a 56 million year rhythm in north american sedimentation during the phanerozoic abstract long term 10 myr fluctuations in climate sea level and sedimentation have been documented in the stratigraphic record but the lack of well constrained data series has made it difficult to rigorously evaluate cyclic periodic or quasi periodic changes at this scale here we utilize a new compilation of the coverage area of sedimentary rocks in north america to investigate the dominant modes orders of stratigraphic variability and to evaluate potential long period cyclic changes in sedimentation on the continent during the phanerozoic our analysis resolves two principal temporal modes of variability 1 a strongly sinusoidal mode with a periodicity of 56 myr 3 myr and 2 a longer term phanerozoic mode the m curve linked to the wilson cycle which is indistinguishable from a stochastic autoregressive process the newly identified 56 myr cycle in sedimentation delineates most of the cratonic sequences that have previously been identified qualitatively in north america but here we propose a quantitative redefinition that includes nine distinct units and two mega sequences the timing of the 56 myr beat in sedimentation is consistent with an orogenic oscillator source or an oscillatory dynamic in mantle convection and its tempo is statistically similar to a known rhythm in number of marine animal genera in the global fossil record thus the identification of a significant periodic signal in the sedimentary record of north america provides new evidence for an important tectonic and or mantle scale cyclic process that links both large scale biological evolution and physical environmental change

persistent influence of obliquity on ice age terminations since the middle pleistocene transition radiometric dating of glacial terminations over the past 640 000 years suggests pacing by earth s climatic precession with each glacial interglacial period spanning four or five cycles of 20 000 years however the lack of firm age estimates for older pleistocene terminations confounds attempts to test the persistence of precession forcing we combine an italian speleothem record anchored by a uranium lead chronology with north atlantic ocean data to show that the first two deglaciations of the so called 100 000 year world are separated by two obliquity cycles with each termination starting at the same high phase of obliquity but at opposing phases of precession an assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration

the plio pleistocene 405 kyr climate cycles abstract the 405 kyr cycles in proxy records for the east asian summer monsoon and global ice volume intensified and became phase locked to eccentricity forcing at 4 5 ma we revised previous forcing mechanism hypothesis for pliocene intensification of the 405 kyr cycles in paleoclimatic records and proposed that the establishment of salinity difference between the pacific ocean and the caribbean sea at 4 5 ma triggered an ocean air positive feedback mechanism this feedback mechanism caused simultaneous climate cooling and east asian summer monsoon intensification and made the two different climate components have a clipped response to insolation forcing and thus intensified sensitivity to eccentricity variations weakening of the 405 kyr cycles in monsoon and ice volume records between 2 and 1 ma mid pleistocene transition was likely to be attributed to frequency modulation that transfer power of the 405 kyr band to the 100 kyr band which was triggered by changes in the oceanic carbon storage of the southern ocean

cyclostratigraphy and the problem of astrochronologic testing abstract when milankovitch cycles are preserved in the geologic record they provide a direct link between chronometer and climate change and thus a remarkable opportunity to constrain the evolution of the surficial earth system the identification of such cycles has allowed exploration of the geologic record with unprecedented temporal resolution and has spurred the development of a rich theoretical framework for climatic change accompanying these successes however has been a persistent skepticism how does one reliably test for astronomical forcing pacing in stratigraphic and paleoclimate data especially when time is poorly constrained from this perspective it would seem that the merits and promise of astrochronology a phanerozoic time scale measured in 20 000 to 400 000 year increments also serves as its achilles heel if the confirmation of such geologically short temporal rhythms defies rigorous hypothesis testing the implications are substantial since much of our understanding of paleoclimate change throughout the cenozoic and beyond is firmly rooted in astrochronologic interpretation in this study a conceptual framework for assessing earth system response to astronomical insolation changes and the propagation of that signal into the geologic record is used as a guide to understand the nature of the problem of astrochronologic testing this framework emphasizes three challenges contamination stratigraphic distortion and temporal calibration a statistical optimization method timeopt meyers 2015 is formulated as a solution to these three challenges providing an approach for astrochronologic testing that objectively evaluates time scale uncertainty while simultaneously identifying an optimal model for climate and depositional system response to astronomical forcing new extensions to the technique are presented allowing explicit reconstruction of distortions to the primary forcing that are known to be omnipresent in the stratigraphic record to illustrate the utility of this approach it is applied to five well studied stratigraphic series throughout the phanerozoic supporting their astronomical origin and yielding constraints on the evolution of the earth system and the astronomical solutions themselves future directions that build on this foundation are discussed including the utility of process based null models approaches for earth system transfer function reconstruction and mapping out ancient solar system behavior and earth moon history using the geologic archive of milankovitch cycles the timeopt approach recognizes astronomy geochronology paleoclimatology and depositional system reconstruction as a unified geoscientific inverse problem

multicentennial agulhas leakage variability and links to north atlantic climate during the past 80 000 years new high resolution sea surface temperature sst and sea surface salinity sss estimates are presented from the agulhas bank slope in the atlantic sector of the agulhas corridor using planktic foraminiferal globigerinoides ruber 18o and mg ca derived sst by focusing on the last 80 000 years this is the first fine scale agulhas leakage record that overlaps in time with much of the greenland ice core record of abrupt climate changes in the north atlantic region the multi centennial profiles indicate instances of warm sst and or increased sss coincident with northern hemisphere cool periods followed by northern hemisphere warming these periods of enhanced sst and sss in the agulhas corridor occur at the last glacial termination t1 and during north atlantic cold episodes associated with heinrich h meltwater events to a first order approximation the timing of maximal salinity events in relation to periods of north atlantic freshwater perturbation is consistent with the concept suggested by climate models that enhanced agulhas leakage provides for buoyancy compensation and can potentially trigger increased convective activity in the north atlantic thereby restoring atlantic overturning circulation after relatively weak states

the sensitivity of northern hemisphere ice sheets to atmospheric forcing during the last glacial cycle using pmip3 models the evolution of northern hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one general circulation model cosmos by comparing the simulated results to geological reconstructions we first show that the modelled climate is capable of capturing the main features of the ice sheet evolution however large deviations exist likely due to the absence of nonlinear interactions between ice sheet and other climate components the model uncertainties of the climate forcing are examined using the output from nine climate models from the paleoclimate modelling intercomparison project phase iii the results show a large variability in simulated ice sheets between the different models we find that the ice sheet extent pattern resembles summer surface air temperature pattern at the last glacial maximum confirming the dominant role of surface ablation process for high latitude northern hemisphere ice sheets this study shows the importance of the upper boundary condition for ice sheet modelling and implies that careful constraints on climate output is essential for simulating realistic glacial northern hemisphere ice sheets

laboratory approach to the study of elastic anisotropy on rock samples the experimental approach hardware and software to the study of the elastic anisotropy of rocks on spherical samples under hydrostatic pressure up to 400 mpa is discussed a substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media the innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude several options and results obtained with the innovated laboratory equipment are presented

testing competing forms of the milankovitch hypothesis a multivariate approach we test competing forms of the milankovitch hypothesis by estimating the coefficients and diagnostic statistics for a cointegrated vector autoregressive model that includes 10 climate variables and four exogenous variables for solar insolation the estimates are consistent with the physical mechanisms postulated to drive glacial cycles they show that the climate variables are driven partly by solar insolation determining the timing and magnitude of glaciations and terminations and partly by internal feedback dynamics pushing the climate variables away from equilibrium we argue that the latter is consistent with a weak form of the milankovitch hypothesis and that it should be restated as follows internal climate dynamics impose perturbations on glacial cycles that are driven by solar insolation our results show that these perturbations are likely caused by slow adjustment between land ice volume and solar insolation the estimated adjustment dynamics show that solar insolation affects an array of climate variables other than ice volume each at a unique rate this implies that previous efforts to test the strong form of the milankovitch hypothesis by examining the relationship between solar insolation and a single climate variable are likely to suffer from omitted variable bias

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

distribution and inferred age of exfoliation joints in the aar granite of the central swiss alps and relationship to quaternary landscape evolution abstract exfoliation joints are well known natural fractures limited to near the ground surface relatively few details however are known about their distribution and age in the swiss alps exfoliation joints follow the landscape surface at the time of their formation the age of the associated landscape feature then provides a maximum age of exfoliation joints while landscape forms can change through time exfoliation joints preserve elements of former landscape morphologies by their undisturbed orientations the grimsel region of the central alps is well suited for analyzing the impact of erosional episodes and accompanying stress changes on exfoliation joint formation in granitic rocks mapping above and below ground revealed that exfoliation joints are widespread and occur between valley bottoms and mountain crests within glacial inner and hanging u shaped trough valleys glacial cirques and steep mountain crests and predominantly fluvial landforms gently inclined linear slopes above the inner trough valleys narrow inner valley gorges and steep v shaped side gullies based primarily on their geometric properties at the ground surface three exfoliation joint types were distinguished in our study area 1 closely spaced

lake level changes and hominin occupations in the arid turkana basin during volcanic closure of the omo river outflows to the indian ocean in the east african rift the western margin of lake turkana northern kenya exposes mio plio pleistocene lake sediments with dated volcanic horizons constraining basin dynamics at the astronomical time scale since the late pliocene coastal archaeological sites have formed within the lacustrine dynamics here lake levels are reconstructed from 2 4 to 1 7 ma using sedimentary facies and water depth controlled sediment association the lacustrine stratigraphy is measured with a total station and cyclostratigraphy is derived from tephrochronology the water depths are evaluated from paleochemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry our reconstruction highlights that lake turkana rose during 100 ka insolation eccentricity maxima periods in response to higher monsoonal inputs of the omo river however lake turkana also expanded through an insolation minimum at 2 17 1 95 ma this asynchronous lake phase coincides with volcanic closure of the omo river and lake turkana outflow sill to the east and the indian ocean an archaeological hiatus occurs during this endorheic lake phase and alkalinity increases at the beginning of the hiatus the lake rose again during insolation eccentricity maxima at 1 9 1 7 ma and a new outflow sill opened to the west and the nile basin hominin coastal occupations return during this exorheic freshwater lake phase

plio pleistocene climate evolution trends and transitions in glacial cycle dynamics abstract we describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5 3 myr in particular we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic 18 o when the exponential trend in 18 o variance is removed its spectral power exhibits strong proportional responses to amplitude modulations in orbital forcing over most of the plio pleistocene precession responses correlate with modulations in forcing for the last 5 myr but 41 kyr response is sensitive to obliquity modulation only before 1 4 myr where responses are sensitive to modulations in forcing we demonstrate that glacial cycles are orbitally forced rather than being self sustained or paced by orbital changes the shapes of glacial cycles have several nonlinear properties which may be indicative of glacial interglacial differences in climate sensitivity or response time the saw tooth asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation and the relative duration of interglacial stages decreases at 1 4 myr collectively trends in the shape of glacial cycles and the sensitivity of 18 o to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2 5 and 1 4 myr but show no significant change associated with the appearance of strong 100 kyr cycles during the mid pleistocene transition

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

testing astronomically tuned age models astrochronology is fundamental to many paleoclimate studies but a standard statistical test has yet to be established for validating stand alone astronomically tuned time scales those lacking detailed independent time control against their astronomical insolation tuning curves shackleton et al 1995 proposed that the modulation of precession s amplitude by eccentricity can be used as an independent test for the successful tuning of paleoclimate data subsequent studies have demonstrated that eccentricity like amplitude modulation can be artificially generated in random data following astronomical tuning here we introduce a new statistical approach that circumvents the problem of introducing amplitude modulations during tuning and data processing thereby allowing the use of amplitude modulations for astronomical time scale evaluation the method is based upon the use of the hilbert transform to calculate instantaneous amplitude following application of a wide band precession filter and subsequent low pass filtering of the instantaneous amplitude to extract potential eccentricity modulations statistical significance of the results is evaluated using phase randomized surrogates that preserve the power spectrum structure of the data but have randomized amplitude modulations application of the new testing algorithm to two astronomically tuned data sets demonstrates the efficacy of the technique and confirms the presence of astronomical signals additionally it is demonstrated that a minimal tuning approach using at maximum one precession cycle per 100 kyr eccentricity cycle does not introduce systematic frequency modulations even when a narrow band pass filter is applied allowing direct comparison of data amplitudes and orbital eccentricity

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

coupled 100 kyr cycles between 3 and 1 ma in terrestrial and marine paleoclimatic records earth s climate over the last one million years experienced several 100 kyr glacial cycles but no simple forcing mechanism has been identified numerous studies have tried to explain strong 100 kyr glacial cycles without recognizable forcing which has come to be known as the 100 kyr problem few studies have examined 100 kyr band paleoclimatic signals before 1 ma a recent study has demonstrated that benthic oxygen and carbon isotope records are phase locked and amplitude coupled at the 100 kyr band but that neither is phase locked to and amplitude coupled with the 100 kyr eccentricity signal between 3 and 1 ma this phasing and amplitude mismatch of the 100 kyr band between 3 and 1 ma between marine records and the eccentricity forcing signal has been called the late pliocene early pleistocene 100 kyr problem however it remains unknown whether terrestrial paleoclimate records are consistent with marine records at the 100 kyr band here i show that loess monsoon records from china are amplitude coupled with benthic oxygen and carbon isotope records at the 100 kyr band but not with the 100 kyr eccentricity forcing between 3 and 1 ma this observation provides further evidence in support of a free 100 kyr oscillation as the cause of the 100 kyr band amplitude variability in paleoclimatic records between 3 and 1 ma in contrast benthic oxygen isotope records and loess monsoon records at the 100 kyr band are not amplitude coupled with 100 kyr benthic carbon isotope records over the last 0 4 million years indicating that the late pleistocene 100 kyr climatic cycles may not result exclusively from a free oscillation

hemispheric sea ice distribution sets the glacial tempo the proxy record of global temperature shows that the dominant periodicity of the glacial cycle shifts from 40 kyr obliquity to 100 kyr eccentricity about a million years ago using climate model simulations here we show that the pace of the glacial cycle depends on the pattern of hemispheric sea ice growth in a cold climate the sea ice grows asymmetrically between two hemispheres under changes to earth s orbital precession because sea ice growth potential outside of the arctic circle is limited this difference in hemispheric sea ice growth leads to an asymmetry in absorbed solar energy for the two hemispheres particularly when eccentricity is high even if the annual average insolation is similar in a warmer climate the hemispheric asymmetry of the sea ice decreases as mean arctic and antarctic sea ice decreases diminishing the precession and eccentricity signals and explaining the dominant obliquity signal 40 kyr before the mid pleistocene transition

tibet forcing of mid pleistocene synchronous enhancement of east asian winter and summer monsoons revealed by chinese loess record the mid pleistocene transition mpt of the global climate system marked by a shift of previously dominant 41 ka cycles to lately dominant 100 ka cycles roughly in the mid pleistocene is one of the fundamental enigma in the quaternary climate evolution the process and origin of the mpt remain of persistent interest and conjecture here we present high resolution astronomically tuned magnetic susceptibility ms and grain size records from a complete loess paleosol sequence at chaona on the central chinese loess plateau these two proxies are well known sensitive indicators to the east asian summer and winter monsoons respectively the records reveal a remarkable two step simultaneous enhancement of the east asian summer and winter monsoons at 0 9 ma and 0 64 ma respectively accompanied with an onset of a clear 100 ka cycle at 0 9 ma and of a final predominant 100 ka cycle starting at 0 64 ma the mid pleistocene stepwise rapid uplift of the tibetan plateau could be the mechanism driving the simultaneous enhancement of east asian summer and winter monsoons and the shift of the periodicities during the mpt by complex positive feedbacks 2012 university of washington

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

carbonate ions orbits and mg ca at odp 1123 abstract the accuracy of the magnesium calcium palaeotemperature proxy has been questioned in particular because the ratio of magnesium to calcium in foraminiferal tests could be affected by local or global changes in carbonate ion concentrations in deep water a related question regarding the technique is its problematic phase relationship to orbital eccentricity mg ca records of intermediate and deep waters typically show a phase lead with respect to orbital eccentricity this calls into question either the validity of the mg ca palaeotemperature proxy or the assumption that orbital eccentricity is pacing the 100 kyr climate oscillations or both this paper addresses these questions and suggests that a phase lead of the type observed at odp 1123 is unlikely to be generated by the operation of the carbonate ion effect and might be attributable to heat storage in the oceans during low eccentricity episodes

significant increase in relief of the european alps during mid pleistocene glaciations the effect of expanded glaciation on the relief of mountain ranges is debated chronometric and model data from the european alps suggest that relief in the rhone valley was enhanced as a result of the increased incision of the valley following the mid pleistocene climate transition

glacial variability over the last two million years an extended depth derived agemodel continuous obliquity pacing and the pleistocene progression abstract an agemodel not relying upon orbital assumptions is estimated over the last 2 ma using depth in marine sediment cores as a proxy for time agemodel uncertainty averages 10 ka in the early pleistocene 2 1 ma and 7 ka in the late pleistocene 1 ma to the present twelve benthic and five planktic 18 o records are pinned to the agemodel and averaged together to provide a record of glacial variability major deglaciation features are identified over the last 2 ma and a remarkable 33 out of 36 occur when earth s obliquity is anomalously large during the early pleistocene deglaciations occur nearly every obliquity cycle giving a 40 ka timescale while late pleistocene deglaciations more often skip one or two obliquity beats corresponding to 80 or 120 ka glacial cycles which on average give the 100 ka variability this continuous obliquity pacing indicates that the glacial theory can be simplified an explanation for the 100 ka glacial cycles only requires a change in the likelihood of skipping an obliquity cycle rather than new sources of long period variability furthermore changes in glacial variability are not marked by any single transition so much as they exhibit a steady progression over the entire pleistocene the mean variance skewness and timescale associated with the glacial cycles all exhibit an approximately linear trend over the last 2 ma a simple model having an obliquity modulated threshold and only three adjustable parameters is shown to reproduce the trends timing and spectral evolution associated with the pleistocene glacial variability

sea ice as the glacial cycles climate switch role of seasonal and orbital forcing a box model of the coupled ocean atmosphere sea ice and land ice climate system is used to study glacial interglacial oscillations under seasonally and orbitally varying solar forcing the dominant 100 kyr oscillation in land ice volume has the familiar sawtooth shape of climate proxy records and to zeroth order it does not depend on the seasonal and milankovitch forcing the sea ice controls via its albedo and insulating effects the atmospheric moisture fluxes and precipitation that enable the land ice sheet growth this control and the rapid growth and melting of the sea ice allow the sea ice to rapidly switch the climate system from a growing ice sheet phase to a retreating ice sheet phase and to shape the oscillation s sawtooth structure a specific physical mechanism is proposed by which the insolation changes act as a pacemaker setting the phase of the oscillation by directly controlling summer melting of ice sheets this mechanism is shown to induce deglaciations during periods of lower summer insolation superimposed on the 100 kyr are the linear milankovitch forced frequencies of 19 23 and 41 kyr the transition from 41 kyr glacial cycles to 100 kyr cycles one million years ago may be explained as being due to the activation of the sea ice switch at that time this would be the case if sea ice extent was more limited during the warmer climate of the early pleistocene

late pliocene early pleistocene 100 ka problem 1 little is known about the 100 ka ice volume cycles immediately before 1 ma except that they are coherent with the 100 ka eccentricity cycles here we show that ice volume and ocean circulation change global carbon mass balance are phase locked and highly coupled regarding amplitude envelopes at the 100 ka band but neither is phase locked to and amplitude coupled to the 100 ka eccentricity orbital forcing signal between 3 1 ma we describe this phasing and amplitude mismatch at the 100 ka band between 3 1 ma between eccentricity forcing and paleo ice volume records as the late pliocene early pleistocene 100 ka problem a free 100 ka oscillation internal to our climate system especially those related to oscillations of atmospheric co2 concentration operating on an earth characterized by a high inertia deep thermohaline ocean that can store carbon and heat might hold the key for the late pliocene early pleistocene 100 ka problem

