10be signature of the matuyama brunhes transition from the heqing paleolake basin abstract we present a new 10be record spanning the matuyama brunhes m b reversal from the heqing paleolake basin in southern china it provides a robust proxy for past geomagnetic variations that can be compared with paleomagnetic records the m b transition is identified as a pronounced maximum of authigenic 10be 9be ratio between 768 6 and 778 5 ka that is consistent with all other available 10be proxy records from marine ice and loess archives however it is offset by approximately 0 60 cm depth from the magnetic signature of the polarity transition recorded in the same sediments we attribute this offset to the lock in effect of the remanence acquisition process which is similar to the phenomenon that exists in marine sediments we suggest that after eliminating the climatic hydrological signal the heqing sediments may be used as an archive for atmospheric 10be production rate changes the combination of magnetic remanence measurements and the cosmogenic 10be allows for a more precise geochronology of geomagnetic polarity reversals

strengthening of north american dust sources during the late pliocene 2 7 ma here we present orbitally resolved records of terrestrial higher plant leaf wax input to the north atlantic over the last 3 5 ma based on the accumulation of long chain n alkanes and n alkanl 1 ols at iodp site u1313 these lipids are a major component of dust even in remote ocean areas and have a predominantly aeolian origin in distal marine sediments our results demonstrate that around 2 7 million years ago ma coinciding with the intensification of the northern hemisphere glaciation nhg the aeolian input of terrestrial material to the north atlantic increased drastically since then during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials the close correspondence between aeolian input to the north atlantic and other dust records indicates a globally uniform response of dust sources to quaternary climate variability although the amplitude of variation differs among areas we argue that the increased aeolian input at site u1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in north america and the associated strengthening of glaciogenic dust sources evolutional spectral analyses of the n alkane records were therefore used to determine the dominant astronomical forcing in north american ice sheet advances these results demonstrate that during the early pleistocene north american ice sheet dynamics responded predominantly to variations in obliquity 41 ka which argues against previous suggestions of precession related variations in northern hemisphere ice sheets during the early pleistocene

coupled deep water flow and climate variability in the middle pleistocene north atlantic abrupt changes in the strength of the atlantic meridional overturning circulation comprising northward flow of warm water and a cold southward return flow are implicated in abrupt climate changes in the late pleistocene a sensitive place to assess this circulation is in the cold return flow of deep western boundary currents here in records of flow speed and isotopic composition of surface and bottom waters from a deep western boundary current location near the northern source of north atlantic deep water we show both orbital and millennial scale coupling between deep ocean flow and climate in the middle pleistocene 0 75 0 87 ma when the boundary conditions in terms of the mean state and amplitude of climate change were different from more recent periods the coupling appears as a phased series of events initiated by reduced vertical density gradients and initial ventilation of deep waters the occurrence of these events in interglacials during the middle pleistocene suggests that the millennial scale climate variability in the north atlantic was more pronounced at that time than previously thought this demonstrates that given the right boundary conditions rapid climate shifts can also occur during relatively warm climate conditions

determining the natural length of the current interglacial terglacials can be used to draw analogies with the present provided their duration is known here we propose that the minimum age of a glacial inception is constrained by the onset of bipolar seesaw climate variability which requires ice sheets large enough to produce iceberg discharges that disrupt the ocean circulation we identify the bipolar seesaw in ice core and north atlantic marine records by the appearance of a distinct phasing of interhemispheric climate and hydrographic changes and ice rafted debris the glacial inception during marine isotope sub stage 19c a close analogue for the present interglacial occurred near the summer insolation minimum suggesting that the interglacial was not prolonged by subdued radiative forcing 7 assuming that ice growth mainly responds to insolation and co2 forcing this analogy suggests that the end of the current interglacial would occur within the next 1500 years if atmospheric co2 concentrations did not exceed 240 5 ppmv

high resolution diatom record of paleoceanographic variations across the early middle pleistocene boundary in the chiba section central japan abstract we conducted diatom analyses of a core from the pleistocene marine sequence drilled at the chiba section central japan to reveal detailed paleoceanographic variations across the early middle pleistocene boundary diatom valves are most abundant at 4 5 m below the matuyama brunhes magnetic polarity boundary followed by the second highest abundance at 18 6 m above the boundary which is consistent with the sea level changes inferred from planktonic 18 o data the highest abundance is correlated with the marine isotope stage mis 19 3 sea level highstand and the second highest with the mis 19 1 highstand the abundance of the extinct species actinocyclus ingens is quite low around these sea level highstands whereas it is greatest at the core depth with the minimum diatom total valves which is correlated to the mis 19 2 lowstand cold water diatom species that are characteristic of the oyashio current are dominant but coexist with warm water species of the kuroshio current below a core depth just postdating mis 19 2 above this depth warm diatom species of the kuroshio current become dominant the change in dominant diatoms suggests that the kuroshio front shifted northward just after mis 19 2 and remained in the northern area until at least early mis 18 this shift caused a rapid increase in sea surface temperature by 4 5 c within a sediment thickness of 1 3 m representing 300 years

