a late glacial high resolution site and source temperature record derived from the epica dome c isotope records east antarctica the timing and synchronisation of greenland and antarctic climate events that occurred during the last glacial period are still under debate as is the magnitude of temperature change associated with these events here we present detailed records of local and moisture source temperature changes spanning the period 27 45 kyr bp from water stable isotope measurements deltad and delta 18 o in the recently drilled epica dome c ice core east antarctic plateau using a simple isotopic model site deltat site and source deltat source temperatures are extracted from the initial 50 yr high resolution isotopic records taking into account the changes in seawater isotopic composition the deuterium isotope variability is very similar to the less precise deltad record from the vostok ice core and the site temperature inversion leads to a temperature profile similar to the classical palaeothermometry method due to compensations between source and ocean water corrections the reconstructed deltat site and deltat source profiles show different trends during the glacial the former shows a decreasing trend from the warm al event 38 kyr bp toward the last glacial maximum while the latter shows increasing values from 41 to 28 kyr bp the low frequency deuterium excess fluctuations are strongly influenced by obliquity fluctuations controlling the low to high latitude temperature gradients and show a remarkable similarity with a high resolution southeast atlantic sea surface temperature record a comparison of the temperature profiles site and source and temperature gradient deltat source deltat site with the non sea salt calcium and sodium records suggests a secondary influence of atmospheric transport changes on aerosol variations

changing influence of antarctic and greenlandic temperature records on sea level over the last glacial cycle we use a simple model to analyse the relationship between ice core temperature proxy data and global ice volume eustatic sea level data over the last glacial cycle lgc by allowing the temperature forcing to be a mix of greenlandic and antarctic signals we optimise the proportion of this mixing to fit sea level data we find that sea level forcing is best represented by a mix of antarctic and greenlandic temperature signals through the whole glacial cycle we suggest that a distinct bipolar switch occurs which links eustatic sea level more closely with the antarctic like variability during the glacial period mis 4 3 and 2 and more closely to the greenland like variability during the last termination ti and the interglacial periods holocene and mis 5 this switch may be caused by the spatio temporal distribution of ice sheet collapse perhaps linked to glacial to interglacial changes in deep water distribution in the ocean which in turn drive changes in pole ward heat and moisture transport

towards radiocarbon calibration beyond 28 ka using speleothems from the bahamas we present a new speleothem record of atmospheric 14c between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period the record is based on a comprehensive suite of ams 14c ages using new low blank protocols and u th ages using high precision mc icpms procedures atmospheric 14c was calculated by correcting 14c ages with a constant dead carbon fraction dcf of 22 7 5 9 based on a comparison of stalagmite 14c ages with the intcal04 reimer et al 2004 calibration curve between 15 and 11 ka the new 14c speleothem record shows similar structure and amplitude to that derived from cariaco basin foraminifera hughen et al 2004 2006 and the match is further improved if the latter is tied to the most recent greenland ice core chronology svensson et al 2008 these data are however in conflict with a previously published 14c data set for a stalagmite record from the bahamas gb 89 24 1 beck et al 2001 which likely suffered from 14c analytical blank subtraction issues in the older part of the record the new bahamas speleothem 14c data do not show the extreme shifts between 44 and 40 ka reported in the previous study beck et al 2001 causes for the observed structure in derived atmospheric 14c variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity data model comparison indicates that major fluctuations in atmospheric 14c during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity although ocean atmosphere system reorganisation also played a supporting role

multi proxy evidence of millennial climate variability from multiple bahamian speleothems abstract northern hemisphere tropical paleoclimate records support significant changes associated with dansgaard oeschger d o events and heinrich stadials 1 to 6 during the last 64 000 years however few absolutely dated terrestrial records from the western atlantic span the last six heinrich stadials here we present geochemical results from three new stalagmites collected from a cave in the bahamas which encompass heinrich stadials 1 to 6 we build on a previous study of the 13 c and 18 o values of the calcite and 18 o value of fluid inclusions from a single stalagmite from the same cave spanning the last three heinrich stadials absolute geochronometry using u th equilibrium series demonstrates that the stalagmites formed between 63 8 and 13 8 kyr bp the 13 c and 18 o values of the calcite show higher values associated with heinrich stadials 1 6 and lower values during the d o interstadial events the sr ca ratios of the calcite are shown to be relatively invariant while in two of the samples the mg ca ratios track the 13 c values increases in the 18 o values across heinrich stadials 1 6 are interpreted as being driven by lower temperatures the two deeper occurring stalagmites demonstrate increased mg ca ratios and 13 c values during heinrich stadials 1 and 2 which are interpreted as a signal of reduced flow rates in the epikarst and increased water rock interactions as a result of increased aridity which potentially occurred across all six heinrich stadials the observed reductions in mean annual temperature and amount of precipitation across heinrich stadials are proposed to be driven by a reduction in sea surface temperatures in the north atlantic and an expanded bermuda high during d o interstadials the bahamas cave records likely indicate warmer and or wetter climate however the isotopic shifts are not as significant as the isotopic excursions associated with heinrich stadials

reconciling astrochronological and 40ar 39ar ages for the matuyama brunhes boundary and late matuyama chron when five matuyama brunhes m b boundary records from the north atlantic are placed on isotope age models produced by correlation of the 18o record directly or indirectly to an ice volume model the m b boundary lies consistently at the young end of marine isotope stage 19 with a mean age for the midpoint of the reversal of 773 1 ka standard deviation 0 4 kyr 7 kyr younger than the presently accepted astrochronological age for this polarity reversal 780 781 ka two recently proposed revisions of the age of the 40ar 39ar fish canyon sanidine fcs standard to 28 201 0 046 ma and 28 305 0 036 ma would adjust 40ar 39ar ages applicable to the m b boundary and other reversals and excursions back to 1 2 ma to ages older than the new astrochronological ages by 8 24 kyr the variables used to construct the ice volume models cannot account for the discrepancy the fcs standard age that best fits the astrochronological ages is 27 93 ma which is within the uncertainty associated with the commonly used value of 28 02 0 16 ma but younger than the recently proposed fcs ages the edc2 and edc3 age models in the dome c antarctic ice core yield ages of 771 7 ka and 766 4 ka respectively for the 10be flux peak that denotes the paleointensity minimum at the reversal boundary implying that the edc2 rather than edc3 age model is consistent with the observations from marine sediments at least close to the m b boundary

a centennial scale record of vegetation and climate variability from 312 to 240 ka marine isotope stages 9c a 8 and 7e from tenaghi philippon ne greece abstract based on a new centennial scale resolution pollen record from the terrestrial site of tenaghi philippon ne greece we report a series of high amplitude millennial scale forest expansion events during the interval from 312 to 240 ka equivalent to isotopic substages c a of marine isotope stage mis 9 mis 8 and the onset of mis 7e pollen based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the mediterranean region long term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages early middle and late analogous to the glacial substages of the last climatic cycle within this framework forest expansion events occurred during the early glacial equivalent to mis 9c a and the later part of the middle glacial mid to late mis 8 but are absent from the early part of the middle glacial early mis 8 forest expansion events are also detected during the lateglacial and onset of mis 7 associated with a millennial scale climate oscillation across the glacial interglacial transition i e termination iii t iii a peak for peak match between forest expansion events and antarctic temperature maxima suggests interhemispheric coupling of millennial scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see saw the resolution of our record mean 290 yr also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events and highlights differences in the characteristics of early and middle glacial interstadials saw tooth vs plateau profile these differences point to an influence of long term boundary conditions especially global ice volume on the characteristics of millennial scale events

atmospheric methane during the last four glacial interglacial cycles rapid changes and their link with antarctic temperature 1 atmospheric methane ch4 recorded in antarctic ice cores represents the closest ice proxy available for greenland temperature changes beyond times when greenland climate records are available the record over four climatic cycles from the vostok ice core offers the opportunity to study the phase relationship between greenland and antarctic climate changes through detailed ch4 profiles combining american and french analytical efforts we have improved the time resolution of the existing ch4 record from petit et al 1999 spectral analyses reveal high and low frequency variability including a strong precessional component the phase relationship between ch4 and the antarctic temperature proxy d shows a systematic lag of ch4 versus temperature by 1100 200 years on long timescales 50 400 kyr and a more complex behavior over shorter timescales i e 25 kyr suggesting that dansgaard oeschger type of climatic variability and associated interhemispheric linkage are robust features of late quaternary climate

isotope calibrated greenland temperature record over marine isotope stage 3 and its relation to ch4 large temperature variations on millennial time scales in greenland characterised the last ice age abrupt warmings known as dansgaard oeschger do events can be traced in the 18oice record of greenland ice cores however it has been shown that 18oice is not a direct temperature proxy measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer here we present a continuous temperature record based on high resolution 15n measurements and firn model studies it covers a sequence of 9 do events 9 17 during the time period from 38 to 64 kyr bp for which temperature changes of 8 to 15 c were estimated the difference between the modern and the glacial 18oice t relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation a detailed comparison of the temperature evolution with reconstructions of the atmospheric methane ch4 concentration shows that ch4 rises lag temperature increases at the onset of do events by 25 to 70 yr within data resolution the strong correlation between greenland temperature and ch4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent

triple water isotopologue record from wais divide antarctica controls on glacial interglacial changes in 17oexcess of precipitation measurements of the 17oexcess of h2o were obtained from ice cores in west and east antarctica combined with previously published results from east antarctica the new data provide the most complete spatial and temporal view of antarctic 17oexcess to date there is a steep spatial gradient of 17oexcess in present day precipitation across antarctica with higher values in marine influenced regions and lower values in the east antarctic interior there is also a spatial pattern to the change in 17oexcess between the last glacial maximum lgm and holocene periods at coastal locations there is no significant change in 17oexcess at both the west antarctic ice sheet divide site and at vostok east antarctica the lgm to early holocene change in 17oexcess is about 20 per meg atmospheric general circulation model gcm experiments show that both the observed spatial gradient of 17oexcess in modern precipitation and the spatial pattern of lgm to early holocene change can be explained by kinetic isotope effects during snow formation under supersaturated conditions requiring a high sensitivity of supersaturation to temperature the results suggest that fractionation during snow formation is the primary control on 17oexcess in antarctic precipitation variations in moisture source relative humidity play a negligible role in determining the glacial interglacial 17oexcess changes observed in antarctic ice cores additional gcm experiments show that sea ice expansion increases the area over which supersaturating conditions occur amplifying the effect of colder temperatures temperature and sea ice changes alone are sufficient to explain the observed 17oexcess glacial interglacial changes across antarctica

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

climate dependent contrast in surface mass balance in east antarctica over the past 216 ka documenting past changes in the east antarctic surface mass balance is important to improve ice core chronologies and to constrain the ice sheet contribution to global mean sea level change here we reconstruct past changes in the ratio of surface mass balance smb ratio between the epica dome c edc and dome fuji df east antarctica ice core sites based on a precise volcanic synchronization of the two ice cores and on corrections for the vertical thinning of layers during the past 216 000 a this smb ratio denoted smb edc smb df varied between 0 7 and 1 1 being small during cold periods and large during warm periods our results therefore reveal larger amplitudes of changes in smb at edc compared with df consistent with previous results showing larger amplitudes of changes in water stable isotopes and estimated surface temperature at edc compared with df within the last glacial inception marine isotope stages mis 5c and mis 5d the smb ratio deviates by up to 0 2 from what is expected based on differences in water stable isotope records moreover the smb ratio is constant throughout the late parts of the current and last interglacial periods despite contrasting isotopic trends

obliquity and precession as pacemakers of pleistocene deglaciations abstract the milankovitch theory states that the orbital eccentricity precession and obliquity of the earth influence our climate by modulating the summer insolation at high latitudes in the northern hemisphere despite considerable success of this theory in explaining climate change over the pleistocene epoch 2 6 0 01 myr ago it is inconclusive with regard to which combination of orbital elements paced the 100 kyr glacial interglacial cycles over the late pleistocene here we explore the role of the orbital elements in pacing the pleistocene deglaciations by modeling ice volume variations in a bayesian approach when comparing models this approach takes into account the uncertainties in the data as well as the different degrees of model complexity we find that the earth s obliquity axial tilt plays a dominant role in pacing the glacial cycles over the whole pleistocene while precession only becomes important in pacing major deglaciations after the transition of the dominant period from 41 kyr to 100 kyr the mid pleistocene transition we also find that geomagnetic field and orbital inclination variations are unlikely to have paced the pleistocene deglaciations we estimate that the mid pleistocene transition took place over a 220 kyr interval centered on a time 715 kyr ago although the data permit a range of 600 1000 kyr this transition occurring within just two 100 kyr cycles indicates a relatively rapid change in the climate response to insolation

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

a new 27 ky high resolution east antarctic climate record the ice core recently drilled at the dome concordia site on the east antarctic plateau provides a new high resolution isotope record covering part of the last glacial the last transition and the holocene the two step shape of the deglaciation is remarkably similar for all the ice cores now available on the east antarctic plateau the first warming trend ends about 14000 years ago and is followed by the well marked antarctic cold reversal acr with a secondary peak common to all records during the deglaciation there are more similarities between the near coastal site of taylor dome and inland east antarctica than between taylor dome and central greenland however the results for epica do appear to confirm the taylor dome timescale after about 14 ka showing cooling into the acr roughly in phase between greenland and antarctica while the overall deglacial pattern is asynchronous this suggests that the now classical picture of a temperature seesaw between antarctica and greenland may be too simplistic

multifractal detrended fluctuation analysis of the δ 18 o record of ngrip ice core the multifractal properties and scaling behaviors of the long term and recent 2000 year 18o records of ngrip ice core are investigated by the multifractal detrended fluctuation analysis method the generalized hurst exponents multifractal scaling exponents and singularity spectrums of two 18o records are derived to verify the multifractiality of two records and the multifractal behaviors of two records are obviously different which may reflect the climate change of the recent 2000 year time is quite different from one of the long term time in addition the probability distribution analysis of two 18o records is presented to manifest the different multifractality between two 18o records of ngrip ice core our results will be helpful to research the climate change

timing of quaternary geomagnetic reversals and excursions in volcanic and sedimentary archives abstract we review the ages of quaternary magnetic polarity reversals and magnetic excursions improvements in radioisotopic 40ar 39ar dating of reversals and excursions reflect the use of multi collector mass spectrometers along with ultra low backgrounds laser based incremental heating methods and adoption of 28 201 ma for the fish canyon sanidine fcs standard age kuiper et al 2008 these improvements have brought 40ar 39ar ages of reversals and excursions into close correspondence with astrochronological ages based on the correlation of 18o data to lr04 lisiecki and raymo 2005 and in a few cases correlation to ice core chronologies ages of two polarity reversals the matuyama brunhes boundary and base olduvai are at odds with ages given in popular geomagnetic polarity timescales sedimentary records of the laschamp and iceland basin excursion are numerous and widespread and attest to global manifestation and global synchronicity of these excursions records of other quaternary excursions are less numerous the blake excursion 115 ka has been recorded in north atlantic sediments chinese loess indian ocean volcanics and spanish speleothems the santa rosa excursion 932 ka has been recorded in north atlantic and phillipine basin sediments as well as in volcanic rocks from new mexico and galapagos the punaruu excursion 1115 ka has been observed in sediments from the north atlantic and california margin as well as in volcanic rocks on tahiti uniformity of individual excursion ages using astrochronological 40ar 39ar and u th methods argues for synchronous global manifestation of excursions strengthening the usefulness of magnetic excursions and reversals in quaternary stratigraphy

measurements and numerical simulation of fabric evolution along the talos dome ice core antarctica we present measurements of fabrics and microstructures made along the talos dome ice core a core drilled in east antarctica in the framework of the taldice project fabric and average grain size data are analyzed regarding changes in climatic conditions in particular the fabric strength increases sharply going downward from holocene to wisconsin ice following durand et al 2007 this change is associated with a positive feedback between variations in ice viscosity due to variations in dust content and the impact of a shear stress component increasing with depth a viscoplastic self consistent modeling approach is used to simulate the fabric evolution for a perfect dome configuration the discrepancies between the measured and the simulated fabrics highlight the depth ranges where shear strongly affects the fabric strengthening finally the grain size and fabric analyses show the occurrence of dynamic recrystallization mechanisms continuous and discontinuous along the core

the mid pleistocene transition in the tropical pacific a sea surface temperature sst record based on planktonic foraminiferal magnesium calcium ratios from a site in the western equatorial pacific warm pool reveals that glacial interglacial oscillations in sst shifted from a period of 41 000 to 100 000 years at the mid pleistocene transition 950 000 years before the present sst changes at both periodicities were synchronous with eastern pacific cold tongue ssts but preceded changes in continental ice volume the timing and nature of tropical pacific sst changes over the mid pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time

climate variability and ice sheet dynamics during the last three glaciations a composite north atlantic record from dsdp site 609 and iodp site u1308 spans the past 300 000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations hematite stained grains exhibit similar repetitive down core variations within the marine isotope stage mis 8 and 4 2 intervals but little cyclic variability within the mis 6 section there is also no petrologic evidence in terms of detrital carbonate rich heinrich layers for surging of the laurentide ice sheet through the hudson strait during mis 6 rather very high background concentration of iceberg rafted debris ird indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events such as expanded sea ice over deepwater formation sites altered sub tropical precipitation patterns and antarctic warming during high orbital precession and low 65 n summer insolation appear related to high abundance of icelandic glass shards and southward sea ice expansion differing european and north american ice sheet configurations perhaps aided by larger variations in eccentricity leading to cooler summers may have contributed to the relative stability of the laurentide ice sheet in the hudson strait region during mis 6

using holo hilbert spectral analysis to quantify the modulation of dansgaard oeschger events by obliquity abstract astronomical forcing obliquity and precession has been thought to modulate dansgaard oeschger do events yet the detailed quantification of such modulations has not been examined in this study we apply the novel holo hilbert spectral analysis hhsa to five polar ice core records quantifying astronomical forcing s time varying amplitude modulation of do events and identifying the preferred obliquity phases for large amplitude modulations the unique advantages of hhsa over the widely used windowed fourier spectral analysis for quantifying astronomical forcing s nonlinear modulations of do events is first demonstrated with a synthetic data that closely resembles do events recorded in greenland ice cores ngrip grip and gisp2 cores on gicc05 modelext timescale the analysis of paleoclimatic proxies show that statistically significantly more frequent do events with larger amplitude modulation in the greenland region tend to occur in the decreasing phase of obliquity especially from its mean value to its minimum value in the eastern antarctic although statistically significantly more do events tend to occur in the decreasing obliquity phase in general the preferred phase of obliquity for large amplitude modulation on do events is a segment of the increasing phase near the maximum obliquity implying that the physical mechanisms of do events may be different for the two polar regions additionally by using cross spectrum and magnitude squared analyses greenland do mode at a timescale of about 1400 years leads the antarctic do mode at the same timescale by about 1000 years

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

determination of holocene cave temperatures from kr and xe concentrations in stalagmite fluid inclusions from the concentrations of dissolved atmospheric noble gases in water a so called noble gas temperature ngt can be determined that corresponds to the temperature of the water when it was last in contact with the atmosphere here we demonstrate that the ngt concept is applicable to water inclusions in cave stalagmites and yields ngts that are in good agreement with the ambient air temperatures in the caves we analysed samples from two holocene and one undated stalagmite the three stalagmites originate from three caves located in different climatic regions having modern mean annual air temperatures of 27 c 12 c and 8 c respectively in about half of the samples analysed kr and xe concentrations originated entirely from the two well defined noble gas components air saturated water and atmospheric air which allowed ngts to be determined successfully from kr and xe concentrations one stalagmite seems to be particularly suitable for ngt determination as almost all of its samples yielded the modern cave temperature notably this stalagmite contains a high proportion of primary water inclusions which seem to preserve the temperature dependent signature well in their kr and xe concentrations in future work on stalagmites detailed microscopic inspection of the fluid inclusions prior to noble gas analysis is therefore likely to be crucial in increasing the number of successful ngt determinations

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

holocene glacial activity in barilari bay west antarctic peninsula tracked by magnetic mineral assemblages linking ice ocean and atmosphere we investigate the origin and fate of lithogenic sediments using magnetic mineral assemblages in barilari bay west antarctic peninsula ap from sediment cores recovered during the larsen ice shelf system antarctica larissa nbp10 01 cruise to quantify and reconstruct holocene changes in co varying magnetic mineral assemblages we adopt an unsupervised mathematical un mixing strategy and apply it to measurements of magnetic susceptibility as a function of increasing temperature comparisons of the unmixed end members with magnetic observations of northwestern ap bedrock and the spatial distribution of magnetic mineral assemblages within the fjord allow us to identify source regions including signatures for inner bay outer bay and northwestern ap sources we find strong evidence that supports the establishment of a late holocene ice shelf in the fjord coeval with the little ice age additionally we present new evidence for late holocene sensitivity to conditions akin to positive mean southern annual mode states for western ap glaciers at their advanced neoglacial positions this article is protected by copyright all rights reserved

ocean temperature thresholds for last interglacial west antarctic ice sheet collapse the west antarctic ice sheet wais is considered the major contributor to global sea level rise in the last interglacial lig and potentially in the future exposed fossil reef terraces suggest sea levels in excess of 7 meters in the last warm era of which probably not much more than 2 meters are considered to originate from melting of the greenland ice sheet we simulate the evolution of the antarctic ice sheet during the lig with a 3d thermomechanical ice sheet model forced by an atmosphere ocean general circulation model aogcm our results show that high lig sea levels cannot be reproduced with the atmosphere ocean forcing delivered by current aogcms however when taking reconstructed southern ocean temperature anomalies of several degrees sensitivity studies indicate a southern ocean temperature anomaly threshold for total wais collapse of 2 3 c accounting for a sea level rise of 3 4 meters during the lig potential future antarctic ice sheet dynamics range from a moderate retreat to a complete collapse depending on rate and amplitude of warming

on the timing and forcing mechanisms of late pleistocene glacial terminations insights from a new high resolution benthic stable oxygen isotope record of the eastern mediterranean abstract benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the pleistocene however since they often lack independent age control these records are generally bound by a fixed phase relationship between orbital forcing and the climate response e g ice volume changes we present the first long 1 2 ma benthic oxygen isotope record from the eastern mediterranean based on odp sites 967 and 968 which clearly reflects the behavior of global climate on a glacial interglacial scale throughout the late pleistocene time period the age model for our record is based on tuning the elemental ratio of titanium versus aluminum ti al against insolation the ti al record is dominated by the precession related changes in northern african climate i e monsoonal forcing and hence largely independent of glacial interglacial variability we found the largest offset between our chronology and that of the widely applied open ocean stacked record lr04 lisiecki and raymo 2005 for t vii 624 ka which occurred 9 kyr earlier according to our estimates though in agreement with the aicc2012 d ice chronology of epica dome c bazin et al 2013 spectral cross correlation analysis between our benthic 18 o record and 65 n summer insolation reveals significant amounts of power in the obliquity and precession range with an average lag of 5 5 0 8 kyr for obliquity and 6 0 1 0 kyr for precession in addition our results show that the obliquity related time lag was smaller 3 0 3 3 kyr prior to 900 ka than after 5 7 1 1 kyr suggesting that on average the glacial response time to obliquity forcing increased during the mid pleistocene transition much later than assumed by lisiecki and raymo 2005 finally we found that almost all glacial terminations have a consistent phase relationship of 45 45 with respect to the precession and obliquity driven increases in 65 n summer insolation consistent with the general consensus that both obliquity and precession are important for deglaciation during the late pleistocene exceptions are glacial terminations t iiib t 36 and potentially t 32 and t vii t 24 and t 34 which show this consistent phase relationship only with precession only with obliquity our findings point towards an early 1200 ka onset of the mid pleistocene transition vice versa the timing of t vii which can only be explained as a response to obliquity forcing indicates that the transition lasted until at least after mis 15

simulation of glacial interglacial cycles by simple relaxation models consistency with observational results the model of paillard and parrenin earth planet sci lett 227 263 271 2004 was modified to obtain a closer fit to 18o and co2 time series for the last 800 kyr the model performance can be improved if its co2 sensitivity to i65 insolation is eliminated and if different response times are assumed for ablation accumulation of ice correlations between simulated and experimental time series for co2 and ice volume v increase from 0 59 and 0 63 to 0 79 and 0 88 respectively according to these models terminations are produced by i65 amplification through co2 t and t co2 feedbacks in synergy with an extra co2 contribution from the deep ocean this contribution is strongly dependent on ice sheet extent and ice volume or alternatively co2 concentration which is a good proxy of antarctic temperature but is insensitive to southern ocean so insolation on 21 february i60 change of deep so state may be the order parameter for nonlinear deglacial changes according to these models 100 kyr periodicity of glacial cycles arises from the characteristic time of antarctic ice sheet advance to the continental slope

southern ocean sea ice extent productivity and iron flux over the past eight glacial cycles sea ice and dust flux increased greatly in the southern ocean during the last glacial period palaeorecords provide contradictory evidence about marine productivity in this region but beyond one glacial cycle data were sparse here we present continuous chemical proxy data spanning the last eight glacial cycles 740 000 years from the dome c antarctic ice core these data constrain winter sea ice extent in the indian ocean southern ocean biogenic productivity and patagonian climatic conditions we found that maximum sea ice extent is closely tied to antarctic temperature on multi millennial timescales but less so on shorter timescales biological dimethylsulphide emissions south of the polar front seem to have changed little with climate suggesting that sulphur compounds were not active in climate regulation we observe large glacial interglacial contrasts in iron deposition which we infer reflects strongly changing patagonian conditions during glacial terminations changes in patagonia apparently preceded sea ice reduction indicating that multiple mechanisms may be responsible for different phases of co2 increase during glacial terminations we observe no changes in internal climatic feedbacks that could have caused the change in amplitude of antarctic temperature variations observed 440 000 years ago

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

a novel method to study the phase relationship between antarctic and greenland climate 1 a classical method for understanding the coupling between northern and southern hemispheres during millennial scale climate events is based on the correlation between greenland and antarctic ice core records of atmospheric composition here we present a new approach based on the use of a single antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the north and of its antarctic counterpart we applied it to the marine isotope stage mis 5d c transition early in the last glaciation 108 ky bp our results indicate that the antarctic temperature increase occurred 2 ky before the methane increase which is used as a time marker of the warming in the northern hemisphere this result is in agreement with the bipolar seesaw mechanism used to explain the phase relationships documented between 23 and 90 ky bp blunier and brook 2001

astronomical forcing in late eocene marine sediments we use an x ray fluorescence xrf core scanner to obtain records of elemental concentrations in sediment cores from ocean drilling program odp leg 171b site 1052 blake nose atlantic margin of northern florida this record spans the middle to late eocene as indicated by bio and magnetostratigraphy and displays cyclicity that can be attributed to the orbital forcing of a combination of climate ocean circulation or productivity we use the xrf counts of iron and calcium as a proxy of the relative contribution from calcium carbonate and terrestrial material to construct a new composite depth record this new composite depth record provides the basis to extend the astronomically calibrated geological time scale into the middle eocene and results in revised estimates for the age and duration of magnetochrons c16 through c18 in addition we find an apparent change in the dominance of orbitally driven changes in obliquity and climatic precession at around 36 7 ma on our new time scale long term amplitude modulation patterns of eccentricity and obliquity in the data do not seem to match the current astronomical model any more suggesting the possibility of new constraints on astronomical calculations

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

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

glacial terminations as southern warmings without northern control the timing and mechanisms of the transition from a glacial to an interglacial state are controversial an analysis of antarctic ice core records indicates that glacial terminations may begin as millennial scale warmings in the southern hemisphere that unlike previous events are not reversed by abrupt warming in the northern hemisphere

variation of the asian summer monsoon since the last glacial interglacial recorded in a stalagmite from southwest china abstract a number of studies proposed a close link between the climate changes in the asian summer monsoon asm the southern hemisphere sh and high latitudes of the northern hemisphere nh but the mechanisms is still an open question although speleothems 18o records have displayed excellent values in the reconstruction of paleoclimate change at centennial millennial to orbital timescales the significance of speleothems 18o and 13c is still debatable here a high precise 230th dated stalagmite from southwestern china was used to reconstruct the changes of asm and regional hydrological conditions since the last interglacial 3 6 118 1 ka bp by the coupled 18o and 13c we found 1 the easm and ism are synchronous changing on the orbital timescale responding to the change of north hemisphere summer insolation nhsi and high latitude climate change there is a teleconnection between antarctic temperature change and asm through the mascarene high and the somali jet 2 during mis 5d the stalagmite 18o in yangzi cave is nearly 1 5 higher than that in mis 2 the maximum of last glacial this should be attributed to the different isotopic compositions in moisture source of ism and easm and the dynamic changes of monsoon circulations 3 from mis 3 to mis 2 the asm showed a stepped pattern in weakening consistent with the decreasing nhsi and increasing global ice volume 4 the changes in stalagmite 13c indicated the changes of local hydrological conditions and closely correlated with climate changes revealed by stalagmite 18o the effective humidity which determined by temperature evaporation and precipitation dominated the regional hydrological conditions the change of effective humidity recorded in stalagmite 13c by influencing surface biomass and soil co2 production

artifacts resembling budding bacteria produced in placer gold amalgams by nitric acid leaching microscopic filiform morphologies in gold which are indistinguishable from forms originally interpreted as bacterial in origin were produced in the laboratory by treating amalgams made from natural and artificial gold with hot nitric acid textures ranging from cobblestone to deeply crenulated to nodular filiform were produced in the laboratory from all tested natural and artificial gold amalgams analogous textures widespread in alaskan placer gold may have a similar inorganic origin these results indicate that morphology alone cannot be considered adequate evidence of microbial involvement in gold formation

sea ice control of plio pleistocene tropical pacific climate evolution marine proxies of sea surface temperature sst indicate that the tropical pacific thermal gradient intensified through the plio pleistocene and peaked during pleistocene glaciations the cause of this variability which has been linked to the initiation of the walker circulation is uncertain here we hypothesize that plio pleistocene tropical climate variability was coupled to high latitude southern hemisphere climate change specifically sea ice extent we use a coupled ocean atmosphere general circulation model to investigate the influences of sea ice extent and atmospheric co2 on the tropical pacific thermal structure in the model co2 radiative forcing in the absence of any sea ice feedbacks has little influence on the tropical sst gradient a 180 ppm reduction in co2 causes the sst gradient to decrease by 0 4 c in comparison an expansion of southern hemisphere high latitude sea ice reduces tropical ssts and enhances the sst gradient in the tropical pacific by as much as 3 5 c tropical cooling is primarily due to the advection and upwelling of waters into the eastern equatorial pacific that were cooled by sensible heat loss at the sea ice margin in the southern pacific an energy balance analysis indicates that the ocean heat flux into the eastern equatorial pacific decreases by 44 this mechanism provides an intimate coupling between the tropical pacific and the high latitude southern hemisphere through the thermocline circulation

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

a 560 440 ka tephra record from the mercure basin southern italy volcanological and tephrostratigraphic implications integrated electron microprobe analyses empas on glass and sr nd isotope analyses have been performed on 17 tephras from the middle pleistocene mercure lacustrine succession southern apennines two 40ar 39ar ages and the recognition of four relevant tephras from colli albani sabatini and possibly roccamonfina volcanoes allowed us to ascribe the investigated succession to the late marine isotope stage mis 15 12 interval 560 440 ka the sr nd isotopes and major element glass compositions allowed us to attribute 10 out of the other 13 tephras to a poorly known activity of the roccamofina volcano whereas two layers were tentatively attributed to previously unknown middle pleistocene activity of ponza island or campanian volcanoes and one to salina island the tephrostratigraphic correlation of the mercure tephras with the acerno lacustrine pollen record campania also allowed us to evaluate the climatostratigraphic position of the tephras within the framework of the mis 15 12 climatic variability these results were obtained by combining the sr nd isotope ratio with empa and 40ar 39ar geochronological data this confirms the notable consistency of this approach for studying the mediterranean middle pleistocene tephrostratigraphy which despite its great potential for both volcanology and quaternary studies has been hitherto barely explored

pleistocene glacial terminations triggered by synchronous changes in southern and northern hemisphere insolation the insolation canon hypothesis throughout the last 900 kyr the late pleistocene earth has experienced periods of cold glacial climate punctuated by seven abrupt transitions to warm interglacials the so called terminations although most of glacial ice is located in the northern hemisphere nh the southern hemisphere sh seems to play a crucial role in deglaciation variation in the seasonal distribution of solar insolation is one candidate for the cause of these climatic shifts but so far no simple mechanism has been identified here we present a mathematical analysis of variations in midsummer insolation in both hemispheres at 65 latitude applying this analysis to the entire pleistocene the last 2 myr we find that prior to each termination the insolation in both hemispheres increases in concert with a sh lead introducing time and energy thresholds to these overlaps calculated times for the onsets of the seven terminations by this insolation canon exceptional overlaps meeting the two threshold prerequisites are 23 139 253 345 419 546 and 632 kyr bp perfectly matching the geologic record the timing originates from the interplay between the two orbital parameters obliquity and precession explaining why terminations occur at integer multiple of the precessional cycle there is no such constellation between 1 and 2 myr bp the early pleistocene in agreement with earth s climate at that time this change in orbital forcing coincides with the mid pleistocene revolution separating the late from the early pleistocene therefore we hypothesize that the insolation canon is the trigger for glacial terminations

middle to late pleistocene vegetation and climate change in subtropical southern east africa in this study we investigate pleistocene vegetation and climate change in southern east africa by examining plant leaf waxes in a marine sediment core that receives terrestrial runoff from the limpopo river the plant leaf wax records are compared to a multi proxy sea surface temperature sst record and pollen assemblage data from the same site we find that indian ocean sst variability driven by high latitude obliquity exerted a strong control on the vegetation of southern east africa during the past 800 000 yr interglacial periods were characterized by relatively wetter and warmer conditions increased contributions of c3 vegetation and higher sst whereas glacial periods were marked by cooler and arid conditions increased contributions of c4 vegetation and lower sst we find that marine isotope stages mis 5e 11c 15e and 7a 7c are strongly expressed in the plant leaf wax records but mis 7e is absent while mis 9 is rather weak our plant leaf wax records also record the climate transition associated with the mid brunhes event mbe suggesting that the pre mbe interval 430 800 ka was characterized by higher inputs from grasses in comparison to relatively higher inputs from trees in the post mbe interval 430 to 0 ka differences in vegetation and sst of southern east africa between the pre and post mbe intervals appear to be related to shifts in the location of the subtropical front comparison with vegetation records from tropical east africa indicates that the vegetation of southern east africa while exhibiting glacial interglacial variability and notable differences between the pre and post mbe portions of the record likely did not experience such dramatic extremes as occurred to the north at lake malawi

plio pleistocene ice volume antarctic climate and the global δ18o record we propose that from 3 to 1 million years ago ice volume changes occurred in both the northern and southern hemispheres each controlled by local summer insolation because earth9s orbital precession is out of phase between hemispheres 23 000 year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean 18 o or sea level leaving the in phase obliquity 41 000 years component of insolation to dominate those records only a modest ice mass change in antarctica is required to effectively cancel out a much larger northern ice volume signal at the mid pleistocene transition we propose that marine based ice sheet margins replaced terrestrial ice margins around the perimeter of east antarctica resulting in a shift to in phase behavior of northern and southern ice sheets as well as the strengthening of 23 000 year cyclicity in the marine 18 o record

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record

extensive retreat and re advance of the west antarctic ice sheet during the holocene to predict the future contributions of the antarctic ice sheets to sea level rise numerical models use reconstructions of past ice sheet retreat after the last glacial maximum to tune model parameters 1 reconstructions of the west antarctic ice sheet have assumed that it retreated progressively throughout the holocene epoch the past 11 500 years or so 2 4 here we show however that over this period the grounding line of the west antarctic ice sheet which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf retreated several hundred kilometres inland of today s grounding line before isostatic rebound caused it to re advance to its present position our evidence includes first radiocarbon dating of sediment cores recovered from beneath the ice streams of the ross sea sector indicating widespread holocene marine exposure and second ice penetrating radar observations of englacial structure in the weddell sea sector indicating ice shelf grounding we explore the implications of these findings with an ice sheet model modelled re advance of the grounding line in the holocene requires ice shelf grounding caused by isostatic rebound our findings overturn the assumption of progressive retreat of the grounding line during the holocene in west antarctica and corroborate previous suggestions of ice sheet re advance 5 rebound driven stabilizing processes were apparently able to halt and reverse climate initiated ice loss whether these processes can reverse present day ice loss 6 on millennial timescales will depend on bedrock topography and mantle viscosity parameters that are difficult to measure and to incorporate into ice sheet models

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

the mid brunhes event and west antarctic ice sheet stability the complex cyclical nature of pleistocene climate driven by the evolving orbital configuration of the earth is well known but not well understood a major climatic transition took place at the mid brunhes event mbe ca 430 ka ago after which the amplitude of the ca 100 ka climate oscillations increased with substantially warmer interglacials including periods warmer than present recent modelling has indicated that while the timing of these warmer than present transient wpt events is consistent with southern warming clue to a deglaciation forced slowdown of the atlantic meridional overturning circulation the magnitude of warming requires a local amplification for which a candidate is the feedback of significant west antarctic ice sheet wais retreat we here extend this argument based on the absence of wpts in the early ice core record 450 800 ka ago to hypothesize that the mbe could be a manifestation of decreased wais stability triggered by ongoing subglacial erosion

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

evolving southwest african response to abrupt deglacial north atlantic climate change events abstract climate change during the last deglaciation was strongly influenced by the bipolar seesaw producing antiphase climate responses between the north and south atlantic however mounting evidence demands refinements of this model with the occurrence of abrupt events in southern low to mid latitudes occurring in phase with north atlantic climate improved constraints on the north south phasing and spatial extent of these events are therefore critical to understanding the mechanisms that propagate abrupt events within the climate system we present a 19 400 year multi proxy record of climate change obtained from a rock hyrax midden in southernmost africa arid anomalies in phase with the younger dryas and 8 2 ka events are apparent indicating a clear shift in the influence of the bipolar seesaw which diminished as the earth warmed and was succeeded after 14 6 ka by the emergence of a dominant interhemispheric atmospheric teleconnection

glacial interglacial changes in nutrient supply and stratification in the western subarctic north pacific since the penultimate glacial maximum abstract in piston cores from the open subarctic pacific and the okhotsk sea diatom bound 15n 15ndb biogenic opal calcium carbonate and barium were measured from coretop to the previous glacial maximum mis 6 glacial intervals are generally characterized by high 15ndb 8 and low productivity whereas interglacial intervals have a lower 15ndb 5 7 6 3 and indicate high biogenic productivity these data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima consistent with stronger upper water column stratification throughout the subarctic region during colder intervals an early deglacial decline in 15ndb of 2 at 17 5 ka previously observed in the bering sea is found here in the open subarctic pacific record and arguably also in the okhotsk and a case can be made that a similar decrease in 15ndb occurred in both regions at the previous deglaciation as well the early deglacial 15ndb decrease best explained by a decrease in surface nutrient utilization appears synchronous with southern hemisphere associated deglacial changes and with the heinrich 1 event in the north atlantic this 15ndb decrease may signal the initial deglacial weakening in subarctic north pacific stratification and or a deglacial increase in shallow subsurface nitrate concentration if the former it would be the north pacific analogue to the increase in vertical exchange inferred for the southern ocean at the time of heinrich event 1 in either case the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron to nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to bolling allerod warming

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

the last glacial cycle transient simulations with an aogcm a number of transient climate runs simulating the last 120 kyr have been carried out using famous a fast atmosphere ocean general circulation model aogcm this is the first time such experiments have been done with a full aogcm providing a three dimensional simulation of both atmosphere and ocean over this period our simulation thus includes internally generated temporal variability over periods from days to millennia and physical detailed representations of important processes such as clouds and precipitation although the model is fast computational restrictions mean that the rate of change of the forcings has been increased by a factor of 10 making each experiment 12 kyr long atmospheric greenhouse gases ghgs northern hemisphere ice sheets and variations in solar radiation arising from changes in the earth s orbit are treated as forcing factors and are applied either separately or combined in different experiments the long term temperature changes on antarctica match well with reconstructions derived from ice core data as does variability on timescales longer than 10 kyr last glacial maximum lgm cooling on greenland is reasonably well simulated although our simulations which lack ice sheet meltwater forcing do not reproduce the abrupt millennial scale climate shifts seen in northern hemisphere climate proxies or their slower southern hemisphere counterparts the spatial pattern of sea surface cooling at the lgm matches proxy reconstructions reasonably well there is significant anti correlated variability in the strengths of the atlantic meridional overturning circulation amoc and the antarctic circumpolar current acc on timescales greater than 10 kyr in our experiments we find that ghg forcing weakens the amoc and strengthens the acc whilst the presence of northern hemisphere ice sheets strengthens the amoc and weakens the acc the structure of the amoc at the lgm is found to be sensitive to the details of the ice sheet reconstruction used the precessional component of the orbital forcing induces 20 kyr oscillations in the amoc and acc whose amplitude is mediated by changes in the eccentricity of the earth s orbit these forcing influences combine to first order in a linear fashion to produce the mean climate and ocean variability seen in the run with all forcings

millennial scale asian monsoon variability during the late marine isotope stage 6 from hulu cave china a precisely 230 th dated stalagmite 13 c profile from hulu cave china is presented to characterize the frequency and pattern of millennial scale asian monsoon am variability from 160 6 to 132 5 ka evidence for an antiphased relationship of the 13 c and 18 o on the millennial scale suggests that the 13 c is indicative of the local hydrological cycle associated with changes in am strength owing to the 13 c responding to am changes more sensitively than the 18 o we could identify 15 strong am events that correlate to cold intervals recorded in antarctic ice cores within 230 th dating uncertainty this result supports a dynamic link of am strength and southern hemispheric climates via the cross equatorial airflows power spectrum analysis shows a predominant periodicity of 1 5 2 5 ka for the 13 c profile similar to the dansgaard oeschger frequency during the last glacial period moreover the am events are characterized by rapid transitions at the onset suggesting that the observed millennial scale am variability is likely forced by northern high latitude climates via north south shifts of the intertropical convergence zone associated with the bipolar seesaw mechanism as evidence for a common mechanism for ice age terminations a strong am event 134 ka surrounding termination ii is analogous to the bolling allerod warming interval

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

evolution of crustal thickening in the central andes bolivia abstract paleoelevation histories from the central andes in bolivia have suggested that the geodynamic evolution of the region has been punctuated by periods of large scale lithospheric removal that drive rapid increases in elevation at the surface here we evaluate viable times and locations of material loss using a map view reconstruction of the bolivian orocline displacement field to forward model predicted crustal thicknesses two volumetric models are presented that test assumed pre deformation crustal thicknesses of 35 km and 40 km both models predict that modern crustal thicknesses were achieved first in the northern eastern cordillera ec by 30 20 ma but remained below modern in the southern ec until 10 ma the altiplano is predicted to have achieved modern crustal thickness after 10 ma but only with a pre deformation thickness of 50 km including 10 km of sediment at the final stage the models predict 8 25 regional excess crustal volume compared to modern thickness largely concentrated in the northern ec the excess predicted volume from 20 to 0 ma can be accounted for by 1 crustal flow to the wc and or peru 2 localized removal of the lower crust or 3 a combination of the two only models with initial crustal thicknesses 35 km predict excess volumes sufficient to account for potential crustal thickness deficits in peru and allow for lower crustal loss however both initial thickness models predict that modern crustal thicknesses were achieved over the same time periods that paleoelevation histories indicate the development of modern elevations localized removal of lower crust is only necessary in the northern ec where crustal thickness exceeds modern by 20 ma prior to paleoelevation estimates of modern elevations by 15 ma in the altiplano crustal thicknesses match modern values at 10 ma and can only exceed modern values by 5 ma post dating when modern elevations were thought to have been established collectively these models predict that the timing of crustal thickening is consistent with paleoelevation data without requiring large scale removal of lower crust and mantle lithosphere

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

amplitude and phase of glacial cycles from a conceptual model abstract the astronomical theory of climate in which the orbital variations of the earth are taken to drive the climate changes explains many features of the paleoclimatic records nevertheless the precise link between insolation variations and climatic changes during the quaternary remains mysterious in several aspects in particular the largest sea level changes of the past million years occurred when insolation variations were minimal like during stage 11 and vice versa like during stage 7 moreover recent data from terminations ii and iii show surprising phase lead and lag between insolation and sea level variations to explain these paradoxical amplitude and phase modulations we suggest here that deglaciations started when a combination of insolation and ice volume was large enough to illustrate this new idea we present a simple conceptual model that simulates the sea level curve of the past million years with very realistic amplitude modulations and with good phase modulations

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

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

multiple glacial advances in the rangitata valley south island new zealand imply roles for southern hemisphere westerlies and summer insolation in mis 3 glacial advances stratigraphic evidence and extensive optically stimulated luminescence osl geochronology from an 18 km long reach of the middle rangitata valley south island new zealand provide evidence for at least six distinct glacial advances during the last glacial cycle these include four well constrained marine oxygen isotope stage mis 3 and 2 advances at ca 38 ka ca 27 ka ca 21 ka and at 18 ka as well as less well constrained advances in mis 4 and or early mis 3 ice occupied a farther downvalley reach of the rangitata from 38 ka to after 18 ka indicating that near full glacial conditions persisted for most of the last 20 ka of the last glaciation though the glacier still fluctuated significantly as reflected by the numerous distinguishable advances global or regional cooling alone cannot explain the persistence of near maximum glacial conditions for this extended period nor can it explain the occurrence of the largest advances ca 32 ka instead we invoke the northward expansion of the westerlies during mis 3 as the cause for the early widespread glaciation wherein enhanced westerly flow under moderate cooling maximised glacial extents local insolation favoured extended mis 3 glaciation until ca 32 ka increasing summer insolation gradually reduced glacial extents after ca 28 ka

a new late quaternary palaeohydrological record from the humid tropics of northeastern australia abstract high resolution x ray fluorescence xrf is presented as a robust palaeoclimatic proxy suitable for use on late pleistocene to holocene sediments located in a volcanic crater on the atherton tableland in northeastern queensland australia the proxy allows identification of wet and dry shifts in a complex sedimentary sequence comprised of peat gyttja laminated organic rich muds and fine clastic silt rich sediments significant correlation is found between the xrf record and other proxies including magnetic susceptibility humification grain size macrocharcoal 13c and c n and pollen sixteen wetter periods are identified in the 37 ka sedimentary record for bromfield swamp three wetter periods commence in late marine isotope stage 3 nine in the early glacial one in the late de glacial and four in holocene nineteen drier periods are identified four in late mis 3 seven in the early glacial one during the lgm one in the late de glacial period and six in the holocene the xrf record for bromfield swamp is specifically used to identify periods of abrupt climate change marked changes in effective precipitation are detected at 32 690 30 080 24 660 21 870 11 880 10 020 9170 and 5120 cal yr bp the detection of these abrupt climate events may allow correlation with records from terrestrial sites across the southern hemisphere and potentially the northern hemisphere

central mediterranean mid pleistocene paleoclimatic variability and its association with global climate abstract planktonic foraminiferal assemblages were studied at high resolution in core kc01b from the ionian sea quantitative analysis allowed us to distinguish the main climatic features and associated paleoceanographic changes that occurred between marine isotopic stages mis 13 and 9 500 300 ka mis 12 and mis 10 are characterized by relatively temperate conditions and an oligotrophic oceanographic regime in the early part and by colder conditions and nutrient supply in the sub surface water masses in the upper part during these intervals small but distinct peaks of neogloboquadrina pachyderma sinistral sin are detected at times of extremely negative values of the planktonic foraminifera paleoclimatic curve their co occurrence with similar episodes in the atlantic suggests that the climate in the central mediterranean was associated with north atlantic millennial scale climate instability mis 11 and mis 9 are dominated by surficial warm water taxa the climate optimum is reached in the middle part of each of these stages as denoted by the presence of globigerinoides sacculifer and persists for approximately 20 and 6 ka during mis 11 and mis 9 respectively this warming is not constant but is characterized by three distinct intervals with elevated winter temperatures and or weak winter mixing distribution of globigerina bulloides turborotalita quinqueloba and n pachyderma dextral dex indicates that significant environmental changes occur across the transitions from glacial to interglacial mis 12 mis 11 termination v and mis 10 mis 9 termination iv the studied record documents a close linkage between mediterranean climate evolution and higher and lower latitude climate change throughout mis 13 9