a phase space model for pleistocene ice volume article i nfo we present a phase space model that simulates pleistocene ice volume changes based on earth s orbital parameters terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for late pleistocene terminations the average phase at which model terminations begin is approximately 90 90 before the maxima in all three orbital cycles the large variability in phase is likely caused by interactions between the three cycles and ice volume unlike previous ice volume models this model produces an orbitally driven increase in 100 kyr power during the mid pleistocene transition without any change in model parameters this supports the hypothesis that pleistocene variations in the 100 kyr power of glacial cycles could be caused at least in part by changes in earth s orbital parameters such as amplitude modulation of the 100 kyr eccentricity cycle rather than changes within the climate system

chronology of alluvial terrace sediment accumulation and incision in the pativilca valley western peruvian andes abstract the incision and aggradation of the pativilca alluvial fan delta system in the western peruvian andes through quaternary time can be traced in detail using well exposed fill terraces studied by a combination of cosmogenic nuclide dating terrace mapping and paleo erosion rate calculations two alluvial terraces have been dated through depth profile exposure dating using in situ 10be the dating results return an age for the abandonment of the terrace at 200 90 ka in pativilca and 1 2 ma 0 3 ma in barranca these new ages complete the database of previously dated terrace fills in the valley together with the results of the terrace mapping and the absolute ages of the terraces we show that the valley fills are made up of at least four terraces two terraces near the city of pativilca and two terraces in the city of barranca while previous studies have shown two periods of sediment aggradation one period around 100 ka barranca and another period around 30 ka pativilca our new results show two additional periods of sediment aggradation and subsequent incision that have not been reported before finally paleo erosion rates at the time of the deposition of the terrace material were calculated and compared to the available modern estimates the paleo erosion rates vary from 140 12 m ma 1 to 390 40 m ma 1 the period of sediment accumulation prior to the abandonment of the terrace at 200 ka corresponds to a wet phase and a pulse of erosion in contrast the period of sediment accumulation prior to the abandonment of the terrace at 1 2 ma does not correspond to a pulse of erosion and could rather correspond to a change of the base level possibly induced by a sea level rise

early middle pleistocene transitions linking terrestrial and marine realms abstract marked by a progressive increase in the amplitude of climate oscillations an evolving waveform and a shift towards a quasi 100 ky frequency the early middle pleistocene transition empt previously known as the mid pleistocene transition or mid pleistocene revolution 1 4 0 4 ma represents a fundamental transformation in the earth s climate state the empt began with a substantial change in climate dynamics and ended with the mid brunhes event signaling the establishment of a new steady state the reasons for the empt while uncertain appear to involve a non linear response of the earth climate system the physical and biotic responses to this transition amplified by the growth of northern hemisphere ice sheets have been profound two important chronostratigraphic markers characterize the empt the jaramillo subchron 1 070 0 988 ma and the matuyama brunhes chron boundary 773 ka the latter has been chosen as the primary guide for the lower middle pleistocene subseries boundary as it lies at the approximate midpoint of the empt and aids in global recognition both in marine and terrestrial deposits the jaramillo subchron has received less attention but the late early pleistocene is important in europe because it saw the progressive transition from the villafranchian to galerian mammal faunas and expansion of hominins into western and northern europe the jaramillo subchron is represented by marine isotope stages mis 31 to 28 with mis 30 already showing the asymmetrical sawtooth pattern characteristic of the middle pleistocene indeed while variation in the 40 ky band obliquity remains strong throughout the empt low frequency variability begins at around 1250 1200 ky which coincides with a progressive increase in global ice volume against a backdrop of increasingly severe glacial cycles notably during mis 36 34 24 22 the so called 0 9 ma event 16 and 12 pronounced phases of warming are also documented globally including the super interglacial mis 31 the early phase of the empt is characterized by important glaciations beginning with mis 36 and continuing to mis 24 22 a major intensification of the east asian monsoon system intensification of loess deposition in northern europe development of open landscapes in western siberia increased fluvial incision higher amplitude sea level change and spread of large mammals across northern eurasia and a strong reduction in the north atlantic thermohaline circulation in europe the loss of thermophilous plant taxa during the empt and indeed throughout the quaternary is a reminder of the progressive cooling that took place here and elsewhere

origin of the 100 000 year timescale in antarctic temperatures and atmospheric co2 1 a new mechanism is proposed to explain the 100 000 year timescale for variations in antarctic temperatures and atmospheric co2 over the last 650 000 years it starts with fluctuations in the oceanic overturning around antarctica that release co2 up to the atmosphere or trap it in the deep ocean every 50 000 years one of these fluctuations coincides with a changeover in the burial of caco3 in the deep ocean the changeover alters the atmospheric pco2 in a way that augments the tendency of the overturning the augmented overturning then enhances the tendency of the caco3 burial which augments the overturning etc in this way an individual random fluctuation becomes one of the big transitions seen in the antarctic ice cores alternating transitions toward the warm and cold states every 50 000 years produce the 100 000 year timescale the 50 000 year time interval is set by the turnover time for co3 ions in the ocean with respect to the co2 induced weathering of silicate rocks and the burial of caco3 on the seafloor

atlantic overturning responses to obliquity and precession over the last 3 myr this study analyzes 39 atlantic and seven pacific benthic 13c records to characterize obliquity and precession responses in atlantic overturning since 3 ma regional benthic 13c stacks are also analyzed a major transition in orbital responses is observed at 1 5 1 6 ma coincident with the first glacial shoaling of northern component water since 1 5 ma the phases of atlantic benthic 13c records from 2300 to 4000 m depth lag maximum obliquity by 59 6 7 kyr and june perihelion precession forcing by 133 8 5 kyr comparison with north atlantic sea surface temperature suggests that these orbital responses particularly precession in middle deep atlantic 13c are associated with changes in ocean heat transport and overturning rates the mid pleistocene transition had little effect on the obliquity and precession phases of benthic 13c but did result in a 50 decrease in the obliquity power of middle deep atlantic 13c at 0 6 ma

freshwater reservoir effect and the radiocarbon chronology of the cemetery in ząbie poland in the 3rd millennium bc an island on the anskie lake in north eastern poland was seasonally settled by a group of people practicing a syncretic burial ritual exhibiting indigenous and foreign patterns they left behind a small cemetery consisting of at least six graves 14c dates made for samples of human bones until 2009 did not coincide with the expected age of the graves under a new pilot program in 2010 2013 a series of radiocarbon measurements was made for the human bones and an artefact of red deer antler along with analyses of the stable isotopes ratios of carbon 13c and nitrogen 15n in the collagen the results indicate a significant proportion of freshwater food in the diet which caused the radiocarbon dates to be too old due to the freshwater reservoir effect fre based on the dating of the antler unaffected by fre and comparative analysis the reservoir offset for one of the graves was estimated to 740 radiocarbon years the results although limited by a low number of investigated humans and animals indicate indirectly a specialization in the exploitation of local water resources such an economic strategy seems to be characteristic for the societies inhabiting the coasts of the baltic sea and littoral zones of large lakes in the final neolithic and at the beginning of the early bronze age

understanding the variability in freshwater radiocarbon reservoir offsets a cautionary tale abstract freshwater resources in past diets can lead to inaccuracies when attempts are made to ascertain their radiocarbon ages or those of the consumers radiocarbon reservoir effects may lead to significant age offsets when the bones or other tissues of these consumers are radiocarbon dated a number of recent studies have investigated freshwater reservoir offsets however no study thus far has satisfactorily obtained a ubiquitous freshwater reservoir correction due to variability in the ecosystems analysed this study tests the possibility of predicting freshwater reservoir effects from the carbonate alkalinity of the water with measurements on modern fish bone and water samples a predictive capability would be especially valuable in the absence of well preserved archaeological fish bone we surveyed samples from lakes and rivers in varying geological settings in britain and ireland modern fish bone and water samples were analysed to investigate modern radiocarbon offsets from the atmosphere archaeological fish bone was also analysed to examine past reservoir offsets at selected sites stable carbon and nitrogen isotope values were measured to aid in interpretation of any variability in the offsets large freshwater reservoir offsets were measured in some modern and archaeological samples maximum offset 1638 14 c years the freshwater reservoir offsets in the fish bone were highly correlated with alkalinity of water in modern lake sites analysed however a high amount of variation within and between fish species was also evident in the results precluding the possibility of providing regional corrections for freshwater reservoir offsets from alkalinity although this still may provide a general guideline the variability is thought to be due to differences in the diet of individual fish

early onset and origin of 100 kyr cycles in pleistocene tropical sst records abstract the large 100 kyr cycles evident in most late pleistocene 0 0 6 ma paleoclimatic records still lack a satisfactory explanation previous studies of the nature of the transition from the early pleistocene 1 2 1 8 ma 41 kyr dominated climate regime to the 100 kyr world have been based almost exclusively on benthic foraminiferal oxygen isotopic 18o data it is generally accepted that the late pleistocene 100 kyr cycles represent a newly evolved sensitivity to eccentricity precession superimposed on an earlier and largely constant response to obliquity and precession forcing however orbitally resolved pleistocene sea surface temperature sst records from a variety of oceanic regions paint a rather different picture of the global climate transition across the mid pleistocene transition mpt 0 6 1 2 ma reanalysis of these sst records shows that 1 an early onset of strong 100 kyr like cycles in two low frequency bands 120 145 kyr and 60 80 kyr derived from the bundling of two three obliquity cycles into grand cycles obliquity subharmonics occurred in tropical sst records during the early pleistocene 2 these two early pleistocene periods converge into the late pleistocene 100 kyr period in tropical sst records 3 the dominance of 100 kyr sst power in the late pleistocene coincides with a dramatic decline in the 41 kyr sst power and 4 the correlation of timing of glacial terminations with eccentricity precession variation could well extend back into the early pleistocene we demonstrate that most of these features also occur in 18o records but in a much more subtle manner these features could be explained in two plausible ways a shift in climate sensitivity from obliquity to eccentricity precession a modified version of the conventional view or an increasingly nonlinear response to orbital obliquity across the mpt however our examination of the development of 100 kyr cycles favors an obliquity bundling mechanism to form late pleistocene 100 kyr cycles we therefore suggest that the late pleistocene 100 kyr climatic cycles are likely a nonlinear response to orbital obliquity although the timing of late pleistocene 100 kyr climatic cycles and their early forms appears to be paced by eccentricity precession

carbon cycle instability as a cause of the late pleistocene ice age oscillations modeling the asymmetric response a dynamical model of the pleistocene ice ages incorporating many of the qualitative ideas advanced recently regarding the possible role of ocean circulation chemistry temperature and productivity in regulating long term atmospheric carbon dioxide variations has been constructed this model involves one additional term and free parameter beyond that included in a previous model b saltzman and a sutera 1987 providing the capacity for an asymmetic for example saw toothed response it is shown that many of the main features exhibited by the 18o derived ice record and the vostok core 13c derived carbon dioxide record in the late pleistocene can be deduced as a free oscillatory solution of the model including a rapid deglaciation during which a spike of high co2 and a rapid surge in north atlantic deep water production occurs it is expected that the addition of reasonable levels of external for example earth orbital forcing will enable the model to account for a significant amount of the remaining observed variance and covariance of the slow response climatic variables over the full pleistocene including the mid pleistocene transition

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

high precision u pb zircon ca id tims dates from western european late visean bentonites three new u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry dates obtained from late visean belgian bentonites are reported and are used to estimate the periodicity of early warnantian shallowing upwards carbonate parasequences that are interbedded with the dated bentonites early warnantian parasequences exhibit mean cycle periodicity values that are consistent with the c 100 ka milankovitch cycle which is the dominant milankovitch frequency recognized from recent pleistocene glacial records and thus strengthen the arguments for 1 these sedimentary cycles being of glacio eustatic origin and 2 the initiation of the main phase of late palaeozoic glaciation before the start of or during earliest warnantian times the new dates also provide additional high precision age constraints for the improved calibration of the mississippian time scale using the new dates the stratigraphical age of the clyde plateau volcanic formation midland valley of scotland is revised from holkerian to early asbian supplementary material u pb zircon ca id tims data tables and the method of the mean cycle periodicity calculations are available at www geolsoc org uk sup18747

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

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

new high precision u pb dates from western european carboniferous tuffs implications for time scale calibration the periodicity of late carboniferous cycles and stratigraphical correlation we present three new high precision u pb zircon chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims dates from western european carboniferous diagenetically altered volcanic ash layers bentonites and tonsteins that occur interbedded with cyclic siliciclastic sedimentary rocks the dates constrain the average periodicity of western european late carboniferous arnsbergian to early langsettian cyclic sedimentation to between 89 and 124 ka per cycle this is consistent with the 100 ka short eccentricity milankovitch cycle and supports previous suggestions that the cycles are the product of glacio eustasy cyclostratigraphic tuning of namurian cycles to the 100 ka eccentricity cycle revises the timing of the global mississippian pennsylvanian boundary to c 323 9 ma ca id tims dates also facilitate correlation between different facies belts where biostratigraphical correlations are difficult correlation between eastern and western european sequences confirms that the base of the moscovian stage is located within the duckmantian westphalian b western european regional substage supplementary materials zircon separation and concentration procedures u pb zircon ca id tims methods and data table average periodicity calculations for western and central european namurian and westphalian sedimentary cycles and procedures for recalibrating legacy 40 ar 39 ar dates are available at www geolsoc org uk sup18547

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

dispersal in the ordovician speciation patterns and paleobiogeographic analyses of brachiopods and trilobites abstract the middle to late ordovician was a time of profound biotic diversification paleoecological change and major climate shifts yet studies examining speciation mechanisms and drivers of dispersal are lacking in this study we use bayesian phylogenetics and maximum likelihood analyses in the r package biogeobears to reanalyze ten published data matrices of brachiopods and trilobites and produce time calibrated species level phylogenetic hypotheses with estimated biogeographic histories recovered speciation and biogeographic patterns were examined within four time slices to test for changes in speciation type across major tectonic and paleoclimatic events statistical model comparison showed that biogeographic models that incorporate long distance founder event speciation best fit the data for most clades which indicates that this speciation type along with vicariance and traditional dispersal were important for paleozoic benthic invertebrates speciation by dispersal was common throughout the study interval but notably elevated during times of climate change vicariance events occurred synchronously among brachiopod and trilobite lineages indicating that tectonic climate and ocean processes affected benthic and planktotrophic larvae similarly middle ordovician inter oceanic dispersal in trilobite lineages was influenced by surface currents along with volcanic island arcs acting as stepping stones between areas indicating most trilobite species may have had a planktic protaspid stage these factors also influenced brachiopod dispersal across oceanic basins among laurentia avalonia and baltica these results indicate that gyre spin up and intensification of surface currents were important dispersal mechanisms during this time within laurentia surface currents hurricane tracks and upwelling zones controlled dispersal among basins increased speciation during the middle ordovician provides support for climatic facilitators for diversification during the great ordovician biodiversification event similarly increased speciation in laurentian brachiopod lineages during the hirnantian indicates that some taxa experienced speciation in relation to major climate changes overall this study demonstrates the substantial power and potential for likelihood based methods for elucidating biotic patterns during the history of life

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

the late quaternary glaciations as the response of a three component feedback system to earth orbital forcing abstract a climatic feedback system previously described consisting of three prognostic nonlinear equations governing the mass of ice sheets the mass of marine and continental marginal ice and the mean ocean temperature is forced by a representation of the effects of external earth orbital variations with reasonable amplitudes for the eccentricity obliquity and precession forcing the free oscillatory solutions of major period near 100 kyr can be modified in a way that substantially agrees with the 18o derived observations of ice mass evolution in particular a proper structure variance spectrum and phase lock of the major variations are obtained over the last 400 kyr an analysis of the sensitivity of these results to variations in the model parameters and to random perturbations shows that the solution is robust for small changes in all but a few of the equation coefficients concomitant variability in the marine ice mass ocean temperature and net radiation at the top of the atmospher

the early middle pleistocene transition of asian summer monsoon abstract the global climate cyclicity transferred from an early pleistocene mode dominated by the obliquity periodicity to a new middle pleistocene state dominated by the eccentricity periodicity in the absence of any significant changes in orbital forcing known as the early middle pleistocene transition empt is an unresolved issue of milankovitch orbital theory here we contribute new insights into the orbital characteristic and dynamics of the asian summer monsoon precipitation changes across the empt spectral analyses of precipitation over the past 1 6 myr reconstructed from a new loess magnetic susceptibility stack suggest that the empt of the summer monsoon precipitation characterized by a shift from obliquity to eccentricity rhythm occurred over a 640 kyr long term period from 1 24 to 0 6 ma rather than quasi instantaneously on a much shorter duration the eccentricity cyclicity initiated as early as 1 24 ma subsequently intensified and became the dominated pacing from 1 1 ma while obliquity weakened at 1 1 ma and significantly weakened at 0 7 ma these empt characteristics of the summer monsoon precipitation reflect complex impacts from global climate systems and regional climate changes in the northern and southern hemispheres and in both low and high latitude regions

plio pleistocene high low latitude climate interplay a mediterranean point of view abstract the high low latitude climate interplay during the plio pleistocene global cooling is not yet well understood insight on the mediterranean region can provide some clues about past significant climate changes since the basin reflects the climate dynamics of both high latitude and low latitude regions being connected to the north atlantic and subjected to monsoon influence here we shade light on this connection problem by performing a spectral analysis on an eastern mediterranean stack of planktonic records spanning the last 5 ma and by further comparing it to north atlantic and pacific deep and surface water records our main conclusion is that the mediterranean detected the main global climate transitions over the last 5 myr although sapropel depositions indicate that it remained influenced by the african summer monsoon during the whole interval our analysis reveals that until 2 2 ma the mediterranean planktonic record is driven by regional processes dominated by precession the progressive emergence of the 41 kyr frequency in the mediterranean records around 2 8 ma suggests that since this date the mediterranean was more and more affected by the high latitude climate dynamics forcing than by the low latitude one moreover during the ongoing plio pleistocene cooling the 41 kyr frequency signal in the mediterranean records anticipated high latitude deep water response to the intensification of the northern hemisphere glaciations nhg and lagged the signal in tropical latitudes finally toward 1 2 ma the results suggest that the progressive shift from the 41 kyr to the 100 kyr frequency was led by the northern high latitudes overall our results confirm that the mediterranean is an ideal site to study the interplay between high and low latitude climates

vegetation response to obliquity and precession forcing during the mid pleistocene transition in western mediterranean region odp site 976 abstract the odp leg 161 site 976 alboran sea is a deep sea section sampled at a water depth of 1108 m in the western mediterranean sea pollen analysis provides a vegetation and climate record of the mid pleistocene transition mpt roughly one million years ago the age model tied to biostratigraphic events was revised by aligning the pollen climate index pci to mediterranean kc01b and global lr04 oxygen isotope records the studied time slice spans the interval 1 09 ma mis 31 to 0 90 ma mis 23 across this interval past phytogeography of nowadays extinct taxa which were rare allows a successful application of the modern analogues technique mat to quantitative climate reconstructions for the mpt five long term obliquity related vegetation successions o1 to o5 and eight short term precession related vegetation successions p1 to p8 are observed within the studied interval these vegetation successions regardless of their duration show the same pattern the progressive replacement of temperate trees by mountainous taxa and then by herbs and steppe maxima precession related successions correspond therefore to as dramatic vegetation changes as those driven by obliquity including a final steppe phase under deteriorated climate conditions wavelet analysis of the pci record shows that the western mediterranean experienced a shift at 1 01 ma from precession dominated frequencies 1 05 1 01 ma to obliquity dominated frequencies 1 01 0 9 ma there is therefore an apparent discrepancy between wavelet analysis results and vegetation dynamic analysis which suggests that obliquity and precession are recorded throughout the entire studied interval this discrepancy could result from the fact that the pci record sums somehow similar vegetation changes wet to dry occurring at different periodicities such a complex vegetation dynamics is mathematically rendered through a single parameter i e principal component which does not successfully catch the subtle combinations of variability occurring at two close periodicities furthermore the pollen inferred early pleistocene vegetation dynamic and climate of the western mediterranean region does not show a decrease of the obliquity response relative to the precession response at the onset of the mpt

the radiocarbon reservoir effect new evidence from the cemeteries of the middle and lower dnieper basin ukraine abstract this paper presents preliminary results of new radiocarbon dating of human faunal and fish skeletal remains from a number of the cemeteries from the middle and lower dnieper basin ukraine the results appear to demonstrate the presence of a radiocarbon reservoir effect during the neolithic eneolithic periods the first time that this has been identified in this region the data indicate that the radiocarbon reservoir effect is currently only evident during these periods and not in the earlier epipalaeolithic mesolithic periods prompting the suggestion that the radiocarbon reservoir effect is associated with elevated fish consumption from the neolithic period onwards

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

the role of orbital forcing in the early middle pleistocene transition abstract the early middle pleistocene transition empt is the term used to describe the prolongation and intensification of glacial interglacial climate cycles that initiated after 900 000 years ago during the transition glacial interglacial cycles shift from lasting 41 000 years to an average of 100 000 years the structure of these glacial interglacial cycles shifts from smooth to more abrupt saw toothed like transitions despite eccentricity having by far the weakest influence on insolation received at the earth s surface of any of the orbital parameters it is often assumed to be the primary driver of the post empt 100 000 years climate cycles because of the similarity in duration the traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity this eccentricity myth is due to an artefact of spectral analysis which means that the last 8 glacial interglacial average out at about 100 000 years in length despite ranging from 80 000 to 120 000 years with the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial interglacial cycles some argue that post empt deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle we review these current theories and suggest that though phase locking between orbital forcing and global ice volume may occur the chaotic nature of the climate system response means the relationship is not consistent through the last 900 000 years

pleistocene sea surface temperature evolution early cooling delayed glacial intensification and implications for the mid pleistocene climate transition the mid pleistocene climate transition mpt is defined by the emergence of high amplitude quasi 100 ka glacial interglacial cycles from a prior regime of more subtle 41 ka cycles this change in periodicity and amplitude cannot be explained by a change in external astronomical forcing here we review and integrate published records of sea surface temperatures ssts to assess whether a common global expression of the mpt in the surface ocean can be recognized and examine our findings in light of mechanisms proposed to explain climate system reorganization across the mpt we show that glacial interglacial variability in ssts is superimposed upon a longer term cooling trend in oceanographic systems spanning the low to high latitudes regional variability exists in the timing of the onset and magnitude of cooling but in most cases a long term cooling trend begins or intensifies from 1 2 ma marine isotope stage mis 35 34 the sst cooling accompanies a long term trend towards higher global ice volume as recorded in benthic foraminifera 18o but predates a step like increase in 18o at 0 9 ma mis 24 22 that is argued to reflect expansion of continental ice sheets the strongest expression of pleistocene cooling is found during glacial stages whereas minor or negligible trends in interglacial temperatures are identified however pronounced cooling during both glacial and interglacial maxima is evident at 0 9 ma alongside the long term sst cooling trends quasi 100 ka cycles begin to emerge in both the sst and 18o records at 1 2 ma and become dominant with the expansion of the ice sheets at 0 9 ma we show that the intensified glacial stage cooling is accompanied by evolving pco2 abyssal ocean ventilation atmospheric circulation and or dust inputs to the southern ocean these changes in diverse environmental parameters suggest that glacial climate boundary conditions evolved across the mpt in turn these modified boundary conditions may have altered climate sensitivity to orbital forcing by placing pre existing ice sheets closer to some threshold of climate ice sheet response

3d velocity distribution of p and s waves in a biotite gneiss measured in oil as the pressure medium comparison with velocity measurements in a multi anvil pressure apparatus and with texture based calculated data abstract ultrasonic measurements of the 3d velocity distribution of p and s waves were performed on a spherical sample of a biotite gneiss from the outokumpu scientific drill hole measurements were done at room temperature and pressures up to 400 and 70 mpa respectively in a pressure vessel with oil as a pressure medium a modified transducer sample assembly and the installation of a new mechanical system allowed simultaneous measurements of p and s wave velocities in 132 independent directions of the sphere on a net in steps of 15 proper signals for p and s waves could be recorded by coating the sample surface with a high viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements the 3d seismic measurements revealed a strong foliation related directional dependence anisotropy of p and s wave velocities which is confirmed by measurements in a multi anvil apparatus on a cube shaped specimen of the same rock both experimental approaches show a marked pressure sensitivity of p and s wave velocities and velocity anisotropies with increasing pressure p and s wave velocities increase non linearly due to progressive closure of micro cracks the reverse is true for velocity anisotropy 3d velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation cpo of major minerals show that the intrinsic bulk anisotropy is basically caused by the cpo of biotite constituting about 23 vol of the rock including the shape of biotite grains and oriented low aspect ratio microcracks into the modelling increases bulk anisotropy an important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences particularly in shear wave velocities it is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer sample assembly on the spherical sample with a point source and point receiver the first break at the velocity arrival time is suggested to define group velocities in most cases whereas the receivers in the multi anvil apparatus recorded the flat part of the wavefront that is phase velocities

eccentricity forcing of pliocene early pleistocene climate revealed in a marine oxygen isotope record milankovitch theory that climate is controlled by variations in the earth s orbital parameters has gained wide acceptance for its ability to account for two climate cycles a 23 kyr cycle that is phase locked to the precession driven insolation cycle and a 41 kyr cycle that is phase locked to the obliquity driven insolation cycle1 6 but explaining the observed 100 kyr climate cycle in terms of milankovitch theory especially for the late pleistocene ice age cycle remains controversial in spite of a strong correlation with the 100 kyr cycle in the earth s orbital eccentricity5 one problem is that eccentricity affects insolation mainly by modulating the precession cycle its direct contribution to radiation change is too small 0 1 to effect the observed climate change directly5 7 another is the absence of a late pleistocene ice volume cycle in oxygen isotope records to match the 404 kyr component of the eccentricity cycle5 8 here we examine an oxygen isotope record spanning the interval 1 2 to 5 2 million years ago before the late pleistocene ice age regime we find 404 kyr and 100 kyr climate cycles which are coherent with eccentricity and which have amplitudes that are similar to the coexisting 23 kyr cycle analysis of these low frequency cycles suggests that they originate through an asymmetrical response mechanism that preferentially introduces variance into the climate system from the warmer portions of the eccentricity modulated precession cycle our data thus support eccentricity s role in the origin of low frequency oxygen isotope cycles before the late pleistocene ice age

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

is the spectral signature of the 100 kyr glacial cycle consistent with a milankovitch origin spectral analysis techniques traditionally applied to proxy climate records have involved the use of specialized windowing functions because of the finite length of the record available these have the effect of artificially broadening the spectral peaks such that closely spaced peaks may not be fully resolved alternatively use of a simple boxcar window following muller and macdonald 1997b will maximize the spectral frequency resolution this is achieved at the expense of potential truncation artifacts manifested as spurious peaks in the spectra although in the spectral analyses presented here such additional peaks are not significant in addition simple methods like this are not able to place any confidence intervals on the results global ice volume proxy records obtained

orbital forcing of plio pleistocene climate variation in a qaidam basin lake based on paleomagnetic and evaporite mineralogic analysis abstract inland asian aridification is threatening the global ecological system under continued global warming requiring a full understanding of its forcing mechanisms past geological studies in this region focus mainly on initiation timing and million year timescale variations in aridification few studies address the relationship between aridification and insolation forcing here we present a paleomagnetic and evaporite mineralogic study of the 476 m long huatugou htg section ca 3 9 to 2 1 ma from the western qaidam basin the results show that the drying of this part of the basin began by at least 3 9 ma furthermore we show that the relative content variation of evaporite minerals was dominated by 100 kyr cyclicity during the pliocene this is consistent with the result from the xining area during the late eocene these results suggest that mid latitude lacustrine evaporite minerals in semi arid to arid regions are particularly sensitive to eccentricity forcing improving understanding of aridification forcing at orbital timescales

the middle pleistocene transition by frequency locking and slow ramping of internal period the increase in glacial cycle length from approximately 41 to on average 100 thousand years around 1 million years ago called the middle pleistocene transition mpt lacks a conclusive explanation we describe a dynamical mechanism which we call ramping with frequency locking rfl that explains the transition by an interaction between the internal period of a self sustained oscillator and forcing that contains periodic components this mechanism naturally explains the abrupt increase in cycle length from approximately 40 to 80 thousand years observed in proxy data unlike some previously proposed mechanisms for the mpt a rapid increase in durations can be produced by a rapid change in an external parameter but this assumes rather than explains the abruptness in contrast models relying on frequency locking can produce a rapid change in durations assuming only a slow change in an external parameter we propose a scheme for detecting rfl in complex computationally expensive models and motivate the search for climate variables that can gradually increase the internal period of the glacial cycles

measuring quaternary time a 50 year perspective over the last 50 years there have been significant developments in the range and sophistication of the chronological tools now available to quaternary scientists notable milestones include the introduction of new methods e g optically stimulated luminescence cosmogenic radionuclide dating ice layer counting molecular clocks and the refinement of established techniques e g accelerator mass spectrometry 14c dating 14c calibration high precision uranium series dating argon argon dating cryptotephra analysis developing new techniques and methodologies for measuring quaternary time is not an end in itself however it is stimulated by a parallel need which is a deeper understanding of the mode pattern and rates of environmental processes and how different processes inter connect here we review some of the important limitations that continue to constrain our ability to provide coherent chronologies for quaternary environmental reconstructions at both millennial and sub millennial timescales we focus our discussion on two unique stratigraphic templates first the marine oxygen isotope sequence that spans the full quaternary period and second the greenland ice core record which provides a basis for dating environmental changes through the last glacial cycle

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

identification of erosional mechanisms during past glaciations based on a bedrock surface model of the central european alps the bedrock topography beneath the quaternary cover provides an important archive for the identification of erosional processes during past glaciations here we combined stratigraphic investigations of more than 40 000 boreholes with published data to generate a bedrock topography model for the entire plateau north of the swiss alps including the valleys within the mountain belt we compared the bedrock map with data about the pattern of the erosional resistance of alpine rocks to identify the controls of the lithologic architecture on the location of overdeepenings we additionally used the bedrock topography map as a basis to calculate the erosional potential of the alpine glaciers which was related to the thickness of the lgm ice we used these calculations to interpret how glaciers with support by subglacial meltwater under pressure might have shaped the bedrock topography of the alps we found that the erosional resistance of the bedrock lithology mainly explains where overdeepenings in the alpine valleys and the plateau occur in particular in the alpine valleys the locations of overdeepenings largely overlap with areas where the underlying bedrock has a low erosional resistance or where it was shattered by faults we also found that the assignment of two end member scenarios of erosion related to glacial abrasion plucking in the alpine valleys and dissection by subglacial meltwater in the plateau may be adequate to explain the pattern of overdeepenings in the alpine realm this most likely points to the topographic controls on glacial scouring in the alps the flow of lgm and previous glaciers were constrained by valley flanks while ice flow was mostly divergent on the plateau where valley borders are absent we suggest that these differences in landscape conditioning might have contributed to the contrasts in the formation of overdeepenings in the alpine valleys and the plateau

combined obliquity and precession pacing of late pleistocene deglaciations a new statistical test shows that precession as well as obliquity contributes to the pacing of deglaciations in the late pleistocene the glacial cycles that characterize earth s climate history are paced by variations in earth s orbital orientation relative to the sun into the middle pleistocene about a million years ago glacial cycles were paced by 40 000 year cycles in earth s tilt or obliquity since then 100 000 year variations in orbital eccentricity seem to have dominated although it has been speculated that a combination of obliquity and precession orbital axis orientation might conspire to pace deglaciations firm quantitative evidence has not emerged peter huybers now uses advances in timing and statistics to show that indeed obliquity and precession simultaneously pace deglaciations milankovitch1 proposed that earth resides in an interglacial state when its spin axis both tilts to a high obliquity and precesses to align the northern hemisphere summer with earth s nearest approach to the sun this general concept has been elaborated into hypotheses that precession2 obliquity3 4 or combinations of both5 6 7 8 could pace deglaciations during the late pleistocene9 10 earlier tests have shown that obliquity paces the late pleistocene glacial cycles4 11 but have been inconclusive with regard to precession whose shorter period of about 20 000 years makes phasing more sensitive to timing errors4 11 12 no quantitative test has provided firm evidence for a dual effect here i show that both obliquity and precession pace late pleistocene glacial cycles deficiencies in time control that have long stymied efforts to establish orbital effects on deglaciation are overcome using a new statistical test that focuses on maxima in orbital forcing the results are fully consistent with milankovitch s proposal but also admit the possibility that long southern hemisphere summers contribute to deglaciation

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

links between eccentricity forcing and the 100 000 year glacial cycle the 100 000 year glacial cycles are generally thought to be driven by the eccentricity of the earth s orbit statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100 000 year eccentricity cycle variations in the eccentricity 100 000 yr obliquity 41 000 yr and precession 23 000 yr of earth s orbit have been linked to glacial interglacial climate cycles it is generally thought that the 100 000 yr glacial cycles of the past 800 000 yr are a result of orbital eccentricity1 2 3 4 however the eccentricity cycle produces negligible 100 kyr power in seasonal or mean annual insolation although it does modulate the amplitude of the precession cycle alternatively it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle5 6 7 here i use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100 000 yr glacial cycles using cross wavelet phase analysis i show that the relative phase of eccentricity and glacial cycles has been stable since 1 2 myr ago supporting the hypothesis that 100 000 yr glacial cycles are paced8 9 10 by eccentricity4 11 however i find that the time dependent 100 000 yr power of eccentricity has been anticorrelated with that of climate since 5 myr ago with strong eccentricity forcing associated with weaker power in the 100 000 yr glacial cycle i propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing which disrupts the internal climate feedbacks that drive the 100 000 yr glacial cycle this supports the hypothesis that internally driven climate feedbacks are the source of the 100 000 yr climate variations12

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression