direct determination of the timing of sea level change during termination ii an outcrop within the last interglacial terrace on barbados contains corals that grew during the penultimate deglaciation or termination ii we used combined 230th and231pa dating to determine that they grew 135 8 0 8 thousand years ago indicating that sea level was 18 3 meters below present sea level at the time this suggests that sea level had risen to within 20 of its peak last interglacial value by 136 thousand years ago in conflict with milankovitch theory predictions orbital forcing may have played a role in the deglaciation as may have isostatic adjustments due to large ice sheets other corals in the same outcrop grew during oxygen isotope 18o substage 6e indicating that sea level was 38 5 meters below present sea level about 168 0 thousand years ago when compared to the 18o signal in the benthic v19 30 v19 28 record at that time the coral data extend to the previous glacial cycle the conclusion that deep water temperatures were colder during glacial periods

evidence from u th dating against northern hemisphere forcing of the penultimate deglaciation milankovitch proposed that summer insolation at mid latitudes in the northern hemisphere directly causes the ice age climate cycles1 this would imply that times of ice sheet collapse should correspond to peaks in northern hemisphere june insolation but the penultimate deglaciation has proved controversial because june insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier2 3 4 5 6 7 8 there is a clear signature of the penultimate deglaciation in marine oxygen isotope records but dating this event which is significantly before the 14c age range has not been possible here we date the penultimate deglaciation in a record from the bahamas using a new u th isochron technique after the necessary corrections for recoil mobility of 234u and 230th and a small age correction for sediment mixing the midpoint age for the penultimate deglaciation is determined to be 135 2 5 kyr ago this age is consistent with some coral based sea level estimates but it is difficult to reconcile with june northern hemisphere insolation as the trigger for the ice age cycles potential alternative driving mechanisms for the ice age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean atmosphere system or changes in atmospheric co2 concentration controlled by a process in the southern hemisphere

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

an outsider s review of the astronomical theory of the climate is the eccentricity driven insolation the main driver of the ice ages abstract although the astronomical theory of the climate also known as the milankovitch theory explains a number of key features of the paleoclimate time series especially frequency and phase distribution in terms of orbital influence on the waxing and waning of ice sheets it still faces several important unresolved challenges in this review we discuss five main challenges we believe the theory must resolve in order to survive 1 the large amplitude of the 100 ky ice age cycles 2 the switch from 41 ky to 100 ky long glaciations around 0 9 ma bp 3 the absence of significant spectral power at 413 ky over the past 1 2 ma 4 the variation in glacial cycle duration in the last 800 ky and 5 the presence of non orbital spectral peaks in the climate record but in spite of these problems we conclude that the milankovitch theory may still be a viable one at least in the original sense of hays et al science 194 1976 1121 that orbital changes somehow influenced the ice ages many investigators ourselves included appear to see the impact of orbital forcing in the data clear evidence of astronomical forcing as well as evidence which suggests that the climate system responds nonlinearly to all milankovitch orbital frequencies

transience and persistence in the depositional record of continental margins 1 continental shelves and coastal plains are large persistent depositional landforms which are stationary nonmigrating at their proximal ends and characterized by relatively steady long term growth in detail however their surface form and stratigraphic record is built of transient freely migrating landscape elements we derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time based upon tens of thousands of empirical measurements a stochastic noisy diffusion model with drift predicts all the gross features of the empirical data it satisfies first order goals of describing both the surface morphology and stratigraphic completeness of depositional systems the model crossover from noise dominated to drift dominated behavior corresponds to the empirical crossover from transport dominated autogenic transient behavior to accommodation dominated subsidence persistent behavior which begins at timescales of 102 103 years and is complete by scales of 104 105 years because the same long term scaling behavior emerges for off shelf environments it is not entirely explicable by steady subsidence fluctuations in sediment supply and routing probably have significant influence at short term transient scales the exponents of the scaling relations vary with environment particularly the prevalence of channeled sediment transport at very small scales modeling sediment transport as a diffusive process is inappropriate our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging

linear and non linear response of late neogene glacial cycles to obliquity forcing and implications for the milankovitch theory constraints are given for the geometry and time lags of the prominent obliquity paced glacial stages 100 98 and 96 which mark a major phase in northern hemisphere nh glaciations during the late pliocene 2 56 2 4 ma ago for this purpose a high resolution benthic 18o record was constructed from the astronomically tuned mediterranean odp site 967 and decomposed into an ice volume and an annual nh 40 80 n temperature component using an inverse modelling approach our results indicate that the dominant 41 ky component in 18o lags obliquity by 6 5 0 6 ky which approximates late pleistocene estimates maximum minimum ice volume growth occurred in phase with obliquity minima maxima which invoked low high total summer energy conditions that reduced increased ice sheet ablation sea level dropped 60 70 m during full glacial conditions similar to late pleistocene ice core and marine 18o records our late pliocene 18o record reveals significant power at 28 ky which appear to be bound to the major glacial terminations we argue that this beat most likely reflects the sum frequency of the 41 ky prime and its multiples of 82 and 123 ky supporting the theory that the late neogene glacial cycles are primarily determined by the linear and non linear response mechanisms of the ice sheets to the obliquity forcing evidence for such a scenario may come from the alignment between the devils hole 18o chronology and the sum of the filtered linear and non linear obliquity related components of late pleistocene climate records suggesting that the 28 ky beat is intrinsic to the climate system or at least an important constituent of the annual high latitude nh temperature changes that have set the stage for the geometry of the glacial interglacial variability throughout the course of the pliocene and pleistocene

south china sea surface water evolution over the last 12 myr a south north comparison from ocean drilling program sites 1143 and 1146 1 planktonic foraminifera pf from ocean drilling program odp sites 1143 and 1146 in the southern and northern south china sea scs respectively were quantitatively analyzed in order to reconstruct the sea surface environment over the last 12 myr the observed decrease in deep dwelling pf species after 10 ma at both sites is interpreted to reflect a depression of the upper water thermocline corresponding to the closure of the indonesian seaway around 11 9 ma this upper water column structure implies the intensification of equatorial pacific warm currents and the initial formation of the western pacific warm pool wpwp during the early late miocene the consistent pattern of south north thermocline evolution and the synchronous disappearance of globoquadrina dehiscens 9 8 ma at both sites 1143 and 1146 together imply that the entire scs was likely under the influence of the newly developed wpwp at 10 ma after 8 ma sea surface temperatures and thermocline variations evolved differently between the southern and northern scs the total deep dwelling pf fauna at site 1143 decreased gradually in abundance from 6 6 to 2 ma indicating a deepening of the thermocline in the southern scs in contrast deep dwelling pf species increased in abundance from 3 1 to 2 ma at site 1146 reflecting a shoaling of the thermocline in the northern scs this south north contrast reflects two major environmental regimes 1 the southern scs which has mainly been under the influence of the wpwp since the late late miocene and 2 the northern scs where effects of the east asian winter monsoon have prevailed especially since the late pliocene estimate of past sea surface temperatures ssts at site 1143 suggests a relatively stable and warm environment in the southern scs since about 2 5 ma with an increased influence of warm subsurface waters after the mid pleistocene transition 1 2 0 9 ma in the northern scs however a gradual decrease in winter sst recorded at site 1146 over the last 4 myr records east asian monsoon evolution especially the enhancement of the east asian winter monsoon between 3 1 and 2 ma

environmental implications of the magnetic record in pleistocene lacustrine sediments of the qaidam basin ne tibetan plateau abstract the application of magnetic proxies in paleoclimate studies has the advantage of fast and non destructive measurement procedures which is an important precondition for obtaining high resolution datasets within a manageable time frame here we demonstrate the advantage of using magnetic proxies for a 940 m long drill core comprising lacustrine sediments from the qaidam basin ne tibetan plateau which was previously dated by magnetostratigraphy and optical stimulated luminescence osl dating comparison of three independent mass specific magnetic susceptibility datasets confirms the horizontal homogeneity of the drill core at scales of several cm 3 the potential linkage of to astronomical forcing is suggested by spectral analysis magnetic grain size and mineralogy dependent parameters were used to evaluate possible scenarios explaining the variation moreover using additional palynological results we demonstrate the correlation of with climatic constraints thereby showing the climate sensitivity of higher and lower values are related to dry and more humid conditions respectively our results lead us to conclude that variations are caused by the interference of two driving mechanisms low temperature oxidation in the catchment area and a changing catchment area in summary this study confirms the informative value of magnetic proxies for detecting paleoenvironmental change in high resolution

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

crossover and peaks in the pleistocene climate spectrum understanding from simple ice age models the power spectrum provides a compact representation of the scale dependence of the variability in time series at multi millennial time scales the spectrum of the pleistocene climate is composed of a set of narrow band spectral modes attributed to the regularly varying changes in insolation from the astronomical change in earth s orbit and rotation superimposed on a continuous background generally attributed to stochastic variations quantitative analyses of paleoclimatic records indicate that the continuous part comprises a dominant part of the variance it exhibits a power law dependency typical of stochastic self similar processes but with a scale break at the frequency of glacial interglacial cycles here we discuss possible origins of this scale break the connection between the continuous background and the narrow bands and the apparently modest spectral power above the continuum at these scales we demonstrate that the observed scale break around 100 ka can have a variety of different origins and does not imply an internal time scale of correlation as implied by the simplest linear stochastic model

a detection of milankovitch frequencies in global volcanic activity a rigorous detection of milankovitch periodicities in volcanic output across the pleistocene holocene ice age has remained elusive we report on a spectral analysis of a large number of well preserved ash plume deposits recorded in marine sediments along the pacific ring of fire our analysis yields a statistically significant detection of a spectral peak at the obliquity period we propose that this variability in volcanic activity results from crustal stress changes associated with ice age mass redistribution in particular increased volcanism lags behind the highest rate of increasing eustatic sea level decreasing global ice volume by 4 0 3 6 k y and correlates with numerical predictions of stress changes at volcanically active sites these results support the presence of a causal link between variations in ice age climate continental stress field and volcanism

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

long climatic time series from sediment physical property measurements abstract with an accurate understanding of the lithologic dependence of pre compaction porosity in pelagic sediments it should be possible to calculate mass accumulation rate histories of sedimentary phases to generate proxy carbonate logs from core density scans and from seismic profiles and to reconstruct the mechanical and chemical processes that occur during burial and lithification we demonstrate that routinely made continuous gamma ray attenuation porosity evaluator grape wet bulk density measurements of sediments show a positive relationship to carbonate content in a variety of pelagic environments mineralogically related differences in packing rather than differences in grain density appear to control wet bulk density variations a hyperbolic model calibrated at dsdp odp drill ites quantifies the relationship of density to carbonate content in different pelagic environments the curvilinear relationships appear to converge to a similar wet bulk density 1 71 0 07 g cm3 porosity 58 at 100 carbonate content but they exhibit differing porosity at zero carbonate content wet bulk densities for a given carbonate content depend on the non carbonate mineralogy and grain size and increase systematically from opal to clay to quartz lithic fragment dominated settings because contrasts in sediment wet bulk density control the seismic response of unlithified sediments it should be possible to generate carbonate profiles remotely in carbonate rich settings after core calibration of the seismic system our model can generate long proxy carbonate curves with a typical sample spacing of 0 6 1 cm from existing grape data bases in equatorial pacific equatorial atlantic and northern atlantic locations over the past 6 m y these time series are used to investigate the long term evolution of climate in the milankovitch frequency band as well as to reconstruct patterns of carbonate sedimentation over time sedimentation bears the imprint of milankovitch cyclicity superimposed on long term trends the switch in carbonate sedimentation from 41 kyr periodicity during the matuyama chron to dominant 100 kyr periodicity in brunhes chron previously described in the north atlantic occurs in equatorial atlantic and pacific locations as well the lithological dependency of porosity in uncompacted pelagic sediments also has important implications for understanding later compaction and diagenetic modification of pelagic sediments in particular the grape observations suggest that differential burrow flattening observed in lithified limestone marl alternations results from mechanical and pressure solution compaction of strata that had strong primary porosity differences rather than from diagenetic unmixing of carbonate

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

neogene carbonate burial in the pacific ocean 1 i have compiled caco3 mass accumulation rates mars for the period 0 25 ma for 144 deep sea drilling project and ocean drilling program drill sites in the pacific in order to investigate the history of caco3 burial in the world s largest ocean basin this is the first synthesis of data since the beginning of the ocean drilling program sedimentation rates caco3 contents and bulk density were estimated for 0 5 myr time intervals from 0 to 14 ma and for 1 myr time intervals from 14 to 25 ma using mostly data from initial reports volumes there is surprisingly little coherence between caco3 mar time series from different pacific regions although regional patterns exist a transition from high to low caco3 mar from 23 20 ma is the only event common to the entire pacific ocean this event is found worldwide the most likely cause of lowered pelagic carbonate burial is a rising sea level trend in the early miocene the central and eastern equatorial pacific is the only region with adequate drill site coverage to study carbonate compensation depth ccd changes in detail for the entire neogene the latitude dependent decrease in caco3 production away from the equator is an important defining factor of the regional ccd which shallows away from the equatorial region examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production productivity from changes in bottom water chemistry dissolution upon carbonate burial

astronomical calibration of the matuyama brunhes boundary consequences for magnetic remanence acquisition in marine carbonates and the asian loess sequences we have compiled 19 records from marine carbonate cores in which the matuyama brunhes boundary mbb has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes by correlation of the 18o data to a timescale based on astronomical forcing we estimate astronomical ages for each of the mbb horizons in all but one record the mbb occurs within stage 19 most magnetostratigraphic sections in asian loess place the mbb within a loess interval since loess deposition is presumed to be associated with glacial intervals loess horizons should correspond to even numbered oxygen isotope stages a glacial age for the mbb is at odds with the results presented here which firmly place the mbb within interglacial stage 19 inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed the mean of the stage 19 age estimates for the mbb is 777 9 1 8 n 18 inclusion of the single stage 20 age results in a mean of 778 8 2 5 n 19 the astronomical age estimate of the mbb compares favorably with an unweighted mean of 778 2 3 5 n 10 from a compilation of 40ar 39ar results of transitional lava flows combining the two independent data sets yields a grand mean of 778 0 1 7 n 28 the new compilation shows virtually no trend in placement of the mbb within isotope stage 19 as a function of sediment accumulation rate we interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment water interface separating the cores into two geographic regions an indo pacific caribbean ipc group and an atlantic group results in a significant difference in the position of the mid point of the reversal with respect to the astronomical time scale the data presented here suggest a difference of several thousand years between the two regions this observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest systematic differences in remanence acquisition or by genuine differences in the timing of the directional changes between the two regions

coarse fraction fluctuations in pelagic carbonate sediments from the tropical indian ocean a 1500 kyr record of carbonate dissolution appendix table al is available with entire article onmicrofiche order from the american geophysical union 2000florida avenue n w washington d c 20009 documentp94 001 2 50 payment must accompany order we examined coarse fraction contents of pelagic carbonates deposited between 2000 and 3700 m water depth in the tropical indian ocean using ocean drilling program odp sites 722 owen ridge arabian sea and 758 ninetyeast ridge eastern equatorial indian ocean and four giant piston cores collected by the french r v marion dufresne during the seymama expedition over the last 1500 kyr coarse fraction records display high amplitude oscillations with an irregular wavelength on the order of 500 kyr these oscillations can be correlated throughout the entire equatorial indian ocean from the seychelles area eastward to the ninetyeast ridge and into the arabian sea changes in grain size mainly result from changes in carbonate dissolution as evidenced by the positive relationship between coarse fraction content and a foraminiferal preservation index based on test fragmentation the well known mid bruhes dissolution cycle represents the last part of this irregular long term dissolution oscillation the origin of this long term oscillation is still poorly understood our observations suggest that it is not a true cycle it has an irregular wavelength and we propose that it may result from long term changes in ca flux to the ocean sites 722 and 758 18o records provide a high resolution stratigraphy that allows a detailed intersite comparison of the two coarse fraction records over the last 1500 kyr site 722 2030 m lies above the present and late pleistocene lysocline the lysocline shoaled to the position of site 758 2925 m only during the interglacial intervals that occurred between about 300 and 500 ka peterson and prell 1985a despite these supralysoclinal positions of the two sites short term changes in coarse fraction contents are correctable from one site to another and probably result from regional or global dissolution pulses by stacking the normalized coarse fraction records from sites 722 and 758 we constructed a composite coarse fraction index ccfi curve in which most of the local signals cancelled out the last 800 kyr of this curve appear to compare extremely well with the composite dissolution index curve from core v34 53 ninetyeast ridge which unambiguously records past variations of carbonate dissolution in the equatorial indian ocean peterson and prell 1985a in the late pleistocene the ccfi variations are mainly associated with glacial interglacial changes they show strong 100 and 41 kyr periodicities but no clear precession related periodicities as proposed earlier by peterson and prell 1985a the lack of precession frequencies may suggest that the regional carbonate dissolution signal is driven by changes in deepwater circulation we cannot totally reject the possibility however that low temporal resolution and or bioturbation degrade somehow the precessional signal at odp sites 722 and 758 in contrast spectral density of dissolution cycles in the giant 53 m long piston core md900963 maldives area displays clear maxima centered on the precession frequencies 23 and 19 kyr 1 as well as on the kyr 1 frequency but shows little power at the 100 kyr 1 frequency these high frequency changes most probably result from changes in surface productivity associated with monsoon variability dissolution at this site may be ultimately controlled by the oxidation of organic matter which appears to be incorporated into the sediments in greater quantity during periods of weak sw monsoon and or increased dry ne monsoon

consequences of pacing the pleistocene 100 kyr ice ages by nonlinear phase locking to milankovitch forcing 1 the consequences of the hypothesis that milankovitch forcing affects the phase e g termination times of the 100 kyr glacial cycles via a mechanism known as nonlinear phase locking are examined phase locking provides a mechanism by which milankovitch forcing can act as the pacemaker of the glacial cycles nonlinear phase locking can determine the timing of the major deglaciations nearly independently of the specific mechanism or model that is responsible for these cycles as long as this mechanism is suitably nonlinear a consequence of this is that the fit of a certain model output to the observed ice volume record cannot be used as an indication that the glacial mechanism in this model is necessarily correct phase locking to obliquity and possibly precession variations is distinct from mechanisms relying on a linear or nonlinear amplification of the eccentricity forcing nonlinear phase locking may determine the phase of the glacial cycles even in the presence of noise in the climate system and can be effective at setting glacial termination times even when the precession and obliquity bands account only for a small portion of the total power of an ice volume record nonlinear phase locking can also result in the observed quantization of the glacial period into multiples of the obliquity or precession periods

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

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

use of nonlinear chaos inversion in predicting deep thin lithologic hydrocarbon reservoirs a case study from the tazhong oil field of the tarim basin china abstractwith the gradual disappearance of traditional structural reservoirs widely distributed deep thin lithologic reservoirs developed in continental and transitional sedimentary environments may offer significant petroleum reserves reservoir characterization through conventional impedance inversion methods without appropriate selection of regularization parameters and other empirical constraints cannot easily detect and assess these reserves however due to their size variation and features that conceal them we have evaluated a nonlinear chaos inversion method that uses well data and seismic facies to characterize the oil and gas reservoirs of the tazhong oil field in the tarim basin china the inverted results exhibited high agreement with the well data in highlighting the interfaces and lithologic bodies this integrated method also provided enhanced resolution of depositional contacts and variable lithologic bodies specifically the approach was able to describe a highly variable approximat

quaternary time scale for the ontong java plateau milankovitch template for ocean drilling program site 806 a 2 m y oxygen isotope record of globigerinoides sacculifer from the ontong java plateau based on cores from ocean drilling program leg 130 is dated by matching variations to an orbital template the procedure allows us to present the most complete quaternary record available for the western equatorial pacific the template generating algorithm describes a balance between growth and melting of ice following basic milankovitch theory ice growth is taken as constant while melting is taken to depend on summer insolation current ice mass and average past ice mass template settings must be changed once between 1 and 1 2 ma to reflect a major shift in climate template fits are strikingly good over much of the record and can be used to detect and fill gaps from core breaks and other disturbances one result of template dating is an exact age for the brunhes matuyama magnetic reversal boundary at 790 5 ka as well as several other precise dates 900 ka for the middle pleistocene climate shift 1070 1240 and 1450 ka for isotope stages 31 37 and 47 respectively sedi mentation rates fluctuate between 18 and 28 m m y a ca 400 ka cycle being the most prominent major anomalies arise within the transitional regime 1 2 to 1 ma the origin of the cycles is unknown we propose productivity variations in the western equatorial pacific

quantifying closed basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in earth history such as carbon cycle perturbations and glacial interglacial cycles geochemical measurements of biogenic carbonate for example 18o 13c 87sr 86sr li u sr and mg are indicators of hydrologic variability in lake systems throughout the geologic record in this study we present a new closed basin lake modeling approach hybim the hydrologic balance inverse model that employs a system of total differential equations and uses the measured 18o sr ca and mg ca of biogenic carbonate to determine changes in temperature runoff and lake evaporation using equally spaced time steps these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate we use a monte carlo approach to account for uncertainty in the input parameters such as 18o temperature relationships partition coefficient uncertainty and watershed solute chemistry for illustrative purposes we apply the model to two ostracod valve datasets covering different timescales 1 the cretaceous songliao basin northeast china and 2 holocene lake miragoane haiti modern water measurements of water isotopes and cation concentrations from each location are required as model inputs we compare our modeling results with author interpretations and geologic observations the modeling approach presented in this study can be applied to other closed basin lake records can be modified for other calcifying species for example gastropods or mollusks or with calibration to inorganic lacustrine carbonate in addition this approach holds promise for extension with additional proxy measurements that is d u ca or li ca and changing source area on tectonic timescales using proxies that reflect changing source lithology that is sr and pb isotopes future incorporation of age model uncertainty in the monte carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

seismic reflectivity of the sediment covered seafloor effects of velocity gradients and fine scale layering summary knowledge of the reflectivity of the sediment covered seabed is of significant importance to marine seismic data acquisition and interpretation as it governs the generation of reverberations in the water layer in this context pertinent but largely unresolved questions concern the importance of the typically very prominent vertical seismic velocity gradients as well as the potential presence and magnitude of anisotropy in soft surficial seabed sediments to address these issues we explore the seismic properties of granulometric end member type clastic sedimentary seabed models consisting of sand silt and clay as well as scale invariant stochastic layer sequences of these components characterized by realistic vertical gradients of the p and s wave velocities using effective media theory we then assess the nature and magnitude of seismic anisotropy associated with these models our results indicate that anisotropy is rather benign for p waves and that the s wave velocities in the axial directions differ only slightly because of the very high p t os wave velocity ratios in the vicinity of the seabed our models nevertheless suggest thats wave triplications may occur at very small incidence angles to numerically evaluate the p wave reflection coefficient of our seabed models we apply a frequency slowness technique to the corresponding synthetic seismic wavefields comparison with analytical plane wave reflection coefficients calculated for corresponding isotropic elastic half space models shows that the differences tend to be most pronounced in the vicinity of the elastic equivalent of the critical angle as well as in the post critical range we also find that the presence of intrinsic anisotropy in the clay component of our layered models tends to dramatically reduce the overall magnitude of the p wave reflection coefficient as well as its variation with incidence angle

astronomical solutions for paleoclimate studies over the last 3 million years three solutions numerical qtd90 semi analytical la90 and analytical ber90 for the planetary and precessional elements of the earth have recently become available they allow the computation of the fundamental astroclimatic parameters eccentricity climatic precession and obliquity the agreement between these different solutions is remarkably good reflecting their accuracy in such a way that they can be considered reliable enough for paleoclimate studies over at least 3 myr the difference between these solutions in eccentricity is less than 0 005 over this time interval while the differences in obliquity and climatic precession are larger but mainly due to phase lag between the solutions at 3 myr bp ber90 leads la90 by 6 x 10 3 yrs and qtd90 by 9 x 10 3 yrs for the obliquity and it leads la90 by 2 x 10 3 yrs and qtd90 by 4 x 10 3 yrs for the climatic precession

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

age and duration of the matuyama brunhes geomagnetic polarity reversal from 40ar39ar incremental heating analyses of lavas abstract constraints on the timing of geomagnetic polarity reversals have come mainly from k ar or more recently 40 ar 39 ar age determinations of lavas or their k rich phenocrysts that erupted prior or subsequent to particular geomagnetic events we have obtained 40 ar 39 ar isochron ages using incremental heating techniques on groundmass separates phenocryst poor whole rock samples or plagioclase from eight basaltic to andesitic lavas that erupted during the matuyama brunhes m b polarity transition at four geographically dispersed sites these eight lavas range from 784 6 7 1 ka to 770 8 5 2 ka 1 errors the weighted mean 778 7 1 9 ka gives a high precision age that is remarkably consistent with revised astronomical age estimates for the m b polarity transition 6 12 13 despite uncertainties in absolute calibration of 40 ar 39 ar ages relative to mineral standards used as neutron fluence monitors our age determinations are consistent with five other 40 ar 39 ar studies focused on the m b transition these results confirm that the earlier k ar based geomagnetic polarity time scale underestimated the age of the m b reversal by about 6 none of the eight isochron ages are distinguishable from one another at the 95 confidence level however we are tantalizingly close to testing for the duration of this reversal one lava at the base of a sequence of transitionally magnetized flows in chile and the uppermost lava in a similar sequence on maui are only just indistinguishable in age at the 95 confidence level and preserve different magnetic orientations we suggest that the 12 kyr difference in age represents an upper limit for the duration of the reversal and is similar to the period of low magnetic field intensity associated with records of the m b reversal from deep sea sediment cores together with the short duration 2 kyr of the directional reversal observed in several different marine sediment sections our data suggest that reversal of the field s direction could have occurred at slightly different times depending on the position of the recording site

the whiteness hypothesis reflectivity inversion chaos and enders the earth s reflectivity is one of the principal targets of seismic exploration for oil and gas it exhibits some fascinating properties it is blue it is fractal in all probability it reflects the output of a chaotic generator i examine some of these characteristics here specifically i look at the statistical properties of a canonical chaotic model and i examine the effect of multiples on the statistical properties of seismograms generated from primary reflectivities this article is a tribute to enders robinson he is a pioneer who has inspired many he inspires many to this day i am one of them

limitations on stratigraphic analyses due to incomplete age control and their relevance to sedimentary paleomagnetism abstract a major limitation in the analysis of physical quantities measured from a stratigraphic core is incomplete knowledge of the depth to age relationship for the core records derived from diverse locations are often compared or combined to construct records that represent a global signal time series analysis of individual or combined records is commonly employed to seek quasi periodic components or characterize the timescales of relevant physical processes assumptions that are frequently made in the approximation of depth to age relationships can have a dramatic and harmful effect on the spectral content of records from stratigraphic cores a common procedure for estimating ages in a set of samples from a stratigraphic core is to assign based on complementary data the ages at a number of depths tie points and then assume a uniform accumulation rate between the tie points imprecisely dated or misidentified tie points and naturally varying accumulation rates give rise to discrepancies between the inferred and the actual ages of a sample we develop a statistical model for age uncertainties in stratigraphic cores that treats the true but in practice unknown ages of core samples as random variables for inaccuracies in the ages of tie points we draw the error from a zero mean normal distribution for a variable accumulation rate we require the actual ages of a sequence of samples to be monotonically increasing and the age errors to have the form of a brownian bridge that is the errors are zero at the tie points the actual ages are modeled by integrating a piecewise constant randomly varying accumulation rate in each case our analysis yields closed form expressions for the expected value and variance of resulting errors in age at any depth in the core by monte carlo simulation with plausible parameters we find that age errors across a paleomagnetic record due to misdated tie points are likely of the same order as the tie point discrepancies those due to accumulation rate variations can be as large as 30 kyr but are probably less than 10 kyr we provide a method by which error estimates like these can be made for similar stratigraphic dating problems and apply our statistical model to an idealized marine sedimentary paleomagnetic record both types of errors severely degrade the spectral content of the inferred record we quantify these effects using realistic tie point ages their uncertainties and depositional parameters

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

a 1 0 myr record of glacial north atlantic intermediate water variability from odp site 982 in the northeast atlantic changes in the intermediate water structure of the north atlantic were reconstructed using benthic foraminiferal 13c at ocean drilling program odp site 982 for the past 1 0 myr during most terminations of the late pleistocene melting of icebergs and low salinity surface waters caused production of glacial north atlantic intermediate water to cease resulting in decreased ventilation of the middepth north atlantic poor ventilation of intermediate water masses lasted well into some interglacial stages until upper north atlantic deep water nadw production resumed under full interglacial conditions the magnitude of benthic 13c minima and ice rafted debris maxima at terminations at site 982 generally match the degree of glacial suppression of nadw inferred from site 607 these processes may be related and controlled by the spatial and seasonal extent of sea ice cover during glaciations in the nordic seas

an investigation of the spectral properties of primary reflection coefficients this paper investigates the form of the nonwhiteness found in the reflection coefficients from a wide variety of rock sequences around the world in all but one case densities are taken as constant due to the paucity of suitable density data the reflection sequences are pseudo white only above a corner frequency below which their power spectrum falls away according to a power law f where is between 0 5 and 1 5 this spectrum can be adequately modelled in practice very simply with an arma 1 1 process which acts on a white innovation sequence the corollary of this is that before wavelet estimation methods are applied all of which except those based on synthetic seismograms presuppose white reflection sequences or deconvolution filters estimated seismic traces should be filtered with the inverse of this process interestingly the estimated arma processes group themselves into two clearly differentiated categories having very different indices of predictability or strictly indices of linear determinism the two categories apparently correlate precisely with two kinds of sedimentation one which consists largely of sequences of rocks with repeating properties called repetitive in this paper but perhaps loosely describable as cyclic and the other which is randomly bedded with no apparent pattern of components the former has indices of predictability which are two to four times as great as those of the latter another probably related property is that for the repetitive sequences tends to be greater than that for non repetitive rock columns the observed power spectra are shown to be consistent with a simple model for the logarithm of acoustic impedance consisting of a mixture of processes where the distribution of time scale parameters is reciprocal detailed effects of block averaging and sampling the logs are shown to depend on the type of sequence under examination

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

detection of significant climatic precession variability in early pleistocene glacial cycles abstract despite having a large influence on summer insolation climatic precession is thought to account for little variance in early pleistocene proxies of ice volume and deep water temperature various mechanisms have been suggested to account for the dearth of precession variability including meridional insolation gradients interhemispheric cancellation of ice volume changes and antiphasing between the duration and intensity of summer insolation we employ a method termed empirical nonlinear orbital fitting enof to estimate the amplitudes of obliquity and precession forcing in early pleistocene proxies and their respective leads or lags relative to the timing of orbital variations analysis of a high resolution north atlantic benthic 18 o record comprising data from iodp sites u1308 and u1313 indicates a larger precession contribution than previously recognized with an average precession to obliquity amplitude ratio of 0 51 0 30 0 76 95 confidence interval in the rate of change of 18 o between 3 and 1 ma averaged when eccentricity exceeds 0 05 this ratio rises to 1 18 0 84 1 53 additional support for precession s importance in the early pleistocene comes from its estimated amplitude covarying with eccentricity analyses of other benthic 18 o records yielding similar orbital amplitude ratios and use of an orbitally independent timescale also showing significant precession precession in phase with northern hemisphere summer intensity steadily intensifies throughout the pleistocene in agreement with its more common identification during the late pleistocene a northern hemisphere ice sheet and energy balance model run over the early pleistocene predicts orbital amplitudes consistent with observations when a cooling commensurate with north atlantic sea surface temperatures is imposed these results provide strong evidence that glaciation is influenced by climatic precession during the late pliocene and early pleistocene and are consistent with hypotheses that glaciation is controlled by northern hemisphere summer insolation

effect of flood basalt stratigraphy on the phase of seismic waveforms recorded offshore faroe islands abstractthe generation of short period multiples between highly heterogeneous layers of basalt flows can strongly alter transmitted seismic wavefields these layers filter and modify penetrating waves producing apparent attenuation and phase changes in the observed waveforms we investigated the waveform and apparent phase changes of the primary seismic signal using mainly the maximum kurtosis approach we compared the seismic recordings from two short offset vertical seismic profiles vsps with synthetic seismograms generated from sonic logs in the same wells and we found that short period multiples cause a rapid broadening of the primary arrivals and strong apparent phase changes within a short depth interval below the top of the basalt flows relatively large uncertainties were associated with estimating constant phase shifts of the seismic arrivals within the topmost 250 m of the basalt sequences where complex scattering occurred within this interval of the brugdan i well a phase only compensat

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

evaluating the success of astronomical tuning pitfalls of using coherence as a criterion for assessing pre pleistocene timescales the imprint of orbital variations on the geological record of climatic variability is well documented especially for the plio pleistocene there is considerable interest in developing very high resolution timescales through the cenozoic and into the mesozoic by tuning geological records to the assumed astronomical forcing since the precession signal is so highly amplitude modulated it is widely believed that high coherence between record and assumed forcing in the precession band is an indication that the timescale is probably correct because coherence is supposed to provide a measure of the degree of common amplitude modulation we show that this is misleading even a sinusoidal variation that has been tuned to an insolation record shows highly significant coherence at the 23 kyr and 19 kyr precession frequencies coherence is a good indication that the tuning has generated a consistent phase relationship but complex demodulation is a better tool for assessing the relationship between amplitude modulation in the data and in the hypothetical forcing

stratigraphic completeness and resolution in an ancient mudrock succession funded by nerc fellowship grant number ne i02089x 1 santander student project scholarship grant

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

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

a minimal cost function method for optimizing the age depth relation of deep sea sediment cores the question of an optimal age depth relation for deep sea sediment cores has been raised frequently the data from such cores e g 18o values are used to test the astronomical theory of ice ages as established by milankovitch in 1938 in this work we use a minimal cost function approach to find simultaneously an optimal age depth relation and a linear model that optimally links solar insolation or other model input with global ice volume thus a general tool for the calibration of deep sea cores to arbitrary tuning targets is presented in this inverse modeling type approach an objective function is minimized that penalizes 1 the deviation of the data from the theoretical linear model whose transfer function can be computed analytically for a given age depth relation and 2 the violation of a set of plausible assumptions about the model the data and the obtained correction of a first guess age depth function these assumptions have been suggested before but are now quantified and incorporated explicitly into the objective function as penalty terms we formulate an optimization problem that is solved numerically by conjugate gradient type methods using this direct approach we obtain high coherences in the milankovitch frequency bands over 90 not only the data time series but also the the derived correction to a first guess linear age depth function and therefore the sedimentation rate itself contains significant energy in a broad frequency band around 100 kyr the use of a sedimentation rate which varies continuously on ice age time scales results in a shift of energy from 100 kyr in the original data spectrum to 41 23 and 19 kyr in the spectrum of the corrected data however a large proportion of the data variance remains unexplained particularly in the 100 kyr frequency band where there is no significant input by orbital forcing the presented method is applied to a real sediment core and to the specmap stack and results are compared with those obtained in earlier investigations

tracing time in the ocean a brief review of chronological constraints 60 8 kyr on north atlantic marine event based stratigraphies abstract well resolved event based stratigraphies in marine sediments spanning a significant portion of the last glacial period 60 8 kyr provide a unique opportunity for time stratigraphic correlation in the north atlantic region here we review the current methods available to chronologically constrain these event based stratigraphies highlighting in particular the value of tephrochronology as an independent tool to validate correlations between records while the intimate protocols lowe et al 2008 blockley et al 2011 are equally applicable to marine and terrestrial records spatially and temporally variable marine radiocarbon reservoir age effects mres provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool despite the inherent uncertainties associated with tuning we conclude that the mid points of the common abrupt warming transitions associated with the well defined millennial scale climate oscillations the dansgaard oeschger d o cycles observed in the oxygen isotopes of the greenland ice cores and north atlantic sea surface temperature sst records currently provide the most robust correlation tie points from which to derive age control in this invited intimate special issue article we propose a new protocol for establishing marine event based chronostratigraphies in the north atlantic region and focus on areas of chronological potential in palaeoceanographic research

relative geomagnetic paleointensity and δ18o at odp site 983 gardar drift north atlantic since 350 ka abstract at odp site 983 relative geomagnetic paleointensity and planktic and benthic 18o records have been acquired for the last 350 kyr the mean sedimentation rate in this interval is 11 3 cm kyr magnetic properties and hysteresis ratios indicate that pseudo single domain magnetite is the remanence carrier volume susceptibility k anhysteretic arm and isothermal irm remanence values vary by a factor of 3 4 well within the criteria usually cited for paleointensity studies natural remanent magnetization nrm is normalized by arm and irm to acquire the paleointensity proxy arithmetic means of nrm arm and nrm irm calculated for five demagnetization steps in the 25 45 mt range constitute the relative paleointensity estimates some paleointensity lows particularly those at 40 120 and 188 ka are associated with directional excursions of the field especially the event at 188 ka referred to here as the iceland basin event that constitutes a short lived polarity reversal for the last 200 kyr the records can be correlated with other high resolution paleointensity records such as those from the labrador sea mediterranean somali basin and sulu sea implying that the millennial scale features are globally synchronous a labeling system for paleointensity features is proposed that ties prominent highs and lows to oxygen isotope stages

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

linear and nonlinear couplings between orbital forcing and the marine δ18o record during the late neocene previous investigations of the response of plio pleistocene climatic records to long term orbitally induced changes in radiation have considered a linear response of climate while the second order statistics of power spectra and cross spectra provide necessary information on linear processes insight into the nonlinear characteristics of pliocene and pleistocene climate is not provided by these statistical quantities second order statistics do not contain the phase information necessary to investigate nonlinear phase coupled processes such information is provided by higher order statistical quantities in particular bispectral analysis indicates that nonlinear couplings are present in the climatic radiative forcing at the milankovitch frequencies through a linear transfer this forcing produces similar nonlinear couplings in deep sea sedimentary oxygen isotope records odp site 677 and dsdp site 607 from 1 0 to 0 ma during the late neogene this analysis suggests that during the late pleistocene the dominance of the 100 000 year cycle in the climate record is consistent with a linear resonant response to eccentricity forcing in the period from 2 6 to 1 0 ma a change in the nature of the climatic response to orbital forcing is indicated as phase couplings present in the isotopic time series are not similar to the phase couplings present in the insolation forcing third order moments skewness and asymmetry are used to quantify the shape of the climatic response from 2 6 ma to present an increase in the asymmetry sawtoothness of the oxygen isotopic records is accompanied by a corresponding decrease in the skewness peakedness of the records this indicates an evolution in the nature of the phase coupling within the climate system these results may provide important constraints useful in development of models of paleoclimate

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

analysis and modelling of gravity and piston coring based on soil mechanics the effects of gravity and piston corers on the dimensional accuracy of marine sediment cores is analysed using principles of soil mechanics a model for the coring process is built around the feedback that arises and develops between the core barrel and the sampled sediment this model for sediment response is applied to different hypothetical coring scenarios which are then compared to real examples providing insights into the specific effects of each sampling method and the development of these effects down core four cores from a single location on the iberian margin are found to contain stratigraphically intact successions that differ in length by a factor of up to 2 7 due solely to the different effects of each coring method these dimensional discrepancies are attributed to the combined effects of over sampling in the upper portions of the piston cores due to cable rebound causing upward piston acceleration and under sampling dominant in the basal portions of the open barrel gravity type cores it is suggested that heavier piston corers deployed on longer lighter cables are prone to greater over sampling ratios over longer stratigraphic intervals due to the increased likelihood and extent of cable rebound cable rebound may also give rise to double penetration of gravity corers resulting in repeated stratigraphic intervals knowledge of the dimensional accuracy of marine sediment cores is essential to an evaluation of past sedimentation rates and hence interpretations of past depositional processes it is therefore essential that we recognise the sampling effects of each coring method and their variability down core lest coring artefacts be interpreted as sedimentary signals different core types may be more suited to different palaeoceanographic investigations hence failing the development of a practical cable deployed recoilless piston corer a combination of a variety of core types will permit the best acquisition of the in situ stratigraphic truth our results suggest that a large diameter dc 20 30 cm square barrel gravity corer for the top 10 12 m combined with a cylindrical piston corer below 10 m may provide the least deformed material

a comparison of competing explanations for the 100 000 yr ice age cycle there currently exists no consensus as to the cause of the ice ages of the late pleistocene many of the competing hypotheses have been formulated into mathematical models which enables a rigorous comparison to be made spectral analysis fails to distinguish rival models using regression analysis we examine the relative performance of several models each representative of a different type of modeling approach as explanations of both the global ice volume and also the time rate of change of the global ice volume we find there is no objective evidence in the record in favor of any particular model the respective merits of the different theories must therefore be judged on physical grounds

a depth derived pleistocene age model uncertainty estimates sedimentation variability and nonlinear climate change 1 a new chronology of glaciation spanning the last 780 000 years is estimated from 21 marine sediment cores using depth as a proxy for time to avoid biasing this depth derived age estimate the depth scale is first corrected for the effects of sediment compaction to provide age uncertainty estimates the spatial and temporal variability of marine sediment accumulation rates are estimated and modeled as an autocorrelated stochastic process depth derived ages are estimated to be accurate to within 9000 years and within this uncertainty are consistent with the orbitally tuned age estimates nonetheless the remaining differences between the depth and orbitally tuned chronologies produce important differences in the spectral domain from the 18o record using the depth derived ages we infer that there are weak nonlinearities involving the 100 kyr and obliquity frequency bands which generate interaction bands at sum and difference frequencies if an orbitally tuned age model is instead applied these interactions are suppressed with the system appearing more nearly linear

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

geostatistical inversion of seismic and ground penetrating radar reflection images what can we actually resolve 1 estimation of the spatial statistics of subsurface velocity heterogeneity from surface based geophysical reflection survey data is a problem of significant interest in seismic and ground penetrating radar gpr research a method to effectively address this problem has been recently presented but our knowledge regarding the resolution of the estimated parameters is still inadequate here we examine this issue using an analytical approach that is based on the realistic assumption that the subsurface velocity structure can be characterized as a band limited scale invariant medium our work importantly confirms recent numerical findings that the inversion of seismic or gpr reflection data for the geostatistical properties of the probed subsurface region is sensitive to the aspect ratio of the velocity heterogeneity and to the decay of its power spectrum but not to the individual values of the horizontal and vertical correlation lengths

a test for the presence of covariance between time uncertain series of data with application to the dongge cave speleothem and atmospheric radiocarbon records 1 statistical measures of the relationships between time series are generally altered by the presence of errors in timing i e when applied to time uncertain series for example the covariance sampled between two time series which in truth covary will generally be decreased by errors in timing most previous work on this subject has sought to maximize some goodness of fit between time uncertain series either heuristically or through more quantitative methods however there is a danger that unrelated records can be made to appear to covary by time adjustment here we propose a statistical test for the presence of covariance between time uncertain series wherein the probability of obtaining a maximum covariance from randomly realized time uncertain series is assessed using the theory of order statistics the results of this analytical method provide insight into the influence of timing errors upon covariance and are shown to be consistent with results derived from a monte carlo procedure we apply this methodology to evaluate the covariance between a time uncertain stalagmite record and atmospheric radiocarbon during the holocene and find contradictory to previous interpretation that there is insignificant covariance between the two at the 95 confidence level

on sharp spectral lines in the climate record and the millennial peak the existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order thus the appearance of such a spectral peak with a q 20 near 1500 years period in the physical properties of the greenland ice core is intriguing bandwidth less than two cycles in 110 000 years apparently similar phenomena exist in some deep sea cores it is shown however that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately under the nyquist criterion sampled at integer multiples of the common year if this peak is therefore discounted climate variability appears as expected to be a continuum process in the millennial band more generally however aliasing of high frequencies must be a concern in any core analysis

a 37 000 year environmental magnetic record of aeolian dust deposition from burial lake arctic alaska abstract environmental magnetism and radiocarbon dating of burial lake sediments constrain the timing and magnitude of regional aeolian deposition for the noatak region of western arctic alaska for the last 37 000 years burial lake 68 43 n 159 17 w 21 5 m water depth is optimally located to monitor regional dust deposition because it is perched above local drainage and isolated from glacial processes cores collected in the summer of 2010 were studied through the application of magnetizations and progressive alternating field af demagnetization of u channel samples with additional data provided by computed tomography ct derived density hysteresis measurements isothermal remanent magnetization irm acquisition experiments organic carbon content biogenic silica physical grain size radiocarbon dating of wood seeds and plant macrofossils point source magnetic susceptibility and x ray fluorescence xrf with similar magnetic properties to regional alaskan loess deposits low coercivity highly magnetic material deposited during the late pleistocene contrasts with a high coercivity weakly magnetic component found throughout the record consistent with locally derived detritus the relative proportion of low coercivity to high coercivity magnetic material defined by the s ratios is used to reconstruct the regional input of dust to the basin over time a four fold decrease in the low coercivity component through the deglacial transition is interpreted to reflect diminished dust input to the region comparisons with potential sources of dust show that the timing of deposition in burial lake is largely consistent with general aridity lack of vegetative cover and increased windiness rather than glacial advances or retreats the influence from subaerial exposure of continental shelves cannot be ruled out as a significant far field source of dust to interior alaska during the last glacial maximum lgm but is unlikely to have been the sole source or to have contributed to increased dust in both the early and late holocene

the spectral description of climate change including the 100 ky energy core records both ice and deep sea suggest that the dominant character is that of a red noise process or random walk examination of a few typical records supports the inference that the contribution of the milankovitch frequencies to climate change at most represents only a small fraction of total climate variance most spectral densities are sufficiently flat that rates of change will be dominated by the highest frequencies present in the forcing a broad maximum near 100 ky period can be readily rationalized without invoking an oscillator one need only suppose that there is an approximate threshold beyond which the climate system collapses the quasiperiodicity is then governed by a combination of the collapse threshold the system memory time scale and the intensity of the stochastic forcing changes in the forcing intensity would lead to a shift in the dominant time scale some inferred spectral power laws may be inaccurate owing to undersampling of the records

correlation of fluviodeltaic aggradational sections with glacial climate history a revision of the pleistocene stratigraphy of rome volcanic horizons interbedded with fluviodeltaic clastic sediments of the tiber and fosso galeria river valleys near rome provide a unique opportunity to date five middle pleistocene fining upward aggradational sections 40 ar 39 ar ages from the interbedded volcanic beds illustrate that aggradation occurred on an approximate 100 k y cycle and was initiated by sea level rise associated with glacial melting the age constraint additionally shows that aggradation occurs rapidly in response to sea level change and thus ages from volcanic strata within the aggradational sections provide high resolution constraint on the timing of relative sea level rise the established chronology is consistent with other glacial proxies and their radioisotopically or orbitally based time scales for the timing of glacial terminations vi and v but is significantly older than most records for the timing of termination iii ultimately the age of each termination should be determined by radioisotopic means and to that end the work here shows that fluviodeltaic sedimentology provides valuable information for middle pleistocene time scale calibration

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