait valuable information on the paleoceanographical evolution in the arctic ocean from mis 6 to the holocene is given through this correlation of records from the central arctic ocean to records off the eurasian continental margin

spatial and temporal arctic ocean depositional regimes a key to the evolution of ice drift and current patterns sediment physical properties measured in cores from all the major ridges and plateaus in the central arctic ocean were studied in order to analyze the spatial and temporal consistency of sediment d

late quaternary records of the atmospheric input of eolian dust to the center of the chinese loess plateau abstract the concentrations of 15 elements and mineral grain size distributions were determined for late quaternary loess sediments from the chinese loess plateau particle size distributions of the loess were approximately log normal for each of three modes i e 0 04 to 1 m diameter 2 to 20 m and 20 to 200 m that integrate the transport and deposition of eolian dust the mass particle size distributions of typical crustal elements si ca fe ti k mn and v in paleosol and loess samples show patterns similar to those of mineral aerosols but higher concentrations occur in the submicrometer sediment particles absolute principal component analysis of the elemental data suggests that the loess can be described in terms of synsedimentary and postdepositional concentration and subvertical migration of caco3 and various elements through the deposit a variety of geochemical indicators in the loess are apparently sensitive to asian monsoon variations these include the mass ratio of course to fine particles the concentration ratios of certain trace elements the elemental fluxes associated with eolian dust and the bulk concentration of ca in the sediments

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

the ascraeus mons fan shaped deposit volcano ice interactions and the climatic implications of cold based tropical mountain glaciation abstract amazonian aged fan shaped deposits extending to the northwest of each of the tharsis montes in the tharsis region on mars have been interpreted to have originated from mass wasting volcanic tectonic and or glacial processes we use new data from mro mgs and odyssey to characterize these deposits building on recent evidence for cold based glacial activity at pavonis mons and arsia mons we interpret the smaller ascraeus fan shaped deposit to be of glacial origin our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat including 1 a ridged facies interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat 2 a knobby facies interpreted to represent vertical downwasting of the ice sheet and 3 complex ridges showing a cusp like structure we also see evidence of volcano ice interactions in the form of 1 an arcuate inward facing scarp interpreted to have formed by the chilling of lava flows against the glacial margin 2 a plateau feature interpreted to represent a subglacial eruption and 3 knobby facies superimposed on flat topped flows with leveed channels interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till we discuss the formation mechanisms of these morphologies during cold based glacial activity and concurrent volcanism on the basis of a mid to late amazonian age 250 380 ma established from crater size frequency distribution data we explore the climatic implications of recent glaciation at low latitudes on mars gcm results show that increased insolation to the poles at high obliquities 45 forces sublimation of polar ice which is transported to lower latitudes and deposited on the flanks of the tharsis montes we assess how local orographic effects the mass balance of the glacier and the position of equilibrium line altitudes all played a role in producing the observed geomorphologies in doing so we outline a glacial history for the evolution of the ascraeus mons fan shaped deposit and compare its initiation growth and demise with those of arsia mons and pavonis mons

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

glacial and interglacial patterns for asian dust transport abstract particle size distributions and depositional fluxes were investigated for present day asian dust and for the late quaternary loess palaeosol sequences from central china the regional scale transport of asian dust during interglacial stages is mainly attributable to non dust storm processes and is dominated by northwesterly surface winds conversely during glacial stages the impact of dust storms on the accumulation of loess is enhanced these regional effects are in contrast to the global dispersal of dust which is associated with transport by upper level westerly winds and is mainly the result of desert dust storms during both glacial and interglacial conditions temporal differences in the dust transport patterns to the loess plateau suggest that the variability in the coarse particle fraction 20 m during interglacial times is not directly attributable to the strong dust storms and dust fall events that have been linked to a strengthening of east asian winter monsoonal winds this is in contrast to the dust deposition rates which are strongly influenced by the monsoonal circulation

quaternary paleoceanography of the central arctic based on integrated ocean drilling program arctic coring expedition 302 foraminiferal assemblages the integrated ocean drilling program iodp arctic coring expedition acex hole 4c from the lomonosov ridge in the central arctic ocean recovered a continuous 18 m record of quaternary foraminifera yielding evidence for seasonally ice free interglacials during the matuyama progressive development of large glacials during the mid pleistocene transition mpt 1 2 0 9 ma and the onset of high amplitude 100 ka orbital cycles 500 ka foraminiferal preservation in sediments from the arctic is influenced by primary sea ice organic input and other environmental conditions and secondary factors syndepositional long term pore water dissolution taking these into account the acex 4c record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages mis 13 37 and although less precise dating is available for older sediments these trends appear to continue through the matuyama the mpt is characterized by nearly barren intervals during major glacials mis 12 16 and 22 24 and faunal turnover mis 12 24 abundant calcareous planktonic mainly neogloboquadrina pachyderma sin and benthic foraminifers occur mainly in interglacial intervals during the brunhes and very rarely in the matuyama a distinct faunal transition from calcareous to agglutinated foraminifers 200 300 ka in acex 4c is comparable to that found in arctic sediments from the lomonosov alpha and northwind ridges and the morris jesup rise down core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100 ka cycles pore water dissolution or both

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

plio pleistocene trends in ice rafted debris on the lomonosov ridge although more than 700 sediment cores exist from the arctic ocean the plio pleistocene evolution of the basin and its marginal seas remains virtually unknown this is largely due the shallow penetration of most of these records and difficulties associated with deriving chronologies for the recovered material the integrated ocean drilling program s iodp expedition 302 arctic coring expedition acex recovered 197 m of neogene quaternary sediment from the circumpolar regions of the lomonosov ridge as detailed analyses of this material emerge research is beginning to formulate a long term picture of paleoceanographic changes in the central arctic ocean this paper reviews the acex plio pleistocene age model identifies uncertainties and addresses ways in which these may be eliminated within the established stratigraphic framework a notable reduction in the abundance of ice rafted debris ird occurs in the early part of the pleistocene and persists until marine isotope stage 6 mis 6 therefore while global oceanographic proxies indicate the gradual growth of terrestrial ice sheets during this time ird delivery to the central arctic ocean remained comparatively low and stable within the resolution of existing data the pleistocene reduction in ird is synchronous with predicted changes in both the inflow of north atlantic and pacific waters which in modern times are known to exert a strong influence on sea ice stability

corrigendum to paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 years earth planet sci lett 252 2006 119 137

reinterpreting climate proxy records from late quaternary chinese loess a detailed osl investigation abstract numerous authors have utilised physical properties of chinese loess and red clay deposits to develop apparently detailed and continuous past climate records from the miocene into the holocene many of these studies have further suggested that the principal climatic agent responsible for the aeolian emplacement and diagenesis of chinese loess the east asian monsoon has fluctuated rapidly on millennial to sub millennial timescales in concert with dramatic changes in the north atlantic dansgaard oeschger cycles and heinrich events and the western pacific el nino southern oscillation much of this evidence is based on reconstructions and age models that are tied to assumptions concerning the nature of loess sedimentation and diagenesis for example the belief that loess sedimentation can be viewed as essentially continuous some authors have however cast doubt on these assumptions and suggest that the application of radiometric techniques may be required to determine their validity recent studies utilising optically stimulated luminescence osl methods have reinforced these doubts and here osl dates obtained at 10 cm intervals from three sites along a transect across the chinese loess plateau have been used in combination with climate proxy evidence to test the existing assumptions that underpin many palaeoclimatic reconstructions from loess in this way the first time continuous and independently dated late quaternary climate reconstruction is developed from loess the data indicate that sedimentation is episodic and that once emplaced loess is prone to pedogenic disturbance diagenetic modification and in some cases erosion the relationships between proxies and sedimentation rates are also assessed and climatic interpretations based on different age models compared the implications of these findings for reconstructions of climate from loess are explored and comparisons are made between the developed palaeoclimate records and evidence from ice and ocean cores this exercise also highlights important information concerning the relative influence of forcing mechanisms behind east asian monsoon change over the late quaternary

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

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

optically stimulated luminescence dating as a tool for calculating sedimentation rates in chinese loess comparisons with grain size records understanding loess sedimentation rates is crucial for constraining past atmospheric dust dynamics regional climatic change and local depositional environments however the derivation of loess sedimentation rates is complicated by the lack of available methods for independent calculation this limits interpretation of the environmental changes revealed by the loess record in particular while the quaternary neogene chinese loess and red clay sequences have the potential to provide detailed records of past sedimentation and climate change there is great uncertainty concerning i the influences on sediment grain size and accumulation and ii their relationship through time and across the depositional region this uncertainty has led to the widespread use of assumptions concerning the relationship between sedimentation rate and grain size in order to derive age models and climate reconstructions to address this uncertainty detailed independent age models based on optically stimulated luminescence dating undertaken at 10 to 40 cm intervals at five sections across the loess plateau in china have been used to calculate sedimentation rates and make comparisons with grain size changes over the late pleistocene and holocene the results demonstrate that sedimentation rates are site specific extremely variable over millennial timescales and that this variation is often not reflected in grain size changes in the central part of the loess plateau the relationship between grain size and sedimentation rate appears most complex suggesting an interplay between local conditions at source and sink and a changing emplacement mechanism this observation further undermines the common use of loess sedimentation age models that rely on a derived relationship between grain size and sedimentation rate from a type section the results also highlight the difficulty in assigning specific environmental causes to sedimentation rate changes and to a lesser extent grain size shifts

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

on the interpretation of chinese loess as a paleoclimate indicator the records of wind blown dust i e loess in china are some of the most important terrestrial records of past climate changes stretching back over the last 10 ma in the paleoclimate literature intervals of increased dust generation have been almost always interpreted as being associated with more intense or prolonged wintertime conditions here it is shown that in accordance with modern observations dust outbreaks in asia are predominantly springtime phenomena during spring frequent cyclogenesis in the lee of the mongolian altai and the passage of strong cold fronts produce the intense windstorms that loft and entrain dust into the air the meteorology governing such outbreaks is likely robust in past climates contrary to the common paleoclimate presumption it is actually the breakdown of the siberian high that permits the dust producing windstorms to occur the importance of cold fronts in generating such windstorms suggests that cooling of high latitude climate during the miocene or during glacial intervals might play a significant role in the signal recorded in the loess deposits the unique springtime factors that generate dust storms are an example of why the common partitioning of asian climate into a winter and summer monsoon is oversimplified and can be misleading

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

alkenone temperature estimates for the east sea during the last 190 000 years abstract the late quaternary records of alkenone based sea surface temperature sst from a core located in the western margin of the east sea japan sea showed that the estimated temperature fluctuated greatly the variability being consistent with orbital scale global climate records during the period of marine isotope stage mis 6 the alkenone temperatures were low 7 10 c whereas during mis 5 5 the temperature increased rapidly up to 21 c during the entire period of mis 5 the temperature decreased from 21 c to 13 c then the temperature fluctuated between 10 c and 15 c during miss 4 and 3 after that it continued to fluctuate between 15 c and 17 c variation in the east sea sst is considered to be closely related to changes in the east asian monsoon system and seawater transport by the tsushima warm current the glacial surface cooling could be associated with the strong winter monsoon and or weakened summer monsoon in east asia during the glacial period when the sea level was low the influx of warm water was restricted and this might have enhanced the lowering of the surface temperature these conditions most likely caused significant changes in surface water circulation a basin scale cyclonic gyre might have occurred in the east sea without the development of the subpolar front during the interglacial period the surface warming seems to be related to the intensified summer monsoon system the high stand of the sea level and climate change most likely caused the development of cyclonic and anti cyclonic gyres in the north and south respectively and the subpolar front in the central part of the sea

a 2000 year dust storm record from lake sugan in the dust source area of arid china 1 arid northwestern china is considered to be a major source of atmospheric dust supply to the northern hemisphere however dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region hydrologically closed lakes in dust source areas act as a trap providing the opportunity to trace the history of dust emission or eolian activity here we present the results of dust storm proxies and a dust storm history from lake sugan in the qaidam basin a dust source area on the northern qinghai tibetan plateau grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred in combination with a sediment chronology generated by counting annual laminations a 2000 year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments frequent and or intensive dust storms occurred during the intervals ad 300 500 ad 1180 1240 and ad 1500 1700 the occurrence of dust storms largely coincided with the strengthening of the siberian high with colder air masses from high latitudes such as during the little ice age frequently encroaching into the dust source areas in northwestern china our results suggest that wind strength plays an important role in dust emissions in arid source areas however dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the qaidam basin

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossil abundances across the arctic basin biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossils across the arctic basin