stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

tectonic implications of rapid cooling of lower plate rocks from the buckskin rawhide metamorphic core complex west central arizona lower plate rocks exposed in the buckskin rawhide metamorphic core complex west central arizona underwent a pronounced increase in cooling rate 7 12 m y after the onset of extensional tectonic denudation at ca 27 ma a detailed 40 ar 39 ar study of lower plate rocks exposed near planet peak in the southwest part of the core complex indicates that the highest level mylonitic rocks exposed in the complex cooled below 350 c prior to 20 1 ma at an average rate of 15 c m y thereafter the cooling rate of these rocks increased progressively peaking at 280 80 c m y prior to initial exposure of the core between 15 1 and 13 3 ma published k ar 40 ar 39 ar and fission track ages for the most recently unroofed lower plate rocks exposed at the northeastern end of the core complex are consistent with a similar cooling history although the abrupt increase in cooling rate occurred as many as 5 m y later in this area because the increase in the cooling rate appears to have occurred progressively later toward the northeast it is unlikely to reflect changes in slip rate it appears to have coincided with cooling below 350 300 c and thus is interpreted to reflect steepening of the detachment system above the brittle ductile transition thermochronological data from lower plate rocks in the planet peak area together with constraints on their initial exposure at the surface are consistent with an increase in the dip of the detachment from le 5 at midcrustal depths where it was represented by a shear zone to at temperatures below 200 150 c lower plate rocks at both ends of the core complex probably cooled at rates 130 c m y which can not be reconciled with the average dip le 25 and slip rate 6 12 mm yr for the detachment fault given the likely geothermal gradient 25 c km during the early stages of extension this implies that cooling did not keep pace with denudation at upper crustal levels the very high cooling rates are interpreted to have primarily reflected the development of a pronounced thermal discontinuity across the detachment fault possibly 100 c as hot lower plate rocks were transported to shallow crustal levels rapid cooling of the lower plate at these levels may have been enhanced by interaction with fluids derived from the upper plate consistent with models that link the shallow level

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

relative paleointensity rpi in the latest pleistocene 10 45 ka and implications for deglacial atmospheric radiocarbon abstract we report magnetic properties and relative paleointensity rpi proxies from a suite of 10 conventional piston cores and kasten cores from the sw iberian margin collected during cruise jc089 of the rss james cook in august 2013 mean sedimentation rates are in the 10 20 cm kyr range age models were acquired by correlation of ca ti and zr sr xrf core scanning data to l reflectance from the cariaco basin that is in turn tied to the greenland ice core chronology the natural remanent magnetization nrm is represented by a single magnetization component carried by a low coercivity mineral magnetite although reflectance and bulk magnetic properties indicate the presence of a high coercivity hematitic magnetic phase possibly from eolian dust the presence of fine grained hematite means that the sediments are not ideal for rpi studies however the detrital hematite does not appear to contribute to the nrm or anhysteretic remanent magnetization arm in order to test the usefulness of the rpi data we construct a stack of 12 rpi records from the sw iberian margin for the 0 45 ka interval and compare it with a stack of 12 globally distributed marine and lake records chosen on the basis of mean sedimentation rates 15 cm kyr and superior age models the two stacks are similar but different from published rpi stacks particularly for the 10 30 ka interval and imply a virtual axial dipole moment vadm high at 15 18 ka followed by a drop in field strength from 15 to 13 ka a revised vadm estimate calculated from greenland 10be ice core flux using a contemporary age model is remarkably consistent with the new overall rpi stack based on iberian margin and global rpi records the elevated atmospheric 14c levels of the last ice age cannot however be fully explained by this rpi stack although relative changes such as the long term drop in atmospheric 14c from 30 to 15 ka are reproduced supporting the hypothesis of a combined influence of production rate and ocean ventilation on 14c during the last ice age

absolute calibration of the greenland time scale implications for antarctic time scales and for δ14c abstract we propose a new age scale for the two ice cores grip and gisp2 that were drilled at greenland summit based on accelerator mass spectrometry 14c dating of foraminifera in core md95 2042 paleoceanography 15 2000 565 calibrated by means of recently obtained paired 14c and 230th measurements on pristine corals marine radiocarbon calibration curve spanning 10 500 to 50 000 years bp thousand years before present based on paired 230th 234u 238u and 14c dates on pristine corals geological society of america bulletin 2003 submitted for publication the record of core md95 2042 can be correlated very precisely to the greenland ice cores between 30 and 40 ka bp our scale is 1 4 ka older than the grip ss09sea time scale journal of quaternary science 16 2001 299 at the older end of marine isotope stage 3 we use published 230th dates from speleothems to calibrate the record using this scale we show a 14c record that is broadly consistent with the modelled record earth planet sci lett 200 2002 177 and with the data of hughen et al science 303 2004 202 but not consistent with the high values obtained by beck et al science 292 2001 2453 or by voelker et al radiocarbon 40 1998 517 we show how a set of age scales for the antarctic ice cores can be derived that are both fully consistent with the greenland scale and glaciologically reasonable

geomagnetic dipole strength and reversal rate over the past two million years independent records of relative magnetic palaeointensity from sediment cores in different areas of the world can be stacked together to extract the evolution of the geomagnetic dipole moment1 2 and thus provide information regarding the processes governing the geodynamo so far this procedure has been limited to the past 800 000 years 800 kyr ref 3 which does not include any geomagnetic reversals here we present a composite curve that shows the evolution of the dipole moment during the past two million years this reconstruction is in good agreement with the absolute dipole moments derived from volcanic lavas which were used for calibration we show that at least during this period the time averaged field was higher during periods without reversals but the amplitude of the short term oscillations remained the same as a consequence few intervals of very low intensity and thus fewer instabilities are expected during periods with a strong average dipole moment whereas more excursions and reversals are expected during periods of weak field intensity we also observe that the axial dipole begins to decay 60 80 kyr before reversals but rebuilds itself in the opposite direction in only a few thousand years

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

paleomagnetism of lake van sediments chronology and paleoenvironment since 350 ka abstract in the framework of the paleovan project a high resolution paleomagnetic and rock magnetic study was carried out on a 149 m sedimentary sequence recovered from ahlat ridge in the deepest part of the lake van eastern turkey icdp site 5034 2 high sedimentation rates average 30 cm ka allow high resolution measurements of natural remanent magnetization nrm magnetic susceptibility anhysteretic remanence arm and hence of anhysteretic susceptibility arm over the last 350 ka the carrier of the remanence is detrital titanomagnetite largely from volcanic sources based on the similarity of magnetite grain size of tephra layers and the other lacustrine lithologies observed in a plot of the versus arm bulk magnetic parameters often covary with paleoclimatic signals in the lake van sediments a correlation exists between variations of and arm intensity and glacial interglacial marine isotopic stages as well as dust flux and temperatures observed in ice cores from greenland and antarctica the quality of the paleomagnetic record is compromised by weak nrm intensities as well as by the presence of tephra and turbidites throughout the sequence nonetheless a correlation is observed between the relative paleointensity rpi record based on nrm arm and the calibrated piso rpi stack that supports the independently derived age model for the site

magnetic record of deglaciation using forc pca sortable silt grain size and magnetic excursion at 26 ka from the rockall trough ne atlantic research supported by us nsf grants 0850413 and 1014506 and the european research council under the european union s seventh framework programme fp 2007 2013 erc grant agreement no 320750 the uk nerc and bgs funded the recovery of core md04 2822

chlorine 36 evidence for the mono lake event in the summit grip ice core abstract a distinct peak has been discovered in the 36 cl data from the grip ice core between the dansgaard oeschger d o events 6 and 7 at approximately 32 kyr bp this peak can be attributed to a minimum of the geomagnetic dipole field associated with the mono lake event since the 36 cl peak reflects a higher production rate of all cosmogenic radionuclides it has an impact on the 14 c dating of the last ice age furthermore it provides an additional time marker similar to a peak found earlier corresponding to the laschamp event at approximately 39 kyr bp

beryllium 10 in the greenland ice core project ice core at summit greenland concentrations of the cosmogenic isotope 10be have been measured in more than 1350 samples from the greenland ice core project grip ice core drilled at summit greenland although a dust associated component of 10be retained by 0 45 m filters in some of the samples complicates the interpretations the results confirm that the first order origin of 10be concentration variations is changes in precipitation rate associated with different climate regimes this effect is seen not only between glacial and interglacial periods but also during the shorter dansgaard oeschger interstadials by contrast the 10be data do not support the interpretation of rapidly varying accumulation i e climate during the last interglacial they can however be used to help place limits on the origin of the ice in these events after taking into account variable snow accumulation effects variations in the 10be flux are observed probably caused by solar and geomagnetic modulation but possibly also by primary cosmic ray variations the most dramatic is a 10be peak 40 000 years ago similar to that found in the vostok ice core thus permitting a very precise correlation between climate records from arctic and antarctic ice cores the 36cl 10be ratio considering either total or only ice associated 10be shows significant variability over the whole core depth thus confirming the difficulty in using this parameter for dating ice cores

a 580 kyr paleomagnetic record from the sub antarctic south atlantic ocean drilling program site 1089 1 we report geomagnetic directional paleosecular variation relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth mcd at south atlantic ocean drilling program odp site 1089 40 56 2 s 9 53 64 e 4620 m water depth the age model is provided by high resolution oxygen isotope stratigraphy augmented by radiocarbon dates from the upper 8 mcd of nearby piston core rc11 83 mean sedimentation rates at site 1089 are in the range of 15 to 20 cm kyr two intervals during the brunhes chron at 29 6 mcd 190 ka and at 48 mcd 335 ka have component magnetization directions with positive reverse polarity inclination however the excursional directions are heavily overprinted by the postexcursional field magnetite is the dominant carrier of magnetic remanence and occurs in the pseudosingle domain psd grain size an additional higher coercivity magnetic carrier characterized by low unblocking temperatures 350 c is assumed to be authigenic pyrrhotite a decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate indicating diagenetic reduction of magnetite despite down core changes in magnetic mineralogy normalized intensity records from site 1089 are comparable with high resolution paleointensity records from the north atlantic e g odp sites 983 and 984 sediment properties and sedimentation patterns within the cape site 1089 and iceland sites 983 and 984 basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation variations in normalized intensity from site 1089 therefore appear to reflect changes in global scale geomagnetic field intensity

timing of quaternary geomagnetic reversals and excursions in volcanic and sedimentary archives abstract we review the ages of quaternary magnetic polarity reversals and magnetic excursions improvements in radioisotopic 40ar 39ar dating of reversals and excursions reflect the use of multi collector mass spectrometers along with ultra low backgrounds laser based incremental heating methods and adoption of 28 201 ma for the fish canyon sanidine fcs standard age kuiper et al 2008 these improvements have brought 40ar 39ar ages of reversals and excursions into close correspondence with astrochronological ages based on the correlation of 18o data to lr04 lisiecki and raymo 2005 and in a few cases correlation to ice core chronologies ages of two polarity reversals the matuyama brunhes boundary and base olduvai are at odds with ages given in popular geomagnetic polarity timescales sedimentary records of the laschamp and iceland basin excursion are numerous and widespread and attest to global manifestation and global synchronicity of these excursions records of other quaternary excursions are less numerous the blake excursion 115 ka has been recorded in north atlantic sediments chinese loess indian ocean volcanics and spanish speleothems the santa rosa excursion 932 ka has been recorded in north atlantic and phillipine basin sediments as well as in volcanic rocks from new mexico and galapagos the punaruu excursion 1115 ka has been observed in sediments from the north atlantic and california margin as well as in volcanic rocks on tahiti uniformity of individual excursion ages using astrochronological 40ar 39ar and u th methods argues for synchronous global manifestation of excursions strengthening the usefulness of magnetic excursions and reversals in quaternary stratigraphy

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

a high resolution 60 kyr record of the relative geomagnetic field intensity from lake towuti indonesia abstract past changes in the earth s magnetic field can be highlighted through reconstructions of magnetic paleointensity many magnetic field variation features are global and can be used for the detailed correlation and dating of sedimentary records on the other hand sedimentary magnetic records also exhibit features on a regional rather than a global scale therefore the development of regional scale magnetic field reconstructions is necessary to optimize magnetic paleointensity dating in this paper a 60 thousand year kyr paleointensity record is presented using the core tow10 9b of lake towuti located in the island of sulawesi indonesia as a part of the ongoing research towards understanding the indonesian environmental history and reconstructing a high resolution regional magnetic record from dating the sediments located in the east sulawesi ophiolite belt the bedrock surrounding lake towuti consists of ultramafic rocks that render the lake sediments magnetically strong creating challenges in the reconstruction of the paleointensity record these sediment samples were subject to a series of magnetic measurements followed by testing the obtained paleointensity records resulting from normalizing natural remanent magnetization nrm against different normalizing parameters these paleointensity records were then compared to other regional as well as global records of magnetic paleointensity the results show that for the magnetically strong lake towuti sediments an anhysteretic remanent magnetization arm is the best normalizer a series of magnetic paleointensity excursions are observed during the last 60 kyr including the laschamp excursion at 40 kyr bp that provide new information about the magnetic history and stratigraphy of the western tropical pacific region we conclude that the paleointensity record of lake towuti is reliable and in accordance with the high quality regional and global trends

rapid transient changes in northeast atlantic deep water ventilation age across termination i 1 a sequence of accelerator mass spectrometry ams 14c dates performed on benthic and planktonic foraminifera from a northeast atlantic deep sea core md99 2334k 37 48 n 10 10 w 3146 m permit the reconstruction of deep water 14c ventilation ages across the last deglaciation the records from md99 2334k have been placed on the gisp2 timescale via the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ calcite 18o on the basis of a range of estimates for past source water 14c this permits the estimation of 14c projection ventilation ages for comparison with benthic planktonic 14c age differences although the accurate estimation of past ventilation ages is precluded by unknown deep water 14c source signatures and by uncertainty regarding the extent of deep water mixing it is clear that deep water ventilation in the northeast atlantic was significantly reduced during the last glaciation increased abruptly coincident with the bolling allerod warming and rapidly became reduced again during the younger dryas cold reversal the character of these changes is consistent with a varying dominance of north atlantic deep water nadw versus antarctic bottom water aabw parallel benthic 13c deep water temperature tdw and deep water 18o 18odw estimates support this inference the fact that deglacial changes in the deep water radiocarbon content of the northeast atlantic run parallel to opposite changes in atmospheric radiocarbon content and in parallel with greenland temperature fluctuations unequivocally implicates changes in ocean circulation in deglacial climate evolution and illustrates the capacity for the deep ocean to respond and contribute to abrupt climate change

improvements in long core measurement techniques applications in palaeomagnetism and palaeoceanography we report on new developments in the long core measurement techniques using u channels in connection with new small access cryogenic magnetometers with these new instruments u channel samples allow us to measure a wide range of magnetic parameters along entire core length with a spatial resolution and accuracy virtually equivalent to that obtained using discrete cubic samples an additional advantage is that the sediment disturbance when sampling is significantly less when using u channels we present comparisons of results from both continuous and discrete measurements and examine the effectiveness of minimal deconvolution using various techniques examples of continuous measurements of low field susceptibility nrm arm irm hrc from north atlantic deep sea cores show that it is possible to generate logs of combination of parameters related to rock magnetic characteristics of the sediments useful in palaeoceanography in particular the continuous method allows us to rapidly detect core regions with fast changing magnetic parameters useful for correlation between cores and also for understanding changes in palaeo environmental conditions the fast scan also allows us to detect regions of the core where the rock magnetic parameters are suitable or not suitable for palaeomagnetic studies related to changes in the geomagnetic field such as the relative changes in palaeointensity

geomagnetic moment variation and paleomagnetic excursions since 400 kyr bp a stacked record from sedimentary sequences of the portuguese margin abstract a paleomagnetic study was performed in clayey carbonate sedimentary sequences deposited during the last 400 kyr on the portuguese margin northeast atlantic ocean declination and inclination of the stable remanent magnetization present recurrent deviations from the mean geomagnetic field direction the normalized intensity documents a series of relative paleointensity rpi lows recognized in other reference records three directional anomalies occurring during rpi lows chronologically correspond to the laschamp excursion 42 kyr bp the blake event 115 122 kyr bp and the icelandic basin excursion 190 kyr bp a fourth directional anomaly recorded at 290 kyr bp during another rpi low defines the portuguese margin excursion four non excursional rpi lows are recorded at the ages of the jamaica pringle falls mamaku calabrian ridge 1 and levantine excursions the rpi record is characterized by a periodicity of 100 kyr paleointensity lows often coinciding with the end of interglacial stages this record sets the basis of the construction of an authigenic 10be 9be record from the same sedimentary sequences carcaillet et al this issue

authigenic 10be 9be ratio signatures of the cosmogenic nuclide production linked to geomagnetic dipole moment variation since the brunhes matuyama boundary geomagnetic dipole moment variations associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium 10 10 be production rates authigenic 10 be 9 be ratios proxy of atmospheric 10 be production from oceanic cores therefore complete the classical information derived from relative paleointensity rpi records this study presents new authigenic 10 be 9 be ratio results obtained from cores md05 2920 and md05 2930 collected in the west equatorial pacific ocean be ratios from cores md05 2920 md05 2930 and md90 0961 have been stacked and averaged variations of the authigenic 10 be 9 be ratio are analyzed and compared with the geomagnetic dipole low series reported from global rpi stacks the largest 10 be overproduction episodes are related to dipole field collapses below a threshold of 2 10 22 am 2 associated with the brunhes matuyama reversal the laschamp 41 ka excursion and the iceland basin event 190 ka other significant 10 be production peaks are correlated to geomagnetic excursions reported in literature the record was then calibrated by using absolute dipole moment values drawn from the geomagia and pint paleointensity value databases the 10 be derived geomagnetic dipole moment record independent from sedimentary paleomagnetic data covers the brunhes matuyama transition and the whole brunhes chron it provides new and complementary data on the amplitude and timing of millennial scale geomagnetic dipole moment variations and particularly on dipole moment collapses triggering polarity instabilities

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

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

geomagnetic field excursion recorded 17 ka at tianchi volcano china new 40ar 39ar age and significance new 40ar 39ar dating of a comenditic lava atop tianchi volcano china indicates eruption at 17 1 0 9 ka the flow interior records a pair of transitional virtual geomagnetic poles and a low paleointensity of 25 t thus it records a geomagnetic field excursion that is younger than the 41 ka laschamp or 32 ka auckland excursions implications are 1 following a repose of several tens of kyr tianchi volcano became highly active immediately following termination of the last glaciation maximum the flare up of silicic eruptions may reflect rapid deglaciation of the edifice 2 a 17 ka age for the tianchi excursion provides the first direct radioisotopic evidence that excursional behavior which is imprecisely dated and less well documented magnetically at several other sites is a global feature of geodynamo behavior 3 during the brunhes chron 13 well dated excursions cluster into two periods including seven between 17 and 212 ka and six between about 530 and 730 ka

radiocarbon evidence for alternating northern and southern sources of ventilation of the deep atlantic carbon pool during the last deglaciation recent theories for glacial interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a bipolar ventilation seesaw however the viability of this hypothesis has been contested and robust evidence in its support is lacking here we present a record of north atlantic deep water radiocarbon ventilation which we compare with similar data from the southern ocean a striking coherence in ventilation changes is found with extremely high ventilation ages prevailing across the deep atlantic during the last glacial period the data also reveal two reversals in the ventilation gradient between the deep north atlantic and southern ocean during heinrich stadial 1 and the younger dryas these coincided with periods of sustained atmospheric co2 rise and appear to have been driven by enhanced ocean atmosphere exchange primarily in the southern ocean these results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer term global climate transitions

padm2m a penalized maximum likelihood model of the 0 2 ma palaeomagnetic axial dipole moment summary we present a new time varying model for palaeomagnetic axial dipole moment padm for the past 2 myr and compare it with earlier virtual axial dipole moment vadm reconstructions which have been based on stacking and averaging scaled relative palaeointensity records the padm is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood pml approach to recover a cubic b spline representation of axial dipole field variations on million year timescales the pml method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average vadm reconstructions we apply the pml method to a set of 96 032 published data 1800 palaeointensities from igneous rocks 3300 archaeointensities and 86 relative palaeointensity time series of variable lengths and resolutions two models are discussed padm2mp is a trial model based on a subset of the nine longest available sedimentary records padm2m uses a comprehensive data set 76 records 81 446 data 10 records were eliminated and is our preferred model padm2m has a lower mean than existing vadm reconstructions but shows similarities in long period variability some differences in timing amplitude and resolution of certain features can be attributed to variations in age assignments others result from our more comprehensive data set and a reduction in bias attributable to pml modelling padm2m has an average axial dipole moment over 0 2 ma of 5 3 1022 am2 with a standard deviation of 1 5 1022 am2 the brunhes chron average 6 2 1022 am2 is higher than for earlier epochs of matuyama 4 8 1022 am2 as seen in some previous studies the power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 102 myr 1 we see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

biogenic magnetite detrital hematite and relative paleointensity in quaternary sediments from the southwest iberian margin magnetic properties of late quaternary sediments on the sw iberian margin are dominated by bacterial magnetite observed by transmission electron microscopy tem with contributions from detrital titanomagnetite and hematite reactive hematite together with low organic matter concentrations and the lack of sulfate reduction lead to dissimilatory iron reduction and availability of fe ii for abundant magnetotactic bacteria magnetite grain size proxies arm and arm irm and s ratios sensitive to hematite vary on stadial interstadial timescales contain orbital power and mimic planktic 18 o the detrital biogenic magnetite ratio and hematite concentration are greater during stadials and glacial isotopic stages reflecting increased detrital magnetite input during times of lowered sea level coinciding with atmospheric conditions favoring hematitic dust supply magnetic susceptibility on the other hand has a very different response being sensitive to coarse detrital multidomain md magnetite associated with ice rafted debris ird high susceptibility and or magnetic grain size coarsening mark heinrich stadials hs particularly hs2 hs3 hs4 hs5 hs6 and hs7 as well as older heinrich like detrital layers indicating the sensitivity of this region to fluctuations in the position of the polar front relative paleointensity rpi records have well constrained age models based on planktic 18 o correlation to ice core chronologies however they differ from reference records e g piso particularly in the vicinity of glacial maxima mainly due to inefficient normalization of rpi records in intervals of enhanced hematite input

south atlantic and north atlantic geomagnetic paleointensity stacks 0 80 ka implications for inter hemispheric correlation recent coring of high deposition rate atlantic sediments has led to the development of north atlantic napis and south atlantic sapis geomagnetic paleointensity stacks the sapis stack comprises five records from the sub antarctic south atlantic 41 471s 6 101e four are from piston cores collected during the ocean drilling program odp leg 177 site survey cruise earth planet sci lett 175 2000 145 the other is odp site 1089 leg 177 j geophys res 2001 submitted for publication all but one 4 pc03 of the sapis cores have oxygen isotope records which are used in conjunction with lithologic and geomagnetic variability to derive an optimized correlation to site 1089 the site 1089 age model is derived by mapping the benthic and planktic isotope data to those from nearby core rc11 83 which has 14 calibrated radiocarbon ages in the 11 41 ka interval below this level the chronology is derived by matching the site 1089 benthic oxygen isotope data to the specmap stack the napis stack comprises six records from a wide area of the north atlantic philos trans r soc ser a 358 2000 1009 correlation between cores was based on marine isotopic stage boundaries augmented by millennial scale features heinrich events and fluctuations in concentration dependent magnetic parameters napis was placed on the gisp2 chronology using the marine to ice core oxygen isotope correlation proposed by voelker et al radiocarbon 40 1998 517 for one of the napis cores in the resulting age model the laschampevent recorded in five of six cores falls in a very narrow o1 kyr age range and coincides with the 10 be and 36 cl peak measured in the ice cores comparison of the two stacks placed on their own independent age models indicates that common millennial scale paleointensity features are preserved although more work is needed to define the true global content of the paleointensity record as well as the precise age of many features it is readily apparent that paleointensity can provide a global correlation tool at a resolution unattainable from isotope data alone r 2002 published by elsevier science ltd

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

changes in the carbon cycle during the last deglaciation as indicated by the comparison of 10be and 14c records the variations in atmospheric radiocarbon c 14 concentration during the last 50 000 years can be attributed to changes in the c 14 production rate due to changes in solar activity the geomagnetic field and or interstellar galactic cosmic ray flux and to changes in the global carbon cycle the relative contributions of these processes is the subject of current debate although the discrepancies between the various reconstructions of the past atmospheric radiocarbon concentration increase with age the relatively good agreement over the last 25 000 years allows a quantitative discussion of the causes of the observed c 14 variations for this period using be 10 measurements from greenland summit ice cores we show that in addition to solar and geomagnetically induced production rate changes significant changes in the carbon cycle have to be considered to explain the measured c 14 concentrations there is evidence that these changes are connected to 1 global deglaciation and 2 climate changes in the north atlantic region on centennial to millennial time scales related to changes in the ocean circulation differences between be 10 and geomagnetic field records however suggest that uncertainties of about 20 still exist in determinations of past changes in the c 14 production rate c 2004 elsevier b v all rights reserved less

relative paleointensity rpi and age control in quaternary sediment drifts off the antarctic peninsula abstract lack of foraminiferal carbonate in marine sediments deposited at high latitudes results in traditional oxygen isotope stratigraphy not playing a central role in quaternary age control for a large portion of the globe this limitation has affected the interpretation of quaternary sediment drifts off the antarctic peninsula in a region critical for documenting past instability of the west antarctic ice sheet wais and antarctic peninsula ice sheet apis here we use piston cores recovered from these sediment drifts in 2015 during cruise jr298 of the rrs james clark ross to test the usefulness for age control of relative paleointensity rpi data augmented by scant 18o data thermomagnetic and magnetic hysteresis data as well as isothermal remanent magnetization irm acquisition curves indicate the presence of prevalent magnetite and subordinate oxidized magnetite maghemite in the cored sediments the magnetite is likely detrital maghemite is an authigenic mineral associated with surface oxidation of magnetite grains which occurs preferentially in the oxic zone of the uppermost sediments and buried oxic zones deposited during prior interglacial climate stages low concentrations of labile organic matter apparently led to arrested pore water sulfate reduction explaining oxic zone burial and downcore survival of the reactive maghemite coatings at some sites maghemitization has a debilitating effect on rpi proxies whereas at other sites maghemite is less evident and rpi proxies can be adequately matched to the rpi reference template published rpi data at odp site 1101 located on drift 4 can be adequately correlated to contemporary rpi templates probably as a result of disappearance dissolution of maghemite at sediment depths 10 m

climatic and oceanographic changes in the northeast atlantic reflected by magnetic properties of sediments deposited on the portuguese margin during the last 340 ka abstract rock magnetic parameters measured along two giant piston cores md95 2040 40 34 n 9 51 w and md95 2042 37 47 n 10 09 w collected off the portuguese margin related to other proxy climatic data have been used to reconstruct magnetic mineralogical changes of in relation to environmental and climatic conditions over the north atlantic western europe and northwest africa during the last three climatic cycles since isotope stage 10 thin discrete layers containing coarse grains of titano magnetite are associated with events of iceberg discharge during heinrich events 1 6 heinrich quat res 29 1988 142 that have equivalent events in isotope stages 5 8 concentrations of fine grained ti magnetite and hematite goethite varying in phase opposition are directly linked with alternations of cold and warm climatic periods spectral analyses of the rock magnetic signals reveal milankovitch periods at 100 and 41 ka confirming the relationship with long term climatic changes at high latitudes the nature ti magnetite and size range of the finest ferrimagnetic fraction as well as its variation suggest a control by deep currents carrying a colloidal clayey fraction from remote sources iceland faeroes mid atlantic ridge variation of hematite goethite contents is linked with transport by rivers and winds from the neighbouring continent a tight correlation with the d o cycles in greenland ice records confirms that north atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka

u channel track for susceptibility measurements 1 a lightweight transportable and inexpensive magnetic susceptibility track for u channel samples is described the track utilizes a sapphire instruments 3 3 cm square coil having a response function of shape similar to that of the 2g enterprises u channel magnetometer and a half peak width of 3 cm the instrument has been calibrated using a u channel standard made of manganese dioxide the software incorporates automated track control and measurement drift correction susceptibility measurements on this system compare favorably with the 45 mm circular bartington loop used for u channel samples at the laboratoire des sciences du climat et de l environnement gif sur yvette france and with data from the whole core susceptibility track aboard the ocean drilling program research vessel joides resolution

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

dynamics of the earth magnetic field in the 10 75 kyr period comprising the laschamp and mono lake excursions new results from the french chaine des puys in a global perspective abstract we report here on a new paleomagnetic directions and intensities and coupled k ar and 40 ar 39 ar analysis of 35 different flows emplaced in the chaine des puys during the 75 to 10 kyr interval which contains the mono lake and laschamp excursions there is a remarkable agreement between the new set of absolute volcanic intensities and published sedimentary glopis 75 and cosmogenic 10 be and 36 cl records the laschamp and mono lake excursions are clearly revealed by a very significant intensity drop at 41 2 1 6 ka and 34 2 1 2 ka respectively the duration of the laschamp excursion is 1500 yr and about 640 yr when the drop of paleointensity or the directional change are considered respectively the intensity drop at the mono lake is twice as short in the 7 ka interval separating the two excursions the field intensity recovers to almost non transitional values the rate of decrease of the field intensity during these excursions attains 18 nt yr for the laschamp and even greater value 33 nt yr for the mono lake this figure is for the laschamp excursion similar to the present field intensity decrease in the last two centuries so that one may wonder whether such a high rate of change may be characteristic of an impending geomagnetic event reversal or excursion we suggest that the name auckland excursion should be used for the present day called mono lake

effects of u th rich grain boundary phases on apatite helium ages abstract single grain apatite u th sm he ages he ages from non detrital samples sometimes show larger dispersions than can be explained by known sources of age dispersion such as grain size radiation damage parent zonation fracturing or intracrystalline inclusions we present observations and model age bias effects of an additional source of apatite he age dispersion observed in some cases u th rich grain boundary phases gbps precipitated on apatite crystal surfaces apatite grains from several samples with dispersed apatite he ages are coated or partially coated by reddish orange gbps rich in fe u and th these gbps are heterogeneous in thickness grain coverage and composition and have effective u concentrations eu up to 1000 ppm these phases may have large effects on the bulk eu and 4he compositions of apatite grains and can produce significant he age biases the direction and magnitude of this age bias is primarily a function of four factors 1 the host grain s size 2 the gbps thickness and eu relative to the host grain 3 the timing of gbp formation relative to the cooling age of the host grain and 4 whether the gbps are preserved and analyzed with the grain during he dating some of the most severe effects occur when gbps formed before or near the time of the apatite cooling age but were lost just prior to analysis for example during mineral separation in this case gbps of commonly observed thicknesses 1 10 m with eu 2 10 times that of the host apatite grain implant enough 4he into typical sized apatite grains to produce hundreds of percent positive age biases in contrast when u th rich gbps are preserved and analyzed with apatite grains the resulting he ages can be negatively biased though the heterogeneity variable preservation and ambiguous formation ages of gbps preclude a general quantitative and practical solution to this problem our model demonstrates that observed age dispersions in some samples are consistent with the effects of u th rich grain boundary phases and illustrates the conditions under which and by how much they will bias he ages

a high resolution authigenic 10be 9be record of geomagnetic moment variations over the last 300 ka from sedimentary cores of the portuguese margin a high resolution study of authigenic be isotopes 10be and 9be combined with continuous relative paleointensity records has been performed along the same marine sedimentary sequences from the portuguese margin n e atlantic covering the past 300 ka in order to assess relationships between geomagnetic moment variations and 10be production rate variations a carefull examination of the various ways of taking into account environmental disturbing effects on the authigenic 10be concentration leads to the conclusion that the most reliable proxy of cosmonuclide production rates is presently the authigenic 10be 9be ratio eight intervals of significant authigenic 10be 9be enhancement evidence geomagnetic moment drops related to global paleomagnetic excursions some being already admitted others being proposed as new geomagnetic features since contrarily to sedimentary magnetic remanence the authigenic 10be 9be records dipole moment variations without significant acquisition delay it provides better constraints on their timing comparison of 10be 9be and benthic 18o records from the same cores suggests that dipole moment lows preferentially occured during or at the end of interglacial episodes with a quasi period of 100 ka

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

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

depositional framework and controls on mixed carbonate siliciclastic gravity flows pennsylvanian permian shelf to basin transect south western great basin usa mixed carbonate siliciclastic sediment gravity flow deposits of late pennsylvanian to early permian age are exposed in the death valley owens valley region of east central california the mexican spring unit constitutes the upper part of the keeler canyon formation and is characterized by turbidites debris flow deposits and megabreccias all of mixed carbonate siliciclastic composition the mixed composition of the keeler canyon formation provides an opportunity to link facies architecture to controls on depositional system development depositional relationships indicate that the deposits represent a non channellized base of slope carbonate apron system with inner outer and basinal facies associations these gravity flow deposits are characterized by repeated stacked small scale 100 m coarsening and thickening upward cycles contemporaneous outer shelf and upper slope deposits of the tippipah limestone are exposed at syncline ridge on the nevada test site the deposits consist of carbonate buildups directly overlain by cross bedded quartz rich sandstone and conglomerate which filled channels that traversed across the previously existing carbonate shelf detritus was transported to the west down the upper slope by gully systems that fed the temporally persistent base of slope apron of the upper part of the keeler canyon formation this style of deposition differs from point sourced siliciclastic submarine fan depositional systems however the keeler canyon system has lithofacies similar to some sandy siliciclastic turbidite systems such as the delta fed submarine ramp facies model which is a line sourced shelf fed system that is not supply limited the mixed clastic apron systems of the keeler canyon formation differ from classical carbonate aprons in that the former is characterized by an abundance of sedimentary cycles controls on the development of these cycles and of the facies distribution may have resulted from changes in type and rate of sediment supply relative sea level changes and or tectonic events interpretation of the data is focused on relative changes in sea level as the most significant control on development of the depositional system relative sea level changes serve two important functions 1 they provide a mechanism for bringing coarse siliciclastic and bioclastic grains together on the outer shelf and 2 shelf margin collapse may be initiated during relative lowstands allowing for transport of the sediment to the deep basin and development of deep basinal cycles therefore an abundance of mixed clastic gravity flow deposits such as these in the rock record may be an indicator of periods of high frequency changes in relative sea level which is a characteristic of late palaeozoic sea level history

geomagnetic field intensity during the last 60 000 years based on 10be and 36cl from the summit ice cores and 14c abstract based on 10 be 36 cl and 14 c records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic the geomagnetic field derived from the 10 be flux to summit in central greenland agrees well with independent geomagnetic field intensity reconstructions however compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20 000 to 30 000 years bp 36 cl from the grip ice core agrees well with the 10 be record for the last ice age and hence also the reconstructed geomagnetic field based on the tree ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the holocene a comparison of radiocarbon based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10 000 years bp

enhanced productivity on the iberian margin during glacial interglacial transitions revealed by barium and diatoms the portuguese margin is at a critical location for studies of the ocean s behaviour during glacial interglacial climatic changes and the rapid accumulation rates of the sediments enable high resolution palaeoclimatic investigation the sedimentary record of the past 350 ka has been investigated in a 35 m long core from 3 5 km water depth on the slope at 40 n by geochemical isotopic and micropalaeontological techniques the caco3 content of this core as a function of time contains significant milankovitch orbital frequencies of 18 8 23 7 38 0 and 100 6 ka but these are driven primarily by dilution by clay flux variations rather than by caco3 productivity variations the largest signals in the productivity indicators corg ba al and diatom abundance are all observed as simultaneous peaks at the oxygen isotope stage boundaries 10 9 and 6 5 with the signal magnitude in the order 10 9 6 5 for all three indicators smaller coincident signals in corg ba al but not diatoms are also observed at the oxygen isotope stage 2 1 boundary other less prominent peaks in the corg and ba al profiles occur elsewhere including heinrich event horizons but these are not always simultaneous and none contain evidence of the dissolution prone diatom microfossils the 10 9 6 5 and 2 1 oxygen isotope stage transitions represent the three most extreme glacial interglacial sea level rises in the past 350 ky possibly in the same sequence of magnitude when sea level rose rapidly by 120 m from glacial low stands to interglacial high stands the productivity signals at these transitions are contained within 5 ka including bioturbation

tertiary sedimentary rocks associated with the harcuvar core complex in arizona u s a insights into paleogeographic evolution during displacement along a major detachment fault system abstract geologic mapping and analysis of oligocene miocene sedimentary rocks in the upper plate of the buckskin rawhide detachment fault system west central arizona reveals a complex paleogeographic history during fault displacement involving shifting sediment source areas and multiple drainage reversals within the study area four upper plate fault blocks are capped by homoclinal sedimentary sections that display fanning dip relationships indicating concurrent tilting and sedimentation during deposition of these strata upper plate sedimentation was intermittently confined to separate half graben while at other times rapid rates of aggradation relative to fault displacement resulted in burial of ridges separating sub basins four sedimentary assemblages recognized within the study area can be correlated between fault blocks on the basis of lithologic similarity stratal position provenance paleocurrent data and sparse geochronologic constraints the basal assemblage consists of lacustrine rocks and interfingering fluvial strata composed of detritus derived from the granitic terrane surrounding the northern part of the study area these sediments were deposited during the earliest stages of tilting of upper plate fault blocks and inferred displacement along the buckskin rawhide detachment fault system the lower assemblage which directly overlies the basal assemblage consists of fine grained lacustrine deposits sandy conglomerate and breccia during lower assemblage deposition mass flow dominated alluvial fans were derived from source areas consisting mainly of mesozoic and paleozoic rocks exposed to the south of the study area these source areas may have been associated with the breakaway fault of the detachment system or with fault blocks stranded above structurally elevated parts of the footwall tilting of fault blocks continued during deposition of the lower assemblage and strongly affected dispersal patterns and lithofacies distributions lacustrine sediments were deposited mainly within large deep sub basins and with few exceptions lower assemblage streams followed half graben axes the middle assemblage consists of conglomerate and sandstone deposited by an extensive south directed stream system that probably flowed off undistended parts of the hanging wall across extended parts and locally onto the footwall tilting of upper plate fault blocks continued during middle assemblage deposition but rapid burial of escarpments by sediment permitted relatively unobstructed southward drainage the upper assemblage consists of sandy conglomerate deposited by a northeast directed system of broad shallow streams these deposits display a variety of clast types including tertiary mylonitic sedimentary and volcanic rocks that were eroded from the upwarped footwall of the core complex and overlying klippen upper assemblage streams maintained relatively consistent northeasterly flow even during the early stages of deposition when some fault blocks were still rotating

palaeomagnetic intensities from 14 c dated lava flows on the big island hawaii 0 21 kyr thellier thellier experiments were carried out on 216 lava samples collected by the usgs on the big island 35 individual flows from the kilauea mauna loa and hualalai volcanoes are represented and independent radiocarbon dating of the flows yields absolute ages ranging from 290 to 20 240 yrs old the palaeomagnetic analysis was carried out at the laboratoire des sciences du climat et de l environnement in gif sur yvette france in two custom built large capacity furnaces that have been specifically designed to minimise oxidation the temperature steps were adapted to accommodate the characteristic loss of magnetisation at low temperatures seen in the curie balance results and the use of half size samples allowed secondary experiments to be carried out where necessary the strict picrit 03 selection criteria were rigorously applied to the data and a high success rate of 53 has been achieved on a sample level the flow averaged results almost double the existing 14c dated palaeointensity dataset for this time window and confirm a period of high intensity over the past 4 kyr preceded by a period in which the dipole moment was weaker however the values attained in this study are on average higher than previously published data reliability of these values is discussed

oversampling of sedimentary series collected by giant piston corer evidence and corrections based on 3 5 khz chirp profiles 1 the depth scale accuracy of marine sedimentary series collected by coring is of key importance for the precise calculation of sedimentation rates and fluxes for three giant piston cores collected during the interpole md99 114 international marine past global changes study images v cruise md99 2227 md99 2246 and md99 2251 the 3 5 khz chirp profiles recorded on board are compared to synthetic seismograms computed from physical property logs measured on cores in each case the perfect match of main deep reflectors requires a significant upward shift of the water sediment w s interface in the synthetic seismograms with respect to the 3 5 khz profiles since no drastic perturbation of the physical property logs is observed this upward shift is interpreted as resulting from a significant sediment oversampling in the upper part of the cores the affected depth intervals are consistent with the thickness of the perturbed zones observed in penetrometry and anisotropy of magnetic susceptibility records 10 15 m to retrieve the true in situ sediment thickness a linear depth correction is applied between consecutive acoustic reflectors to achieve a perfect match between the synthetic seismogram and the corresponding 3 5 khz profiles depth correction laws amount of material excess as a function of initial depth are deduced from this resynchronization procedure first estimations of upper core oversampling rates range from 30 core md99 2227 to 37 core md99 2246 moreover we observe that some undersampling may also exist in the lower part of the sediment cores

cross correlation of cielab color reflectance data from archive photographs and line scan images of sediment archive color photographs particularly of sites where sediment is no longer available are an underused resource that potentially contains detailed paleoenvironmental information to investigate this potential two sets of digital images were taken at different times of loess glaciolacustrine and deep sea sediments the first image set was taken using standard digital cameras lighting conditions and sediment surface preparation varied in a similar way to characteristics likely to be encountered in archive photographs the second image set was taken by a high resolution line scan camera with an integrated light source cielab commission internationale de l eclairage color reflectance data were obtained from both image sets and analyzed by cross correlation of the three reflectance parameters l a and b l reflectance is the most compromised by differences in ambient lighting or moisture content textural distinctions appear to be an important factor influencing the cross correlations and produce multiple relatively weak solutions for the glaciolacustrine sediments whereas the texturally uniform loess and deep sea sediments produce a single best fit solution comparison of a reflectance records from an undated marine sequence with a chronologically constrained sequence from the same site indicates the potential to apply color reflectance to produce preliminary age models

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

high resolution paleomagnetic secular variations and relative paleointensity since the late pleistocene in southern south america abstract paleomagnetic inclination declination and relative paleointensity were reconstructed from the sediments of laguna potrok aike in the framework of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado here we present the u channel based full vector paleomagnetic field reconstruction since 51 2 ka cal bp the relative paleointensity proxy rpi was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the chrm interval nrm arm 10 40 mt a grain size influence on the rpi was removed using a correction based on the linear relationship between the rpi and the median destructive field of the natural remanent magnetisation mdf nrm the new record is compared with other lacustrine and marine records and stacks from the mid to high latitudes of the southern hemisphere revealing consistent millennial scale variability the identification of the laschamp and possibly the mono lake geomagnetic excursions and a direction swing possibly associated to the hilina pali excursion at 20 ka cal bp nonetheless a global scale comparison with other high resolution records located on the opposite side of the earth and with various dipole field references hint at a different behaviour of the geomagnetic field around southern south america at 46 ka cal bp

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

implications for sedimentation changes on the iberian margin over the last two glacial interglacial transitions from 230thexcess 0 systematics abstract the portuguese margin is well suited for studies of the contrasts in north atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate this paper reports a 230thexcess 0 based study of sediment accumulation over the past 140 ky a period which includes the last two glacial interglacial transitions in two cores at 2 4 and 3 5 km water depth on a slope transect at 40 n although the independently determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13 2 and 10 5 g cm 2 ky 1 in the two cores conventional application of the 230thexcess 0 method yields consistently lower fluxes with means of 3 5 and 3 8 g cm 2 ky 1 these 230thexcess 0 estimates are interpreted as representations of the regional depositional flux through time this 230thexcess 0 regional flux is composed of a carbonate flux of

odp site 1063 bermuda rise revisited oxygen isotopes excursions and paleointensity in the brunhes chron an age model for the brunhes chron of ocean drilling program odp site 1063 bermuda rise is constructed by tandem correlation of oxygen isotope and relative paleointensity data to calibrated reference templates four intervals in the brunhes chron where paleomagnetic inclinations are negative for both u channel samples and discrete samples are correlated to the following magnetic excursions with site 1063 ages in brackets laschamp 41 ka blake 116 ka iceland basin 190 ka pringle falls 239 ka these ages are consistent with current age estimates for three of these excursions but not for pringle falls which has an apparent age older than a recently published estimate by 28 kyr for each of these excursions termed category 1 excursions virtual geomagnetic poles vgps reach high southerly latitudes implying paired polarity reversals of the earth s main dipole field that apparently occurred in a brief time span 2 kyr in each case several times shorter than the apparent duration of regular polarity transitions in addition several intervals of low paleomagnetic inclination low and negative in one case are observed both in u channel and discrete samples at 318 ka mis 9 412 ka mis 11 and in the 500 600 ka interval mis 14 15 these category 2 excursions may constitute inadequately recorded category 1 excursions or high amplitude secular variation

a redesigned kasten core barrel and sampling technique abstract a modified kasten core barrel was developed to obtain cores with nearly 100 sediment retrieval while minimizing disturbance of the sediment water interface one side of the 15 15 cm square barrel is doubled by a second movable plate which can be moved upwards by a series of hand screws thus enabling complete sideways extrusion of the core this produces a set of subcores or slabs of equal quality with preserved stratigraphy which can be x rayed subsampled stored or frozen for geochemical studies the new kasten core barrel is effective in rough weather inexpensive to build easy to handle and enables fast core processing on board

uptake of excess co2 by an outcrop diffusion model of the ocean a carbon cycle model is presented in which direct ventilation of intermediate and deep ocean waters in high latitudes is taken into account the 1 dimensional ocean model is an extension of a box diffusion model including a deep sea outcrop at the surface if both are calibrated in a consistent way the outcrop diffusion ocean takes up more excess co2 than the box diffusion ocean because the outcropping deep water is essentially virgin as to fossil co2 two calibration methods are compared using the distribution either of natural or of bomb produced 14c the latter leads to a higher oceanic uptake of excess co2 than the former and to a better agreement with the observed atmospheric increase long term model responses are also discussed

a new high resolution geomagnetic relative paleointensity record for the north american holocene a comparison of sedimentary and absolute intensity data a new high resolution paleointensity record for north america has been constructed using holocene sediments from lake pepin minnesota lake pepin sediments yield the same holocene paleosecular variation curve as nearby lake st croix and satisfy all of the criteria recommended for paleointensity studies absolute paleointensity data for north america recorded by holocene volcanic and archeomagnetic samples provide an independent record of geomagnetic field paleointensity against which the relative intensity records from lake pepin and lake st croix can be compared since the absolute field paleointensity is known a priori the effects of the magnetic recording assemblage can be isolated anhysteretic remanent magnetization arm is the best choice among normalization parameters for the lake pepin sediments as the natural remanent magnetization nrm normalized by arm shows no coherence with magnetic grain size proxies and yields a record of relative paleointensity peaks and troughs whose amplitudes are very similar to those in the archeomagnetic arcmag and lake st croix data sets features with a wavelength of 1000 years are correlative between the three paleointensity records nrm normalized by saturation isothermal remanent magnetization sirm and by susceptibility shows grain size dependences that cause errors in the amplitudes of paleointensity features nrm sirm and nrm are not coherent with their normalizers but are both strongly coherent with independent grain size proxies such as the median destructive field of the nrm and hcr we successfully removed the grain size dependences from nrm sirm by applying a correction function based on the linear relationship between normalized intensity and the median destructive field of the nrm

the laschamp geomagnetic dipole low expressed as a cosmogenic 10 be atmospheric overproduction at 41 ka authigenic 10be 9be ratiomeasurementswere performed at high resolution along a portuguese margin deep sea core 37 48 n 10 09w spanning the 20 50 ka time interval in order to reconstruct variations in atmospheric cosmogenic 10be production rates and derive the related geomagnetic dipole moment modulation a complementary approach consisting in 230thxs normalized 10be deposition rate determination on selected samples confirmed the reliability of the authigenic 10be 9be record this study constitutes the first successful comparison of the two widely used normalization techniques of 10be concentrations for both methods the presented results herein evidence a factor of 2 cosmogenic nuclide overproduction linked to a minimum dipole moment associated with the laschamp excursion the latter is stratigraphically constrained beneath heinrich event 4 its age is estimated at 41 ka on the basis of direct correlation between the series of rapid paleoclimatic events recorded in the portuguese margin sediments and in the greenland ice sheet and is confirmed by calibrated radiocarbon dating carried out on the same sediments the remarkable agreement between the authigenic 10be 9be and the greenland ice cores 10be deposition rate records attests to their global significance this new authigenic 10be 9be record has been combined with that previously obtained at the same site to produce a stacked record that is calibrated using absolute values of virtual dipole moment determined on lava flows this provides a reconstruction of dipole geomagnetic moment variations over the 20 50 ka interval independent frompaleomagnetically constrainedmethods that documents the laschamp dipole low but fails to express any dipole low related to t e mono lake excursion this high resolution record responds to the necessity of supplementing the knowledge of the atmospheric 14c variations in the 30 45 ka interval during which the 14c calibration curve suffers from a lack of accurate data and during which a discrepancy of about 5500 yr between the 14c and u th ages is due to the laschamp geomagnetic dipole low such new high resolution datasets from records obtained from different latitudes will be required to make significant advances in understanding the causes of atmospheric 14c variations

a high resolution record of atmospheric 14c based on hulu cave speleothem h82 abstract the development of a calibration of atmospheric radiocarbon 14c is a significant scientific goal because it provides the means to link the numerous 14c dated paleoclimate records to a common timescale with absolutely dated records and thereby improve our understanding the relationships between the carbon cycle and climate change currently few calibration datasets that directly sample the atmospheric 14c reservoir are available beyond the end of the dendro dated holocene tree ring record at 12 6 kyr bp before 1950 ad in the absence of suitable true atmospheric records 14c calibrations beyond this age limit are based largely on marine data that are complicated by the marine reservoir effect which may have varied over the glacial cycle in this paper we present a high resolution record of u th series and 14c measurements from hulu cave speleothem h82 spanning 10 6 26 8 kyr bp corrections for detrital 230th are negligible and the contribution of 14c free geologic carbon to the speleothem calcite is small 5 6 and is stable across major climate shifts the time series provides a 16 kyr record of atmospheric 14c as well as an updated age model for the existing hulu cave 18o record the 14c data are in good overall agreement with existing marine and terrestrial 14c records but comparisons with the cariaco basin marine 14c record through the deglacial interval reveal that the cariaco reservoir age appears to have varied during parts of the younger dryas and heinrich stadial 1 cold events this highlights the importance of developing extended high resolution marine and terrestrial 14c records as a means of detecting changes in ocean circulation over the glacial cycle

a complete terrestrial radiocarbon record for 11 2 to 52 8 kyr b p radiocarbon 14c provides a way to date material that contains carbon with an age up to 50 000 years and is also an important tracer of the global carbon cycle however the lack of a comprehensive record reflecting atmospheric 14c prior to 12 5 thousand years before the present kyr b p has limited the application of radiocarbon dating of samples from the last glacial period here we report 14c results from lake suigetsu japan 35 35 n 135 53 e which provide a comprehensive record of terrestrial radiocarbon to the present limit of the 14c method the time scale we present in this work allows direct comparison of lake suigetsu paleoclimatic data with other terrestrial climatic records and gives information on the connection between global atmospheric and regional marine radiocarbon levels

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

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

consistent dating for antarctic and greenland ice cores we are hereby presenting a new dating method based on inverse techniques which aims at calculating consistent gas and ice chronologies for several ice cores the proposed method yields new dating scenarios simultaneously for several cores by making a compromise between the chronological information brought by glaciological modeling i e ice flow model firn densification model accumulation rate model and by gas and ice stratigraphic constraints this method enables us to gather widespread chronological information and to use regional or global markers i e methane volcanic sulfate beryllium 10 tephra layers etc to link the core chronologies stratigraphically confidence intervals of the new dating scenarios can be calculated thanks to the probabilistic formulation of the new method which takes into account both modeling and data uncertainties we apply this method simultaneously to one greenland ngrip and three antarctic epica dome c epica dronning maud land and vostok ices cores and refine existent chronologies our results show that consistent ice and gas chronologies can be derived for depth intervals that are well constrained by relevant glaciological data in particular we propose new and consistent dating of the last deglaciation for greenland and antarctic ice and gas records

archeoint an upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment 1 this paper presents a compilation of intensity data covering the past 10 millennia archeoint this compilation which upgrades the one of korte et al 2005 contains 3648 data and incorporates additional intensity and directional data sets a large majority of these data 87 were acquired on archeological artifacts and the remaining 13 correspond to data obtained from volcanic products the present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria we show that 50 of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects potsherds the stability of the magnetization and the data dispersion the temporal and geographical distributions of this sub data set are similar to those of the main data set with 72 of the data dated from the past three millennia and 76 obtained from western eurasia approximately half of the selected intensity data are associated with at least an inclination value to constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western eurasian data we introduce a first order regional weighting scheme based on the definition of eight widely distributed regions of 30 width within which the selected data are numerous enough the regional curves of virtual axial dipole moments vadm and of mixed vadm virtual dipole moments vdm averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components the computation of global vadm and mixed vadm vdm variation curves assuming an equal weight for each region yields a dipole evolution marked by a distinct minimum around 0 b c a d followed by a maximum around the third fourth century a d a second minimum is present around the eighth century a d this variation pattern is compatible with the one deduced from earlier more

a 190 drop in atmosphere s δ14c during the mystery interval 17 5 to 14 5 kyr reconstructions of atmospheric 14c for the deglacial period reveal a 190 10 drop between 17 5 and 14 5 kyr before present during the mystery interval while it appears that the major contributor must be the mixing between an isolated low radiocarbon abyssal reservoir and the remainder of the ocean a combination of 14c measurements on coexisting benthic and planktic foraminifera shells and 13c 12c measurements on benthic foraminifera make it difficult to identify a sufficiently large volume for this reservoir an alternative scenario based on higher 14c production rates between about 38 and 18 kyr ago would escape the need for a large isolated reservoir prior to the mystery interval but instead would call for a better ventilated ocean afterwards the addition of 14c deficient sedimentary carbon appears not to be an important contributor while the unlikely explanation that the half life of 14c is 15 greater than the accepted value 5730 yr would eliminate the steady decrease in the 14c c over the last 40 kyr it would not explain the steep drop which occurred between 17 5 and 14 5 kyr

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

reduced ventilation and enhanced magnitude of the deep pacific carbon pool during the last glacial period it has been proposed that the ventilation of the deep pacific carbon pool was not significantly reduced during the last glacial period posing a problem for canonical theories of glacial interglacial co2 change however using radiocarbon dates of marine tephra deposited off new zealand we show that deep 2000 m 2000 m and shallow sub surface ocean atmosphere 14c age offsets i e reservoir or ventilation ages in the southwest pacific increased by 1089 and 337 yrs respectively reaching 2689 and 1037 yrs during the late glacial a comparison with other radiocarbon data from the southern high latitudes suggests that broadly similar changes were experienced right across the southern ocean if like today the southern ocean was the main source of water to the glacial ocean interior these observations would imply a significant change in the global radiocarbon inventory during the last glacial period possibly equivalent to an increase in the average radiocarbon age 2 km 2 km of 700 yrs 700 yrs simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean s mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric co2 possibly accounting for nearly half of the glacial interglacial co2 change if confirmed these findings would underline the special role of high latitude shallow sub surface mixing and air sea gas exchange in regulating atmospheric co2 during the late pleistocene

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

quaternary magnetic and oxygen isotope stratigraphy in diatom rich sediments of the southern gardar drift iodp site u1304 north atlantic abstract the sediment sequence from integrated ocean drilling program iodp site u1304 53 03 40 n 33 31 78 w water depth 3024 m on the southern gardar drift north atlantic ocean covers the last 1 8 myr with a mean sedimentation rate of 15 cm kyr at site u1304 paleomagnetic directional and relative paleointensity rpi records have been generated for the last 1 5 myr and benthic oxygen isotope data for the last 1 myr the age model for site u1304 was established by matching 18o and rpi data to calibrated reference records prominent intervals of diatom mats at site u1304 are associated with the latter stages of interglacial marine isotope stages mis 9 11 13 15 21 27 and 35 and with the weak glacial of mis 14 the deposition of diatom mats and associated diluted magnetic mineral concentrations leads to weak magnetizations and susceptibilities in these intervals comparison of histograms of paleomagnetic directions and rpi from diatom rich sediments and from surrounding silty clays indicates that although results from diatom rich sediments are more scattered the occurrence of diatom mats does not appreciably distort the paleomagnetic directional and rpi records site u1304 sediments record the matuyama brunhes boundary 772 ka the jaramillo subchron 993 1071 ka and the cobb mountain subchron 1193 1219 ka as well as three apparent geomagnetic excursions in the matuyama chron interpreted as the kamikatsura santa rosa punaruu and gardar excursions at 888 ka 1124 ka and 1463 ka respectively the site u1304 rpi record can be correlated with the piso 1500 rpi stack and with other high resolution rpi records from the north atlantic ocean wavelet analyses performed on the site u1304 rpi record and a new high resolution north atlantic paleointensity stack for the last 1500 kyr hinapis 1500 comprising ocean drilling program odp sites 983 984 and iodp sites u1306 and u1304 did not reveal significant orbital power

links between tropical rainfall and north atlantic climate during the last glacial period the last glacial period was marked by dramatic climate fluctuations sediment records from the cariaco basin and the arabian sea suggest that cooling in the north atlantic region was tightly coupled with a southward displacement of the intertropical convergence zone and a weakening of the indian summer monsoon

persistent link between solar activity and greenland climate during the last glacial maximum changes in solar activity have previously been proposed to cause decadal to millennial scale fluctuations in both the modern and holocene climates1 direct observational records of solar activity such as sunspot numbers exist for only the past few hundred years so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as 10be and 14c from ice cores and tree rings2 3 here we present a high resolution 10be record from the ice core collected from central greenland by the greenland ice core project grip the record spans from 22 500 to 10 000 years ago and is based on new and compiled data4 5 6 using 14c records7 8 to control for climate related influences on 10be deposition we reconstruct centennial changes in solar activity we find that during the last glacial maximum solar minima correlate with more negative 18o values of ice and are accompanied by increased snow accumulation and sea salt input over central greenland we suggest that solar minima could have induced changes in the stratosphere that favour the development of high pressure blocking systems located to the south of greenland as has been found in observations and model simulations for recent climate9 10 we conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and last glacial maximum climate conditions

tectonics of mid tertiary extension along a transect through west central arizona large magnitude miocene extension in west central arizona occurred primarily along three imbricate northeast dipping normal faults the structurally highest of these faults the gently dipping buckskin rawhide detachment fault accommodated approximately 66 km of crustal extension whereas the two structurally lower faults accommodated a total of about 20 km extension due to this large magnitude extension an area at the earth s surface that was 10 to 20 km wide is now over a 100 km wide and crystalline rocks with mid tertiary mylonitic fabrics uncovered by detachment faulting are exposed over roughly 2000 km in the harcuvar metamorphic core complex most of the upper plate of the buckskin rawhide detachment fault was largely undeformed by internal extension only the thin tapered end of the upper plate was highly extended during extension the lower plate must have flexed to conform to the listric underside of the upper plate and to have flattened to its present subhorizontal form as it was uncovered grooves on the underside of the upper plate were apparently imposed on the pliable lower plate as it was denuded forming extension parallel folds in the lower plate low flexural strength characterized the lower plate during denudation and a highly mobile low viscosity deeper crust must have effectively decoupled the upper crust from the mantle lithosphere

response of iberian margin sediments to orbital and suborbital forcing over the past 420 ka here we report 420 kyr long records of sediment geochemical and color variations from the southwestern iberian margin we synchronized the iberian margin sediment record to antarctic ice cores and speleothem records on millennial time scales and investigated the phase responses relative to orbital forcing of multiple proxy records available from these cores iberian margin sediments contain strong precession power sediment redness a and 570 560 nm and the ratio of long chain alcohols to n alkanes c26oh c26oh c29 are highly coherent and in phase with precession redder layers and more oxidizing conditions low alcohol ratio occur near precession minima summer insolation maxima we suggest these proxies respond rapidly to low latitude insolation forcing by wind driven processes e g dust transport upwelling precipitation most iberian margin sediment parameters lag obliquity maxima by 7 8 ka indicating a consistent linear response to insolation forcing at obliquity frequencies driven mainly by high latitude processes although the lengths of the time series are short 420 ka for detecting 100 kyr eccentricity cycles the phase relationships support those obtained by shackleton antarctic temperature and the iberian margin alcohol ratios c26oh c26oh c29 lead eccentricity maxima by 6 kyr with lower ratios increased oxygenation occurring at eccentricity maxima co2 ch4 and iberian sst are nearly in phase with eccentricity and minimum ice volume as inferred from pacific 18oseawater lags eccentricity maxima by 10 kyr the phase relationships derived in this study continue to support a potential role of the earth s carbon cycle in contributing to the 100 kyr cycle

40ar 39ar ages of precambrian manganese ore minerals from sweden india and morocco in order to test their chronometric potential 40ar 39ar stepheating and 4he analyses have been carried out on five manganese ore minerals of the hollandite cryptomelane series from three precambrian manganese deposits ultevis sweden sitapar india bachkoun morocco samples from the metamorphic occurrences ultevis and sitapar yielded ar ages of 1 8 ga and 0 95 ga interpreted as the age of postmetamorphic cooling hollandites ultevis and of an early k introducing alteration process subsequent to amphibolite facies metamorphism cryptomelanes sitapar both data are consistent with known chronologies of the svecokarelian and satpura orogenic cycles a date of 670 ma obtained for a hollandite from a volcanogenic vein deposit bachkoun however contrasts with published extrusion ages of 580 560 ma for the volcanic host rocks ouarzazate series probably due to incorporation of excess argon the use of the 40ar 39ar technique together with multiple isotope systematics made it nevertheless possible to establish a reasonable estimate of a mineralization age close to 580 ma measurement of fractional ar losses during vacuum step heating 500 1600 c although indicating good ar retentivities failed to define model diffusion parameters because of non linear arrhenius arrays helium diffusion results 200 1200 c indicated retention of radiogenic 4he by the samples corroborated by u he mineral dates between 0 96 and 0 31 ga potassium bearing manganese oxides are therefore able to retain argon possibly also 4he through geological times and may thus provide ages of ore forming processes and perhaps later cooling and alteration stages

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

paleomagnetic overprints in ocean sediment cores and their relationship to shear deformation caused by piston coring 1 we use paleomagnetic data from cores collected at ocean drilling program site 1062 on the bahama outer ridge as well as observations from prior cruises to quantify the nature and to assess the causes of drilling overprints the largest overprint arises from an isothermal remanent magnetization that is imparted to the core during coring or core retrieval a second type of overprint is apparent only in soft sediments collected with a piston corer and has coercivities and unblocking temperatures that completely overlap those of the primary remanent magnetization which means it cannot be removed by standard demagnetization methods this demagnetization resistant overprint can produce significant biases in paleomagnetic observations particularly those from split core sections we hypothesize that shearing which occurs as a result of friction on the inside wall of the piston corer as it rips through sediments and cuts a core deflects the ancient magnetization we develop and test a model that predicts how shear deformation can rotate remanence carrying grains and deflect the paleomagnetic remanence of a split core section using the shear model predictions and directions measured on split core sections and u channel samples from the undeformed core center we estimate the average deformation sustained and then correct the split core data for biases caused by shear deformation the reduction in the deviations between corrected split core data and u channel data is statistically significant indicating that the shear model is capable of accounting for a significant portion of the systematic biases observed in paleomagnetic observations obtained from piston cores

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka

synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation antarctic ice core data reveal that the atmosphere experienced abrupt centennial increases in co2 concentration during the last deglaciation 18 thousand to 11 thousand years ago establishing the role of ocean circulation in these changes requires high resolution accurately dated marine records here we report radiocarbon data from uranium thorium dated deep sea corals in the equatorial atlantic and drake passage over the past 25 000 years two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric co2 rises at 14 8 thousand and 11 7 thousand years ago we interpret these radiocarbon enriched signals to represent two short lived less than 500 years overshoot events with atlantic meridional overturning stronger than that of the modern era these results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation

environmental factors as complicating influences in the recovery of quantitative geomagnetic field paleointensity estimates from sediments we have recently recovered replicate records of the earth s magnetic field relative paleointensity for 12 71 000 years bp from marine sediments of the western north atlantic ocean our records are remarkably similar to two other recently published relative paleointensity records from marine and lacustrine sediments in europe this suggests to us that even over this wide region sediments may serve as reasonable correlatable recorders of fluctuations in the strength of the earth s magnetic field if this is true then similar records from around the globe could eventually provide valuable information about the deep earth processes which create the field we note however that our intensity record is significantly correlated with the down core ratio of magnetic susceptibility to anhysteretic remanent magnetism arm this ratio is a measure of the relative grain size of magnetite the primary magnetic mineral in these sediments and as such is a sediment magnetic property which is controlled only by the local depositional environment and indirectly by global climate we are concerned that the european records may be similarly biased by climatic or other environmental factors possibly synchronous with ours we caution that extreme care must be taken to understand and remove any such magnetic influences from sediment relative paleointensity records before they are used as quantitative estimators of the past intensity of the earth s magnetic field