central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

the sedimentary framework of northern spencer gulf south australia abstract northern spencer gulf is the landward extremity of a shallow marine embayment which occupies a structural depression that overlies a major precambrian lineament situated in a warm temperate climate the low rainfall and high evaporation have created high salinities resulting in an hydrological inverse estuary modern sedimentation is dominantly biogenic carbonate to mixed terrigenous carbonate it is controlled by a mesotidal regime with occasional storm surges minor wave activity and a prolific growth of seagrass in shallow water the skeletal detritus consists of bivalves gastropods forams echinoids coralline algae and bryozoa the subtidal zone between 10 25 m is divided morphologically into two provinces the wide southern part has a relatively smooth floor but the northern part is narrower and the seafloor is either scoured free of loose sediment or covered with wide belts of megaripples the subtidal zone between 0 10 m is everywhere dominated by seagrass meadows the seagrasses are largely posidonia australis and p sinuosa and occupy broad depositional platforms and discrete offshore banks the seagrass meadows produce and trap mollusc foram detritus resulting in the accumulation of very poorly sorted organically bound structureless carbonate muddy sand intertidal and supratidal zone sediments are very extensive the intertidal zone includes bare sand flats or those covered by the seagrass zostera dense mangroves avicennia marina from mean sea level to spring high tide level are followed progressively by a halophytic samphire association and an atriplex saltbush association extensive algal mats occur with the halophytes and extend into the mangrove forests the sediments are muddy and only moderately calcareous the supratidal zone consists mainly of bare carbonate flats some stranded beach ridges and coastal dunes the carbonate flats contain discoidal gypsum crystals in weakly layered fenestral calcitic mud coastal changes during historic time are limited and the dominant sedimentary regime in northern spencer gulf is the vertical growth of seagrass areas to form intertidal sand flats

quaternary seismic stratigraphy of northern spencer gulf south australia abstract high resolution continuous seismic reflection profiles of northern spencer gulf which is shallower than 25 m show seismic discordances and bed reflectors to depths of 20 m below the seafloor comparison with vibrocore data indicates a correspondence of seismic discordances with major stratigraphic boundaries often enhanced by pedogenesis holocene marine sediments generally form a thin during each successive quaternary marine inundation the broad and generally flat seafloor became covered by thin sheet drapes of muddy sand and sandy mud such flat areas became progressively restricted by the encroaching growth of marginal accretionary platforms and seagrass banks ephemeral lakes or sabkhas were established as well as beach ridges aeolian sand dunes and distal alluvial fans

palynological evidence for the latest oligocene early miocene paleoelevation estimate in the lunpola basin central tibet uplift of the tibetan plateau is ultimately driven by the cenozoic collision between the indian and eurasian plates and their continued convergence one approach for studying the tibetan plateau uplift is to verify the paleoelevation changes from collision to present day this is important for understanding both the tectonics and the climatic effects the new high resolution palynological record of the uppermost oligocene to the lowest miocene strata from the lunpola basin indicates that the vegetation types during the latest oligocene earliest miocene were dominated by mixed coniferous broadleaved forests being different from the modern steppe vegetation by using the coexistence approach to the fossil pollen records after calibration the effects of temperature difference and the lapse rate a maximum paleoelevation of 3190 100 m asl was estimated in the lunpola basin in the latest oligocene earliest miocene being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region

climate science timing is everything during deglaciations links between various climate records for the north atlantic ocean and the mediterranean sea have helped to identify a potential mechanism that enhanced sea level rise during the last interglacial time interval see letter p 197 a central goal of palaeoclimate research is that of deciphering the mechanisms responsible for major state shifts in the earth system such as between glacial and interglacial conditions this has proven difficult enough even for the last glacial termination t i much less termination ii t ii which ended glacial conditions about 130 000 years ago gianluca marino et al use new and existing data to demonstrate a link within uncertainties between heinrich stadial 11 hs11 a prominent northern hemisphere cold event and the timing of peak sea level rise during t ii a strong southern hemisphere warming also occurred during hs11 consistent with the idea of a bipolar seesaw that would probably have promoted antarctic ice sheet melting in contrast rapid sea level rise in t 1 clearly postdated heinrich stadial 1 possibly in response to differing co2 and insolation conditions during t i and t ii fundamentally different mechanisms seem to be at work in triggering glacial terminations

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

variations of water stable isotopes delta o 18 in two lake basins southern tibetan plateau 18 o measurements based on systematic sampling and isotopic modeling have been adopted to study the controls of stable isotopes in lake water in two lake basins lakes yamdrok tso and puma yum tso at two different elevations on the southern tibetan plateau temporally 18 o values in precipitation and lake water display a seasonal fluctuation in both lakes spatially 18 o values in the two lake basins increase by 10 from the termini of glaciers to the lake shores by 1 from the lake shores to the lake center and by 0 4 from the water surface to depth in these lakes the clear annual 18 o variations indicate that lake water mixes sufficiently in a short time model results show that glacial meltwater and surface lake water temperature are not the dominant factors in the balance process of stable isotopes in lake water equilibrium 18 o values decrease by 0 8 for yamdrok tso lake and 0 6 for puma yum tso lake when glacial meltwater contributions to these lakes shrink by 60 18 o ratios increase rapidly during the initial stages and take a longer time to approach the equilibrium value

paleocene to pliocene low latitude high elevation basins of southern tibet implications for tectonic models of india asia collision cenozoic climate and geochemical weathering the elevation history of the tibetan plateau promises insight into the mechanisms and dynamics that develop and sustain high topography over tens of millions of years we present the first nearly continuous cenozoic elevation history from two sedimentary basins on the southern tibetan plateau within the latest cretaceous to eocene gangdese arc oxygen isotope and 47 clumped isotope compositions of nonmarine carbonates allow us to constrain carbonate formation temperature and reconstruct the paleoprecipitation record of the eocene to pliocene oiyug basin and paleocene to eocene penbo basin we exploit the systematic decrease of surface temperature and meteoric water 18o values with elevation to derive paleoelevation estimates for these basins minimally altered and unaltered pedogenic and lacustrine carbonates from the oiyug basin yield 47 cdes relative to the carbon dioxide equilibrium scale cdes values of 0 625 to 0 755 which correspond to temperatures of 1 30 c using a 47 thermometer for low temperature carbonates similarly the penbo basin yielded 47 cdes values of 0 701 to 0 726 corresponding to temperatures of 6 12 c the apparent evidence for survival of primary clumped isotope values in the face of substantial burial and heating is an important result for the field of carbonate clumped isotope thermometry our paleoelevation estimates for the eocene to pliocene oiyug basin 6 5 4 1 km support previous evidence that high elevations were attained in southern tibet by at least ca 30 ma stable isotope results allow for the possibility of significant topographic subsidence during the miocene as a result of regional extension in the penbo basin our paleoelevation estimates for the paleocene to eocene nianbo formation 4 4 1 3 1 7 km and eocene pana formation 4 1 1 2 1 6 km extend the altitude record of the southern tibetan plateau to pre india asia collision these results support the lhasaplano model of an andean type continental margin tectonic system the rise of the himalayas and tibet is often invoked to understand isotopic proxies for global chemical weathering in the cenozoic and has constrained the debate on the nature of co2 climate weathering feedbacks the nature of the tibetan paleoelevations from pre to postcollision as presented here indicates that high relief at low latitude prevailed on the asian margin much earlier than previously thought thus high topography alone at low latitude is not sufficient to account for the cenozoic weathering proxy record

north atlantic sea surface temperatures for the last 1 1 million years summary a 1 2 ma time series of north east atlantic sea surface temperature sst has been assembled from the spliced record of piston core k 708 7 0 68 0 ma and hydraulic piston cores taken in nearby dsdp hole 552a 1 2 0 68 ma a no analogue fauna precludes making credible sst estimates in the interval 1 2 1 1 ma but the record above 1 1 ma is suitable for sst estimates and related time series analysis the amplitude of sst variation is considerably higher in the brunhes than in the upper matuyama this is due both to colder glacial sst minima after 0 85 ma and to increasingly warm interglacial sst maxima from 0 7 to 0 4 ma the dominant periodicity in the sst signal is centred near 95 000 years it increases in amplitude by a factor of four from the bottom of the record to the top with the largest increase occurring between 0 7 and 0 4 ma this suggests a relatively gradual evolution of 100 000 year power over half a million years of the late quaternary rather than a single abrupt change at 0 9 ma significant but progressively smaller spectral peaks occur at periods of 54 000 41 000 31 000 23 000 and 19 000 years both the 54 000 year and 31 000 year signals may be a response to insolation forcing by minor obliquity terms long term 18 o records show small responses by the ice sheets at or near these two periods indicating the probable initial response of the climate system to these insolation rhythms in phase relationships between 18 o and sst at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag the mechanism by which such small insolation and ice volume signals become enhanced in the sst record is not clear

statistical analysis of grain size distribution in pleistocene sediments from lake biwa japan abstract time series of grain size distributions from pleistocene sediments deposited in lake biwa during the past 550 millennia show dominant periods of 40 000 and 20 000 yr that are very close to those predicted by the milankovitch theory as well as a period of about 70 000 yr not directly predicted by this theory the 70 000 yr period is strongest followed by the 20 000 yr period the sequences also show that coarser particles were deposited in general during strong solar insolation whereas finer particles were deposited during weak insolation

modelling late cenozoic isostatic elevation changes in the barents sea and their implications for oceanic and climatic regimes preliminary results late cenozoic isostatic changes in the elevation of the barents sea are simulated using a numerical model isopach maps of the deposits off present day bear island and storfjorden troughs made earlier are used to calculate the thickness of sediment cover removed from the respective drainages basins at various time intervals during the last 2 3 ma results indicate that barents sea was subaerially exposed at 2 3 ma and major parts of it became submarine after 1 ma barents sea today receives around 40 of the warm and saline north atlantic waters flowing into the scotland greenland ridge and about half of the atlantic water entering the arctic ocean it thus has an important role to play in the present day ocean circulation pattern in the polar north atlantic region and water mass transformations that take place in the greenland iceland norwegian sea and the arctic ocean the effects of an uplifted barents sea on the oceanic regime and the arctic sea ice cover under the present day forcings fields are studied using the miami isopycnic coordinate ocean model preliminary results indicate that a subaerial barents sea causes an increased input of warm atlantic waters into the arctic ocean through the fram strait which results in warming of the atlantic water masses in the arctic ocean followed by a reduction in the sea ice cover the obtained findings can be used to explain the apparent discrepancy in the late cenozoic record of the sub arctic and arctic regions whereby fennoscandia iceland and greenland are envisaged to have been covered by major ice sheets during late pliocene whereas high arctic areas such as svalbard and ne greenland were apparently free of any major ice r 2002 elsevier science ltd all rights reserved

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

biostratigraphy and late cenozoic paleoceanography of the arctic ocean foraminiferal lithostratigraphic and isotopic evidence detailed studies of benthonic foraminifera stable isotopes and lithofacies in cores from the southeastern alpha ridge central arctic ocean reveal some new aspects of arctic ocean paleoceanography high ratios of benthonic to planktonic foraminifera are found in most of the quaternary sediment units and ratios of 1 1 appear to characterize the arctic deep water sediments benthonic foraminifera in the carbonate mud unit m show a succession of calcareous species reflecting increased influx of norwegian sea bottom water to the arctic ocean during the past 0 4 m y foraminiferal and lithological data indicate less uniform sedimentation during a warmer interval from 0 4 to 0 6 ma when most of the silty lutite unit l was deposited at the cesar site lower pleistocene units j to i contain less limestone and more dolomite and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera upper pliocene units h to ab contain rare limestone and relatively large amounts of do lomite and quartz sand middle to upper pliocene units ab to a3 are marked by abundant sand sized ferromanganese coated particles which in many cases have a silt nucleus hence much of the coarse sand in these units does not indicate increased ice rafting the pliocene sediments mostly contain a low diversity assemblage of agglutinated foraminifera but a mixed calcareous arenaceous fauna occurs in a short interval above the matuyama gauss boundary 2 4 ma stable isotopic curves occur within sequences which broadly correspond to stages 1 9 of the global record below stage 9 the record is discontinuous strong vertical mixing apparently prevailed during most of the pliocene and early pleistocene then decreased during the past 0 4 m y owing to damping by a perennial ice cover isotopic and foraminiferal data however suggest that an interval of perennial sea ice also occurred during the late pliocene at the time of the earliest glacial event recorded in the north atlantic

a dual channel approach to lithoseismics using high frequencies and their application as a way round the synchronous bubble oscillation sbo phenomenon this paper describes an application of high resolution continuous seismic reflection profiling in which a recent development in seismic source technology a miniature high power high frequency electrodynamic boomer type transducer and a synchronous dual channel signal processor were operated together to minimise low frequency induced bubble oscillation associated with wake entrapped and other air bubbles by taking advantage of the natural low pass filter effect of the sub bottom and the limitations of the dynamic range of simple single channel graphic recorders a split dual channel record was produced one with shallow real high resolution penetration and a second with conventional system noise level limited penetration

timing and structure of the mid pleistocene transition records from the loess deposits of northern china abstract the mid pleistocene transition mpt from obliquity to eccentricity forced climate variations has been extensively documented within the oceanic realm using a collection of orbitally tuned records of palaeoclimatic change from the loess sequences of northern china we have analysed terrestrial palaeomonsoon behaviour since 1 5 ma and characterised the structure of the mpt wavelet analysis of a stacked magnetic susceptibility record from the loess sequences indicates that the onset of 100 kyr cyclicity was synchronous in both global ice volume and the east asian monsoon system however analysis in the time domain reveals that during the mpt interim period the east asian winter monsoon appears to have weakened whilst global ice volume was increasing indicating that the palaeomonsoon was not the primary forcing mechanism responsible for driving the global climatic change

pleistocene paleoceanographic correlations northern greenland sea to central arctic ocean abstract correlation of pleistocene paleoceanographic events across parts of the polar seas is accomplished with core mg 123 from the swedish ymer 80 cruise the 8 72 m sediment core one of the longest recovered from any part of the arctic ocean contains abundant microfossils and coarser grain sediment that are useful in interpretation and correlation of pleistocene events with shorter sediment cores in the central arctic ocean faunal and sediment correlations are constrained by 18 o correlations and a time series analysis that matches several possible sedimentation rates for mg 123 with central arctic ocean sedimentation rates and provides a best fit correlation of the cores the results of this study provide the first correlation of northern greenland sea southern arctic ocean sediment with that of the central arctic ocean more than 1000 km distant oceanic circulation patterns between the areas during the pleistocene involved increased circulation during interglacials with reduced circulation during glacials subpolar water was not present in the northern greenland sea during the past 600 000 years during this time alternating phases of the climate cycle show a strong relationship to the 100 000 year milankovitch cycle

central arctic ocean response to pleistocene earth orbital variations abstract three central arctic ocean sediment cores were sampled for percentage carbonate number of foraminifera and texture these three parameters were used in spectral analyses to test the idea that the ice covered arctic ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice free oceans the record for two of the cores represents approximately 1 my and the record for the third approximately 400 000 yr the 100 000 yr frequency is well represented in all of the cores a 40 000 yr frequency may be present as well an unexpected 70 000 yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity the strong 100 000 yr signal confirms that in spite of ice feedback the arctic ocean has responded to orbital forcing in much the same manner as have ice free oceans

orbital signature of interglacials a specific orbital configuration high obliquity combined with the june perihelion marked the beginning of the past three interglacials this suggests that the primary cause of the glacial cycle may be astronomical an astronomical climate index aclin is introduced which combines the three orbital variables in the time lag bivariant model designed to predict the major climate changes in the late and middle pleistocene and in the near future aclin closely correlates with the major climatic events revealed by independently dated proxy climate indicators of the past 130 000 yr it successfully differentiates the interglacials and displays a 100 000 yr periodicity it predicts an early end of the present inter glacial and the start of a new one in 114 000 yr

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

anomalous south atlantic lithologies confirm global scale of unusual mid pleistocene climate excursion abstract carbonate rich nannofossil oozes are the typical sediments deposited under the low productivity regime of the subtropical gyre in the south atlantic surface productivity has remained virtually constant during the late pleistocene schmiedl and mackensen palaeogeogr palaeoclimatol palaeoecol 130 1997 43 80 increasing slightly only during the most extreme glacial periods recently the puzzling occurrence of thick monospecific diatom layers ethmodiscus rex has been reported within the carbonaceous sequences of two sediment cores in the south atlantic gyre schmieder et al earth planet sci lett 179 2000 539 549 the layers dated 544 534 ka are isochronous and record a period of increased organic carbon flux above them at 530 524 ka unusually high carbonate contents are recorded this double feature of anomalous lithologies is unique in the sediment record of the last 1500 kyr and can be related to the terminal event of the mid pleistocene climate transition mpt the mpt is characterized by reduced thermohaline circulation and stronger carbonate dissolution schmieder et al earth planet sci lett 179 2000 539 549 reduced circulation and a more stratified water column may have trapped nutrients in deep nitrate pools and may have fostered favorable conditions for the development of deep dwelling populations of e rex the onset of more turbid conditions led to the rapid settling of diatom populations subsequently introduced nutrients to the surface layer and improved calcite preservation thus creating a biogenic silica carbonate double peak the carbonate peak is synchronous with an unusual mid pleistocene sapropel observed in the mediterranean which is attributed to a massive odd monsoon over central africa rossignol strick et al nature 392 1998 269 272 since summer insolation was relatively low during this time the formation of this thick sapropel cannot be explained in terms of current understanding of astronomical forcing rossignol strick et al nature 392 1998 269 272 a non linear response to a 400 kyr low frequency climatic cycle as discussed for the mediterranean sapropel is not confirmed by data from our south atlantic core records

an 80 year summer temperature history from the xiao dongkemadi ice core in the central tibetan plateau and its association with atmospheric circulation abstract the climate significance of oxygen isotopes from the central tibetan plateau ctp ice cores is a debated issue because of large scale atmospheric circulation a high resolution 18 o record was recovered from the xiao dongkemadi xd ice core which expanded the spatial coverage of 18 o data in this region annual average 18 o correlated significantly with nearby mjjas air temperatures suggesting the 18 o can be used as a proxy to reconstruct regional climate change the reconstructed temperature anomaly is related to the regional and global warming trends and the greater warming amplitude since 1970s is related to the elevation dependency of the warming signal the close relationship of the warming to variations in glacier mass balances and discharge reveal that recent warming has led to obvious glacier shrinkage and runoff increase correlation analysis suggests that monsoon and westerly moisture substantially influence the ctp ice core records along with an increase in their level of contribution to the xd core accumulation in recent decades and confirms a teleconnection of regional climate of the ctp ice cores with climate parameters in the indian and north atlantic oceans

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

analysis of lithic technology of lower pleistocene sites and environmental information in the nihewan basin north china the nihewan basin is an important area for studying the evolution of early hominids in china among 15 recently discovered and reported lower pleistocene sites in the basin eight majuangou xiaochangliang dachangliang banshan donggutuo feiliang huojiadi xujiapo have been specifically analyzed by the authors this paper is a synthesis of results of analysis of lithic technology and palaeoenvironmental information of these sites three distinct arrangements of techniques are identified from the eight sites which represent the different lithic techniques cognitive capability and cultural contents the dgt core from donggutuo indicates that the cognitive capability and the culture deepness of early hominids in china surpassed expectations re evaluation is required of early human technology and behavioral mode in china

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

paleoclimate record for northwind ridge western arctic ocean core nwr 5 from northwind ridge in the western arctic ocean contains a climatic record that extends back for over 1 million years dark brown beds with abundant planktonic foraminifers represent interglacial conditions whereas glacial and transitional conditions are represented by lithologies barren or nearly barren of planktonic foraminifers we conclude that seven and possibly all nine interglacials of the brunhes magnetic chronozone the last 780 000 years are represented in nwr 5 for about the last 800 000 years the western arctic ocean apparently had a permanent thick ice cover and was unable to support significant populations of planktonic foraminifers except during major interglacials when seasonally open and high productivity surface waters occurred at least along the basin margins our results support previous interpretations that climate variations in the arctic are in phase with glacial interglacial cycles observed in other proxy records of the brunhes

synchronization of the climate system to eccentricity forcing and the 100 000 year problem the 100 000 year problem refers to an apparent mismatch between the strength of solar forcing associated with the 100 000 year cycle of eccentricity in the earth s orbit and the amplitude of glacial interglacial cycles numerical analyses suggest that recent glacial interglacial cycles can instead be explained by a phase locking between internal climate oscillations and the 413 000 year eccentricity cycle

stable isotopic variations in modern herbivore tooth enamel plants and water on the tibetan plateau implications for paleoclimate and paleoelevation reconstructions stable isotope analyses of fossil teeth and other authigenic minerals have been used to reconstruct the paleoenvironment and paleoelevation of the tibetan plateau the accuracy of such reconstructions is limited by the lack of a comprehensive modem comparative database from the region we analyzed the carbon and oxygen isotopic compositions delta c 13 and delta o 18 values of tooth enamel from modem herbivores the delta c 13 values of gasses and the delta o 18 values of water samples collected from various elevations within the tibetan plateau to examine their relationships with modem environment elevation the delta c 13 values of enamel samples from horses yaks and goats display a narrow range of variation with a mean of 10 7 1 4 parts per thousand n 301 indicating that these modem herbivores were feeding predominantly on c3 plants consistent with the current dominance of c3 vegetation in the region some of the samples have delta c 13 values between 7 3 and 10 parts per thousand although these higher delta c 13 values could suggest consumption of some c4 plants by the animals the lack of significant seasonal delta c 13 variations within individual teeth indicates that these higher enamel delta c 13 values are due to consumption of c3 plants experiencing water stress and or some cam plants rather than c4 plants our data show that the conservative cut off delta c 13 value for a pure c3 diet within the tibetan plateau should be 8 parts per thousand for modem herbivores and 7 parts per thousand or even 6 5 parts per thousand for fossils if the region was as and in the past as today in contrast to the small intra tooth delta c 13 variations within individual teeth serial enamel samples display large intra tooth delta o 18 variations reflecting seasonal variations in the delta o 18 of meteoric water the mean delta o 18 values of tooth enamel from yaks and horses show a strong correlation with water delta o 18 values confirming that the delta o 18 of tooth enamel from obligate drinker generally tracks the 6180 of meteoric water unfortunately elevation alone cannot explain most of the variance in the delta o 18 of precipitation and tooth enamel suggesting that quantitative reconstruction of the paleoelevation of the tibetan plateau using re constructed delta o 18 values of paleo meteoric water from fossil enamel or other oxygen bearing minerals is not warranted for a given environment horses have the lowest enamel delta o 18 values while goats display the highest enamel delta o 18 values among the species studied the large inter species delta o 18 variations are likely due to differences in physiology and diet drinking behavior of the animals this underscores the importance of species specific studies when interpreting delta o 18 data of fossil mammalian teeth in a stratigraphic sequence as a record of paleoclimate changes c 2008 elsevier b v all rights reserved

predicting paleoelevation of tibet and the himalaya from δ18o vs altitude gradients in meteoric water across the nepal himalaya the 18o value of meteoric water varies with elevation providing a means to reconstruct paleoelevation if the 18o values of paleowater are known in this study we determined the 18o values of water 18omw from small tributaries along the seti river and kali gandaki in the nepal himalaya we found that 18omw values decrease with increasing altitude for both transects 18omw vs altitude along the kali gandaki in west central nepal fit a second order polynomial curve consistent with increasing depletion of 18o with increasing elevation as predicted by a rayleigh type fractionation process this modern 18omw vs altitude relationship can be used to constrain paleoelevation from the 18o values of miocene pliocene carbonate 18oc deposited in the thakkhola graben in the southern tibetan plateau paleoelevations of 3800 480 m to 5900 350 are predicted for the older tetang formation and 4500 430 m to 6300 330 m for the younger thakkhola formation these paleoelevation estimates suggest that by 11 ma the southern tibetan plateau was at a similar elevation to modern

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

δ18o and δd systematics in the surficial waters of the gaula river catchment area kumaun himalaya india abstract the 18 o and d measurements of surface waters streams springs lakes and precipitation from the gaula river catchment area of kumaun himalaya are reported the d and 18 o values are positively correlated as has been the case with waters from several other regions the lake waters are found to be enriched in 18 o and d compared with the neighbouring regions owing to evaporation estimates of mean total evaporation during the dry season range from 10 to 25 spring water samples collected from various altitudes from 915 m to 2150 m display variations in values showing an altitude effect of 0 1491 per 100m elevation

pleistocene calcite lysocline and paleocurrents of the central arctic ocean and their paleoclimatic significance most previous references to the depth of the arctic ocean calcite lysocline have been based on comparison with the known north atlantic carbonate compensation depth foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central arctic ocean these data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past 1 5 m y interrupted by 300 m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past 1 5 m y low abundances commonly occur in coarse textured sediment and are interpreted to represent low productivity during major deglaciations within certain equivalent lithostratigraphic units representing the past 1 5 m y there is an absence of foraminifera in cores from depths greater than 2450 m this absence of foraminifera is interpreted to be due to dissolution dissolution intervals are associated with fine grain sediments interpreted to represent interglacial and early glacial climate conditions the interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the atlantic ocean but is complementary with the hypothesis that formation of norwegian greenland sea deep water ngdw and cold canada basin deep water occurs during interglacials paleocurrent data from the lomonosov ridge and the adjacent makarov basin are interpreted to indicate that during periods of increased glacial ice influx into the arctic ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present this is in accord with the idea that ngdw affects intermediate and deep water circulation in the central arctic ocean and hence the calcite lysocline level

ice sheets in transition it is now well known that periodic variations in ice age climate correspond to variations in earth s orbit around the sun 1 2 however some notable aspects of this climate variability appear to have little or no relation to orbital forcing one such example is the middle pleistocene transition mpt which began at some time after 1 25 million years ago before the mpt climate was dominated by low amplitude 41 000 year cycles over the course of the mpt these were replaced by dominant high amplitude 100 000 year cycles in the absence of any change in orbital forcing see the first figure 3 on page 704 of this issue elderfield et al 4 provide important new insights into ice age variability and the origin and timing of the mpt

geochemical constraints on the formation of late cenozoic ferromanganese micronodules from the central arctic ocean in order to determine geochemical compositions of late cenozoic arctic seawater oxide fractions were chemically separated from 15 samples of hand picked ferromanganese micronodules 50 300 pm the success of the chemical separation is indicated by the fact that 97 of the sr in the oxide fraction is seawater derived rare earth element ree abundances of the arctic micronodule oxide fractions are much lower than those of bulk fe mn nodules from other ocean basins of the world e g 33 vs 145 ppm nd but the arctic oxides are enriched in ce relative to nd ce nd 2 2 f 0 5 and have convex upward shale normalized ree patterns ndn gdn 0 61 f 0 06 gdn ybn 1 5 0 2 ndn yb 0 9 f 0 2 typical of other hydrogenous and diagenetic marine fe mn oxides bulk sediment samples from the central arctic ocean have ree abundances and patterns that are characteristic of those of post archean shale non detrital fractions calcite oxide coatings of recent arctic foraminifera have ree abundances and patterns similar to those of recent foraminifera from the atlantic ocean electron microprobe analyses n 178 of transition elements in 29 arctic fe mn micronodules from five different stratigraphic intervals of late cenozoic sediment indicate that oxide accretion occurred as a result of hydrogenetic and diagenetic processes close to the sediment seawater interface transition element ratios suggest that no oxide accretion occurred during transitions from oxic to suboxic diagenetic conditions only k is correlated with si and al and ratios of these elements suggest that they are associated with illite or phillipsite ca and mg are correlated with mn which indicates variable substitution of these elements from seawater into the manganate phase the geochemical characteristics of arctic fe mn micronodules indicate that the rees of the oxide fractions were ultimately derived from seawater however because of minute contributions of sr from siliciclastic detritus during diagenesis or during the chemical leaching procedure sr isotope compositions of the oxide fractions cannot be used to trace temporal changes in the sr sr ratio of arctic seawater or to improve the chronostratigraphy 0 1997 elsevier science b v kevwords 87sr 86sr arctic ocean ferromanganese nodules marine sediments rare earth elements

carbonate time series of the quaternary and late miocene sediments in the pacific ocean a spectral comparison abstract the variance of the quaternary carbonate record of core rc11 209 from the equatorial pacific is almost twice as large as that for the upper miocene of dsdp site 158 from the same region spectral analysis of the carbonate time series shows that the miocene record is dominated by very low frequency components with a concentration of variance near the frequency corresponding to a period of about 400 kyr the quaternary record is also dominated by low frequency components but has in addition concentrations of variance spectral peaks at frequencies corresponding to periods near 100 and 40 kyr cross spectral analysis indicates that both records are coherent with the calculated record of eccentricity of the earth s orbit and that the quaternary record in addition shows coherence with the calculated record of axial tilt these variations in the earth s orbital parameters can then be used to tune the time scales of these two records based on the similarity in the amount of variance in the two records near the 400 kyr period and the observed relationship between carbonate fluctuations and variations in global ice volume as indicated by oxygen isotope measurements it is proposed that the dominant 400 kyr cycle has been associated directly or indirectly with long term fluctuations in the antarctic ice cap since its formation in mid miocene times the major difference in the quaternary carbonate spectrum lies in the marked increase in variance at frequencies associated with the 100 kyr period this increase is thought to be linked directly or indirectly with glacial to interglacial fluctuations of the northern hemisphere ice sheets

preliminary results from the chemical records of an 80 4 m ice core recovered from east rongbuk glacier qomolangma mount everest himalaya high resolution chemical records from an 80 4m ice core from the central himalaya demonstrate climatic and environmental changes since 1844 the chronological net accumulation series shows a sharp decrease from the mid 1950s which is coincident with the widely observed glacier retreat a negative correlation is found between the ice core 18o record and the monsoon precipitation for indian region 7 the temporal variation of the terrestrial ions ca2 and mg2 is controlled by both the monsoon precipitation for indian regions 3 7 and 8 located directly south and west of the himalaya and the dust storm duration and frequency in the northern arid regions such as the taklimakan desert china the nh4 profile is fairly flat until the 1940s then substantially increases until the end of the 1980s with a slight decrease during the 1990s which may reflect new agricultural practices the so4 2 and no3 profiles show an apparent increasing trend especially during the period 1940s 80s moreover so4 2 concentrations for the east rongbuk glacier core are roughly double that of the nearby dasuopu core at xixabangma himalaya due to local human activity including that of climbing teams who use gasoline for cooking energy and transport

sequence stratigraphy of mississippi fan related to oxygen isotope sea level index 1 the techniques of sequence stratigraphy were applied to the analysis of stratal patterns on seismic data from the mississippi fan to outline a method for 1 understanding the processes and growth patterns of modern submarine fans and 2 predicting reservoir and seal for exploration in deep water settings we developed a sea level index from the oxygen isotope record for the last 3 5 m y tied to limited biostratigraphic control to provide a time framework within which the depositional patterns were analyzed analysis of the seismic data reveals that at least thirteen depositional sequences comprise the bulk of the mississippi fan section the base of each sequence is defined by an erosional unconformity in a proximal position that can be traced regionally across the fan complex with its correlative conformity seismic facies analysis of individual sequences suggests that the mississippi fan is characterized by the cyclic stacking of individual lowstand systems tract deposits consisting dominantly of the lowstand basin floor and lowstand slope fans lowstand slope fans consisting of leveed channel complexes are volumetrically the greatest component of the mississippi fan lowstand basin floor fans commonly are sandy and thin and are associated with the base of each depositional sequence these fans are characterized by a mounded stratal geometry

a model based determination of spatial variation of precipitation δ18o over china abstract many works show the dependence of precipitation 18o on altitude and latitude as a result of air temperature change the assumption that these quantitative relations can hold across a large geographical region can be used to give a rough estimation of local precipitation 18o where there is on direct observation of precipitation 18o although there truly exists uncertainty in the estimation an effect was made in this paper to establish the precipitation 18o pattern over the whole china based on regional topography and the 18o of meteoric precipitation this paper established a quantitative relationship between 18o in precipitation and latitude and altitude using the existing 18o data from 55 sites over china the model describes as 18oppt 0 0073lat2 0 3261lat 0 0015alt 9 7776 and was used to generate a higher resolution map of mean annual 18o for precipitation over china using geographic information system software integrating with latitude altitude and the moisture cycle this determination of the spatial distribution of 18o in modern precipitation of china provides important information for ancient climate and stable isotope hydrology studies

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

an overview of the post messinian paleoenvironmental history of the western mediterranean a review of the pliocene pleistocene paleoenvironmental history of the western mediterranean is presented based on micropaleontological and geochemical studies of ocean drilling program odp leg 107 material and marine outcrops in southern italy the calcareous plankton biochronology proposed for the mediterranean by rio et al 1990 and 1991a provides the necessary age control for determining the timing of major climatic and oceanographic changes in the region the early pliocene period in the mediterranean was not a time of warm stable climate rather it was marked by relatively high amplitude climatic oscillations in marginal areas these climatic oscillations resulted in the rhythmic deposition of limestone marl couplets which have an average duration of approximately 19 000 years it is proposed that these sedimentary couplets are the result of precessionally induced changes in monsoon intensity which in turn cause variability in coastal divergence and upwelling the 18o and the calcareous plankton foraminifera and coccoliths records for tyrrhenian sea odp site 653 reveal a cooling of surface waters at 3 1 ma coincident with this cooling is an increase in the frequency of diatomite formation in southern italy bianco section the global cooling at 2 4 ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the mediterranean region this climate change may have altered the mediterranean water balance resulting in the establishment of antiestuarine water exchange with the atlantic at this time the 18o record for site 653 is also marked by a sharp cooling across the pliocene pleistocene boundary in the boundary stratotype section at vrica this cooling is manifested as an increase in the abundance of the planktonic foraminifer neogloboquadrina pachyderma

stable isotope stratigraphy of the arctic ocean fram strait to central arctic abstract a comparison of stable isotope and textural records of sediment cores from the fram strait and central arctic ocean to isotopic records from low latitude oceans indicates that the arctic mediterranean responded dynamically to climatic change during the pleistocene core mg 123 from the fram strait shows at least four significant low 18 o intervals 5 high 13 c intervals and five intervals with a low amount of coarse sediment the association of high 18 o values with coarse sediment intervals indicates increased glacial ice in the fram strait during glacial phases of the climate cycle peaks within the low 18 o intervals increase in magnitude from oldest to youngest suggesting that glacial interglacial transitions are pulsed the magnitude of the different low 18 o intervals increases from oldest to youngest this is interpreted to indicate that there has been a progressive intensification of the oceanographic response to glacial interglacial transitions in the fram strait during the past 524 ky time series spectral analysis suggests an age of approximately 524 ky for the oldest sediment in core mg 123 yielding an average sedimentation rate of approximately 1 66 cm 1000 yr stable isotope records from the central arctic ocean indicate that sedimentation rates are on the order of 1 3 mm 1000 yr the isotope records support the established central arctic ocean lithostratigraphy coarse sediment deposition in the central arctic is not as clearly related to glacial conditions as it is in the fram strait the oxygen isotope range of central arctic ocean records is accentuated relative to the global ice volume signal recorded from lower latitude cores this may be caused by variations in salinity temperature and thickness of the arctic ocean s low salinity surface layer oceanographic responses to climatic change recorded in the fram strait are also recorded in the central arctic ocean but with decreased resolution due to the magnitude of difference in the sedimentation rates between the two areas

a novel palaeoaltimetry proxy based on spore and pollen wall chemistry understanding the uplift history and the evolution of high altitude plateaux is of major interest to a wide range of geoscientists and has implications for many disparate fields currently the majority of palaeoaltimetry proxies are based on detecting a physical change in climate in response to uplift making the relationship between uplift and climate difficult to decipher furthermore current palaeoaltimetry proxies have a low degree of precision with errors typically greater than 1 km this makes the calculation of uplift histories and the identification of the mechanisms responsible for uplift difficult to determine here we report on advances in both instrumentation and our understanding of the biogeochemical structure of sporopollenin that are leading to the establishment of a new proxy to track changes in the flux of uv b radiation over geological time the uv b proxy is based on quantifying changes in the concentration of uv b absorbing compounds uacs found in the spores and pollen grains of land plants with the relative abundances of uacs increasing on exposure to elevated uv b radiation given the physical relationship between altitude and uv b radiation we suggest that the analysis of sporopollenin chemistry specifically changes in the concentration of uacs may offer the basis for the first climate independent palaeoaltimetry proxy owing to the ubiquity of spores and pollen in the fossil record our proposed proxy has the potential to enable the reconstruction of the uplift history of high altitude plateaux at unprecedented levels of fidelity both spatially and temporally

the elevation history of the tibetan plateau and its implications for the asian monsoon abstract the determination of the evolving palaeoaltitude of the tibetan plateau since the india eurasia collision underpins our understanding of how orography in central asia affects the intensity of the monsoon and hence global climate change palaeoaltitudes however cannot be measured directly and need to be inferred from proxy observations that are usually model dependent differing tectonic models for the behaviour of the lithosphere during continental collision have contrasting implications for the elevation of the plateau however two techniques recently employed for determining palaeo elevation are independent of tectonic models the first involving the variation with altitude of oxygen isotopes in precipitation and the second involving the change of leaf morphology with moist static energy of the atmosphere elevation studies have focused on southern tibet largely due to the relative ease of access to the region there is a remarkable unanimity amongst the diverse techniques applied that the altitude of the southern plateau has not significantly changed since at least the mid miocene ca 15 ma arguing for an onset of the monsoon system during or before the early miocene a range of tectonic studies suggest that the northern and eastern parts of the plateau are younger geomorphological features but there are few quantitative constraints of the timing of elevation from these regions of tibet since both the elevation and the surface area of the plateau impact on atmospheric circulation palaeoaltitude studies need to be extended to chart the increasing areas of elevated land surface through time

a simple rule to determine which insolation cycles lead to interglacials the pacing of glacial interglacial cycles during the quaternary period the past 2 6 million years is attributed to astronomically driven changes in high latitude insolation however it has not been clear how astronomical forcing translates into the observed sequence of interglacials here we show that before one million years ago interglacials occurred when the energy related to summer insolation exceeded a simple threshold about every 41 000 years over the past one million years fewer of these insolation peaks resulted in deglaciation that is more insolation peaks were skipped implying that the energy threshold for deglaciation had risen which led to longer glacials however as a glacial lengthens the energy needed for deglaciation decreases a statistical model that combines these observations correctly predicts every complete deglaciation of the past million years and shows that the sequence of interglacials that has occurred is one of a small set of possibilities the model accounts for the dominance of obliquity paced glacial interglacial cycles early in the quaternary and for the change in their frequency about one million years ago we propose that the appearance of larger ice sheets over the past million years was a consequence of an increase in the deglaciation threshold and in the number of skipped insolation peaks

quaternary history of sea ice and paleoclimate in the amerasia basin arctic ocean as recorded in the cyclical strata of northwind ridge the 19 middle early pleistocene to holocene bipartite lithostratigraphic cycles observed in high resolution piston cores from northwind ridge in the amerasia basin of the arctic ocean provide a detailed record of alternating glacial and interglacial climatic and oceanographic conditions and of correlative changes in the character and thickness of the sea ice cover in the amerasia basin glacial conditions in each cycle are represented by gray pelagic muds that are suboxic laminated and essentially lacking in microfossils macrofossils trace fossils and generally in glacial erratics interglacial conditions are represented by ochre pelagic muds that are oxic and bioturbated and contain rare to abundant microfossils and abundant glacial erratics the synglacial laminated gray muds were deposited when the central amerasia basin was covered by a floating sheet of sea ice of sufficient thickness and continuity to reduce downwelling solar irradiance and oxygen to levels that precluded photosynthesis maintenance of a biota and strong oxidation of the pelagic sediment except during the early part of 3 of the 19 synglacial episodes when it was periodically breached by erratic bearing glacial icebergs the floating arctic ocean sea ice sheet was sufficiently thick to block the circulation of icebergs over northwind ridge and presumably other areas of the central arctic ocean interglacial conditions were initiated by abrupt thinning and breakup of the floating sea ice sheet at the close of glacial time which permitted surges of glacial erratic laden icebergs to reach northwind ridge and the central arctic ocean where they circulated freely and deposited numerous and relatively thick erratic clast rich beds breakup of the successive synglacial sea ice sheets initiated deposition of the interglacial ochre mud units under conditions that allowed sunlight and increased amounts of oxygen to enter the water column resulting in photosynthesis and biologic productivity and strong oxidization of the pelagic sediment the lithostratigraphy of northwind ridge suggests that during at least late pleistocene time glacial conditions in the arctic ocean were initiated abruptly and continued unabated until terminated also abruptly by onset of the succeeding interglacial warming variations in abundance of glacial erratics within the interglacial units of the late pleistocene indicate that during at least most interglacial episodes northern north america was glaciated but with generally diminishing severity until onset of the succeeding continental glaciation magnetostratigraphy suggests that the glacial interglacial cycles on northwind ridge had an average periodicity of approximately 93 5 k y during the brunhes normal and approximately 105 k y during the latter part of the matuyama reverse polarity zone these average periodicities are close to the 100 k y temperature cycles found in north atlantic deep water sediments of the brunhes normal polarity chron which have been ascribed to forcing by a milankovitch eccentricity cycle they are also close however to the average interval 101 k y between the aperiodic glacial terminations in the 500 k y pleistocene continental climate record from devil s hole nevada which have been ascribed to nonlinear feedbacks within the earth s atmosphere ice sheet ocean system

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

oxygen 18 salinity relationship simulated by an oceanic general circulation model the distribution of h218o in the ocean is simulated using an oceanic general circulation model gcm surface isotopic fluxes prescribed to this model are derived from an atmospheric gcm which ensures their consistency the oceanic gcm is initialized with a homogeneous composition and redistributes isotopic gradients so as to equilibrate with the atmosphere a good agreement is found between the observations and the simulation concerning i the interbasin h218o gradients especially the atlantic being more enriched than the pacific as well as the meridional gradients and ii the h218o salinity relationship

the submarine quaternary stratigraphy of northern spencer gulf south australia abstract the seafloor morphology and lithology of northern spencer gulf south australia is related to successive transgressions and regressions accompanying glacial and non glacial periods vibrocoring has revealed a veneer of holocene bioclastics and a sequence of pleistocene marine strata which display varying degrees of pedogenesis oxidation decalcification and clay illuviation the contact between the holocene and pleistocene sediments is marked by either a thin alluvial or aeolian horizon or by a soil horizon of variable development the pleistocene marine strata have been assigned to four formations older pleistocene marine beds mambray fm false bay fm and lowly point fm based on superposition of lithofacies and intervening pedogenic horizons a sequence of slightly altered laminated lagoonal clays lowly point formation and bryozoan rich limestones false bay formation has been encountered in deeper parts of the gulf stratigraphically below these is a widespread weathered marine unit mambray formation which contains abundant remains of the bivalve anadara trapezia and the foraminifer marginopora vertebralis species absent from the present biota this unit in turn is underlain by a sedimentary sequence strongly altered by pedogenesis and clay illuviation older pleistocene marine beds its original marine character has been largely obliterated a dearth of fluvial gravels and sand from the vibrocores as well as evidence from palaeosols indicate that a predominantly semi arid to arid climate has persisted in the northern gulf region since ca 125 000 yrs ago and that there has been little subsequent terrigenous material transported to the gulf

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

a strong control of the south american seesaw on the intra seasonal variability of the isotopic composition of precipitation in the bolivian andes water stable isotopes d in tropical regions are a valuable tool to study both convective processes and climate variability provided that local and remote controls on d are well known here we examine the intra seasonal variability of the event based isotopic composition of precipitation ddzongo in the bolivian andes zongo valley 16 20 s 67 47 w from september 1st 1999 to august 31st 2000 we show that the local amount effect is a very poor parameter to explain ddzongo we thus explore the property of water isotopes to integrate both temporal and spatial convective activities we first show that the local convective activity averaged over the 7 8days preceding the rainy event is an important control on ddzongo during the rainy season 40 of the ddzongo variability is captured this could be explained by the progressive depletion of local water vapor by unsaturated downdrafts of convective systems the exploration of remote convective controls on ddzongo shows a strong influence of the south american seesaw sass which is the first climate mode controlling the precipitation variability in tropical south america during austral summer our study clearly evidences that temporal and spatial controls are not fully independent as the 7 day averaged convection in the zongo valley responds to the sass our results are finally used to evaluate a water isotope enabled atmospheric general circulation model lmdz iso using the stretched grid functionality to run zoomed simulations over the entire south american continent 15 n 55 s 30 85 w we find that zoomed simulations capture the intra seasonal isotopic variation and its controls though with an overestimated local sensitivity and confirm the role of a remote control on d according to a sass like dipolar structure 2011 elsevier b v

what are the climate controls on δd in precipitation in the zongo valley bolivia implications for the illimani ice core interpretation abstract controversy has surrounded the interpretation of the water isotopic composition d or 18o in tropical and subtropical ice cores in south america although recent modeling studies using agcm have provided useful constraints at interannual time scales no direct calibration based on modern observations has been achieved in the context of the recent ice core drilling at nevado illimani 16 39 s 67 47 w in bolivia we examine the climatic controls on the modern isotopic composition of precipitation in the zongo valley located on the northeast side of the cordillera real at about 55 km from nevado illimani monthly precipitation samples were collected from september 1999 to august 2004 at various altitudes along this valley first we examine the local and regional controls on the common d signal measured along this valley we show that 1 local temperature has definitely no control on d variations and 2 local rainout is a poor factor to explain d variations we thus seek regional controls upstream the valley potentially affecting air masses distillation based on backtrajectory calculations and using satellite data trmm precipitation noaa olr and direct observations of precipitation iaea gnip we show that moisture transport history and the degree of rainout upstream are more important factors explaining seasonal d variations analysis of a 92 yr simulation from the echam 4 model t30 version implemented with water stable isotopes confirms our observations at seasonal time scale and emphasize the role of air masses distillation upstream as a prominent factor controlling interannual d variations lastly we focus on the isotopic depletion along the valley when air masses are lifted up our results suggest that if the temperature gradient between the base and the top of the andes was higher by a few degrees during the last glacial maximum lgm less than 10 of the glacial to interglacial isotopic variation recorded in the illimani ice core could be accounted for by this temperature change it implies that the rest of the variation would originate from wetter conditions along air masses trajectory during lgm

tibetan plateau summer monsoon northward extent revealed by measurements of water stable isotopes a program of individual precipitation events and river water sampling and of water isotopic measurements d 18o was carried out during summer 1996 along a northeast southwest transect of the tibetan plateau the spatial distribution of both 18o and deuterium excess d d 8 18o of the precipitation reveals three distinct regions simulations with a simple isotopic model and seasonal isotopic variations measured at two extreme south and north locations support our interpretation in terms of different summer moisture origins 1 south of the himalayan mountains the moisture provided by the indian monsoon has been recycled over the indian peninsula 2 between the himalayas and the tanggula mountains the oceanic moisture is directly transported from the bay of bengal along the brahmaptra river valley 3 north of the tanggula mountains the moisture is not provided by the monsoon anymore but by continental water recycling

planktic foraminiferal and sea surface temperature record during the last 1 myr across the subtropical front southwest pacific planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature sst for the last 1 million years myr are compared between core sites to the north odp 1125 178 faunas and south dsdp 594 374 faunas of the present location of the subtropical front stf east of new zealand faunas beneath cool subtropical water stw north of the stf are dominated by dextral neogloboquadrina pachyderma globorotalia inflata and globigerina bulloides whereas faunas to the south are strongly dominated by sinistral n pachyderma 80 95 in glacials with increased g bulloides 20 50 and dextral n pachyderma 15 50 in interglacials beneath subantarctic water or saw canonical correspondence analysis indicates that at both sites sst and related factors were the most important environmental influences on faunal composition greater climate related faunal fluctuations occur in the south significant faunal changes occur through time at both sites particularly towards the end of the mid pleistocene climate transition mis18 15 e g decline of globorotalia crassula in stw disappearance of globorotalia puncticulata in saw and during mis8 5 interglacial sst estimates in the north are similar to the present day throughout the last 1 myr to the south interglacial ssts are more variable with peaks 4 7 c cooler than present through much of the early and middle pleistocene but in mis11 mis5 5 and early mis1 peaks are estimated to have been 2 4 c warmer than present these high temperatures are attributed to southward spread of the stf across the submarine chatham rise along which the stf appears to have been dynamically positioned throughout most of the last 1 myr for much of the last 1 myr glacial sst estimates in the north were only 1 2 c cooler than the present interglacial except in mis16 mis8 mis6 and mis4 2 when estimates are 4 7 c cooler these cooler temperatures are attributed to jetting of saw through the mernoo saddle across the chatham rise and or waning of the stw current to the south glacial sst estimates were consistently 10 11 c cooler than present similar to temperatures and faunas currently found in the vicinity of the polar front one interpretation is that these cold temperatures reflect thermocline changes and increased circumpolar surface water spinning off the subantarctic front as an enhanced bounty gyre along the south side of the chatham rise for most of the last 1 myr the temperature gradient across the stf has been considerably greater than the present 4 c during glacial episodes the stf in this region did not migrate northwards but instead there was an intensification of the temperature gradient across it interglacials 4 11 c glacials 8 14 c

modern precipitation stable isotope vs elevation gradients in the high himalaya comment on a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene by david b rowley et al earth planet sci lett 188 2001 253 268

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology