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

new contributions to chinese plio pleistocene magnetostratigraphy abstract a new collection of over 500 orientated hand samples of which 180 are red clays from a 195 m loess red clay section near xian 109 12 e 34 12 n china has been dated by magnetic stratigraphy biostratigraphic and previous magnetostratigraphic investigations gave a maximum age for the chinese loess of 2 4 ma implying that the underlying red clay formation is pliocene in age the present study yields a clearly defined magnetic polarity stratigraphy in good agreement with a polarity time scale developed by earlier workers an interpretation of this magnetostratigraphy suggests a basal age for the loess series in this region of 2 5 ma and a minimum age for the base of the red clay formation which is also the base of the section of 5 0 ma

paleointensity variation across the matuyama brunhes polarity transition observations from lavas at punaruu valley tahiti 1 we have conducted a paleointensity study of the matuyama brunhes m b polarity transition recorded in 34 successive lava flows of punaruu valley on tahiti a reversed polarity is obtained from the lower part of the record major directional changes are derived from the middle part of the record and a normal polarity is recorded in the upper part of the record these paleomagnetic directions and five 40ar 39ar ages yielding a weighted mean of 771 8 1 ka indicate that 30 lava flows recorded the geomagnetic field across the m b transition the 215 specimens from 32 flows were subjected to the double heating technique of the shaw method combined with low temperature demagnetization ltd dht shaw method yielding 73 successful results from 18 flows for the reversed polarity period just prior to the major directional changes paleointensity shows an oscillation like variation between 3 and 38 t corresponding to virtual dipole moments vdms between 0 9 1022 and 9 6 1022 am2 for the major directional changes a weak paleointensity of 5 t is obtained which gives a vdm of 1 0 1022 am2 for the normal polarity period paleointensities are 14 21 t giving vdms of 3 5 5 2 1022 am2 for the reversed polarity period just prior to the major directional changes a linear relationship with a correlation coefficient of 0 96 is recognized on the diagram of vdm versus virtual geomagnetic pole latitude this linear relationship may be a precursory feature of the geodynamo at the onset of the m b transition

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

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

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

the δ15n of nitrate in the southern ocean nitrogen cycling and circulation in the ocean interior we report analyses of the nitrogen isotopic composition of nitrate in the eastern indian and pacific sectors of the southern ocean in this paper we focus on the subsurface data as well as data from the deep waters of other ocean basins nitrate 15n is relatively invariant in much of the abyssal ocean i e below 2 5 km with a value of 4 8 0 2 observed in lower circumpolar deep water north atlantic deep water and central pacific deep water the isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean the southern ocean surface being an important exception in the subantarctic zone north of the polar frontal zone the nitrate 15n of upper circumpolar deep water is 0 7 greater than that of lower circumpolar deep water this isotopic enrichment appears to result from denitrification in the low latitude water masses with which upper circumpolar deep water communicates the isotopic enrichment of upper circumpolar deep water is diminished in the antarctic probably because of the remineralization of sinking organic n which has a low 15n in the antarctic relative to the other water masses of the southern ocean the subantarctic thermocline has a very low nitrate 15n for its nitrate concentration because of exchange with the low latitude thermocline where this isotopic signature appears to originate this signature of the low latitude thermocline has two probable causes 1 mixing with low nitrate surface water and 2 the oxidation of newly fixed n

the shaw method of palaeointensity determinations and its application to recent volcanic rocks summary our new version together with previous versions of the shaw method has been compared by applying them to recent volcanic samples for which we have well determined palaeointensity values although the earlier modifications to the shaw method give a linear portion to the nrm trm diagram of all the specimens about half of the calculated palaeointensities deviate by more than 20 per cent from the expected values this may be caused by alteration of the magnetic minerals during the laboratory heating or by chemical alteration prior to the laboratory experiments the new modification uses a double heating of samples above the curie temperature in the laboratory after heating the specimen twice in the same field the measured intensity from the second heating is compared with the laboratory field intensity if the difference is larger than the experimental error then we assume that the anhysteretic remanent magnetization arm correction is not applicable and the sample is therefore rejected this technique provides a powerful criterion with which to select samples using this selection technique palaeointensities are generally within 10 per cent difference of the expected values with a success rate of about 40 per cent

geomagnetic field intensity during the last 5 myr ltd dht shaw palaeointensities from volcanic rocks of the society islands french polynesia summary on the basis of the thellier palaeointensities reported so far it has been thought that the time averaged virtual dipole moment vdm and virtual axial dipole moment vadm for the last few million years are almost the same as the present geomagnetic dipole moment 8 1022 a m2 this estimate has been called into question however because recent studies have revealed that the thellier method occasionally overestimates palaeointensities by as much as twice the true values in contrast a recently developed palaeointensity technique namely the double heating technique of the shaw method combined with low temperature demagnetization the ltd dht shaw method can yield expected field intensities from samples which give unreliable palaeointensities using the thellier method therefore we have measured absolute palaeointensities from 0 5 4 6 ma volcanic rocks from the society islands french polynesia mainly using the ltd dht shaw method as a result 195 out of 361 samples passed the selection criteria some of which are compared with additional results obtained with coe s version of the thellier method in the thellier experiments 18 out of 40 samples passed the criteria giving palaeointensities both consistent and inconsistent with the ltd dht shaw results these samples are characterized mostly by two segmented arai diagrams if we take the ltd dht shaw palaeointensities 24 reliable site means are available and give a mean vadm of 3 64 2 10 1022 a m2 this is nearly half of the mean of the 0 5 ma thellier data selected from the latest palaeointensity database 7 46 3 10 1022 a m2 n 458 as well as the present dipole moment the ltd dht shaw palaeointensities newly determined in this study suggest that the present day field is so strong that it may not be typical of the past geomagnetic field

environmental magnetic study of a xeralf chronosequence in northwestern spain indications for pedogenesis article i nfo magnetic enhancement of a and b horizons during soil development is a common phenomenon to better understand the exact mechanism for the magnetic enhancement especially the mineral transformation pathways systematic rock magnetic studies were conducted on a xeralf chronosequence in northwestern spain a positive correlation was found between the average grain size and the concentration of pedogenic maghemite particles with the exception of some a horizons in which multiple factors seem to influence the nature and concentration of neoformed ferrimagnets it is argued that the interaction between the positively charged iron oxides and the anionic ligands present in the solution of these acidic soils plays an important role in this respect the time trends of the average grain size of pedogenic ferrimagnets and the strong correlation between the concentrations of hematite and maghemite in the magnetically enhanced horizons a and b are consistent with the hypothesis of a gradual formation of maghemite later converted into hematite via a precursor most likely ferrihydrite therefore this study provides strong evidence for the dynamic evolution of magnetic minerals upon pedogenesis

improvements in procedure and paleointensity selection criteria picrit 03 for thellier and thellier determinations application to hawaiian basaltic long cores abstract in this paper we first describe the paleointensity furnaces and the procedures specifically designed to minimize oxidation of the samples during thellier and thellier paleointensity experiments routinely used at gif we also propose some improvements to the set of criteria commonly used to select the results of the thellier experiments in order to further increase the reliability of paleointensity determination finally to be included in databases the new set of paleointensity criteria picrit 03 paleointensity criteria in 2003 is discussed and the results obtained from two long hawaiian basaltic cores the scientific observation hole 4 soh 4 and the hawaiian scientific drilling project 1 hsdp1 are used to illustrate its effectiveness some of the results are re evaluated and a new composite record of absolute paleointensity and inclination spanning 420 kyr is presented the inclination values obtained from the two cores combined support the hypothesis of persistent shallow inclinations at hawaii in intensity the upper 100 kyr are covered by the data from soh 4 with 309 reliable determinations out of 766 examined obtained from 143 units which belong to the kilauea volcano at the top of this core the 341 reliable data covering the 100 420 kyr interval are from 149 units of core hsdp1 belonging to the mauna kea volcano the interval 320 to 420 kyr is particularly detailed because of high extrusion rate of the volcano the use of more stringent criteria decreases the number of determinations considered as reliable in previous publications but it improves their accuracy and robustness

influence of open ocean nitrogen supply on the skeletal δ15n of modern shallow water scleractinian corals abstract the isotopic composition of skeleton bound organic nitrogen in shallow water scleractinian corals hereafter cs 15 n is an emerging tool for studying the marine nitrogen cycle in the past the cs 15 n has been shown to reflect the 15 n of nitrogen n sources to corals with most applications to date focusing on the anthropogenic terrestrial n inputs to reef environments however many coral reefs receive their primary n sources from the open ocean and the cs 15 n of these corals may provide information on past changes in the open ocean regional and global n cycle using a recently developed persulfate denitrifier based method we measured cs 15 n in modern shallow water scleractinian corals from 8 sites proximal to the open ocean at sites with low open ocean surface nitrate concentrations typical of the subtropics and tropics measured cs 15 n variation on seasonal and annual timescales is most often less than 2 in contrast a broad range in cs 15 n of 10 is measured across these sites with a strong correlation between cs 15 n and the 15 n of the deep nitrate supply to the surface waters near the reefs while cs 15 n can be affected by other n sources as well and can vary in response to local reef conditions as well as coral symbiont physiological changes this survey indicates that when considering corals proximal to the open ocean the 15 n of the subsurface nitrate supply to surface waters drives most of the cs 15 n variation across the global ocean thus cs 15 n is a promising proxy for reconstructing the open ocean n cycle in the past

palaeointensity study of the oshima 1986 lava in japan implications for the reliability of the thellier and ltd dht shaw methods abstract we have performed a palaeointensity study of the oshima 1986 lava in order to examine the reliability of the thellier and ltd dht shaw methods with special reference to high temperature oxidation states of magnetic grains coe s version of the thellier method was applied to fifteen specimens from five block samples the palaeointensities determined by this thellier method ranged from 44 8 to 59 0 t with an average of 51 0 4 1 t n 15 they are systematically higher than the expected intensity 45 5 t from the dgrf 1985 since the in situ magnetic survey at the sampling site indicates no strong local magnetic anomaly these high palaeointensities are overestimation probably due to some rock magnetic property and or some thermal alteration during the experiments microscopic observations show that the samples where some titanomagnetites surrounding vesicles were classified with intermediate oxidation indices of iii v gave 10 30 higher palaeointensity values therefore the erroneously high thellier palaeointensities have a relation to the high temperature oxidation state for eight of the fifteen specimens used in the thellier experiments the applied dc field was perpendicular to the primary nrm component for quantitative evaluation of laboratory induced chemical remanent magnetisation crm directional changes of nrm thermally demagnetised during the thellier experiments indicate that most of the samples more or less acquired crm due to laboratory heating suggesting that some magnetic phase with high blocking temperatures was produced for the specimens of intermediate oxidation level the crm appears to have been gradually acquired at relatively low temperatures 400 c it would appear to be difficult to detect this gradual thermal alteration with the standard ptrm check weak field susceptibility measurements and hysteresis parameter changes we also applied the double heating technique of the shaw method combined with low temperature demagnetisation ltd dht shaw method to seven specimens from the same block samples the palaeointensities determined by the ltd dht shaw method yielded an average of 46 4 4 7 t n 6 which agrees with the expected intensity indicating no dependence on the high temperature oxidation states

mineralogy micromorphology and chemical analysis of andosols on the island of sao miguel azores abstract a study concerning soil genesis was conducted on surface and buried volcanic soils of sao miguel island azores of eight soil profiles three were selected for detailed study of pedogenesis a series of techniques which include chemical micromorphological xrd and dxrd analysis micropicking on impregnated soil blocks tem eds and ir spectroscopy analyses were used the soils showed an incipient to moderate degree of weathering as typically occurs in many young volcanic districts four different stages of soil development were clearly identified the first stage of soil development was characterised by dominance of primary minerals and some allophane and ferrihydrite formation with an feo fed ratio of about 0 86 lom soil the second stage of soil development was indicated by halloysite and ferrihydrite formation in the lower horizons along with an feo fed ratio of about 0 62 san surface soil the third stage of soil development was characterized by halloysite and ferrihydrite formation in the lower horizon but also by clay illuviation and stronger pumice weathering and an feo fed ratio of about 0 51 san buried soil the fourth stage of soil development concerned the lix soils buried soils older than 5000 years bp which had a much higher content in hydrated halloysite and considerable amounts of goethite and hematite these soils exhibit the most expressed weathering features and an feo fed ratio of about 0 25 the presence of young surface soils and well developed buried soils can be explained by i the longer pedogenesis of buried soils or possibly by ii the presence of a climate more seasonal than that of the present day

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

geomagnetic field intensity and inclination records from hawaii and the reunion island geomagnetic implications abstract we report on new paleointensity and inclination records obtained in hawaii from 386 samples drilled in 137 subaerial flows of the hsdp2 long basaltic core that we have combined in a composite record with the other hawaiian results to produce a unique and accurate lava record of absolute geomagnetic field intensity and inclination at hawaii for the last 405 kyr these data are considered together with published results from la reunion island for about the same time period in order to compare them to model results in hawaii when recognized excursional periods are omitted the average vadm vdm value is about 8 2 8 4 1022 am2 and the inclination is on the average 29 8 i e about 6 shallower than the expected value at this location gad value in the reunion island we selected published results in which both inclination and intensities values are obtained using modern methods and strict criteria the average vadm vdm is 9 4 2 3 8 7 2 3 1022 am2 and the average inclination value when transitional data are ignored is 44 4 2 4 about 7 steeper than the gad value these results compared with model intensities predicted by dynamo solutions that incorporate lateral variations in core mantle boundary heat flow derived from seismic tomography are too high for both localities but they decrease as the amplitude of thermal boundary anomalies increases with strong boundary heat flow the model inclination anomaly at hawaii fits with the data but at la reunion model inclination anomalies have the wrong sign this comparison indicates that strong boundary heat flow anomalies give the best fit to the data and that future improvements will be obtained by proportionally increasing both the rayleigh number and the amplitude of heat flow variations

from andic non allophanic to non andic allophanic inceptisols on alkaline basalt in mediterranean climate a toposequence study in the marghine district sardinia italy abstract the properties of a non andic allophanic inceptisol pom1 and two andic non allophanic inceptisols flm5 and spm8 representative of a toposequence on basanite rocks of mt st antonio central western sardinia marghine sub region were analyzed to better elucidate factors and processes that lead to a different expression of andic properties and allophane formation in xeric mediterranean environment a series of laboratory techniques including physical chemical micromorphological x ray diffraction xrd scanning electron microscopy sem analyses were used all soils are usually rich in organic carbon dystric at the great group level with saturation base from 72 to 10 and with ph from subalcaline to acidic allophanic inceptisol appears more intensely weathered than non allophanic inceptisols volcanic glass content is in any case negligible pom1 formed on the plateau shows a shallow solum 45 cm with a 2 horizon that meets all the criteria for andic soil properties the amounts acid oxalate extractable al o and si o together with pyrophosphate extractable al p typifies such a pedon as allophanic inceptisol 0 19 p al o 2 the allophanic inceptisol pom1 is located at the plateau of the toposequence where lower surface runoff greater water infiltration rate the absence of significant erosion and colluvial movement may have increased the degree of weathering processes in these conditions the prolonged soil moistness prevents the transformation of short order components on the whole the results emphasize the role of topography and the importance of al fe amorphous compounds in expressing soil andic properties and allophane content versus the volcanic origin of parent material and the insufficiency of volcanic glass the results also suggest that the occurrence of soil with andic properties and significant allophane content in hot and dry environments like the mediterranean climate in sardinia may be more widespread than expected

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

geomagnetic paleointensity deduced for the last 300 kyr from unzen volcano japan and the dipolar nature of the iceland basin excursion abstract we have conducted paleointensity measurements of lavas and pyroclastic flows from unzen volcano japan they have been shown in a previous study to contain a record of brunhes chron secular variation with one flow recording a transitional direction senbongi geomagnetic excursion 191 17 ka various rock magnetic analyses indicate that the main magnetic carriers of samples are ti poor titanomagnetites which have mixtures of single domain sd and or pseudo sd and multi domain grain sizes the low temperature demagnetization ltd double heating test dht shaw method yielded 209 successful results from 56 sites giving 27 acceptable site mean paleointensities for the past 5 300 kyr when excluding the senbongi excursion data and two other data points the data give an average virtual dipole moment vdm of 7 69 10 22 a m 2 with a standard deviation of 2 51 10 22 a m 2 n 24 this is consistent with the selected 80 site mean thellier paleointensity data from the latest paleointensity database with an average vdm of 7 64 10 22 a m 2 and a standard deviation of 2 56 10 22 a m 2 paleointensity measurements on samples that record the senbongi excursion which is claimed to correlate with the iceland basin excursion provide a value of 7 74 9 37 t using the ltd dht shaw method this corresponds to an average standard deviation vdm of 2 19 10 22 a m 2 0 21 10 22 a m 2 when calibrating sedimentary records that capture the iceland basin excursion by averaging the ltd dht shaw vdms obtained from the pre and post excursional period the records give consistent vdm values with the volcanic senbongi record during the excursion this indicates that variation of the geomagnetic field direction and intensity during the iceland basin excursion can be well represented by a simple dipolar variation

goethite and hematite in a climosequence in southern brazil and their application in classification of kaolinitic soils abstract the goethite hematite goethite ratio of 11 profiles of oxisols ultisols and inceptisols along a 600 km e w transect in s brazil varied systematically with climatic and soil factors the ratio increased with decreasing mean annual air temperature increasing excess moisture rainfall minus evapotranspiration increasing soil organic carbon and decreasing ph this is explained in light of the current concept of goethite and hematite formation in soils higher temperatures favor hematite whereas higher excess moisture higher organic carbon and lower ph favor goethite a basis is suggested for using goethite and hematite in the mineralogical classes at the family level of soil taxonomy

no evidence for strong fields during the r3 n3 icelandic geomagnetic reversal a previous study of the r3 n3 icelandic reversal which corresponds probably to the matuyama reunion reversal provided relatively large virtual dipole moments when the pole is close to equator to check these former results obtained using the shaw paleointensity method we resampled the very same sections and flows and reanalysed the samples using the thellier method 38 lava units and one baked horizon from 4 sections provide intermediate r3 n3 paleofield directions most of them possibly related to a single eruption display similar directions corresponding to the near equator vgp cluster unfortunately most of the intermediate lava flows are thermally unstable as attested by the irreversibility of the susceptibility versus temperature k t curves which precludes their use for paleointensity purpose the rest of the units provide fairly reversible k t curves and a near magnetite tc due to fe rich titanomagnetite resulting from oxyexsolution at high temperature 25 baked units or lava flows of this kind yield reliable thellier paleointensity data average paleostrengths of 44 7 14 9 t and 32 5 22 9 t were found for the reversed r3 and the normal n3 polarity zones respectively combining these non transitional paleostrengths with other thellier data from over the world indicates that the pliocene dipole moment was close to 8 1022 a m2 the average paleostrength is reduced to 11 3 3 0 t during the r3 n3 transition we find no indication for the strong fields 20 4 to 38 6 t previously obtained by the shaw method thus our results do not confirm the existence of large virtual dipole moments when the pole approaches the equator

superparamagnetism of two modern soils from the northeastern pampean region argentina and its paleoclimatic indications summary the magnetic susceptibility carried by pedogenic fine grained ferrimagnets has been widely used as paleoclimatic proxy to elucidate long term paleoclimatic variations for windblown terrestrial loess paleosol sequences however the magnetic properties of the lithogenic parentmaterialcanmaskthepedogenicsignals inthisstudy wesystematicallyinvestigatedthe origin of the superparamagnetism of two modern soils from the northeastern humid pampean region argentina developed on loess materials of different mineralogical composition the samples were treated with the citrate bicarbonate dithionite cbd reagent which is known to dissolve the submicron pedogenic ferrimagnets while leaving unaltered the coarse grained ones the magnetic material accounting for the frequency dependent magnetic susceptibility peak at about 50 k remained in the residuals and is independent of the pedogenic processes in addition pedogenic ferrimagnetic particles in the two soils have a magnetic signature comparable to that of the soils from the chinese loess plateau it is also suggested that the for the bulk samples does not seem to be a reliable paleoclimatic proxy for the pampean soils investigated in this study instead the cbd soluble magnetic signals could be more useful to detect paleoenvironmental variations in this region these new findings provide improved understanding of the magnetic assemblage in the pampean loess soils and make it feasible to retrieve the paleoclimatic signals carried by the pedogenic cbd soluble iron oxides after removing the effects of the lithogenic inputs

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

lithological factors affecting magnetic susceptibility of subtropical soils zhejiang province china abstract magnetic susceptibility was measured on subtropical soils formed on a range of parent materials in zhejiang province china to demonstrate the influence of parent material lithologies on the amount and vertical distribution of in the soils we found that the values of soils vary by up to two orders of magnitude with their parent material lithologies soils formed on igneous rocks with high values showed high absolute and distinctly decreased compared with values of parent materials the values of soils formed on basalt andesite and granodiorite were 250 10 8 m 3 kg 1 the values of soils formed on granite and other neutral and acid igneous rocks ranged from 50 10 8 to 120 10 8 m 3 kg 1 in most of the soils formed on sedimentary rocks enhancement in upper horizons of soils was found compared with parent material this enhancement was believed to be pedogenic formation of superparamagnetic sp stable single domain ssd magnetic grains which are characterized by high values of frequency dependent susceptibility fd and anhysteretic remanent magnetization arm soils formed on sedimentary rocks with a very low initial and iron content showed a low value throughout the profile it was found that there is a highly significant relationship between the values of soils and their dithionite citrate bicarbonate solution dcb soluble iron contents fe d the values of soils in chronosequences formed on alluvium and two marine deposits increased as soils became older it is suggested that the values can be used as a tool for determining the relative age in chronosequence studies

controls on sedimentary nitrogen isotopes along the chile margin chilean margin sedimentary n isotope records have been the focus of paleoceanographic studies examining the extent of water column denitrification in the eastern south pacific in the past here we use 15n 14n of nitrate and surface sedimentary n along the chilean coast to investigate the relative contributions of water column denitrification and surface nitrate assimilation by phytoplankton to the sedimentary n isotope record off northern and central chile subsurface enrichment of 15no3 is associated with the lowest oxygen concentrations and maximum nitrate deficits the product of water column denitrification locally at 21 s and through the transport of denitrified waters to the south while elevated the 15n of pycnocline nitrate shows no distinct trend with distance from the omz and is nearly homogenous within the shallow subsurface layer presumably due to lateral circulation along the margin moreover an isotopically depleted and relatively uniform layer exists within the shallow subsurface possibly as a result of the remineralization of newly fixed nitrogen that may work to further homogenize the 15n of the upwelling nitrate whereas the high 15n of sedimentary n in the region is clearly a product of denitrification and its isotopic imprint on nitrate along the margin the northward increase in sedimentary 15n from higher southern latitudes also reflects the degree of surface layer nitrate consumption by phytoplankton the northward increase in sedimentary 15n corresponds to a regional decrease in the surface nitrate concentration and isotopic fractionation during nitrate assimilation is apparent in shallow nitrate 15n a comparison of the 15n in shallow subsurface nitrate and sedimentary n suggests that north of 30 s nearly complete nitrate consumption causes the 15n of sediments to converge on that of the nitrate supply such that denitrification should be the dominant signal in downcore 15n records from these latitudes moreover the lateral homogeneity of the denitrification signal in the subsurface within this region suggests that such records will provide robust reconstructions of denitrification intensity

a detailed geomagnetic record from chinese loess abstract a collection of over 100 individually orientated hand samples was obtained from a 335 m loess section near lanzhou northern china previous studies defined the brunhes matuyama b m boundary and jaramillo normal subchron within the section the position of these magnetic markers led to the suggestion of a basal age for the section of 1 3 ma this disagrees significantly with a date of 2 45 ma for the onset of loess accumulation at lochuan 500 km to the east of lanzhou the present study considers the section in far greater detail and has derived a complex magnetostratigraphy isolating seven normal events within the lower 130 m of the section a simple interpretation of this magnetostratigraphy suggests a basal age for the section in the region of 2 4 ma however the relative chronology of the loess palaeosol sequence although appearing to confirm this basal age has revealed that this simple interpretation of the magnetostratigraphy may not be justified

late quaternary tephra derived paleosols in central italy s carbonate apennine range stratigraphical and paleoclimatological implications abstract detailed stratigraphical pedological and geochronological 14c dating research was carried out on numerous sections located in the carbonate apennine range of central italy two paleosols late pleistocene pedomarker a and holocene pedomarker b in age were recognized as having developed from air fall pyroclastic material given their special properties and widespread distribution both soils represent valuable markers in the late quaternary stratigraphy of central italy information about the climatic conditions that have influenced their pedogenesis through time has been obtained pedomarker a formed under temperate wet conditions related to the last interstadial fluctuations of the pleniglacial its development ceased after ca 30 ka because of the onset of last glacial maximum dry cold conditions pedomarker b formed at the beginning of the holocene under udic and perudic soil moisture regimes its development ceased in some localities because of a change towards a drier climate after ca 4 5 ka petrographic and geochemical characteristics of the parent materials are discussed and correlations with the campanian ignimbrite pedomarker a and neapolitan yellow tuff pedomarker b both related to activity in the phlegrean fields are proposed

the hidden nature of parent material in soils of italian mountain ecosystems abstract soils with andic features are known to be very important as regards both ecosystem fertility and susceptibility to land degradation in recent years there has been an increasing number of finds of these soils in non volcanic mountain ecosystems nvme in different parts of the world under different environmental settings in italian nvme there has been extensive investigation proving that these soils have a much wider distribution than previously thought but despite these important findings very little is known about their genesis or properties against this background our investigation aims to question the nature of parent material in andic soils in italian nvme we consider this question fundamental for proper understanding of such soils we address the question of the parent material by highlighting similarities dissimilarities between soils and their underlying bedrocks and ascertaining whether soils developed as a result of in situ weathering or because of eolian inputs the study was conducted on 41 soil profiles distributed throughout italian nvme performing an integrated analysis of i grain size distribution gsd by laser granulometry ii end member modelling of obtained gsd iii soil bedrock differences in magnetic susceptibility and iv soil bedrock differences based on the geochemistry of 38 elements the final results from these investigations show that the investigated soils are mainly derived from eolian sediments and that weathering of the underlying bedrock plays a minor role two main types of eolian parent materials seem to coexist in different proportions according to the soil type eolian sediments with a similar composition of the underlying bedrock termed autochthonous loess and eolian sediments of volcanic type pyroclasts autochthonous loess represents the main component of the parent material in the following studied soils aluandic andosols cambisols phaeozems and podzol 67 63 44 and 73 respectively all these soils exhibit low to moderate andic features volcanic type eolian sediments constitute about 90 of the parent material in most andic soils that are silandic andosols but occur in different proportions in most of the investigated soils the nature of soil parent materials surprisingly follows a clear trend with latitude with autochthonous loess characterizing most parent materials in northern italy whilst volcanic sediments form most parent materials in the south in accordance with their latitude other soils exhibit an intermediate behaviour

geomagnetic paleointensities at hawaii between 3 9 and 2 1 ma preliminary results abstract thellier thellier experiments have been conducted on 454 samples from different sequences of the waianae and koolau volcanoes in oahu hawaii the sampled interval as determined by k ar dating spans from 3 9 to 2 1 ma results from 89 samples from 41 flows meet restrictive reliability criteria and provide the first paleointensity estimates from hawaii for the sampled period with good temporal resolution on this time interval the vadm shows ample fluctuations from a minimum of 2 3 1022 am2 to a maximum of 11 5 1022 am2 about an average value of 7 0 2 3 1022 am2 suggesting that fluctuations of the geomagnetic field strength comparable in amplitude to the time averaged value may be a characteristic of the field during both the reverse mammoth chron and the normal chron between the mammoth and the kaena the field strength appears to increase with time

late pleistocene climatic variations as recorded in two italian maar lakes lago di mezzano lago grande di monticchio abstract sediment profiles from two maar lakes lago di mezzano central italy and lago grande di monticchio southern italy were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20 000 yr of the last glaciation the chronological framework is provided by calibrated radiocarbon ages varve counting calculation of sedimentation rates and tephrochronology in the time slice between 34 000 and 14 000 cal bp periods of increased minerogenic input are observed in both lacustrine records interrupted by periods of low minerogenic input these cyclic variations have an average recurrence time of 1785 yr for lago di mezzano and 2875 yr for lago grande di monticchio comparing well with marine and ice core data explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff the higher precipitation evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from lago grande di monticchio show a contemporary development of steppe vegetation an indicator for cool dry climatic conditions this may be connected with a southward shift of the westerlies and a reinforced jet stream agreement of lacustrine data from italy with late pleistocene glacial events in central italy with events recorded in marine archives from the north atlantic heinrich events and with oxygen isotope data from greenland ice cores is interpreted as evidence for the late pleistocene climate in europe being influenced by north atlantic climatic forcing which may be related to dansgaard oeschger cycles

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

nitrogen isotope ratios of nitrate and n anomalies in the subtropical south pacific nitrogen isotopic ratios of nitrate 15n no3 were analyzed above 1000 m water depth along 17 s in the subtropical south pacific during the revisit woce p21 cruise in 2009 the 15n no3 and n values were as high as 17 and as low as 18 mol n l 1 respectively at depths around 250 m east of 115 w but were as low as 5 and as high as 1 mol n l 1 respectively in subsurface waters west of 170 w the relationships among no3 concentrations n values 15n no3 values and oxygen and nitrite concentrations suggest that a few samples east of 90 w were from suboxic and nitrite accumulated conditions and were possibly affected by in situ water column denitrification most of the high 15n no3 and negative n waters were probably generated by mixing between subantarctic mode water from the southern ocean and oxygen deficit zone water from the eastern tropical south pacific with remineralization of organic matter occurring during transportation moreover the relationship between 15n no3 and n values as well as trichodesmium abundances and size specific nitrogen fixation rates at the surface suggest that the low 15n no3 and positive n subsurface waters between 160 e and 170 w were generated by the input of remineralized particles created by in situ nitrogen fixation mainly by trichodesmium spp therefore the 15n values of sediments in this region are expected to reveal past changes in nitrogen fixation or denitrification rates in the subtropical south pacific

trace element geochemistry in topsoil from east china the concentrations of 23 trace elements in 50 topsoil samples collected from sites ranging between 18 19 n and 49 13 n in east china were analyzed sc ti v cr mn co ni cu zn ga and ta have mean contents more than two times higher than in the continental upper crust three elements rb sr and ba are present at lower concentrations than in the continental upper crust finally a group of elements consisting of ge y zr nb sc hf pb th and u are present at concentrations 1 2 times higher than in the continental upper crust however concentrations of trace elements are mainly affected by parent rock the contents of sc ti v cr mn co and cu for 29 soils from basalt were found to increase from north to south whereas rb sr and ba contents were found to decrease in addition element concentration shows a close relationship with annual average temperature aat as well as annual average precipitation aap since the 29 soils are all from basalt the trends of the elemental contents should reflect the influence of climate which determines the intensity of weathering these elemental trends suggest that the content of certain elements may indicate the intensity of basalt weathering ba nb and sr nb ratios were both found to have good correlations with aat and aap in this study which means that these ratios can also indicate the intensity of chemical weathering of basalt

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

coupled nitrate nitrogen and oxygen isotopes and organic matter remineralization in the southern and pacific oceans 1 the difference between nitrate 15n and 18o or 15 18 is sensitive to organic matter remineralization and tracks the modification of nitrate as it passes from the deep pacific ocean through the southern ocean surface and into the intermediate depth pacific circumpolar deep water cdw is upwelled with a nitrate 15 18 of 3 0 and appears unaltered by nitrate assimilation in the antarctic surface however within subantarctic mode water samw the primary conduit of deep sea nutrients to the lower latitudes nitrate 15n and 18o are both higher than cdw while nitrate 15 18 is as low as 1 5 the lower samw nitrate 15 18 results from the production of low 15n organic matter during partial assimilation of the surface nitrate pool followed by its sinking and remineralization back to nitrate lowering the 15n of thermocline nitrate more than its 18o as samw flows toward the lower latitudes nitrate 15 18 is expected and observed to increase because complete surface ocean nitrate consumption produces sinking nitrogen with a 15n similar to that of the nitrate supplied from below such that remineralization lowers the 18o of nitrate but not its 15n nitrate 15 18 is also used to estimate a surprisingly high low latitude sinking nitrogen 15n of 9 0 suggesting a major effect of 14no3 loss by tropical denitrification on middepth nitrate basin wide the remineralization of this high sinking nitrogen 15n increases nitrate 15 18 as deep as the southward moving pacific deep water which supplies cdw this relatively high 15 18 is then lowered to the observed cdw value by the remineralization of southern ocean sinking nitrogen with a low 15n

soil development in a quaternary fluvio lacustrine paleosol sequence in southern italy abstract the aim of this paper is to enrich our knowledge of an important paleosol succession located in bojano basin of the southern apennines italy with new pedological geochemical and magnetic data the studied area consists of alluvial and fluvial lacustrine sequences 160 m dating from the middle pleistocene 0 5 ma the study area shows the presence of recent soil consisting of well developed andosols rs and several clastic sedimentary levels alternating with four layers solum i ii iii and iv of paleosols soil and paleosols were analyzed by laser grain size distribution gsd diffuse reflectance spectroscopy drs trace elements and magnetic properties in order to evaluate the relative contributions of pedogenic and detrital components results showed that the finest pedogenic ferrimagnetic grains exhibit two trends with respect to the degree of pedogenesis indicate two different pedoclimate formations the paleosol sequence consists of highly weathered vertisols solum i and iv and of less weathered entisols solum ii iii the recent soil andosol has a strong bimodal distribution formed mostly by coarse silt size particles related to the volcanic parent material solum i showed a sharp unimodal clay gsd while solum iii and iv were composed of bimodal gsd with high percentages of fine silt size particles on the basis of the trace element content and gt fd ratio all solum i ii iii iv exhibited low weathering pedogenesis compared with rs and negligible contribution to the magnetic properties of the coarse fractions this occurs in vertisols which developed under humid temperate climates solum i and siv and formed below the layer of neapolitan yellow tuff developed after 12 15 ka bp in solum ii iii the finest sedimentary levels the low rate of pedogenesis could have developed under more cold climatic conditions after the last eruption campanian ignimbrite 39 ka in the late pleistocene

late quaternary variability of sedimentary nitrogen isotopes in the eastern south pacific ocean 1 we present high resolution bulk sedimentary 15n data from the southern edge of the present day oxygen minimum zone of the eastern south pacific the record is interpreted as representing changes in water column nitrogen removal during the last 70 000 years we found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales these fluctuations were not related to other millennial scale changes like the northern hemisphere s dansgaard oeschger climate swings or local changes in primary productivity so appear to be dictated by the southern hemisphere s climate rhythm this is preliminarily corroborated by an overall agreement between our 15n data and the sedimentary proxy of ice sheet dynamics in patagonia which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern south pacific intermediate waters finally potential implications on late quaternary changes in atmospheric co2 concentrations are discussed

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

two normal paleomagnetic polarity intervals in the lower matuyama chron recorded in the shungura formation omo valley southwest ethiopia abstract two hundred fifty meters of fluvio lacustrine deposits were sampled from the 760 meter thick shungura formation to study magnetostratigraphy within the lower matuyama chron two to three block samples at different positions were collected from 46 units in the section characteristic remanent magnetization chrm is isolated at temperatures between 390 c and 620 c or alternating fields between 25 and 100 mt the chrm is carried by detrital magnetite and maghemite directional analyses revealed three reversed and three normal polarity zones r3 n3 r2 n2 r1 n1 in the sequence the overall mean direction d s 359 1 i s 3 4 95 3 9 n 44 differs marginally from the expected mean dipole field direction d 1 0 i 8 8 95 2 3 n 26 besse j courtillot v 2003 apparent and true polar wander and the geometry of the geomagnetic field in the last 200 million years j geophys res 108 b10 2469 doi 10 1029 2003jb002684 using stratigraphic scaling between 40 ar 39 ar and k ar isotopic age data brown f h mcdougall i davies i maier r 1985 an integrated plio pleistocene chronology for the turkana basin in delson e ed ancestors the hard evidence alan r liss inc new york pp 82 90 mcdougall i brown f h 2006 precise 40 ar 39 ar geochronology for the upper koobi fora foramtions turkana basin northern kenya j geo soc lond 163 205 220 the normal zones n3 n2 and n1 are dated between 2 06 0 01 2 08 0 01 ma 2 15 0 01 2 20 0 01 ma and at 1 93 0 02 ma respectively these age estimates imply that n1 represents the bottom of the olduvai subchron while n2 and n3 might represent reunion subchrons if the sedimentation rates are assumed to be constant the duration for the older reunion i subchron is about four to seven times 57 15 kyr that currently adopted by the recent gpts cande s c kent d v 1995 revised calibration of the geomagnetic polarity timescale for the late cretaceous and cenozoic j geophys res 100 6093 6095 and the younger reunion ii subchron has a shorter duration of 18 25 kyr

validity of the ltd dht shaw and thellier palaeointensity methods a case study of the kilauea 1970 lava the double heating technique of the shaw method with low temperature demagnetisation ltd dht shaw method for determination of geomagnetic palaeointensity is applied to samples exhibiting high temperature oxidation states from the kilauea 1970 lava hawaii island results are obtained for 11 of the 12 specimens prepared from five block samples yielding an average palaeointensity of 38 2 2 8 t n 11 1 this value is consistent with the expected value determined from dgrf 1970 35 8t and does not appear to be significantly dependent on the high temperature oxidation state coe s version of the thellier method was also applied to nine specimens prepared from the same block samples and successful results were obtained for seven specimens giving an average palaeointensity of 43 2 8 4 t n 7 although this average is statistically consistent with the expected value the results include erroneously high palaeointensities 52 1 and 55 4 t for specimens from one block sample of intermediate high temperature oxidation state the present results therefore reinforce the broader applicability of the ltd dht shaw method for samples with high temperature oxidation states compared with coe s version of the thellier method it is also shown that the samples yielding overestimated thellier palaeointensities tend to fall close to the mixing line between single domain and or pseudo single domain and multidomain components on the day plot this relationship may be useful as a pre selection technique for application of the thellier method 2004 elsevier b v all rights reserved

surface subsidence induced by the crandall canyon mine utah collapse insar observations and elasto plastic modelling summary the crandall canyon mine utah collapse in 2007 august resulted in a total of nine fatalities we processed data from the alos satellite acquired before and after the collapse to quantify surface subsidence associated with the collapse to better understand the collapse process the deformationshowsasteepv shapedpatternofsubsidencewithslightasymmetry wecompare the fit of four different models that simulate the subsidence pattern the first two models use elastic half space rheology we find that collapse alone cannot explain the observations and a component of normal faulting is required to fit the data the second set of models simulates collapseinelasto plasticmedia onlyasmallcomponentofnormalfaultingisrequiredinthese models we suggest that considering elasto plastic material behaviour is particularly important for shallow deformation modelling where microfractures and other non elastic rheology are common disregarding this material behaviour can lead to biased model parameter estimates

paleomagnetic and geochronological identification of the reunion subchron in ethiopian afar this paper reports the paleomagnetic and geochronological analysis of a suite of samples from a basaltic fault related scarp of pliocene age in the central part of the afar depression ethiopia paleomagnetic work uncovers a clear characteristic remanent magnetization carried by titano magnetites with high unblocking temperatures close to the curie temperature of pure magnetite the characteristic direction based on 27 non transitional flows is d 8 1 o i 10 1 o 5 4 1 o this is consistent with earlier determinations of the clockwise tectonic rotation due to rift propagation and overlap of the block to which the section belongs magnetic stratigraphy consists of a succession from bottom to top of 16 reversed 7 normal and 4 reversed flows one flow at the upper normal to reverse transition demonstrates complex behavior upon thermal and alternating field af demagnetization which is due to remagnetization by the overlying flow k ar dating of five samples provides consistent determinations averaging 2 07 0 05 ma all ages agree with this average given their rather large individual uncertainties from 0 04 to 0 08 ma at the lc level comparison with recent reference geomagnetic polarity timescales gpts indicates that the normal subchron recorded in the gamarri section must be linked with one of the r6union event s the normal subchron and an earlier episode of large secular variation could provide the best volcanic record of a double r6union event although uncertainties in ages are too large to allow unequivocal inferences our age determination for the r6union event is in better agreement with earlier determinations of mcdougall and watkins 1973 than with a more recent value proposed by baksi et al 1993 and used in the gpts

paleointensity results from the jurassic new constraints from submarine basaltic glasses of odp site 801c 1 tholeiite of the oldest oceanic crust was drilled during odp legs 129 and 185 at hole 801c in the western pacific fresh appearing submarine basaltic glass sbg was recovered from the tholeiites 167 ma which has been shown to be nearly ideal for determining absolute paleointensity paleointensities of the younger off axis alkalic basalts 160 ma overlying the tholeiites had been studied earlier here we report results from the older tholeiitic on axis sequence we subjected a total of 73 specimens from 17 cooling units to absolute paleointensity experiments of these 30 specimens and six cooling unit averages met our strictest reliability criteria yielding an average of 11 9 3 9 t the bulk of evidence suggests a paleolatitude of the site of 14 s with an uncertainty of 10 this translates the intensity to a value for the virtual axial dipole moment of 28 zam2 slightly lower than values determined from the plagioclase crystals in the three cooling units of the younger alkalic basalts overlying the tholeiites tarduno cottrell 2005 our value is low when compared to the long term median value of the field of 42 zam2 our results and those of the published literature therefore support the contention of a low magnetic field strength in the jurassic average of 28 14 zam2 n 138 individual estimates as initially suggested by prevot et al 1990 our interpretation of the body of available data argue for low field strengths for the entire jurassic extending into the early cretaceous

modeling how surface nitrogen fixation influences subsurface nutrient patterns in the north atlantic 1 we represented mechanistically the process of nitrogen n fixation and associated n anomalies in the atlantic ocean using a three dimensional coupled physical biogeochemical model available direct measurements of n fixation rates in the atlantic ocean are compiled and these along with observed n anomalies constrain the model the model n fixation rate for the whole atlantic domain is 2 1 1012 moln yr 1 the model generated n anomaly shows the observed feature of a subsurface maximum when plotted on isopycnal surfaces the model generated n anomaly bears little relation to the pattern of n fixation at the surface however the highest n fixation rates should be spatially related to n distribution if particulate export is remineralized at depths in the same region where the n fixation occurred we performed case studies varying remineralization and advection to clarify the genesis of the n anomaly and to determine the reasons underlying differences between n anomalies and n fixation rate patterns these studies indicated that the difference between these two patterns was created by both horizontal advection of excess n compared to phosphorus p and preferential remineralization of p compared to n n fixation and preferential p remineralization create high n anomalies both at the surface and in subsurface waters in the tropical atlantic which are transported into the northwestern north atlantic by western boundary currents and subsequently subducted as a result the highest n anomalies are located not in the tropics but in the northwestern north atlantic

paleointensity across the reunion event in ethiopia abstract paleointensity experiments have been conducted on a volcanic series of 33 flows which recorded the geomagnetic reunion event successive determinations of absolute paleointensity from 20 flows indicate that the reunion event would actually be characterized by two successive periods of low field intensity with a total duration not in excess of 30 kyr the first period has a mean paleointensity of 12 t and shows significant deviations from initial reverse polarity but no signs of fully normal polarity it is followed by field recovery then a decrease prior to the second directional episode the second period has a mean paleointensity of 17 t and is associated with full normal directions and thus likely a dominantly dipolar configuration these results are compatible with a simple earthlike magnetic field model with a large decrease in dipole field strength which yields local emergence of relatively stronger non dipole components field characteristics from this configuration would be different at different locations and could explain the variability of the paleomagnetic records collected around the world we propose that the absence of field recovery following the event is responsible for not leading to a durable polarity interval

nitrogen isotopic composition of organic matter from a 168 year old coral skeleton implications for coastal nutrient cycling in the great barrier reef lagoon abstract ongoing human activities are known to affect nitrogen cycling on coral reefs but the full history of anthropogenic impact is unclear due to a lack of continuous records we have used the nitrogen isotopic composition of skeleton bound organic matter cs 15 n in a coastal porites coral from magnetic island in the great barrier reef as a proxy for n cycle changes over a 168 yr period 1820 1987 ad the magnetic island inshore reef environment is considered to be relatively degraded by terrestrial runoff given prior cs 15 n studies from other regions there was an expectation of both secular change and oscillations in cs 15 n since european settlement of the mainland in the mid 1800s surprisingly cs 15 n varied by less than 1 5 despite significant land use change on the adjacent mainland over the 168 yr measurement period after 1930 cs 15 n may have responded to changes in local river runoff but the effect was weak we propose that natural buffering against riverine nitrogen load in this region between 1820 and 1987 is responsible for the observed stability in cs 15 n in addition to coral derived skeletal 15 n we also report for the first time 15 n measurements of non coral derived organic n occluded within the coral skeleton which appear to record significant changes in the nature of terrestrial n inputs in the context of previous cs 15 n records most of which yield cs 15 n changes of at least 5 the magnetic island coral suggests that the inherent down core variability of the cs 15 n proxy is less than 2 for porites

sedimentology and clast fabric of subaerial debris flow facies in a glacially influenced alluvial fan abstract a large alluvial fan 2 km2 constructed between 11 000 and 7000 years b p at the mouth of cinquefoil creek in interior british columbia canada is identified as glacially influenced debris flow dominated the fan was rapidly constructed during and immediately after deglaciation when large volumes of glacial debris were resedimented downslope fans of this type are widespread in the glaciated portion of the north american cordillera diamict facies deposited as debris flows account for 48 of the fan volume sheetflodd gravels 37 and other facies 15 diamicts show three facies types crudely bedded facies containing rafts of soft sediment that are attributed to downslope collapse and mixing of heterogeneous glacial deposits these occur within the core of the fan massive and weakly graded inverse to normal diamict facies derived from the downslope flow of weathered volcanic bedrock occur within a well defined bed that can be traced across the entire fan the occurrence of weakly graded facies as lateral equivalents to massive facies within the same bed implies the partial development of turbulent high velocity streams within a viscous debris flow moving over a slope of 6 clast fabrics in these facies show weakly clustered a axes dipping up and downslope comparable to other debris flows and lahars the cinquefoil fan its internal structure and facies provides a good modern analogue for ancient diamictite sequences deposited in areas of active uplift rifting and glaciation

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

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

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined