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

the paleomagnetic record at iodp site u1307 back to 2 2 ma eirik drift off south greenland abstract integrated ocean drilling program iodp expedition 303 to the north atlantic in 2004 recovered a 175 m quaternary sedimentary section at iodp site u1307 located on the northern part of the eirik drift south of greenland the seafloor at site u1307 at 2575 m water depth is situated within the water depth range of the present day main axis of the western boundary under current wbuc but lies on the nw side of the drift crest and is partly shielded from it the uppermost 120 meters of sediment sequence were sampled with u channels along a composite section which combines the two holes drilled at this site an age model was obtained by identification of polarity reversals back to the reunion subchron 2 1 ma and then refined in the 0 1 5 ma interval by correlation of the relative paleointensity rpi record to the piso paleointensity stack the site u1307 relative paleointensity rpi record is compared with the piso and epapis pacific stacks neighboring iodp sites from eirik drift sites u1305 and u1306 and with the ocean drilling program odp site 984 record that extends beyond piso magnetite grain size and concentration proxies are compared to sites u1305 and u1306 records in the context of the past evolution of the wbuc

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

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

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

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

the eirik drift a long term barometer of north atlantic deepwater flux south of cape farewell greenland abstract the eirik drift lies on the slope and rise off the southern tip of the greenland margin where it formed under the influence of the north atlantic deep western boundary current the drift contains a semi continuous and often expanded sedimentary record ranging from early eocene to holocene and so contains a record of bottom current strengths over decadal to millennial time scales these variations in current strength can be related to changes in thermohaline circulation and climate the drift body is composed of four seismic sequences with a number of internal discontinuities reflecting a variety of palaeoceanographic events three secondary ridges are observed trending to the nw from the main ridge crest the presence of these ridges which have been active since the early pliocene suggests that the deep current separates into three strands as it crosses the eirik drift with each strand depositing a separate ridge variation in the degree of lateral migration within the early to late pliocene sequence between ridges reflects local variation in the angle of slope on which the ridges formed cyclicity of reflector amplitude within the late pliocene to pleistocene sequence could reflect changes in carbonate accumulation and deep current strength linked to glacial interglacial variations

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

the deep western boundary current at cape farewell results from a moored current meter array abstract an analysis is made of data from 30 aanderaa recording current meters rcms set on nine moorings located east of cape farewell the southern tip of greenland the purpose of the measurements was to allow for the estimation of transport in the deep western boundary current dwbc below a depth of about 1500 m the records commenced in september 2005 and lasted from 9 5 to 11 5 months after calibration of the raw data 12 h averages of temperature and current were derived and the latter employed to estimate the flow across and along the array direction the 9 5 month average transport of water colder than 3 c was found to be 7 8 sv 1 sv 1 106 m3 s 1 with a standard error of 0 8 sv for water denser than 27 85 kg m 3 the transport is calculated as 4 5 sv whether either of these values is significantly different from comparable measurements made 500 km upstream cannot be determined in marked contrast for 27 8 kg m 3 the transport is estimated as only 9 0 sv smaller than the wi

when seamounts subduct data from an array of seismometers on the sea floor show the complex pattern of earthquakes around subducted seamounts

magnetic excursions in the late matuyama chron olduvai to matuyama brunhes boundary from north atlantic iodp sites the sedimentary record of late matuyama magnetic excursions between the end of the olduvai subchron and the matuyama brunhes boundary has relied on north atlantic odp sites 983 984 and individual recordings at odp site 1021 from the california margin and core md972143 from the west philippine sea north atlantic iodp sites u1305 u1306 u1307 eirik drift off se greenland and site u1308 central atlantic provide new records from u channel samples and discrete 8 cm3 cubic samples collected from multiple holes drilled at each site the results confirm the existence of the intra jaramillo punaruu bjorn gardar and gilsa excursions and possibly the kamikatsura excursion these excursions are not recorded at all sampled sites although they do correspond to excursions recorded at odp sites 983 984 and to relative paleointensity rpi minima recorded at all studied sites for some records including that of the bjorn excursion 1251 ka antipodal magnetization directions yield virtual geomagnetic poles vgps that reach high northern latitudes implying that the excursion involved reversal of the main axial dipole field on the other hand excursions are often partially and inadequately recorded attributable to a combination of the brevity of geomagnetic excursions bioturbation and filtering of the magnetization signal by the drm detrital remanent magnetization acquisition process non uniform sedimentation rates at millennial centennial scales and possibly unrecognized drilling sampling disturbance

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

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

fluctuations in deep western north atlantic circulation on the blake outer ridge during the last deglaciation variations in the mean grain size of the detrital silt fraction from four piston cores along a depth transect on the blake outer ridge were used to examine paleocirculation patterns and intensity between 2650 and 3818 m for the late pleistocene and holocene prior to 12 kyr circulation was focused on the upper part of the ridge above 2700 m and may have corresponded to enhanced levels of intermediate water production in the north atlantic deepwater circulation during deglaciation underwent a two step decrease to minimum speeds from 15 5 to 13 5 kyr followed by a three step increase to maximum speeds at 10 kyr minima in circulation at 13 5 and 12 kyr can be directly associated with oxygen isotopic evidence for advection of reduced salinity surface water to the north atlantic additional circulation minima at 15 and 10 5 kyr may also be the result of reduced salinity from high latitude meltwater discharge evidence for a drop to moderate circulation intensity during the holocene is supported by isolated geochemical records but could also be explained by decoupling of ocean ventilation rates from bottom circulation or a change in sediment provenance at the end of deglaciation

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

magnetic stratigraphy constraints on the matuyama brunhes boundary recorded in a loess section at the southern margin of chinese loess plateau although the matuyama brunhes boundary mbb in the chinese loess plateau clp is very important in reliably correlating quaternary loess with other sediments in the world particularly with marine and polar ice cores its exact stratigraphic position remains controversial previous investigations usually placed the mbb between paleosol unit s8 and loess unit l8 in various locations to better understand the spatial differences in the mbb position a high resolution paleomagnetic study was conducted in a loess section of the lantian basin at the southern margin of the clp the results show that the mbb is situated in the middle of the relatively weak paleosol unit s7 consistent with a recent report on the mbb based on a be 10 study from the xifeng and luochuan loess sections of the central clp however the regional anomalously low magnetic susceptibility in paleosols s7 and s8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size then the mbb in the yushan section can be correlated with the bottom of paleosol s7 corresponding to the older part of interglacial marine isotope stage 19 this result temporally reconciles the striking discrepancy of the position of the mbb recorded in between loess and other typical sedimentary sequences and further confirms that the stratigraphic position of the mbb could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the clp in the yushan section the high frequency variations of paleomagnetic directions during a long period of similar to 31 ka before the mbb however could not be attributed to a genuine response to the true geomagnetic behaviour moreover the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background a multiproxy based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern clp

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

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

non volcanic tremor associated with the march 2010 gisborne slow slip event at the hikurangi subduction margin new zealand 1 non volcanic tremor accompanies slow slip events at most circum pacific subduction zones previously the hikurangi subduction margin new zealand and the boso peninsula of japan have been noted as exceptions where slow slip which occurs at shallow depth compared to other subduction zones does not generate seismic tremor the lack of tremor observations raises questions whether tremor and slow slip are manifestations of the same process and whether different temperature and pressure conditions influence the physical mechanism of tremor production analysis of seismic data during the march 2010 gisborne slow slip event new zealand reveals that this slow slip event at the northern hikurangi margin is accompanied by tremor with distinctive characteristics compared to local microearthquakes both the gisborne area of new zealand and the boso peninsula of japan are underlain by thick accumulations of sedimentary rocks that likely inhibit the observation of low amplitude tremor due to high attenuation discovery of tremor in new zealand suggests that tremor may always accompany slow slip and that its apparent absence at the boso peninsula the hikurangi margin prior to this study and any future regions discovered to experience slow slip without concurrent tremor may be the effect of highly attenuating sediments

a 750 kyr detrital layer stratigraphy for the north atlantic iodp sites u1302 u1303 orphan knoll labrador sea abstract integrated ocean drilling program iodp sites u1302 u1303 drilled on the se flank of orphan knoll labrador sea preserve a record of detrital layers and other proxies of hydrographic change that extend the record of ice sheet ocean interactions through most of the brunhes chron the age model is built by tandem matching of relative paleointensity rpi and oxygen isotope data 18o from neogloboquadrina pachyderma sin to reference records indicating a mean brunhes sedimentation rate of 14 cm kyr sedimentation back to marine isotope stage mis 18 is characterized by detrital layers that are detected by higher than background gamma ray attenuation gra density peaks in x ray fluorescence xrf indicators for detrital carbonate ca sr and detrital silicate si sr and an ice rafted debris ird proxy wt 106 m the age model enables correlation of site u1302 03 to iodp site u1308 in the heart of the central atlantic ird belt where an age model and a similar set of detrital layer proxies have already been derived ages of heinrich h layers h1 h2 h4 h5 and h6 are within 2 kyr at the two sites h0 h3 and h5a are not observed at site u1308 and agree with previous work at orphan knoll within 3 kyr at site u1308 brunhes detrital layers are restricted to peak glacials and glacial terminations back to marine isotope stage mis 16 and have near synchronous analogs at site u1302 03 detrital layers at site u1302 03 are distributed throughout the record in both glacial and most interglacial stages we distinguish heinrich like layers associated with ird from detrital layers marked by multiple detrital layer proxies including ca sr but usually not associated with ird that may be attributed to lofted sediment derived from drainage and debris flow events funneled down the nearby northwest atlantic mid ocean channel namoc the prominent detrital layers at sites u1302 03 and u1308 can be correlated to millennial scale features in the chinese speleothem monsoon record over the last 400 kyr implying a link between monsoon precipitation and laurentide ice sheet lis instability the detrital layer stratigraphy at site u1302 03 provides a long record of lis dynamics against which other terrestrial and marine records can be compared

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

diachronous benthic δ18o responses during late pleistocene terminations 1 benthic 18o is often used as a stratigraphic tool to place marine records on a common age model and as a proxy for the timing of ice volume sea level change however skinner and shackleton 2005 found that the timing of benthic 18o change at the last termination differed by 3900 years between one atlantic site and one pacific site these results suggest that benthic 18o change may not always accurately record the timing of deglaciation we compare benthic 18o records from 20 atlantic sites and 14 pacific sites to evaluate systematic differences in the timing of terminations in benthic 18o analysis of sedimentation rates derived from the alignment of benthic 18o suggests a statistically significant atlantic lead over pacific benthic 18o change during the last six terminations we estimate an average pacific benthic 18o lag of 1600 years for terminations 1 5 slightly larger than the delay expected from ocean mixing rates given that most glacial meltwater probably enters the north atlantic we additionally find evidence of 4000 year pacific 18o lags at approximately 128 ka and 330 ka suggesting that stratigraphic correlation of 18o has the potential to generate age model errors of several thousand years during terminations a simple model demonstrates that these lags can be generated by diachronous temperature changes and do not require slower circulation rates most importantly diachronous benthic 18o responses must be taken into account when comparing atlantic and pacific benthic 18o records or when using benthic 18o records as a proxy for the timing of ice volume change

deep western boundary current variability in the subtropical northwest atlantic ocean during marine isotope stages 12 10 high resolution 125 500 year temporal resolution sortable silt mean grain size data of subtropical northwest atlantic ocean drilling program odp leg 172 site 1061 monitor fluctuations of the deep western boundary current dwbc throughout marine oxygen isotope stages mis 12 10 330 460 kyr in great detail comparison with foraminiferal stable isotope data from the same site and odp site 1063 bermuda rise data of poli et al 2000 shows that the dwbc shoals during glacial times in relation to a reduced north atlantic deep water production and increased advection of southern ocean waters superimposed fluctuations in the flow speed position of the dwbc at a semiprecession scale are persistent throughout mis 10 12 and independent of the glacial state additional millennial scale variations in dwbc flow speed parallel surface water cooling events and ice rafted debris episodes especially at the transition of mis 11 10 indicating the sensitivity of deep current flow variations to changes in the surface water conditions these millennial scale variations are amplified when benthic foraminiferal 18o values exceed 3 8 and may be related to the transition of an ice volume threshold where climate variability is possibly amplified by feedback mechanisms associated with ice sheet growth

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

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

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

relative paleointensity and environmental magnetism since 1 2 ma at iodp site u1305 eirik drift nw atlantic abstract integrated ocean drilling program iodp expedition 303 to the north atlantic in 2004 recovered rapidly deposited deep sea sediments at iodp site u1305 on eirik drift located south of greenland at 3460 m water depth along the path of the western boundary under current wbuc about 200 m of sediment was sampled with u channels from the composite section providing a continuous record of paleomagnetic field directions and relative paleointensity rpi variations covering the past 1 2 myr the age model based on an oxygen isotope record is consistent with the fit of the rpi record to a calibrated template and indicates higher sedimentation rates during interglacials relative to glacial epochs magnetite grain size and concentration proxies indicate higher concentrations of magnetite with larger grain sizes during interglacials enhanced interglacial deposition can be attributed to a combination of elevated entrainment of terrigenous detritus into the wbuc due to glacial retreat on continents flanking the upstream path of the wbuc east greenland and iceland and of increased bottom current wbuc vigor leading to elevated transport and deposition at the site during interglacials this pattern is opposite to observations of flow of the antarctic circum polar current acc in the south indian ocean which suggests an inter hemispheric antiphase in marine circulation at the milankovitch scale with strong circulation in the deep north atlantic when the acc is weak and vice versa

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

complexity in matuyama brunhes polarity transitions from north atlantic iodp odp deep sea sites abstract integrated ocean drilling program iodp expedition 303 to the north atlantic provided 16 records of the matuyama brunhes polarity transition mbt based on u channel and discrete samples from holes drilled at three sites sites u1304 u1305 and u1306 that have mean brunhes sedimentation rates of 16 18 cm kyr the mbt occurs during the transition from marine isotope stage mis 19c to mis 18e with mid point at 773 ka and a transition duration of 8 kyr combining the new mbt records including one new record for the top jaramillo with previously published north atlantic mbt records odp sites 983 984 and 1063 yields a total of more than 20 high sedimentation rate polarity transition records the mbt yields a repetitive pattern of transitional field states as virtual geomagnetic poles vgps move from high southern latitudes to loop over the pacific group in ne asia and transit into the mid latitude south atlantic before reaching high latitudes in the northern hemisphere the vgps for the top jaramillo transition feature a loop over the pacific then a ne asia group before transit over the indian ocean to high southerly latitudes the north atlantic mbt records described here contrast with longitudinally constrained vgp paths for the mbt indicating that relatively low sedimentation rate 4 cm kyr records of the mbt are heavily smoothed by the remanence acquisition process and do not adequately represent the mbt field the vgps at the mbt and top jaramillo as measured in the north atlantic have similarities with excursion iceland basin vgp paths and were apparently guided by maxima in downward vertical flux similar to those seen in the modern non dipole nd field implying longevity in nd features through time

circulation and transport in the western boundary currents at cape farewell greenland the circulation and volume transports in the western boundary currents around cape farewell greenland are derived from full depth hydrographic and velocity measurements from august september 2005 the western boundary currents from surface to seafloor transport 40 5 8 1 sv southwards in the irminger sea and 53 8 10 8 sv northwards in the labrador sea the deep western boundary current dwbc defined as water with potential density greater than 27 80 kg m 3 transports 12 3 2 5 sv southwards in the irminger sea the deep water transport is reduced south of cape farewell where it changes flow direction from southwards to northwards the south corner at a section over the eirik ridge a bathymetric feature extending southwest of cape farewell the dwbc transports 8 7 1 7 sv westwards the reduction in transport at the south corner is associated with decreased velocities within the deepest layers and the volumetric loss of the most saline deep water types the observations suggest that the part of the shallow and deep western boundary currents diverge at the south corner downstream in the eastern labrador sea the deep water transport is increased to 19 7 3 9 sv northwards with the addition of recirculating denser deep waters the representativeness of the results from the semi synoptic survey are discussed with reference to companion current meter measurements of the dwbc

late pleistocene relative geomagnetic paleointensity from the deep labrador sea regional and global correlations abstract three long piston cores from the deep labrador sea appear to record late pleistocene variations of relative paleointensity of the geomagnetic field two cores extend at least into isotope stage 6 the other into stage 5 in addition to 18o 13c and ams 14c stratigraphies correlation between cores is facilitated by the presence of rapidly deposited high detrital carbonate dc and low detrital carbonate ldc layers some of which correlate to the north atlantic heinrich events hysteresis ratios and rock magnetic parameters indicate that the magnetic assemblage in the cores is pseudo single domain magnetite except for deglacial intervals and dc and ldc layers normalized remanence records show strong correlation for a range of normalizers k karm and sirm and no correlation with bulk magnetic parameters paleointensity records from the three cores are consistent when only dc and ldc layers are used for correlation suggesting that relative paleointensity can be used as a regional correlation tool consistent paleointensity features from the labrador sea indian ocean and mediterranean sea suggest that the sediments are recording dipole field variations although the composite record from two labrador sea cores is strongly correlated to a composite of the mediterranean indian ocean records the chronologies are inconsistent indicating apparent discrepancies in the isotopic and ams 14c chronologies used in the mediterranean indian ocean and labrador sea respectively

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

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

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

changes in grain size and magnetic fabric at blake bahama outer ridge during the late pleistocene marine isotope stages 8 10 abstract odp sites 1055 1062 on the blake bahama outer ridge bbor are characterized by high sedimentation rates which allow high resolution analyses to reconstruct the behavior of the deep western boundary current dwbc as a function of depth along the bbor the odp sites provide an intermediate and deep water transect from 1800 to 4760 m water depths we focused on the time interval from 350 to 250 ka marine isotope stages mis 10 2 8 3 grain size and magnetic properties were analyzed with centennial to millennial scale time resolution integrating the results of grain size analyses lightness and magnetic properties the changes in the vertical position and the intensity of the dwbc core were inferred during glacial periods mis 10 2 and 8 4 8 3 the dwbc core was located at around 2200 m water depth whereas it deepened to 3000 m or more during warm periods interglacial stage 9 3 and interstadial 8 5 between these periods the dwbc core moved to shallower depth 2500 3000 m and its intensity increased which generally provided coarser sediments to a broad depth range from 2100 to 4800 m furthermore the magnetic properties imply that the dwbc supplied carbonate material other than terrigenous sediments to the deeper sites during mis 9 the depositional processes at site 1062 are characterized by sudden influxes of fine carbonate rich sediments which gradually decreased with time paleocurrent directions inferred from the direction of the great axis of the magnetic fabric are consistent with the modern topography at sites 1055 1056 1058 and 1060 during the relatively warm period from stages 9 3 to 8 5 at site 1062 the deepest site which exhibits a mud wave field the inferred flow direction is parallel to the bathymetric contours during warm periods while the nearly cross wave direction seemingly dominated during the other periods it appears that topographic position may have affected the scattering of azimuth plots moreover there is a possibility that the changes in flow direction correlate with climate changes

radiocarbon simulations for the glacial ocean the effects of wind stress southern ocean sea ice and heinrich events simulations of oceanic radiocarbon for the last glacial maximum are presented using a three dimensional global ocean circulation model forced with glacial background states according to various reconstructions we investigate the influence of sea surface temperatures sea ice margins wind stress and antarctic sea ice formation on the glacial tracer distribution and meridional overturning circulation the aim of these sensitivity studies is to reconcile available radiocarbon data from marine sediments with reconstructed sea surface temperatures and estimated sea ice production rates model runs with a modified freshwater balance in the southern ocean mimicking increased brine release due to enhanced divergence of antarctic sea ice arrive at radiocarbon values close to observations these experiments also yield abyssal temperatures and salinities which are consistent with recent inferences in the simulation with the best agreement with radiocarbon observations north atlantic deep water export is reduced by 40 compared to present day while antarctic bottom water flow is intensified to similar strength in the south atlantic transient simulations show that glacial freshwater discharge into the north atlantic can cause abrupt increases of atmospheric radiocarbon as observed during heinrich event 1 however the effect is only significant in scenarios with a massive short time discharge at the beginning which is followed by low level freshwater input for the rest of the event or if it is assumed that the meridional overturning circulation was already in a modern operational mode

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

an atlantic lead over pacific deep water change across termination i implications for the application of the marine isotope stage stratigraphy globally synchronous changes in glacioeustatic sea level provide a particularly useful stratigraphic reference in the study of glacial interglacial climate change and form the basis for the marine isotope stage mis system which posits a dominant glacioeustatic signal in benthic foraminferal 18o however benthic 18o strictly does not represent a pure sea level record and it is shown here that due to local changes in deep water hydrography the mis 2 1 boundary i e benthic 18o change occurred 4000 years later in the deep eastern equatorial pacific than in the deep northeast atlantic this discrepancy is too large to be attributed entirely to the pacific lag that may be expected due to the mixing time of the ocean basins instead multiple proxies including benthic foraminiferal mg ca suggest that the large offset in benthic 18o most probably resulted from a late rise in deep water temperature at the pacific site and a series of coupled deep water temperature and 18o changes at the northeast atlantic site these findings have important implications for the application of the mis stratigraphy and the interpretation of benthic 18o records in general as they show that benthic 18o fluctuations and mis boundaries from different hydrological settings may be significantly diachronous these results call into question the leads and lags that we might infer from a naive interpretation of benthic 18o as a sea level proxy with a direct bearing on the mechanisms that we may propose to explain glacial interglacial climate transitions

source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern north atlantic magnetic properties of eight particle size ranges from nine locations in iceland and 26 locations in southern greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment these terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand fine pseudo single domain psd size magnetic grains dominate the magnetic assemblage of all icelandic fractions in contrast greenlandic samples possess greater variation in magnetic grain size only fine silt and clay are as magnetically fine as the icelandic psd grains while greenlandic silts and sands are dominated by coarser psd and multi domain grains these observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between icelandic and greenlandic sources using these results to examine magnetic grain size records from marine sediment cores collected across the northern north atlantic suggests that source not just transport controlled physical grain size has a significant impact on determining the magnetic grain size at a particular location homogeneity of magnetic grain size in icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding iceland and their ability to buffer large environmental changes

diagenetic alteration of magnetic minerals in labrador sea sediments iodp sites u1305 u1306 and u1307 1 in order to reveal the potential effects of early diagenesis on magnetic minerals in deep sea sediments we studied early diagenetic zones and magnetic mineral characteristics of lower pliocene hemipelagic sediment samples from iodp sites u1305 u1306 and u1307 on eirik drift labrador sea all samples analyzed were unlithified silty clay sediments recovered by a piston corer from depths down to 200 meters composite depth mcd based on shipboard interstitial water geochemistry we divided the sediment column from each site into six early diagenetic zones magnetite fe3o4 was present at all analyzed depths whereas maghemite fe2o3 was found only above the iron reduction zone we attribute this to associated changes in interstitial redox conditions which induced preferential dissolution of maghemitized surfaces on magnetite grains mineral magnetic results indicate a general down hole change in mean grain size of magnetic minerals at site u1307 which has relatively low organic carbon contents the diagenetic zones occur at greater depths than at the other studies sites this suggests that interstitial oxygen levels at this site remained high enough to degrade organic matter through oxic bacterial activity and that detrital magnetic minerals have been preserved even at depth

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

mid brunhes magnetic excursions in marine isotope stages 9 13 14 and 15 286 495 540 and 590 ka at north atlantic iodp sites u1302 3 u1305 and u1306

foraminifer isotope study of the pleistocene labrador sea northwest north atlantic iodp sites 1302 03 and 1305 with emphasis on paleoceanographical differences between its inner and outer basins article i nfo coresraisedduringiodpexpedition303offsoutherngreenland eirikridgesite1305 andoffthelabradorcoast orphanknollsite1302 1303 wereanalyzedtoestablishanisotopestratigraphy respectivelyforthe inner and outer basins of the labrador sea ls these isotopic data also provide information on the atlantic meridional overturning circulation amoc notably with regard to the intensity of the western boundary under current wbuc which is tightly controlled by the production of denmark strait overflow water dsow and the production of labrador sea water lsw in the inner basin through winter cooling and convection the upper 184 m of sediment at eirik ridge spans marine isotope stages mis 32 to 1 at this site two distinct regimes are observed prior to mis 20 the isotopic record resembles that of the open north atlantic records of the interval

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

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

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

sequence of events from the onset to the demise of the last interglacial evaluating strengths and limitations of chronologies used in climatic archives the last interglacial lig represents an invaluable case study to investigate the response of components of the earth system to global warming however the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies this feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the lig here we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span 140 100 ka encompassing the penultimate deglaciation the lig and the glacial inception climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described quantitative estimates of the associated absolute and relative age uncertainties are provided recommendations are subsequently formulated on how best to define absolute and relative chronologies future climato stratigraphic alignments should provide 1 a clear statement of climate hypotheses involved 2 a detailed understanding of environmental parameters controlling selected tracers and 3 a careful evaluation of the synchronicity of aligned paleoclimatic records we underscore the need to 1 systematically report quantitative estimates of relative and absolute age uncertainties 2 assess the coherence of chronologies when comparing different records and 3 integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations finally we provide a sequence of major climatic events with associated age uncertainties for the period 140 105 ka which should serve as a new benchmark to disentangle mechanisms of the earth system s response to orbital forcing and evaluate transient climate simulations

nd and pb isotope signatures of the clay size fraction of labrador sea sediments during the holocene implications for the inception of the modern deep circulation pattern holocene on the basis of sediment supply variations for the last 12 kyr three sources have contributed to the sediment mixture the north american shield the pan african and variscan crusts and the mid atlantic ridge clay isotope signatures indicate two mixtures of sediment sources the first mixture 12 2 6 5 ka is composed of material derived from the north american shield and from a young crustal source from 6 5 ka onward the mixture is characterized by a young crustal component and by a volcanic component characteristic of the midatlantic ridge since the significant decrease in proximal deglacial supplies the evolution of the relative contributions of the sediment sources suggests major changes in the relative contributions of the deep water masses carried by the western boundary undercurrent over the past 8 4 kyr the progressive intensification of the western boundary undercurrent was initially associated mainly with the transport of the northeast atlantic deep water mass until 6 5 ka and with the denmark strait overflow water thereafter the establishment of the modern circulation at 3 ka suggests a reduced influence of the denmark strait overflow water synchronous with the full appearance of the labrador seawater mass our isotopic data set emphasizes several changes in the relative contribution of the two major components of north atlantic deep water throughout the holocene index terms 4267 oceanography general paleoceanography 4558 oceanography physical sediment transport 1040 geochemistry isotopic composition chemistry 9325 information related to geographic region atlantic ocean 9604 information related to geologic time cenozoic keywords clay size fraction sedimentary mixings deep circulation nd and pb isotopes north atlantic labrador sea

age through tandem correlation of quaternary relative paleointensity rpi and oxygen isotope data at iodp site u1306 eirik drift sw greenland abstract planktic oxygen isotope 18 o and relative paleointensity rpi data are used in tandem to generate an age model for the last 1 myr from integrated ocean drilling program iodp site u1306 drilled on the crest of the eirik drift sw greenland in 2272 m water depth for the 1 1 5 ma interval the age model is based on rpi alone due to insufficient foraminifera for isotope analyses utilizing rpi and 18 o in tandem allows recognition of low 18 o events prior to glacial terminations i iii iv v vii viii ix and x that are independently supported by radiocarbon dates through the last deglaciation and are attributed to local or regional surface water effects at site u1306 quaternary sedimentation rates mean 15 cm ka are elevated during peak glacials and glacial onsets and are reduced during interglacials in contrast to the pattern at site u1305 in 3460 m water depth at the distal toe of the drift 191 km sw of site u1306 the contrasting sedimentation rate pattern appears to hold for the entire 1 5 myr record the slackening and or shoaling due to lowered salinity of the deep western boundary current dwbc during glacial intervals coincided with greater sediment supply to site u1306 whereas the deepening and possibly increased vigor of the dwbc during interglacial intervals boosted sediment supply to site u1305