an early carboniferous paleomagnetic pole for gondwanaland new results from the mount eclipse sandstone in the ngalia basin central australia paleomagnetism of fourteen diamond drill cores from the uppermost devonian lower carboniferous mount eclipse sandstone in the ngalia basin central australia has been studied the samples were oriented using the borehole directions bedding planes identified in the drill cores and regional bedding attitudes three magnetic remanent components have been revealed 1 a drilling induced low to moderate temperature remanence c1 from all the drill cores which is oriented parallel to the drill cores and is most likely a combination of isothermal remanent magnetization and piezoremanent magnetization 2 a moderate to high temperature syndeformational overprint c2 d 226 7 i 82 3 95 6 2 k 68 9 in 65 samples from nine drill cores which was probably acquired during the mid to late carboniferous mount eclipse movement and 3 a moderate to high temperature likely primary remanence c3 d 057 1 i 36 9 95 9 6 k 29 6 from 64 samples in nine drill cores which exhibits a positive fold test c2 and c3 are found only in reddish siltstones and sandstones whereas c1 is best developed in grey reduced sandstones and siltstones a palynological examination gives an early to mid visean early carboniferous age of deposition for samples carrying the interpreted primary component c2 gives a mid to late carboniferous pole at 32 1 s 119 5 e with a95 11 9 which is in agreement with results of a previous study on surface outcrops c3 when combined with results from one drill core in a previous study gives a visean pole at 37 6 s 52 6 e with a95 8 7 this pole suggests a south polar position for central africa during the early carboniferous and therefore indicates the existence of a large ocean between gondwanaland and laurussia at that time the paleo south pole shifted from central africa in the early carboniferous 340 5 ma to east antarctica in the mid to late carboniferous 310 10 ma with a minimal continental drifting rate of 15 20 cm yr

reliability of palaeozoic palaeomagnetic poles and apwp of gondwanaland abstract a review of reliable palaeomagnetic data from gondwana palaeozoic rocks supports the apparent polar wander path apwp initially proposed by morel and irving this path or versions of it has recently gained favour with a number of groups the apwp suggests that during the mid palaeozoic gondwanaland was very mobile no palaeomagnetic pole position s has been yet reported that confirms the contentious segment of apwp from the late ordovician to the early silurian the apwp implies that the south pole moved rapidly from north africa in the ordovician to a position off southern south america by the silurian back to central africa by the early carboniferous and across gondwanaland to australia by the late carboniferous the distribution of palaeozoic tillites independently supports such a mobilistic gondwanaland the palaeomagnetic and tectonic evidence are compatible with the lachlan fold belt of australia having been in place since the mid devonian

tephra layers in the siple dome and taylor dome ice cores antarctica sources and correlations 1 volcanic ash or tephra layers are found in the taylor dome siple dome a and siple dome b ice cores significant shard concentrations are found at a number of depths in all three cores electron and ion microprobe analyses indicate that the geochemical composition of most layers is basaltic basanitic or trachytic and the geochemical signatures of the layers suggest derivation from the pleiades volcanic center mt melbourne volcano or small mafic centers probably in the royal society range area presence of tephra layers suggests an episode of previously unrecognized antarctic volcanic activity between 1776 and 1805 a d from at least two volcanic centers a strong geochemical correlation d 3 49 and 3 97 with a value of 4 considered identical is observed between tephra layers at depth of 79 2 m in the taylor dome ice core and layers between 97 2 and 97 7 m depth in the siple b core this correlation and the highly accurate depth age scale of the siple b core suggest that the age of this horizon in the taylor dome ice core presented by steig et al 1998a 2000 should be revised downward to the younger age of 675 25 years before 1995 this revised chronology is consistent with vertical strain measurements presented by hawley et al 2003

palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

evidence of the eldgja iceland eruption in the gisp2 greenland ice core relationship to eruption processes and climatic conditions in the tenth century glaciochemical studies and the evaluation of tephra in the gisp2 ice core provide information on the characteristics and potential environmental and climatic effects of the mid to late ad 930s voluminous fissure eruption of eldgja iceland the similarity in the chemical composition of basaltic glass shards found in a section of core dated at ad 938 4 compared to proximal glass from the eldgja eruption verifies the presence of eldgja debris a dacitic glass present in the same layer probably originated from eldgja as well in which case eldgja was the primary contributor of sulphur rich aerosols to the atmosphere in the late ad 930s we cannot completely exclude the possibility that another explosive eruption in the ad 930s produced this dacitic glass estimated maximum stratospheric loading is 100 x 1012 g h 2so4 over a 3 6 year period following the eruption but loading could be as low as half of that value a search of historical and proxy records for the late ad 930s to early 940s fail to show a co

ice core paleovolcanic records from the st elias mountains yukon canada 1 we previously reported a record of regionally significant volcanic eruptions in the north pacific using an ice core from eclipse icefield st elias mountains yukon canada the acquisition of two new ice cores from eclipse icefield along with the previously available eclipse icefield and mount logan northwest col ice cores allows us to extend our record of north pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3 5 km comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible especially for the largest eruptions such as katmai a d 1912 correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one third of the eruptions recorded in st elias ice cores are from alaskan and kamchatkan volcanoes although there are several moderately large volcanic explosivity index vei 4 eruptions recorded in only one core from eclipse icefield the use of multiple cores provides signals in at least one core from all known vei 4 eruptions in alaska and kamchatka since a d 1829 tephrochronological evidence from the eclipse ice cores documents eruptions in alaska westdahl redoubt trident and katmai kamchatka avachinsky kliuchevoskoi and ksudach and iceland hekla several unidentified tephra bearing horizons with available geochemical evidence suggesting alaskan and kamchatkan sources were also found we present a reconstruction of annual volcanic sulfate loading for the north pacific troposphere based on our ice core data and we provide a detailed assessment of the atmospheric and climatic effects of the katmai eruption

inter hemispheric transport of volcanic ash from a 1259 a d volcanic eruption to the greenland and antarctic ice sheets a strong volcanic sulfuric acid signal corresponding to an age of 1259 a d has been reported in ice cores from greenland antarctica and arctic canada tiny 5 m volcanic glass shards were reported previously in samples from this layer in an ice core from the south pole here we report the discovery of volcanic glass shards from a contemporaneous layer in an ice core from summit greenland the major element composition of the glass shards in the greenland sample are identical to those from the south pole confirming the assumption that has been made previously that the sulfuric acid signal in the ice cores is an inter hemispheric time stratigraphic marker the composition of these glass shards is similar to those produced by a 550 700 yrs b p eruption of el chichon volcano in mexico suggesting that it may be the source of the widely dispersed material

the msissi norite revisited k ar dating petrography and paleomagnetism the msissi norite in morocco 30 93 n 4 71 w from where one of the paleomagnetic reference pole for africa in devonian times has been derived has been revisited and dated petrological examination shows that the rock is an alkaline gabbro teschenite k ar analyses on fresh biotite yield a 136 139 ma age which infirms the supposed devonian age the paleomagnetic study displays several distinct magnetic components

a glaciochemical survey of the summit region greenland spatial representativene ss and an understanding of controls on chemical species distribution are essential requirements of any significant ice core investigation snowpit studies provide an essential tool in this process in preparation for the central greenland deep drilling effort a series of snowpits was sampled in detail for oxygen isotopes major anions major cations total acidity and radionuclides the results of this sampling program are used to define 1 the chemical composition of the snow in the region 2 the input timing and spatial distribution of major chemical species 3 the potential dependence of

late devonian carbonate magnetostratigraphy from the oscar and horse spring ranges lennard shelf canning basin western australia a b s t r a c t the late devonian was a time of major evolutionary change encompassing the fifth largest mass extinction the frasnian famennian event in order to establish a chronological framework for global correlation before during and following the frasnian famennian mass extinction we carried out a coupled magnetostratigraphic and biostratigraphic study of two stratigraphic sections in the upper devonian carbonate reef complexes of the lennard shelf in the canning basin western australia magnetostratigraphy from these rocks provides the first high resolution definition of the late devonian magnetic polarity timescale a 581 m reference section and an 82 m overlapping section through the marginal slope facies napier formation of the oscar range as well as a 117 m section at horse spring virgin hills formation were sampled at decimeter to meter scale for magnetostratigraphy conodont biostratigraphy was used to correlate both sections and link magnetostratigraphic polarity zones to a globally established biostratigraphy as table characteristic remanent magnetization chrm with dual polarities ne shallowly upward and sw shallowly downward is recovered from 60 of all samples with magnetite inferred to be the chief magnetic carrier from thermal demagnetization characteristics these directions define a geomagnetic pole at 49 5 s 285 8 e and 95 2 4 n 501 placing the canning basin at 9 9 s during the late devonian consistent with carbonate reef development at this time ac onservative interpretation of the magnetostratigraphy shows the recovery of multiple reversals from both sections not including possible cryptochrons and short duration magnetozones field tests for primary remanence include positive reversal tests and matching magnetozones from an overlapping section in the oscar range as trong correlation was found between magnetic polarity stratigraphies of the oscar range and horse spring sections and we correlate 12 magnetostratigraphic packages the relative stratigraphic thicknesses of the isochronous sediments from these two sections indicate that carbonate accumulation was 4 5 faster in the middle slope deposits at oscar range than in the more distal lower slope horse spring deposits for the middle frasnian through famennian the magnetic field during the late devonian underwent a relatively high reversal frequency with good potential for regional and global correlation and should prove useful in deciphering a high resolution chronostratigraphy across the lennard shelf to enable higher confidence examination of reef development across a major biotic crisis

el chichon volcanic debris in an arctic tropopause fold a research flight with the noaa wp 3d aircraft revealed evidence for stratospheric tropospheric exchange within the arctic through tropopause folding on the flank of the polar vortex observations showed descent of the tropopause and of stratospheric ozone to 700 mb along the west coast of greenland measurements of condensation nuclei and analysis of high volume impactor samples documented the presence of volcanic debris probably from the 1982 el chichon eruption including h2so4 droplets within the polar vortex and associated tropopause fold

out of tune the dangers of aligning proxy archives abstract tuning is a widespread technique to combine date and interpret multiple fossil proxy archives through aligning supposedly synchronous events between the archives the approach will be reviewed by discussing a number of literature examples ranging from peat and tephra layers to orbital tuning and 18o series from marine and ice deposits potential problems will be highlighted such as the dangers of circular reasoning and unrecognised chronological uncertainties and some solutions suggested fossil proxy research could become enhanced if tuning were approached in a more quantitative reliable and objective way and especially if individual proxy archives were non tuned and kept on independent time scales

abrupt and moderate climate changes in the mid latitudes of asia during the holocene a multiple parameter dating technique was used to establish a depth age scale for a 171 3 m 145 87 m w e surface to bedrock ice core bl2003 recovered from the cold recrystallization accumulation zone of the western belukha plateau 4115 m a s l in the siberian altai mountains the ice core record presented visible layering of annual accumulation and of delta o 18 delta d stable isotopes and a clear tritium reference horizon a steady state glacier flow model for layer thinning was calibrated and applied to establish a depth age scale four radiocarbon c 14 measurements of particulate organic carbon contained in ice core samples revealed dates for the bottom part of bl2003 from 9075 1221 cal a bc at 145 2 0 1 m w e 0 665 m w e from the bedrock to 790 93 ad at 121 1 m w e depth sulfate peaks coincident with volcanic eruptions the tunguska meteorite event and the 1842 dust storm were used to verify dating analysis of the bl2003 ice core reveals that the modern altai glaciers were formed during the younger dryas yd similar to 10 950 to similar to 7500 cal a bc and that they survived the holocene climate optimum hco similar to 6500 to similar to 3600 cal a bc and the medieval warm period mwp similar to 640 to similar to 1100 ad a decrease in air temperature at the beginning and an abrupt increase at the end of the yd were identified intensification of winds and dust loading related to asian desert expansion also characterized the yd during the yd major ion concentrations increased significantly up to 50 times for na background up to 45 times for ca2 and mg2 and up to 20 times for so42 relative to the recent warm period from 1993 to 2003 a warm period lasted for about three centuries following the yd signaling onset of the hco a significant and prolonged decrease in air temperature from similar to 2000 to similar to 600 cal a bc was associated with a severe centennial drought scd a sharp increase in air temperatures after the scd was coincident with the mwp after the mwp a cooling was followed gradually with further onset of the little ice age during the modern warm period 1973 2003 an increase in air temperature is noted which nearly reaches the average of hco and mwp air temperature values

spatio temporal variability in volcanic sulphate deposition over the past 2 kyr in snow pits and firn cores from amundsenisen antarctica in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably abstract in the framework of the european project for ice coring in antarctica epica a comprehensive glaciological pre site survey has been carried out on amund senisen dronning maud land east antarctica in the past decade within this survey four intermediate depth ice cores and 13 snow pits were analyzed for their ionic compos ition and interpreted with respect to the spatial and temporal variability of volcanic sul phate deposition the comparison of the non sea salt nss sulphate peaks that are related to the well known eruptions of pinatubo and cerro hudson in ad1991 revealed sulphate depositions of comparable size 15 8 3 4 kg km 2 in 11 snow pits there is a tendency to higher annual concentrations for smaller snow accumulation rates the combination of seasonal sodium and annually resolved nss sulphate records allowed the establishment of a time scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition using a robust outlier detection algo rithm 49 volcanic eruptions were identified between ad165 and 1997 the dating uncer tainty is 3 years between ad1997 and 1601 around 5 years between ad1601 and 1257 and increasing to 24 years at ad165 improving the accuracy of the volcanic chronology during the penultimate millennium considerably

a 4100 year record of explosive volcanism from an east antarctica ice core extensive archives of volcanic history are available from ice cores recovered from the antarctic and greenland ice sheets that receive and preserve sulfuric acid fallout from explosive volcanic eruptions the continuous detailed average 1 2 samples per year sulfate measurements of a 200 m ice core from a remote east antarctica site plateau remote provide a record of southern hemisphere volcanism over the last 4100 years this extends the volcanic record beyond the last 1000 years covered by previous antarctic ice cores an average of 1 3 eruptions per century is recorded in east antarctic snow during the last 4100 years the record shows that on average eruptions have been more frequent and more explosive during the most recent 2000 years than in the previous 2100 years intervals up to 500 years are observed in which few explosive volcanic signals are detected these periods include 2000 1500 b c no eruptions 500 1 b c two eruptions and 700 1200 a d two eruptions this new plateau remote volcanic record is compared with those from previous antarctic ice cores covering the last 1000 years in terms of dates for volcanic events the new record is in excellent agreement with the earlier records however significant discrepancies are found between these records in relative signal magnitude volcanic flux of several well known events the discrepancies among the records may be explained by the differences in the glaciology at the ice core sites analytical techniques used for sulfate and sulfuric acid measurement and the selection of detection thresholds for volcanic signals comparison with greenland ice core volcanic records indicates that during the last millennium nine large low latitude eruptions contributed significant amounts of volcanic aerosols to the atmosphere of both hemispheres potentially affecting global climate in contrast only one or possibly two such eruptions are found in the first millennium a d

the armorica microplate fact or fiction critical review of the concept and contradictory palaeobiogeographical data abstract the problem of an armorica microplate detached from gondwana and having had during part of the palaeozoic an independent latitudinal evolution is reconsidered in terms of a critical review of the palaeomagnetic data that were the very roots of this concept and through an alternative approach based on palaeoclimatic and palaeobiogeographical data palaeomagnetic data for the silurian and the devonian of the south european regions supposedly constituting the armorica microplate remain rare and ambiguous those from gondwana are more numerous but contradictory enough to give rise to diverging models regarding the latitudinal evolution of this continent consequently the reality of an armorica microplate cannot be considered as established on the contrary lithological indicators of palaeoclimate and palaeobiogeographical data are in total harmony and indicate that in actual fact the southern european regions remained permanently closely connected with gondwana of which they composed the northern margin although repeatedly maintained for more than 20 years the concept of an armorica microplate can thus be considered a fiction this conclusion should lead to the dismissal of geodynamical models proposed for the variscan belt to which this concept was integrated and are contradicted by inescapable palaeobiogeographical constraints

