inferring surface water equilibrium calcite δ18o during the last deglacial period from benthic foraminiferal records implications for ocean circulation the ocean circulation modifies mixed layer ml tracer signals as they are communicated to the deep ocean by advection and mixing we develop and apply a procedure for using tracer signals observed upstream by planktonic foraminifera and downstream by benthic foraminifera to constrain how tracer signals are modified by the intervening circulation and by extension to constrain properties of that circulation a history of ml equilibrium calcite 18o 18oc spanning the last deglaciation is inferred from a least squares fit of eight benthic foraminiferal 18oc records to green s function estimated for the modern ocean circulation disagreements between this history and the ml history implied by planktonic records would indicate deglacial circulation changes no deviations from the modern circulation are diagnosed because the two estimates of ml 18oc agree within their uncertainties over the deglaciation but diagnostics suggest data collection and modeling procedures useful for inferring circulation changes uncertainties of benthic derived ml 18oc are lowest in the high latitude regions chiefly responsible for ventilating the deep ocean additional high resolution planktonic records constraining these regions are of particular utility benthic records from the southern ocean where data are sparse appear to have the most power to reduce uncertainties in benthic derived ml 18oc understanding the spatiotemporal covariance of deglacial ml 18oc will also improve abilities of 18oc records to constrain deglacial circulation

abrupt changes in antarctic intermediate water circulation over the past 25 000 years the formation and circulation of antarctic intermediate water has varied over glacial interglacial timescales a neodymium record from the atlantic ocean basin suggests that changes in circulation may have been driven by changes both in antarctic intermediate water formation in the southern ocean and in the strength of north atlantic meridional overturning

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

sea surface temperatures of the western arabian sea during the last deglaciation 1 in this study we present a sea surface temperature sst record from the western arabian sea for the last 20 000 years we produced centennial scale d 18 o and mg ca sst time series of core niop929 with focus on the glacial interglacial transition the western arabian sea is influenced by the seasonal ne and sw monsoon wind systems lowest ssts occur during the sw monsoon season because of upwelling of cold water and highest ssts can be found in the low productivity intermonsoon season the mg ca based temperature record reflects the integrated sst of the sw and ne monsoon seasons the results show a glacial interglacial sst difference of 2c which is corroborated by findings from other arabian sea cores at 19 ka b p a yet undescribed warm event of several hundred years duration is found which is also reflected in the d 18 o record a second centennial scale high sst low d 18 o event is observed at 17 ka b p this event forms the onset of the stepwise yet persistent trend toward holocene temperatures highest mg ca derived ssts in the niop929 record occurred between 13 and 10 ka b p interglacial sst is 24c indicating influence of upwelling the onset of arabian sea warming occurs when the north atlantic is experiencing minimum temperatures the rapid temperature variations at 19 17 and 13 ka b p are difficult to explain with monsoon changes alone and are most likely also linked to regional hydrographic changes such as trade wind induced variations in warm water advection

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

formation and spreading of arabian sea high salinity water mass the formation and seasonal spreading of the arabian sea high salinity water ashsw mass were studied based on the monthly mean climatology of temperature and salinity in the arabian sea north of the equator and west of 80 e on a 2 2 grid the ashsw forms in the northern arabian sea during winter and spreads southward along a 24 sigma t surface against the prevailing weak zonal currents the eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of india during the southwest monsoon the northern part of the core shoals under the influence of the findlater jet while the southern part deepens throughout the year the southward extent of the ashsw is inhibited by the equatorial currents the atmospheric forcing that leads to the formation of ashsw was delineated using the monthly mean climatology of heat and freshwater fluxes monsoon winds dominate all the flux fields during summer june september while latent heat release during the relative calm of the winter november february monsoon driven by cool dry continental air from the north results in an increased density of the surface layer thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern arabian sea during winter and drive convective formation of ashsw

advected glacial seawater preserved in the subsurface of the maldives carbonate edifice abstract analysis of both conservative and reactive geochemical tracers in pore fluids extracted from sediment cores from the maldives inner sea reveal extensive interstitial water masses whose origins lie in glacial intermediate water advected laterally through the maldives carbonate edifice these drillcores recovered during expedition 359 of the international ocean discovery program penetrate late oligocene to recent sediments including carbonate platform slope pelagic and drift facies combined shipboard and shore based analyses of the pore fluids show linearly co varying changes in the concentration of chloride and 18 o and d values of 25 mm 1 2 and 9 respectively additionally pore fluid strontium concentrations and calcium isotope ratios are strongly anti correlated with each other multiple reversals in these geochemical properties with depth indicate the existence of several distinct interstitial water masses these variations are interpreted as representing the different ages and reactive histories of young pleistocene and holocene waters advecting through the much older sedimentary formations in particular the elevated chloride concentrations and water isotope ratios suggest that seawater from the last glacial maximum is preserved in the subsurface where it occupies over 400 m of the sediment column within mid to late miocene sediments these pore fluids constrain the properties of an intermediate depth glacial water mass that had higher salinity and 18 o and d values than the average glacial ocean this system represents a unique archive yielding the most direct observations of glacial seawater to date as well as a demonstration of the long lasting potential for water rock interaction in carbonate platform systems

multidecadal variations in the early holocene outflow of red sea water into the arabian sea we present holocene stable oxygen isotope data from the deep arabian sea off somalia at a decadal time resolution as a proxy for the history of intermediate upper deep water these data show an overall 18o reduction by 0 5 between 10 and 6 5 kyr b p superimposed upon short term 18o variations at a decadal centennial timescale the amplitude of the decadal variations is 0 3 prior and up to 0 6 subsequent to 8 1 kyr b p we conclude from modeling experiments that the short term 18o variations between 10 and 6 5 kyr b p most likely document changes in the evaporation precipitation balance in the central red sea changes in water temperature and salinity cause the outflowing red sea water to settle roughly 800 m deeper than today

lagrangian measurement of steep directionally spread ocean waves second order motion of a wave following measurement buoy abstractthe notion that wave following buoys provide less accurate measurements of extreme waves than their eulerian counterparts is a perception commonly held by oceanographers and engineers forr

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

changes in eastern pacific ocean ventilation at intermediate depth over the last 150 kyr bp the circulation patterns of the deep glacial pacific ocean are still debated difficulties arise due to the scarcity of reliable paleoceanographic records that can document the past movements and properties of pacific ocean water masses here we jointly use delta 13 c and delta 18 o measured on the epibenthic foraminifer cibicidoides wuellerstorfi from the md02 2529 sediment core collected at 1619 m water depth in the eastern equatorial pacific to monitor changes in water mass circulation spanning the past 150 kyr bp after the extraction of short term centennial to millennial scale delta 13 c and delta 18 o changes which were similar to 1 0 and 0 5 parts per thousand respectively we observed that these rapid delta 13 c and 8180 shifts were closely interrelated during the last 150 kyr bp a comparison of md02 2529 with other benthic delta 13 c records localized to the north and south of the core location revealed that md02 2529 was alternately bathed by a northern nutrient rich and a southern nutrient poor water mass the comparison provided a diagnostic for the latitudinal movements of a sharp water mass front that was particularly evident during marine isotope stages 4 and 3 on the millennial timescale by considering that delta 13 c is an indicator of the northern vs southern origin of the water that bathed the md02 2529 coring site in the past we found that a north pacific water mass that occasionally spreads to the eastern pacific ocean as deep as 1600 m and as far south as 8 degrees n was responsible for shifts toward the positive delta 18 o we observed in the past we then used the delta 13 c delta 18 o relationship to reconstruct latitudinal temperature and or salinity gradients of the water mass that were linked to changes in the northern and or the southern water mass end members evolution of the delta 13 c delta 18 o relationship spanning the past 150 kyr bp has shed light on how hydrological processes occurring at northern and southern high latitudes are transmitted to the ocean s interior through water mass advection c 2010 elsevier b v all rights reserved

enhanced arabian sea intermediate water flow during glacial north atlantic cold phases abstract during the last glacial period polar ice cores indicate climate asynchrony between the poles at the millennial time scale yet surface ocean circulation in large parts of the globe varied in tune with greenland temperature fluctuations suggesting that any anti phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the atlantic ocean here we present data from the north western indian ocean which indicate that the timing of maxima in northward extensions of glacial antarctic intermediate water gaaiw coincides with dramatically reduced thermohaline overturn in the north atlantic associated with the heinrich ice surge events he the repeated expansion of the gaaiw during hes recorded far north of the equator in the arabian sea suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter hemisphere asynchronous climate change behavior at the millennial time scale

antarctic sea ice and the control of pleistocene climate instability a hypothesis is presented for the origin of pleistocene climate instability based on expansion of antarctic sea ice and associated changes in the oceans salinity structure the hypothesis assumes that thermohaline overturning is dominated by the reconfigured conveyor of toggweiler and samuels 1993b in which deepwater upwelling is restricted to high southern latitudes the reconfigured conveyor is shown to be potentially stabilized in an on mode by precipitation at high southern latitudes and potentially destabilized into on and off modes by the counteracting influence of antarctic sea ice the mechanism is clarified by the use of a hydraulic analogue we hypothesize that this mechanism accounts for dominant patterns of thermohaline overturning and climate instability between pleistocene warm and cold periods the hypothesis is shown to be consistent with a range of paleoceanographic evidence and to potentially account for details of observed rapid climate changes during glacial and interglacial periods including aspects of interhemispheric timing

accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation 1 abrupt decreases of the atlantic meridional overturning circulation moc during the late pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater triggering disruption of northward marine heat transport and causing global climate changes here we provide measurements of excess sedimentary 231 pa 230 th from a high accumulation sediment drift deposit in the ne atlantic that record a sequence of sudden variations in the rate of moc associated deep ocean ventilation and surface ocean climatology the data series reveal a sequential decrease in the moc rate at 18 0 ka bp ago that coincides with only transient and localized freshwater inputs this change represents a substantial though not total cessation in moc that predates the major heinrich h1 meltwater event by at least 1 200 years these results highlight the potential of targeted freshwater perturbations in promoting substantial moc changes without a direct linking with catastrophic freshwater surges citation hall i r s b moran r zahn p c knutz c c shen and r l edwards 2006 accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation geophys res lett 33 l16616 doi 10 1029 2006gl026239

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

on the link between the two modes of the ocean thermohaline circulation and the formation of global scale water masses a close link between the formation of global scale water masses such as north atlantic deep water nadw and antarctic intermediate water aaiw and two stable modes of the thermohaline circulation thc is investigated in a coupled model in the upper 2 3 km of the atlantic the thc modes are characterized by meridional overturning circulations of opposite sign with either a dominance of the aaiw cell over the nadw cell off thc mode or vice versa on thc mode a transition between these thc modes is controlled by the relationship between the densities in the source regions of formation of aaiw and nadw water masses this is shown by applying a freshwater perturbation in the region of enhanced aaiw formation in the southern ocean to obtain a hysteresis loop of the nadw circulation transitions between the two modes of the thc occur when the densities in the source regions of aaiw and nadw become comparable to each other

transit time distributions in a global ocean model abstract results from a simulation of the ocean transit time distribution ttd for global and regional ocean surface boundary conditions are presented based on a 5000 yr integration using the parallel ocean program ocean general circulation model the ttd describes the probability that water at a given interior point in the ocean was at some point on the ocean surface a given amount of time ago it is shown that the spatial distribution of ocean ttds can be understood in terms of conventional wisdom regarding time scales and pathways of the ventilated thermocline and the thermohaline circulation driven deep ocean circulation the true mean age from the model the first moment of the ttd is demonstrated to be very large everywhere because of very long tailed distributions regional ttd distributions are presented for distinct surface boundary subregions and it is shown how these can help in the interpretation of the global ttd the spatial structure of each regional ttd is shown to become essential

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

new arabian sea records help decipher orbital timing of indo asian monsoon abstract a recent study suggested that indian monsoonal proxies commonly used in the arabian sea in general productivity proxies could be impacted by changes in the atlantic overturning rate amoc throughout a control on the nutrient delivery into the euphotic zone this oceanic mechanism could lead to a misunderstanding between the indian summer monsoon sm and orbital forcing and could confuse a direct comparison with other archives derived from other monsoonal sub systems such as east asian or african records here we analyze three independent proxies bromine foraminifera assemblages and grain size extracted from a marine sediment core md04 2861 covering the last 310 ka and retrieved in the northern arabian sea near the makran margin an area influenced by summer and winter indian monsoon the grain size proxy deals with the regional continental climate through fluvial and eolian processes it cannot be linked to changes in nutrient content of amoc and present the same phase relationship timing than the other sm proxies this demonstrates that the productivity signals bromine in the northern arabian sea are mainly controlled by sm dynamics and not amoc modulated nutrients at orbital scale changes we thus build a multi proxy record of sm variability i e sm stack using statistical tools principal component analysis further compiled on an age model constructed independently from orbital tuning we find that strong sm lag by 9 1 ka the nh summer insolation maximum minimum of precession june 21 perihelion and obliquity maximum in the precession band and by 6 1 3 ka in the obliquity band these results are consistent with previous studies based on marine and terrestrial records in both indian and asian regions except asian speleothems our study supports the hypothesis that internal climate forcing decreased ice volume together with the increase of latent heat export from the southern indian ocean set the timing of strong indo asian summer monsoons within both the precession and obliquity cycle the external forcing direct sensible heating initiate monsoonal circulation strong indian winter monsoon wm occurs between ice maxima and northern hemisphere sensible heat minima indicating that both act to strengthen wm circulation the summer and winter monsoons are in antiphase in the precession band suggesting that the two systems are dynamically linked

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

distant origin of circulation changes in the indian ocean during the last deglaciation abstract well dated benthic foraminifera isotopic records reveal that circulation changes repeatedly took place in the tropical indian ocean around 2000 m depth over the last deglaciation we show that the observed changes can be explained by large scale reorganization of intermediate water masses in the atlantic and indian oceans more specifically during heinrich event 1 and the younger dryas while the formation of north atlantic deep water was greatly reduced brine formation in the north atlantic and nordic seas led to the production of intermediate waters that extended far enough in the south atlantic to be deflected by the circumpolar currents into the indian ocean basin creating a circulation branch at intermediate depths that was more active than today in contrast during the last glacial maximum the bolling allerod and after the younger dryas there was no rapid transport of intermediate waters from the north atlantic to the south atlantic or indian ocean around 2000 m depth

numerical modeling of neotectonic movements and the state of stress in the north caucasus foredeep 1 this paper examines modern tectonic processes and the state of stress in the north caucasus along three profiles that cross its eastern central and western parts using the models of crustal structure along these profiles we solved the following inverse problem to find boundary conditions in this study velocity at side boundaries and bottom of the model that provide the best fit of calculated vertical movements at the top of the model and vertical neotectonic movements during the late quaternary our modeling shows that during the late quaternary geodynamics of the eastern and central parts has been controlled by regional intraplate compression normal to the greater caucasus belt the western part has been strongly influenced by tectonic processes taking place in the eastern black sea the calculated slow flow patterns and stress fields showed good agreement with the distribution of seismic events results of focal mechanisms inversions and gps data

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

three dimensional isoneutral potential vorticity structure in the indian ocean the three dimensional isoneutral potential vorticity structure of the indian ocean is examined using world ocean circulation experiment and national oceanic and atmospheric administration conductivity temperature depth data and historical bottle data the distribution of the potential vorticity is set by the indian ocean s source waters and their circulation inside the basin the lower thermocline has a high potential vorticity signal extending westward from northwest of australia and a low signal from the subantarctic mode water in the south the antarctic intermediate water inflow creates patches of high potential vorticity at intermediate depths in the southern indian ocean below which the field becomes dominated by planetary vorticity indicating a weaker meridional circulation and weaker potential vorticity sources wind driven gyre depths have lower potential vorticity gradients primarily due to same source waters homogenization and western shadow zones are not observed the effect dominates the effect of the somali current and the red sea water on the potential vorticity distribution isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the circumpolar deep water fills the basins in deep western boundary currents indicating a strong meridional circulation north of the antarctic circumpolar current the lower gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical indian ocean suggests that rossby waves will travel 1 3 times faster than standard theory predicts to the south several pools of homogenized potential vorticity appear in the upper 2000 m of the southern ocean where gyres previously have been identified south of australia the abyssal potential vorticity structure is set by a combination of the antarctic circumpolar current and the bathymetry

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

staged fine grained sediment supply from the himalayas to the bengal fan in response to climate change over the past 50 000 years abstract the bengal fan as the largest submarine fan in the world receives a large amount of sediments discharged from the himalayas through the ganges brahmaputra g b river system however previous studies of this system seldom focused on the role of channels which are widely developed in the bengal fan in sediment transportation over the last glacial cycle here we discuss the coupled sedimentary archive in two gravity cores along the active channel in the bengal fan our findings are based on grain size clay minerals and sr and nd isotope compositions of these two sediment cores end member modeling of grain size data reveals that the intermediate end member represents the flux of distal fluvial particles from the g b river system the fine end member denotes regional sediment supply of weathered volcanic materials especially from the eastern indian peninsula and the coarse end member probably reflects nearby terrigenous input aeolian input and or volcanic glass sediment provenance analysis based on clay minerals and sr and nd isotopes confirmed sediment supply from the g b river system which was characterized by high illite percentage high 87sr 86sr ratios and low end values especially during five stages 50 45 ka 42 37 ka 31 28 5 ka 24 20 ka and 14 9 ka during these stages heavy fine grained sediment supply from the g b river system was discharged into the study area under the influence of climate change rather than sea level fluctuation additionally emphasizing the importance of channels in the sediment transport process moreover we find a significant alteration of sediment sources at 26 ka which may be related to conversion of the deep water currents in the bay of bengal

sensitivity of altitudinal vegetation in southwest china to changes in the indian summer monsoon during the past 68000 years abstract reconstructing vegetation changes during a glacial interglacial cycles in southwest sw china is crucial for understanding the amplitude of palaeoclimatic dynamics associated with orbital forcing and evolution of the indian summer monsoon ism however few studies on the relationship between paleoclimate and ecosystem changes have covered all of the last glacial interglacial cycle or any other which limits understanding of the ism s variability and its impact on mountain flora in particular knowledge of responses of vertical vegetation belts in margins of the high tibetan plateau to glacial and subglacial mis3 climate changes is poor to improve understanding we have studied a continuous core extending back to mis4 from tengchong qinghai volcanic lake in yunnan province identification of quercus pollen by scanning electron microscopy showed that most of the abundant oak pollen in the core can be assigned to mountainous taxa of sclerophyllous quercus living today on the high tibetan plateau their current distribution indicates that the maximum downward shift of vertical vegetation belts during the last glacial period corresponds to a 5 5 c drop in temperature based on altitudinal lapse rates in accordance with mean annual temperature mat reconstruction from biomarkers in the same core our data clearly suggest that conditions were wet during mis3 and humidity highest at 38 56 kyr the wetting appears to have started after the last glacial termination indicating that the initial deglacial ism intensification lagged behind rises in temperature and summer insolation the highest charcoal concentrations and evidence of expansion of open vegetation coincide with the apparent onset of deglaciation 18 16 kyr these observations indicate that this was the driest period likely linked with reductions in the polar ice volume and delayed tibetan glacier melting which absorbed massive amounts of atmospheric heat and caused regional aridity our pollen data clearly correlate with rapid changes such as younger dryas and heinrich events and marine records from the indian ocean confirming climate teleconnection through ice volumes and global ocean circulation and that the ism is a key factor driving south north transportation of energy and moisture the multi proxy data reveal with high confidence that the holocene optimum in the region was between 9 and 4 kyr bp and followed by weakening of the ism accompanied by increasing anthropogenic disturbance of the vegetation

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate