rapid oscillations in vostok and grip ice cores we investigate the spectral properties of climatic times series derived from two recent ice cores in greenland and east antarctica we find that the signals behave in a similar way in the high frequency part of their spectra the rapid oscillations found in the grip ice core were closely correlated to heinrich events a comparable spectral feature is detected in the vostok ice core we discuss the possibilities of connections between the two hemispheres and proper ice sheet oscillations in the light of simple oscillating climate models

late quaternary paleotemperatures derived from a speleothem from cango caves cape province south africa abstract an oxygen isotope temperature record over a large part of the past 30 000 yr has been obtained for the southern cape province of south africa by combining data on the isotopic composition of a stalagmite from a deep cave with that of a confined groundwater aquifer in the same region results show that temperatures during the last glacial maximum were on average about 6 c lower than those today with peaks up to 7 c lower a detailed analysis of the past 5000 yr suggests multiple fluctuations with generally lower temperatures 1 2 c around 4500 and 3000 yr b p the carbon isotopic composition of the stalagmite indicates significant vegetation changes between the late pleistocene and today and also during the second half of the holocene

10 be in ice at vostok antarctica during the last climatic cycle we have previously reported accelerator mass spectrometer measurements of the cosmogenic isotope 10be half life 1 5 myr in an 906 m ice core recovered at dome c antarctica1 in addition to an enhanced concentration during a period of reduced solar activity maunder minimum ad 1645 1715 2 we found substantially increased concentrations during that part of the core corresponding to the last ice age both effects have been confirmed and extended in greenland ice cores3 4 the recovery of a 2 083 m ice core at vostok antarctica5 together with an extended oxygen isotope chronology reported elsewhere in this issue6 permits an extension of 10be studies over the whole of the last climatic cycle 125 kyr we report here such measurements which show an excellent correlation with the oxygen isotope and thus presumably climate record over the whole of this period the results imply that precipitation rates in the antarctic during the last interglacial were similar to those of the holocene but were roughly halved during the last glaciation

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

synchronous high frequency oscillations in tropical sea surface temperatures and north atlantic deep water production during the last glacial cycle stable isotopic measurements of g sacculifer and c wuellerstorfi in a core from the western equatorial atlantic imply that there are parallel suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3 low values of g sacculifer 18o accompany high values of c wuellerstorfi 13c linking warmer sea surface temperatures ssts in the tropics with increased production of lower north atlantic deep water nadw the amplitude of the 18o oscillations is 0 6 or 2 3 c which is superimposed on a glacial interglacial amplitude of about 2 1 using the g sacculifer 18o data we calculate that surface waters were colder during stage 2 than calculated by climap 1976 1981 the longer period 2 kyr oscillations in air temperature recorded in the greenland and antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial atlantic the magnitude of these oscillations in tropical sst is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone the apparent synchroneity of equatorial sst and polar air temperature changes as well as the amplitude of the sst changes at the equator are consistent with the climate effects expected from changes in the atmosphere s greenhouse gas content h2ovapor co2 and ch4

long term climatic changes indicated by crystal growth in polar ice the reconstruction of palaeotemperatures from polar ice samples is essentially based on the isotopic composition of the ice in this paper we propose a new and independent way to obtain such data by using crystal size change profiles from central antarctica dome c and vostok ice cores data we suggest that crystal growth rate is mainly driven by a built in memory9 of the surface temperature conditions at the time of deposition a semi empirical model of crystal grain growth is proposed leading to last glacial maximum holocene temperature change estimates in good agreement with isotope interpretations however the possible palaeocli matic application of this model suffers some limitations connected in particular with in situ strain conditions

