spectral analysis of unevenly spaced climatic time series using clean signal recovery and derivation of significance levels using a monte carlo simulation abstract we present a monte carlo based method for the determination of errors associated with frequency spectra produced by the clean transformation of roberts et al 1987 the monte carlo procedure utilises three different types of simulation involving a data stripping operation and the addition of white and red noise to the analysed time series the simulations are tested on both synthetic and real data sets demonstrating the ability of the procedures to extract coherent information from time series characterised by the low signal to noise ratio that is typical of many palaeoclimatic records significance levels derived for the monte carlo spectra of four time series from the vostok ice core are utilised in the study of eccentricity components contained within the palaeoclimatic archive since 420 ka inversion of the vostok frequency spectra into the time domain reveals the differing influence of orbital parameters in the palaeoclimatic proxy records as well as the relative magnitudes of the eccentricity components contained in the time series of greenhouse gas concentration ice volume and local temperature

a composite record of late pleistocene relative geomagnetic paleointensity from the wilkes land basin antarctica abstract we report high resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the wilkes land basin wlb east antarctica in the frame of the italian australian wilkes land glacial history wega project the studied cores with a length of ca 4 m each were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise and consist of very fine grained sediments paleomagnetic measurements were carried out on u channel samples apart from a low coercivity magnetic overprint removed after the first steps of alternating field demagnetization each core is characterized by a well defined characteristic remanent magnetization paleomagnetic inclinations fluctuate around the expected value of ca 77 for such high latitude sites and always indicate normal magnetic polarity short period oscillations to anomalously shallow paleomagnetic inclinations up to 20 were identified at different levels of the sampled sequences positive reverse inclination values were however not observed specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences for each core we reconstructed curves of relative paleointensity rpi as computed by nrm 20 mt and nrm 20 mt arm 20 mt variation of the geomagnetic field an original age model was established by tuning the individual rpi curves with the available global and regional reference rpi stacks paleomagnetic results supported by other limited bio and chronostratigraphic constraints establish that all the cores are late pleistocene in age two provide an expanded record of the last ca 30 ka pc18 and pc19 three span the last ca 100 200 and 300 ka respectively pc25 pc27 and pc26 and one reaches back to ca 780 ka pc20 approaching the brunhes matuyama transition thus the wega paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the brunhes chron the individual normalized rpi records were merged in a wega rpi stacking curve spanning the last 300 kyr the comparison of the wega rpi individual and stacked curves with the global references rpi stacks shows that geomagnetic paleointensity variations with periods longer than a few to tens kyr depending on the sedimentation rate can be safely recognized in this sector of the peri antarctic margins furthermore the stacking of the individual chrm inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the brunhes chron supporting the validity of the age models the reconstructed average sediment accumulation rates for the individual cores range from 0 6 to 19 cm ka and are compatible with their position within the wlb with the lowest rates found close to the ridge of the sedimentary drifts moreover the high resolution age models obtained in this study provide original constraints to assess chronology rates and amplitudes of the climatic and environmental processes affecting this key area of the peri antarctic margins during the late pleistocene

holocene paleoceanography of the northwest passage canadian arctic archipelago abstract a series of cores box and piston were collected at 2 key locations in lancaster sound cores 2004 804 009 bc and pc and barrow strait cores 2005 804 004 bc and pc in the canadian arctic archipelago to document the evolution of sea surface conditions in the main axis of the northwest passage during the holocene time period reconstruction of sea surface parameters summer temperature and salinity duration of sea ice cover were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators the chronology of these cores is based on calibrated ams 14c dates 210pb analyses and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field cals7 k 2 our age models for both cores indicate that 009 pc spans the last 11 100 cal bp while 004 pc encompasses the last 10 800 cal bp calculated sedimentation rates are in the range of 43 140 cm kyr for core 009 pc and 15 118 cm kyr for core 004 pc allowing for a millennial time scale resolution in each core our results indicate relatively harsh conditions in lancaster sound between 10 800 and 9000 cal bp summer temperatures 2 c cooler than at present which we associate with the presence of active ice streams in northernmost baffin bay and a weak west greenland current this is followed by a warming trend up to 3 c higher than present that took place between 8500 and 5500 cal bp which we associate with the holocene thermal maximum and to a large scale atmospheric pattern such as the arctic oscillation operating at the millennial time scale this is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa a gradual cooling of sea surface temperature and increased sea ice follow this from 5500 cal bp until the modern period in barrow strait harsh sea surface conditions prevailed from 11 100 to 5500 cal bp with summer temperatures as low as 4 c cooler than at present the warming trend occurred later in this region between 5500 and 1000 cal bp after which a gradual cooling is observed until the modern period the apparent shift or opposite warming trends between lancaster sound and barrow strait after 5500 cal bp could be the result of a change in atmospheric circulation patterns related to a possible shift in the ao mode from ao to ao comparison of ice core 18o record from devon island ice cap and the reconstructed sea surface temperature from core 009 pc suggests a strong atmospheric oceanic coupling throughout the holocene in this area

rock magnetic properties and relative paleointensity stack between 13 and 24 kyr bp calibrated ages from sediment cores lake moreno patagonia argentina we conducted a detailed study of natural remanence and rock magnetic properties on three sediment cores from lake moreno patagonia argentina based on these measurements we constructed a relative paleointensity stack for the period 13 24 kyr bp calibrated ages rock magnetic properties of the sediment cores showed uniform magnetic mineralogy and grain size suggesting that they were suitable for relative paleointensity studies the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteretic remanent magnetisation at 20 mt arm20 mt the saturation of the isothermal remanent magnetisation at 20 mt sirm20 mt and the low field magnetic susceptibility k spectral analysis showed that the normalised records were not affected by local environmental conditions the recorded pseudothellier paleointensity was compared with records obtained from conventional normalising methods comparing the paleointensity curves with others obtained previously in other lakes in the area has allowed us to reach reliable conclusions about centennial scale features 2008 elsevier b v all rights reserved

variations of the geomagnetic field during the holocene relative paleointensity and inclination record from the west pacific odp hole 1202b abstract we conducted detailed rock magnetic investigations on 36 m of drill core collected during ocean drilling program leg 195 at hole 1202b 24 48 24 n 122 30 00 e in the southern okinawa trough with the goal of extracting a reliable paleointensity signal with centennial resolution an age depth model was established from a chronology obtained by accelerator mass spectromety 14c dating the sedimentary section spans almost the entire holocene 0 9 4 kyr and exhibits sedimentation rates close to 400 cm kyr the magnetic properties are dominated by stable pseudo single domain magnetite high field hysteresis data and the grain size sensitive ratio of anhysteretic remanent magnetization arm to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations magnetic parameters vary by a factor of 4 thereby fulfilling the usual criteria for a relative paleointensity study the relative geomagnetic paleointensity was obtained by normalizing the intensity of natural remanent magnetization nrm by the arm and the low field magnetic susceptibility both normalizations yield nearly identical results r 0 89 spectral analysis indicates that the record is not significantly affected by local environmental conditions comparison of this west pacific paleointensity curve with other curves suggests a geomagnetic origin for the signal millennial scale features of our record correlate to variations of the archeomagnetic dipole moment this suggest that the sediments at hole1202b recorded changes of the geomagnetic field over the studied time interval

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

geomagnetic field intensity changes in sweden between 9000 and 450 cal bp extending the record of archaeomagnetic jerks by means of lake sediments and the pseudo thellier technique the pseudo thellier technique was applied to recover relative palaeointensity pt rpi estimates from four piston cores retrieved from a holocene lake sediment sequence in the province of smaland central southern sweden a time depth model between 11 000 and 450 cal bp was based on a combination of calibrated radiocarbon ages and the ages of established palaeomagnetic secular variation psv features that were transferred from a varve dated regional master curve in fennoscandia significant peaks in geomagnetic field intensity occurred at similar to8400 similar to6400 3900 and 2800 cal bp the maximum field intensity at 2800 cal bp was associated with the most rapid change in the direction of the geomagnetic vector while the high resolution sedimentary data show that significant century scale increases and decreases in relative field intensity between 4000 and 2000 cal bp were associated with abrupt changes jerks in the direction of the geomagnetic vector archaeomagnetic jerks younger than 2000 years were not reproduced in this multiple sediment core study on the other hand the pt rpi reconstructions display century to millennial scale trends between 5000 and 450 cal bp that are coherent with archaeomagnetic data sets from western europe and central asia this agreement indicates that palaeointensity may be used as a relative dating technique across this region fennoscandian psv and rpi records for the earlier holocene do not show the same rapid style of vector movement which suggests that northern europe has been affected by a more turbulent geodynamo since similar to4000 cal bp c 2004 elsevier b v all rights reserved less

exploration plays in the mersin basin turkish mediterranean sea there are a number of large neogene basins in the ne mediterranean region including the antalya mut mersin adana iskenderun and northern part of latakia basins figure 1 the broader area is subdivided by major structural features such as the aksu missis andirin kyrenia zone ecemis fault goksu fault and dead sea east anatolian faults figure 2 there are some locally important smaller fault systems as well that trend approximately parallel to the major structures e g kozan aslantas and yumurtalik faults

paleosecular variations since 9000 yr bp as recorded by sediments from maar lake shuangchiling hainan south china abstract high resolution paleosecular variation psv can play an important role in sediment dating and for understanding the temporal characteristics of the geodynamo of the earth s magnetic field in this article based on magnetic susceptibility correlation a composite sediment profile has been compiled from a 16 m long core hn 2 and a 8 m deep well hn 3 in shuangchiling maar lake a crater basin located on hainan island southern china fine and homogeneous silty clay corroborates with a stable continuous and undisturbed deposition a u channel based paleomagnetic study constrained by ams14c chronology derived from leaves plant debris and woods and supported by rock magnetic data indicates that the lake sediments document a reliable paleosecular variation psv record since 9000 cal year bp comparison of our psv features with other records from lakes biwa japan erhai china baikal russia as well as archaeomagnetic records demonstrate that the inclination pattern is generally synchronous within chronological uncertainties suggesting further psv dating may be valuable for stratigraphic correlation on a regional scale

on the persistence of geomagnetic flux lobes in global holocene field models abstract to investigate the longevity and robustness of high latitude flux patches in the geomagnetic field at the core mantle boundary we present time dependent models of the geomagnetic field for the past 7000 years our models use the same data set as previously used for time dependent archaeomagnetic field modelling but constrained with additional priori models from time averages of field models covering the last 150 400 and 3000 years we find that the data are consistent with flux patches existing in both north and south hemispheres for the past 7000 years and that the northern hemisphere patches at least have highly dynamic behaviour simple averaging of the historical field may not be appropriate to obtain a characteristic time averaged model of the field for comparison with other geophysical observables our results should inform geodynamo studies of thermal core mantle coupling and of possible long term structure in the geomagnetic field

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

deciphering lake and maar geometries from seismic refraction and reflection surveys in laguna potrok aike southern patagonia argentina abstract laguna potrok aike is a bowl shaped maar lake in southern patagonia argentina with a present mean diameter of 3 5 km and a maximum water depth of 100 m seismic surveys were carried out between 2003 and 2005 in order to get a deeper knowledge on the lake sediments and the deeper basin geometries a raytracing model of the laguna potrok aike basin was calculated based on refraction data while sparker data were additionally used to identify the crater wall discordance and thus the upper outer shape of the maar structure the combined data sets show a rather steep funnel shaped structure embedded in the surrounding santa cruz formation that resembles other well known maar structures the infill consists of up to 370 m lacustrine sediments underlain by probably volcanoclastic sediments of unknown thickness the lacustrine sediments show a subdivision into two sub units a the upper with seismic velocities between 1500 and 1800 m s 1 interpreted as unconsolidated muds and b the lower with higher seismic velocities of up to 2350 m s 1 interpreted as lacustrine sediments intercalated with mass transport deposits of different lithology and or coarser grained sediments the postulated volcanoclastic layer has acoustic velocities of 2400 m s 1 the lake sediments were recently drilled within the pasado project in the framework of the international continental scientific drilling program icdp cores penetrated through lacustrine unconsolidated sediments down to a depth of 100 m below lake floor this minimal thickness for the unconsolidated and low velocity lithologies is in good agreement with our raytracing model

environmental history of southern patagonia unravelled by the seismic stratigraphy of laguna potrok aike laguna potrok aike located in southernmost patagonia argentina 52s is a 100 m deep hydrologically closed lake that probably provides the only continental southern patagonian archive covering a long and continuous interval of several glacial to interglacial cycles in the context of the planned international continental scientific drilling program initiative potrok aike maar lake sediment archive drilling project several seismic site surveys that characterize in detail the sedimentary subsurface of the lake have been undertaken long sediment cores recovered the material to date and calibrate these seismic data laguna potrok aike is rimmed steeply circular in shape with a diameter of 3ae5 km and is surrounded by a series of subaerial palaeoshorelines reflecting varying lake level highstands and lowstands seismic data indicate a basinwide erosional unconformity that occurs consistently on the shoulder of the lake down to a depth of 33 m below 2003 ad lake level marking the lowest lake level during late glacial to holocene times cores that penetrate this unconformity comprise marine isotope stage 3 dated sediments 45 kyr bp 3ae5 m below and post 6800 cal yr bp transgressional sediments above the unconformity this middle holocene transgression following an unprecedented lake level lowstand marks the onset of a stepwise change in moisture as shown by a series of up to 11 buried palaeoshorelines that were formed during lake level stillstands at depths between 30 and 12 m two series of regressive shorelines between 5800 to 5400 and 4700 to 4000 cal yr bp interrupt the overall transgressional trend in the basin mound like drift sediments occur after 6000 cal yr bp documenting the onset of lake currents triggered by a latitudinal shift or an increase in wind intensity of the southern hemispheric westerlies over laguna potrok aike at that time furthermore several well defined lateral slides can be recognized the majority of these slides occurred during the mid holocene lake level lowering when the slopes became rapidly sediment charged because of erosion from the exposed shoulder sediments around 7800 and 4900 cal yr bp several slides went down simultaneously probably triggered by seismic shaking

palaeosecular variation of the earth s magnetic field during the last 10000 years based on the annually laminated sediment of lake nautajarvi central finland a palaeomagnetic study of the lake nautajarvi sediment sequence in central finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for holocene stratigraphic correlation and age control based on x ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the lake nautajarvi varve sequence which covers nearly 10000 years with an estimated counting error of less than 1 and a mean sedimentation rate of 0 66 mm yr 1 we reconstructed a record of the palaeomagnetic secular variation psv of the earth s magnetic field in this nearly 7 m long section of clastic organic varves mineral magnetic measurements indicated that pseudosingle domain magnetite is the major carrier of the remanence psv shows many of the familiar features of declination and inclination that have previously been recorded in northern europe in addition the lake nautajarvi record contains a continuous record of relative palaeoi

a high resolution relative paleointensity record from the gerlache boyd paleo ice stream region northern antarctic peninsula herein we document and interpret an absolute chronological dating attempt using geomagnetic paleointensity data from a post glacial sediment drape on the western antarctic peninsula continental shelf our results demonstrate that absolute dating can be established in holocene antarctic shelf sediments that lack suitable material for radiocarbon dating two jumbo piston cores of 10 m length were collected in the western bransfield basin the cores preserve a strong stable remanent magnetization and meet the magnetic mineral assemblage criteria recommended for reliable paleointensity analyses the relative paleomagnetic intensity records were tuned to published absolute and relative paleomagnetic stacks which yielded a record of the last 8500 years for the post glacial drape four tephra layers associated with documented eruptions of nearby deception island have been dated at 3 31 3 73 4 44 and 6 86 0 07 ka using the geomagnetic paleointensity method this study establishes the dual role of geomagnetic paleointensity and tephrochronology in marine sediments across both sides of the northern antarctic peninsula

holocene geocentric dipole tilt model constrained by sedimentary paleomagnetic data paleomagnetic data although undeniably limited have been used to constrain complex time varying geomagnetic field models here we present four different versions of a time varying geocentric dipole model for the past approximately 9000 years based on a limited selection of sedimentary paleomagnetic data with good spatial coverage the robustness of the modeling approach is evaluated using modern magnetic observation station data provided by the world data centre for geomagnetism in edinburgh and we discuss the magnitude of the error introduced by insufficient data coverage the prediction in terms of directional variations is tested against paleomagnetic data from 63 different sedimentary sites and compared to results from recently published spherical harmonic geomagnetic field models we find that the dipole estimate can explain the paleomagnetic data almost as well as the more complicated spherical harmonic models specific areas and records are identified where there are significant differences between the performance of the dipole estimate and the spherical harmonic models our results suggest that many of the differences between the dipole model predictions and the paleomagnetic data can be related to poor paleomagnetic quality and or the lack of accurate and precise time control inherent to some of the records these results agree with valet et al 2008 who suggested that the cals7k 2 model probably underestimates the dipole contribution in order to reduce the misfit between the inversion and the data we conclude that better paleomagnetic data and associated time control are needed to improve global geomagnetic field models less

holocene secular variation in western north america paleomagnetic record from fish lake harney county oregon an 8 9 m composite section of lake sediment from fish lake steens mountain southeastern oregon has provided a high resolution record of holocene geomagnetic secular variation in western north america the section is composed of overlapping core segments with stratigraphic control based on six tephra layers and other thin distinct bands and with age control from 37 radiocarbon dates the 455 paleomagnetic samples possess a strong and stable magnetic remanence which is carried by pseudo single domain magnetite paleomagnetic records for individual core segments show low scatter and high serial correlation and where the segments overlap there is excellent agreement between records the azimuthal orientation of the composite section was recovered from the known direction of the geomagnetic field at the time of the climactic eruption of mount mazama tephra which is present in fish lake both internal and external evidence including the correspondence with an archaeomagnetic record from the southwestern united states support the conclusion that the fish lake record represents the history of geomagnetic field behavior during at least the last 10 000 years b p analysis of that record reveals that the average geomagnetic direction can not be distinguished from that of a geocentric axial dipole field and that the overall circularity of the field was clockwise but the detailed behavior was quite complex angular standard deviations of both field directions and virtual geomagnetic poles differ significantly from the values predicted from theoretical models of secular variation but are consistent with those of other holocene records when the record from fish lake is compared to the proposed type curve for east central north america there is excellent agreement for the past 6000 years provided the curves are offset by about 400 years this offset corresponds to a rate of westward drift of about 0 062 yr beyond about 6000 radiocarbon years ago good agreement between the two curves occurs when there is no offset suggesting that the field was standing rather than drifting during this time

geomagnetic field intensity north atlantic deep water circulation and atmospheric δ14c during the last 50 kyr we present simulated records of past changes in the atmospheric 14c for the last 50 kyr due to changes in geomagnetic field intensity and in the strength of the north atlantic deep water nadw a new geomagnetic record was used largely based on the napis 75 record laj et al phil trans r soc london a 358 2000 1009 1025 which has been extended for the 0 20 kyr interval using archeomagnetic and volcanic data past changes of the nadw were derived from a mineral magnetic study of the cores used in the construction of napis 75 two box models of different complexity 4 and 17 boxes were used to simulate the carbon cycle calculated records of 14c are consistent with experimental determinations for the last 24 kyr for older ages the records calculated with variable oceanic circulation conditions reach values as high as 600 with an average of 500 between 20 and 40 kyr with maxima around 21 30 and 38 kyr gisp2 age model while low values are observed prior to 42 kyr although large inconsistencies in experimental data preclude precise comparison the average record simulated with the 17 box model is overall consistent with the icelandic sea record voelker et al radiocarbon 40 1998 517 534 42 2000 437 452 except for the extremely high peak observed in this record at 40 5 kyr on the other hand the results recently reported from a stalagmite recovered from a submerged cave in the bahamas beck et al science 292 2001 2453 2458 are inconsistent with all our model simulations in the 20 45 kyr interval the improved geomagnetic record combined with the new nadw profile allows us to give a modeled evaluation of the relative contribution of these factors to changes in atmospheric 14c the average simulation provides a first order modeled correction for conventional radiocarbon ages older than 25 kyr for which no calibration curve is available as yet

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

palaeomagnetism of holocene and late pleistocene sediments from lago di mezzano and lago grande di monticchio italy initial results abstract palaeomagnetic records of the geomagnetic secular variation reaching back to 31 and 102 kyr cal bp respectively were obtained from two sediment cores from lago di mezzano central italy and two cores from lago grande di monticchio southern italy intra lake correlation was based on continuous high resolution susceptibility measurements and discrete dry density samples characteristic remanent magnetization chrm of all 4800 samples was determined by analysis of the results of progressive alternating field af demagnetization intra lake comparison of the resulting chrm directions confirms that the inclination and declination records reflect the palaeosecular variation of the local geomagnetic field composite curves of geomagnetic palaeosecular variations psv were created for each lake in order to compare the reconstructed psv records with those from lac du bouchet massif central france and lac de joux switzerland the good agreement in the general patterns of the inclination and declination records of all lakes mentioned above confirms the reconstructed psv records of the italian lakes investigated

paleosecular variations 0 19 000 years recorded by sediments from escondido lake argentina abstract paleomagnetic and sedimentological studies carried out on four cores about 11 m long from the bottom sediments of escondido lake southwestern argentina are described this lake is geologically related to the set of lakes of glacial origin located in western patagonia using several magnetic studies the predominance of pseudo single single domain magnetite as main carrier as well as an increase of concentration and grain size with depth was determined the pairs of magnetic susceptibility and intensity of remanent magnetization profiles show a good correlation with the sedimentological macroscopic descriptions and also with those of shorter cores previously studied the stability of the natural remanent magnetization was investigated by alternating field demagnetization within lake correlation was based on lithology magnetic susceptibility and intensity of remanent magnetization because the patterns of these parameters showed similarity for every core radiocarbon dating suggests higher deposition rates during the early stage of the lacustrine basin late pleistocene the transfer function depth age also allowed constructing a secular variation record from south argentina for the past 19 000 years the declination and inclination logs show some anomalous directions at about 18 000 calibrated years

late quaternary paleomagnetic field secular variation from two minnesota lakes detailed paleomagnetic records from the wet sediments of two minnesota lakes are the basis for estimating the local secular variation of the earth s magnetic field during late quaternary time results from lake st croix cover the interval 0 9500 years b p and results from kylen lake cover the interval 4000 14 000 years b p paleomagnetic data were recovered from two replicate cores in each lake by sampling the sediments at 3 to 10 cm intervals analysis of the potential errors in the results indicates that all cores were correctly oriented in the vertical plane but that some azimuthal offsets of individual core segments did occur various methods for correcting the occasional azimuthal offsets are described the final paleomagnetic data sets from each lake show a high degree of internal consistency these results also show close correspondence 1 between the two lakes 2 with the known historic magnetic field variation and 3 with paleomagnetic results from dated archeological material and lava flows from the western united states rock magnetic analysis of the lake sediments indicates that the natural remanent magnetization is the result of a physical remanence acquisition process detrital remanent magnetization active at or near the sediment water interface there is no evidence for a systematic inclination error in the results statistical analysis of vector time series determined from the paleomagnetic data indicates that both the field vector and virtual geomagnetic pole vgp distributions are non fisherian and essentially axial dipolar when averaged over 10 000 years spectral analysis of the scalar inclination and declination suggests that the field behavior is separable into a dominant low frequency dipolelike waveform period of 9500 years and a higher frequency band irregular waveform fundamental period of 2400 years with multiples at 1200 800 and 600 years that may represent the nondipole field this irregular waveform is interpreted as resulting from zonal drift of the nondipole field past minnesota on the basis of waveform morphology and vgp circularity zonal drift of the nondipole field plus a low frequency dipole variation can account for almost all of the observed paleomagnetic field variation

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

late pleistocene dust deposition in the patagonian steppe extending and refining the paleoenvironmental and tephrochronological record from laguna potrok aike back to 55 ka abstract paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern south america here we present a continuous record for the past 55 ka from the maar lake laguna potrok aike 51 58 s 70 23 w southern patagonia argentina previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of oxygen isotope stage ois 3 59 29 ka whereas a second core from the centre of the basin comprised the last 16 ka tephrostratigraphical constraints and osl ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites high resolution xrf and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in antarctica this is therefore the first evidence for contemporaneity of aeolian deposition in both the target area antarctica and in the major source area of patagonia during the holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times the identification of a minor lake level lowering at approximately 4 cal ka bp allows to refine earlier paleoenvironmental reconstructions for the holocene within error margins the osl ages are consistent with published radiocarbon dated records offering hence a valuable tool for further studies of the sediments from laguna potrok aike the new chronology confirms the age of three tephra layers up to now only found in laguna potrok aike sediments and ascribed to ois 3

geomagnetic palaeosecular variation 0 13 000 yr bp as recorded in sediments from three maar lakes from the west eifel germany summary geomagnetic palaeosecular variation psv profiles have been obtained from 12 cores raised from three maar lakes in the west eifel germany age control is provided by varve chronology analysis of mean inclinations suggests that a post depositional remanent magnetization pdrm was acquired in all three lakes a lock in time of 150 yr corresponding to an average lock in depth of 24 cm has been determined from a comparison with archaeomagnetic sv data stacked psv results demonstrate directional geomagnetic field behaviour through the late and post glacial in central europe and show good agreement with the holocene british master curve turner thompson 1982 psv results suggest that westward drift of the non dipole field was not persistent over the last 13 000 yr spectral analyses yield declination variations with durations of about 1800 yr in the younger holocene 0 5000 yr bp and 4300 yr between 5000 and 13 000 yr bp the inclination exhibits swings of 1000 yr duration in the younger holocene and about 2000 yr in the older part moreover inclination spectra suggest the presence of one inclination variation with a very long duration approaching the length of the time span investigated 8600 yr

geomagnetic secular variations over the last 6500 years as recorded by sediments from the lakes of south argentina summary regional type curves depicting secular variations in declination and inclination through the last 6700 calendar years constructed for southwestern argentina about 41 s 71 30 w by stacking palaeomagnetic data derived from lake sediment cores are described and analysed the data consist of records from four lakes which have been previously studied el trebol brazo campanario moreno and escondido and are here integrated within lake correlation was based on magnetic susceptibility and intensity of the natural remanent magnetization nrm interlake correlation was derived from declination and inclination patterns and a set of radiocarbon age determinations the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the spectrum obtained from spectral analysis of declination d and inclination i at the same time shows major peaks at periodicities of about 3400 1600 and 1200 yr for both parameters in order to test the stability of the periodicities obtained spectral analysis has been applied to every 3500 yr time span at intervals of 500 yr for both records patterns of circularity during the last 6700 yr appear to recur with a near constant interval of about 2000 yr both open and closed loops are associated with clockwise and counter clockwise circularity

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

paleosecular variations recorded by holocene pleistocene sediments from lake el trebol patagonia argentina paleomagnetic studies carried out on six cores from the bottom sediments from lake el trebol south argentina are described measurements of directions declination and inclination d and i and intensity of natural remanent magnetisation nrm magnetic susceptibility at low and high frequency specific x and volumetric k isothermal remanent magnetisation irm saturation isothermal remanent magnetisation sirm back field and anhysteric remanent magnetisation arm were carried out stability of the nrm was investigated by alternating field demagnetisation rock magnetic studies suggest that the main carriers of magnetisation are ferrimagnetic minerals predominantly pseudo single domain magnetite records of nrm and k show a good correlation with the sedimentological description and also with those of shorter cores previously studied the tephra layers were identified from the lithologic profiles and also from the magnetic susceptibility logs due to their different chronological meaning and their rather bad behaviour as magnetic recorder these layers were removed from the sequence and the gaps that were produced along the profiles by the removal were closed obtaining a shortened depth radiocarbon age estimates from these cores and from earlier studies allow us to construct a paleosecular variation psv record for the past 24 000 years these results show good correlation with the previous one the spectrum obtained from spectral analysis shows major peaks at periodicities of about 1150 1500 2490 3630 5240 and 11 810 years both clockwise and counterclockwise precession of the geomagnetic vector is evident from analysis of the bauer plots with a preponderance of clockwise movement

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

the mid cenozoic succession and evolution of the mut basin southern turkey and its regional significance abstract the hitherto poorly known mut basin occupies a position that is critical to our understanding of the later cenozoic history of south central turkey the biostratigraphic and sedimentological study reported here reveals an extended and complex pattern of basin evolution and enables the history of this basin to be compared in detail with that of adjacent south turkish basins the oldest basin fill deposits are demonstrated to be oligocene to earliest miocene in age and comprise alluvial redbeds thick lacustrine deposits and thin lagoonal sediments mainly supplied from northern tauride sources this mainly terrestrial megasequence resulted from an early oligocene phase of crustal extension leading to rapid trap door subsidence and the formation of narrow e w trending troughs this phase was terminated by a minor marine incursion and through reactivation of basement faults during renewed extension in the earliest miocene the overlying miocene succession thus rests with local angular discordance upon tilted and gently deformed oligocene and older rocks subsequent subaerial erosion created an irregular pre burdigalian palaeotopography that strongly influenced the nature thickness and distribution of the early miocene basin fill in palaeotopographic depressions the miocene sequence commences with alluvial fan braidplain and meander belt redbeds formed in river systems that flowed mainly south and southeast these pass up and laterally into more extensive lagoonal and shallow marine mixed clastic carbonate units yielding late burdigalian to early langhian microfaunas marking the inception of the main miocene marine transgression in this area episodic northwards marine advance led to isolation of the northerly source of siliciclastic detritus and resulted in periodic onlap of mid to inner shelf fine grained carbonates with thin clastic intercalations that include isolated coralgal build ups calcarenite mounds and sand waves at the peak of miocene transgression mid serravallian thick reefal limestones were deposited far to the north and also formed on top of basement highs forming the southern and eastern flanks of the basin significant influxes of coarse and fine siliciclastics from the north attest to periodic progradational events that are more conspicuous and protracted in the late serravallian and tortonian however muddy deeper shelf conditions prevailed throughout the middle miocene in the central part of the basin while stronger currents and unstable slopes characterise the constricted marine strait in the southeast of the basin near silifke in terms of their sequential arrangement palaeoenvironmental and tectonic evolution the oligo miocene sediments of the mut basin closely resemble coeval sequences in the adjacent ecemis aktoprak and karsanti northern adana basins and share a similar history involving complex interplay between regional tectonics and eustasism deeper water oligo miocene sequences in the outboard troughs such as the southern adana basin and the kyrenia misis andirin complex yield more subtle signatures of these tectonic and eustatic events the differences between these basins are attributable to the influence of regional kinematic elements generated during the reorganisation of plate boundaries in the northeast mediterranean that followed final suturing of the arabian and anatolide plates in the mid cenozoic

high resolution paleomagnetic records from laguna potrok aike patagonia argentina for the last 16 000 years 1 holocene and late glacial records documenting variations in direction and intensity of the geomagnetic field during the last 16 000 cal bp are presented for southern patagonia this continuous high resolution terrestrial record from laguna potrok aike 51 58 s 70 23 w was recovered within the salsa south argentinean lake sediment archives and modeling project mineral magnetic measurements indicate that pseudo single domain magnetite is the major carrier of the remanence allowing the reliable determination of stable natural remanent magnetization inclinations and declinations from alternating field demagnetization and principal component analysis paleomagnetic secular variation records reveal most of the familiar features of declination and inclination that have previously been reported in other records from south argentina but conspicuous centennial scale differences are also observed the results illustrate the potential of paleosecular variations records for dating sedimentary sequences in southern south america

deconvolution of long core paleomagnetic data of ocean drilling program by akaike s bayesian information criterion minimization deconvolution of long core paleomagnetic data of the ocean drilling program odp was developed based on bayesian statistics samples of deep sea sediments obtained by drilling with an advanced piston corer are subjected to pass through measurements by a cryogenic magnetometer aboard the odp s research vessel joides resolution which provide continuous paleomagnetic records deconvolution of the magnetometer output was developed in order to obtain more detailed variations of the magnetization than permitted by the spatial resolution of the pickup coil approximately 11 cm the magnetization vector was modeled as a smoothly changing sequence parametrized by l2 norm of second order difference and then deconvolved using a matrix calculation as a smoothness constrained least squares method the optimum smoothness was obtained by minimizing akaike s bayesian information criterion which is a measure of the logarithm of the likelihood this deconvolution scheme was applied to pass through data artificially produced by convolving synthetic reversal record and adding a gaussian noise the amplitude of the noise was estimated and the variations shorter than the spatial resolution of the sensor were obtained the deconvolution also was applied to the real pass through data from holes 769a and 769b measured at intervals of 5 mm the deconvolution revealed variations of the magnetizations with a maximum spatial resolution of about 2 cm the magnetizations after deconvolution were in good agreement with magnetization values measured separately on cube samples taken at intervals of 5 or 10 cm

holocene sea ice history and climate variability along the main axis of the northwest passage canadian arctic 1 palynological geochemical and physical records were used to document holocene paleoceanographic changes in marine sediment core from dease strait in the western part of the main axis of the northwest passage core 2005 804 006 pc latitude 68 59 552 n longitude 106 34 413 w quantitative estimates of past sea surface conditions were inferred from the modern analog technique applied to dinoflagellate cyst assemblages the chronology of core 2005 804 006 pc is based on a combined use of the paleomagnetic secular variation records and the cals7k 2 time varying spherical harmonic model of the geomagnetic field the age depth model indicates that the core spans the last 7700 cal years b p with a sedimentation rate of 61 cm ka 1 the reconstructed sea surface parameters were compared with those from barrow strait and lancaster sound cores 2005 804 004 pc and 2004 804 009 pc respectively which allowed us to draw a millennial scale holocene sea ice history along the main axis of the northwest passage manwp overall our data are in good agreement with previous studies based on bowhead whale remains however dinoflagellate sea surface based reconstructions suggest several new features the presence of dinoflagellate cysts in the three cores for most of the holocene indicates that the manwp was partially ice free over the last 10 000 years this suggests that the recent warming observed in the manwp could be part of the natural climate variability at the millennial time scale whereas anthropogenic forcing could have accelerated the warming over the past decades we associate holocene climate variability in the manwp with a large scale atmospheric pattern such as the arctic oscillation which may have operated since the early holocene in addition to a large scale pattern more local conditions such as coastal current tidal effects or ice cap proximity may have played a role on the regional sea ice cover these findings highlight the need to further develop regional investigations in the arctic to provide realistic boundary conditions for climatic simulations

a paleomagnetic record from lake lama northern central siberia abstract two cores from lake lama northern central siberia with lengths of 19 and 11 m respectively were subjected to detailed magnetostratigraphic investigations directions of the characteristic remanent magnetisation chrm were derived from vector analysis of the results from alternating field a f demagnetisation yielding records for the last 18 000 years bp the sediments show a distinct change in sedimentation pattern at around 14 500 years bp from a highly variable to a monotonous sedimentation with anoxic conditions in the lake sediments during the last 11 500 years bp the oxic anoxic boundary is reflected in all rock magnetic parameters measured and the magnetic mineral fraction is affected by reductive dissolution of iron bearing minerals here mainly magnetite therefore no record of relative paleointensity could be achieved but as intra and inter lake comparison of the obtained inclination and declination records have shown the directions of the geomagnetic field recorded in the sediments from lake lama were not severely affected by the partial dissolution of the remanence carrying minerals

holocene dynamics of the arctic s largest ice shelf ice shelves in the arctic lost more than 90 of their total surface area during the 20th century and are continuing to disintegrate rapidly the significance of these changes however is obscured by the poorly constrained ontogeny of arctic ice shelves here we use the sedimentary record behind the largest remaining ice shelf in the arctic the ward hunt ice shelf ellesmere island canada to establish a long term context in which to evaluate recent ice shelf deterioration multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in disraeli fiord in response to the formation of the ward hunt ice shelf and its fluctuations through time our results show that the ice shelf was absent during the early holocene and formed 4 000 years ago in response to climate cooling paleoecological data then indicate that the ward hunt ice shelf remained stable for almost three millennia before a major fracturing event that occurred 1 400 years ago after reformation 800 years ago freshwater was a constant feature of disraeli fiord until the catastrophic drainage of its epishelf lake in the early 21st century

late palaeogene neogene evolution of the triple junction region near maras south central turkey the marao region of turkey includes the anatolian arabian african triple junction the african arabian margin is marked by left lateral transtension along the dead sea kara su rift motion on the anatolian arabian boundary is partitioned between the left lateral east anatolian fault and a fold thrust belt termed the engizek zone equivalent to the bitlis suture further east the african anatolian boundary lies along the cyprus misis andirin trend and is expressed near the triple junction as the aslantao iskenderun zone now undergoing slow left lateral transtension the neogene evolution of these boundaries is largely recorded in the stratigraphy and structure of the basins that lie along the anatolian arabian lice basin and anatolian african aslantao iskenderun basin boundaries these basins appear to have developed in the early miocene along major strike slip zones large half graben in the pre neogene 9basement9 of the western misis andirin block developed contemporaneously with motion on the anatolian african boundary these extensional features evolved subsequent to the intense shattering of the mesozoic carbonate sequence in the misis andirin block and its mixing with panels of deep water palaeogene strata to form an extensionally disrupted assemblage transpression and conversion of both anatolian african and anatolian arabian boundaries to fold thrust belts occurred in the late miocene transpression continues along the anatolian arabian boundary but transtension has recurred along the anatolian african boundary since the pliocene

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

variations in the geomagnetic dipole moment over the last 12 000 years summary an analysis has been made of archaeointensity data for the past 12 000 years there are 3243 results from diverent areas of the world covering the past 12 000 years of these 2203 are from the european region and 1040 are from the rest of the world the archaeointensity data set analysed in the present study is almost three times larger than that used by mcelhinny senanayake 1982 although there is no major diverence between our global data and the earlier data the data for the non european region have been improved and we now have a data set for asia

hydrological variability in southeastern patagonia and explosive volcanic activity in the southern andean cordillera during oxygen isotope stage 3 and the holocene inferred from lake sediments of laguna potrok aike argentina abstract seismic reflection studies in the maar lake laguna potrok aike 51 58 s 70 23 w revealed an erosional unconformity associated with a sub aquatic lake level terrace at a water depth of 30m radiocarbon dated multi proxy sediment studies of a piston core from this location indicate that the sediment below this discontinuity has an age of 45kyr bp oxygen isotope stage 3 and was deposited during an interval of high lake level in comparison to the holocene section geochemical indicators of this older part of the record either point towards a different sediment source or to a different transport mechanism for oxygen isotope stage 3 sediments holocene sedimentation started again before 6790cal yr bp providing a sediment record of hydrological variability until the present geochemical and isotopic data indicate a fluctuating lake level until 5310cal yr bp during the late holocene the lake level shows a receding tendency nevertheless the lake level did not drop below the 30m terrace to create another unconformity the geochemical characterization of volcanic ashes reveals evidence for previously unknown explosive activity of the reclus and mt burney volcanoes during oxygen isotope stage 3

a high resolution holocene paleomagnetic secular variation and relative paleointensity stack from eastern canada abstract a high resolution holocene paleomagnetic secular variation psv and relative paleointensity rpi stack was constructed using u channel paleomagnetic data from six radiocarbon constrained marine sedimentary sequences raised along the main axis of the laurentian channel eastern canada from its head to its mouth centennial to millennial scale declination and inclination features of the eastern canadian stack can be correlated within the dating uncertainties with other holocene north american icelandic and european psv records suggesting a common possibly hemispheric in character geomagnetic origin both magnetic inclination and declination of the eastern canadian stack are generally consistent with the time varying spherical harmonic model of the geomagnetic field cals7k 2 notably during the last 4000 cal bp in addition the eastern canadian holocene rpi stack reveals similar millennial and even centennial time scale variations consistent with some virtual axial dipole moment vadm reconstructions derived from absolute paleointensity data as well as with north american lacustrine rpi records accordingly these results suggest that the holocene paleomagnetic secular variation in north america is significantly driven by large scale 5000 km geomagnetic field changes at these timescales

spatial distribution of cones and satellite detected lineaments in the pali aike volcanic field southernmost patagonia insights into the tectonic setting of a neogene rift system abstract the relationships between the distribution and morphometric features of eruptive structures scoria and spatter cones maar tuff rings and the fracture network were investigated in the pliocene quaternary pali aike volcanic field southernmost patagonia argentina chile the alkali basaltic basanitic magmas which erupted in this area have nearly primary magma compositions and often bear mantle xenoliths hence magma ascent from deep seated reservoirs was probably very fast with no significant stagnation at crustal levels field surveys and satellite image analysis led to the identification of up to 467 eruptive structures and four main nw se ne sw e w and n s fracture systems the spatial distribution of eruptive cones and fractures was investigated through the computation of power law exponents df for self similar clustering the self similarity of cones and fractures was defined between lower and upper cut offs which were in turn related to the thickness of the fractured mechanical layer the fractal character of cones and fracture distribution clustering in the pali aike volcanic field area was thus correlated with crustal thickness the self similarity of fractures was used to establish the relative chronology of the detected fracture systems the self similar clustering exponent is highest in the e w and nw se fracture systems df 1 78 and 1 77 respectively and lowest in the n s system df 1 65 the self similar clustering of eruptive structures is well defined df 1 45 the intense volcano tectonic activity in the pali aike area marks a major pliocene quaternary phase in the development of the magellan neogene rift system

holocene paleomagnetic secular variation records from the western equatorial pacific ocean abstract we have carried out detailed rock magnetic and paleomagnetic studies on a suite of four deep sea sediment cores from indonesia and the philippine islands which form a transect from 6 3 n to 10 6 s the cores have average sediment accumulation rates of 35 65 cm kyr that all yield high resolution paleomagnetic secular variation psv records the psv records contain 44 correlatable inclination and declination features that corroborate the individual psv records and indicate that they are all continuous with no significant stratigraphic gaps thirty four ams radiocarbon dates provide a high resolution time stratigraphic framework for the psv records which extend from 0 18 000 yrs bp these are the first high resolution holocene psv records ever recovered from anywhere on earth within 17 of the equator almost 1 3 of the earth s surface area statistical analysis of the holocene psv records indicates that they have i anomalies of 5 to 9 consistent with 5 ma averaged results the strong similarity in i anomaly pattern of holocene and longer term 5 ma averaged psv data suggest that the dynamo process causing the anomaly is largely described by holocene psv by contrast the holocene psv records have vgp angular dispersions that are significantly lower than 5 ma averaged psv data yet significantly higher than psv data averaged over only the last few thousand years this difference indicates that whatever dynamo process causes the overall directional variability of the earth s magnetic field is not totally described by recent last few thousand year psv or even by late quaternary last 20 000 yrs psv

tectonic controls on stratigraphic evolution of the adana basin turkey the neogene adana basin of se turkey was initiated after thrust emplacement of the tauride belt to the north of the basin seismic reflection profiles across the southern part of the adana basin provide information on structural and stratigraphic evolution of the basin based on seismic character and the identification of unconformities three megasequences and two mega sequence boundaries are identified the first megasequence is partly coincident with an early miocene rifting event and it comprises reefs that have grown on fault footwall crests with fore and back reef sediments in intervening lows subsequent rapid flexurally induced subsidence generated an underfilled basin which was then passively filled by turbiditic sediments megasequence 2 showing aggradational character on seismic profiles further extensional faulting and coupled sinistral wrench faulting took place after the deposition of megasequence 2 erosional truncation of its upper part is followed by the deposition of continental and shallow marine sediments of megasequence 3 which shows localized progradational sequences characteristic of shallow water deposition further minor extensional faulting took place after the deposition of megasequence 3

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

paleosecular variation and paleointensity records for the last millennium from southern south america laguna potrok aike santa cruz argentina abstract high resolution paleo and rock magnetic studies were performed on a group of four sediment cores from laguna potrok aike santa cruz argentina representing the time period ad 1300 2000 the rock magnetic analyses show that the main magnetic mineral is titano magnetite with a concentration between 0 01 and 0 08 and a grain size of 4 15 m this study is helpful in order to complete the paleosecular variation psv and paleointensity type curves for south america which do not have a detailed record for the last millennium the comparison with the study carried out for lake el trebol shows a very good agreement supporting that psv records of south western argentina can be developed into a stratigraphic correlation tool on a regional scale

holocene geomagnetic secular variation records from north eastern australian lake sediments summary secular variation records have been obtained from cores from lakes barrine and eacham two north eastern australian volcanic crater lakes the results from several cores have been stratigraphically correlated and then stacked and smoothed the chronology provided by radiocarbon dating indicates that the lake eacham sequence spans the last 5700 calendar years the time scale for the lake barrine record is less weil constrained but it

a controlled in situ investigation of the relationship between stress velocity and induced seismicity a p wave velocity survey was performed after the excavation of a cylindrical horizontal tunnel through homogenous visibly unfractured granite an image of the velocity structure around the tunnel indicated a distinct zone of high velocity corresponding to a zone of increased elastic stresses where a break out notch formed perpendicular to this zone a region of decreased velocity was found associated with a region of tensile elastic stress the stress changes are believed to have preferentially opened and closed pre existing micro fractures in the rock thereby decreasing and increasing the p wave velocity additional velocity decreases are also attributed to creation of new fractures the excavation induced microseismicity is found to be generally associated with the high velocity region adjacent to the notch and appears to be located along the boundary between the fractured low velocity and high velocity regions

dating of holocene western canadian arctic sediments by matching paleomagnetic secular variation to a geomagnetic field model a recently recovered w6 m long holocene sedimentary sequence piston core 2004 804 650 collected from the beaufort sea western canadian arctic was dated by combining the paleomagnetic secular variation psv and a time varying spherical harmonic model of the geomagnetic field cals7k 2 a u channel based paleomagnetic study reveals the presence of a stable single component of magnetization mad 5 carried by low coercivity ferrimagnetic minerals most likely magnetite in the pseudo single domain grain size range an age depth model spanning the last w6000 calbp was established from nine paleomagnetic tie points obtained by comparing the magnetic declination profiles of core 650 and the cals7k 2 model output in order to verify the robustness of the method both the magnetic inclination and the relative paleointensity rpi records of core 650 were then compared with western north american lacustrine and volcanic holocene psv records as well as with previously published rpi records from the beaufort and chukchi seas several common magnetic inclination features and similar millennial scale fluctuations are detected among the records supporting a common geomagnetic origin of the records and implying consistency of the derived age model these results show the potential of using both the cals7k 2 model output and psv of the geomagnetic field as a practical dating tool

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

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

a stacked record of relative geomagnetic paleointensity for the past 270 kyr from the western continental rise of the antarctic peninsula paleomagneticandrockmagnetic investigations were carriedout onfourgravity coresrecoveredfrom the westerncontinental rise of the antarctic peninsula during the sedano ii cruise of rv ogs explora the studied cores each about 6 5 m long were collected at a depth of 3700 4100 m below the sea level on the distal gentle side of sediment drift 7 and consist of very fine grained sediments spanning through various glacial interglacial cycles detailed analysis of the paleomagnetic and rock magnetic data allowed toreconstruct relative paleointensity rpi records nrm20 mt arm20 mt for eachcore weestablished arefined agemodel for the studied sequences by correlating individual sedano rpi curves to the global rpi stack sint 800 y guyodo j p valet global changes in intensity of the earth s magnetic field during the past 800 kyr nature 399 1999 249 252 the individual normalized sedano rpi records are in mutual close agreement they were thus merged in a rpi stacking curve spanning the last 270 kyr and showing a low standard deviation this study also points out that rpi records may provide a viable tool to date otherwise difficult to datesedimentarysequences suchasthosedepositedalongperi antarctic margins thenewrpichronologyindicatesthat thesampled sedimentary sequenceisyoungerthanpreviouslythought andallowsanew high resolutioncorrelation tooxygenisotope stages furthermore we recognized variations in the rock magnetic parameters that appear to be climatically driven with changes in therelative proportionoftwomagnetic mineralpopulationswithdistinctcoercivities rockmagnetic andlithological trendsobserved in the sedano cores indicate that during the climatic cycles of the late pleistocene this sector of the peri antarctic margin was subjected to subtle yet identifiable environmental changes confirming a relatively higher instability of the west antarctic ice sheet with respect to the east antarctic counterpart

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

holocene history of the larsen a ice shelf constrained by geomagnetic paleointensity dating a sedimentary record collected from beneath the former lar sen a ice shelf reveals the holocene history of the larsen a re gion the record begins with the transition from grounded ice to a floating ice shelf completed by 10 7 6 0 5 ka and ends with the modern recession the record contains several late holocene dia tomaceous ooze layers that suggest proximity to productive open water events radiocarbon ages obtained from these sediments were complicated by the presence of detrital and reworked carbon we have eliminated these complications and constructed a chro nology for the larsen a ice shelf history via tuning of the geo magnetic field paleointensity record with a reference curve this approach provides chronological control to sediment sequences that lack appropriate material for radiocarbon dating geomag netic paleointensity features with wavelengths of 2 3 k y can be recognized and interhemispherically correlated illustrating the po tential to use geomagnetic paleointensity variations as a global cor relation and dating tool at sub milankovitch time scales

environment and climate of the last 51 000 years new insights from the potrok aike maar lake sediment archive drilling project pasado in this introductory paper we summarize the history and achievements of the potrok aike maar lake sediment archive drilling project pasado an interdisciplinary project embedded in the international continental scientific drilling program icdp the stringent multiproxy approach adopted in this research combined with radiocarbon and luminescence dating provided the opportunity to synthesize a large body of hydrologically relevant data from laguna potrok aike southern patagonia argentina at this site lake level was high from 51 ka until the early holocene when the southern hemisphere westerlies shw were located further to the north at 9 3 ka cal bp the shw moved southward and over the latitude of the study area 52 degrees s causing a pronounced negative water balance with a lake level decrease of more than 50 m two millennia later the shw diminished in intensity and lake level rose to a subsequent maximum during the little ice age since the 20th century a strengthening of the shw increased the evaporative stress resulting in a more negative water balance a comparison of our data with other hydrological fluctuations at a regional scale in south eastern patagonia provides new insights and also calls for better chronologies and high resolution records of climate variability

holocene paleomagnetic records from the st lawrence estuary eastern canada centennial to millennial scale geomagnetic modulation of cosmogenic isotopes two long holocene piston cores md99 2220 and md99 2221 were raised from the st lawrence estuary eastern canada because of the expanded holocene sediment sequence this location provides a u channel based paleomagnetic study supported by an accelerator mass spectrometry ams 14c chronology rock magnetic and sedimentological data indicates that these sediments provide a paleomagnetic directional secular variation psv and relative paleointensity rpi proxy records for the last 8500 cal bp sedimentation rates vary from 1 2 to 4 2 m kyr comparison of inclination and declination features with other north american holocene psv records are generally consistent and temporal offsets are within chronological uncertainties the normalized natural remanent magnetization intensity record a rpi proxy from the postglacial sediments of core 2220 compares favorably with north american and european holocene rpi records at millennial and even some centennial timescales comparisons between core 2220 rpi proxy and the 10be flux record from the greenland summit gisp2 ice core finkel and nishiizumi j geophys res 102 1997 26699 26706 and a 14c production rate record bond et al science 294 2001 2130 2136 suggest that geomagnetic modulation may control the millennial and even some centennial scale variability within cosmogenic isotope records this implies that the core 2220 rpi record reflects changes in global scale geomagnetic field at these timescales

paleointensity studies on holocene pleistocene sediments from lake escondido argentina abstract relative changes in geomagnetic field intensity over the last 16 000 years bp were recovered from the study of four cores obtained from lake escondido south argentina rock magnetic analysis shows that the main magnetic mineral is magnetite the concentrations being mainly between 0 01 and 0 1 and the grain size between 1 and 8 m in order to fulfil the criteria for assessing the reliability of paleointensity data derived from sediments rev geophys 31 1993 319 the samples whose concentrations and size are beyond this range were rejected the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteric remanent magnetisation arm100 mt the saturation of the isothermal remanent magnetisation sirm and the low field magnetic susceptibility k coherence function analysis indicates that the records are not significantly affected by local environmental conditions this suggests that the variations in normalised remanence are mostly likely due to geomagnetic paleointensity fluctuations arm100 mt is the best normaliser for the lake escondido sediments the record of relative paleointensity nrm20 mt arm100 mt shows peaks and troughs whose amplitudes are similar to those in the st lawrence estuary lake baikal lake pepin and larsen a ice shelf data set and a stack of archeomagnetic data given as virtual axial dipole moment vadm

geomagnetic secular variations 0 14 000 yr bp as recorded by lake sediments from argentina summary palaeomagnetic and sedimentological studies carried out on the bottom sediments from three lakes in western argentina are described at the within lake level five lithological units could be broadly defined and were useful as a general guide in defining detailed correlations based on the magnetic susceptibility k and intensity of remanent magnetization j in one of the three lakes el trebol it was possible to derive a closer lithologically based correlation and this was consistent with that based on the magnetic parameters inter lake correlation was derived from the inclination and declination patterns considered as a pair also taking account of a set of radiocarbon age determinations to remove any ambiguities all the individual measurements were transformed to a time scale prior to stacking to produce type curves the records for laguna el trebol and brazo de campanario extend back to about 6000 radiocarbon years before present while lago morenito provides a record extending back to about 14000 radiocarbon years before present the records exhibit variations with similar overall characteristics to those previously obtained for europe and north america but there appears to be no correlation with the northern hemisphere patterns on a swing to swing basis both clockwise and anticlockwise precession of the geomagnetic vector is evident both from spectral analysis of declination inclination pairs and vgp paths

lateglacial and holocene wet dry cycles in southern patagonia chronology sedimentology and geochemistry of a lacustrine record from laguna potrok aike argentina a high resolution multiproxy geochemical approach was applied to the sediments of laguna potrok aike in an attempt to reconstruct moist and dry periods during the past 16 000 years in south eastern patagonia the age depth model is inferred from ams 14 c dates and tephrochronology and suggests moist conditions during the lateglacial and early holocene 16 000 8700 cal bp interrupted by drier conditions before the beginning of the holocene 13 200 11 400 cal bp data also imply that this period was a major warm phase in southeastern patagonia and was approximately contemporane ous with the younger dryas chronozone in the northern hemisphere 12 700 11 500 cal bp after 8650 cal bp a major drought may have caused the lowest lake level of the record since 7300 cal bp the lake level rose and was variable until the little ice age which was the dominant humid period after 8650 cal bp