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

a high resolution paleointensity stack of the past 14 to 68 ka from black sea sediments abstract detailed paleo and mineral magnetic analyses of a sediment composite record from the southeastern black sea yielded a high resolution well dated paleointensity record though hampered by some larger hiatuses in some cores and contaminated by diagenetically formed greigite the paleomagnetic composite record obtained from the preserved primary detrital magnetite phase reflects a highly dynamic geomagnetic field during the last glacial period relative variations of paleointensity inferred from the sediments magnetisations were converted into a record of the virtual axial dipole moment vadm lowest vadm values are linked with the laschamp 0 50 10 22 a m 2 at 41 0 ka the norwegian greenland sea 1 5 10 22 a m 2 at 64 5 ka and the mono lake 3 0 10 22 a m 2 at 34 5 ka geomagnetic excursions the fully reversed field during the laschamp excursion exhibits a vadm of 2 0 10 22 a m 2 which is more than 25 of the present day axial dipole moment 7 628 10 22 a m 2 rates of change calculated from the black sea vadm record also give some information on how to assess the global decay of the present day geomagnetic field which is significantly enhanced in the area of the south atlantic anomaly comparison with provided c 14 and 10 be records confirm partly in the very detail the non linear anti correlation of geomagnetic field intensity and the production of cosmogenic radionuclides in the earth s upper atmosphere however discrepancies in the timing of lows and highs in the compiled records points out that the combination of different data sets from different archives remains a challenge

giant magnetofossils and hyperthermal events abstract magnetotactic bacteria biomineralize magnetic minerals with precisely controlled size morphology and stoichiometry these cosmopolitan bacteria are widely observed in aquatic environments if preserved after burial the inorganic remains of magnetotactic bacteria act as magnetofossils that record ancient geomagnetic field variations they also have potential to provide paleoenvironmental information in contrast to conventional magnetofossils giant magnetofossils most likely produced by eukaryotic organisms have only been reported once before from paleocene eocene thermal maximum petm 55 8 ma sediments on the new jersey coastal plain here using transmission electron microscopic observations we present evidence for abundant giant magnetofossils including previously reported elongated prisms and spindles and new giant bullet shaped magnetite crystals in the southern ocean near antarctica not only during the petm but also shortly before and after the petm moreover we have discovered giant bullet shaped magnetite crystals from the equatorial indian ocean during the mid eocene climatic optimum 40 ma our results indicate a more widespread geographic environmental and temporal distribution of giant magnetofossils in the geological record with a link to hyperthermal events enhanced global weathering during hyperthermals and expanded suboxic diagenetic environments probably provided more bioavailable iron that enabled biomineralization of giant magnetofossils our micromagnetic modelling indicates the presence of magnetic multi domain i e not ideal for navigation and single domain i e ideal for navigation structures in the giant magnetite particles depending on their size morphology and spatial arrangement different giant magnetite crystal morphologies appear to have had different biological functions including magnetotaxis and other non navigational purposes our observations suggest that hyperthermals provided ideal conditions for giant magnetofossils and that these organisms were globally distributed much more work is needed to understand the interplay between magnetofossil morphology climate nutrient availability and environmental variability

great thrust earthquakes and aseismic slip along the plate boundary of the makran subduction zone the makran subduction zone of iran and pakistan exhibits strong variation in seismicity between its eastern and western segments and has one of the world s largest forearcs we determine the source parameters for 14 earthquakes at makran including the great mw 8 1 earthquake of 1945 the only instrumentally recorded great earthquake at makran we determine the loci of seismic and aseismic slip along the plate boundary and we assess the effects of the large forearc and accretionary wedge on the style of plate boundary slip we apply body waveform inversions and for small magnitude events use first motions of p waves to estimate earthquake source parameters for the 1945 event we also employ dislocation modeling of uplift data we find that the earthquake of 1945 in eastern makran is an interplate thrust event that ruptured approximately one fifth the length of the subduction zone nine smaller events in eastern makran that are also located at or close to the plate interface have thrust mechanisms similar to that of the 1945 shock seaward of these thrust earthquakes lies the shallowest 70 80 km of the plate boundary we find that this segment and the overlying accretionary wedge remain aseismic both during and between great earthquakes this aseismic zone as in other subduction zones lies within that part of the accretionary wedge that consists of largely uconsolidated sediments seismic velocities less than 4 0 km s the existence of thrust earthquakes indicates that either the sediments along the plate boundary in eastern makran become sufficiently well consolidated and de watered about 70 km from the deformation front or older lithified rocks are present within the forearc so that stick slip sliding behavior becomes possible this study shows that a large quantity of unconsolidated sediment does not necessarily indicate a low potential for great thrust earthquakes in contrast to the east the plate boundary in western makran has no clear record of historic great events nor has modem instrumentation detected any shallow thrust events for at least the past 25 years most earthquakes in western makran occur within the downgoing plate at intermediate depths the large change in seismicity between eastern and western makran along with two shallow events that exhibit right lateral strike slip motion in central makran suggest segmentation of the subduction zone two paleozoic continental blocks dominate the overriding plate the boundary between them is approximately coincident with the transition in seismicity although relative motion between these blocks may account for some of the differing seismic behavior the continuity of the deformation front and of other tectonic features along the subduction zone suggests that the rate of subduction does not change appreciably from east to west the absence of plate boundary events in western makran indicates either that entirely aseismic subduction occurs or that the plate boundary is currently locked and experiences great earthquakes with long repeat times evidence is presently inconclusive concerning which of these two hypotheses is most correct the presence of well defined late holocene marine terraces along portions of the coasts of eastern and western makran could be interpreted as evidence that both sections of the arc are capable of generating large plate boundary earthquakes if that hypothesis is correct then western makran could produce a great earthquake or it could rupture as a number of segments in somewhat smaller magnitude events alternatively it is possible that western makran is significantly different from eastern makran and experiences largely aseismic slip at all times a knowledge of the velocity structure and nature of the state of consolidation or lithification of rocks at depth in the interior portion of the forearc of western makran should help to ascertain whether that portion of the plate boundary moves aseismically or ruptures in large to great earthquakes a resolution of this question has important implications for seismic hazard not only for western makran but also for other margins such as the cascadia subduction zone of western north america where historical thrust events have not occurred

paleointensity assisted chronostratigraphy of detrital layers on the eirik drift north atlantic since marine isotope stage 11 1 four piston cores collected in 1999 and 2002 from the eirik drift southern labrador sea off se greenland provide paleomagnetic environmental magnetic and oxygen isotope records back to marine isotope stage 11 age models for the cores are based on a combination of planktonic oxygen isotope data relative geomagnetic paleointensity proxies and the identification of geomagnetic excursions laschamp and iceland basin environmental magnetic data delineate two distinct detrital signals interpreted to reflect the behavior of the surrounding ice sheets greenland and laurentide to orbital and millennial scale climate forcing broad decimeter scale intervals of increased magnetic concentration and grain size occur during the early part of interglacial marine isotopic stages mis 1 5 7 9 and 11 discrete centimeter scale layers recognized by magnetic concentration and grain size sensitive parameters gamma ray attenuation gra bulk density and carbonate content are observed in glacial and interglacial stages as well as during terminations on the basis of glacial reconstructions on greenland during the last termination the broad decimeter scale coarser grained intervals can be attributed to detrital influx associated with the retreat of the terrestrial based greenland ice sheet in the early holocene a similar magnetic signal observed within interglacial mis 5 7 9 and 11 indicates similar greenland ice sheet behavior during these time intervals two types of centimeter scale detrital layers are also recognized back to mis 11 detrital carbonate dc layers reflect predominately ice rafted debris ird deposition while the low detrital carbonate ldc layers reflect mass movement as evidenced by sharp basal contacts graded bedding and traction structures likely from the greenland slope some detrital layers on eirik drift particularly the dc layers can be tentatively correlated to detrital layers observed in the central north atlantic and to those documented on the southern side of the labrador sea at orphan knoll

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 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

an optimized scheme of lettered marine isotope substages for the last 1 0 million years and the climatostratigraphic nature of isotope stages and substages a complete and optimized scheme of lettered marine isotope substages spanning the last 1 0 million years is proposed lettered substages for marine isotope stage mis 5 were explicitly defined by shackleton 1969 but analogous substages before or after mis 5 have not been coherently defined short term discrete events in the isotopic record were defined in the 1980s and given decimal style numbers rather than letters but unlike substages they were neither intended nor suited to identify contiguous intervals of time substages for time outside mis 5 have been lettered or in some cases numbered piecemeal and with conflicting designations we therefore propose a system of lettered substages that is complete without missing substages and optimized to match previous published usage to the maximum extent possible our goal is to provide order and unity to a taxonomy and nomenclature that has developed ad hoc and somewhat chaotically over the decades our system is defined relative to the lr04 stack of marine benthic oxygen isotope records and thus it is grounded in a continuous record responsive largely to changes in ice volume that are inherently global this system is intended specifically for marine oxygen isotope stages but it has relevance also for oxygen isotope stages recognized in time series of non marine oxygen isotope data and more generally for climatic stages which are recognized in time series of non isotopic as well as isotopic data the terms stage and substage in this context are best considered to represent climatostratigraphic units and thus climatic stages and climatic substages because they are recognized from geochemical and sedimentary responses to climate change that may not have been synchronous at global scale

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

origin of the northern indus fan and murray ridge northern arabian sea interpretation from seismic and magnetic imaging abstract the nature and origin of the sediments and crust of the murray ridge system and northern indus fan are discussed the uppermost unit consists of middle miocene to recent channel levee complexes typical of submarine fans this unit is underlain by a second unit composed of hemipelagic to pelagic sediments deposited during the drift phase after the break up of india seychelles africa a predrift sequence of assumed mesozoic age occurring only as observed above basement ridges is composed of highly consolidated rocks different types of the acoustic basement were detected which reflection seismic pattern magnetic anomalies and gravity field modeling indicate to be of continental character the continental crust is extremely thinned in the northern indus fan lacking a typical block faulted structure the indian continent ocean transition is marked on single mcs profiles by sequences of seaward dipping reflectors sdr in the northwestern arabian sea the indian plate margin is characterized by several phases of volcanism and deformation revealed from interpretation of multichannel seismic profiles and magnetic anomalies from this study thinned continental crust spreads between the northern murray ridge system and india underneath the northern indus fan

twin tsunamis triggered by the 12 january 2010 haiti earthquake on 12 january 2010 a magnitude m w 7 0 earthquake occurred 25 km west southwest of haiti s capital port au prince causing an estimated 316 000 fatalities thereby exceeding any previous loss of life from a similar size earthquake in addition tsunami waves triggered by the earthquake caused at least three fatalities at petit paradis due to a complete lack of tsunami awareness the international tsunami survey team itst was deployed within weeks of the event and covered the greater bay of port au prince and more than 100 km of hispaniola s southern coastline the collected survey data include more than 21 tsunami heights along with observations of coastal land level change maximum tsunami heights of 3 m have been measured for two independently triggered tsunamis

long term secular variation of the geomagnetic field during the last 200 kyr recorded in sediment cores from the western equatorial pacific we have conducted a paleomagnetic study of five hemipelagic clay cores of 4 7 m in length obtained from the west caroline basin western equatorial pacific the purpose of this study is to clarify the long term secular variation of the geomagnetic field during the last 200 kyr using both intensity and directional changes one core was dated using oxygen isotope ratios 18o and characteristic magnetic susceptibility variations of about a factor of four allowed precise correlation between all cores the magnetic mineralogy is estimated to be dominated by magnetite of single domain sd and or pseudo single domain psd state the magnetic mineralogy and grain size are uniform throughout the cores which enabled us to obtain relative paleointensity variations as well as directional changes remanent intensity normalized by anhysteretic remanent magnetization arm indicates that sharp intensity drops to 20 of the present field occurred at about 40 and 190 kyr b p with a broader decrease around 110 kyr b p the former two are accompanied by anomalous remanent directions suggesting short polarity reversals or excursions their ages are close to those of the previously reported laschamp excursion and biwa i event a prominent intensity peak occurred immediately preceding the possible excursion at 40 kyr b p our results are in general similar to the recently reported datasets spanning the last 80 140 kyr from the somali basin the mediterranean and the sulu sea 1 3 the inclination record shows long term cyclic changes of several degrees in amplitude the intervals of the recurring variation are 40 50 kyr which is longer than the core s memory and is close to the milankovitch frequency associated with the change in obliquity of earth s rotational axis we infer that an external force such as orbital forcing could be a cause of the long term secular variation

geomagnetic field evolution during the laschamp excursion abstract since the last geomagnetic reversal 780 000 years ago the earth s magnetic field repeatedly dropped dramatically in intensity this has often been associated with large variations in local field direction but without a persistent global polarity flip the structure and dynamics of geomagnetic excursions and especially the difference between excursions and polarity reversals have remained elusive so far for the best documented excursion the laschamp event at 41 000 years bp we have reconstructed the evolution of the global field morphology by using a bayesian inversion of several high resolution palaeomagnetic records we have obtained an excursion scenario in which inverse magnetic flux patches at the core mantle boundary emerge near the equator and then move poleward contrary to the situation during the last reversal leonhardt r fabian k 2007 paleomagnetic reconstruction of the global geomagnetic field evolution during the matuyama brunhes transition iterative bayesian inversion and independent verification earth planet sci lett 253 172 195 these flux patches do not cross the hydrodynamic boundary of the inner core tangent cylinder while the last geomagnetic reversal began with a substantial increase in the strength of the non dipolar field components prior to the laschamp excursion both dipolar and non dipolar field decay at the same rate this result suggests that the nature of an upcoming geomagnetic field instability can be predicted several hundred years in advance even though during the laschamp excursion the dipolar field at the earth s surface was dominant the reconstructed dynamic non dipolar components lead to considerable deviations among predicted records at different locations the inverse model also explains why at some locations no directional change during the laschamp excursion is observed

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

geomagnetic paleointensity for the last 100 kyr from the sub antarctic south atlantic a tool for inter hemispheric correlation abstract we report relative paleointensity proxy records from four piston cores collected near the agulhas ridge and meteor rise south atlantic the mean sedimentation rate of the cores varies from 24 cm kyr to 11 cm kyr the two cores with mean sedimentation rates over 20 cm kyr record positive remanence inclinations at 40 41 ka coeval with the laschamp event age models are based on oxygen isotope data from three of the cores augmented by radiocarbon ages from nearby core rc11 83 and by correlation of paleointensity records for the one core with no oxygen isotope data the relative paleointensity proxy records are the first from the south atlantic and from the high to mid latitude southern hemisphere prominent paleointensity lows at 40 ka and 65 ka as well as many other features can be correlated to paleointensity records of comparable resolution from the northern hemisphere the records are attributable in large part to the global scale field and therefore have potential for inter hemispheric correlation at a resolution difficult to achieve with isotope data alone

the iceland basin excursion age duration and excursion field geometry the iceland basin geomagnetic excursion coincided with the marine isotope stage mis 6 7 boundary the age and duration of the excursion at seven north atlantic sites with sufficient isotope data are estimated by matching marine isotope stage mis 7a 7c to a calibrated template two criteria for defining the excursion virtual geomagnetic pole vgp latitudes 0 and 40 n yield excursion durations of 1 4 and 2 5 kyr respectively the midpoints of the excursion are in the 189 192 ka range with a mean of 190 2 ka although component magnetization directions are generally well defined rapid changes in field direction during a time of low field intensity are not adequately recorded during the excursion vgps transit southward over africa and the south atlantic reach high southern latitudes at the culmination of the excursion with partial recovery in relative paleointensity rpi and then track northward through the western pacific the high southern latitude vgps and the recovery in rpi imply that the earth s main axial dipole reversed polarity during the excursion if only for 1 kyr implying that excursions can be manifested globally and are important in millennial scale stratigraphy vgp clustering in the south atlantic and nw pacific roughly coincide with maxima in the vertical downward component of the modern nondipole nd field determined at the earth s surface which implies that the nd field became dominant as the geocentric dipole field weakened during the excursion and also that the nd field configuration is long lived on multimillennial timescales

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

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

late pleistocene evolution of the ocean s carbonate system abstract we demonstrate that the carbonate record from a single site ocean drilling program site 1089 in the deep south atlantic represents a qualitative high resolution record of the temporal evolution of the carbonate saturation state of the deep sea the record is especially notable because it is free from many of the complications that limit other records low sedimentation rates blurring by chemical erosion bioturbation etc the pattern of carbonate variability is characteristic of indo pacific cores with high carbonate glacials and low carbonate interglacials wt carbonate lags changes in benthic 18 o by an average of 7 6 kyr and carbonate variations are in phase with the rate of change first derivative of benthic 18 o intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations these observations represent two fundamentally different responses of the marine carbonate system the lagged response of carbonate to 18 o reflects a steady state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial the site 1089 carbonate signal is remarkably similar to inferred changes in the sr ca of seawater for the past 250 kyr which implies that both carbonate dissolution and seawater sr ca may be controlled by sea level induced changes in the location of carbonate deposition shelf basin fractionation during glacial to interglacial cycles the transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and dic in the ocean i e carbonate compensation comparison of the site 1089 carbonate and vostok p co 2 records suggests a role of deep sea co 3 2 variations for governing at least some second order features of the atmospheric p co 2 signal in order to quantify this role however measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep sea co 3 2

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

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

climate connections between the hemisphere revealed by deep sea sediment core ice core correlations abstract correlation of southern ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean s thermohaline circulation over the last 80 000 years our observations suggest that while north atlantic deep water variability manifests itself clearly in southern ocean nutrient proxy records over periods as short as 500 yr this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales in particular the proxy records indicate that on average northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr

cyclone gonu storm surge in oman super cyclone gonu is the strongest tropical cyclone on record in the arabian sea gonu caused coastal damage due to storm surge and storm wave impact as well as wadi flooding high water marks overland flow depths and inundation distances were measured in the coastal flood zones along the gulf of oman from 1 to 4 august 2007 the high water marks peaked at ras al hadd at the eastern tip of oman exceeding 5 m the storm surge of gonu is modeled using the advanced circulation model adcirc the multi hazard aspect is analyzed by comparing observations from cyclone gonu with the 2004 indian ocean tsunami

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

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

extension across the indian arabian plate boundary the murray ridge summary seismic reflection profiles from the murray ridge in the gulf of oman northwest indian ocean show a significant component of extension across the predominantly strike slip indian arabian plate boundary the murray ridge lies along the northern section of the plate boundary where its trend becomes more easterly and thus allows a component of extension the dalrymple trough is a 25 km wide steep sided halfgraben bounded by large faults with components of both strike slip and normal motion the throw at the seabed of the main fault on the southeastern side of the halfgraben reaches 1800 m the northwest side of the trough is delineated by a series of smaller antithetic normal faults wide angle seismic gravity and magnetic models show that the murray ridge and dalrymple trough are underlain by a crystalline crust up to 17 km thick which may be continental in origin any crustal thinning due to extension is limited and no new crust has been formed we favour a plate model in which the indian arabian plate boundary was initially located further west than the owen fracture zone possibly along the oman continental margin and suggest that during the oligocene early miocene indian ocean plate reorganization the plate boundary moved to the site of the present owen fracture zone and that motion further west ceased at this time deformation began along the murray ridge with both the uplift of basement highs and subsidence in the troughs tilting the lowest sedimentary unit qalhat seamount was formed at this time subsequent sediments were deposited unconformably on the tilted lower unit and then faulted to produce the present basement topography the normal faulting was accompanied by hanging wall subsidence footwall uplift and erosion flat lying recent sediments show that the major vertical movements have ceased although continuing earthquakes show that some faulting is still active along the plate boundary

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

deconvolution of u channel paleomagnetic data near geomagnetic reversals and short events 1 the deconvolution scheme of oda and shibuya 1996 designed for half core data from the pass through magnetometer aboard the joides resolution has been adapted for treatment of u channel data the program was tested using u channels from ocean drilling program odp site 1090 a significant increase in resolution of the u channel data can be achieved by deconvolution resulting in data comparable with that obtained by continuous discrete sampling large amplitude changes of the magnetization vector revealed by the deconvolution treatment are in good agreement with the results obtained on discrete samples extracted from the same u channels application of this procedure to u channel data from odp sites 983 and 984 over a short time interval around 1 255 ma permitted enhanced definition of the so called bjorn geomagnetic event

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 1994 shikotan earthquake tsunamis the 1994 shikotan earthquake was one of the greatest earthquakes in recent years with a magnitude of m s 8 0 a tsunami survey was conducted by russian and u s geophysicists from october 16 30 1994 less than two weeks after the earthquake the survey results and a numerical hindcast simulation are reported tsunami focusing effect at locations supposedly sheltered by the island chain is discussed based on the obtained data tsunamis which attacked shikotan island are characterized as long waves the order of 10 20 min wave period with a positive leading wave possible consequences of the positive leading wave form are discussed in relation to the observed minimal destruction of beach vegetation and relatively small transport of marine sediment onto the shore the high quality tide gage record in malokurilskaya bay indicates the occurrence of a 53 cm subsidence at the site

deformation at plate boundaries around the gulf of oman abstract seismic studies during charles darwin cruise 18 86 focused on three zones of deformation the makran accretionary prism the murray ridge owen fracture zone system and the continental margin of east oman a multichannel seismic reflection profile across the makran margin clearly imaged the imbricate thrust slices and their bounding faults a bottom simulating reflector bsr 500 800 m beneath the seabed marking the base of a gas hydrate stability zone may be traced across most of the profile the heat flow variation estimated from changes in the depth of this reflector shows evidence for localised fluid expulsion reflection profiles across the murray ridge show evidence for active extension along a series of major normal faults the rift structure is segmented with the fault polarity changing between segments a combined reflection and wide angle study of the east oman margin shows a deep offshore basin underlain by crust only 5 km thick and bounded by a basement ridge interpreted as a tilted fault block the wide angle data suggest a sleeply dipping moho beneath the margin the large lateral changes in crustal thickness may be explained by episodes of margin parallel shear

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

geomagnetic assisted stratigraphy and sea surface temperature changes in core md94 103 southern indian ocean possible implications for north south climatic relationships around h4 abstract new records of past sea surface temperatures ssts were derived in the 30 50 kyr b p time interval from a core located at 45 s in the southern indian ocean md94 103 to investigate the climatic phasing between the southern indian ocean the greenland and the antarctic ice the magnetic signal of core md94 103 was synchronized at better than millennial accuracy in the vicinity of the laschamp geomagnetic to a reference record napis 75 already placed on the gisp2 age model coccolithophorid and diatom species abundances both point to a cooling of surface waters during h4 specific diatoms also indicate lower salinity waters during the same time interval these observations do not support the idea that the south hemisphere warmed 1 5 2 kyr before the north hemisphere nature 394 1998 739 rather alkenone derived ssts suggest that cold conditions have characterized the surface waters in the south latitudes during h4 and h5 and that temperature at evaporation sites contributed to the isotopic events a1 and a2 visible in the isotopic records of central antarctica earth planet sci lett 177 2000 219 ssts obtained from foraminifera assemblages depict somewhat different temperature patterns possibly indicative of water stratification

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

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

the mis 11 paradox and ocean circulation role of millennial scale events the role of millennial scale climate variability in supplementing the astronomical forcing of glacial interglacial transitions remains a major unresolved question here we compare the occurrence and character of terminal ice rafting events in both the north and south atlantic during the last deglaciation termination i ti and during the transition between marine isotope stages mis 12 and 11 or termination v tv we show that tv experienced a massive terminal ice rafting event in the north atlantic that was more intense and longer lasting than heinrich event 1 h1 of the last deglaciation this massive ice rafting event was linked to cold stadial conditions and reduced deep water formation in the north atlantic in parallel with warming at high southern latitudes similar to the bipolar seesaw pattern exhibited during h1 over the last deglaciation we propose that the particular intensity and duration of the tv ice rafting event resulted from the especially large volume of northern hemisphere ice sheets during mis12 in turn the unusually long duration and large amplitude of tv likely resulted from the exceptionally prolonged collapse of the amoc during the tv heinrich stadia and from a subsequent transient amoc overshoot with respect to later mis11 interglacial circulation furthermore we suggest that the intense heinrich stadial of tv contributed to the deglaciation primarily via meridional heat transport anomalies that would have enhanced the incipient warming arising from relatively weak insolation forcing and only secondarily via co2 release

age and duration of laschamp and iceland basin geomagnetic excursions in the south atlantic ocean abstract age models for new records of the laschamp and iceland basin excursions from the eastern flank of the south atlantic mid ocean ridge 44 15 s 14 22 w are derived from radiocarbon dates and from matching sea surface temperature records to antarctic epica air temperature records from ice cores the onset of the laschamp excursion occurred during antarctic isotopic maximum aim 10 consistent with its occurrence during greenland interstadial 10 the end of the laschamp excursion occurred prior to aim 9 in greenland stadial 10 the age model is supported by synchroneity of directional and relative paleointensity manifestations of the laschamp excursion in the marine core with peaks in epica 10 be and nitrate flux the iceland basin excursion is synchronous with the final phase of the transition from marine isotope stage mis 7a to mis 6e as recorded in the epica d record the onset of the laschamp and iceland basin excursions defined here by component inclinations 40 occurred at 41 4 ka and 190 0 ka and durations are 1 kyr and 3 5 kyr respectively although these estimates depend on the criteria used to define the directional excursions by comparison with laschamp and iceland basin excursion records from the north atlantic ocean the two excursions are synchronous at centennial timescales between the two hemispheres based on synchronization of the gicc05 and aicc2012 age models for greenland and antarctic ice cores

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

owen fracture zone the arabia india plate boundary unveiled we surveyed the owen fracture zone at the boundary between the arabia and india plates in the nw indian ocean using a high resolution multibeam echo sounder owen cruise 2009 for search of active faults bathymetric data reveal a previously unrecognized submarine fault scarp system running for over 800 km between the sheba ridge in the gulf of aden and the makran subduction zone the primary plate boundary structure is not the bathymetrically high owen ridge but is instead a series of clearly delineated strike slip fault segments separated by several releasing and restraining bends despite an abundant sedimentary supply by the indus river flowing from the himalaya fault scarps are not obscured by recent deposits and can be followed over hundreds of kilometres pointing to very active tectonics the total strike slip displacement of the fault system is 10 12 km indicating that it has been active for the past 3 to 6 ma if its current rate of motion of 3 1 mm yr 1 has remained stable we describe the geometry of this recent fault system including a major pull apart basin at the latitude 20 n and we show that it closely follows an arc of small circle centred on the arabia india pole of rotation as expected for a transform plate boundary

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

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

response of south atlantic deep waters to deglacial warming during terminations v and i abstract new deep sea core data from the atlantic sector of the southern ocean covering mis12 to mis10 and the last deglaciation show a clear lag of the changes in deep water properties with respect to changes in surface conditions the development of a chronology based on the correlation of southern ocean sea surface temperature with air temperature over antarctica allows the quantification and comparison of phase lags within the marine records during termination v tv and termination i ti deglacial changes in the south atlantic are interpreted as the response to changes in the state of the atlantic meridional ocean circulation amoc the warming of south atlantic surface waters and air temperature over antarctica at the beginning of both tv and ti is attributable to a reduction in interhemispheric heat transport due to the weakening of the amoc comparison of our results with climber 2 simulations indicates that the response of bottom waters seen in the benthic isotopic records delayed with respect to south atlantic surface warming can be explained by the increased inflow of north atlantic deep water nadw to the south atlantic site at the time of the amoc recovery reconstructed sea surface temperature at our south atlantic site exhibits a cold spell at the end of tv resembling the antarctic cold reversal of the last deglaciation the presence of cold spells during tv and ti may be explained by the fact that the recovery of the amoc took place early during the termination in both cases the sequence of events is similar during both terminations however the magnitude of the phase shifts between south atlantic surface and deep waters conditions differs from one termination to the other suggesting variations in the magnitude and duration of the amoc perturbation

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

deep sea sediment records of the laschamp geomagnetic field excursion 41 000 calendar years before present 1 we have recovered two new high resolution paleomagnetic records of the laschamp excursion 41 000 calendar years b p from deep sea sediments of the western north atlantic ocean the records document that the laschamp excursion was characterized locally by 1 declination changes of 120 2 inclination changes of more than 140 3 1200 year oscillations in both inclination and declination 4 near 90 out of phase relationships between inclinations and declinations that produced two clockwise loops in directions and virtual geomagnetic poles vgps followed by a counterclockwise loop 5 excursional vgps during both intervals of clockwise looping 6 magnetic field intensities less than 10 of normal that persisted for almost 2000 years 7 marked similarity in excursional directions over 5000 km spatial scale length and 8 secular variation rates comparable to historic field behavior but persisting in sign for hundreds of years all of these features with the exception of anomalously large directional amplitude are consistent with normal magnetic field secular variation comparison of our laschamp excursion paleomagnetic records with other late quaternary excursion records suggests that there is a group of excursions which we term class i which have strikingly similar patterns of field behavior and likely share a common cause as part of the overall core dynamo process three general models of secular variation are described that can qualitatively produce class i excursions on the basis of these observations we conclude that class i excursions epitomized by the laschamp excursion are more closely related to normal secular variation and are not necessarily a prelude to magnetic field reversal

variable remanence acquisition efficiency in sediments containing biogenic and detrital magnetites implications for relative paleointensity signal recording widespread geological preservation of biogenic magnetite makes it important to assess how such particles contribute to sedimentary paleomagnetic signals we studied a sediment core from the south china sea that passes the strict empirical criteria for magnetic uniformity used in relative paleointensity studies such assessments are based routinely on bulk magnetic parameters that often fail to enable identification of mixed magnetic mineral assemblages using techniques that enable component specific magnetic mineral identification we find that biogenic and detrital magnetites occur in approximately equal concentrations within the studied sediments we analyzed normalized remanence signals associated with the two magnetite components to assess whether co occurring biogenic and detrital magnetites record geomagnetic information in the same way and with the same efficiency paleomagnetic directions for the two components have no phase lag which suggests that the biogenic and detrital magnetites acquired their magnetizations at equivalent times however we find that the biogenic magnetite is generally 2 4 times more efficient as the detrital magnetite in contributing to the natural remanent magnetization nrm despite their approximately equal magnetic contributions variations in the concentration and efficiency of remanence acquisition of the two components suggest that a significant part of the nrm is controlled by nongeomagnetic factors that will affect relative paleointensity recording we recommend that methods suited to the detection of variable recording efficiency associated with biogenic and detrital magnetites should be used on a routine basis in relative paleointensity studies

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

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

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

the global reach of the 26 december 2004 sumatra tsunami numerical model simulations combined with tide gauge and satellite altimetry data reveal that wave amplitudes directionality and global propagation patterns of the 26 december 2004 sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid ocean ridge topographic waveguides

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

relative paleointensity of the geomagnetic field over the last 200 000 years from odp sites 883 and 884 north pacific ocean ocean drilling program sites 883 and 884 were cored as part of a three site depth transect down the slopes of detroit seamount in the north pacific ocean continuous mineral magnetic and paleomagnetic measurements were made using u channel samples for sediments that span the last 200 kyr thermomagnetic and high field hysteresis data indicate that the magnetic mineralogy of the clay rich sediments at the two sites is dominated by pseudo single domain magnetite in a narrow range of grain sizes and concentrations thereby meeting established criteria for relative paleointensity studies the natural remanent magnetization nrm has been normalized using the anhysteretic remanent magnetization arm and the low field magnetic susceptibility the nrm arm and nrm records are nearly identical for both cores furthermore coeval horizons in the two cores can be correlated by matching 100 magnetic susceptibility features over the 15 m length of both cores coherence function analysis indicates that the records are not significantly affected by local environmental conditions these factors suggest that the large scale variations in normalized remanence are most likely due to geomagnetic paleointensity fluctuations dating constraints are provided by a 18o stratigraphy from site 883 our north pacific paleointensity versus age curve is similar to a published record from the western caroline basin and a recently proposed global paleointensity curve offsets up to 10 kyr in the timing of paleointensity features between our composite north pacific record and the global curve may result from imprecisions in the dating of our record nevertheless the correspondence between the paleointensity records suggests that in suitable sediments paleointensity of the geomagnetic field can give a globally coherent dominantly dipolar signal

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

lituya bay landslide impact generated mega tsunami 50th anniversary on july 10 1958 an earthquake mw 8 3 along the fairweather fault triggered a major subaerial landslide into gilbert inlet at the head of lituya bay on the southern coast of alaska the landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history the mega tsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis a cross section of gilbert inlet was rebuilt at 1 675 scale in a two dimensional physical laboratory model based on the generalized froude similarity a pneumatic landslide tsunami generator was used to generate a high speed granular slide with controlled impact characteristics state of the art laser measurement techniques such as particle image velocimetry piv and laser distance sensors lds were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland piv provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup the entire process of a high speed granular landslide impact may be subdivided into two main stages a landslide impact and penetration with flow separation cavity formation and wave generation and b air cavity collapse with landslide run out and debris detrainment causing massive phase mixing formation of a large air cavity similar to an asteroid impact in the back of the landslide is highlighted a three dimenional pneumatic landslide tsunami generator was designed constructed and successfully deployed in the tsunami wave basin at osu the lituya bay landslide was reproduced in a three dimensional physical model at 1 400 scale the landslide surface velocities distribution was measured with piv the measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models

effects of bathymetry on tsunami propagation application of ray tracing to tsunamis ray tracing of seismic surface waves is applied to tsunami propagation to examine bathymetric effect along its propagation path computations are made for trans pacific tsunamis and for near field tsunamis in the japan sea for tsunamis across the pacific ocean the comparison to a uniform ocean shows that focusing and defocusing due to bathymetry are significant for some combinations of source and receiver for example the refraction of rays is predominant at the east pacific rise for the tsunami from chile the tsunamis in the japan sea are strongly affected by the shallow yamato rise the predicted arrival time and amplitude distribution generally agree with the observations from an actual tsunami since the computation can be made very quickly the method is useful for preliminary analysis of tsunami propagation such as in an operational warning system or in the determination of computational area for finite difference computation

contribution of seasonal sub antarctic surface water variability to millennial scale changes in atmospheric co2 over the last deglaciation and marine isotope stage 3 the southern ocean is thought to have played a key role in past atmospheric carbon dioxide co2 atm changes three main factors are understood to control the southern ocean s influence on co2 atm via their impact on surface ocean pco2 and therefore regional ocean atmosphere co2 fluxes 1 the efficiency of air sea gas exchange which may be attenuated by seasonal or annual sea ice coverage or the development of a shallow pycnocline 2 the supply of co2 rich water masses from the sub surface and the deep ocean which is associated with turbulent mixing and surface buoyancy and or wind forcing and 3 biological carbon fixation which depends on nutrient availability and is therefore influenced by dust deposition and or upwelling in order to investigate the possible contributions of these processes to millennial scale co2 atm variations during the last glacial and deglacial periods we make use of planktonic foraminifer census counts and stable oxygen and carbon isotope measurements in the planktonic foraminifera globigerina bulloides and neogloboquadrina pachyderma sinistral from marine sediment core md07 3076q in the sub antarctic atlantic these data are interpreted on the basis of a comparison of core top and modern seawater isotope data which permits an assessment of the seasonal biases and geochemical controls on the stable isotopic compositions of g bulloides and n pachyderma s based on a comparison of our down core results with similar data from the southeast atlantic cape basin we infer past basin wide changes in the surface hydrography of the sub antarctic atlantic we find that millennial scale rises in co2 atm over the last 70 ka are consistently linked with evidence for increased spring upwelling and enhanced summer air sea exchange in the sub antarctic atlantic parallel evidence for increased summer export production would suggest that seasonal changes in upwelling and air sea exchange exerted a dominant influence on surface pco2 in the sub antarctic atlantic these results underline the role of southern ocean dynamics in particular their seasonal variations in driving millennial scale variations in co2 atm

geomagnetic field behavior during the iceland basin and laschamp geomagnetic excursions a simple transitional field geometry we present four new records of the iceland basin excursion ibe and five new records of the laschamp excursion le obtained from rapidly deposited marine sediments in the north atlantic ocean the nordic seas the gulf of mexico the south china sea and the southern indian ocean marked minima in relative paleointensity correspond with the paleomagnetic directional changes associated with all of the excursion records the virtual geomagnetic pole vgp paths of the four ibe records are all similar the vgps move southward over europe and africa reaching the southern hemisphere three reach antarctica and then move to more eastern longitudes before returning northward over australia and east asia describing a large counterclockwise loop the same vgp pattern is observed in other published records the vgp paths observed for the le are similar to those of the ibe however they loop clockwise instead of counterclockwise despite the different sense of looping the marked similarity among the paths for the two excursions suggests that a similar relatively simple geometry dominated the transitional field during both the ibe and the le similar dynamo mechanisms must therefore have been active in the earth s core for both excursions the duration of the excursions is estimated at 2 000 years which supports the suggestion that a difference exists between the mechanisms for excursions and reversals however the coincidence of the longitudinal bands for vgps associated with excursions compared to some reversal paths could also indicate an inherent link between the mechanisms for reversals and excursions

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

the generating mechanisms of the august 17 1999 izmit bay turkey tsunami regional tectonic and local mass instabilities causes abstract the m w 7 4 earthquake that affected the northwestern part of turkey on august 17 1999 and in particular the gulf of izmit had dramatic consequences also as regards tsunami generation the main cause of the earthquake was a dextral strike slip rupture that took place along different segments of the western part of the north anatolian fault wnaf the rupture process involved not only a number of distinct strike slip fault segments but also dip slip ancillary faults connecting the main transcurrent segments the general picture was further complicated by the occurrence of subsidence and liquefaction phenomena especially along the coasts of the izmit bay and in the sapanca lake tsunami effects were observed and measured during post event surveys in several places along both the northern and the southern coasts of the bay the run up heights in most places were reported to lie in the interval 1 3 m but in the small town of degirmendere where a local slump occurred carrying underwater buildings and gardens of the waterfront sector eyewitnesses reported water waves higher than 15 m the purpose of this work is to investigate on the causes of the tsunami by means of numerical simulations of the water waves we show that the tsunami was a complex event consisting at least of the combination of a regional event due to tectonic causes and of a local event associated with the mass failure as to the first we are able to demonstrate that the observed tsunami cannot be explained only in terms of the sea bottom dislocation produced by the main right lateral dislocation but that the prominent contribution comes from the displacement associated with the secondary shallow normal faults furthermore the large waves and effects seen in degirmendere can be explained as the consequence of the slump by means of a stability analysis based on an original method making use of the limit equilibrium concept we show that the slump was highly stable before the earthquake and that it was triggered by seismic waves simulation of the tsunami induced by the slump was carried out by a two step numerical code that computes the landslide motion first and then the generated water wave propagation it is shown that the computed local tsunami matches the experimental data

magnetotactic bacterial abundance in pelagic marine environments is limited by organic carbon flux and availability of dissolved iron article i nfo article history magnetotactic bacteria intracellularly biomineralize magnetite of an ideal grain size for recording palaeomagnetic signals however bacterial magnetite has only been reported in a few pre quaternary records because progressive burial into anoxic diagenetic environments causes its dissolution deep sea carbonate sequences provide optimal environments for preserving bacterial magnetite due to low rates of organic carbon burial and expanded pore water redox zonations such sequences often do not become anoxic for tens to hundreds of metres below the seafloor nevertheless the biogeochemical factors that control magnetotactic bacterial populations in such settings are not well known we document the preservation of bacterial magnetite which dominates the palaeomagnetic signal throughout eocene pelagic carbonates from the southern kerguelen plateau southern ocean we provide evidence that iron fertilization associated with increased aeolian dust flux resulted in surface water eutrophication in the late eocene that controlled bacterial magnetite abundance via export of organic carbon to the seafloor increased flux of aeolian iron bearing phases also delivered iron to the seafloor some of which became bioavailable through iron reduction our results suggest that magnetotactic bacterial populations in pelagic settings depend crucially on particulate iron and organic carbon delivery to the seafloor

paleomagnetic reconstruction of the global geomagnetic field evolution during the matuyama brunhes transition iterative bayesian inversion and independent verification abstract the earth s magnetic field changed its polarity from the last reversed into today s normal state approximately 780 000 years ago while before and after this so called matuyama brunhes reversal the earth magnetic field was essentially an axial dipole the details of its transitional structure are still largely unknown here a bayesian inversion method is developed to reconstruct the spherical harmonic expansion of this transitional field from paleomagnetic data this is achieved by minimizing the total variational power at the core mantle boundary during the transition under paleomagnetic constraints the validity of the inversion technique is proved in two ways first by inverting synthetic data sets from a modeled reversal here it is possible to reliably reconstruct the gauss coefficients even from noisy records second by iteratively combining four geographically distributed high quality paleomagnetic records of the matuyama brunhes reversal into a single geometric reversal scenario without assuming an a priori common age model the obtained spatio temporal reversal scenario successfully predicts most independent matuyama brunhes transitional records therefore the obtained global reconstruction based on paleomagnetic data invites to compare the inferred transitional field structure with results from numerical geodynamo models regarding the morphology of the transitional field it is found that radial magnetic flux patches form at the equator and move polewards during the transition our model indicates an increase of non dipolar energy prior to the last reversal and a non dipolar dominance during the transition thus the character and information of surface geomagnetic field records is strongly site dependent the reconstruction also offers new answers to the question of existence of preferred longitudinal bands during the transition and to the problem of reversal duration different types of directional variations of the surface geomagnetic field continuous or abrupt are found during the transition two preferred longitudinal bands along the americas and east asia are not predicted for uniformly distributed sampling locations on the globe similar to geodynamo models with cmb heatflux derived from present day lower mantle heterogeneities a preference of transitional vgps for the pacific hemisphere is found the paleomagnetic duration of reversals shows not only a latitudinal but also a longitudinal variation even the paleomagnetically determined age of the reversal varies significantly between different sites on the globe the described bayesian inversion technique can easily be applied to other high quality full vector reversal records also its extension to inversion of secular variation and excursion data is straightforward

deep sea sedimentary analogs for the vostok ice core 1 many applications of the vostok ice core depend critically on the ability to make stratigraphic ties to marine records in the adjacent southern ocean here we present oxygen isotopic records from high accumulation rate sites in the south atlantic sector of the southern ocean collected for the purpose of complementing the recently extended d record from the vostok ice core the combination of several planktonic foraminiferal 18o records from northern subantarctic piston cores demonstrates that all of the millennial scale oscillations expressed in the vostok ice core over the last 60 ky are also present in marine records the observations also support the assumption that the millennial scale oscillations common to both marine and ice archives are synchronous thus providing a rationale for extending the marine ice core comparison through the last 400 000 years making use of a marine drilled core odp site 1089 by aligning the phase of these common abrupt events we anchor the vostok chronology to an orbitally tuned marine sediment chronology a refinement that allows examination of a variety of paleoclimatological issues such as the relationship between deep ocean variability and antarctic polar climate for example this exercise suggests that over at least the 4 major deglaciation events the primary orbital scale changes in the chemistry and most likely the temperature of the deep southern ocean were synchronous with changes in atmospheric pco2 and polar air temperatures we also find that the deuterium excess in the ice core resembles marine foraminiferal 13c records and that the deuterium excess is synchronous with an anomalous foraminiferal 18o signal the residual between normalized versions of vostok d and foraminiferal 18o these observations demand a tight link between the vostok isotopic record and the air sea interaction of the subantarctic zone

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