δ15n of n2 in air trapped in polar ice a tracer of gas transport in the firn and a possible constraint on ice age gas age differences with respect to gas transport the fim near the surface of an ice sheet can be divided into three zones the uppermost is a convective zone located just below the surface of the ice sheet in which the air is rapidly flushed by convective exchange with the overlying atmosphere below the convective zone there is a diffusive air column in which diffusion is rapid but there is no convection between the bottom of the diffusive air column and the bubble close off region there may be a nondiffusive zone in which diffusion is so slow that negligible gas transport occurs the diffusive air column is characterized by progressive enrichment with depth of 15n in n2 and heavy isotopes of gases in general as predicted using the barometric equation in this paper we present data on the 15n of n2 in recently trapped air samples from 12 ice cores along with numerous downcore samples from byrd vostok and dome c bubble close off depths for these cores calculated from a densification model ranged from 51 to 114 meters below the surface mbs we used these data and the barometric equation to calculate the thickness of the diffusive air column and found that it comprised 46 to 93 of the total firn thickness at our study sites paleo close off depths calculated from the densification model for glacial sections of byrd vostok and dome c are 15 25 m deeper than close off depths today diffusive column heights calculated from 15n varied in a more complex manner the diffusive column height at byrd appears to have decreased from 74 m during the last glacial period to 50 m during the holocene at vostok and dome c the diffusive column height calculated from 15n increase from about 65 m during the last glacial period to about 80 m in the holocene we use records of surface temperature and co2 at byrd and vostok along with their respective chronologies to constrain the ice age gas age difference age throughout the section of the vostok ice core corresponding to the last glacial termination in principle age values calculated from these data can be used to discriminate whether gas in the fim mixes to the bubble close off depth or to a depth equivalent to the diffusive column height in practice however uncertainties in the chronology of byrd and vostok are too great to allow us to distinguish between these two possibilities one can only say that at the time of the last termination age for vostok was between 3 and 10 5 kyr previous estimates fall within this range

source of hydrocarbons in marine sediments in lutzow holm bay antarctica abstract we have made an attempt to reconstruct the paleoenvironment of the coastal region around syowa station in lutzow holm bay antarctica using organic compounds in marine sediments a 129 cm long core sample of the oceanic sediment was collected at 69 14 48 s 39 11 33 e in lutzow holm bay 14c age showed a smooth pattern of change from about 3000 ybp at the surface to 14 000 ybp at the bottom except for a change of age in the range of 80 120 cm depth n c21 was dominant in the low hydrocarbon content sections at the depths of 0 5 60 65 and 120 125 cm of the core whereas long chain alkanes c22 c23 c24 were dominant in the high hydrocarbon content sections at the depths of 45 50 and 90 95 cm these characteristic distribution patterns of n alkanes suggested that their major source probably is mixed altered and or recycled material and recent organic material possibly derived from marine organisms the differences in the 13c values of individual alkanes from the high and low hydrocarbon content sections of the core were not appreciable suggesting a common source for these compounds 13c values for organic matter in different sections of the core range from 26 0 to 28 5 indicating that its major source is marine organisms

estimating horizontal stresses for mudrocks under one dimensional compression abstract we examine horizontal stresses in mudrocks for the case of one dimensional mechanical compression through laboratory measurements of the horizontal to vertical effective stress ratio i e k 0 previous empirical relationships which predict horizontal stresses as a function of depth or overburden stress are site specific and cannot easily be generalized the k 0 values of various resedimented mudrocks from a diverse range of geologic origins have been investigated for effective stresses ranging from 0 1 to 100 mpa the value of k 0 during normal compression k 0nc varies systematically as a function of both stress level and mudrock composition k 0nc generally increases with stress level and values as high as 0 90 have been measured at effective stresses approaching 100 mpa this finding implies that high horizontal stresses can develop at depth solely due to normal mechanical compression and that tectonic stresses creep or geologic unloading are not necessary correlations have been developed which allow k 0nc to be estimated from a mudrock s liquid limit an easily and inexpensively measured property which reflects both the quantity and type of clay minerals present in a mudrock high liquid limit smectite rich mudrocks display a more rapid increase in k 0nc with increasing stress compared to more silty low liquid limit mudrocks k 0 measurements made on laboratory resedimented specimens compare well with measurements made on intact core samples as well as in situ tests tests carried out to examine k 0 for overconsolidated materials show that k 0 during unloading can be well approximated by a power law function originally proposed by schmidt 1966 an original equation is proposed to describe k 0 during reloading our experimental results reveal sediment behavior at high stress levels that has not been previously observed and provide useful information on how horizontal stresses evolve within basins

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

parameter variability of undrained shear strength and strain using a database of reconstituted soil tests during construction the mobilization of undrained shear strength must be limited to avoid soil failure soil strains must be controlled to avoid compromising structural serviceability to assess f

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

orbital changes and climate at the 41 000 period of orbital tilt summer insolation forces a lagged response in northern ice sheets this delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics these ice driven responses lead to late phased changes in atmospheric co2 that provide positive feedback to the ice sheets and also project late 41 k forcing across the tropics and the southern hemisphere responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes at the 22 000 year precession period northern summer insolation again forces a lagged ice sheet response but with muted transfers to proximal regions and no subsequent effect on atmospheric co2 most 22 000 year greenhouse gas responses have the early phase of july insolation july forcing of monsoonal and boreal wetlands explains the early ch4 response the slightly later 22 k co2 response originates in the southern hemisphere the early 22 k ch4 and co2 responses add to insolation forcing of the ice sheets the dominant 100 000 year response of ice sheets is not externally forced nor does it result from internal resonance internal forcing appears to play at most a minor role the origin of this signal lies mainly in internal feedbacks co2 and ice albedo that drive the gradual build up of large ice sheets and then their rapid destruction ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

elastic shear modulus of soft clays from shear wave velocity measurement case records comprising the results of down hole seismic surveys collected at nine sites worldwide together with comparative results of laboratory bender element tests on reconstituted clay samples were examined in an attempt to quantify the shear modulus of normally consolidated clays at very small strains of the order of 0 0001 the shear modulus gmax under the current state of stresses is given in a formula which includes a newly proposed void ratio function an empirical expression incorporating the new void ratio function is also proposed for practical use in estimating gmax profiles with depth in natural soil deposits from routinely available borehole data in addition effects of soil structure and ageing on gmax are discussed on the basis of a case record on a examine les dossiers de cas comprenant les resultats de releves sismiques a foration descendante obtenus dans dix points du globe ainsi que les resultats comparatifs d essais d elements de flexion en laboratoire sur des echantillons d

late quaternary erosion events in lowland and mid altitude tasmania in relation to climate change and first human arrival abstract the establishment of a chronology of landscape forming events in lowland and mid altitude tasmania essential for assessing the relative importance of climatic and human influences on erosion and for assessing present erosion risk has been limited by the small number of ages obtained and limitations of dating methods in this paper we critically assess previous tasmanian studies list published radiocarbon ages considered to be dependable present new radiocarbon and thermoluminescence tl ages for 25 sites around tasmania and consider the evidence for the hypotheses that erosion processes at low and mid altitudes have been 1 purely climatically controlled and 2 influenced both by climatic and anthropogenic increased fire frequency effects a total of 94 dependable finite ages calibrated for radiocarbon and as measured for tl and optically stimulated luminescence osl determinations are listed for deposits comprising dunes colluvium alluvium and loess like aeolian deposits two fall in the 100 ka period 15 fall in the period 65 35 ka and 77 fall in the period 35 0 3 ka there was a sustained increase in erosion recorded in the period 35 15 ka as reflected by a greater number of dated aeolian deposits during this period we considered three possible biases that may have affected the age distribution obtained the limitations of radiocarbon dating sampling bias and preservation bias sampling bias may have favoured more recent dune strata but radiocarbon dating and preservation biases are unlikely to have significantly distorted the age distribution obtained long but intermittent aeolian deposition is recorded at two sites southwood b c 59 28 ka and dunlin dune c 29 14 ka but there is no evidence of regional loess deposits such as found in new zealand the timing of increased erosion in tasmania between 35 and 30 ka approximately coincides with the intermittent ten fold increase of dust accumulation between 33 and 30 ka in the antarctic dome c ice core the absence of widespread erosion before 35 ka the abrupt increase of erosion around this time the frequent association of erosion products with charcoal the arrival of people in tasmania at c 40 cal ka and the known use of fires by aborigines to maintain areas of non climax vegetation suggest that ecosystem disturbance by anthropogenic fires in a drier climate than that presently prevailing may have contributed to erosion in lowland and mid altitude tasmania after 35 ka thus the tasmanian erosion record provides circumstantial support for the proposition that human dispersal in southeast australia was accompanied by significant ecological change

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

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

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

cold climate during the closest stage 11 analog to recent millennia abstract the early part of marine isotopic stage 11 near 400 000 years ago provides the closest analog to holocene insolation levels of any interglaciation during the era of strong 100 000 year climatic cycles the ch 4 concentration measured in vostok ice fell to 450 ppb and co 2 values to 250 ppm these natural decreases contrast with the increases in recent millennia and support the early anthropogenic hypothesis of major gas emissions from late holocene farming during the same interval d values fell from typical interglacial to nearly glacial values indicating a major cooling in antarctica early in stage 11 other evidence suggests that new ice was accumulating during the closest insolation analog to the present day a major increase in 18 o atm at vostok a similar increase in marine 18 o values and re initiation of ice rafting in the nordic sea the evidence permits extended 20 000 year intervals of stage 11 interglacial warmth in the antarctic and north atlantic yet it also requires that this warmth ended and a new glacial era began when insolation was most similar to recent millennia the holocene co 2 anomaly was produced only in part by direct anthropogenic emissions over half of the anomaly resulted from the failure of co 2 values to fall as they had during previous interglaciations because of natural responses including a sea ice advance in the antarctic and ice sheet growth in the northern hemisphere

pleistocene sea levels from raised coral reefs of haiti the elevations and ages of a sequence of three uplifted pleistocene coral reefs on the northwest peninsula of haiti have been determined with the assignment of a sea level of 6 meters relative to the present day at 130 000 years before present and constant uplift of the reefs the data indicate that sea level stood 10 and 13 meters at 108 000 and 81 000 years before present respectively these results are in substantial agreement with those reported for barbados and new guinea and support the hypothesis of constant uplift for each area sea level data from raised reefs indicate that the interglacial marine oxygen isotope oscillations during oxygen isotope stage 5 are a result of 30 percent ice volume effects and 70 percent temperature effects

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

continental oxygen isotopic record of the last 170 000 years in jerusalem abstract a long radiometrically dated oxygen isotopic record of continental climatic variations since the penultimate glaciation was obtained from a stalagmite deposited in a sealed cave in jerusalem this record shows that speleothems have the potential of assigning dates to long and short term climatic events with possible refining of milankovitch tuning of ice and marine records which themselves are not datable short term 1000 yr events are very significant in the region reaching 50 of glacial interglacial fluctuations the mediterranean sea was the most probable source of local precipitation throughout the last glacial cycle

wave induced pore pressures around submarine pipelines abstract for the response of an undisturbed seabed to water waves there exists a number of solutions based on the concept of linear consolidation theory they all lead to the result that the pore pressure satisfies the laplace equation at least when incompressibility of the pore fluid is assumed this suggests that the flow around an embedded object e g a submarine pipeline is also governed by the laplace equation either exactly or approximately in this paper a number of such problems is solved using complex function theory and the technique of conformal mapping the hydrodynamical force is calculated from the solution for the pore pressure a good agreement is obtained with existing solutions a comparison is also made with a numerical solution based on the finite element method it is concluded that the hydrodynamical force acting upon a submarine pipeline is about ten to thirty percent of the buoyancy of the pipe depending on the maximum wave load and the burial depth

deuterium excess record from central greenland over the last millennium hints of a north atlantic signal during the little ice age a stacked water isotope record for summit central greenland has been established covering approximately the last 900 years measurements of 18o and d in the grip deep ice core and the 230 m core s93 allow the reconstruction of a millennial record of the deuterium excess in a near annual resolution a short period of particularly high values of the deuterium excess at the beginning of the fourteenth century may be associated with the medieval warm period mwp the little ice age lia might be represented by a 100 year period of very low excess values in the sixteenth and seventeenth centuries using a simple isotope model 18o and deuterium excess are interpreted in terms of surface temperature variations over central greenland and over the subtropical north atlantic greenland s principal vapor source region an estimated cooling of 0 7 c of subtropical sea surface temperatures ssts during the little ice age and a warming of 0 6 c during the short warm period in the medieval is in agreement with previous studies over periods of about 100 years an antiphasing between gradually decreasing 18o and increasing deuterium excess is observed interannual to decadal scale variability associated to the north atlantic oscillation may be responsible for this anti phase relationship an alternative explication is a north south oscillation in north atlantic sea surface temperatures associated with short term changes in the thermohaline circulation

late pleistocene sediments and environmental change at plaza creek falkland islands south atlantic late pleistocene organic rich sediments exposed in coastal bluffs near the head of plaza creek east falkland have yielded conventional and ams 14c dates of between 36 and 28 ka bp and possess a pollen spectrum dominated by grasses indicating a vegetation assemblage similar to that of the present day although some sample dates are anomalous and contamination by non contemporaneous carbon cannot be ruled out entirely the age estimates are consistent with evidence and dates from antarctica south america and the amphi north atlantic for climate shifts to interstadial conditions at around that time the organic rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting grain size characteristics suggest that these sediments may have been emplaced by solifluction shallow translational landsliding and surface wash in at least five mass wasting episodes some of the mass wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka bp at san carlos east falkland and with periods of cirque and valley glaciation identified in the uplands of the falkland islands the similarity between late pleistocene interstadial holocene and present day pollen assemblages and the lack of vegetation change within these periods is characteristic of most cool temperate southern ocean islands and may reflect the lack of sensitivity of the vegetation to climate change and or a lack of climate variability for the time intervals covered 1998 john wiley sons ltd

the power spectral density of atmospheric temperature from time scales of 10 2 to 106 yr after removing annual variability power spectral analyses of local atmospheric temperature from hundreds of stations and ice core records have been carried out from time scales of 10 2 to 106 yr a clear sequence of power law behaviors is found as follows 1 from 40 ka to 1 ma a flat spectrum is observed 2 from 2 ka to 40 ka the spectrum is proportional to f 2 where f is the frequency and 3 below time scales of 2 ka the power spectrum is proportional to f 1 2 at time scales less than 1 month we observe that the power spectra of continental stations become proportional to f 3 2 while maritime stations continue to have power spectra proportional to f 1 2 down to time scales of 1 day to explain these observations we model the vertical transport of heat in the atmosphere as a stochastic diffusion process the power spectrum of temperature fluctuations at the earth s surface expected from this model equation in a two layer geometry with thermal and eddy diffusion properties appropriate to the atmosphere and the ocean and a radiation condition at the top of the atmosphere agrees with the observed spectrum the difference in power spectra between continental and marine stations can be understood with this approach as a consequence of the air mass above a maritime station exchanging heat with both the atmosphere above and the ocean below while a continental station exchanges heat mostly with the atmosphere above

temporal relationships of carbon cycling and ocean circulation at glacial boundaries evidence from high sedimentation rate south atlantic deep sea cores indicates that global and southern ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice sheet growth and retreat respectively no consistent lead lag relationships are observed during abrupt millennial warming events during the last ice age allowing for the possibility that ocean circulation triggered some millenial climate changes at the major glacial interglacial transitions the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets

a numerical investigation of ice lobe permafrost interaction around the southern laurentide ice sheet permafrost existed around and under marginal parts of the southern laurentide ice sheet during the last glacial maximum the presence of permafrost was important in determining the extent form and dynamics of ice lobes and the landforms they produced because of influences on resistance to basal motion and subglacial hydrology we develop a two dimensional time dependent model of permafrost and glacier ice dynamics along a flowline to examine i the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology and ii the influence of permafrost on ice motion and surface profile the model is applied to the green bay lobe which terminated near madison wisconsin during the last glacial maximum simulations of ice advance over permafrost indicate that the bed upstream of the ice sheet margin was frozen for 60 200 km at the glacial maximum permafrost remained for centuries to a few thousand years under advancing ice and penetrated sufficiently deep tens of meters into the underlying aquifer that drainage of basal meltwater became inefficient likely resulting in water storage beneath the glacier our results highlight the influence of permafrost on subglacial conditions even though uncertainties in boundary conditions such as climate exist

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

the zambezi river tectonism climatic change and drainage evolution abstract the longitudinal profile of the zambezi river forms two concave upwards sections with their boundary at the victoria falls this form has been ascribed to the process of pediplantation and the victoria falls identified as one of several knick points that have traversed the river since the breakup of gondwanaland an alternative model explains the river s long profile by suggesting that the upper and middle zambezi evolved as entirely separate river systems which only joined together in comparatively recent times the alluvial sequence of the middle zambezi is described and interpreted in terms of the latter hypothesis the river capture event caused a change in grade and is marked by a deposit believed to record a cataclysmic flood capture is inferred to have resulted from overtopping of the lake that formed the end sink of the proto upper zambezi rather than from headward erosion of the proto middle zambezi this event is dated from archaeological evidence to the peak of the last interglacial at the end of the middle pleistocene subsequent drainage diversions between the middle zambezi and the kalahari are interpreted as the product of rifting of the chobe graben and aggradation of the chobe swamps river capture by overtopping implies high rainfall over central southern africa at the peak of the last interglacial which is contrary to predictions that africa s rain belts then lay north of their modern mean positions this anomaly is resolved by postulating a southern polar warming episode at that time and agrees with suggestions that the last interglacial was marked by large scale ablation of the west antarctic ice sheet

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

wave induced stresses in a saturated poro elastic sea bed beneath a rectangular caisson sea waves incident on a rigid caisson induce stresses in the sea bed by the direct action of wave pressure and by the vibration of the caisson under the assumption that the sea bed is an isotropic poro elastic half space saturated with water the dynamics of the two phases are governed by biot s equations to circumvent the difficulties of solving the coupled equations an approximate scheme is applied to achieve an analytic solution the problem can first be reduced to a series of classical elastostatic problems which can be solved by complex variables and then corrected for seepage near the mudline numerical results are presented des vagues marines qui frappent un caisson rigide engendrent des contraintes dans le fond marin en raison de l action directe de la pression des ondes et de la vibration du caisson si l on considere le fond marin comme un semi espace poro elastique isotrope sature d eau la dynamique des deux phases est regie par les equations de biot afin de contourner les difficultes que

high frequency paleovariability in climate and co2 levels from vostok ice core records the high resolution of the vostok records provides a unique look at the causes of paleoclimatic variability during the last complete glacial cycle the records present strong evidence for the interaction between orbital forcing and internal physico chemical mechanisms of variability this interaction appears to account for the great wealth of spectral features found in the records

eemian tropical and subtropical african moisture transport an isotope modelling study during the last interglacial insolation maximum eemian mis 5e the tropical and subtropical african hydrological cycle was enhanced during boreal summer months the climate anomalies are examined with a general circulation model echam4 that is equipped with a module for the direct simulation of 18o and deuterium h218o and hdo respectively in all components of the hydrological cycle a mechanism is proposed to explain the physical processes that lead to the modelled anomalies differential surface heating due to anomalies in orbital insolation forcing induce a zonal flow which results in enhanced moisture advection and precipitation increased cloud cover reduces incoming short wave radiation and induces a cooling between 10 n and 20 n the isotopic composition of rainfall at these latitudes is therefore significantly altered increased amount of precipitation and stronger advection of moisture from the atlantic result in isotopically more depleted rainfall in the eemian east african subtropics compared to pre industrial climate the east west gradient of the isotopic rainfall composition reverses in the eemian simulation towards depleted values in the east compared to more depleted western african rainfall in the pre industrial simulation the modelled re distribution of 18o and d is the result of a change in the forcing of the zonal flow anomaly we conclude that the orbitally induced forcing for african monsoon maxima extends further eastward over the continent and leaves a distinct isotopic signal that can be tested against proxy archives such as lake sediment cores from the ethiopian region

dating the vostok ice core by an inverse method using the chronological information available in the vostok records we apply an inverse method to assess the quality of the vostok glaciological timescale the inversion procedure provides not only an optimized glaciological timescale and its confidence interval but also a reliable estimate of the duration of successive events our results highlight a disagreement between orbitally tuned and glaciological timescales below 2700 m i e 250 kyr b p thousands of years before present this disagreement could be caused by some discontinuity in the spatial variation of accumulation upstream of vostok moreover the stratigraphic datings of central greenland ice cores grip and gisp2 appear older than our optimized timescale for the late glacial this underlines an unconsistency between the physical assumptions used to construct the vostok glaciological timescale and the stratigraphic datings the inverse method allows the first assessment of the evolution of the phase between vostok climatic records and insolation this phase significantly varies with time which gives a measure of the nonlinear character of the climatic system and suggests that the climatic response to orbital forcing is of different nature for glacial and interglacial periods we confirm that the last interglacial as recorded in the vostok deuterium record was long 16 2 2 kyr thousands of years however midtransition of termination ii occurred at 133 4 2 5 kyr bp which does not support the recent claim for an earlier deglaciation finally our study suggests that temperature changes are correctly estimated when using the spatial present day deuterium temperature relationship to interpret the vostok deuterium record

was the greenland ice sheet thinner in the late wisconsinan than now ice of wisconsinan origin which constitutes the basal layers of the ice caps in arctic canada and greenland flows three to four times more readily than the holocene ice above a model based on simple ice sheet profile theory is set up for the thickness response of the interior ice sheet regions to the progressive thinning of this soft layer the model is applied to calculate the thickness response of the greenland ice sheet at the locations dye 3 and crete and of the devon island ice cap in arctic canada it is concluded that the mechanism contributes significantly to the thickness change of the greenland ice sheet presently at a rate of about 1 cm yr 1 and that this rate of change will persist potentially over thousands of years to come as regards the devon island ice cap most of the estimated 15 thickness increase has already been accomplished a further consequence is that in the late wisconsinan ice thicknesses of the interior regions of the greenland ice sheet were likely to have been no greater and possibly even less than at present in spite of the larger geographical extent of the ice sheet it is argued that the glacial interglacial cycles of accumulation rate and ice temperature are likely to enhance this ice thickness variation

analysis of wave induced liquefaction of sand beds this paper describes finite element analyses of wave induced liquefaction of sand beds the authors were motivated by previous experimental results in which a series of centrifuge wave tank tests were performed on loosely packed fresh deposits of sand with viscous scaling introduced the principal finding was that the resistance to liquefaction under progressive waves was considerably smaller than the resistance exhibited under standing waves an important factor for this marked difference was suggested to be the rotation of the principal stress axes that occurs under progressive wave loading the present study extends an existing cyclic plasticity constitutive model to account for the effect of stress axis rotation of sands this model was incorporated into a finite element analysis procedure which was applied to soil responses to progressive wave and standing wave loading the predicted results compare well with observed soil behaviour the predicted effective stress paths and associated stress strain

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

vostok ice core climatic response to co2 and orbital forcing changes over the last climatic cycle vostok climate and co2 records suggest that co2 changes have had an important climatic role during the late pleistocene in amplifying the relatively weak orbital forcing the existence of the 100 kyr cycle and the synchronism between northern and southern hemisphere climates may have their origin in the large glacial interglacial co2 changes

middle late holocene palynology and marine mollusks from archipielago cormoranes area beagle channel southern tierra del fuego argentina abstract the palynology and marine mollusks of a marine sequence from rio ovando 54 51 s 68 35 w archipielago cormoranes beagle channel has been studied in order to reconstruct paleoenvironmental conditions during the middle late holocene the dinoflagellate cyst assemblages from rio ovando sequence reflect fjord estuarine environments close to terrestrial ice field affected by glacier meltwater discharge and characterized by short term oscillations of sea surface water parameters the base of the section which is dated at about ca 4160 14 c yr b p 4736 cal yr b p palynological subzone ro 2c is characterized by a high species diversity of dinocyst and mollusks and it is immediately followed by an interval palynological subzone ro 2b characterized by the presence of the echinidinium islandinium complex and the monospecific mytilus mollusk assemblage this subzone registers an inverse correlation between nothofagus dombeyi type and echinidinium islandinium complex concentration values during ca 4160 14 c yr b p 4736 cal yr b p 4064 14 c yr b p 4540 cal yr b p suggesting a variable climatic condition probably related to neoglacial episodes occurred in the southern patagonia andes during this interval the pollen assemblages permit direct correlations with the onshore palynostratigraphy from southern of tierra del fuego the high percentages of nothofagus dombeyi type recorded throughout most of the profile strongly suggest the presence of a closed forest confirming the existence of a variable cool and wet climate for the archipielago cormoranes area during the middle late holocene

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

deuterium excess in an east antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum a continuous deuterium excess profile d d 8 18o was obtained from the dome c ice core spanning 32 000 yr it exhibits significant variations over this period in particular d was 4 5 lower around 18 000 yr bp than over the past 7 500 yr interpreted as reflecting higher relative humidity estimated 90 over the oceanic areas providing moisture for antarctic precipitation

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

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

late glacial and holocene vegetation and environment of campbell island far southern new zealand campbell island lies 600 km southeast of the new zealand mainland scrub grassland rushes and large leaved forb vegetation grow on the deep peats that cover nearly the entire island campbell isl

carbon and nitrogen stable isotope analysis of northwest european horse bone and tooth collagen 40 000 bp present palaeoclimatic interpretations abstract carbon and nitrogen stable isotope ratios of bone and tooth dentine collagen from 142 horses were analysed to consider the potential of isotopic analysis of faunal remains as a palaeoenvironmental and palaeoclimatic proxy a general trend through time towards lighter 13 c values was observed but with an obvious depletion at the late glacial holocene transition horse 13 c values appear to track plant 13 c although phenomenon such as the canopy effect may influence faunal 13 c values we believe that the influence on plants of increasing atmospheric co 2 is the primary factor in the change in faunal 13 c values at the late glacial holocene transition a post glacial depletion in horse 15 n values is observed in areas proximal to glacial retreat although no data is available in these areas during the last glacial maximum horse 15 n values are presumed to reflect plant 15 n values depleted plant nitrogen may be attributed to a number of factors e g water availability temperature cycling of nitrogen in the soil soil nutrient availability especially phosphorus in the post glacial period and the type of mycorrhizal associations formed with plant these effects may be interrelated and be linked such that a positive feedback can give a non linear response to a single parameter

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

undrained young s modulus of fine grained soils abstracta reliable estimate of secant undrained young s modulus eu is necessary to quantify the undrained settlement of structures underlain by fine grained soils a large number of ck0uc triaxial tests have been carried out on eight resedimented clays to establish the effects of soil composition applied shear stress overconsolidation and vertical consolidation stress on the magnitude of eu these tests were performed at effective stresses ranging from 0 02 to 100 mpa low plasticity soils tend to have a higher eu compared with high plasticity soils the effect of composition diminishes as the applied shear stress increases overconsolidated oc soil has a higher undrained modulus than normally consolidated nc soil though a change in the overconsolidation ratio of oc soil does not have a significant effect on eu regression analyses performed on the experimental data define relationships for eu as a function of stress level for both nc and oc soil

deep sea sedimentary analogs for the vostok ice core 1 many applications of the vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent southern ocean here we present oxygen isotopic records from high accumulation rate sites in the south atlantic sector of the southern ocean collected for the purpose of complementing the recently extended d record from the vostok ice core the combination of several planktonic foraminiferal 18o records from northern subantarctic piston cores demonstrates that all of the millennial scale oscillations expressed in the vostok ice core over the last 60 ky are also present in marine records the observations also support the assumption that the millennial scale oscillations common to both marine and ice archives are synchronous thus providing a rationale for extending the marine ice core comparison through the last 400 000 years making use of a marine drilled core odp site 1089 by aligning the phase of these common abrupt events we anchor the vostok chronology to an orbitally tuned marine sediment chronology a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and antarctic polar climate for example this exercise suggests that over at least the 4 major deglaciation events the primary orbital scale changes in the chemistry and most likely the temperature of the deep southern ocean were synchronous with changes in atmospheric pco2 and polar air temperatures we also find that the deuterium excess in the ice core resembles marine foraminiferal 13c records and that the deuterium excess is synchronous with an anomalous foraminiferal 18o signal the residual between normalized versions of vostok d and foraminiferal 18o these observations demand a tight link between the vostok isotopic record and the air sea interaction of the subantarctic zone

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr