a low order model of the heinrich event cycle if heinrich events result from free oscillations in the size and basal melting conditions of the laurentide ice sheet a rigorous quantitative analysis of ice sheet physics should describe their dynamics to explore this possibility i exploit two characteristic timescales which arise from ice sheet physics to construct a relaxation oscillator model of the north atlantic s heinrich events the numerical implementation of this model confirms the notion that the periodicity of heinrich events approximately 7 000 years is determined by the gross properties of a steady glacial climate e g an annual average sea level temperature of 10 c and an adiabatic lapse rate

climate change and tectonic activity during the early pliocene warm period from the ostracod record at lake qinghai northeastern tibetan plateau abstract the early pliocene warm period epwp 5 3 ma is sometimes thought to be a useful analogue for a future warmer world and thus the boundary conditions and drivers of climate in the epwp may provide valuable lessons for understanding how a future warmer world might unfold lake qinghai is located on the northeastern margin of the tibetan plateau tp and is affected by both monsoon climate and westerlies circulation it is sensitive to the climate drivers of these systems its sediments accumulated over the cenozoic period are a rich source of information for climate tectonics and environmental changes of the period we present a high resolution ostracod record from a lake qinghai sediment core with a record of the period 5 10 2 60 ma thus covering the epwp ostracods appear at 4 63 ma and are most abundant until 3 58 ma while a body of water was present at the core site this suggests a phase of humid climate and an intensified asian summer monsoon asm which is consistent with a warmer and wetter climate in the early pliocene within this period the ostracod record shows some variabilities in lake level with deeper periods suggesting more intense asm compared to those with shallower water the disappearance of ostracods at 3 58 ma may provide evidence for the uplift of qinghai nanshan south of qinghai lake since this is when the asm intensified

a marine sediment component interpretation based on diffuse reflectance spectrophotometry from northern south china sea sediment core md972148 abstract the sediment components of high resolution marine sediment cores are extremely important for revealing past climatic and environmental changes however analysis of deep sea sediments presents a number of exceptional challenges especially for the northern south china sea scs which receives substantial amounts of suspended sediments from numerous rivers including both the world s largest river in south china and a small mountain river from southwestern taiwan this study applies rapid and low cost color reflectance analysis in combination with multivariate analysis techniques to examine the overall trends of major mineral component variations in sediment core md972148 from the northern scs the first order derivative central difference reflectance data from 400 to 700 nm yields five major factors which accounted for 89 7 of the variance for the input matrix collocating with varimax rotated principal component analysis vpca through spss software and comparing with the first order derivative spectra of known minerals from a laboratory at kent state university and the usgs library the three leading factors represent kaolinite illite goethite and hematite although the last two factors have no significant correspondences with known minerals we found these two factors have similar variation patterns with the abundances of the foraminifer species globigerinoides sacculifer and globigerina bulloides in the downcore our research shows that diffuse reflectance spectrophotometry drs is a useful method for rapidly examining the sediment components to verify the mechanisms and connections between some sediment components and their color reflectances will require future research

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

1500 year cycle dominated holocene dynamics of the yellow river delta china the world s mega deltas are extremely important from a human perspective and attract considerable effort to reveal their evolution growth related driving forces and human impacts here we report a case study on the holocene deltaic evolution of the yellow river through development of a conceptual model which is compared with paleo proxy to analyze the forcing acting on the delta the main conclusion is that superlobe switching was modulated by the 1500 year cycle cooling in mongolia in response to strong bond ird events which is coincident with warming in eastern china due to a strong kuroshio current enhances the meridional temperature gradient which then increases cyclone frequency and activates dust storms and terrestrial erosion throughout the catchment enhanced erosion supplies great amounts of material to the yellow river and causes channel evulsion and superlobe development expressed as dominant 1500 year cycle at the same time summer monsoon and solar forcing are uncorrected with deltaic evolution on these timescales therefore we conclude that holocene dynamics of the delta on a millennial timescale was dominated by winter cyclone activity across northern china and mongolia

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

enhanced marine productivity off western north america during warm climate intervals of the past 52 k y studies of the santa barbara basin off the coast of california have linked changes in its bottom water oxygen content to millennial scale climate changes as recorded by the oxygen isotope composition of greenland ice through the use of detailed records from a sediment core collected off the magdalena margin of baja california mexico we demonstrate that this teleconnection predominantly arose from changes in marine productivity rather than changes in ventilation of the north pacific as was originally proposed

correlation of climate cycles in middle mississippi valley loess and greenland ice two complete late wisconsin loess successions in the middle mississippi river valley reveal 39 and 41 alternating paleosol a and c horizons striking changes in soil color iron content and carbonate content define four major and two minor paleosol a horizon complexes which were interpreted to represent wisconsin interstadials 1 2 3 4 and semiinterstadials 1 5 and 2 5 respectively the timing of wisconsin interstadials matches that of corresponding greenland interstadials midcontinent loess and greenland ice records as well as rates of atmospheric 14c production have periodicities in common suggesting a solar influence only a persistent heat and moisture supply could produce prominent paleosol complexes near the continental ice margin this record suggests that el nino southern oscillation variability has amplified solar forcing and resultant tropical heat and moisture transport played a significant role in millennial and centennial scale climate cycles during the late wisconsin glaciation over the northern hemisphere

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

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

earth s precession cycle and quaternary climatic change in tropical africa high abundances of the freshwater diatom melosira spp reflecting eolian input from dry lake beds in tropical africa occur in deep sea sediments of the equatorial atlantic at discrete times during the late quaternary1 2 we report here an approximately 260 kyr record of melosira accumulation in an equatorial atlantic sediment core and demonstrate significant influence of the earth s precessional cycle on the climate of tropical africa

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

neogene changes in southern ocean sedimentation based on mass accumulation rates at four continental margins 1 high resolution mass accumulation rates mar were determined from lithologic logs based on downhole log and continuous core data for six sites at four continental margins around the southern ocean total mar was calculated at ocean drilling program odp site 1095 on the margin of the antarctic peninsula and odp site 1165 on the margin of prydz bay antarctica carbonate and noncarbonate terrigenous mar were calculated for odp sites 1123 and 1124 east of new zealand and sites 1168 and 1172 west and southeast of tasmania shifts in carbonate mar are seen around tasmania and new zealand at 23 and 14 ma suggesting changes in deep water circulation and surface carbonate productivity at these times carbonate mar dropped at sites 1124 and 1168 at 23 ma and increased at 14 ma at sites 1123 1168 and 1172 the overall character of total mar at antarctic sites 1095 and 1165 is a continual and relatively constant decrease in total mar during the neogene with periods of stepwise decrease one such decrease is seen at 14 ma at site 1165 coincident with increased carbonate mar in new zealand and tasmania sites 1123 1124 1168 and 1172 and likely related to mid miocene expansion of the east antarctic ice sheet another step drop in total mar is seen at 9 ma at site 1165 possibly reflecting diversion of sediment to a newly formed prydz channel fan

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

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

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

ice rafted debris associated with binge purge oscillations of the laurentide ice sheet the north atlantic sediment record suggests quasi periodic 7000 to 12 000 year period ice rafted debris ird depositions during at least the last glacial period the cause of these heinrich events as they are commonly known is not fully understood however they may point to surges of the ice stream that drained the hudson bay hudson strait region of the laurentide ice sheet we investigate a simple conceptual model of ice stream instability the binge purge model to suggest ways in which the ice stream could have entrained sufficient debris to account for the estimated mass of ird associated with a typical heinrich ird layer in the north atlantic 1 0 0 3 1015 kg we find that freezing of debris laden ice at the bed of the ice stream during the brief 750 years surge phase of the ice stream s hypothesized binge purge cycle can incorporate up to 5 1 1015 kg this amount is sufficient to meet the constraints of the north atlantic sediment record but by no means verifies the binge purge model as the cause of heinrich events

late cretaceous precessional cycles in double time a warm earth milankovitch response late cretaceous climatic cycles are reflected in lithological and magnetic variations in carbonate sediments from south atlantic deep sea drilling project site 516f at a paleolatitude of roughly 30 s magnetic susceptibility cycles 20 to 60 centimeters in length appear to be controlled by the precession of the equinoxes cyclicity is particularly robust within a 24 meter interval in the lower campanian where overtone spectral peaks are observed as well as secondary susceptibility maxima within individual precession cycles one model for this behavior is that sedimentation in the narrow cretaceous south atlantic was controlled by equatorial climate dynamics with the precessional insolation signal rectified by the large land masses surrounding the ocean basin

sediment colour analysis from digital images and correlation with sediment composition sediment colour records can be extracted from digital images of sediment core surfaces which provide the spatial resolution needed to measure colour in laminated sediments digital cameras sample colour in three broad wavelengths red green and blue which are subsequently translated into the cie l a b colour space methods to extract calibrated colour values are discussed in this paper l a and b values are correlated with geochemical analyses of cm scale bulk sediment samples the sediments are from a suite of laminated and homogenous sections containing organic matter carbonate biogenic opal and lithogenic material in variable proportions total organic carbon toc content has the dominant effect on sediment colour results show that there is a strong correlation with lightness l for toc values between 0 5 and 10 but that sediment lightness becomes saturated at higher toc concentrations biogenic opal content cannot be resolved using the l a b colour space biogenic opal in itself has a light colour but it tends to occur in darker coloured sediments because of a positive correlation between opal and toc content carbonate content in the measured sections is generally less than 25 at which values its effect on colour is obscured by the other sediment components the geological society of london 2006

climate variability and ice sheet dynamics during the last three glaciations a composite north atlantic record from dsdp site 609 and iodp site u1308 spans the past 300 000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations hematite stained grains exhibit similar repetitive down core variations within the marine isotope stage mis 8 and 4 2 intervals but little cyclic variability within the mis 6 section there is also no petrologic evidence in terms of detrital carbonate rich heinrich layers for surging of the laurentide ice sheet through the hudson strait during mis 6 rather very high background concentration of iceberg rafted debris ird indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events such as expanded sea ice over deepwater formation sites altered sub tropical precipitation patterns and antarctic warming during high orbital precession and low 65 n summer insolation appear related to high abundance of icelandic glass shards and southward sea ice expansion differing european and north american ice sheet configurations perhaps aided by larger variations in eccentricity leading to cooler summers may have contributed to the relative stability of the laurentide ice sheet in the hudson strait region during mis 6

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

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

the matuyama brunhes boundary interval 500 900 ka in north atlantic drift sediments summary ocean drilling program odp sites 984 and 983 located on north atlantic sediment drifts provide high resolution records across the matuyama brunhes boundary at odp site 984 bjorn drift iceland basin the mean sedimentation rate in the 500 900 ka interval is 12 cm kyr 1 based on an age model derived by matching the planktonic and benthic oxygen isotope records to an ice volume model the matuyama brunhes polarity transition at site 984 as defined by virtual geomagnetic polar vgp latitudes 50 has an apparent duration of 7 kyr with a mid point at 773 5 ka compared with 772 5 ka at neighbouring site 983 outside the polarity transition at both sites 984 and 983 excursions in vgp latitudes to values 20 at 540 590 and 670 ka correspond to troughs in the palaeointensity record new u channel palaeomagnetic data across the matuyama brunhes boundary for working and archive halves of core sections from three holes at both sites 984 and 983 augment data published by channell lehman 1997 and are compared with back to back 1 cm 3 discrete samples clusters of vgps in the south atlantic and northeast asia in both u channel and discrete sample records imply that polarity transition fields have characteristics similar to the modern non axial dipole nad field

modeling 100 000 year climate fluctuations in pre pleistocene time series a number of pre pleistocene climate records exhibit significant fluctuations at the 100 000 year 100 ky eccentricity period before the time of such fluctuations in global ice volume the origin of these fluctuations has been obscure results reported here from a modeling study suggest that such a response can occur over low latitude land areas involved in monsoon fluctuations the twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100 ky and 400 ky power in the modeled temperature field the magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record and simulated fluctuations resemble those found in records of triassic lake levels

physical properties of reykjanes ridge sediments and their linkage to high resolution greenland ice sheet project 2 ice core data five gravity cores taken from the reykjanes ridge have been used to establish a link between sediment physical properties and atmospheric records documented by 18o variations in greenland ice cores over the last 45 000 calendar years marine gamma ray attenuation porosity evaluator density and magnetic susceptibility variations could be linked with the ice core dansgaard oeschger and bond cycles this is supported by ice rafted detritus ird grain size the quartz feldspar ratio and carbonate isotopic and foraminiferal records the covariation of the sediment physical properties and 18o in greenland ice indicates a coupling of atmospheric temperature and paleocirculation variations gradual reduced bottom currents iceland scotland overflow water and enhanced iceberg discharges have been reconstructed for cold atmospheric periods relative to interstadial times in the study area the magnetic susceptibility signal is not related to the ice rafted detritus input but most probably reflects the variations of the iceland scotland overflow water intensity transporting titanomagnetite into the reykjanes ridge region

high resolution record of export production in the eastern equatorial pacific across the eocene oligocene transition and relationships to global climatic records 1 understanding changes in export production through time provides insight into the response of the biological pump to global climate change particularly during periods of rapid climate change in this study we consider what role changes in export production may have had on carbon sequestration and how this may have contributed to the onset of the eocene oligocene transition eot in addition we consider if these export production variations are dominantly controlled by orbitally driven climate variability to accomplish these objectives we report changes in export production in the eastern equatorial pacific eep from site u1333 across the eot reconstructed from a high resolution record of marine barite accumulation rates bar bar fluctuations suggest synchronous declines in export production associated with the two step increases in oxygen isotopes that define the transition the reduction in productivity across the eot suggests that the biological pump did not contribute to carbon sequestration and the cooling over this transition we also report a previously undocumented peak in eep export productivity before the eot onset this peak is consistent with export production proxies from the southern ocean potentially implying a global driver for this precursor event we propose that this enhanced export production and the associated carbon sequestration in the late eocene may have contributed to the pco2 drawdown at the onset of antarctic glaciation

geomagnetic paleointensity and directional secular variation at ocean drilling program odp site 984 bjorn drift since 500 ka comparisons with odp site 983 gardar drift normalized remanence relative geomagnetic paleointensity records for the last 500 kyr can be matched between two iceland basin ocean drilling program odp sites 984 and 983 and correlated with other high resolution records directional secular variation is however not easily correlated between sites due to inadequate recording at these mean sedimentation rates 12 15 cm kyr of the characteristic high frequency variability of the directional record both sites record the iceland basin event at 186 189 ka in which the characteristic magnetization component rotates through 180 and back coincident with a paleointensity low that lasted about 3 kyr other brunhes chron geomagnetic excursions appear to be manifest as intervals of higher amplitude secular variation during lows in paleointensity there is a tendency for paleointensity lows to correlate with peak interglacials in the oxygen isotope records however this does not translate into a correlation between paleointensity and percent carbonate or between paleointensity and magnetic concentration or grain size parameters

the reunion subchronozone at odp site 981 feni drift north atlantic abstract at ocean drilling program site 981 the reunion subchron is recorded from the marine isotopic stage mis 81 82 boundary to mis 79 as a single normal polarity zone spanning the 2 115 2 153 ma interval according to the age model produced by matching the site 981 18 o record to an orbitally tuned reference record the duration of the reunion subchron 38 kyr is almost four times that assumed in current geomagnetic polarity timescales high interval sedimentation rates 18 cm kyr during mis 81 at site 981 have resulted in an unusually detailed record of the subchron virtual geomagnetic poles during the onset and demise of the reunion subchron trace a series of mainly anticlockwise loops over eastern asia

foraminiferal faunal evidence for glacial interglacial variations in the ocean circulation and the upwelling of the gulf of tehuantepec mexico abstract three marine sediment cores from the gulf of tehuantepec eastern tropical north pacific were used to determine variations in upwelling intensity and surface circulation patterns over the last 26 kyr bp changes in foraminiferal assemblages at glacial interglacial timescale indicate a sequence of three major palaeoceanographic events in the study area 1 the late pleistocene including the last glacial maximum lgm dominated by a neogloboquadrina dutertrei globorotalia menardii assemblage indicative of a stable thermocline stratified water column and greater persistence of warm equatorial waters in the region 2 the termination 1 dominated by a globigerinita glutinata assemblage which indicates mixed surface water and transitional conditions between upwelling and stratified water column episodes changes in sedimentation rates and a clear reduction of the faunal abundances at this time could be the result of eustatic sea level change 3 the holocene dominated by a globigerina bulloides globigerinoides ruber assemblage indicates periods of elevated productivity intense upwelling and the establishment of the modern ocean conditions these findings are consistent with climate model results that suggest that regional surface ocean and upwelling conditions are mostly linked to changes in atmospheric circulation over the laurentide ice sheet and shifts in the latitudinal position of the intertropical convergence zone

new antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in antarctica gravity surveying is challenging in antarctica because of its hostile environment and inaccessibility nevertheless many ground based airborne and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s we present the first modern antarctic wide gravity data compilation derived from 13 million data points covering an area of 10 million km2 which corresponds to 73 coverage of the continent the remove compute restore technique was applied for gridding which facilitated levelling of the different gravity datasets with respect to an earth gravity model derived from satellite data alone the resulting free air and bouguer gravity anomaly grids of 10 km resolution are publicly available these grids will enable new high resolution combined earth gravity models to be derived and represent a major step forward towards solving the geodetic polar data gap problem they provide a new tool to investigate continental scale lithospheric structure and geological evolution of antarctica

evaluating color reflectance spectral methods for estimating biogenic contents of south china sea sediments abstract the biogenic contents of marine sediment cores are useful proxies for revealing past oceanic and climatic variability color reflectance spectral methods provide a rapid and non destructive avenue for acquiring high resolution biogenic content data from the split surfaces of marine sediment cores this study presents new results on the applications of color reflectance methods for determining the biogenic contents of sediment cores retrieved from the south china sea scs a dynamic setting that receives biogenic components such as carbonate total organic carbon toc and opal from the sea and terrestrial sediments transported by the pearl river and kao ping river from the north and the sunda shelf from the south our study found that the color reflectance methods that are based on a regionally limited calibration provide more optimal estimates of the biogenic content of marine cores from the scs than do basin scale calibration methods though the regional calibrations appear to be successful our analyses indicate the complexity of applying color reflectance methods in marine sediment core studies we also performed a controlled experiment that was designed to quantitatively test how the carbonate content increased the influence of color reflectance changes using outcropped pleistocene aged sediment samples taken from the moon world mw in southwestern taiwan as control data the results of this experiment suggest that the regression equations for estimating caco 3 content based on core data are not solely driven by input variables responding directly to caco 3 content changes and that the composition of terrestrial sediment inputs into the scs are complicated both spatially and temporally our studies also suggest that a better understanding of the compositional changes of terrestrial sediment inputs into the scs will be required to minimize the uncertainties of biogenic content estimations by color reflectance methods

mid to late holocene indian winter monsoon variability from a terrestrial record in eastern and southeastern coastal environments of sri lanka the southeastern coastal plain of sri lanka contains holocene sediment archives representing the winter monsoon variability because this region is protected from both summer monsoon and cyclonic rainfall chemical biological mineralogical and physical climate proxies were studied in sediment cores extracted from three different coastal estuaries and lagoons situated on the southeastern coast to derive winter monsoon variability these cores displayed minimum influence of sea level related changes in sediments clay normalized proxy records suggest intervals of aridity from 7300 to 6750 semi aridity from 6250 to 4600 yr bp and aridity from 4000 to 3000 and 1100 to 500 cal yr bp with a short wet interval from 6500 to 6250 cal yr bp and a wet interval from 3000 to 1500 yr bp our results match the timing of previously published climate events for holocene variations in the indian summer monsoon wavelet analysis of the detrended climate proxy records identify significant periodicities at 2

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

calcareous nannofossil changes during the mid pleistocene revolution paleoecologic and paleoceanographic evidence from north atlantic site 980 981 abstract new quantitative data on calcareous nannofossil assemblages through 583 1138 thousand years ago kyr have been acquired in high sample resolution 2 3 ky at northern atlantic odp ocean drilling program site 980 981 assemblage composition reflects a temperate paleobioprovince suggesting significant influx of warm north atlantic current at the site location during the mid pleistocene transition between marine isotope stage mis 35 and 15 three intervals have been described based on changes in nannofossil composition and abundance fluctuations of taxa reticulofenestrids are abundant just in the first interval mis 35 22 which is also characterised by the absence of gephyrocapsa 4 m and c pelagicus s l the latter occurring in upper mis 24 only the second interval corresponds to the expanded warm mis 21 that is accompanied by high carbonate content absence of both nannofossil reworking and ice rafted debris ird higher abundance of c leptoporus 5 8 m and h carteri and absence of c pelagicus s l and medium gephyrocapsids the third interval mis 20 15 records the occurrence of c pelagicus s l and medium gephyrocapsa generally higher abundance and higher amplitude fluctuations of helicoliths and absence of reticulofenestrids the major changes in nannofossil assemblages seem to be the result of combined paleoenvironmental factors related to sea surface water features temperature and nutrient availability sea ice cover and possibly to deep and intermediate water production of both northern and southern hemisphere origin during glacial and interglacial phases complex inter relationships between environmental parameters and evolutionary ecological factors are inferred to explain the patterns of coccolithus pelagicus subspecies whose distribution and abundance fluctuations are compared with the available patterns of turborotalia quinqueloba and neogloboquadrina pachyderma left coiled at site 980 and with the c pelagicus subspecies patterns from north atlantic dsdp deep sea drilling project site 607 and south atlantic odp site 1090 data collected provide additional information on stratigraphic distribution of selected taxa the first occurrence fo of gephyrocapsa omega is confirmed as a diachronous event even in the atlantic ocean while the first and last common occurrence fco lco of r asanoi appear as diachronous and synchronous events respectively on a global scale

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

sub milankovitch cycles in periplatform carbonates from the early pliocene great bahama bank high resolution bulk sediment magnetic susceptibility and aragonite content and 18o records from two different planktonic foraminifera species were analyzed in an early pliocene core interval from the straits of florida ocean drilling program site 1006 the 18o record of the shallow dwelling foraminifera g sacculifer and the aragonite content are dominated by sub milankovitch variability in contrast magnetic susceptibility and the 18o record of the deeper dwelling foraminifera g menardii show precession cycles the relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent great bahama bank was triggered directly by atmospheric processes rather than by sea level change we propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial pacific sea surface temperatures under present day conditions

digital image analysis of outcropping sediments comparison to photospectrometric data from quaternary loess deposits at şanoviţa romania and achenheim france abstract the possibility to use colour data as extracted from two selected loess paleosol sequences is discussed here colour data are a fast and inexpensive method of proxy data generation we compare the outcome from analysing outcrop images taken by digital cameras in the field and spectral colour data as determined under controlled laboratory conditions by nature differences can be expected due to variations in illumination moisture and sample preparation outcrop inclination may be an issue for photographs correction for this is possible when marks can be used for rectification in both cases the data extracted from the images match the visual impression of the photos well and are useful for obtaining a more quantitative measure for field observations smoothness as measured by autocorrelation is high for an image from achenheim france where an image with a width of ca 1 1 m and a depth of 1 6 m was analysed data from a narrower image part from anovi a romania are noisier in both cases a significant correlation between data extracted by digital image analysis and laboratory measurements could be established suggesting that image analysis is a useful tool where outcrop and light conditions allow good photographs with similar illumination especially where high resolution proxy data is required

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

paleoclimate of southwestern china for the past 50 000 yr inferred from lake sediment records abstract long sediment cores 12 5 and 13 5 m from two lakes in yunnan province were used to infer the paleoclimate of southwest china over the past 50 000 yr during the holocene and marine isotope stage mis 3 bio induced carbonate precipitation and organic matter om production was high suggesting warm temperatures and high primary productivity in contrast sediment inorganic carbon ic and organic carbon oc concentrations were low in last glacial deposits from 38 000 to 12 000 cal yr b p indicating cool temperatures and low productivity the 50 000 yr record has alternating peaks of carbonate and coarse grain 38 m quartz that reflect warm moist interglacial or interstadial conditions alternating with cold dry glacial or stadial conditions respectively spectral analysis of the carbonate and quartz signals reveals power concentrated at periods of 7200 and 8900 cal yr respectively that may reflect a nonlinear climate response to precessional forcing at a time of reduced eccentricity modulation mcintyre and molfino 1996 oxygen isotope values of calcite from yunnan lake cores indicate the summer monsoon was weak during the last glaciation from 50 000 to 12 000 cal yr b p the summer monsoon intensified between 12 000 and 8000 cal yr b p but weakened gradually in response to insolation forcing during the mid to late holocene our results support the overpeck et al 1996 model that posits a weak summer monsoon during the last glaciation that responded nonlinearly to insolation forcing when its intensity was affected by eurasian snow cover and ice sheet extent the summer monsoon intensified and responded linearly to seasonal insolation forcing in the holocene when ice volume diminished

characteristics of the deep ocean carbon system during the past 150 000 years σco2 distributions deep water flow patterns and abrupt climate change abstract studies of carbon isotopes and cadmium in bottom dwelling foraminifera from ocean sediment cores have advanced our knowledge of ocean chemical distributions during the late pleistocene last glacial maximum data are consistent with a persistent high co2 state for eastern pacific deep water both tracers indicate that the mid depth north and tropical atlantic ocean almost always has lower co2 levels than those in the pacific upper waters of the last glacial maximum atlantic are more co2 depleted and deep waters are co2 enriched compared with the waters of the present in the northern indian ocean 13c and cd data are consistent with upper water co2 depletion relative to the present there is no evident proximate source of this co2 depleted water so i suggest that co2 depleted north atlantic intermediate deep water turns northward around the southern tip of africa and moves toward the equator as a western boundary current at long periods 15 000 years milankovitch cycle variability is evident in paleochemical time series but rapid millennial scale variability can be seen in cores from high accumulation rate series atlantic deep water chemical properties are seen to change in as little as a few hundred years or less an extraordinary new 52 7 m long core from the bermuda rise contains a faithful record of climate variability with century scale resolution sediment composition can be linked in detail with the isotope stage 3 interstadials recorded in greenland ice cores this new record shows at least 12 major climate fluctuations within marine isotope stage 5 about 70 000 130 000 years before the present

millennial scale climate variability in the subpolar north atlantic ocean during the late pliocene 1 large amplitude millennial scale climate oscillations have been identified in late pleistocene climate archives from around the world these oscillations appear to be of larger amplitude during times of enlarged ice sheets this observation suggests the existence of a relationship between large amplitude millennial variations in climate and extreme glacial conditions and therefore that the emergence of millennial scale climate variability may be linked to the pliocene intensification of northern hemisphere glaciation inhg here we test this hypothesis using new late pliocene high resolution 400 year records of ice rafted debris deposition and stable isotopes in planktic foraminiferal calcite globigerinoides ruber generated from integrated ocean drilling program site u1313 in the subpolar north atlantic a reoccupation of the classic deep sea drilling project site 607 our records span marine oxygen isotope stages mis 103 95 2600 to 2400 ka the first interval during inhg 3 5 to 2 5 ma in which large amplitude glacial interglacial cycles and inferred sea level changes occur our records reveal small amplitude variability at periodicities of 1 8 to 6 2 kyr that prevails regardless of inter glacial state with no significant amplification during the glacials mis 100 98 and 96 these findings imply that the threshold for the amplification of such variability to the proportions seen in the marine archive of the last glacial was not crossed during the late pliocene and in view of all available data likely not until the mid pleistocene transition

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

mid to late holocene organic carbon export variability at the southern boundary of the california current an approach based on diffuse spectral reflectance of marine sediment cores here we present the results obtained from diffuse spectral reflectance dsr on the visible wave spectra on a 4 5 m long calypso kasten core md02 2506 c2 collected from the san lazaro basin slb with the aim of reconstructing the mid to late holocene variability in export production in the california current system ccs we applied an r mode maximum likelihood factor analysis on the first derivative of the diffuse spectral reflectance we then compared the factor scores obtained with this method and the organic carbon oc content of the core in order to establish a statistical transfer function between both variables we eliminated high frequency noise with the aid of singular spectral analysis ssa from both records increasing the correlation between both variables r 0 71 p 0 001 these results indicated that dsr can be used as a reliable proxy of the oc content in high resolution slb sediments which we used to reconstruct past ccs organic carbon export variability our findings suggest changes in organic carbon production and export from the mid to late holocene most likely resulting from changing influences on the slb due to the interaction of the pacific decadal oscillation pdo and el nino

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

environmental change during the penultimate glacial cycle a high resolution pollen record from odp site 1144 south china sea abstract in order to study environmental change within the penultimate glacial cycle mis 6 5 a total of 385 pollen samples with an average time resolution of 530 years were analyzed from odp site 1144 20 3 18 n 1170 25 14 e northeastern south china sea a characteristic feature of pollen diagram is the alternating peaks of pine and herbs generally corresponding to the glacial cycle pine dominates in the interglacial herb pollen dominates in the glacial a detailed comparison shows that the pollen assemblages changed earlier at the glacial interglacial transition between mis 6 and 5 termination ii than the ice volume indicated by the oxygen isotope record implying that mid low latitude climate warming preceded high latitude ice sheet retreat responses of pollen assemblages to orbital and suborbital cyclicities and to monsoon variations are also discussed

threshold behavior of millennial scale variability in deep water hydrography inferred from a 1 1 ma long record of sediment provenance at the southern gardar drift 1 integrated ocean drilling program iodp site u1314 of the north atlantic is a critical sedimentary archive record of subpolar deep water from the southern gardar drift for which we derived an age model of orbital resolution for the last 1 8 ma this chronology combined with high resolution cm scale x ray fluorescence core scanning measurements of major elements allows tracking changes in terrigenous provenance during the last 1 1 ma low potassium to titanium k ti ratios reflect enhanced transport of basalt derived titanomagnetites during warm climate intervals while high k ti ratios indicate a dominance of acidic sediment sources typical for glacial and stadial events changes in k ti and magnetic concentration at site 1314 are coeval with fluctuations in smectite content and grain size data from nearby piston cores suggesting that the provenance changes are mainly controlled by variable flow of the iceland scotland overflow water an important branch of north atlantic deep water furthermore k ti variations on orbital time scales show a striking similarity to the deep sea 13c record from odp site 607 pervasive features of the k ti time series during and after the mid pleistocene transition are suborbital changes similar to dansgaard oeschger and bond oscillations that appear to be strongly amplified during ice growth phases when global benthic 18o was within the range of 4 1 4 6 per mil the strong increase in variability of sediment provenance and subsequently deep hydrography at benthic 18o values below 4 1 suggests that the extent of glaciations and therefore sea level corresponding to this value constitutes an important physical threshold that was persistent at least for the last 1 1 ma

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

exploring globorotalia truncatulinoides coiling ratios as a proxy for subtropical gyre dynamics in the northwestern atlantic ocean during late pleistocene ice ages we explore the use of the coiling direction of planktic foraminifer globorotalia truncatulinoides in sediment cores from the northwestern subtropical atlantic ocean as a proxy for variations in the intensity of the western boundary of the subtropical gyre over the past 280 kyr core top sediments from the study region are dominated by the left coiling variety consistent with the deep permanent thermocline at the study sites knr140 37pc and ocean drilling program site 1059 downcore g truncatulinoides sinistral maxima occur in conjunction with 14 out of the 25 northern and southern hemisphere precession maxima contained in the study interval the agreement between the dominance of left coiling tests and the precession index of the southern hemisphere in particular supports a link between a deep thermocline in the northwestern subtropical atlantic and northward flow of equatorially sourced warm surface currents a situation analogous to the late holocene interglacial marine oxygen isotope stage mis 5 lacks g truncatulinoides s minima attesting to the relative stability of the western boundary during an interval of prolonged global warmth g truncatulinoides s disappear during the glacial extremes of mis 2 6 and 8 implying a weaker western boundary current at these times our results support that the coiling direction of this species is sensitive to variations in hydrography of the western boundary of the subtropical gyre because of the association between g truncatulinoides s and precession maxima in both hemispheres results support the importance of oceanic heat transport in half precession climate variability in the north atlantic

nonlinear variability of the climatic system from singular and power spectra of late quaternary records stable isotope records from seven marine cores and one ice core provide invaluable information on the intricate behavior of the climatic system over time scales of 104 to 105 years these records in conjunction with a simple coupled climate model help us understand major mechanisms of paleoclimatic variability the time intervals covered by the records include the last glacial interglacial cycle in spite of the difference in the nature of the records common features are revealed by advanced spectral analysis tools the dominant features are the presence of orbital frequencies on the one hand and a low number of internal degrees of freedom on the other the climatic system appears therefore to act on the quaternary time scales considered as a forced nonlinear oscillator the internal mechanisms giving rise to the aperiodic oscillations include ice albedo feedback precipitation temperature feedback and interactions between the ice sheets and the bedrock

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

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

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

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

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

sediment color record from the northeast atlantic reveals patterns of millennial scale climate variability during the past 500 000 years a 500 000 yr long deep sea sediment color record from the northeast atlantic was investigated to reconstruct the evolution of late pleistocene climate variability on millennial time scales variations of the red green color intensity are probably caused by climatically induced changes in the ice rafted input of red colored iron bearing terrigenous material to the core site the resolution of the age model impedes the detection of distinct spectral features at sub milankovitch periodicities hence millennial scale climate variability is quantified as time dependent variance of the high pass filtered color time series the course of the estimated variance shows distinct patterns which can be linked to continental ice mass during the past 500 000 yr large amplitude millennial scale climate variability occurs only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 40 of the lowering during the last glacial maximum

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

high frequency climate linkages between the north atlantic and the mediterranean during marine oxygen isotope stage 100 mis100 high resolution records of mediterranean and north atlantic deep sea sediments indicate that rapid changes in hydrology and climate occurred during marine oxygen isotope stage 100 mis100 at 2 52 ma which exhibits characteristics similar to late pleistocene dansgaard oeschger bond cycles and heinrich events as in the late pleistocene north atlantic oceanographic and atmospheric changes were probably transmitted into the mediterranean by some combination of surface water inflow and atlantic mediterranean atmospheric pressure gradients our data suggest that the mechanism s responsible for sub milankovitch and millennial scale climate oscillations were the same over at least the past 2 6 ma notwithstanding the transition from the 41 kyr dominated glacial cycles of the late pliocene to the 100 kyr cycles of the late pleistocene

why does the amazon water flow to the north after its discharge abstract through a simple model it is demonstrated that earth s sphericity the beta effect imposes a severe constraint on the discharge pattern near the equator using either bottom or lateral friction to counter the beta effect in the vorticity balance the flow in the far field is confined to boundary layers either along the solid boundaries that are open on the anticyclonic side or along the equator to the west of the point source thus for all possible orientation of the radial boundaries flanking the point source there are either one or two branches receptive of the discharge in the far field depending on whether the open angle spanned by the two boundaries excludes the east direction even when the branching is permissible it is further argued based on symmetry of the governing equation that the outflow is strongly favored toward the branch that deviates more from the east direction numerical solutions show that the bulk of the diversion of the discharge to this branch occurs within one fri

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

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

paleomagnetic record at odp site 980 feni drift rockall for the past 1 2 myrs 1 a detailed record of variations in the direction and intensity of the geomagnetic field over the past 1 2 myrs has been obtained from an 120 m thick sedimentary section cored at odp site 980 on the feni drift north atlantic the record has high resolution due to high mean sedimentation rates 11 3 cm kyr for the brunhes chron and 5 5 cm kyr for the matuyama chron paleomagnetic measurements every 1 cm along u channel samples and high quality isotopic age control the iceland basin event is manifest by virtual geomagnetic poles crossing the equator at 190 ka the base of the recovered section lies immediately below the cobb mountain subchronozone that occurs within marine isotope stage 35 normalized remanence data can be correlated to paleointensity records from odp sites 983 and 984 700 km to the nw from site 980 and with lower resolution paleointensity data from the pacific ocean differences between the site 980 paleointensity record and the pacific records are attributed to variable sedimentation rates variable quality age control and inadequacies in the normalization procedure used to derive the paleointensity proxies

geomagnetic palaeointensities and astrochronological ages for the matuyama brunhes boundary and the boundaries of the jaramillo subchron palaeomagnetic and oxygen isotope records from odp site 983 we have measured relative geomagnetic palaeointensity proxies palaeomagnetic directions and 18 o for the 700 1100 ka interval from odp site 983 gardar drift north atlantic where mean sedimentation rates are ca 13 cm kyr 1 the age model was generated by matching the benthic 18 o data to the ice volume model and confirmed by tuning the precessional components of both signals for the matuyama brunhes boundary mbb and the boundaries of the jaramillo subchronozone the duration of the polarity reversal process defined by virtual geomagnetic polar latitudes of less than 45 is ca 5 kyr whereas the generally accepted astrochronological estimates for the boundaries of the jaramillo subchronozone lie within the polarity transitions as recorded at site 983 the astrochronological age for the matuyama brunhes polarity transition 780 ka is ca 5 kyr older than the onset of this transition at site 983 775 ka the polarity reversals lie within palaeointensity lows with abrupt recovery of palaeointensity post reversal there is no progressive sawtooth decrease in palaeointensity within the jaramillo subchronozone or between the top of the jaramillo and the mbb but rather within polarity chrons several short intervals of low palaeointensity which sometimes coincide with high amplitude secular variation orbital 100 and 41 kyr periods are present in the palaeointensity record as they are not obviously attributable to climate lithology in these records they may be a feature of the geomagnetic field itself

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

orbital and suborbital climate variability in the sulu sea western tropical pacific 1 a detailed record of planktic 18o from a sediment core in the sulu sea located between the south china sea and the western pacific warm pool reveals that for the past 400 kyr 1 kyr 1000 years 18o variability on orbital timescales is similar to that caused by changes in ice volume alone this result indicates that in the sulu sea temperature driven changes in planktic 18o on orbital times scales were generally compensated for by the effects of sea level and changes in seasonal monsoon intensity on the local freshwater budget as well as by other changes in the tropical hydrologic cycle and their attendant effects on surface water 18o increased freshening of the western tropical pacific warm pool is reminiscent of la nina conditions however we argue that the mean tropical climate state was not more la nina like than today on broader spatial scales suborbital variability occurred in the sulu sea throughout the past 400 kyr suggesting little sensitivity to ice volume or to glacial interglacial changes in tropical hydrology variations on 4 10 kyr timescales appear to be linked to those in the north atlantic region suggesting a common forcing of that variability we suggest that sulu sea salinity variations were a response to suborbital climate variability in the north atlantic region transmitted via changes in the intensity of the east asian summer monsoon we suggest that a north atlantic origin of that tropical suborbital variability can be reconciled with weak glacial amplification in the tropics if the tropical response is nonlinear

major pleistocene stages in a carbon perspective the south china sea record and its global comparison 1 carbon isotope sequences at ocean drilling program site 1143 south china sea reveal a long term cyclicity of 500 kyr that is superimposed on the glacial cycles and is present in long 13c sequences from all oceans the quaternary 13c record is punctuated by four 13c maximum events 13cmax i which began in marine isotope stage mis 3 around 50 60 kyr ago 13cmax ii mis 13 0 47 0 53 ma 13cmax iii mis 27 29 0 97 1 04 ma and 13cmax vi mis 53 57 1 55 1 65 ma as the same cyclicity is also found in carbonate curves the 13cmax events must denote major reorganization in the carbon reservoir of the global ocean they also are associated with major changes in glacial cyclicity such as the mid brunhes event following 13cmax ii and the mid pleistocene revolution following 13cmax iii which in turn were associated with expansion of the ice sheets from a carbon perspective therefore the quaternary period has passed through three major stages and each appears to represent a further step in ice cap development

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

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

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