millennial scale variability in western tropical atlantic surface ocean hydrography during the early pliocene abstract we use high resolution oxygen isotope data 18o from planktonic foraminifera in the western tropical atlantic ocean ocean drilling program leg 154 site 925 to investigate millennial scale climate variability during an interval of relative climate warmth the early pliocene for this purpose we have chosen a 100 kyr long time interval from 4 13 to 4 24 ma and subsampled it to obtain an average time step of 800 yr we reconstruct changes in upper ocean hydrography using the 18o values of globigerinoides sacculifer a mixed layer dweller and neogloboquadrina dutertrei a thermocline dweller their oxygen isotopic difference 18o is taken as a measure of the mixed layer to thermocline thermal gradient time series analysis indicates that significant concentration of variance exists in the g sacculifer and n dutertrei at sub milankovitch periods of between 8 and 4 kyr and in the 18o record between 13 and 8 kyr wavelet analysis illustrates that the suborbital variance is only present in the record when the amplitude of the precessional signal is large between 4 24 and 4 20 ma in this particular portion of the record however we observe positive 18o excursions in the individual 18o time series thus the suborbital periods evident in the spectra may reflect harmonics associated with asymmetrical time series because the excursions only occur when precession forcing is also strong we suggest that there is a relationship between the proxy records and climate although we cannot conclude that it is cyclical in nature the 18o record on the other hand is characterized by positive as well as negative excursions we observe significant concentration of variance close to half precession during the portion of the record when precession forcing is also strong which we believe reflects a close although nonlinear response of the western tropical surface ocean to low latitude insolation forcing

unraveling the forcings controlling the vegetation and climate of the best orbital analogues for the present interglacial in sw europe the suitability of mis 11c and mis 19c as analogues of our present interglacial and its natural evolution is still debated here we examine the regional expression of the holocene and its orbital analogues over sw iberia using a model data comparison approach regional tree fraction and climate based on snapshot and transient experiments using the loveclim model are evaluated against the terrestrial marine profiles from site u1385 documenting the regional vegetation and climatic changes the pollen based reconstructions show a larger forest optimum during the holocene compared to mis 11c and mis 19c putting into question their analogy in sw europe pollen based and model results indicate reduced mis 11c forest cover compared to the holocene primarily driven by lower winter precipitation which is critical for mediterranean forest development decreased precipitation was possibly induced by the amplified mis 11c latitudinal insolation and temperature gradient that shifted the westerlies northwards in contrast the reconstructed lower forest optimum at mis 19c is not reproduced by the simulations probably due to the lack of eurasian ice sheets and its related feedbacks in the model transient experiments with time varying insolation and co2 reveal that the sw iberian forest dynamics over the interglacials are mostly coupled to changes in winter precipitation mainly controlled by precession co2 playing a negligible role model simulations reproduce the observed persistent vegetation changes at millennial time scales in sw iberia and the strong forest reductions marking the end of the interglacial optimum

suborbital scale surface and deep water records in the subtropical north atlantic implications on thermohaline overturn abstract we reconstruct millennial scale variations in sea surface hydrography and deep water flow in the northwestern subtropical atlantic ocean drilling program leg 172 sites 1056 and 1063 with a focus on marine isotope stage mis 9 together with published records from this region the new data also afford a longer term perspective on millennial scale changes in meridional overturning circulation spanning two full interglacial intervals mis 9 and 11 as well as two full glacial intervals mis 10 and 12 planktic foraminiferal 18o values indicate relatively stable conditions during the peak warmth of mis 9 but three large cold excursions disrupt the otherwise smooth transition toward glacial mis 8 there is no unique response in the site 1063 benthic foraminiferal 13c values that would suggest a concomitant decrease in the relative flux of nadw during these events similarly there is no persistent correlation between millennial scale variations in surface and deep water hydrography over the entire mis 8 13 interval while millennial scale variations at the sea surface are most pronounced during glacial intervals and the transitions toward glacial intervals millennial scale variations in the deep water hydrography tend to be largest during the warm periods this observation supports that rapid changes in thermohaline circulation are sensitive to driving forces other than those directly related to ice sheet size time series analysis shows that spectral power in the benthic foraminiferal 13c record contains periodicities related to the second 10 kyr and fourth harmonics 5 kyr of precession in this record 20 kyr pointing to the importance of tropical processes

forcing of atlantic equatorial and subpolar millennial cycles by precession abundance cycles of the marine alga florisphaera profunda centered on a period of 7600 carbon 14 years 8400 calendar years are present in high resolution records from the equatorial atlantic spanning 0 to 45 000 years ago these cycles correlate with heinrich events 1 through 5 which document rapid changes in continental ice melting around the subpolar north atlantic these variations in f profunda are a direct response to modulation in zonal wind driven divergence produced by a precessional component of orbital variation during a time of reduced eccentricity modulation

marine and terrestrial climate variability in the western mediterranean sea during marine isotope stages 20 and 19 abstract the climate variability within late marine isotope stage mis 20 and mis 19 is examined with particular reference to the response of marine and terrestrial realms in the area surrounding the alboran sea western mediterranean sea sediment samples from the ocean drilling program site 976 were used to derive high temporal resolution average resolution of 450 years palynological pollen and spores and calcareous plankton coccolithophores and foraminifera records these data together with the new 18og bulloides make it possible to discuss the paleoenvironmental changes within a well constrained chronological frame cooler phases including late mis 20 and several cold spells during mis 19b a are marked on land by the expansion of open vegetation formations dominated by steppe and semi desert taxa at the same time the western mediterranean sea is marked by the incursion of north atlantic polar water planktonic taxa mis 19c and interstadials of mis 19b a are characterized by the spread of prevalent temperate forest taxa that parallel the expansion of warm water calcareous plankton taxa during periods of lighter 18o climate variations at both precessional and millennial to sub millennial time scales expressed by on land and marine signals highlight the sensitivity of the western mediterranean area to both orbital forcing and rapid internal oscillations of the climate systems involving remote connections with north hemisphere high latitudes the correlation within the central western mediterranean and north atlantic climate dynamics including the time spatial gradients related to regional and global climate processes contributes to the reconstruction of the earth climate dynamics and marine vs land responses in full early middle pleistocene transition these new evidences also provide an opportunity to improve knowledge of mis 19c now considered due to its orbital geometry the best orbital analogue to the holocene

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

milankovitch band forcing of sub milankovitch climate variability during the pleistocene climate variability at periods from 10 kyr to 12 kyr that originates from milankovitch band forcing is quantified at three locations for the late pleistocene eastern equatorial pacific ocean drilling program site 846 eastern equatorial atlantic odp site 663 and northeastern atlantic deep sea drilling project site 609 variability at these periods is not present in the primary milankovitch forcing so no linear linkage to milankovitch band variations is possible however these periods are equal to harmonics of precession band oscillations the magnitude of interactions between processes that occur at different timescales can only be resolved in time series data through application of higher order statistics through such an application we demonstrate that up to 75 of the variance in the 10 to 12 kyr band in the sediment records is nonlinearly transferred from precession band 19 23 kyr variations within the millennial to sub milankovitch band defined as the band of variance ranging from 15 to 2 kyr approximately 1 3 of the variability in the records studied is consistent with a low frequency milankovitch band origin this variability may derive from high sensitivity of the tropics to summertime insolation in both hemispheres relative to wintertime insolation a mechanism having equatorial origin and related to low latitude precession variations appears consistent with the observations because the phase coupling between 10 to 12 kyr oscillations and precession is resolved this result has implications for development of models which seek to explain global climate variations on this timescale

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

tropically driven climate shifts in southwestern europe during mis 19 a low eccentricity interglacial the relative roles of high versus low latitude forcing of millennial scale climate variability are still not well understood here we present terrestrial marine climate profiles from the southwestern iberian margin a region particularly affected by precession that show millennial climate oscillations related to a nonlinear response to the earth s precession cycle during marine isotope stage mis 19 mis 19 has been considered the best analogue to our present interglacial from an astronomical point of view due to the reduced eccentricity centred at 785 ka in our records seven millennial scale forest contractions punctuated mis 19 superimposed to two orbitally driven mediterranean forest expansions in contrast to our present interglacial we evidence for the first time low latitude driven 5000 yr cycles of drying and cooling in the western mediterranean region along with warmth in the subtropical gyre related to the fourth harmonic of precession these cycles indicate repeated intensification of north atlantic meridional moisture transport that along with decrease in boreal summer insolation triggered ice growth and may have contributed to the glacial inception at 774 ka the freshwater fluxes during mis 19ab amplified the cooling events in the north atlantic promoting further cooling and leading to mis 18 glaciation the discrepancy between the dominant cyclicity observed during mis 1 2500 yr and that of mis 19 5000 yr challenges the similar duration of the holocene and mis 19c interglacials under natural boundary conditions

early middle pleistocene deep circulation in the western subtropical atlantic southern hemisphere modulation of the north atlantic ocean early middle pleistocene climate and deep ocean hydrography have been reconstructed using oxygen and carbon isotope ratio measurements in planktonic and benthic foraminifera from a high deposition rate sedimentary succession recovered at the bermuda rise in the northern sargasso sea ocean drilling program leg 172 site 1063 the site s water depth makes it sensitive to changes in the balance between north atlantic deep water nadw and antarctic bottom water aabw in the deep north atlantic allowing the evaluation of perturbations in deep water production at different timescales millennial scale fluctuations superimposed on the longer period oscillations of orbital origin occurred during all the observed climate states the highest amplitude sub milankovitch fluctuations were mainly associated with interglacials particularly after the intensification of the glacial regime at c 900 ka using the benthic carbon isotope signal as a water mass tracer and by comparing the delta 13c record to a suite of drill sites in the north atlantic and pacific oceans it has been possible to infer that the relative strength of aabw production varied through time as did that of nadw a scenario in which the two different source components of deep water can undergo dramatic changes in their circulation regime through time should be taken into consideration when evaluating the role of thermohaline circulation in global climate change

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

origin of millennial scale climate signals in the subtropical north atlantic we present a high resolution planktonic foraminiferal stable isotope record globigerinoides ruber spanning marine oxygen isotope stages miss 6 through 8 in the northwestern subtropical atlantic ocean ocean drilling program leg 172 site 1059 the record fills a gap to produce an about 1 3 myr long continuous time series of high frequency 1 12 kyr surface ocean hydrography the first of this kind we test the hypothesis that the suborbital climate signals i e half and quarter precession cycles are linked to precession forcing in tropical latitudes semiprecession cycles present between 0 and 320 ka are of the right periodicity to relate to the dominant precession forcing 23 kyr these cycles are evident as double peaks within the given precession framework and there is good match in the amplitude modulation of the filter output and the 18o time series quarter precession cycles dominate the suborbital spectra between 320 ka and 1 3 ma periodicities are close to those expected from the harmonics of the dominant precession peaks in the 18o record but present in the time series only intermittently and their amplitude modulation does not match that of the primary precession period thus only the half precession cycles evidence a response to low latitude insolation such as that introduced by insolation maxima at the equinoxes or solstices during the course of a precession cycle additionally we find well defined rapid 1 5 2 kyr variations across the first of the interglacial maxima of mis 7 adding to evidence of non ice sheet related forcing factors in driving climate instabilities

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

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

a record of bottom water temperature and seawater δ18o for the southern ocean over the past 440 kyr based on mg ca of benthic foraminiferal uvigerina spp the sensitivity to temperature of mg ca ratios in the shallow infaunal benthic foraminifera uvigerina spp has been assessed core top calibrations over 1 20 c show a range in sensitivity of 0 065 0 084 mmol mol c but few data are available spanning the temperature range anticipated in deep sea records over glacial interglacial cycles in contrast to epibenthic foraminiferal species carbonate ion saturation appears not to affect mg ca significantly a method based on estimating the ratio of the temperature sensitivity of foraminiferal mg ca to that of 18ocalcite shows that sensitivity for mg ca at the high end of the observed core top range 0 1 mmol mol c is required for consistency with lgm holocene differences in each property as constrained by independent proxy data this is supported by a mg ca record for uvigerina spp generated for the southern ocean over the past 440 000 years from ocean drilling program site 1123 chatham rise new zealand the record shows variability that correlates with climate oscillations the lgm deep ocean temperature derived from the mg ca record is 1 1 0 3 c transformation to temperature allows estimates to be made of changes in bottom water temperature and seawater 18o and comparison made with literature records analysis reveals a 2 5 kyr lead in the record of temperature over calcite 18o and a longer lead over seawater 18o this is a reflection of larger phase offsets at eccentricity periods phase offsets at tilt and precession are within error zero

solar forced dansgaard oeschger events and their phase relation with solar proxies 1 north atlantic climate during glacial times was characterized by large amplitude switchings the dansgaard oeschger do events with an apparent tendency to recur preferably in multiples of about 1470 years recent work interpreted these intervals as resulting from a subharmonic response of a highly nonlinear system to quasi periodic solar forcing plus noise this hypothesis was challenged as inconsistent with the observed variability in the phase relation between proxies of solar activity and greenland climate here we reject the claim of inconsistency by showing that this phase variability is a robust generic feature of the nonlinear dynamics of do events as described by a model this variability is expected from the fact that the events are threshold crossing events resulting from a cooperative process between the periodic forcing and the noise this process produces a fluctuating phase relation with the periodic forcing consistent with proxies of solar activity and greenland climate

early onset and tropical forcing of 100 000 year pleistocene glacial cycles between 1 5 and 0 6 myr ago the period of the earth s glacial cycles changed from 41 kyr the period of the earth s obliquity cycles to 100 kyr the period of the earth s orbital eccentricity1 2 which has a much smaller effect on global insolation the timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research3 here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles the latter of which are phase coupled to both precession and eccentricity in the tropical and extra tropical atlantic ocean we find that about 1 5 myr ago tropical semiprecession cycles with periods of about 11 5 kyr started to propagate to higher latitudes coincident with a growing amplitude envelope of the 100 kyr cycles evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100 kyr cycles4 combining our results with consideration of a modern analogue we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1 5 myr ago strengthened the semiprecession cycle in the northern hemisphere and triggered the transition to sustained 100 kyr glacial cycles

high resolution foraminifer stable isotope record of mis 19 at montalbano jonico southern italy a window into mediterranean climatic variability during a low eccentricity interglacial abstract understanding millennial and sub millennial climate variability during past low eccentricity interglacials similar to the holocene is important for forecasting the evolution of climate and natural variability the ideale section montalbano jonico southern italy studied here provides one of the best records of mis 19c the closest orbital analog to the holocene this exposed marine series covers termination ix to the inception of mis 18 with very high sedimentation rates i e 90 200 cm ka we present 1 benthic 18o and 13c records at 90 200 year time resolution 2 a new 40ar 39ar age of 774 1 0 9 ka for tephra layer v4 matuyama brunhes transitional period and 3 new calcareous plankton palynological and authigenic 10be 9be data our new bayesian depth age model suggests a 11 5 3 4 ka 95 confidence duration for the climatic optimum the 18o series reveals millennial scale oscillations with sharp transitions

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

the pacemaker always rings twice we generated new long high resolution climate proxy records from deep sea drilling project dsdp sites 607 and 609 in the subpolar north atlantic over the interval 225 970 ka which have pronounced variability at periods f 1 7 kyr variance in our north atlantic climate proxy records is shown using bispectral and cross bispectral methods to be explainable as harmonics and or combination tones of orbital scale climatic variability of the north atlantic region itself thus the timing and amplitude of high frequency climate change in the north atlantic region appears to be a nonlinear function of variations in high latitude climate at milankovitch frequencies

climate signatures through marine isotope stage 19 in the montalbano jonico section southern italy a land sea perspective abstract a multi proxy record based on calcareous plankton dinocysts pollen mineralogy and grain size has been acquired from the ideale section the portion of montalbano jonico succession southern italy that could host the gssp for the middle pleistocene the direct correlation between marine and terrestrial proxies provides a valuable indication of atmospheric and oceanic connections the record shows a distinct climate variability well expressed by the vegetational changes sediment input into the basin and sea surface water modifications biotic proxies indicate that during the study interval periods of prevailing subpolar transitional surface water conditions were concurrent with steppe and halophytic vegetation erosional processes on the hillslopes and terrigenous supply during these periods were likely favored due to reduced arboreal vegetation as attested to by sediment composition and pollen assemblages temperate subtropical surface water conditions were concomitant with prevalent expansions of thermophilous arboreal plants and moister conditions on land which likely promoted chemical weathering leading to an enhanced supply of kaolinite and smectite in the basin a relationship between mineral content and the nature of the outcropping units in the source area as well as sea level fluctuations has also been considered a well defined period of polar subpolar water incursion ranging from 793 2 ka to 788 1 ka matches the major expansion of steppic vegetation on land and the increase of terrigenous supply into the basin it likely represents the local response to north atlantic ice rafted debris deposition short lived warming cooling episodes punctuate the latest part of mis 20 and are tentatively correlated with analogue climate phases predating mis 1 inception full interglacial conditions of mis 19c lasting 10 6 kyr started at 784 3 ka and were characterized by warm oligotrophic and stratified surface waters coupled with forest expansion suggesting prevalent warm and humid conditions on land a potential sapropel like interval is identified within mis 19c and correlated to i cycle 74 the mis 19c 19b transition is marked at 773 2 ka by the reestablishment of millennial scale variability similarly to north atlantic marine and ice core records the results improve the paleoclimate framework of a middle pleistocene reference section and add further insight regarding climate development across mis 19 and on potential similarities with its closest holocene analogue

impact of suborbital climate changes in the north atlantic on ice sheet dynamics at the mid pleistocene transition pervasive feature across our study negative excursions in the benthic d 18 o time series observed at the times of ird events may be related to glacio eustatic changes due to ice sheets retreats and or to changes in deep hydrography time series analysis on surface water proxies ird sst and planktonic d 18 o of the interval between mis 31 to mis 26 shows that the timing of these millennial scale climate changes are related to half precessional 10 kyr components of the insolation forcing which are interpreted as cross equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator

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

diffuse spectral reflectance as a proxy for percent carbonate content in north atlantic sediments diffuse reflectance records from fern drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the fern drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing abstract diffuse reflectance records from feni drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the feni drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing

stability of ice on the moon with rough topography abstract the heat flux incident upon the surface of an airless planetary body is dominated by solar radiation during the day and by thermal emission from topography at night motivated by the close relationship between this heat flux the surface temperatures and the stability of volatiles we consider the effect of the slope distribution on the temperature distribution and hence prevalence of cold traps where volatiles may accumulate over geologic time we develop a thermophysical model accounting for insolation reflected and emitted radiation and subsurface conduction and use it to examine several idealized representations of rough topography we show how subsurface conduction alters the temperature distribution of bowl shaped craters compared to predictions given by past analytic models we model the dependence of cold traps on crater geometry and quantify the effect that while deeper depressions cast more persistent shadows they are often too warm to trap water ice due to the smaller sky fraction and increased reflected and reemitted radiation from the walls in order to calculate the temperature distribution outside craters we consider rough random surfaces with a gaussian slope distribution using their derived temperatures and additional volatile stability models we estimate the potential area fraction of stable water ice on earth s moon for example surfaces with slope rms 15 corresponding to length scales 10 m on the lunar surface located near the poles are found to have a 10 exposed cold trap area fraction in the subsurface the diffusion barrier created by the overlaying regolith increases this area fraction to 40 additionally some buried water ice is shown to remain stable even beneath temporarily illuminated slopes making it more readily accessible to future lunar excavation missions finally due to the exponential dependence of stability of ice on temperature we are able to constrain the maximum thickness of the unstable layer to a few decimeters

millennial scale variability of deep water temperature and δ18odw indicating deep water source variations in the northeast atlantic 0 34 cal ka bp 1 paired measurements of mg ca and 18occ calcite 18o in benthic foraminifera from a deep sea core recovered on the iberian margin md99 2334k 37 48 n 10 10 w 3 146 m have been performed in parallel with planktonic 18occ analyses and counts of ice rafted debris ird the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ allows the proxy records from md99 2334k to be placed confidently on the gisp2 time scale this correlation is further corroborated by ams 14c dates benthic mg ca measurements in md99 2334k permit the reconstruction of past deep water temperature tdw changes since 34 cal ka bp calendar kiloyears before present using these tdw estimates and parallel benthic 18occ measurements a record of deep water 18o 18odw has been calculated results indicate greatly reduced tdw in the deep northeast atlantic during the last glaciation until 15 cal ka bp when tdw warmed abruptly to near modern values in parallel with the onset of the bolling allerod interstadial subsequently tdw reverted to cold glacial values between 13 4 and 11 4 cal ka bp in parallel with the younger dryas cold reversal and the h0 ice rafting event similar millennial scale tdw changes also occurred during the last glaciation indeed throughout the last 34 cal ka millennial 18odw and tdw changes have remained well coupled and are linked with ird pulses coincident with heinrich events 3 2 1 and the younger dryas when transitions to lower tdw and 18odw conditions occurred in general millennial tdw and 18odw variations recorded in md99 2334k describe an alternation between colder low 18odw and warmer high 18odw conditions which suggests the changing local dominance of northern sourced north atlantic deep water nadw versus southern sourced antarctic bottom water aabw the observed similarity of the tdw and gisp2 18oice records would therefore suggest a common component of variability resulting from the coupling of nadw formation and greenland climate a link between greenland stadials and the incursion of cold low 18odw aabw in the deep northeast atlantic is thus implied which contributes to the relationship between greenland climate and the millennial benthic 18occ signal since 34 cal ka bp

north atlantic surface circulation during the 1990 s observed with satellite tracked drifters a new compilation of lagrangian velocity observations describes the state of the north atlantic surface circulation during the 1990s gridded fields of velocity and eddy kinetic energy eke are constructed from trajectories of more than 1500 15 m drogued satellite tracked surface drifters in service between january 1990 and december 1999 this time period overlaps a coordinated field study of circulation and variability in the north atlantic completed between 1996 2000 as part of the world ocean circulation experiment we describe the construction of a self consistent drifter climatology present decadal mean quasi eulerian velocity and eke fields computed on a 1 grid and compare these results with contemporary satellite measurements detailed discussion of the inferred surface circulation is focused on three regions 1 the gulf stream and north atlantic current 2 the labrador sea and subpolar gyre and 3 the caribbean sea the swiftest drifter motions were found in the equatorial region and along the tropical subtropical and subpolar western boundaries the maximum instantaneous speed determined from a single quality controlled and filtered drifter observation was 273 cm s 1 in the gulf stream southeast of cape cod the highest eke value in the north atlantic 2790 cm2 s 2 was found in the gulf stream just downstream of the new england seamounts over most of the atlantic basin drifter derived eke values were found to be o 100 cm2 s 2 higher than corresponding values derived from satellite altimetry in the labrador sea a region of sharply elevated eke appears to be geographically related to the localized ejection of drifters and by extension mass and kinetic energy from the energetic west greenland current between 60 and 62 n when compared to drifter measurements made in the late 1970s our results suggest but do not statistically confirm an enhancement and slight northward shift of the zonal gulf stream extension such a shift is consistent in sign with expectations based on observed interdecadal variations in wind stress and subtropical gyre potential energy associated with the north atlantic oscillation

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

authigenic 10be 9be ratio signature of the matuyama brunhes boundary in the montalbano jonico marine succession geomagnetic dipole moment gdm lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide beryllium 10 10be production hence the reconstruction of atmospheric 10be production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach independent from paleomagnetic measurements to decipher past gdm fluctuations this is particularly important in the montalbano jonico succession south italy since it is candidate to host the global stratotype section and point of the middle pleistocene stage but where the magnetostratigraphic positioning of the matuyama brunhes boundary mbb has not been available up to now this study presents 1 original authigenic 10be cosmogenic nuclide and 9be stable isotope results and 2 new high resolution benthic oxygen isotope record covering termination ix and marine isotope stage mis 19 a robust chronological framework is established on the basis of i our oxygen isotope stratigraphy using the strong analogies between mis 1 and mis 19c in terms of orbital forcing and co2level and ii one precise 40ar 39ar date obtained in the tephra layer v4 the authigenic 10be 9be ratio record marks the atmospheric 10be overproduction linked to the dipole low accompanying the mbb transition with a characteristic twofold increase of the 10be production at the end of mis 19c and early mis 19b this signature is similar to those described in both marine and ice core records the detailed chronostratigraphy constrained by a radiometrically dated tephra layer 773 9 1 3ka within the mbb interval makesit possible to discuss the structure and to assess the timing of the 10be production changes and thus the mbb geomagnetic variations with an unprecedented accuracy for a marine archive sedimentation rates 80cm ka these new cosmogenic nuclide production signatures provide the only missing constraint required for retaining the montalbano jonico succession as a global scale correlation reference section for the early middle pleistocene boundary

filtering of milankovitch cycles by earth s geography abstract earth s land sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation we examine this modification in the frequency domain by generating 800 000 yr time series of maximum summer temperature in selected regions with a linear two dimensional seasonal energy balance climate model previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land although the observed response in the geologic record is sometimes significantly different than modeled here differences attributable to model limitations and feedbacks involving the ocean atmosphere cryosphere system there are several results of significance 1 in mid latitude land areas the orbital signal is translated linearly into a large 10 c seasonal temperature response 2 although the modeled seasonal response to orbital forcing on antarctica is 6 c the annual mean temperature effect

brief sea level fall event and centennial to millennial sea level variations during marine isotope stage 19 in osaka bay japan detailed sea level variation was investigated for marine isotope stage mis 19 based on diatom and grain size analyses of a marine sequence in a core of the osaka group diatom sea level proxies represent precession related signals correlated with highstands mis 19 3 and 19 1 and lowstand mis 19 2 astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka 1 a rapid sea level fall event was found in the earliest mis 19 demonstrated by several independent sea level proxies of diatom and grain size this event began with a rapid sea level drop followed by a gradual recovery at about 783 782 ka a maximum abundance of pelagic diatom taxa at a core depth of 402 20 m evidently shows the highest sea level peak in mis 19 supported by many other proxies based on the diatom data sea level change across mis 19 1 is characterized by centennial to millennial fluctuations the sea level fall event began just after the onset of a cooling event previously reported from the same core observations of a comparable sea level fall signal in many deep sea core records suggest the event is global

the marine isotope stage 19 in the mid latitude north atlantic ocean astronomical signature and intra interglacial variability abstract since the seminal work by hays et al 1976 a plethora of studies has demonstrated a correlation between orbital variations and climatic change however information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial scale climate variability is still fragmentary the marine isotope stage mis 19 an interglacial centred at around 785 ka provides an opportunity to pursue this question and test the hypothesis that the long term processes set up the boundary conditions within which the short term processes operate similarly to the current interglacial mis 19 is characterised by a minimum of the 400 kyr eccentricity cycle subdued amplitude of precessional changes and small amplitude variations in insolation here we examine the record of climatic conditions during mis 19 using high resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the north atlantic integrated ocean drilling program expedition 306 site u1313 in order to assess the stability and duration of this interglacial and evaluate the climate system s response in the millennial band to known orbitally induced insolation changes benthic and planktonic foraminiferal 18o values indicate relatively stable conditions during the peak warmth of mis 19 but sea surface and deep water reconstructions start diverging during the transition towards the glacial mis 18 when large cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal the glacial inception occurred at 779 ka in agreement with an increased abundance of tetra unsaturated alkenones reflecting the influence of icebergs and associated meltwater pulses and high latitude waters at the study site after having combined the new results with previous data from the same site and using a variety of time series analysis techniques we evaluate the evolution of millennial climate variability in response to changing orbital boundary conditions during the early middle pleistocene suborbital variability in both surface and deep water records is mainly concentrated at a period of 11 kyr and additionally at 5 8 and 3 9 kyr in the deep ocean these periods are equal to harmonics of precession band oscillations the fact that the response at the 11 kyr period increased over the same interval during which the amplitude of the response to the precessional cycle increased supports the notion that most of the variance in the 11 kyr band in the sedimentary record is nonlinearly transferred from precession band oscillations considering that these periodicities are important features in the equatorial and intertropical insolation these observations are in line with the view that the low latitude regions play an important role in the response of the climate system to the astronomical forcing we conclude that the effect of the orbitally induced insolation is of fundamental importance in regulating the timing and amplitude of millennial scale climate variability

analysis and interpretation of holocene sea level data the geography of the geoid1 and the lack of an acceptable methodology and definition of terms for sea level studies have impeded the realization of the objectives of the international geological correlation programme project 61 on holocene sea level changes2 these were to establish a graph of the trend of mean sea level over the globe and the relationship between sea level climate change and the global ice budget2 a solution to the problems of correlation is proposed here the use of terms transgression and regression has been a major cause of misinterpretation2 and the terms transgressive overlap and regressive overlap have been proposed as descriptive lithostratigraphic terms in which no process is implied3 5 the processes involved in the development of coastal stratigraphical sequences are dependent on the position and rate of change of sea level and these sequences contain evidence of tendencies of sea level6 8 the application of the concept of sea level tendency permits meaningful correlations between rising and subsiding areas and introduces an objectivity to correlation schemes showing transgression sequences 9 10

to tune or not to tune detecting orbital variability in oligo miocene climate records article i nfo article history we address the problem of detecting quasi periodic variability at orbital frequencies within pre pleistocene climate records using depth derived and orbitally tuned chronologies many studies describing orbital vari ability in pre pleistocene sediment hosted isotope records employ climatic records that are set on orbitally tuned chronologies without accounting for the bias in spectral power estimates introduced by orbital tuning in this study we develop a method to quantify the effects of tuning upon spectral estimates and in particular to more properly determine the statistical significance of spectral peaks associated with orbital frequencies we apply this method to two marine sediment 18 o records spanning the oligo miocene from odp cores 1090 and 1218 we find that using linear age depth relationships reveals statistically significant spectral peaks matching eccentricity in core 1090 and obliquity and precession in core 1218 where the last appears most significant tuning the chronologies to the orbital solutions of laskar et al 2004 increases the statis tical significance of the precession peak whereas the obliquity and eccentricity peaks become indistinguish able from those expected from tuning noise this result can be understood in that tuning records with high signal to noise ratios tends to lead to more significant spectral peaks whereas a linear age depth relationship is better suited for detecting peaks when signal to noise ratios are low we also demonstrate this concept using synthetic records

stability of north atlantic water masses in face of pronounced climate variability during the pleistocene 1 geochemical profiles from the north atlantic ocean suggest that the vertical 13c structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the pleistocene despite large changes in ice volume and iceberg delivery from nearby landmasses the most anomalous 13c profiles are from the extreme interglaciations of the late pleistocene this compilation of data suggests that unlike today an extreme interglaciation the two primary sources of northern deep water norwegian greenland sea and labrador sea subpolar north atlantic had different characteristic 13c values over most of the pleistocene we speculate that the current open sea ice conditions in the norwegian greenland sea are a relatively rare occurrence and that the high 13c deep water that forms in this region today is geologically unusual if northern source deep waters can have highly variable 13c then this likelihood must be considered when inferring past circulation changes from benthic 13c records

the valle di manche section calabria southern italy a high resolution record of the early middle pleistocene transition mis 21 mis 19 in the central mediterranean abstract the on land marine valle di manche section crotone basin calabria southern italy one of the candidates to host the gssp of the middle pleistocene ionian stage preserves a manifold record of independent chronological paleoclimatic and stratigraphic proxies that permit a straightforward correlation with marine and terrestrial reference records at the global scale in particular the section holds an excellent record of the matuyama brunhes magnetic reversal which occurs in the midst of marine isotope stage mis 19 we report on a complete revision of the section that improves dramatically the available dataset especially in the stratigraphic interval straddling the lower middle pleistocene boundary our benthic 18o record provides evidence that the matuyama brunhes transition the stratigraphic position of which is marked by a prominent tephra the pitagora ash occurred during full mis 19 in agreement with many records worldwide we obtained an age of 786 9 5 ka for the matuyama brunhes magnetic reversal and pinpointed the paleomagnetic transition of to a 3 cm thick interval indicating that the event was very fast since the section fulfills all the requirements to host the gssp of the ionian stage we propose that the boundary should be placed at the base of the pitagora ash ca 12 5 cm below the midpoint of the matuyama brunhes reversal

sea surface dynamics and palaeoenvironmental changes in the north atlantic ocean iodp site u1313 during marine isotope stage 19 inferred from coccolithophore assemblages abstract coccolithophore assemblages recovered from integrated ocean drilling program iodp site u1313 are investigated to reconstruct the palaeoceanographic evolution of a sector of the north atlantic during marine isotope stage mis 19 790 760 ka at orbital suborbital and millennial time scales the end of the glacial mis 20 is marked by the arrival of cold waters deriving from ice melting at higher latitudes as recorded by coccolithus pelagicus pelagicus the mis 19c is characterised by an extension of warmer north atlantic transitional waters natw reflecting the intensification of subtropical gyre influence on site u1313 identified by an increase in warm species umbilicosphaera sibogae the influence on the site of cooler natw is inferred from higher percentages of gephyrocapsa margereli which starts increasing from 779 ka finally the transition from mis 19a to mis 18 is characterised by a southward shift of the palaeoceanographic system due to a southward extension of the subpolar front as indicated by an increase of cold subspecies c pelagicus pelagicus the evolution of the palaeoproductivity proxy records number of coccoliths g of sediment and nannofossil accumulation rate nar and the abundances of small gephyrocapsa g margereli u sibogae and c pelagicus pelagicus show that fluctuations in sea surface productivity and alternations between cooling and warming phases occurred on the precessional timescale spectral analyses of u sibogae number of coccoliths g of sediment and nar indicate a significant concentration of variance close to half precession 10 kyr this reflects a nonlinear response of the mid latitude north atlantic surface ocean to low latitude insolation forcing furthermore millennial to multi centennial instability in sea surface dynamics is highlighted by spectral and wavelet analyses of u sibogae g margereli and c pelagicus pelagicus percentages number of coccoliths g of sediment and nar which reveal the occurrence of rapid events related to stadial and interstadial type conditions

millennial scale hydrographic changes in the northwestern pacific during marine isotope stage 19 teleconnections with ice melt in the north atlantic abstract marine isotope stage mis 19 has been suggested as the best orbital analogue of the present interglacial period thus its paleoenvironmental reconstruction will provide valuable information on future climate change excluding anthropogenic impacts the kuroshio current the largest western boundary current in the northwestern pacific transports large amounts of heat and water poleward and strongly influences both east asian and global climates however the responses of the kuroshio current to the variable intensity of the atlantic meridional overturning circulation amoc under this orbital configuration remain unknown here we provide new centennial scale resolution oxygen isotope 18 o records throughout mis 19 using benthic as well as subsurface and surface planktonic foraminifera from the chiba composite section a marine succession sequence in central japan to reconstruct detailed paleoceanographic variations in the northwestern pacific and reveal the response of the kuroshio current to climate variability in the north atlantic under this orbital configuration the vertical water temperature structure and its gradient t based on 18 o profiles elucidates the latitudinal oscillations of the kuroshio extension front kef on a millennial scale during the late mis 19 and mis 20 19 transition in association with amoc disruption reactivation due to freshwater discharges into the north atlantic the power spectra of the surface 18 o and t show half precession periodicity throughout mis 19 which probably originated from equatorial insolation at equinoxes co occurring with the orbital perihelion this periodicity was especially strong during mis 19c during which paleoceanographic records from the north atlantic show minor variations in the amoc and freshwater discharge our results suggest that millennial scale oceanographic variation and stability along the kef under this orbital configuration are influenced by both north atlantic climate variability and tropical insolation forcing

a 1 ma record of sea surface temperature and extreme cooling events in the north atlantic a perspective from the iberian margin abstract the iberian margin is a sensitive area to track high and low latitude processes and is a key location to understand major past climatic and oceanographic changes here we present new biomarker data from iodp site u1385 shackleton site 1017 336 ka that when combined with existing data from cores md01 2443 4 last 335 ka allows us to assess the evolution of sea surface temperature sst and meltwater influx over the last 1 ma at the iberian margin interglacial periods throughout the last 1 ma show sst close to 20 c even during the so called luke warm interglacials that are marked by relatively low atmospheric co2 concentrations during glacial periods extremely cold stadial events are recognized at the iberian margin and are very likely related to meltwater discharges from the european and british irish ice sheets into the ne atlantic which were transported southwards by the portugal current we subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials 1 from 1017 to 900 ka only minor sporadic freshwater input occurred during deglaciations 2 from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations which results in abrupt deglacial sst shifts 3 from 675 to 450 ka only a few very short lived events are recorded and seldom is there freshwater input at the iberian margin 4 during the last 450 ka the extreme cold events occurred under full glacial conditions with particularly severe events during mis 6 and 8 we propose these mid glacial events are associated with a strong discharges of european ice sheet eis the fact that these extreme cold events do not coincide with deglaciations questions the role of european ice sheet discharges in triggering deglaciations

north atlantic millennial scale climate variability 910 to 790 ka and the role of the equatorial insolation forcing abstract the mid pleistocene transition mpt was the time when quasi periodic 100 kyr high amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing leading to the establishment of the characteristic pattern of late pleistocene climate variability it has long been known that the interval around 900 ka stands out as a critical point of the mpt when major glaciations started occurring most notably in the northern hemisphere here we examine the record of climatic conditions during this significant interval using high resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the north atlantic integrated ocean drilling program expedition 306 site u1313 we have considered the time interval from late in marine isotope stage mis 23 to mis 20 910 to 790 ka our data indicate that interglacial mis 21 was a climatically unstable period and was broken into four interstadial periods which have been identified and correlated across the north atlantic region these extra peaks tend to contradict previous studies that interpreted the mis 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters cooling events in the surface record during mis 21 were associated with low benthic carbon isotope excursions suggesting a coupling between surface temperature changes and the strength of the atlantic meridional overturning circulation time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10 7 kyr and 6 kyr which is in agreement with the second and forth harmonic of precession the excellent correspondence between the foraminifera 18 o records and insolation variations at the equator in march and september suggests that a mechanism related to low latitude precession variations advected to the high latitudes by tropical convective processes might have generated such a response this scenario accounts for the presence of oscillations at frequencies equal to precession harmonics at site u1313 as well as the occurrence of higher amplitude oscillations between the mis22 21 transition and most of mis 21 times of enhanced insolation variability

unexpected weak seasonal climate in the western mediterranean region during mis 31 a high insolation forced interglacial marine isotope stage 31 mis 31 is an important analogue for ongoing and projected global warming yet key questions remain about the regional signature of its extreme orbital forcing and intra interglacial variability based on a new direct land sea comparison in sw iberian margin iodp site u1385 we examine the climatic variability between 1100 and 1050 ka including the super interglacial mis 31 a period dominated by the 41 ky obliquity periodicity pollen and biomarker analyses at centennial scale resolution provide new insights into the regional vegetation precipitation regime and atmospheric and oceanic temperature variability on orbital and suborbital timescales our study reveals that atmospheric and sst warmth during mis 31 was not exceptional in this region highly sensitive to precession unexpectedly this warm stage stands out as a prolonged interval of a temperate and humid climate regime with reduced seasonality despite the high insolation precession minima values forcing we find that the dominant forcing on the long term temperate forest development was obliquity which may have induced a decrease in summer dryness and associated reduction in seasonal precipitation contrast moreover this study provides the first evidence for persistent atmospheric millennial scale variability during this interval with multiple forest decline events reflecting repeated cooling and drying episodes in sw iberia our direct land sea comparison shows that the expression of the suborbital cooling events on sw iberian ecosystems is modulated by the predominance of high or low latitude forcing depending on the glacial interglacial baseline climate states severe dryness and air sea cooling is detected under the larger ice volume during glacial mis 32 and mis 30 the extreme episodes which in their climatic imprint are similar to the heinrich events are likely related to northern latitude ice sheet instability and a disruption of the atlantic meridional overturning circulation amoc in contrast forest declines during mis 31 are associated to neither sst cooling nor high latitude freshwater forcing time series analysis reveals a dominant cyclicity of about 6 ky in the temperate forest record which points to a potential link with the fourth harmonic of precession and thus low latitude insolation forcing

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes