rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

middle miocene southern ocean cooling and antarctic cryosphere expansion magnesium calcium data from southern ocean planktonic foraminifera demonstrate that high latitude similar to55degreess southwest pacific sea surface temperatures ssts cooled 6degrees to 7degreesc during the middle miocene climate transition 14 2 to 13 8 million years ago stepwise surface cooling is paced by eccentricity forcing and precedes antarctic cryosphere expansion by similar to60 thousand years suggesting the involvement of additional feedbacks during this interval of inferred low atmospheric partial pressure of co2 pco 2 comparing ssts and global carbon cycling proxies challenges the notion that episodic pco2 drawdown drove this major cenozoic climate transition sst salinity and ice volume trends suggest instead that orbitally paced ocean circulation changes altered meridional heat vapor transport triggering ice growth and global cooling

phosphogenesis and weathering of shelf sediments from the southeastern united states implications for miocene δ13c excursions and global cooling the enormous phosphorite deposits of the southeastern united states indicate intense upwelling but contain small amounts of organic carbon the authors propose that deposition of organic rich sediment on continental shelves in the southeastern united states and elsewhere during marine transgressions in the late oligocene and early to middle miocene resulted in global positive delta sup 13 c shifts and the formation of early diagenetic phosphorite multiple reworking and supergene weathering from subaerial exposure during miocene marine regressions oxidized most of the organic carbon and resulted in the return of delta sup 13 c to its preexcursion value the estimated phosphorite content of the southeastern united states requires sufficient organic carbon burial 10 sup 15 kg carbon to support a 1 per thousand delta sup 13 c excursions sea level fluctuations organic carbon burial phosphogenic episodes and possibly global cooling during the cenozoic

paleoceanography of the east equatorial pacific over the past 16 myr and pacific atlantic comparison high resolution benthic foraminiferal δ18o and δ13c records at iodp site u1337 abstract we present astronomically tuned high resolution 3 4 kyr 15 8 myr long benthic foraminiferal 18 o and 13 c records from iodp site u1337 in the east equatorial pacific which provide a reference standard for stratigraphic correlation of deep sea sediments a long term glaciation history over the past 15 8 myr has been recorded in the 18 o two of the most significant glaciation events include the east antarctic ice sheet expansion eaie at 13 8 ma and the final onset of the northern hemisphere glaciation nhg in 3 3 2 5 ma a series of miocene and pliocene glaciation events exist between the eaie and nhg which are important glaciation attempts before the earth finally entered the full icehouse world in the late pleistocene a long term ocean carbon isotope decrease over the past 15 8 myr has been recorded in the 13 c ocean circulation change was the major cause of the ocean carbon isotope decrease in 9 4 8 1 ma and 4 0 ma whereas strengthened continental chemical weathering controlled the long term ocean carbon isotope decrease in most of the time of the past 15 8 myr the divergence in benthic foraminiferal 13 c and end provides strong evidence of significant ocean circulation change between 12 1 and 9 2 ma which was probably related to the formation of the isthmus of panama the internal feedbacks such as continental weathering and sea surface temperature change have great potential for modulating the weak 100 and 400 kyr signals in astronomical forcing into strong 100 and 400 kyr signals in global ice volume and carbon cycle

fracture apertures from electrical borehole scans three dimensional finite element modeling was performed to investigate the response to fractures of the formation microscanner mark of schlumberger which records high resolution electrical scans of the borehole wall it is found that the equation w carmbrx0l describes over two orders of magnitude of resistivity contrasts between borehole mud and the formation the relationship between fracture width w in mm formation sensitivity rx0 mud resistivity rm and the additional current flow a caused by the presence of the fracture a is the additional current which can be injected into the formation divided by the voltage integrated along a line perpendicular across the fracture trace coefficient c and exponent b are obtained numerically from forward modeling tool standoffs of up to 2 5 mm and fracture dips in the range from 0 to 40 were found to have an insignificant effect on the above relation a three step approach to detect trace and quantify fractures is used potential fractures in formation

the evolution and environmental significance of glaciochemistry during the ablation period in the north of tibetan plateau china in order to explore the glaciochemistry of shiyi glacier in the central qilian mountains a total of 142 samples have been collected for fresh snow surface snow snowpit and meltwater from july 2012 to november 2013 the results indicated cations dominated the glaciochemistry especially the high ca2 concentration relatively high cl and na concentrations were mainly contributed by desert dust aerosols and the atmospheric aerosols from warm water bodies such as the black caspian and aral seas the analysis also confirmed the chemical ions in fresh snow are mainly contributed by atmospheric wet deposition surface snow is mainly influenced by dry deposition and snowpits are influenced by both atmospheric deposition and leaching process while meltwater is influenced by water rock interactions the profile of ionic concentration in the snowpit became more smoothed during ablation period owing to the influence of leaching the elution sequence of the snowpit in the shiyi glacier was so42 k ca2 mg2 na cl no3 the chemical concentrations for meltwater are mainly influenced by water dilution and soil thawing the ions in snow in the central qilian mountains showed relatively lower concentrations than in the western qilian mountains tianshan mountains and altai mountains it was closer to balance than in glaciers in the central tibetan plateau but was higher than in the southern tibetan plateau different ionic sources and dissolution process had caused the differences of chemical composition for fresh snow surface snow snowpit and meltwater and these chemical compositions reflected the atmospheric background values in the northern tibetan plateau c 2014 elsevier ltd and inqua all rights reserved

variations in melt layer frequency in the gisp2 ice core implications for holocene summer temperatures in central greenland the rare melt features in the gisp2 central greenland deep ice core have decreased in frequency over the most recent 7000 years calibration of this change in melt frequency against modern spatial variation of melt frequency and temperature in central greenland and against modern temporal variability of temperatures in central greenland indicates that mean mid summer temperatures have cooled over the most recent 7000 years probably by slightly more than l c if variability of summer temperatures has not changed comparison to grip isotopic records from central greenland and to the melt record from the agassiz ice cap arctic canada suggests some seasonal and regional coherence for this cooling signal as well as for a cold event about 8000 8500 bp

reorganization of pacific deep waters linked to middle miocene antarctic cryosphere expansion a perspective from the south china sea article i nfo article history changes in intermediate and deep ocean circulation likely played a significant role in global carbon cycling and meridional heat moisture transport during the middle miocene climate transition 14 ma high resolution middle miocene 16 13 ma benthic foraminifer stable isotope records from the south china sea reveal a reorganization of regional bottom waters which preceded the globally recognized middle miocene 1 18 o increase 13 8 ma by 100 000 years an observed reversal of the benthic foraminifera 13 c gradient between odp sites 1146 2092 m and 1148 3294 m 13 9 13 5 ma is interpreted to reflect an

astronomically tuned plio pleistocene benthic δ 18 o record from south china sea and atlantic pacific comparison based on benthic foraminiferal n 18 o from odp site 1143 a 5 myr astronomical timescale for the west pacific plio pleistocene was established using an automatic orbital tuning method the tuned brunhes matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0 78 ma the tuned ages for several planktonic foraminifer bio events also agree well with published dates and new ages for some other bio events in the south china sea were also estimated the benthic n 18 o from site 1143 is highly coherent with the earth s orbit etp both at the obliquity and precession bands for the last 5 myr and at the eccentricity band for the last 2 myr in general the 41 kyr cycle was dominant through the plio pleistocene although the 23 kyr cycle was also very strong the 100 kyr cycle became dominant only during the last 1 myr a comparison of the benthic n 18 o between the atlantic odp 659 and the east and west pacific 846 and 1143 reveals that the atlantic pacific benthic oxygen isotope difference ratio vn 18 oatlpac displays an increasing trend in three time intervals 3 6 2 7 ma 2 7 2 1 ma and 1 5 0 25 ma each of the intervals begins with a rapid negative shift in vn 18 oatlpac followed by a long period with an increasing trend corresponding to the growth of the northern hemisphere ice sheet this means that all three intervals of ice sheet growth in the northern hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the atlantic as compared to that of the pacific followed by its gradual relative cooling this general trend superimposed on the frequent fluctuations with glacial cycles should yield insights into the processes leading to the boreal glaciation cross spectral analyses of the vn 18 oatlpac with the earth s orbit suggests that after the initiation of northern hemisphere glaciation at about 2 5 ma obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo ocean a 2002 elsevier science b v all rights reserved

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

minimal influence of recrystallization on middle miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial pacific stable carbon and oxygen isotopes 13c and 18o of foraminiferal tests are amongst the most important tools in paleoceanography but the extent to which recrystallization can alter the isotopic composition of the tests is not well known here we compare three middle miocene 16 13 ma benthic foraminiferal stable isotope records from eastern equatorial pacific sites with different diagenetic histories to investigate the effect of recrystallization to test an extreme case we analyzed stable isotope compositions of benthic foraminifera from integrated ocean drilling program site u1336 for which the geochemistry of bulk carbonates and associated pore waters indicates continued diagenetic alteration in sediments 14 7 ma despite this diagenetic overprinting the amplitudes and absolute values of the analyzed u1336 stable isotopes agree well with high resolution records from better preserved sites u1337 and u1338 nearby our results suggest that although benthic foraminiferal tests of all three sites show some degree of textural changes due to recrystallization they have retained their original stable isotope signatures the good agreement of the benthic foraminiferal stable isotope records demonstrates that recrystallization occurred extremely rapidly 100 kyr after deposition this is confirmed by the preservation of orbital cyclicities in u1336 stable isotope data and 18o values being different to inorganic calcite that would precipitate from u1336 pore waters during late recrystallization the close similarity of the benthic foraminiferal stable isotope records between the sites allows the well resolved paleomagnetic results of site u1336 to be transferred to sites u1337 and u1338 improving the global geological timescale

melt features in ice cores from site j southern greenland some implications for summer climate since ad 1550 horizontal and vertical distributions of melt features ice layers were examined using two ice cores 206 6 and 101 5 m deep 1 m apart from site j 66 51 9 n 46 15 9 w 2030 m a s l the temperature at 10 m was 16 3 c we observed 2804 melt features with a total thickness of 30 32 m in the 206 6 m core corresponding to 16 4 by volume of the ice equivalent core length horizontal distribution of melt features was examined by correlating melt feature thicknesses in the two cores the correlation coefficient was 0 71 n 514 for each melt feature in the two cores it was maximum for data passed through 5 and 40 year low pass filters a significant relationship p 0 005 n 36 was obtained for the vertical distribution of melt features and the june temperature on the west coast of greenland jakobshavn using this june temperatures at jakobshavn since 1550 were estimated there are three periods 1685 1705 1835 70 and 1933 45 during which mean june temperatures clearly decreased when they were estimated to he 0 1 0 4 and 0 2 c lower than the average for the whole period 1550 1989 the first two cold periods have been identified in melt features of the dye 3 and devon island ice cores and in a tree ring profile from yukon territory canada melt feature percentages in the site j ice core have increased since about 1945 probably reflecting summer temperature warming on the ice sheet

the elution of ions through field and laboratory snowpacks it has been recognised for many years that the first fraction of meltwater from a melting snowpack contains a much higher concentration of ions than that of the bulk or average snow of which the pack is comprised foster 1 978 johannessen and henriksen 1978 this process leads to the so called acid flush in the spring and can have severe ecological effects on lakes and streams hagen and langeland 1 973 leivestad and muniz 1 976 national research council of canada 1 981 we have studied elution of ions through a snowpack on folgefonna near bergen norway and in the laboratory in the field we collected meltwater samples at hourly intervals for a period of 4 d at the start of the melt season and analyzed them for ph no so ci na mg2 ca2 and k 2 m cores were also collected at the beginning and end of the experiment in order to study bulk changes in snow composition the meltwaters showed a diurnal cycle with high ionic concentrations around noon with no and so levels rising by factors of up to four and six fold compared to the average concentrations on the first day cllevels peaked much later after the no and so levels had decreased and only reached 2 3 times their lowest concentrations ph values were strongly correlated with no and s02levels suggesting that a significant proportion of these ani ns wer in the form of strong acids the laboratory experiments involved slow melting of snow samples collected in the cairngorm mountains scotland and also showed that no and so and also mg2 and k ions were removed from the snow preferentially whilst na and cltended to remain longer the position of h within the ion elution sequence is unclear due to uncertainties in the absolute determination of ph in the field measurements but the laboratory experiments confirm the differential rates of elution shown in the norwegian snowpack and reaffirms its importance in the acidification of streams during spring

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

subsidence of the northern south china sea and formation of the bashi strait in the latest miocene paleoceanographic evidences from 9 myr high resolution benthic foraminiferal δ 18 o and δ 13 c records abstract we present astronomically tuned high time resolution 3 4 kyr benthic foraminiferal 18o and 13c records between 9 ma and 5 ma from ocean drilling program odp site 1143 in the southern south china sea scs we found that the late miocene ocean carbon shift lmocs which was linked with the late miocene early pliocene biogenic bloom also occurred in the northern and southern scs a marked deep water 13c gradient as much as 1 0 of the northern and southern scs was observed between 6 5 ma and 5 9 ma which was probably caused by the significant difference in paleoproductivity between the northern and southern scs the deep 13c gradient was likely produced by rapid tectonic subsidence in the northern scs at 6 0 ma and the final formation of the bashi strait at 6 5 ma a reversed benthic 13c gradient of the northern and southern scs was also observed between 1 2 ma and 0 35 ma which was probably caused by the consecutive closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma further semi enclosed the scs basin and made the paleoproductivity the major factor influencing the deep water 13c leading to the reversed deep water 13c gradient of the northern and southern scs between 1 2 ma and 0 35 ma

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

frequency variations of the earth s obliquity and the 100 kyr ice age cycles variations in the earth s orbital parameters modulate the seasonal distribution of solar radiation and thereby induce changes in the earth s climate1 periodicities in the geological climate record with cycles of 100 41 and 23 kyr have been linked with changes in eccentricity obliquity and precession of the equinoxes respectively2 3 but although the eccentricity does vary with a 100 kyr period the effect on the incoming solar radiation is rather weak relative to the signals from obliquity and precession variations the 100 kyr signal in the climate record should therefore be of negligible intensity yet it is observed instead to dominate the record internal nonlinear processes within the climate system have been proposed to account for this fact4 14 in contrast i show here that variations in the frequency of the obliquity cycle can give rise to strong 100 kyr forcing of climate

seasonal variability of ionic concentrations in surface snow and elution processes in snow firn packs at the pgpi site on urumqi glacier no 1 eastern tien shan china to investigate the effects of both non meltwater and meltwater related post depositional processes on chemical species within the snow firn pack a research program the program for glacier processes investigation was initiated in july 2002 by the tien shan glaciological station chinese academy of sciences the seasonal variability of the ionic concentrations in surface snow samples and ion elution behavior in the snow firn pack were assessed from surface samples collected year round and 1011 samples collected from a snow pit at weekly intervals from september 2003 through september 2004 the results indicate that elevated ionic concentrations in spring and summer result from asian dust storm derived aerosol input and other aerosols entrained in precipitation potential sources of these chemical species are explored using correlation and factor analyses the elution sequence through the snow firn pack was determined to be so4 2 c a 2 n a n o3 c l k m g 2 n h4 the elution of ions at the sampling site was found to be driven primarily by air temperature and became evident when a diurnal mean temperature of 3 68c was attained at 0 38c all of the year round new ionic input was leached from the snow

some comments on climatic reconstructions from ice cores drilled in areas of high melt poor consideration has been given in many arctic circum polar ice core studies to the effect of summer snow melt on chemistry stable isotope concentrations and time scales many of these corps are drilled close to the firn line where melt is intense some come from below the firn line where accumulation is solely in the form of super imposed ice in all cases seasonal signals are reduced or removed and in some time gaps develop during periods of excessive melting which situate the drill site in the ablation zone consequently cross correlations of assumed synchronous events among the cores are invalid so that time scales along the same cores differ between authors by factors of over 2 many so called climatic signals are imaginary rather than real by reference to published analyses of cores from the superimposed ice zone on devon ice cap koerner 1970 and meighen ice cap koerner and paterson 1974 it is shown how melt affects all the normally well established ice core proxies and leads to their misinterpretation despite these limitations the cores can give valuable low resolution records for all or part of the holocene they show that the thermal maximum in the circum polar arctic occurred in the early holocene this maximum effected negative balances on all the ice caps and removed the smaller ones cooler conditions in the second half of the holocene have caused the regrowth of these same ice caps

vertical thermal gradient history in the eastern equatorial pacific during the early to middle miocene implications for the equatorial thermocline development knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical pacific multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline although the secular thermocline development has been documented back to the late miocene the early to middle miocene interval has rarely been examined in addition relationships with the dynamic antarctic ice sheets remain unclear here we investigate the vertical thermal gradient in the upper water column at integrated ocean drilling program site u1337 in the eastern equatorial pacific eep throughout the early to middle miocene 23 1 to 11 7 ma the gradient increased over the miocene climatic optimum whereas it decreased during the east antarctic ice sheet expansion eaie comparison of the eep record with its western equatorial pacific wep counterpart suggests that sea surface temperature was more stable in the wep than in the eep we further estimated equatorial thermocline from two diagonal gradients between the eep and the wep thermocline shoaled from 16 7 to 15 7 ma and tilt weakened between 16 5 and 13 8 ma the onset of the monterey excursion and the reduced antarctic ice sheet volume would have affected thermocline depth and tilt respectively thermocline depth was likely much deeper compared to pliocene to modern conditions furthermore a 4 point based distribution of isotherms 4di index was used as a metric of the evenness or unevenness of the isotherm distributions the 4di index considerably reduced at around the eaie and other mi events reflecting the evenly distributed isotherms under a more glaciated antarctica

anthropogenic sulfate and asian dust signals in snow from tien shan northwest china snow samples were collected from a 0 5 m snowpack at glacier no i and near bogda feng eastern tien shan northwest china samples that were melted in the field were analyzed for chloride nitrate sulfate sodium potassium magnesium calcium and microparticles eight samples were returned frozen and were analyzed for the above ions plus ammonium acetate formate methylsulfonate and hydrogen peroxide there was no significant difference in measured major ion concentrations between the melted and frozen samples measured cations in both sets of samples were two to three times greater than measured anions calcium and sodium are the dominant cations while sulfate is the dominant measured anion high ion burdens are associated with dusty layers in the snowpack indicating that dust from the vast arid regions of central asia is the dominant source for major ions in tien shan snow the significant increase in sulfate and decrease in the cation anion ratio in bogda eng snow relative to glacier no i snow suggest that anthropogenic emissions from urtimqi are an important source of sulfate to precipitation downwind from the city

geochemistry of dust aerosol over the eastern pamirs abstract the pamirs are situated in the inner part of the asian continent a region which plays a critical role in asian dust emission and transport this study measured the elemental composition of atmospheric dust aerosol samples collected during the period between july 2004 and april 2006 at mt muztagata eastern pamirs at a high altitude 38 17 n 75 01 e 4430 m the muztagata aerosol samples show ca al 0 7 and fe al 0 7 ratios that are distinguishable from those from other sites the la th ratios averaging 2 30 2 36 and th u ratios averaging 2 75 3 11 indicate typical eolian deposition the dust aerosol samples have very similar rare earth element ree patterns with relative enrichment of light ree a slight depletion of heavy ree and a strongly negative europium anomaly eu values averaging 0 65 the muztagata dust shows homogeneity of composition during the sampling period with minor variations due to seasonal effects and possible different air mass suggesting the possibility of a well mixed atmospheric background dust on a regional scale the zonal westerlies dominate and the longitude circulations are relatively very weak for dust transport dynamics in the pamirs and tien shan regions our results demonstrate a distinct difference in elemental composition between dust over the eastern pamirs and that over inilchek central tien shan indicating that the asian dust emission regions have great variations in their chemical properties and provide a better constraint on the climatic impact of asian dust

late pliocene monsoon linkage in the tropical south china sea the onset of northern hemisphere glaciation nhg 2 7 ma ago coincided with prominent climate changes in the tropical regions such as the african and the asian monsoons however the relationship between tropical and sub tropical monsoonal variations and high northern latitude ice sheet expansion as well as processes such as late pliocene tropical sea surface temperature sst change is not clear our late pliocene 2 5 3 3 ma monsoon proxy records and mg ca derived sst records at ocean drilling program odp site 1143 from the southern south china sea scs reveal that while tropical sst shows a stepwise decrease of 2 3 c during this period the east asian monsoon gradually strengthens in response to the onset of the nhg at the 41 kyr and 23 kyr bands ice volume change lags tropical sst by 4 kyr but leads the east asian monsoon by 12 17 kyr our finding highlights the significant role of the tropical pacific region in driving global climate change in the late pliocene which has invariable leading phase relative to the ice volume change as in the late pleistocene however the east asian monsoon shows a linear response to the onset of the nhg in the late pliocene with much bigger phase lagged at the 41 kyr and 23 kyr bands than in the pleistocene which suggests that at the obliquity and precession bands the phases of the plio pleistocene east asian monsoon variations relative to the global ice volume changes are not constant but variable therefore the east asian monsoons are not only simply driven by northern summer insolation at the precession period but also modulated by global ice volume change in high latitudes

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

paleoceanographic significance of neogene benthic foraminiferal changes in a southwest pacific bathyal depth transect temporal changes in benthic foraminiferal assemblages were quantitatively examined 63 m fraction in four southwest pacific deep sea neogene sequences in a depth transect between approximately 1300 and 3200 m to assist in evaluating paleoceanographic history the most conspicuous changes in benthic foraminiferal assemblages occurred in association with paleoclimatic changes defined at least in part by oxygen isotopic changes the largest centered at 15 ma early middle miocene is represented by an increase in the relative frequencies ofepistominella exigua which underwent a major upward depth migration at that time this was contemporaneous with the well known positive oxygen isotopic shift in the early middle miocene in sites 588 and 590 most of the increase in relative abundances ofe exigua occurred during the middle to later part of the 18o shift following major growth of the east antarctic ice sheet later assemblage changes occurred at 8 5 and 6 5 ma these associations indicate that the benthic foraminiferal assemblages in this depth transect largely adjusted to changes in deep waters related to antarctic cryospheric evolution in general the neogene benthic foraminiferal assemblages in this region underwent little change during the last 23 million years this faunal conservatism suggests that deep sea environments underwent relatively little change in the southwest pacific during much of the neogene although paleoceanographic changes did occur partly in response to high latitude cryospheric evolution these were not of sufficient magnitude to create major deep sea faunal changes in this part of the ocean the benthic foraminiferal assemblages are dominated by individuals smaller than 150 m most taxonomic turnover occurred in the larger 150 m size fractions

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

trace element and physical response to melt percolation in summit greenland snow surface melt on a glacier can perturb the glaciochemical record beyond the natural variability while the centre of the greenland ice sheet is usually devoid of surface melt many higharctic and alpine ice cores document frequent summertime melt events current hypotheses interpreting melt affected ice core chemistry rely on preferential elution of certain major ions however the precise nature of chemistry alteration is unknown because it is difficult to distinguish natural variability from melt effects in a perennially melt affected site we use eight trace element snow chemistry records recovered from summit greenland to study spatial variability and melt effects on insoluble trace chemistry and physical stratigraphy due to artificially introduced meltwater differences between non melt and melt affected chemistry were significantly greater than the spatial variability in chemistry represented by nearest neighbour pairs melt perturbed trace elements particularly rare earth elements retained their seasonal stratigraphies suggesting that trace elements may serve as robust chemical indicators for annual layers even in melt affected study areas results suggest trace element transport via meltwater percolation will deposit eluted material down pit in refrozen areas below the nearest surface chemistry peak in our experiments snow chemistry analyses are more sensitive to melt perturbations than density changes or unprocessed near infrared digital imagery

obscuring of long eccentricity cyclicity in pleistocene oceanic carbon isotope records abstract long eccentricity 400 kyr cycles in carbon isotope records from the pacific and atlantic oceans and the mediterranean sea of the past 5 0 ma are compared all records show maximum 13c values 13cmax at eccentricity minima during the pliocene but this relationship obscured in the pleistocene after 1 6 ma in particular for the open ocean deep water 13c records since a clear anti phase relationship was set up between oceanic 18o and 13c in the 100 kyr band from this time we attribute the obscured 400 kyr signal to a major change in the oceanic carbon reservoir probably associated with restructure of the southern ocean a similar change occurred in the miocene at 13 9 ma when the 400 kyr cyclicity in 13c records flattened out together with a drastic cooling and antarctic ice sheet expansion a remarkable exception is the mediterranean surface water 13c record which remained paced by the long term eccentricity cycle throughout the pliocene and pleistocene suggesting a low latitude climatic origin of the 400 kyr signal that is independent of glacial interglacial forcing since the earth is currently passing through an eccentricity minimum it is crucial to understand the nature of the 13cmax events

the evolution of pco2 ice volume and climate during the middle miocene abstract the middle miocene climatic optimum 17 15 ma mco is a period of global warmth and relatively high co2 and is thought to be associated with a significant retreat of the antarctic ice sheet ais we present here a new planktic foraminiferal 11b record from 16 6 to 11 8 ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to co2 these new data demonstrate that the evolution of global climate during the middle miocene as reflected by changes in the cyrosphere was well correlated to variations in the concentration of atmospheric co2 what is more within our sampling resolution 1 sample per 300 kyr there is no evidence of hysteresis in the response of ice volume to co2 forcing during the middle miocene contrary to what is understood about the antarctic ice sheet from ice sheet modelling studies in agreement with previous data we show that absolute levels of co2 during the mco were relatively modest 350 400 ppm and levels either side of the mco are similar or lower than the pre industrial 200 260 ppm these new data imply the presence of either a very dynamic ais at relatively low co2 during the middle miocene or the advance and retreat of significant northern hemisphere ice recent drilling on the antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the ais did occur during the middle miocene but the complete loss of the ais was unlikely consequently it seems that ice volume and climate variations during the middle miocene probably involved a more dynamic ais than the modern but also some component of land based ice in the northern hemisphere

paleobiogeography and historical biogeography of the non marine caenogastropod family melanopsidae abstract we investigate the distributions of representatives of the family melanopsidae gastropoda caenogastropoda cerithioidea from the late cretaceous to present day the present contribution discusses and partly revises former schemes of melanopsid dispersal during the cenozoic all of which were based on outdated stratigraphic and tectonic concepts as well as an incompletely considered fossil record conflating a comprehensive and stratigraphically well constrained fossil record modern paleogeographical reconstructions and contemporary climate data our goal is to present a thorough model of melanopsid distribution and its changes over the cenozoic as well as its paleogeographical and climatic constraints the family melanopsidae evolved about 90 ma ago in the late turonian from brackish cerithioidean ancestors cretaceous and paleogene species occur in marginal marine to brackish environments along the shores of the tethys and paratethys seas the extant clades of melanopsis likely derive from the evolution of freshwater melanopsis on the balkan peninsula back in the late early miocene up to the pliocene freshwater species spread toward southwestern and southeastern europe and successively replaced brackish water representatives paralleling a general decline of latter systems during the late cenozoic the southwards expansion of melanopsis and its simultaneous retreat from northern latitudes resulted in the disjunct distribution pattern observed today the genus holandriana first appeared in northern italy in the late early miocene the genera microcolpia and esperiana both first occurred in the late miocene and likely derive from brackish water melanopsis species native to peri paratethyan lakes the present day biogeographic isolation of the three latter genera and melanopsis roots in the climatic deterioration and the disappearance of major lake systems in southeastern europe while thermophilous melanopsis retreated to the warm dry climates of the mediterranean and middle east holandriana microcolpia and esperiana adapted to the seasonal cold temperate climate of southeastern and eastern europe and some species became restricted to thermal springs

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

on the origin of the long period sawtooth shape of the late pleistocene paleoclimate records the first derivative of the earth s orbital eccentricity the first time derivative of the earth s orbital eccentricity function is sawtooth shaped and closely mimics the 100 000 yr cycles of the oxygen isotope 18o time series the proxy for global ice volume change of the last 800 000 yr conversely numerical integration of the data s variance closely reproduces the orbital eccentricity function for the same interval such long lived strong correlation does not appear to be coincidental is consistent with the physics of ice sheets and with the time history of their advance and retreat

x ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 myr in the southern south china sea with benthic foraminiferal d 18 o reveal that phases of the east asian summer monsoon abruptly changed by more than 90 at 4 0 ma 2 75 ma 1 0 ma and 0 6 ma relative to global ice volume at the obliquity and the precession bands over the past 5 myr strong 400 kyr and 100 kyr cycles in the k al and ti al records consistently exist over the past 5 myr particularly these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65 n indicating an eccentricity forcing of the east asian summer monsoon the chemical weathering recorded in the elemental records of odp site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity the obliquity and the precession bands over the late pliocene and pleistocene

orbitally paced variations of water availability in the se asian monsoon region following the miocene climate transition abstract middle miocene earth had several boundary conditions similar to those predicted for future earth including similar atmospheric p co 2 and substantial antarctic ice cover but no northern hemisphere ice sheets we describe a 12 m outcrop of the terrestrial yanwan section in the tianshui basin gansu china following the miocene climate transition 13 9 13 7 ma it consists of 25 cm thick caco 3 cemented horizons that overprint siltstones every 1 m we suggest that stacked soils developed in siltstones under a seasonal climate with a fluctuating water table evidenced by roots clay films mottling presence of caco 3 nodules and stacked carbonate nodule 13 c and 18 o profiles that mimic modern soils we suggest that the caco 3 cemented horizons are capillary fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration rates pet evidenced by sharp upper and basal contacts micrite sparite and root pore cements the caco 3 of the cemented horizons and the carbonate nodules have similar mean 18 o and 13 c values but the cements have significantly smaller variance in 13 c and 18 o values and a different 18 o versus 13 c slope supporting the conclusion that these carbonates are from different populations the magneto stratigraphic age model indicates obliquity pacing of the arid conditions required to form the caco 3 cemented horizons suggesting an orbital control on water availability we suggest two possible drivers for the obliquity pacing of arid conditions 1 variability in the cross equatorial pressure gradient that controls summer monsoon asm strength and is influenced by obliquity paced variations of antarctic ice volume and 2 variability in western pacific ocean east asian continent pressure gradient controlled by the 25 45 n meridional insolation gradient we also suggest that variations in aridity were influenced by variations in pet and sensible heating of the regional land surface which are both influenced by precession controlled 35 n summer insolation we then use orbital configurations to predict lithology coincidence of obliquity minima strong asm and 35 n summer insolation maxima strong asm drives strong asm and high pet resulting in soil formation in an environment with relatively large seasonal changes in water availability coincidence of obliquity maxima weak asm and 35 n summer insolation maxima strong asm moderates the asm results in high pet and thus drives overprinting of soils by capillary fringe carbonates above a deepened and relatively stable water table coincidence of obliquity and insolation minima also moderates the asm but results in low pet and thus a high water table which explains the previously documented occurrence of aquatic plants in this section this context allows us to assign an orbital configuration to atmospheric p co 2 determined from the paleosols our best estimate of p co 2 during the times of intermediate ice volume is 475 650 230 ppmv median value with error reported as 84th 16th percentile values southern hemisphere control of asm variability during the middle miocene may have resulted in larger orbital scale water availability variations compared with the pleistocene

closing an early miocene astronomical gap with southern ocean δ18o and δ13c records implications for sea level change we present orbital scale resolution 10 kyr benthic foraminiferal 18o and 13c records from the kerguelen plateau ocean drilling program odp sites 751 and 747 from 14 5 20 0 ma spanning the miocene climate optimum mco 15 17 ma our records fill a critical gap from 17 18 ma a time when many other deep sea records are affected by dissolution we tested the fidelity of published magneto biostratigraphic age models for these sites by astronomically tuning to the 405 kyr eccentricity cycle a comparison of spectral estimates between the untuned and tuned records as well as coherency with laskar s 2004 eccentricity solution revealed quasi 100 kyr cyclicity in 18o and 13c there is only a weak signal associated with the 41 kyr obliquity cycle likely due to the 10 kyr sampling limiting resolution the 18o variations point to persistent 405 and quasi 100 kyr modulations of temperature and sea level changes through the early to middle miocene as predicted by astronomical solutions with changing dominance of the 100 and 41 kyr beat comparison of 18o records with early to middle miocene sequences from the new jersey shelf northeast australian margin bahamas and maldives suggests that the dominant sea level period preserved is the 1 2 myr obliquity cycle with sequence boundaries associated with 18o increases or maxima on the new jersey margin higher order sequences reflect the quasi 100 kyr eccentricity cycles as modulated by 405 kyr cycles we suggest that nesting of stratigraphic cycles is a function of 1 pervasive though changing milankovitch forcing of global mean sea level change and 2 preservation that depends on sufficient sediment supply and accommodation

simulation of long eccentricity 400 kyr cycle in ocean carbon reservoir during miocene climate optimum weathering and nutrient response to orbital change 1 deep sea foraminiferal 13c records contain abundant 400 kyr cycles indicating a link between eccentricity forcing and ocean carbon reservoir change here we simulate the oceanic 13c maxima events forced by the earth s orbital geometry during the miocene climate optimum mco 17 14 ma using a box model the simulated results of both surface and deep water 13c display co varying 400 kyr cycle modulated by orbital parameters weathering induced carbon input will change the burial ratio of carbonates to organic carbon and further result in periodic changes in the oceanic 13c the increase of riverine nutrient input which is synchronous with riverine carbon input often stimulates primary productivity and burial of organic carbon our results support that eccentricity maxima minima enhance reduce weathering intensity and nutrient supply which lead to minima maxima of 13c the prominent 400 kyr cycle of ocean carbon reservoir is interpreted as likely caused by a long memory of carbon in the ocean

the 800 year long ion record from the lomonosovfonna svalbard ice core we present a high resolution record of water soluble ion chemistry from a 121 m ice core spanning about 800 years the core is well dated to 2 3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1 3 of the core this core suffers from modest seasonal melt and so we present concentration data in decadal running means to minimize percolation effects sea salt ions na cl mg2 and k account for more than 70 of all ions in general sea salt ion concentrations are rather variable and have no clear association with climatic variations sulfate with 74 being from non sea salt sources has higher concentrations than seen on vestfonna ice cap but lower than in ny alesund aerosols suggesting central spitsbergen receives more marine westerly air masses than ny alesund but more sulfate enriched easterly air masses than nordaustlandet clear anthropogenic impacts are found for sulfate nitrate and ammonium and probably excess chloride after the mid twentieth century with sulfate showing a significant rise by the end of the nineteenth century sulfate and methanesulfonate concentrations correlate well during the twentieth century and it is clear that most of the preindustrial sulfate is of biogenic origin terrestrial component ca2 has the highest concentrations in the coldest part of the little ice age suggesting more windy conditions transporting local terrestrial dust to the ice cap all ion concentrations decrease at the end of the twentieth century which reflects loss of ions by runoff with non sea salt magnesium being particularly sensitive to melting

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

timing and magnitude of miocene eustasy derived from the mixed siliciclastic carbonate stratigraphic record of the northeastern australian margin article eustasy is a key parameter to understand sedimentary sequences on continental margins and to reconstruct continental ice volume in the cenozoic but timing and magnitude of global sea level changes remain controversial especially for the miocene epoch we analyzed sediment cores recovered from the marion plateau offshore northeastern australia during ocean drilling program odp leg 194 to define the mechanisms and timing of sequence formation on mixed carbonate siliciclastic margins and to estimate the amplitude of miocene eustatic adjustments we identified sequence boundaries on seismic reflection lines significantly revised the existing biostratigraphic age models and investigated the sedimentary response to sea level changes across the marion plateau we subdivided the miocene sediments into three sequence sets comprising a set of prograding clinoforms a muddy prograding carbonate ramp evolving into an aggrading platform and a lowstand ramp evolving into a backstepping ramp we recognized eight individual sequences dated at 18 0 ma 17 2 ma 16 5 ma 15 4 ma 14 7 ma 13 9 ma 13 0 ma and 11 9 ma we demonstrate that sequences on the marion plateau are controlled by glacio eustasy since sequence boundaries are marked by increases in 18 o deep sea miocene isotope events mi1b mbi 3 mi2 mi2a mi3a mi3 mi4 and mi5 respectively which reflects increased ice volume primarily on antarctica our backstripping estimates suggest that sea level fell by 26 28 m at 16 5 ma 26 29 m at 15 4 ma 29 38 m at 14 7 ma and 53 81 m at 13 9 ma combining backstripping with 18 o estimates yields sea level fall amplitudes of 27 1 m at 16 5 ma 27 1 m at 15 4 ma 33 3 m at 14 7 ma and 59 6 m at 13 9 ma we use a similar approach to estimate eustatic rises of 19 1 m between 16 5 and 15 4 ma 23 3 m between 15 4 and 14 7 ma and 33 3 m between 14 7 and 13 9 ma these estimates can be combined into a eustatic curve that suggests that sea level fell by 53 69 m between 16 5 and 13 9 ma this implies that at least 90 of the east antarctic icesheet was formed during the middle miocene the new independent amplitude estimates are crucial as the miocene is the geologic epoch for which the new jersey margin sea level record is poorly constrained

eccentricity forcing of pliocene early pleistocene climate revealed in a marine oxygen isotope record milankovitch theory that climate is controlled by variations in the earth s orbital parameters has gained wide acceptance for its ability to account for two climate cycles a 23 kyr cycle that is phase locked to the precession driven insolation cycle and a 41 kyr cycle that is phase locked to the obliquity driven insolation cycle1 6 but explaining the observed 100 kyr climate cycle in terms of milankovitch theory especially for the late pleistocene ice age cycle remains controversial in spite of a strong correlation with the 100 kyr cycle in the earth s orbital eccentricity5 one problem is that eccentricity affects insolation mainly by modulating the precession cycle its direct contribution to radiation change is too small 0 1 to effect the observed climate change directly5 7 another is the absence of a late pleistocene ice volume cycle in oxygen isotope records to match the 404 kyr component of the eccentricity cycle5 8 here we examine an oxygen isotope record spanning the interval 1 2 to 5 2 million years ago before the late pleistocene ice age regime we find 404 kyr and 100 kyr climate cycles which are coherent with eccentricity and which have amplitudes that are similar to the coexisting 23 kyr cycle analysis of these low frequency cycles suggests that they originate through an asymmetrical response mechanism that preferentially introduces variance into the climate system from the warmer portions of the eccentricity modulated precession cycle our data thus support eccentricity s role in the origin of low frequency oxygen isotope cycles before the late pleistocene ice age

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

climate response to orbital forcing across the oligocene miocene boundary spectral analyses of an uninterrupted 5 5 million year my long chronology of late oligocene early miocene climate and ocean carbon chemistry from two deep sea cores recovered in the western equatorial atlantic reveal variance concentrated at all milankovitch frequencies exceptional spectral power in climate is recorded at the 406 thousand year ky period eccentricity band over a 3 4 million year period 20 to 23 4 my ago ma as well as in the 125 and 95 ky bands over a 1 3 million year period 21 7 to 23 0 ma of suspected low greenhouse gas levels moreover a major transient glaciation at the epoch boundary approximately 23 ma mi 1 corresponds with a rare orbital congruence involving obliquity and eccentricity the anomaly which consists of low amplitude variance in obliquity a node and a minimum in eccentricity results in an extended period approximately 200 ky of low seasonality orbits favorable to ice sheet expansion on antarctica

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

eccentricity pacing of eastern equatorial pacific carbonate dissolution cycles during the miocene climatic optimum the miocene climatic optimum mco similar to 16 9 to 14 7ma provides an outstanding opportunity to investigate climate carbon cycle dynamics during a geologically recent interval of global warmth we present benthic stable oxygen o 18 and carbon c 13 isotope records 5 12kyr time resolution spanning the late early to middle miocene interval 18 to 13ma at integrated ocean drilling program iodp site u1335 eastern equatorial pacific ocean the u1335 stable isotope series track the onset and development of the mco as well as the transitional climatic phase culminating with global cooling and expansion of the east antarctic ice sheet at similar to 13 8ma we integrate these new data with published stable isotope geomagnetic polarity and x ray fluorescence xrf scanner derived carbonate records from iodp sites u1335 u1336 u1337 and u1338 on a consistent astronomically tuned timescale benthic isotope and xrf scanner derived caco3 records depict prominent 100kyr variability with 400kyr cyclicity additionally imprinted on c 13 and caco3 records pointing to a tight coupling between the marine carbon cycle and climate variations our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the mco with 75 carbonate loss occurring at paleodepths ranging from similar to 3 4 to similar to 4km in the eastern equatorial pacific ocean carbonate dissolution maxima coincide with warm phases o 18 minima and c 13 decreases implying that climate carbon cycle feedbacks fundamentally differed from the late pleistocene glacial interglacial pattern where dissolution maxima correspond to c 13 maxima and o 18 minima carbonate dissolution cycles during the mco were thus more similar to paleogene hyperthermal patterns

impacts of orbital forcing and atmospheric carbon dioxide on miocene ice sheet expansion the processes causing the middle miocene global cooling which marked the earth s final transition into an icehouse climate about 13 9 million years ago myr ago 1 4 remain enigmatic tectonically driven circulation changes 5 6 and variations in atmospheric carbon dioxide levels 7 8 have been suggested as driving mechanisms but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult here we present high resolution climate proxy records covering the period from 14 7 to 12 7 million years ago from two complete sediment cores from the northwest and southeast subtropical pacific ocean using new chronologies through the correlation to the latest orbital model 9 we find relatively constant low summer insolation over antarctica coincident with declining atmospheric carbon dioxide levels at the time of antarctic ice sheet expansion and global cooling suggesting a causal link we surmise that the thermal isolation of antarctica played a role in providing sustained long term climatic boundary conditions propitious for ice sheet formation our data document that antarctic glaciation was rapid taking place within two obliquity cycles and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change

middle miocene ice sheet dynamics deep sea temperatures and carbon cycling a southern ocean perspective 1 relative contributions of ice volume and temperature change to the global 1 18o increase at 14 ma are required for understanding feedbacks involved in this major cenozoic climate transition a 3 ma benthic foraminifer mg ca record of southern ocean temperatures across the middle miocene climate transition reveals 2 2 c cooling 14 2 13 8 ma indicating that 70 of the increase relates to ice growth seawater 18o calculated from mg ca and 18o suggests that at 15 ma antarctica s cryosphere entered an interval of apparent eccentricity paced expansion glaciations increased in intensity revealing a central role for internal climate feedbacks comparison of ice volume and ocean temperature records with inferred pco2 levels indicates that middle miocene cryosphere expansion commenced during an interval of southern ocean warmth and low atmospheric pco2 the antarctic system appears sensitive to changes in heat moisture supply when atmospheric pco2 was low suggesting the importance of internal feedbacks in this climate transition

obliquity and long eccentricity pacing of the middle miocene climate transition 1 the middle miocene east antarctic ice sheet expansion eaie which is indicated by an abrupt 1 increase in global benthic foraminiferal 18o at 13 8 ma marks the middle miocene climate transition mmct and has been related to astronomically modulated changes in the global carbon cycle here we present high resolution 3 4 kyr benthic foraminiferal 18o and 13c records from iodp site u1337 in the central equatorial pacific which spans the period 12 2 15 8 ma the isotopic records clearly demonstrate significant imprints from periodic variations in the earth s orbital parameters particularly the obliquity 40 kyr and the long eccentricity 400 kyr cycles while the benthic 18o and 13c exhibit nearly identical amplitudes for glacial interglacial cycles from 15 8 to 12 2 ma the long term trends in the benthic 18o and 13c had started to reverse after the beginning of the eaie within the 400 kyr band the benthic 18o and 13c displays a constant phase relationship between 15 8 and 12 2 ma at the 41 kyr band however a phase reversal reaching 180 between 18o and 13c occurs from 13 8 ma to 14 0 ma during the period of the eaie a similar phase relationship of benthic foraminiferal 18o and 13c at the 400 kyr band and the 41 kyr band is also observed at odp site 1146 from the northern south china sea this phase jump occurs when the long term trends in 18o and 13c split suggesting a decoupling of the global ice volume and ocean carbon reservoir changes during the middle miocene

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

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

early pleistocene glacial cycles and the integrated summer insolation forcing long term variations in northern hemisphere summer insolation are generally thought to control glaciation but the intensity of summer insolation is primarily controlled by 20 000 year cycles in the precession of the equinoxes whereas early pleistocene glacial cycles occur at 40 000 year intervals matching the period of changes in earth s obliquity the resolution of this 40 000 year problem is that glaciers are sensitive to insolation integrated over the duration of the summer the integrated summer insolation is primarily controlled by obliquity and not precession because by kepler s second law the duration of the summer is inversely proportional to earth s distance from the sun

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

preliminary results from measurements of selected trace metals in the snow firn pack on urumqi glacier no 1 eastern tien shan china we present preliminary results on the occurrence of pb cd zn al and fe in dated samples collected from snow firn packs at an altitude of 4130 m on urumqi glacier no 1 eastern tien shan extreme precautions for avoiding contamination were taken throughout the sampling processing transportation and analysis procedures the concentrations of trace metals were determined by a double focusing inductively coupled plasma mass spectrometer in an ultra clean room the average concentrations for these metals in surface snow are in ng g 1 pb 2 4 cd 0 05 zn 10 0 al 100 0 and fe 130 0 these are higher concentrations especially for pb and zn than those in the polar and or low latitude remote areas the data show that the input of trace metals to the snow has a clear seasonal change lower concentrations in surface snow can be found in july through september and higher concentrations from october to march with an exception for january the mean concentrations of the elements in the snow firn pack also indicate seasonal variations and show a marked inverse relationship with temperature possibly a result of meltwater percolation in the snow firn pack

the 41 kyr world milankovitch s other unsolved mystery 1 for most of the northern hemisphere ice ages from 3 0 to 0 8 m y global ice volume varied predominantly at the 41 000 year period of earth s orbital obliquity however summer or summer caloric half year insolation at high latitudes which is widely believed to be the major influence on high latitude climate and ice volume is dominated by the 23 000 year precessional period thus the geologic record poses a challenge to our understanding of climate dynamics here we propose that variations in the insolation gradient between high and low latitudes control high latitude climate and ice volume during the late pliocene and early pleistocene the differential heating between high and low latitudes driven by obliquity controls the atmospheric meridional flux of heat moisture and latent energy which may exert the dominant control on high latitude climate on milankovitch timescales in the two dimensional zonal energy balance models typically used to study the long term evolution of climate the meridional atmospheric moisture flux is usually kept fixed the hypothesis that insolation gradients control the poleward energy fluxes precipitation and ice volume at high latitudes has never been directly examined within the context of an ice sheet model in light of what we know about modern energy fluxes and their relative influence on high latitude climate this possibility should be examined

orbitally paced climate evolution during the middle miocene monterey carbon isotope excursion one of the most enigmatic features of cenozoic long term climate evolution is the long lasting positive carbon isotope excursion or monterey excursion which started during a period of global warmth after 16 9 ma and ended at similar to 13 5 ma approximately 400 kyr after major expansion of the antarctic ice sheet we present high resolution 1 9 kyr astronomically tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern pacific odp sites 1146 and 1237 which shed new light on the middle miocene carbon isotope excursion and associated climatic transition over the interval 17 1 12 7 ma we recog nize three distinct climate phases with different imprints of orbital variations into the climatic signals 1146 and 123 7 delta 18 o delta 13 c 1237 xrt fe fraction 63 pm 1 climate optimum prior to 14 7 ma characterized by minimum ice volume and prominent 100 and 400 kyr variability 2 long term cooling from 14 7 to 13 9 ma principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced delta 13 c increase 3 icehouse mode after 13 9 ma with distinct 100 kyr variability and improved ventilation of the deep pacific the monterey carbon isotope excursion 16 9 13 5 ma consists overall of nine 400 kyr cycles which show high coherence with the long eccentricity period superposed on these low frequency oscillations are high frequency variations 100 kyr which closely track the amplitude modulation of the short eccentricity period in contrast to delta 13 c the delta 18 o signal additionally shows significant power in the 41 kyr band and the 1 2 myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 delta 18 o signal our results suggest that eccentricity was a prime pacemaker of middle miocene climate evolution through the modulation of long term carbon budgets and that obliquity paced changes in high latitude seasonality favored the transition into the icehouse climate c 2007 elsevier b v all rights reserved

astronomically modulated neogene sediment records from the south china sea 1 general global cooling over the neogene has been modulated by changes in earth s orbital parameters investigations of deep sea sediment sequences show that various orbital cycles can dominate climate records for different latitudes or for different time intervals however a comprehensive understanding of astronomical imprints over the entire neogene has been elusive because of the general absence of long continuous records extending beyond the pliocene we present benthic foraminiferal 18o and 13c records over the past 23 ma at ocean drilling program site 1148 in the northern south china sea and construct an astronomically tuned timescale tj08 for these records based on natural gamma radiation and color reflectance data at this site our results show that a 41 ka cycle has dominated sediment records at this location over the neogene displaying a linear response to orbital forcing a 100 ka cycle has also been significant however it is correlated nonlinearly with earth s orbital variations at the 100 ka band the sediment records also display a prominent 405 ka cycle although this cycle was coherent with orbital forcing during the oligocene and the early miocene it was not coherent with earth s orbital variations at the 405 ka band over the whole neogene amplification of northern hemisphere and southern hemisphere glaciation since the middle miocene may be responsible for this change in sedimentary response our benthic foraminifera 18o and 13c records further exhibit amplitude variations with longer periods of 600 1000 1200 and 2400 ka apparently these cycles are nonlinear responses to insolation forcing

development of the east asian monsoon and northern hemisphere glaciation oxygen isotope records from the south china sea abstract oxygen isotope records of the surface dwelling foraminifer globigerinoides ruber from odp site 1143 in the southern south china sea scs are presented for the last 5 ma the g ruber 18o of site 1143 for the past 500 ka is lighter by 0 5 1 0 in interglacial and by 0 1 0 5 in glacial periods than the site 806b record from the ontong java plateau we infer the light glacial interglacial g ruber 18o at site 1143 compared with the open western pacific to have been caused by stronger monsoon induced precipitation over the scs while glacial interglacial planktonic 18o values remained stable over the 3 3 2 5 ma period the benthic cibicidoides wuellerstorfi 18o gradually became positive leading to an obvious slope in their 18o difference 18ob p the stable glacial interglacial g ruber 18o over this period is probably caused by the decrease of sea surface salinity which counteracted the effects of global ice volume and sea surface temperature on the g ruber 18o we interpret that the intensification of the east asian monsoon winds coupled with the northern hemisphere glaciation 3 3 2 5 ma ago likely brought frequent and strong precipitation over the scs and or caused large scale intrusions of borneo alongshore low salinity waters to the southern scs which greatly freshened the scs and decreased its salinity after 2 5 ma especially in the quaternary period the planktonic and benthic 18o show similar variations over glacial interglacial cycles in responding to the waxing and waning of the northern hemisphere continental ice sheet and their relatively stable 18o difference 18ob p indicates a period of steady fluctuations of the east asian monsoon winds the more positive values of 18ob p probably suggest stronger east asian winter monsoon during quaternary glacials whereas the more negative values of 18ob p may imply stronger east asian summer monsoon during quaternary interglacials

on the origin of the 100 kyr cycles in the astronomical forcing 1 investigations during the last 25 years have demonstrated that the astronomically related 19 23 and 41 kyr quasiperiodicities actually occur in long records of the quaternary climate however the same investigations also identified the largest climatic cycle as being about 100 kyr long as the 100 kyr variations in standing insolation due to eccentricity change are too small they cannot be the direct cause of the ice ages this is the reason why most of the modeling studies attempting to explain the relation between the astronomical forcing and climatic change have focused on this 100 kyr cycle in this paper we will show the astronomical origin of the periods at about 100 kyr that characterize the long term variations of eccentricity of its first derivative of the frequency modulation of obliquity and of the inclination of the earth s orbit on the invariable plane of reference five independent values are found between 95 and 107 kyr and a wavelet signature is suggested to test the possible relationships between the astronomical and climatic variables proxy records from deep sea cores and european programme for ice coring in antarctica ice core and modeling results from the louvain la neuve two dimensional model are used for illustration