timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

abrupt change of antarctic moisture origin at the end of termination ii the deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin new data obtained from the european project for ice coring in antarctica dome c east antarctic ice core provide new insights on the sequence of events involved in termination ii the transition between the penultimate glacial and interglacial periods this termination is marked by a north south seesaw behavior with first a slow methane concentration rise associated with a strong antarctic temperature warming and a slow deuterium excess rise this first step is followed by an abrupt north atlantic warming an abrupt resumption of the east asian summer monsoon a sharp methane rise and a co 2 overshoot which coincide within dating uncertainties with the end of antarctic optimum here we show that this second phase is marked by a very sharp dome c centennial deuterium excess rise revealing abrupt reorganization of atmospheric circulation in the southern indian ocean sector

a review of the bipolar see saw from synchronized and high resolution ice core water stable isotope records from greenland and east antarctica numerous ice core records are now available that cover the last glacial cycle both in greenland and in antarctica recent developments in coherent ice core chronologies now enable us to depict with a precision of a few centuries the relationship between climate records in greenland and antarctica over the millennial scale variability of the last glacial period stacks of greenland and antarctic water isotopic records nicely illustrate a seesaw pattern with the abrupt warming in greenland being concomitant with the beginning of the cooling in antarctica at the antarctic isotopic maximum aim in addition from the precise estimate of chronological error bars and additional high resolution measurements performed on the edc and taldice ice cores we show that the seesaw pattern does not explain the regional variability in antarctic records with clear two step structures occurring during the warming phase of aim 8 and 12 our antarctic high resolution data also suggest possible teleconnections between changes in low latitude atmospheric circulation and antarctic without any greenland temperature fingerprint

timing and climate forcing of volcanic eruptions for the past 2 500 years volcanic eruptions contribute to climate variability but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual to decadal temperature variability in the northern hemisphere during the past 2 500 years our results are based on new records of atmospheric aerosol loading developed from high resolution multi parameter measurements from an array of greenland and antarctic ice cores as well as distinctive age markers to constrain chronologies overall cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth century pandemics famines and socioeconomic disruptions in eurasia and mesoamerica while allowing multi millennium quantification of climate response to volcanic forcing

links between iron supply marine productivity sea surface temperature and co2 over the last 1 1 ma received 3 july 2008 revised 9 october 2008 accepted 27 october 2008 published 14 february 2009 1 paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric co2 concentrations however the mechanisms behind glacial interglacial g ig variations in atmospheric co2 concentrations observed in the antarctic ice cores are still not fully understood here we present a new multiproxy data set of sea surface temperatures sst dust and iron supply and marine export productivity from the marine sediment core ps2489 2 odp site 1090 located in the subantarctic atlantic that allow us to evaluate various hypotheses on the role of the southern ocean so in modulating atmospheric co2 concentrations back to 1 1 ma we show that antarctic atmospheric temperatures are closely linked to changes in so surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the european project for ice coring in antarctica epica dome c edc records the close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the g ig cycles of the last 1 1 ma however our data suggest that marine productivity can only explain a fraction of atmospheric co2 changes up to around 40 50 ppmv occurring at glacial maxima in each glacial stage in this sense the good correlation of our sst record to the edc temperature reconstruction suggests that the initial glacial co2 decrease as well as the change in the amplitude of the co2 cycles observed around 400 ka was most likely driven by physical processes possibly related to changes in antarctic sea ice extent surface water stratification and westerly winds position

applicability of unmanned aerial vehicles in research on aeolian processes surface dynamics and instabilities are characteristic of aeolian formation the method of surface comparison is regarded as the most appropriate one for evaluation of the intensity of aeolian processes and the amount of transported sand the data for surface comparison can be collected by topographic survey measurements and using unmanned aerial vehicles time cost for relief microform fixation and measurement executing topographic survey are very high the method of unmanned aircraft aerial photographs fixation also encounters difficulties because there are no stable clear objects and contours that enable to link aerial photographs to determine the boundaries of captured territory and to ensure the accuracy of surface measurements creation of stationary anchor points is irrational due to intense sand accumulation and deflation in different climate seasons in september 2015 and in april 2016 the combined methodology was applied for evaluation of intensity of aeolian processes in the curonian spit temporary signs marks were installed on the surface coordinates of the marks were fixed using gps and then flight of unmanned aircraft was conducted the fixed coordinates of marks ensure the accuracy of measuring aerial imagery and the ability to calculate the possible corrections this method was used to track and measure very small micro rank relief forms 5 10 cm height and 10 20 cm length using this method morphometric indicators of micro terraces caused by sand dunes pressure to gytia layer were measured in a non contact way an additional advantage of the method is the ability to accurately link the repeated measurements the comparison of 3d terrain models showed sand deflation and accumulation areas and quantitative changes in the terrain very clearly

coupling of the hemispheres in observations and simulations of glacial climate change abstract we combine reconstructions climate model simulations and a conceptual model of glacial climate change on millennial time scales to examine the relation between the high latitudes of both hemispheres a lead lag analysis of synchronised proxy records indicates that temperature changes in greenland preceded changes of the opposite sign in antarctica by 400 500 yr a composite record of the dansgaard oeschger events shows that rapid warming cooling in greenland was followed by a slow cooling warming phase in antarctica the amplitudes rates of change and time lag of the interhemispheric temperature changes found in the reconstructions are in excellent agreement with climate model simulations in which the formation of north atlantic deep water is perturbed the simulated time lag between high northern and southern latitudes is mainly determined by the slow meridional propagation of the signal in the southern ocean our climate model simulations also show that increased deep water formation in the north atlantic leads to a reduction of the antarctic circumpolar current through diminishing meridional density gradients in the southern ocean we construct a simple conceptual model of interhemispheric dansgaard oeschger oscillations this model explains major features of the recorded temperature changes in antarctica as well as the general shape of the north south phase relation found in the observations including a broad peak of positive correlations for a lead of antarctica over greenland by 1000 2000 yr the existence of this peak is due to the regularity of the oscillations and does not imply a southern hemisphere trigger mechanism contrary to previous suggestions our findings thus further emphasise the role of the thermohaline circulation in millennial scale climate variability

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

atlantic pacific seesaw and its role in outgassing co2 during heinrich events 1 paleoproxy records indicate that a marked weakening of the atlantic meridional overturning circulation amoc during heinrich events was often accompanied by a notable atmospheric co2 increase however previous modeling studies display conflicting atmospheric co2 responses to an amoc shutdown here we use model simulations combined with paleoproxy records to show that depending on the deep and bottom water transport in the northern and southern pacific ocean during an amoc weakening the ocean can act either as a sink or a source of carbon results from idealized meltwater experiments as well as from a transient experiment covering heinrich stadial 4 suggest that a shutdown of the amoc during heinrich stadials 4 hs4 and 1 hs1 led to an enhancement of antarctic bottom water aabw and north pacific deep water npdw transport we show that enhanced deep and bottom water transport in the pacific ocean ventilates deep pacific carbon through the southern ocean thus contributing to a rise in atmospheric co2 this mechanism yields a good agreement between paleoproxy records and modeling results thus highlighting the possible establishment of an atlantic pacific seesaw during heinrich stadials enhanced aabw and npdw transport could account for most of the observed atmospheric co2 increase during hs4 and for about 30 of the atmospheric co2 increase during hs1

antarctic and global climate history viewed from ice cores a growing network of ice cores reveals the past 800 000 years of antarctic climate and atmospheric composition the data show tight links among greenhouse gases aerosols and global climate on many timescales demonstrate connections between antarctica and distant locations and reveal the extraordinary differences between the composition of our present atmosphere and its natural range of variability as revealed in the ice core record further coring in extremely challenging locations is now being planned with the goal of finding older ice and resolving the mechanisms underlying the shift of glacial cycles from 40 000 year to 100 000 year cycles about a million years ago one of the great mysteries of climate science a discussion of past antarctic and global climate history as seen from antarctic ice cores with an outlook on future goals and drilling priorities

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

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

the thermal threshold of the atlantic meridional overturning circulation and its control by wind stress forcing during glacial climate 1 paleo proxy data suggest that the atlantic meridional overturning circulation amoc was shallower and weaker at the last glacial maximum lgm than at present in this study we have identified the existence of a thermal threshold of the amoc which may explain why many coupled climate models fail to simulate the weaker amoc during the lgm by using results obtained from a coupled climate model and conducting sensitivity simulations with an ocean general circulation model we found that the sudden transition from the present day amoc to the weaker glacial amoc occurs when we gradually change the degree of surface cooling from present day to glacial conditions this result is related to response of deep convection in the northern north atlantic ocean moderate cooling enhances deep convection whereas sufficient cooling results in total covering of sea ice there and suppression of deep convection the findings indicate the existence of a thermal threshold controlling the amoc where the present day type amoc suddenly shifts to the weaker glacial amoc once the surface cooling exceeds this threshold we also demonstrate that wind stress forcing plays a critical role in controlling the value of the thermal threshold our study suggests that slight differences in the degree of surface cooling or wind stress forcing for lgm simulations could lead to the very different response of the amoc during the lgm as reported in previous lgm simulations

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

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

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

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

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

abrupt change in atmospheric co2 during the last ice age 1 during the last glacial period atmospheric carbon dioxide and temperature in antarctica varied in a similar fashion on millennial time scales but previous work indicates that these changes were gradual in a detailed analysis of one event we now find that approximately half of the co2increase that occurred during the 1500 year cold period between dansgaard oeschger do events 8 and 9 happened rapidly over less than two centuries this rise in co2 was synchronous with or slightly later than a rapid increase of antarctic temperature inferred from stable isotopes

glacial abrupt climate changes and dansgaard oeschger oscillations in a coupled climate model 1 there are three fundamental features which characterize large glacial millennial dansgaard oeschger oscillations 1 the climatic transitions were abrupt and large 2 the lengths of both interstadials and stadials and the period of dansgaard oeschger oscillations were not uniform and 3 there were no large millennial oscillations during an early stage of a glacial period and a peak glacial period in this modeling study we offer a consistent explanation for these three features by employing an earth system model of intermediate complexity we demonstrate that a moderate global cooling forces the atlantic meridional overturning circulation moc into an unstable state and hence causes the flip flop of the atlantic moc between a strong mode and a weak mode the durations of both interstadials and stadials associated with these millennial oscillations are modulated by the changing background climate in qualitative agreement with the observations in a warm climate the atlantic moc is strong and stable with the deep water formed mainly by intense heat loss to the atmosphere in a cold climate the atlantic moc is weak and stable and this mode is largely maintained by the process of sea ice brine rejection since the dansgaard oeschger oscillations result from an alternation between these two moc states during an intermediate phase climate we conclude that brine rejection plays a necessary role in the oscillations confirming a hypothesis suggested in some proxy data studies

postseismic motion after the 2001 mw 7 8 kokoxili earthquake in tibet observed by insar time series 1 on november 14th 2001 a mw 7 8 earthquake occurred in the kokoxili region of northern tibet the earthquake ruptured more than 400 km along the western part of the kunlun fault with a maximum of 8 m left lateral slip in this paper we use a multitemporal interferometric sar insar time series technique to map the postseismic motion following the large kokoxili event sar data from envisat descending orbits along five adjacent tracks covering almost the entire ruptured fault length are used to calculate the displacement time series for a period between 2 and 6 years after the earthquake a peak to trough signal of 8 cm in the radar line of sight is observed during the period between 2003 and 2008 two different mechanisms are employed to explain the observed surface displacements namely afterslip and viscoelastic relaxation the observations inverted for afterslip on and below the coseismic rupture plane shows that the maximum slip in the afterslip model is 0 6 m the position of the maximum postseismic slip is located in the middle of two relatively high coseismic slip patches which suggests that afterslip is a plausible mechanism models of viscoelastic stress relaxation in a maxwell half space give a best fitting viscosity for the mid to lower crust of 2 5 1019 pa s and the principal postseismic relaxation process is due to viscous flow in the lower crust to upper mantle however the insar observations are incapable of distinguishing between localized afterslip and distributed viscoelastic relaxation deformation and the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle below 70 km and afterslip in the crust modeling of viscoelastic relaxation in a maxwell half space and also a mixed mechanism model enables us to place an effective viscosity of 2 1019 pa s on the lower crust to mantle of northern tibet

the last interglacial as represented in the glaciochemical record from mount moulton blue ice area west antarctica abstract understanding climate during the last interglacial is critical for understanding how modern climate change differs from purely naturally forced climate change here we present the first high resolution ice core record of the last interglacial and transition to the subsequent glacial period from antarctica and the first glaciochemical record for this period from west antarctica samples were collected from a horizontal ice trench in the mt moulton blue ice area bia in west antarctica and analyzed for their soluble major anions cl no 3 so 4 2 major and trace elements na mg ca sr cd cs ba la ce pr pb bi u as al s ti v cr mn fe co cu zn and water hydrogen isotopes d the last interglacial is characterized by warmer temperatures d weakened atmospheric circulation dust elements seasalts aerosols decreased sea ice extent na nssso 4 2 and decreased oceanic productivity nssso 4 2 a combined examination of mt moulton seasalts dust nssso 4 2 and d records indicates that the last interglacial was extremely stable compared to glacial age climate events and it ended through a long period of gradual cooling unlike that projected for future holocene climate

atmospheric composition 1 million years ago from blue ice in the allan hills antarctica here we present direct measurements of atmospheric composition and antarctic climate from the mid pleistocene 1 ma from ice cores drilled in the allan hills blue ice area antarctica the 1 ma ice is dated from the deficit in 40ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12 m section at the base of a 126 m ice core the 1 ma ice appears to represent most of the amplitude of contemporaneous climate cycles and co2 and ch4 concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion ppb respectively these concentrations together with measured d of the ice are at the warm end of the field for glacial interglacial cycles of the last 800 ky and span only about one half of the range the highest co2 values in the 1 ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka the lowest co2 values are 30 ppm higher than during any glacial period between 450 and 800 ka this study shows that the coupling of antarctic temperature and atmospheric co2 extended into the mid pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in antarctic blue ice areas

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

relations between monterey formation deposition and middle miocene global cooling naples beach section california an oxygen and carbon isotopic stratigraphy has been established for the miocene monterey formation 18 to 8 ma at naples beach santa barbara county california correlation to the deep sea climatic record provides a test of the monterey hypothesis which suggests that organic carbon rich deposition in the monterey formation fostered middle miocene global cooling through drawdown of atmospheric partial co 2 oxygen isotopic correlation of the naples beach section to the deep sea record suggests that increased organic carbon rich deposition coincided closely with deep water cooling and major east antarctic ice sheet growth from 14 5 to 14 1 ma and with a 13 c maximum in deep sea records these results support a corollary of the monterey hypothesis that episodic organic carbon rich deposition within the monterey formation contributed to deep sea 13 c maxima and to synchronous global cooling

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

glacial interglacial changes in mineral dust and sea salt records in polar ice cores sources transport and deposition 1 sea salt and mineral dust records as represented by na and ca2 concentrations respectively in greenland and antarctic ice cores show pronounced glacial interglacial variations for the last glacial maximum lgm mineral dust sea salt concentrations in greenland show an increase of a factor of approximately 80 15 compared to the holocene and significant shifts by a factor of 15 5 during dansgaard oeschger events in antarctica the dust sea salt flux is enhanced by a factor of 15 3 during the lgm compared to the holocene and variations by approximately a factor of 8 1 2 exist in parallel to antarctic warm events primary glacial dust sources are the asian deserts for greenland and patagonia for antarctica ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in greenland ice cores in antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust where the formation of sea salt aerosol from sea ice may play a pivotal role summarizing our latest estimates on changes in sources transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4 7 for mineral dust future improvements in model resolution and in the formulation of source and transport processes together with new ice core records e g on dust size distributions will eventually allow convergence of models and observations

a review of sea ice proxy information from polar ice cores sea ice plays an important role in earth s climate system the lack of direct indications of past sea ice coverage however means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes as such there is a need to develop new proxy records for reconstructing past sea ice conditions here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around antarctica ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial interglacial time scales in the coldest climates however the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator methane sulphonic acid msa in near coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last 160 years and has potential to be extended to produce records of antarctic sea ice changes throughout the holocene however the msa ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non sea ice factors and we summarise some recommended strategies for the further development of sea ice histories from ice core msa for both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the antarctic ice sheets remains an issue that requires further multidisciplinary study despite some exploratory and statistical work the application of either proxy as an indicator of sea ice change in the arctic also remains largely unknown as information about these new ice core proxies builds so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short term climate changes

insolation driven 100 000 year glacial cycles and hysteresis of ice sheet volume comprehensive climate and ice sheet models show that insolation and internal feedbacks between the climate the ice sheets and the lithosphere asthenosphere system explain the 100 000 year period on which the northern hemisphere ice sheets grow and shrink for the past million years earth s climate has been dominated by a 100 000 year cycle of glaciation involving the advance and retreat of the northern hemisphere ice sheets variations in insolation the solar radiation reaching earth s surface caused by constant changes in earth s orbit and orientation to the sun are closely associated with glaciations but the physical mechanisms driving the cycle have remained unclear now ayako abe ouchi and colleagues demonstrate that insolation variations interact with the size of the ice sheets and the solid earth to control the 100 000 year cycles their model shows that internal feedbacks between insolation climate and the elevation of the land beneath the ice sheet allows ice sheets to grow gradually until a maximum size is reached at that point the lowered ice sheet elevation caused by the delayed rebound of the solid earth means that a small increase in insolation can destroy the ice sheet in just a few thousand years the growth and reduction of northern hemisphere ice sheets over the past million years is dominated by an approximately 100 000 year periodicity and a sawtooth pattern1 2 gradual growth and fast termination milankovitch theory proposes that summer insolation at high northern latitudes drives the glacial cycles3 and statistical tests have demonstrated that the glacial cycles are indeed linked to eccentricity obliquity and precession cycles4 5 yet insolation alone cannot explain the strong 100 000 year cycle suggesting that internal climatic feedbacks may also be at work4 5 6 7 earlier conceptual models for example showed that glacial terminations are associated with the build up of northern hemisphere excess ice 5 8 9 10 but the physical mechanisms underpinning the 100 000 year cycle remain unclear here we show using comprehensive climate and ice sheet models that insolation and internal feedbacks between the climate the ice sheets and the lithosphere asthenosphere system explain the 100 000 year periodicity the responses of equilibrium states of ice sheets to summer insolation show hysteresis11 12 13 with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles the hysteresis loop of the north american ice sheet is such that after inception of the ice sheet its mass balance remains mostly positive through several precession cycles whose amplitudes decrease towards an eccentricity minimum the larger the ice sheet grows and extends towards lower latitudes the smaller is the insolation required to make the mass balance negative therefore once a large ice sheet is established a moderate increase in insolation is sufficient to trigger a negative mass balance leading to an almost complete retreat of the ice sheet within several thousand years this fast retreat is governed mainly by rapid ablation due to the lowered surface elevation resulting from delayed isostatic rebound14 15 16 which is the lithosphere asthenosphere response carbon dioxide is involved but is not determinative in the evolution of the 100 000 year glacial cycles

co 2 record in the byrd ice core 50 000 5 000 years bp the analysis of air in polar ice cores revealed 30 lower co2 values during glacial periods than during interglacial periods at present this is confirmed by results from six different ice cores two from greenland and four from antarctica1 5 in all cores the co2 change coincides with the change in the isotopic composition of the ice expressed as either the 18o or d ratio both are indicators for the mean annual surface temperature6 to investigate the relationship between atmospheric co2 concentration changes with changes in climate the atmospheric co2 concentration during and at the end of the last glaciation has to be known in detail to achieve this we have studied a great number of samples from the deep ice core from byrd station westantarctica drilled in 1968 these measurements allow us to reconstruct the atmospheric co02 concentration in the time period 50 000 15 000 yr bp in great detail

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

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

expression of the bipolar see saw in antarctic climate records during the last deglaciation ice core records of climate from greenland and antarctica show asynchronous temperature variations on millennial timescales during the last glacial period 1 the warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres a pattern attributed to the thermal bipolar see saw 2 however a record from the ross sea sector of east antarctica has been suggested to be synchronous with northern hemisphere climate change 3 here we present a temperature record from the talos dome ice core also located in the ross sea sector we compare our record with ice core analyses from greenland based on methane synchronization 4 and find clearly asynchronous temperature changes during the deglaciation we also find distinct differences in antarctic records pointing to differences in the climate evolution of the indo pacific and atlantic sectors of antarctica in the atlantic sector we find that the rate of warming slowed between 16 000 and 14 500 years ago parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over greenland in addition our chronology supports the hypothesis that the cooling of the antarctic cold reversal is synchronous with the bolling allerod warming in the northern hemisphere 14 700 years ago 5 the period from about 8 to 25kyr before present bp includes the climate transition from the last glacial to the holocene as documented from polar ice cores and other climate archives the pattern of climate changes throughout this transition is different between antarctica and the surrounding southern ocean and the northern hemisphere the steady antarctic deglacial warming reaches a first maximum antarctic isotopic maximum aim1 ref 1 followedbyaninterruptiontowardscoolerconditionsduring the antarctic cold reversal acr conversely greenland records show two rapid warming phases at the onset of the dansgaard oeschger 1 do1 event bllingaller dinterstadial b a andthe

influence of west antarctic ice sheet collapse on antarctic surface climate climate model simulations are used to examine the impact of a collapse of the west antarctic ice sheet wais on the surface climate of antarctica the lowered topography following wais collapse produces anomalous cyclonic circulation with increased flow of warm maritime air toward the south pole and cold air advection from the east antarctic plateau toward the ross sea and marie byrd land west antarctica relative to the background climate areas in east antarctica that are adjacent to the wais warm while substantial cooling several c occurs over parts of west antarctica anomalously low isotope paleotemperature values at mount moulton west antarctica compared with ice core records in east antarctica are consistent with collapse of the wais during the last interglacial period marine isotope stage 5e more definitive evidence might be recoverable from an ice core record at hercules dome east antarctica which would experience significant warming and positive oxygen isotope anomalies if the wais collapsed

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation