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

precise ages of the reunion event and huckleberry ridge excursion episodic clustering of geomagnetic instabilities and the dynamics of flow within the outer core the reunion event is one of the earliest recognized periods of normal polarity within the reversed matuyama chron named for the site at which it was first discovered on reunion island it has since purportedly been found globally in both volcanic rocks and sediments and thus has become a key chronostratigraphic marker however geochronologic results from several locations thought to have recorded this event have caused considerable confusion regarding not only its age and duration but also the number of reunion events new 40ar 39ar ages from eight reunion island lavas in three distinct sections are indistinguishable from one another thereby placing the event at 2 200 0 007 0 010 ma2 200 0 007 0 010 ma 2 2 analytical total uncertainty note this format is used throughout the paper the paleomagnetic behavior recorded at two of the island sites shows that the opposite normal polarity was reached and sustained for a period during which several lava flows were erupted whether this can be classified as a very short subchron bounded by a rapid set of back to back reversals or as a special case of a geomagnetic excursion is unclear hence we choose to continue labeling the dynamo activity recorded by these reunion island lavas as an event this event preceded a 38 kyr 38 kyr period of normal polarity that we name the feni subchron after its locality of discovery at odp site 981 the feni subchron was succeeded by the huckleberry ridge excursion for which 40ar 39ar sanidine and u pb zircon ages of 2 077 0 001 0 003 ma2 077 0 001 0 003 ma and 2 084 0 012 0 013 ma2 084 0 012 0 013 ma respectively from member b of the huckleberry ridge tuff in idaho are in agreement these findings suggest that the full normal polarity recorded on reunion island is a singular brief period of unstable field behavior at the onset of a 125 kyr 125 kyr bundling of dynamo instabilities from 2 20 to 2 07 ma disturbances to the axial dipole component of earth s magnetic field during this period and by analogy similar periods of temporally clustered excursions during the early and late portions of the brunhes chron may reflect disruptions to convective flow arising from parcels of material introduced into the outer core from either the inner core or core mantle boundaries a proposition that might be tested by future numerical dynamo simulations

10be evidence for delayed acquisition of remanent magnetization in marine sediments implication for a new age for the matuyama brunhes boundary abstract fluxes of the meteoric cosmogenic radionuclide 10 be vary with changes in the incoming cosmic rays modulated by geomagnetic field intensity variations the variability in the 10 be flux can be used to synchronize ice cores as well as marine sediments by comparison with the relative paleointensity variations of the geomagnetic field however lock in of the paleomagnetic signal at some depth below the sediment water interface in marine sediments through acquisition of a post depositional remanent magnetization pdrm adds uncertainty to synchronization despite the long history of such studies the magnitude of the pdrm lock in depth remains controversial in this article we present clear evidence for a downward offset of the paleointensity minimum relative to the 10 be flux anomaly at the matuyama brunhes m b geomagnetic polarity boundary which we interpret to result from a 15 cm pdrm lock in depth this lock in depth indicates that up to several tens of thousands years of age offset probably occurs when a paleomagnetic record is used for dating marine sediments and the age of the m b boundary should be revised to ca 10 kyr younger which is consistent with a younger ice core derived age of 770 6 ka 2 this cosmogenic age tuning strategy will contribute to refining paleomagnetic based age models for marine sediments and identifying of lead lag relationships for global abrupt environmental changes

why are geomagnetic excursions not always recorded in sediments constraints from post depositional remanent magnetization lock in modelling abstract many geomagnetic excursions have been documented during the brunhes chron however high resolution paleomagnetic studies of sediments often provide evidence of few if any excursions we have investigated the reasons for this observation by modelling the post depositional remanent magnetization pdrm lock in process a cubic lock in function produces more rapid lock in compared to linear and exponential functions proposed in the literature we therefore used a cubic function to model best case scenarios for the quality of the paleomagnetic record when a high frequency geomagnetic input signal is convolved with the sediment lock in function for a wide range of sedimentation rates even for a lock in depth of 10 cm where 95 of the pdrm is locked in 5 cm below the surface mixed layer an input signal containing abundant excursions with 1 kyr duration is smoothed so drastically at low sedimentation rates 1 3 cm kyr that no excursions are recorded excursions are further attenuated by increasing the lock in depth as well as by sampling at discrete stratigraphic intervals the pdrm process acts as a low pass filter for high frequency secular variation signals even at moderate sedimentation rates 10 cm kyr we have also modelled the effects of modulation of sedimentation rate by a climatic forcing function e g insolation even though the average sedimentation rate might be substantial pdrm recording becomes much less reliable in intervals where sedimentation rates are lowest in these cases some excursions are reliably recorded in detail while others may not be recorded at all our modelling suggests that in order to consistently detect the presence of geomagnetic excursions it is ideal to work with sediments that maintain minimum sedimentation rates above 10 cm kyr if the normal spectrum of geomagnetic field behaviour contains abundant excursions failure to document excursions in many apparently high resolution analyses probably results from pdrm lock in within relatively slowly deposited sediments or to unrecognized intervals of slow sedimentation in environments with higher average sedimentation rates

precessional forcing of lacustrine sedimentation in the late cenozoic chemeron basin central kenya rift and calibration of the gauss matuyama boundary the fluviolacustrine sedimentary sequence of the chemeron formation exposed in the barsemoi river drainage tugen hills kenya contains a package of five successive diatomite fluvial cycles that record the periodic development of freshwater lakes within the axial portion of the central kenya rift the overwhelming abundance in the diatomite of planktonic species of the genera aulacoseira and stephanodiscus and the virtual absence of benthic littoral diatoms and detrital material indicate areally extensive deep lake systems a paleomagnetic reversal stratigraphy has been determined and chronostratigraphic tie points established by 40 ar 39 ar dating of intercalated tuffs the sequence spans the interval 3 1 2 35 ma and bears a detailed record of the gauss matuyama paleomagnetic transition the 40 ar 39 ar age for this boundary of 2 589 0 003 ma can be adjusted to concordance with the astronomical polarity time scale apts on the basis of an independent calibration to 2 610 ma 29 kyr older than the previous apts age the diatomites recur at an orbital precessional interval of 23 kyr and are centered on a 400 kyr eccentricity maximum it is concluded that these diatomite fluvial cycles reflect a narrow interval of orbitally forced wet dry climatic conditions that may be expressed regionally across east africa the timing of the lacustrine pulses relative to predicted insolation models favors origination of moisture from the northern africa monsoon rather than local circulation driven by direct equatorial insolation this moisture event at 2 7 2 55 ma and later east african episodes at 1 9 1 7 and 1 1 0 9 ma are approximately coincident with major global climatic and oceanographic events

deep oceanic zonal jets constrained by fine scale wind stress curls in the south pacific ocean a high resolution coupled gcm study 1 oceanic alternating zonal jets at depth have been detected ubiquitously in observations and ocean general circulation models gcms such oceanic jets are generally considered as being generated by purely oceanic processes here we explore a possible air sea interaction induced by surface signatures of the deep zonal jets using an eddy permitting coupled atmosphere ocean gcm cgcm the 23 year cgcm integration reproduces bands of latitudinally narrow alternating jets in the southeast pacific they extend from the sea surface to well below the main thermocline and are embedded in the large scale westward flowing south equatorial current the latter mostly confined above the thermocline these jets generate fine scale sea surface temperature sst anomalies through the advection of zonal temperature gradients the atmospheric boundary layer appears to respond thermally to this fine scale sst field which induces fine scale wind stress anomaly through atmospheric pressure adjustment as indicated by a good spatial correlation between the sst laplacian field and the fine scale wind stress curl a sverdrup calculation on the wind stress field of the cgcm predicts fine scale zonal currents driven by the meridional gradient of the fine scale wind stress curl the positions of these sverdrup currents are generally coincident with those of the original zonal jets and the sverdrup prediction explains roughly half of the amplitudes of the jets while the original cause of the deep zonal jets simulated in our cgcm is unidentified this analysis suggests that there is likely a positive air sea feedback the jets generate fine scale wind stress curl that reinforces themselves through the sverdrup dynamics

geomagnetic field intensity and reversals during the past four million years a long and continuous record of the geomagnetic field intensity shows that intensity variations are dominated by two modes major episodes of field regeneration prevail on timescales of a few thousand years immediately after most reversals whereas stable polarity states are characterized by a slow 0 5 myr relaxation process reversals can be seen as the consequence of a progressive degradation of the dipole field

reconciling astrochronological and 40ar 39ar ages for the matuyama brunhes boundary and late matuyama chron when five matuyama brunhes m b boundary records from the north atlantic are placed on isotope age models produced by correlation of the 18o record directly or indirectly to an ice volume model the m b boundary lies consistently at the young end of marine isotope stage 19 with a mean age for the midpoint of the reversal of 773 1 ka standard deviation 0 4 kyr 7 kyr younger than the presently accepted astrochronological age for this polarity reversal 780 781 ka two recently proposed revisions of the age of the 40ar 39ar fish canyon sanidine fcs standard to 28 201 0 046 ma and 28 305 0 036 ma would adjust 40ar 39ar ages applicable to the m b boundary and other reversals and excursions back to 1 2 ma to ages older than the new astrochronological ages by 8 24 kyr the variables used to construct the ice volume models cannot account for the discrepancy the fcs standard age that best fits the astrochronological ages is 27 93 ma which is within the uncertainty associated with the commonly used value of 28 02 0 16 ma but younger than the recently proposed fcs ages the edc2 and edc3 age models in the dome c antarctic ice core yield ages of 771 7 ka and 766 4 ka respectively for the 10be flux peak that denotes the paleointensity minimum at the reversal boundary implying that the edc2 rather than edc3 age model is consistent with the observations from marine sediments at least close to the m b boundary

a detailed record of paleomagnetic field change from searles lake california 2 the gauss matuyama polarity reversal this new study of the gauss matuyama transition from searles lake california conjoined with other records from the western united states provides interesting insights into the structure of the reversing magnetic field the present study employs improved measurement and data reduction techniques multiple parallel strings of samples and a finer sampling interval than was used in the original study by liddicoat 1982 particularly crucial to this investigation was the use of overprint directions to reconstruct declinations required because the core was rotary drilled the results of this technique were corroborated by employing an independent method that uses anisotropy of magnetic susceptibility to resolve a sediment fabric the fabric facilitated the alignment of core segments the new record reveals that the main swing of the transition occurs over a significantly shorter time span than was found in the original study in addition it brings out several small scale variations that were absent in the old record some of which take the form of relatively rapid jumps in direction that punctuate more steadily varying changes this alternating steady and rapid field change is similar to behavior observed in volcanic records which argues that such behavior is not merely an artifact of episodic volcanism the searles lake record is strongly nonzonal and is defined in the northern hemisphere by a swath of virtual geomagnetic poles vgps stretching from northern eurasia to west africa and to the northwest pacific glen et al 1994 showed that a collection spanning 15 myr of western north american transition and excursion records displays this same pattern indicating that the vgp swath is a persistent feature of the transitional field in addition the compilation reveals that the swath extends into the southern hemisphere outlining a region marked by an absence of poles that is centered on the indian ocean the fact that this pattern is offset from a similar one seen in global compilations suggests that the persistent fields have a significant nondipolar component seven additional records are now available making the western north america data set perhaps the finest regional set of high resolution records consisting of both igneous and sedimentary records the new records which provide an important test of the existence of the vgp pattern strongly support the findings that reveal the presence of persistent long term 15 myr nondipolar transitional fields

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

astronomically tuned plio pleistocene benthic δ 18 o record from south china sea and atlantic pacific comparison based on benthic foraminiferal n 18 o from odp site 1143 a 5 myr astronomical timescale for the west pacific plio pleistocene was established using an automatic orbital tuning method the tuned brunhes matuyama paleomagnetic polarity reversal age agrees well with the previously published age of 0 78 ma the tuned ages for several planktonic foraminifer bio events also agree well with published dates and new ages for some other bio events in the south china sea were also estimated the benthic n 18 o from site 1143 is highly coherent with the earth s orbit etp both at the obliquity and precession bands for the last 5 myr and at the eccentricity band for the last 2 myr in general the 41 kyr cycle was dominant through the plio pleistocene although the 23 kyr cycle was also very strong the 100 kyr cycle became dominant only during the last 1 myr a comparison of the benthic n 18 o between the atlantic odp 659 and the east and west pacific 846 and 1143 reveals that the atlantic pacific benthic oxygen isotope difference ratio vn 18 oatlpac displays an increasing trend in three time intervals 3 6 2 7 ma 2 7 2 1 ma and 1 5 0 25 ma each of the intervals begins with a rapid negative shift in vn 18 oatlpac followed by a long period with an increasing trend corresponding to the growth of the northern hemisphere ice sheet this means that all three intervals of ice sheet growth in the northern hemisphere were accompanied at the beginning by a rapid relative warming of deep water in the atlantic as compared to that of the pacific followed by its gradual relative cooling this general trend superimposed on the frequent fluctuations with glacial cycles should yield insights into the processes leading to the boreal glaciation cross spectral analyses of the vn 18 oatlpac with the earth s orbit suggests that after the initiation of northern hemisphere glaciation at about 2 5 ma obliquity rather than precession had become the dominant force controlling the vertical structure or thermohaline circulation in the paleo ocean a 2002 elsevier science b v all rights reserved

40 ar 39 ar ages of tephras intercalated in astronomically tuned neogene sedimentary sequences in the eastern mediterranean we present new 40 ar 39 ar data for sanidine and biotite derived from volcanic ash layers that are intercalated in pliocene and late miocene astronomically dated sequences in the mediterranean with the aim to solve existing inconsistencies in the intercalibration between the two independent absolute dating methods 40 ar 39 ar sanidine ages are systematically younger by 0 7 2 3 than the astronomical ages for the same ash layers the significance of the discrepancy disappears except for the upper ptolemais ashes which reveal the largest difference if an improved full error propagation method is applied to calculate the absolute error in the 40 ar 39 ar ages the total variance is dominated by that of the activity of the decay of 40 kt o 40 ar f70 and that the amount of radiogenic 40 arp in the primary standard ga1550 biotite f15 if the 40 ar 39 ar ages are calculated relative to an astronomically dated standard the influence of these parameters is greatly reduced resulting in a more reliable age and in a significant reduction of the error in 40 ar 39 ar dating astronomically calibrated ages for taylor creek rhyolite tcr and fish canyon tuff fct sanidine are 28 53f0 02 and 28 21f0 04 ma f1 s e respectively if we start from the more reliable results of the cretan a1 ash layer the most likely explanation for the large discrepancy found for the younger ptolemais ash layers equivalent to fct of 28 61 ma is an error in the tuning of this part of the sequence d 2004 elsevier b v all rights reserved

relative paleointensity stack during the last 250 kyr in the northwest pacific 1 we have conducted a paleomagnetic study of 10 sediment cores recovered from the northwest pacific the purpose is to establish a regional paleointensity stack during the last 250 kyrs nopapis 250 for global coverage of paleointensity data as well as a regional reference for paleointensity assisted stratigraphy in the studied cores reductive dissolution of magnetite appears to have occurred mainly in glacial periods such horizons accompany large decreases in s ratio s 0 3t 1 irm 0 3t sirm 2 as low as 0 90 the sediments are also intercalated by frequent volcanic ash layers prerequisites for reliable relative paleointensity estimation are not satisfied at these horizons we rejected unsuitable data by quantitative criteria based on s ratio and saturation isothermal remanent magnetization sirm and constructed the nopapis 250 curve from the remaining data in the construction of the curve we chose irm as a normalizer because acquisitions of anhysteretic remanent magnetization arm are considered to be influenced by magnetic interactions among magnetic grains in the northwest pacific sediments relative intensity variation of the nopapis 250 gives a standard deviation that is 33 of the average if the normal distribution is assumed the nopapis 250 curve generally shows similar variation patterns compared with other high resolution records reported from other regions many paleointensity lows are recognized in common six out of the nine lows can be correlated with reported excursions in literature

late brunhes polarity excursions mono lake laschamp iceland basin and pringle falls recorded at odp site 919 irminger basin abstract component natural remanent magnetizations derived from u channel and 1 cm3 discrete samples from odp site 919 irminger basin indicate the existence of four intervals of negative inclinations in the upper brunhes chronozone according to the age model based on planktic oxygen isotope data these excursional intervals occur in sediments deposited during the following time intervals 32 34 ka 39 41 ka 180 188 ka and 205 225 ka these time intervals correspond to polarity excursions detected elsewhere known as mono lake laschamp iceland basin and pringle falls the isotope based age model is supported by the normalized remanence paleointensity record that can be correlated to other calibrated paleointensity records for the 0 500 ka interval such as that from odp site 983 for the intervals associated with the mono lake and laschamp excursions virtual geomagnetic poles vgps reach equatorial latitudes and mid southerly latitudes respectively for intervals associated with the iceland basin and pringle falls excursions repeated excursions of vgps to high southerly latitudes indicate rapid directional swings rather than a single short lived polarity reversal the directional instability associated with polarity excursions is not often recorded probably due to smoothing of the sedimentary record by the process of detrital remanence drm acquisition

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

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

wavelet analysis of relative geomagnetic paleointensity at odp site 983 abstract we performed spectral analysis of the record of relative geomagnetic paleointensity obtained at odp site 983 covering the time interval 0 1 1 ma the results confirm the presence of significant power at frequencies corresponding to the earth orbital parameters eccentricity obliquity precession the construction of the evolutionary spectrum allowed us to establish the non stationarity of the signal at those frequencies the subsequent use of wavelet techniques made it possible to demarcate the time intervals over which orbital frequencies are present in the record for those intervals the paleointensity record shows some coherency with the isothermal remanent magnetization normalizer of the natural remanent magnetization and the ratio anhysteretic remanent magnetization k these results suggest that the orbital frequencies embedded in the paleointensity record are the expression of lithologic variations and probably not a characteristic of the geodynamo itself extracting filtering these wavelet components from the site 983 paleointensity record indicates however that this secondary overprint is of sufficiently low level that it has a minor effect on the overall character of the record

generation of the north equatorial undercurrent jets by triad baroclinic rossby wave interactions abstractformation processes responsible for the north equatorial undercurrent neuc jets that appear across the tropical north pacific ocean near 9 13 and 18 n are explored both theoretically and using numerical models with different complexities analyses of an eddy resolving global ocean general circulation model output reveal that the neuc jets have a mode 1 baroclinic vertical structure and are spatially persistent on the interannual and longer time scales this ogcm simulated vertical structure prompts the authors to adopt the simpler nonlinear layer reduced gravity model as well as the baroclinic rossby wave triad interaction theory to unravel the essential processes underlying the neuc jets the seed for the neuc jets originates in annual baroclinic rossby waves driven by the large scale surface wind stress forcing emanating from the ocean basin s eastern boundary these wind forced primary waves are subject to nonlinear triad interactions and break down offshore where the e folding tim

far reaching effects of the hawaiian islands on the pacific ocean atmosphere system using satellite data we detected a wind wake trailing westward behind the hawaiian islands for 3000 kilometers a length many times greater than observed anywhere else on earth this wind wake drives an eastward ocean current that draws warm water from the asian coast 8000 kilometers away leaving marked changes in surface and subsurface ocean temperature standing in the path of the steady trade winds hawaii triggers an air sea interaction that provides the feedback to sustain the influence of these small islands over a long stretch of the pacific ocean

a relative geomagnetic paleointensity stack from ontong java plateau sediments for the matuyama we present a stack of geomagnetic paleointensity estimates for the matuyama chron 0 778 2 582 ma sedimentary magnetizations from 4 ocean drilling program odp cores from the ontong java plateau ojp are analyzed with thermal techniques thellier thellier experiments are used to determine magnetic properties and indicate that a thermal treatment to 250 c can be used for paleointensity estimates the correlated records form a coherent ojp stack which is dated at reversal boundaries a coherent feature with two other data sets spanning the matuyama chron is the occurrence of a 150 kyr cyclicity however the time control of the ojp stack is not accurate except for the 10 tie points at the reversals this could at least in part explain why the three matuyama paleointensity records show no other coherent frequencies

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

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

a summary of brunhes paleomagnetic field variability recorded in ocean drilling program cores the ocean drilling program odp has recovered many long sediment sequences from around the world that contain medium to high resolution paleomagnetic records of brunhes age these records have provided an important new global view of geomagnetic field variability during stable magnetic dipole polarity that could not be recovered by conventional terrestrial or deep sea piston coring the odp paleomagnetic records of directional variability can be routinely recovered and used regionally as a very highresolution relative chronostratigraphic tool 200 yr resolution odp paleomagnetic records of brunhes age relative paleointensity have dramatically improved our understanding of global geomagnetic field intensity these records document the global scale pattern of paleointensity and demonstrate its use as a high resolution relative chronostratigraphic tool that under ideal conditions could have a precision of 500 yr odp paleomagnetic records and associated oxygen isotope chronostratigraphies have also greatly improved our understanding of the number and ages of brunhes geomagnetic field excursions and their relationship to normal directional secular variation and paleointensity variability although significant progress has been made though odp paleomagnetic studies of brunhes aged sediments it is clear that more work is needed to further resolve and define the detailed global pattern of brunhes psv and its relationship to excursions and true polarity reversals

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

an updated astronomical timescale for the plio pleistocene deposits from south china sea and new insights into asian monsoon evolution abstract here we present an improved astronomical timescale since 5 ma as recorded in the odp site 1143 in the southern south china sea using a recently published asian summer monsoon record hematite to goethite content ratio hm gt and a parallel benthic 18o record correlation of the benthic 18o record to the stack of 57 globally distributed benthic 18o records lr04 stack and the hm gt curve to the 65 n summer insolation curve is a particularly useful approach to obtain refined timescales hence it constitutes the basis for our effort our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the odp site 1143 this updated timescale further enables a detailed study of the orbital variability of low latitude asian summer monsoon throughout the plio pleistocene comparison of the hm gt record with the 18o record from the same core reveals that the oscillations of low latitude asian summer monsoon over orbital scales differed considerably from the glacial interglacial climate cycles the popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low latitude asia in low latitude asia some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages vice versa some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages the well known mid pleistocene transition mpt is only identified in the benthic 18o record but not in the hm gt record from the same core this suggests that the mpt may be a feature of high and middle latitude climates possibly determined by high latitude ice sheet dynamics for low latitude monsoonal climate its orbital scale variations respond more directly to insolation and are little influenced by high latitude processes thus the mpt is likely not recorded in addition the hm gt record suggests that low latitude asian summer monsoon intensity has a long term decreasing trend since 2 8 ma with increased oscillation amplitude this long term variability is presumably linked to the northern hemisphere glaciation since then

an ice core perspective on the age of the matuyama brunhes boundary abstract two intervals of enhanced 10be flux thought to be associated with periods of low dipole intensity and identified as the matuyama brunhes transition and a precursor event have been observed in the bottom section of the epica dome c ice core the peaks span 764 776 ka and 788 798 ka on the new edc3 chronology with a stated absolute age uncertainty of 6 ka 2 this chronology uses orbital tuning of atmospheric oxygen 18 18oatm to correct for anomalies in ice flow in the bottom 500 m of the core an additional 28 18oatm data points have been measured to improve resolution and verify the accuracy of the tuning and the stated timescale uncertainty both the dating of the increased 10be and that relative to climatic records are compared to paleointensity records found in orbitally tuned marine sediments the mid point of the 10be peak associated with the m b is approximately 10 ka younger than the age determined radioisotopically from lavas with transitional orientations taking into account recent revisions to the 40ar 39ar dating standard and improved precision climatic constraints on the edc3 agescale make an error of this magnitude in the ice chronology implausible this age difference however is consistent with recent modeling suggesting that directional changes are spatially asynchronous and may precede the dipole intensity minimum in some locations although formally less precise than the published age from astrochronologically dated marine sediments ice core ages are potentially more accurate because they are not subject to lock in depth uncertainties

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

a geomagnetic paleointensity stack between 0 8 and 3 0 ma from equatorial pacific sediment cores 1 we have conducted a paleomagnetic study of six sediment cores taken from the equatorial pacific three from the west caroline basin and three from the manihiki plateau in order to make a relative paleointensity stack during the matuyama and late gauss chrons the age of the bottom of the cores ranges from 1 2 to 3 0 ma the sediments show little downcore changes in the proxies of magnetic grain size and mineralogy and are hence suitable for estimating relative paleointensity the age of the cores is controlled by correlating variations in magnetic concentration magnetic susceptibility and or anhysteretic remanent magnetization arm to target oxygen isotope 18o curves all cores from the manihiki plateau show an upward decrease of the natural remanent magnetization nrm intensity normalized by arm and isothermal remanent magnetization irm with a decrease in sedimentation rate such a trend was removed before being converted to relative paleointensity this observation implies that a sedimentation rate change can affect relative paleointensity estimation relative paleointensity records from the six cores coincide well with each other within uncertainty of age we constructed a stacked curve between 0 8 and 3 0 ma the equatorial pacific paleointensity stack epapis 3ma after adjusting age the number of cores stacked is three to four throughout the record quasiperiodic paleointensity lows occur in the epapis 3ma and corresponding paleointensity lows can be found in previously published records with some shifts in age at least parts of the paleointensity minima seem to be accompanied by geomagnetic excursions the asymmetric sawtooth pattern of paleointensity variations is not observed at the matuyama gauss boundary and thereafter in our record a spectral analysis shows that 100 kyr orbital eccentricity frequency may exist in paleointensity variations during the matuyama and late gauss chrons

millennial scale iceberg surges after intensification of northern hemisphere glaciation iceberg discharges from continental ice sheets are widely believed to have exerted a great influence on global climate but an iceberg discharge regime in early glacial periods after intensification of northern hemisphere glaciation nhg remains largely unclear here we present high resolution rock magnetic records during the period from 2 1 to 2 75 ma after intensification of nhg reconstructed from the subpolar north atlantic although the establishment of the middle pliocene chronology of north atlantic sediments is often a serious problem we overcame it based on findings concerning the properties of magnetic susceptibility and natural gamma radiation reconstructed rock magnetic records indicate that millennial scale iceberg surges were dominant features in the early glacial periods additionally the millennial scale iceberg surges occurred within glacial stages during intervals when ratios of global oxygen isotope stack from benthic foraminifera lr04 18o stack surpassed approximately 3 5 these are comparable to the climatic and environmental changes in pleistocene glacial periods as represented by last glacial dansgaard oeschger cycles suggesting that continental ice sheets have oscillated and calved icebergs in a similar manner since intensification of nhg

40ar 39ar ages and palaeomagnetism of transitionally magnetized volcanic rocks in the society islands french polynesia raiatea excursion in the upper gauss chron summary volcanic rock samples from several sites in the society islands french polynesia were found to be transitionally magnetized to better characterize these geomagnetic events we performed laser heating 40ar 39ar dating and additional palaeomagnetic measurements on these samples the measurements give virtual geomagnetic pole vgp latitudes of 0 7 52 4 n and virtual dipole moment vdm values of 0 433 0 682 1022 a m2 which are typical for the transitional geomagnetic field these transitional events occurred at 2 77 0 02 ma raiatea 3 20 0 03 ma tahaa and 4 40 0 01 ma maupiti considering the reported radioisotopic ages for known geomagnetic events it is suggested the first event is a previously unknown geomagnetic excursion raiatea excursion while the latter two probably correspond to known polarity transitions upper boundary ages of the mammoth reversed subchron and the nunivak normal subchron the existence of the proposed raiatea excursion is supported by the contemporaneous palaeointensity low recognized in the relative palaeointensity stack from the equatorial pacific

southern greenland glaciation and western boundary undercurrent evolution recorded on eirik drift during the late pliocene intensification of northern hemisphere glaciation abstract we present new sedimentological and environmental magnetic records spanning 3 2 2 2 ma during the intensification of northern hemisphere glaciation from north atlantic integrated ocean drilling program site u1307 on eirik drift our new datasets and their high fidelity age control demonstrate that while inland glaciers and potentially also at times restricted iceberg calving margins have likely existed on southern greenland since at least 3 2 ma persistent and extensive iceberg calving glacial margins were only established in this region at 2 72 ma 300 kyr later than in northeastern and eastern greenland despite a dramatic increase in greenland sourced ice rafted debris deposition on eirik drift at this time contemporaneous changes in the bulk magnetic properties of site u1307 sediments and a reduction in sediment accumulation rates suggest a decrease in the delivery of greenland sourced glaciofluvial silt to our study site we attribute these changes to a shift in depositional regime from bottom current dominated to glacial ird dominated between 2 9 and 2 7 ma in response to a change in the depth of the flow path of the western boundary undercurrent relative to our study site

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

observational evidence of alternating zonal jets in the world ocean 1 multiple zonal jets with the east west velocity direction alternating with latitude are discovered in satellite altimetry data the time varying jets are shown to populate every part of the world ocean and its marginal seas and are best seen in the anomaly of geostrophic vorticity at midlatitudes the jets have a meridional wavelength of about 300 kms with r m s sea level velocity and vorticity values of 2 4 cm 6 9 cm s and 1 5 10 6 s 1 correspondingly realistic data from the high resolution ogcm run on the earth simulator are used to justify high vertical coherence of the jets structure and relevance of the jets to an evolving mesoscale eddy field strong coupling between the jets and mesoscale eddies is hypothesized

wind driven zonal jets in the south pacific ocean 1 zonal jets west of the large islands of the south pacific ocean are predicted by theory commonly seen in ocean models with sufficiently high resolution and are beginning to be observed these jets are often taken to reflect the blocking effect of the islands in the south equatorial current through island rule dynamics here it is shown that quasi permanent structures of the basin wide wind field imply the existence of jets formed independently of the islands evidence for the existence of the wind driven jets is found in climatological geostrophic currents the hydrographic structures that produce the jets occur well below the thermocline

integration of volcanic and sedimentary records of paleointensity constraints imposed by irregular eruption rates the reading of absolute paleointensity by lava flows has been simulated by sampling the field intensities from dipole extracted from sedimentary paleointensities and non dipole similar to the present field components results show that specific features in the geomagnetic intensity cannot be reproduced unless a minimum of 10 flows per 100 ky have been emitted however this criteria does not guaranty the high quality of the record which depends also on the temporal control for cases where the volcanic activity is episodic a minimum of 4 dated flows per 100 ky is suggested the construction of a composite curve from volcanic paleointensity intended as a type curve of field intensity changes requires a very large number of data in order to overcome the effects of non dipole components errors in ages and variable sampling the present volcanic database is far from having this resolution to perform this analysis for the last 800 ky

arterial ocean circulation of the southeast indian ocean 1 the time mean ocean circulation for the southeast indian ocean seio is analyzed using a colorwheel to reveal an arterial like structure although quasi zonal the mean circulation in this region is distinctly more complex than previously presented in recent literature the mean flow is derived from an eddy resolving ocean reanalysis of the past 14 years the ocean state is constrained through data assimilation with observed sea level anomaly sea surface temperature and in situ profiles geostrophic currents derived from the reanalyzed mean dynamic topography mdt are validated against two other mdt analyses to show a comparable arterial structure and distribution of scales in particular the broad scale eastward flow is regularly interspersed by narrow bands of the near westward flow meridional sections from the ocean reanalysis reveal a net eastward transport in the surface layer and a net westward flow at mid depth the seasonality of the surface layer flow in the seio appears to have increased decreased eastward mean transport that coincide with seasons of stronger weaker leeuwin current lc whether the narrow bands of mean current and mass flux are simply the average of the eddies or represent an underlying weak jet remains a topic of current debate

stationary mesoscale jet like features in the ocean 1 xbt and float data of the world ocean database 2005 are used to validate new stationary jet like features striations recently found in the high resolution mean dynamic ocean topography mdot two study areas were selected in the eastern parts of the north and south pacific subtropical gyres free of any strong currents appropriate horizontal high pass filtering applied to the ensemble mean temperature at 100 m depth revealed the striation signal coherent with mdot the features are also distinct in the data of depth of 12 c isotherm lying close to the thermocline the striations are oriented nearly zonally and coherent vertically at least through 700 m depth their wavelength is approximately 400 km and the azimuth of wavevector is 13 9 in the northern southern domains correspondence between the striations in observations and ofes ogcm for the earth simulator model as well as the nature of the striations are discussed

zonal jets in the pacific ocean 1 the spatial and temporal properties of zonally coherent jet like structures found in high resolution ocean models is examined we focus on the pacific ocean we find the properties of the jets are not very sensitive to the model configuration distinct differences are found in the persistence and vertical structure of the jets poleward of 30 n and s compared with those in the tropics we make a quantitative comparison between the meridional scale of the jets and the rhines scale we find a local scaling applies in that the horizontal variation of the meridional scale of the jets is consistent with horizontal variations in the rhines scale

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

relative paleointensity rpi and oxygen isotope stratigraphy at iodp site u1308 north atlantic rpi stack for 1 2 2 2 ma narpi 2200 and age of the olduvai subchron 2015 elsevier ltd integrated ocean drilling program iodp site u1308 49 53 n 24 14 w water depth 3871 m provides a record of relative paleointensity rpi and benthic stable isotope stratigraphy back to 3 2 ma the record since 1 5 ma was published previously and here we present the interval from 1 5 ma to 3 2 ma early pleistocene late pliocene the benthic oxygen isotope record in this interval is correlated to marine isotope stage mis 51 to km2 with an apparent hiatus that removed part of the interval spanning mis 104 g2 2 6 2 65 ma at the gauss matuyama boundary the mean sedimentation rate for the 1 5 3 2 ma period is 8 5 cm kyr the age model was built by correlation of the benthic oxygen isotope record to a global stack lr04 apart from the expected polarity reversals three magnetic excursions are recorded punaruu in mis 31 32 at 1092 ka gilsa in mis 54 55 at 1584 ka and a newly recognized excursion labeled porcupine after the nearby porcupine abyssal plain in mis g6 g7 at 2737 ka the ages of polarity reversals at site u1308 on the lr04 time scale are consistent with the current geomagnetic polarity timescale gpts with the exception of the base of the olduvai subchron that occurred in mis 73 corresponding to 1925 ka on the lr04 time scale 25 kyr younger than in the current gpts the rpi record at site u1308 is calibrated using the oxygen isotope age model and combined with four other north atlantic records to obtain a north atlantic rpi stack for 1 2 2 2 ma narpi 2200 that is compared with published rpi stacks epapis sint 2000 and padm2m for 2 2 3 2 ma the site u1308 rpi record is compared with a rpi record from north atlantic iodp site u1314 and with the pacific epapis stack the mean sedimentation rates of the north atlantic sites in narpi 2200 are greater by about an order of magnitude than most of the records incorporated in other stacks the comparison of epapis and narpi 2200 yields an apparent lag for narpi 2200 relative to epapis attributed the epapis age model constructed by correlation of magnetic concentration parameters a proxy for carbonate percentage to a calibrated oxygen isotope record the long rpi record from site u1308 yields a very similar mean value for the brunhes and matuyama virtual axial dipole moments 7 05 1022 am2 implying no polarity bias in the strength of the main geomagnetic dipole in contrast to interpretations from sint 2000 and padm2m the results strengthen the case that rpi can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters kyr

the dynamical subtropical front 1 the southern ocean subtropical front stf is thought to play a key role in the global climate system theory suggests that the latitude of the stf regulates the volume of saline agulhas leakage into the atlantic ocean from the indian here we use satellite sea surface temperature sst and sea surface height ssh data to study the physical characteristics of the stf water mass boundary we find that the strong currents in this region do not align with the surface water mass boundary therefore we provide a new climatology for these currents which we define as the dynamical stf dstf the dstf is the eastward extension of the western boundary current in each basin and is characterized by strong sst and ssh gradients and no seasonal cycle at the center of each basin it merges with the sub antarctic front on the eastern side of basins the stf surface water mass boundary coincides with a separate region of multiple sst fronts we call this the subtropical frontal zone stfz the fronts in the stfz have a large seasonal cycle and no ssh signature despite lying close to the same water mass boundary the dstf and stfz are completely unrelated we therefore suggest the term stf only be used when referring to the surface water mass boundary when studying the strong currents on the western side of basins the term dstf is more relevant and similarly the term stfz better describes the region of enhanced sst gradients towards the east

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

dependence of the duration of geomagnetic polarity reversals on site latitude an important constraint on the processes governing the geodynamo the flow in the outer core responsible for generating earth s magnetic field is the duration of geomagnetic polarity reversals that is how long it takes for earth s magnetic field to reverse1 it is generally accepted that earth s magnetic field strength drops to low levels during polarity reversals and the field direction progresses through a 180 change while the field is weak1 the time it takes for this process to happen however remains uncertain with estimates ranging from a few thousand up to 28 000 years here i present an analysis of the available sediment records of the four most recent polarity reversals these records yield an average estimate of about 7 000 years for the time it takes for the directional change to occur the variation about this mean duration is not random but instead varies with site latitude with shorter durations observed at low latitude sites and longer durations observed at mid to high latitude sites such variation of duration with site latitude is predicted by simple geometrical reversal models in which non dipole fields are allowed to persist while the axial dipole decays through zero and then builds in the opposite direction and provides a constraint on numerical dynamo models

formal subdivision of the quaternary system period present status and future directions abstract the quaternary system period and pleistocene series epoch were defined in 2009 by the global boundary stratotype section and point gssp for the gelasian stage age 2 58 ma which aligns with marine isotope stage mis 103 and approximates the gauss matuyama chron boundary contrary to earlier reports the vrica gssp 1 80 ma was repurposed in 2011 to define the calabrian stage effectively completing the lower pleistocene subseries subepoch the candidate for the middle pleistocene subseries and proposed chibanian stage gssp 774 ka is the chiba section japan it aligns with mis 19 and approximates the matuyama brunhes chron boundary 773 ka the upper pleistocene subseries with a base traditionally marked by the onset of the last interglacial is not yet defined by gssp the holocene series epoch was formally defined in 2008 by a gssp in the ngrip2 greenland ice core with an age of 11 700 yr b2k before 2000 ce and in 2018 was subdivided using climatic events at 8 2 and 4 2 ka into the greenlandian northgrippian and meghalayan stages ages and their corresponding lower early middle upper late subseries subepochs the northgrippian gssp 8236 yr b2k is defined in the ngrip1 greenland ice core and the meghalayan gssp 4250 yr b2k in a speleothem from meghalaya india this subdivision formally introduces the rank of subseries subepoch and incorporates by far the briefest of all stages into the geological time scale using ice cores and a speleothem for gssps is unique to the holocene the presently undefined term anthropocene is already used extensively and like holocene subdivisional terms its functionality will be enhanced by formal definition the anthropocene should not be confused with anthropogenic it reflects a tipping point in the earth system response to the marked intensification of human impacts not simply the fact of human impact the geological anthropocene as currently envisioned would start in the mid twentieth century holding the rank of series and terminating the holocene but not interfering with its subdivision other than to terminate the meghalayan stage

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

sverdrup and nonlinear dynamics of the pacific equatorial currents abstract the sverdrup circulation in the tropical pacific is constructed from satellite scatterometer winds compared with measured ocean currents and diagnosed in an ocean gcm previous depictions of the sverdrup circulation near the equator have shown only weak vertically integrated flows here it is shown that the actual transports are not weak this discrepancy could be due either to inaccuracies in the wind forcing or to sverdrup dynamics being too simple in this region scatterometer winds show a strip of positive curl along the sst front north of the equator in the eastern pacific that is due to wind speed changes induced by the front including that additional element of curl forcing greatly improves the realism of the sverdrup representation but the magnitudes of the equatorial transport are still too small by a factor of about 2 although the nonlinear advective and friction terms are small in the model momentum balance they are o 1 in the vorticity balance especially because their meridi

high resolution climatic monsoonal variability reconstructed from a continuous 2700 year sediment record from northwest himalaya ladakh a chronologically well constrained sedimentary archive from upshi ladakh was studied using a multi proxy approach namely palynology environmental magnetism total organic carbon toc total nit

effects of variable sedimentation rates and age errors on the resolution of sedimentary paleointensity records 1 synthetic u channel records of relative paleointensity have been generated with a numerical model simulating the recording process in sediments variable quality age control and variable sedimentation rates over a time interval of 500 ky simulation results indicate that paleointensity records with mean sedimentation rates up to 15 cm ky can reflect geomagnetic dipole intensity fluctuations with some amplitude differences between individual records of nongeomagnetic origin this study confirms that relative paleointensity records have great potential as a stratigraphic tool and that a stratigraphic precision of a few thousand years can be achieved with records characterized by high sedimentation rates spectral analyses suggest that caution should be used when interpreting the power spectra of individual records and that stacked records should be favored stacked u channel records with mean sedimentation rates of 1 cm ky do not provide reliable spectral information on the dipole intensity for wavelengths shorter than 25 50 ky and their utility is limited to long term trends in paleointensity for higher sedimentation rates the range of spectral information depends on the stack resolution sedimentation rates and the age model the best results are predictably obtained with high sedimentation rates and excellent age control in these cases the power spectra are reliable for wavelengths as short as 4 ky

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

relative paleointensity and inclination anomaly over the last 8 myr obtained from the integrated ocean drilling program site u1335 sediments in the eastern equatorial pacific

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

age calibrated relative paleointensity for the last 1 5 myr at iodp site u1308 north atlantic integrated ocean drilling program iodp site u1308 central north atlantic records paleomagnetic directional and relative paleointensity rpi variations for the last 1 5 myr in 110 m of the sediment sequence at a mean sedimentation rate of 7 3 cm kyr a detailed benthic oxygen isotope record was combined with rpi to produce an integrated high resolution magneto isotopic stratigraphy for site u1308 apart from the well known polarity reversals in this interval the punaruu excursion is recorded at 1092 ka and the cobb mountain subchron in the 1182 1208 ka interval the paleointensity proxies are determined as slopes of nrm versus arm and nrm versus armaq arm acquisition with linear correlation coefficients to monitor the quality of the linear fit the rpi record for site u1308 is compared with the three other paleointensity records one from the western equatorial pacific and two from the north atlantic that cover the same time interval and have accompanying oxygen isotope records the match protocol of lisiecki and lisiecki 2002 is used to optimize the correlation of paleointensity records beginning with the original published age models for each record the match routine is used to optimize the rpi correlations to site u1308 with checks to ensure compatibility with oxygen isotope records squared wavelet coherence wtc indicates significant improvement in rpi and oxygen isotope correlations after matching each rpi record to site u1308 particularly for periods 10 kyr the level of coherence for the atlantic rpi records and the lower resolution pacific record implies synchronous global variability at scales 10 kyr that can be attributed to the axial dipole geomagnetic field

an alternative suggestion for the pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of north atlantic ocean ice rafted debris abstract the onset of abundant ice rafted debris ird deposition in the nordic seas and subpolar north atlantic ocean 2 72 millions of years ago ma is thought to record the pliocene onset of major northern hemisphere glaciation nhg due to a synchronous advance of north american laurentide scandinavian and greenland ice sheets to their marine calving margins during marine isotope stage mis g6 numerous marine and terrestrial records from the nordic seas region indicate that extensive ice sheets on greenland and scandinavia increased ird inputs to these seas from 2 72 ma the timing of ice sheet expansion on north america as tracked by ird deposition in the subpolar north atlantic ocean however is less clear because both europe and north america are potential sources for icebergs in this region moreover cosmogenic dating of terrestrial tills on north america indicate that the laurentide ice sheet did not extend to 39 n until 2 4 0 14 ma at least 180 ka after the onset of major ird deposition at 2 72 ma to address this problem we present the first detailed analysis of the geochemical provenance of individual sand sized ird deposited in the subpolar north atlantic ocean between mis g6 and 100 2 72 2 52 ma ird provenance is assessed using laser ablation lead pb isotope analyses of single ice rafted 150 m feldspar grains to track when an ice rafting setting consistent with major nhg first occurred in the north atlantic ocean during the pliocene intensification of nhg inhg we investigate when the pb isotope composition 206pb 204pb 207pb 204pb 208pb 204pb of feldspars deposited at dsdp site 611 first resembles that determined for ird deposited at this site during mis 100 2 52 ma the oldest glacial for which there exists convincing evidence for widespread glaciation of north america whilst quaternary magnitude ird fluxes exist at site 611 during glacials from 2 72 ma we find that the provenance of this ird is not constant instead we find that the pb isotope composition of ird at our study site is not consistent with major nhg until mis g2 2 64 ma we hypothesise that ird deposition in the north atlantic ocean prior to mis g2 was dominated by iceberg calving from greenland and scandinavia we further suggest that the grounding line of continental ice on northeast america may not have extended onto the continental shelf and calved significant numbers of icebergs to the north atlantic ocean during glacials until 2 64 ma

a geomagnetic paleointensity record of 0 6 to 3 2 ma from sediments in the western equatorial pacific and remanent magnetization lock in depth

a detailed paleomagnetic record between 2 1 and 2 75 ma at iodp site u1314 in the north atlantic geomagnetic excursions and the gauss matuyama transition 1 this study investigated the detailed geomagnetic field variation between 2 1 and 2 75 ma from a sediment core iodp site u1314 with high sedimentation rate 10 cm kyr and good age control characteristic remanent magnetization directions were well resolved by stepwise alternating field demagnetization as a proxy of relative paleointensity natural remanent magnetization nrm normalized by anhysteretic remanent magnetization arm was used after testing that the influence of magnetic interaction in arm is negligible as a result the following features of the geomagnetic field in the studied period have been revealed during the transition of the gauss matuyama g m reversal and the reunion subchron the paleointensity decreased to the value lower than 20 of the average intensity in the whole studied interval in addition to these lows eight paleointensity lows were found associated with large directional changes that satisfy the definition of a geomagnetic excursion four of these have ages close to ages reported for geomagnetic excursions in prior studies whereas the other four excursions have not previously been observed in our results we confirm that the g m transition occurred in marine isotope stage 103 even if we consider the shift in depth due to the lock in process of magnetic particles the temporal variation in paleointensity showed asymmetric behavior associated with the g m transition with a gradual decrease prior to the transition and a rapid recovery after the transition

deep ocean inertia gravity waves simulated in a high resolution global coupled atmosphere ocean gcm 1 in order to investigate the deep ocean inertia gravity waves a high resolution global coupled atmosphere ocean simulation is carried out with a coupling interval of 20 minutes large 10 3 m s 1 root mean square variability of vertical velocity is found in middepths 2000 4000 m which is not reported in previous studies using realistic ocean simulations horizontal distribution of the large variability roughly corresponds to the wintertime atmospheric storm tracks and is stretched equatorward due to dispersion in open ocean with some shadow regions behind the obstacles frequency spectrum of vertical velocity has strong peaks at around f and 2f f is the local inertial period in midlatitudes and has additional peak at around 3 2 f or 3f at some points these results suggest necessity of re evaluation of wind induced near inertial energy with high frequency atmospheric forcing

origin of decadal scale eastward propagating heat content anomalies in the north pacific abstractupper ocean heat content ohc is at the heart of natural climate variability on interannual to decadal time scales providing climate memory and the source of decadal prediction skill in the midlatitude north pacific ocean ohc signals are often found to propagate eastward as opposed to the frequently observed westward propagation of sea surface height another variable that represents the ocean subsurface state this dichotomy is investigated using a 150 yr coupled gcm integration simulated ohc signals are distinguished in terms of two processes that can support eastward propagation higher baroclinic rossby wave rw modes that are associated with density perturbation and spiciness anomalies due to density compensated temperature and salinity anomalies the analysis herein suggests a unique role of the kuroshio oyashio extension koe region as an origin of the spiciness and higher mode rw signals wind forced westward propagating equivalent barotropic rws cause meridional shifts of the sub