eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

comparison of water column co2aq with sedimentary alkenone based estimates a test of the alkenone co2 proxy 1 the stable carbon isotopic compositions of alkenones have been used to interpret the long term history of the partial pressure of atmospheric carbon dioxide pco2 although extensive water column and culture studies document the potential utility and limitations of this approach to date the accuracy of pco2 values derived from sedimentary alkenones remains untested for this study we establish holocene aged alkenone based co2aq estimates co2aq alk from 20 sites along a central pacific ocean transect and compare them against both observed modern water column co2aq and estimated preindustrial concentrations at the depth of alkenone production at each site although the co2aq alk track measured water column values they are conspicuously lower than modern values across the subtropics this offset likely reflects the contributions of anthropogenic co2 in modern surface waters relative to preindustrial concentrations at the time of alkenone production when a model based estimate of anthropogenic co2 is removed from the modern observed values a majority 84 of co2aq alk falls within 20 of modeled preindustrial values consistency between the modeled and alkenone based estimates of preindustrial co2 levels points to the relative accuracy of the alkenone co2 method across a wide range of ocean and biogeographic regimes provided that phosphate concentrations at the depth of haptophyte production are reasonably constrained it further suggests that light limited growth and or active carbon uptake if they occur have a negligible effect on reconstructed co2aq

interpreting temporal patterns in the late quaternary dust flux from asia to the north pacific abstract a comparative study of the literature on the late quaternary accumulation of aeolian dust in china japan and the pacific ocean shows three different temporal patterns of dust signals the main dust sources in asia the deserts and desert margins contain large amounts of wind suspensible allochthonous material commonly an increase in dust accumulation is taken as an indicator of increased aridity in the interior of asia differences among the signals of asian desert dust accumulation in different depositional areas indicate that this interpretation requires critical evaluation the dust supply of the desert regions was maximal during the pleistocene glacial maxima the widespread assumption that these stages were the most arid periods is not necessarily valid additional factors likely to lead to temporal and regional differences in dust accumulation are 1 eustatic sea level changes associated with changes in the amount of exposed shelf material and changes in the extent of sea ice affecting atmospheric changes 2 the frequency of meteorological situations allowing long range dust transport 3 the strength of the dust transporting winds 4 changes in the wet deposition rate and 5 the presence of a dust trapping vegetation cover temporal variations in dustiness in different depositional areas are the result of specific combinations of these factors simplified assumptions concerning the reasons for dust variability may lead to incomplete or even erroneous palaeoecological conclusions

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

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

dispersal and deposition of eolian and fluvial sediments off peru and northern chile relative abundances of quartz and feldspar in fine grained terrigenous sediments have been used to recognize specific continental sediment sources along northwestern south america and to trace the dispersal of specific grain size fractions from these sources to adjacent continental margin and deep sea sedimentary environments quartz feldspar ratios are low 0 6 for all fractions of sediments derived from southern peru and northern chile but such ratios increase systematically in central and northern peru as the importance of granitic and related intrusives increases relative to more basaltic extrusives and gabbroic equivalents limited published analyses of dusts collected offshore prospero and bonatti 1969 are also consistent with a latitudinally varying continental sediment source we find that clay

late pleistocene time series of atmospheric and oceanic variables recorded in sediments from the subarctic pacific time series analyses of atmospheric and oceanic variables in a late pleistocene record from the northwest pacific show the complex relationship of the response of various segments of the climate system to changes in the earth s orbit most variance spectra of time series from this subarctic record contain frequency peaks with periods corresponding to at least one of the major orbital components of eccentricity obliquity or precession although the radiolarian faunal water mass assemblages have prominent spectral peaks with 41 000 year periods which are coherent with obliquity at this frequency only the transitional faunal assemblage contains variance focused at a frequency corresponding to the 100 000 year period of eccentricity three of these faunal time series also show variance concentrated at a frequency with a 20 000 year period these three time series are not coherent at a 20 000 year frequency with either of the dominant spectral peaks of precession they are coherent however with variations in the second harmonic of the obliquity cycle changes in obliquity apparently affect siliceous faunal abundances in the northwest pacific region of this high latitude site more than variations in eccentricity or precession maxima in the time series of quartz abundance occur during low values of eccentricity and high glacial ice volume because atmospheric winds serve as the major source of supply of quartz to the sediments at this site these high quartz values reflect increased aridity at the source region except for short periods during interglacials the characteristics of the surface waters in this region of the subarctic pacific during much of the last 460 000 years were similar to those which exist today in the sea of okhotsk the spectrum of winter sea surface temperature estimates derived from siliceous microfaunal abundances contains dominant frequency peaks at periods of 100 000 41 000 and 23 000 years which are coherent with eccentricity obliquity and precession respectively based upon the relationship of the subarctic front with the dominance of specific faunal asemblages the front was positioned south of its present day location throughout much of the late pleistocene

depth ranges of alkenone production in the central pacific ocean we report analytical results of long chain c 37 c 39 alkenones in the surface sediments taken along a latitudinal transect at 175 e from 48 n to 15 s unsaturation degree of c 37 alkenones u k 37 indicated that alkenone temperature is the highest about 28 3 c in the tropical pacific and decreases toward 48 n about 10 1 c although the latitudinal trend of the alkenone temperature is generally similar to that of the observed sea surface temperature of the surface mixed layer the former exhibits markedly lower values than the latter does in the midlatitude 35 19 n on the basis of the comparisons between water column temperatures and alkenone temperatures in the surface sediments we estimated that in the midlatitudes alkenones are produced in the thermocline waters whereas in the high 48 40 n and low 10 n 2 s latitudes they are produced in the surface mixed layer this result is supported by the depth distribution of emiliania huxleyi and gephyrocapsa oceanica along a 155 w transect in the central pacific the latitudinal distribution of the alkenone production layers estimated from u k 37 is found to be consistent with that of the nitrate suggesting that the depth of alkenone production is mainly controlled by the nutrient supply from deeper waters alkenones in the sediments exhibited relatively large abundances in 43 27 n with a maximum at 30 n which may be explained by high productivity of haptophyte algae in kuroshio extension

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

a 420 000 year record of cyclicity in oceanic and atmospheric processes from the eastern equatorial pacific samples from the upper portion of a cyclic pelagic carbonate sediment sequence in deep sea drilling project dsdp hole 503b 4 0 n 95 6 w are the first group to be analyzed for paleoceanographic and paleoclimatic proxy indicators of ice volume deep ocean and surface water circulation and atmospheric circulation in order to resolve the complex origin of the cyclicity temporal resolution is taken from the 18o time scale most other parameters are calculated in terms of their mass flux to the seafloor caco3 percent in the sediments fluctuates in the well known pacific pattern and is higher during glacial times the fluxes of opal and organic carbon have patterns similar to each other and show a variability of a factor of 2 5 to 4 the longer organic carbon record shows flux maxima during both glacial and interglacial times the accumulation patterns of both opal and organic carbon suggest that the variability in surface water productivity and or seafloor preservation of those materials is not simply correlated to glacial or interglacial periods eolian dust fluxes are greater during interglacial periods by factors of 2 to 5 indicating that eolian source regions in central and northern south america were more arid during interglacial periods the record of eolian grain size provides a semiquantitative estimation of the intensity of the transporting winds the eolian data suggest more intense atmospheric circulation during interglacial periods opposite to the anticipated results we interpret this observation as recording the southerly shift of the intertropical convergence zone to the latitude of hole 503b during glaciations

molecular paleoclimatology reconstruction of climate variabilities in the late quaternary abstract lipid class compounds were studied in the deep sea surface sediments from the central pacific across a latitudinal transect at 175 e 48 n 15 s and a box core from the western tropical pacific to discuss their utility as paleoclimatological indicators higher concentrations of c25 c35 n alkanes were observed in the higher latitudes in the north pacific their latitudinal distributions are similar to the spatial distributions of the observed soil dust concentrations observed in the central north pacific atmosphere suggesting that the sedimentary c25 c35 n alkanes are atmospherically transported from terrestrial higher plants and can be used as an indicator of terrestrial input to ocean environments downcore distributions of total c25 c35 n alkanes suggest that terrestrial input doubled over the western tropical pacific at the lgm and decreased by a factor of two at the last deglaciation period in comparison with the holocene the latitudinal distributions of c17 c20 n alkanes and pristane are higher in the high latitudes and equatorial region probably reflecting the higher primary productivity in surface waters of these oceans the downcore profiles of these compounds as well as total organic carbon long chain alkenones and dinosterol suggest that biological production decreased significantly during the deglaciation period and slightly increased during the lgm compared with that of the holocene the downcore uk37 record suggests that the sst was almost constant over the last 20 000 y which agrees well with the climap results and foraminifera 18o although it disagrees with results from coral sr ca ratios and 18o records

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

an integrated study of the eolian dust in pelagic sediments from the north pacific ocean based on environmental magnetism transmission electron microscopy and diffuse reflectance spectroscopy

flux and grain size variation of eolian dust as a proxy tool for the paleo position of the intertropical convergence zone in the northeast pacific abstract a 328 cm long piston core kodos 02 01 02 collected from the northeast equatorial pacific at 16 12 n 125 59 w was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo position of the intertropical convergence zone itcz the eolian mass fluxes of the lower interval below 250 cm 15 5 7 6 ma are very uniform at 5 1 mg cm2 103 yr while those of the upper interval above 250 cm from 7 6 ma are over 2 times higher than the lower interval at 12 1 mg cm2 103 yr the median grain size of the eolian dusts in the lower interval increases from 8 4 to 8 0 downward while that of the upper interval varies in a narrow range from 8 8 to 8 6 the determined values compare well in magnitude to those of central pacific sediments for the upper interval and equatorial and southeast pacific sediments for the lower interval this result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the itcz and subsequently of the northeast trade winds for a later period when the upper sediments were deposited this interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to central south america for the lower interval and to asia for the upper interval this study suggests that the distinct differences in eolian mass flux and grain size observed across the itcz can be used to trace the paleo latitude of the itcz

linking ocean and continental records of paleoclimate determining accord and discord in the records climate forcing at milankovitch and sub milankovitch frequencies are evaluated by linking climate proxy data from terrestrial and ocean records at two scales of temporal resolution 1 relatively coarse resolution over the last 500 ka and 2 higher resolution over the last 200 ka we determine that climate proxy data from hole 810c rep resent regional atmospheric and oceanic processes by comparison to core v21 146 both from the northwest pacific ocean we then compare records that represent regional deposition from china and the western pacific ocean to focus on determining milankovitch type periodicities grain size and magnetic susceptibility data from hole 810c and baoji china are contrasted using a time sensitive wavelet analysis the analyses indicate a general correspondence to milankovitch frequencies although there is no specific frequency that dominates throughout the records additionally the dominant 100 000 year frequency does not occur at the same time in the records these factors suggest that differ ences in the physical mechanisms of deposition may influence the preserved apparent periodicities in these environ ments lastly climate events over the last 200 000 years in marine and terrestrial records are correlated at a high resolution in the depth domain the last interglacial glacial boundary is consistently placed at the base of a cold period c20 in the terrestrial and marine records however the cold period in the ocean data 18 o is very subdued relative to terrestrial records additionally over the last 200 ka periods of minimum insolation intensity do not correspond lin early to periods of maximum grain size and ice volume variations revealed in the loess and ocean records respectively however during the warm interstadials of the last two glaciations peaks in insolation intensity compare favourably with the times of strongest pedogenic development in the continental records and minimum ice volume in the ocean records resume le forcage du climat a des frequences milankovitch et sous milankovitch est evalue en faisant un lien entre les donnees indirectes de sources terrestres et oceaniques a deux echelles de resolution dans le temps 1 une resolu tion relativement grossiere pour les dernieres 500 ka et 2 une plus haute resolution pour les dernieres 200 ka nous determinons que les donnees indirectes du trou 810c representent des procedes atmospheriques et oceaniques regionaux par rapport a la carotte v21 146 les deux provenant du nord ouest de l ocean pacifique nous avons ensuite compare les registres qui representent une deposition regionale en provenance de la chine et de l ouest de l ocean pacifique afin de se concentrer sur la determination de frequences de type milankovitch des donnees granulometriques et de suscep tibilite magnetique provenant du trou 810c et de baoji china sont mises en contraste au moyen d une analyse tempo relle des ondelettes les analyses indiquent une bonne correspondance generale aux frequences de milankovitch bien qu aucune frequence specifique ne domine a travers les registres de plus la frequence principale de 100 000 ans ne se presente pas au meme moment dans les registres ces facteurs suggerent que des differences dans les mecanismes phy siques de deposition peuvent influencer les periodicites apparentes preservees dans ces environnements finalement dans le domaine de la profondeur il y a correlation a haute resolution entre les registres marins et terrestres des evene ments climatiques au cours des derniers 200 000 ans la derniere limite glaciaire interglaciaire est constamment placee a la base d une periode froide c20 dans les registres marins et terrestres toutefois la periode froide dans les don nees oceaniques 18 o est tres attenuee par rapport aux registres terrestres de plus au cours des dernieres 200 ka des periodes d intensite minimale d insolation ne correspondent pas de facon lineaire aux periodes de granulometrie maximale et de variations des volumes de glace qui sont revelees respectivement dans les registres oceaniques et de loess toutefois au cours des rechauffements interstadiaires des deux dernieres glaciations des sommets dans l intensite d insolation se comparent favorablement avec les temps du plus fort developpement pedogenique dans les re gistres continentaux et avec le volume minimal de glace dans les registres oceaniques traduit par la redaction 848

neogene history of the south pacific tradewinds evidence for hemispherical asymmetry of atmospheric circulation rea d k and bloomstme m k 1986 neogene history of the south pacific tradewmds evidence for hemlsphermal asymmetry of atmospherm circulation palaeogeogr palaeochmatol palaeoecol 55 55 64 eohan dust grains extracted from southeast pacific pelagic sediments provide a neogene record of southern hemisphere atmospherm processes the mass accumulation rate of dust has been low and generally constant at 1 4 mg cm 2 103 y since the late ohgocene eohan grains ze data show an increase from 8 20 3 40 t m older sediments to 7 20 6 80 t m younger materml this shift occurred about 10 5 m y ago and reflects a s gmfmant increase in the intensity of atmospheric circulation then there s no obwous response to the onset of northern hemisphere glacmtmn 2 5 m y ago m these eohan records from the south pacific compamson with existing lnformatmn from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the neogene and that this asymmetry reached its greatest extent between 10 5 and 2 5 ma

aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean rea d k 1990 aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean palaeogeogr palaeoclimatol palaeoecok 78 217 227 the eolian component of pelagic sediments provides a proxy record of atmospheric circulation intensity and of dust transport examination of those records indicates that the atmosphere responds to orbital forcing but that during the past 875 000 years the variability in atmospheric circulation is at much shorter periods than the 100 000 year variation in ice volume the mid brunhes climatic event is well characterized in the eolian grain size records and in records of sea surface phenomena it is not seen in proxy indicators of either deep water or ice volume variability the increase in the amplitude of paleoclimatic variability that denotes the early late pleistocene transition occurs suddenly about 875 000 years ago in the eolian grain size record which is about 20 000 to 25 000 years earlier than the transition in the deep sea caco3 dissolution record or in the 8180 proxy record of ice volume

evidence for orbital forcing of dust accumulation during the early paleogene greenhouse the accumulation of wind blown eolian dust in deep sea sediments reflects the aridity humidity conditions of the continental region supplying the dust as well as the gustiness of the climate system detailed studies of pleistocene glacial interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation milankovitch cycles while the orbital cycles found in sedimentary archives of the pleistocene are intricately related to glacial growth and decay similar global orbital signals recognized in deep sea sediments of early paleogene age the last major greenhouse interval 65 45 million years ago could not have been linked to the waxing and waning of large ice sheets thus orbital signals recorded in early paleogene sediments must reflect some other climate response to changes in solar insolation to explore the potential connection between orbital forcing and the climate processes that control dust accumulation we generated a high resolution dust record for 58 myr old sediments from shatsky rise odp site 1209 paleolatitude 15 n 20 n the dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early paleogene indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate furthermore the relative amplitude of the dust flux response during the early paleogene greenhouse was comparable to that during icehouse climates thus subtle variations in solar insolation driven by changes in earth s orbit about the sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial interglacial states

astronomical theory of the pleistocene ice ages a brief historical review abstract this paper traces the evolution of the astronomical theory of the pleistocene ice ages from its origin in the work of adhemar and croll through its quantitative transformation in the hands of milankovitch to its current renaissance emphasis is given to the interplay between climatic theory and geologic observation from 1941 when milankovitch published his final version of the theory until the early 1970s most attempts to test the theory empirically were carried out in the time domain by comparing the geologic record of climate with predicted climate curves these attempts ran into serious difficulties particularly the inaccuracy of the geologic time scale and the ambiguity of climate predictions early attempts to evaluate the theory with simple radiation balance models appeared to indicate that the climatic response to secular changes in the orbit would be too small to be observed geologically but by the mid 1970s the advent of an improved time scale for pleistocene marine deposits and the availability of long closely sampled records made it possible to arrange generalized but unambiguous tests of the theory in the frequency domain by comparing orbital and climatic spectra these results decisively confirmed the idea that orbital variations significantly influenced the earth s climate during the pleistocene but they did not tell us how this influence was exercised the emphasis of current work has therefore shifted to the identification and quantitative modeling of physical mechanisms by which the climate system responds so dramatically to the predicted rather subtle changes in radiative boundary conditions

storminess control over african dust input to the moroccan atlantic margin nw africa at the time of maxima boreal summer insolation a record of the last 220 kyr abstract precessional forcing of dust flux from northwest africa to the atlantic during the last 220 kyr is recognised through changes in physical and chemical sediment properties sediment colour reflectance magnetic susceptibility x ray fluorescence element intensity in a core from the moroccan margin sediment colour reflectance magnetic susceptibility and ca and fe element intensity changes are thought to be driven by dust input from north africa spectral analysis of the sediment properties records displays a dominant periodicity in the 1 23 kyr 1 frequency band that is associated with the earth s orbital precession peaks in terrigenous supply match precessional minima this suggests a close link between maxima of boreal summer solar radiation monsoon activity and dust generation enhanced precession driven solar radiation would have caused increased seasonal temperature contrasts which amplified atmospheric turbulence and stimulated storminess such a scenario is similar to today s summer conditions when frequent storms cause distinct dust plumes to form in the area and transport fine terrigenous material to the adjacent north atlantic ocean

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

evolving pliocene pleistocene climate a north pacific perspective abstract siliceous microfauna in sediments from north pacific deep sea drilling project sites record the response of the regional surface and near surface waters to global climate change over the past 3 0 ma during the late pliocene 2 7 3 0 ma the northern subtropical and subpolar pacific experienced warmer climate conditions than those of today the first predominant polar assemblage maximum occurs in the north pacific at 2 45 ma signifying this region s response to the initiation of significant northern hemisphere glaciation north pacific faunal data show that late pliocene 1 8 2 5 ma glacial maxima were only about half to two thirds as severe as those which occurred during the late pleistocene low faunal assemblage variability during a 200 ka interval in the latest pliocene 1 6 1 82 ma in the north pacific indicates minimal variations in the surface water properties and climate conditions most like those which existed just prior to 2 5 ma a distinct change in faunal assemblage registered in sediments from site 580 between 1 2 and 1 2 ma marks the first cooling in the north pacific comparable in intensity to those of the late pleistocene since 1 26 ma high amplitude high frequency variations in the north pacific polar assemblage have continued to occur providing further evidence that the interglacial glacial extremes that characterize the late pleistocene have persisted since this time the frequency distribution of north pacific winter sea surface temperature time series for the late pliocene and early pleistocene includes major concentrations of variance power centered at a frequency corresponding to a 41 ka period with variance dominance of the temperature time series for the last 800 ka shifting to lower frequencies 110 ka period

quaternary fluctuations in the northern hemisphere trade winds and westerlies the mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two north pacific cores piston core kk75 02 under the prevailing westerlies and deep sea drilling project site 503 beneath the trade winds have been used to evaluate changes in the intensity of atmospheric circulation and source area aridity over the past 700 000 yr the eolian grain size a direct indicator of wind intensity fluctuates at periodicities similar to those calculated for the earth s orbital parameters of precession obliquity and eccentricity both sites display greater variability in wind intensity prior to 250 000 yr ago eolian accumulation rates an indicator of source area aridity fluctuate at periodicities similar to those of the glacial interglacial cycles lower eolian accumulation rates during colder glacial times most likely reflect increased glacial age humidity at central asian and central american source areas

biogenic sediment regimes in the neogene equatorial pacific iodp site u1338 burial production and diatom community abstract the equatorial pacific experienced significant changes in productivity and microfossil assemblage since 16 million years ago ma we compiled a record of those changes from iodp site u1338 using a reconnaissance of diatom assemblages and high resolution xrf scan chemical profiles 1 2 kyr spacing productivity and caco3 dissolution intervals are defined by sediment component ratios in particular opal clay opal baso4 and caco3 baso4 or caco3 clay there are large abrupt changes in export production in the miocene especially compared to the pleistocene and pliocene and average levels of export production are higher throughout the miocene compared to the pliocene and pleistocene using diatom assemblages and bulk sediment composition the u1338 sediment record is divided into several distinct deposition regimes 1 a middle miocene regime 13 2 ma marked by low diatom numbers and a few short lived productivity intervals 2 a carbonate crash regime distinguished by an older substage 13 2 10 2 ma with relatively high abundances of productivity related diatoms and common productivity related depositional intervals interspersed with caco3 dissolution intervals and a younger carbonate crash substage 10 2 8 0 ma with weaker brief productivity intervals high caco3 dissolution and moderately high numbers of upwelling diatom species 3 the biogenic bloom regime 8 0 4 5 ma marked by extended periods of high opal and caco3 deposition with a maximum between 7 0 and 6 4 ma and 4 a pliocene modern regime 4 5 0 ma with lower productivity and high cyclic caco3 dissolution changes in production and dissolution result from reorganizations of nutrient supply to the equatorial pacific not by higher wind driven upwelling we propose that nutrients were more accessible in the miocene because of a combination of factors including higher organic matter degradation in the upper water column and deep intermediate nutrient pathways that efficiently recycled nutrients to upwelling zones closure of the central american seaway was likely a prime cause of the biogenic bloom

significance of the sedimentary al ti ratio as an indicator for variations in the circulation patterns of the equatorial north atlantic this paper presents results of geochemical investigations conducted on three gravity cores recovered along an e w transect 3 5 n in the equatorial atlantic considering the high terrigenous content of the sediments approximately 12 74 wt al and ti concentrations are predominantly associated with the input of lithogenous phases the terrigenous fraction of western equatorial atlantic sediments is more influenced by material derived from the amazon river than by deposition of african dust particles as a possible route of transport the north equatorial countercurrent is considered fluctuations in al ti records generally reflect changes in the low latitude insolation cycle 19 23 kyr and thus indicate a close coupling to variations of the trade wind systems and continental climate changes however characteristics of the terrigenous signals in the eastern and western equatorial atlantic differ significantly while the precessional signal in the al ti record and low latitude portion in the 18o record are in phase in the eastern equatorial atlantic variations in the terrigenous fraction westward of the mid atlantic ridge precede the marine signal by 2 3 kyr which we ascribe to a shift between trade wind systems of the northern and southern hemispheres

reconstruction of paleoceanographic conditions in the northwestern pacific ocean over the last 500kyr based on calcareous nannofossil and planktic foraminiferal assemblages calcareous nannofossil and planktic foraminiferal assemblages from odp hole 1210a in the northwestern pacific ocean were used to reconstruct surface water conditions for the past 500 kyr stratigraphic control was provided by calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes calcareous nannofossil and planktic foraminiferal assemblages and abundance patterns indicate the unlikelihood of long term milankovitch scale latitudinal shifts of the kuroshio extension over the last 500 kyr and illustrate two successive surface water mass states one that prevailed prior to 300 ka and one that existed after 300 ka the relative abundance of very small placoliths and the absolute abundance of the upper photic zone upz coccolith species decrease abruptly at approximately 300 ka the relative abundance of the lower photic zone lpz species florisphaera profunda greatly increases at the same time although intervals during which the relative abundance of this taxon is very low or absent also occur prior to 300 ka the absolute abundance of planktic foraminifera gradually increased after the 300 ka boundary including peaks of globoconella inflata these assemblage and abundance changes suggest significant modifications to the surface water mass structure surface water was weakly stratified prior to 300 ka but alternated between intensely stratified and vertically mixed after 300 ka changes in the surface water mass structure suggest an intensification of the east asian summer and winter monsoon after 300 ka

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

late cenozoic changes in atmospheric circulation deduced from north pacific eolian sediments abstract isolation and analysis of the eolian component of late cenozoic pelagic sediments from the north pacific provides direct information concerning changes in atmospheric circulation a 50 increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole to equator temperature gradients resulting from the onset of northern hemisphere glaciation at the same time the mass flux of dust from continents to the north pacific increased by a factor of 4 5 apparently reflecting significantly increased continental aridity associated with the late cenozoic glacial ages

source areas and transport mechanisms for freshwater and brackish water diatoms deposited in pelagic sediments of the equatorial atlantic abstract distributions of freshwater and brackish water diatoms from dust samples and modern sediments of the equatorial atlantic demonstrate different transport mechanisms and source areas both melosira spp and stephanodiscus spp are transported via winds from the southern sahara and sahel in northern hemisphere winter the core top distribution of cyclotella striata delineates the extent of the low salinity plume formed by runoff from the zaire river into the extreme eastern atlantic the transport mechanism and source areas for melosira spp during arid phases have not changed appreciably in the last 130 000 yr there is no evidence for long distance transport of freshwater diatoms by the southeast trade winds this study confirms the validity of paleoclimatic research which inferred eolian transport of melosira spp in the winter dust plume from source regions north of the equator although fluviatile input of melosira valves into nearshore sediments cannot be ruled out

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

the micropaleontological character of anomalous calcareous sediments of late pliocene through early pleistocene age below the ccd in the northwestern north pacific ocean calcium carbonate was preserved more than 1 km below the modern calcite compensation depth ccd at odp site 1179 over several short intervals around 2 5 2 4 1 65 and 0 9 0 7 ma this anomalous preservation resulted from a combination of increased production of planktonic foraminiferal tests at the sea surface and increased rate of sedimentation to the sea floor the abundance of dinoflagellate cysts in calcareous sediments records intense plankton blooms and the preservation of oxidationsusceptible round brown brigantedinium cysts in foraminifer rich samples supports the theory of rapid burial the rise in seasurface productivity was driven by enhanced flux of continentally derived limiting nutrients consistent with the pollen evidence of continental aridification cooling and an increase in wind strength the abundant pollen dominated by steppe herb and montane boreal conifer taxa contrasts with lower pollen concentrations dominated by temperate subtropical deciduous tree and taxodium type pollen in non calcareous sediments d 2004 elsevier b v all rights reserved

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

the framework of hydrocarbon generation and migration gulf of mexico continental slope abstract the occurrence of large volumes of crude oil and thermogenic gas in plio pleistocene reservoirs and holocene seeps of the gulf of mexico slope argues that the process of hydrocarbon generation and migration continues at the present time calculated thermal maturity models based on deep seismic stratigraphy indicate that cretaceous and possibly early tertiary sediments are presently within the thermal maturity range for generation and expulsion of crude oil the cretaceous and early tertiary sediments are suggested as possible source rocks because younger sediments are thermally immature for crude oil generation and older sediments are thermally overmature for crude oil preservation the calculated thermal maturity profile for the slope indicates that some generation of crude oil could occur as shallow as 6 km and that liquid hydrocarbons could be preserved as deep as 9 km thermogenic gas is stable at even greater depths migration with a strong vertical component must be invoked to explain thermogenic hydrocarbons in shallow reservoirs and seeps of the slope the great depth at which liquid hydrocarbons and dry gas can be preserved in reservoirs of the gulf of mexico salt basin indicates that huge volumes of prospective section remain essentially unexplored

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

orbital time scale records of asian eolian dust from the sea of japan since the early pliocene abstract a high resolution potassium content record of sediments from integrated ocean drilling program iodp site u1422 drilled in the northern sea of japan was employed to yield an astronomical timescale for this 205 m thick sedimentary archive the k content was quantified using the natural gamma radiation ngr data routinely measured on dv joides resolution the u1422 k wt series shows an increasing trend with time which parallels the growth of north hemisphere ice sheets since 4 ma as revealed by the global benthic foraminifer s oxygen isotope stack lr04 we propose that k content variations reflect changes in the relative contributions of asian eolian dust and volcanic weathering products in response to changes in global ice volume using the shipboard age model constrained by palaeomagnetism and nanofossils datums we tuned the u1422 k content variations to the lr04 stack our tuned age model for site u1422 goes back to 3 9 ma the studied record indicates that asian dust generation is enhanced during periods of global cooling the synchronous variations between the u1422 k record and the lr04 stack also suggest that global cooling played a dominant role in promoting the central asian aridification since 3 9 ma while the uplift of tibetan plateau plays a secondary role considering many disagreements still exists between the timing and amplitude of the qinghai tibetan uplift and the evolution of central asian aridity since the early pliocene

tropical atlantic terrigenous fluxes since 25 000 yrs b p twelve tropical atlantic cores each 14c dated and with 18o records were examined for burial fluxes of terrigenous mostly eolian sediment and biogenic opal and caco3 sediment over the last 25 000 years the similar flux trends through time of these three components within each core indicates that post depositional redistribution of sediment is the strongest control on burial fluxes in the tropical atlantic increased terrigenous dust fluxes apparent during the last glacial maximum in several cores are consistent with several previous studies the lack of significant dust flux maxima following the early holocene monsoon maximum argues strongly against changes in source area humidity aridity being a significant factor in orbital scale eolian dust transport and deposition in this region this suggests that the enhanced glacial influxes of dust to the tropical atlantic are mainly due to changes in transport by winter winds rather than to glacial hyper aridity

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

fluctuation of biogenic and abiogenic sedimentation on the shatsky rise in the western north pacific during the late quaternary abstract sedimentation of biogenic and abiogenic components was studied in cores ngc108 36 36 85 n 158 20 90 e water depth 3390 m and s2612 32 19 84 n 157 51 00 e water depth of 2612 m from the shatsky rise to understand fluctuations in primary productivity and abiogenic sedimentation in the mid latitude of the western north pacific during the late quaternary the mean c organic n atomic ratio of 6 0 7 8 in both cores indicates that organic matter is mainly marine in origin organic carbon is positively correlated with biogenic opal in core ngc108 in contrast to a weak correlation in core s2612 although the maxima of paleoproductivity estimates in both cores generally occur during glacial times the paleoproductivity estimates biogenic opal carbonate ratios and the c organic c carbonate ratios have always been higher in core ngc108 than in core s2612 during the last 180 kyr suggesting that the surface water at site ngc108 could have been influenced more by subarctic water mass than at site s2612 however the opal carbonate ratio in core s2612 remains fairly constant relative to that in core ngc108 which might mean that the transition zone between subarctic and central water was narrower in latitude in at the oxygen isotope stage ois 2 3 boundary ois 4 and ois 6 sedimentation of 13 inorganic elements has been measured in both cores these elements are classified into four groups based on correlation between each element in content 1 terrigenous components al ti fe 2 biogenic calcareous material ca sr 3 biogenic scavenged elements mg zn cr be and 4 the other elements mn ba cu ni the terrigenous mass accumulation rates were elevated in ois 2 3 and 4 and late ois 6 in core ngc108 while they were higher in early ois 1 ois 2 4 and 6 in core s2612 mno 2 and ba might be redistributed during the sub surface reduced condition especially precipitation of particle reactive be which could be accelerated by both enhanced terrigenous input and biogenic vertical transport has fluctuated largely in response to climatic change because of its short residence time on the order of the oceanic mixing time

glacial interglacial variability in the delivery of dust to the central equatorial pacific ocean abstract fluxes of continental mineral aerosols dust were greater during glacial periods than during interglacials throughout most regions of the earth the equatorial pacific ocean was a possible exception to this pattern in that previous studies have reported either greater dust fluxes during interglacials or no consistent glacial interglacial pattern of dust flux we have applied the 230th normalization technique to derive five new records of dust flux from central equatorial pacific ocean sediments in contrast to previous studies which relied on stratigraphic accumulation rates the 230th normalization technique produces internally consistent results revealing fluxes to this region of continental lithogenic material that were positively correlated with global ice volume throughout the past 300 000 yr maximum glacial fluxes of continental mineral aerosols exceed minimum interglacial fluxes by about a factor of 2 similar to changes found elsewhere at low and mid latitudes this amplitude of variability is substantially smaller than that seen in some recent models and these observations provide a calibration point for future model development

late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean rea d k and janecek t r 1981 late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean palaeogeogr palaeoclimatol palaeoecol 36 55 67 eolian dust preserved in deep sea sediment can provide a direct historical record of global atmospheric circulation data from a reasonably complete upper cretaceous section of pelagic sediments recovered at dsdp site 463 in the central north pacific provides a good record of eolian activity during the time period between about 112 hnd 66 m y ago we have isolated the eolian component from these sediments determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition volcanic input is significant during aptian albian and maastrichtian times otherwise continentally derived minerals dominate mass accumulation rates of the continental eolian component range from over 500 mg cm 103yr during the late albian to a low of 5 mg cm2 10 yr during coniacian time for comparison the upper miocene to pleistocene rate averages about 20 mg cm2 103yr the temporal pattern of late cretaceous eolian accumulation of site 463 generally matches known changes in sea level suggesting that source availability is the dominant control of eolian sedimentation during that time

productivity of the glacial ocean discussion of the iron hypothesis an increase in the productivity of the glacial age southern ocean has been postulated to explain the decrease in pc0 of the atmosphere observed in ice cores a plausible mechanism has been proposed elsewhere that productivity is limited by the availability of fe in this region and that the greater supply of eolian dust during glacial time removed this limit recently published evidence from cores from the southern ocean suggests that in fact there was no change in productivity in the assumed manner glacial age productivity was indeed greatly increased in the equatorial pacific and in the eastern boundary upwelling systems the cause presumably was the mechanical action of glacial age winds rather than a greater supply of fe however a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth possibly contributing to nutrient depletion in glacial age deep intermediate waters there is some indication as well of a general decrease in nutrient content in the tropical thermocline in the western pacific during the last several million years a depletion that may have been fostered by increasing supply of dust from emerging asian highlands alternative explanations are available the case for fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for fe supply as opposed to stirring and upwelling

geochemical characterization of contemporary fine detritus in the dead sea watershed abstract reconstruction of paleo synoptic conditions e g past atmospheric circulation involves tracing the origins and routes of transport of particles comprising eolian archives i e desert dust lacustrine deposits that accumulated in the quaternary lakes filling the dead sea basin include remobilized eolian desert dust that was washed to the lakes by floods here we analyze the mineralogical chemical compositions e g mg al ratios and 87sr 86sr and 143nd 144nd end values isotope ratios of fine siliciclastic particles that form the modern surface cover of the dead sea watershed e g loess mountain soils and flood particles that are mobilized to the lake during distinct synoptic conditions the data comprises reference data set that can be used for paleo synoptic interpretation enhancing our ability to decipher the paleoclimate history during the quaternary in the levant the end values and 87sr 86sr ratios of the fine detritus lie between 8 and 6 and 0 7035 to 0 7188 reflecting the values of erosional products of granitoids that are exposed in the sahara and arabia deserts and the unradiogenic sr from local soils in the dead sea watershed particles with low mg al ratios i e 0 17 0 31 are transported by the western winds associated with the mediterranean cyclones transporting dust from the sahara while particles with high mg al ratios 0 27 0 68 are associated with storms blowing dusts from east to the dead sea watershed saudi arabia and syrian deserts during red sea trough synoptic conditions fine particles blown from the sahara deserts during winter storms are rapidly washed to the lake by subsequent floods whereas the particles blown during dry storms associated with red sea trough synoptic conditions accumulate on the surface of the dead sea watershed and can be washed later to the lake during extensive rain events

towards a high resolution global deep sea chronology for the last 750 000 years abstract variations in the ratio of 18 o 16 o as measured in shells of marine calcareous microfossils are primarily dominated by changes in global ice volume hence these variations provide a set of global time lines in deep sea sediments it is likely that the timing of major changes in oxygen isotope values is strongly influenced if not controlled by variations in the geometry of the earth s orbit since the variation of orbital parameters can be accurately calculated the opportunity exists for transforming this orbital chronology into a geological chronology through careful correlation of oxygen isotope records in a set of deep sea cores from the sub antarctic south atlantic and equatorial pacific we have assembled a composite isotopic section spanning the last 750 000 years with an average sedimentation rate of 2 3 cm 1000 years a new chronology for this time period was developed by adjusting the ages of the oxygen isotope stage boundaries in this composite section so as to extend the consistent phase relationships that exist between variations in oxygen isotope ratios and changes in obliquity and precession during the last 300 000 years to the entire 750 000 year record previously identified difficulties in phase locking precession with the filtered isotopic signal between 365 000 and 465 000 years b p have been resolved with the recognition that precessional variations have an average period of 19 000 years and not 23 000 years during this interval since this new age model yields the best match between variations in obliquity and precession and their corresponding frequency components in the oxygen isotope record we believe that it presents the most accurate chronology yet developed for deep sea sediments with this new age model providing the time control power spectral analyses of south atlantic and sub antarctic chemical and biotic indices show that there is a strong tendency for variance to be concentrated at frequencies corresponding to periods of 100 000 41 000 and 23 000 years

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

the mineral dust aerosol cycle during the last glacial maximum the canadian centre for climate modelling and analysis general circulation model gcm is used to investigate the factors influencing the mineral dust distribution at the time of the last glacial maximum lgm simulated deposition rates are used in conjunction with existing paleoclimate data to infer likely characteristics of the mineral dust conditions at that time and identify contributions to the pattern of enhanced dustiness of the lgm relative to the present indicated by ice core and loess data maximal consistency between the gcm the climate long range investigation mapping and prediction climap data set and the ice core data requires approximately a 15 to 30 fold increase in dust production globally during the last glacial maximum relative to the preindustrial holocene in particular regional 10 to 50 fold and 20 fold lgm increases are indicated in eastern asia and south america respectively these implied source enhancements are quite insensitive to the details of the dust model analysis of the contributing factors suggests an increase in fine particle availability in the source regions

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

paleoecological studies at lake patzcuaro on the west central mexican plateau and at chalco in the basin of mexico abstract a 1520 cm sediment core from lake patzcuaro michoacan mexico is 44 000 yr old at the base all parts of the core have abundant pollen of pinus pine alnus alder and quercus oak with frequent abies fir the interval dated from 44 000 to 11 000 yr ago has a homogeneous flora characterized by abundant juniperus juniper pollen and frequent artemisia sagebrush it is believed to represent an appreciably drier and colder climate than at present the holocene at lake patzcuaro is characterized by a moderate increase in pinus pollen and the loss of juniperus pollen as the modern type of climate succeeded alnus was abundant until about 5000 yr ago its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake shore and stream course alder communities for agricultural purposes or it may simply reflect a drying tendency in the climate pollen of zea corn appears at lake patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr b p apparently recording a human population large enough to modify the natural environment as well as the beginning of agriculture a rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion in the most recent period corn is absent from the sediments perhaps reflecting a change in agricultural practices the environment changes at lake patzcuaro are similar to and correlate with those in the cuenca de mexico where diatom stratigraphy from the chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture before 10 000 yr ago climates there were cool and dry and the chalco basin was occupied by a shallow freshwater marsh that drained north to lake texcoco where saline water accumulated by evaporation increases in effective moisture and possible melting of glaciers during the holocene caused lake levels to rise throughout the cuenca de mexico and lake texcoco flooded the chalco basin with brackish water after 5000 yr ago such flooding decreased and shallow freshwater ponds and marshes were restored in the chalco basin this environmental change coincides with the appearance of zea pollen and suggests cultural control of lake levels and salinity

peak intervals of equatorial pacific export production during the middle miocene climate transition the middle miocene climate transition mmct is characterized by an abrupt 1 increase in benthic foraminiferal oxygen isotopes at ca 13 8 ma marking expansion of the antarctic ice sheet and transition of earth9s climate to a cooler relatively stable glacial state also occurring during this period is a globally recognized positive carbon isotope excursion 16 9 13 5 ma in benthic and planktonic foraminifera with shorter carbon isotope maxima cm events linking hypotheses for climate change at the time with the carbon cycle in order to test whether export production in the eastern equatorial pacific is related to the largest such event cm6 coincident with antarctic ice sheet expansion a high resolution 5 k y record of export production at integrated ocean drilling program site u1337 spanning the mmct 14 02 13 43 ma was produced using marine pelagic barite mass accumulation rates export production is elevated with an extended period of more than double present day values these variations are not orbitally paced and provide evidence for a reorganization of nutrients supplied to the eastern equatorial pacific in the miocene and intensification of upwelling if such changes are representative of the entire region then this mechanism could sequester enough carbon to have a significant effect on atmospheric p co 2 however continual delivery of nutrients to the surface waters of the eastern equatorial pacific is required in order to sustain export production without depleting the surface ocean of limiting nutrients this might be accomplished by a change in ocean circulation or a combination of other processes requiring further study

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

twentieth century north atlantic jet variability long records of the latitude and speed of the north atlantic eddy driven jet stream since 1871 are presented from the newly available twentieth century reanalysis these jet variations underlie the variability associated with patterns such as the north atlantic oscillation nao and have considerable societal impact through variations in the prevailing westerly winds while the nao combines variations in the latitude and speed of the jet these two characteristics are shown to have quite different seasonal cycles and interannual variability suggesting that they may have different dynamical influences in general the features exhibited in shorter records are shown to be robust for example the strong skewness of the nao distribution related to this is a clear multimodality of the jet latitude distribution which suggests the existence of preferred positions of the jet decadal variations in jet latitude are shown to correspond to changes in the occurrence of these preferred positions however it is the speed rather than the latitude of the jet that exhibits the strongest decadal variability and in most seasons this is clearly distinct from a white noise representation of the seasonal means when viewed in this longer term context the variations of recent decades do not appear unusual and recent values of jet latitude and speed are not unprecedented in the historical record

simulation of the ice age atmosphere january and july means a simulation of the atmospheric state under ice age conditions 18 000 years before present is presented the t21 atmospheric general circulation model agcm originally developed at the european centre for medium range weather forecasts was used for the calculation of six annual cycles results of the near surface climatology 2 m temperature 10 m wind and precipitation averaged over the last five model years are presented the presentation is restricted to january and july means in order to demonstrate the glacial changes in summer and winter the model s response to ice age boundary conditions was quite consistent with paleogeological data on land and with agcm experiments of other studies although the differences between the mean climate states of the model atmosphere under glacial and modern boundary conditions were statistically significant the basic structure of the simulated atmospheric circulation was not altered substantially

testing global synchronism in peri pacific arc volcanism abstract episodicity of arc volcanism along the pacific rim is quantitatively analysed based on the record preserved by ash layers in deep sea sediments drilled by the deep sea drilling project and the ocean drilling program two major pulses of arc volcanism have been found one during middle miocene times 18 13 ma the other during pliocene quaternary times 5 0 ma these pulses are shown to relate to the tectonic stress regime of the arc lithosphere rather than to subduction rate these episodes of arc volcanism activity coincide with major tectonic events documented on circum pacific subduction zones as a consequence a global control of plate kinematics could influence both volcanic and tectonic evolution of pacific convergent margins

resolving eolian volcanogenic and authigenic components in pelagic sediment from the pacific ocean abstract we measured major and trace element concentrations in the operationally defined chemically extracted residual aluminosilicate component of sediment from ocean drilling program sites 1215 and 1256 in the central and eastern equatorial pacific ocean and found that this residual component contains volcanogenic and authigenic aluminosilicates in addition to inferred eolian material while the residual component younger than 20 ma from the central pacific odp site 1215 is similar compositionally to upper continental crust and suggests an increase in the delivery of asian dust material since 20 ma the residual in sediment older than 20 ma indicates significant amounts of volcanogenic and authigenic materials volcanogenic debris comprises as much as 40 of the residual between 23 40 ma which coincides with the mid tertiary ignimbrite flare up that occurred in much of western north america the residual component extracted from the 50 ma biogenic sediment reflects authigenic signatures seawater like negative cerium anomalies and elevated fe si ratios the previously interpreted increase in an andesitic detrital source in north pacific locations may instead be authigenic material presenting significant challenges for many paleoclimate proxies additionally in the eastern pacific odp site 1256 the residual component contains 70 of volcanogenic material most likely originating from central america and also includes refractory barite the ability to separately identify eolian volcanogenic and authigenic materials in the aluminosilicate component of pelagic sediment allows resolution respectively of the climatic geologic and chemical processes contributing to the paleoceanographic archive in this critical oceanic region

western equatorial pacific productivity and carbonate dissolution over the last 550 kyr foraminiferal and nannofossil evidence from odp hole 807a we analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from odp hole 807a on the ontong java plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr kilo year in the western equatorial pacific our results indicate that productivity was generally higher in glacials than during interglacials and gradually increased since mis 13 carbonate dissolution was weak in deglacial intervals but often reached a maximum during interglacial to glacial transitions carbonate cycles in the western equatorial pacific were mainly influenced by changes of deep water properties rather than by local primary productivity fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations but changed distinctly at similar to 280 kyr before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency after 280 kyr the thermocline was deeper and its fluctuations were at lower amplitude and higher frequency these different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial pacific ocean in this region upwelling the influx of cool nutrient rich waters from the eastern equatorial pacific or of fresh waters from rivers have probably never been important and their influence on productivity has been negligible over the studied period variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern pacific a proxy for the late quaternary history of the central east asian dust flux into the pacific therefore we suggest that the dust flux from the central east asian continent may have been an important driver of productivity in the western pacific c 2007 elsevier b v all rights reserved

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

late pleistocene paleoclimatology of the central equatorial pacific a quantitative record of eolian and carbonate deposition detailed records of vso 6i3c percentage and mass accumulation rate of caco and eolian percentage mass accumulation rate and grainsize generated for core rcl l 210 from the equatorial pacific reveal the timing of paleoclimatic events over the past 950 000 yr the caco percentage record shows the standard pacific correlation of high caco content with glacial periods but displays a marked change of character about 490 000 yr ago with older stages showing much less variability the carbonate mass flux record however does not show such a noticeable change sedimentation rates vary from about 0 5 to 3 0 cm l000 yr and during the past 490 000 yr sections with enhanced sedimentation rates correspond to periods of high caco percentage eolian mass accumulation rates an indication of the aridity of the source region are usually higher during glacial times eolian grainsize an indication of the intensity of atmospheric circulation generally fluctuates at a higher frequency than the loo ooo yr glacial cycle the mid brunhes climatic event centered at 300 000 yr ago appears as a 50 000 yr interval of low intensity and reduced variability of atmospheric circulation furthermore the nature of this entire record changes then with the younger portion indicating less variation in wind intensity than the older part of the record the late matuyama increase in amplitude of paleoclimatic signals begins 875 000 yr ago in the eolian record 25 000 yr before the 6i80 and caco percentage amplitude increases about

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

rare earth element composition of paleo maar sediments latest pleistocene early holocene jeju island korea implications for asian dust record and monsoon climate abstract the rare earth element ree composition of a 4 96 m long sediment core retrieved from the hanon paleo maar in jeju island korea was studied to investigate the east asian monsoon variations during the latest pleistocene to early holocene 22 300 9000 cal bp the studied paleo maar core sediment has two restricted source materials with distinctively different geochemical signatures asian dust blown from central asia especially northern china and mongolia and basement rock composed of trachybasalt the ree characteristics of sediments depend on the relative contribution of these two sources and thus can be used to delineate the monsoon climate in jeju island the proportion of asian dust generally decreased gradually from 67 at 22 300 cal bp indicative of progressive weakening of the winter monsoon strength in central asia integration of the ree data with toc and ms records reveals that the summer monsoon strength in jeju island decreased from 22 300 cal bp until the last glacial maximum at 18 000 cal bp and then increased to 14 000 cal bp the abrupt intensification of the summer monsoon occurred from 14 000 to 13 300 cal bp followed by the weakened summer monsoon from 13 300 to 11 000 cal bp in anti phase with the strengthened winter monsoon in central asia in the early holocene jeju island experienced further intensified summer monsoon strength