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

microparticle content records of the dunde ice core and dust storms in northwestern china abstract dust storms are important atmospheric phenomenon in central asia particularly in the regions bordering deserts arid and semi arid regions dust storms occur quite often in northwestern china there are some research results about past dust storm events using historical archives in china however the archives used cover limited time and area microparticle concentrations in the dunde ice cap qilian mountain of northwestern china represent a continuous record of past dust storms comparison between dust rain frequency reconstructed from historical archives and the ice core record from the dunde ice cap demonstrate that the microparticle record in the dunde ice core is a good indicator of dust storms in northwest china according to the ice core records we can reconstruct the dust storm chronology for historical time during the past 700 years the dust content fluctuated with time and lower frequency variations existed although the linear trend increased over the past 700 years dust content was decreasing since the early 1700s during the little ice age it was slightly higher corresponding to the cold period

tephrabase tephrochronology and the development of a centralised european database tephrabase was launched on the world wide web in 1995 as a tool for tephrochro nological research in order to facilitate the identification correlation and dating of tephra deposits this database may be interrogated through multiple routes including by source volcano date location and tephra chemistry datasets include stratigraphy geochemistry chronology and spatial information currently all the european data refer to late quaternary icelandic sourced tephras post 12 k yr bp the sites 62 where the tephra deposits are found include iceland the united kingdom ireland the faroe islands sweden and russia in addition there are also data on tephra layers in central mexico use of tephrabase highlights the importance of selected geochemical data but this has to be used with care as major element characteristics alone do not always produce unique definitions for single tephra deposits for the most accurate results multiple criteria must be used tephrabase can be found at http www tephrabase org copyright 2007 john wiley sons ltd

micrometre sized volcanic glasses in polar ices and snows explosive volcanic eruptions can follow long cycles of activity1 and the material that they inject into the atmosphere may affect the climate2 we report here the discovery of ultrathin micrometre sized glass shards from such eruptions extracted from both ancient antarctic ices and recent snow samples from greenland in which they have been well preserved by deep freezing when such shards have been preselected using a high voltage electron microscope microanalysis of their eight major constituent elements gives new clues about the origin of major volcanic acid fallout previously detected in the cores including important characteristics of their parent eruptions and reveals complex volcanic ash layers that could reflect periods of world wide enhanced volcanicity moreover the very small reynolds numbers of the micrometre sized shards make them promising tracers of dust transport processes in the ancient atmosphere

paleomagnetism of upper devonian reefal limestones canning basin western australia two conflicting models have been proposed for the middle paleozoic position of gondwana with respect to euramerica a pole from morocco msissi norite that may be of late devonian age suggests that a broad ocean 3 000 km separated the northern continents from gondwana whereas results from mauritania gneiguira supergroup indicate that this ocean had closed by devonian time detailed thermal and alternating field demagnetization experiments have been carried out on red and gray limestones from seven sites 89 samples in an essentially undeformed late devonian reef complex northern canning basin western australia after minor tilt correction the site mean characteristic directions average 42 7 28 9 declination inclination with k 61 6 and 95 7 8 these results position northwestern australia at 15 s latitude in the late devonian a paleolatitude consistent with the presence of a well developed reefal sequence an early age is inferred for these magnetizations on the basis of the occurrence of mixed polarities and the fact that no post devonian directions for australia resemble the observed declinations and inclinations if the smith and hallam reconstruction for gondwana is used the paleomagnetic pole calculated for the late devonian of western australia agrees with the msissi norite result from morocco and suggests that an ocean still separated gondwana from euramerica in the late devonian the pole measured from the gneiguira supergroup in mauritania may be based on remagnetizations of late paleozoic age the directions determined from canning basin limestones are similar in inclination to but differ by 40 in declination from paleomagnetic results from the upper devonian comerong volcanics lachlan fold belt southeastern australia canning basin samples are from the stable craton and comerong volcanics samples are from the tasman fold belt the discrepancy between the two australian results may be best explained by tectonic rotation of the comerong volcanics locality

greenland gisp2 ice core and historical indicators of complex north atlantic climate changes during the fourteenth century the paper uses greenland gisp2 ice core data together with historical documentary information to investigate the nature of climate changes that took place between ad 1270 and 1450 across the north atlantic region detailed deuterium and deuterium excess time series resolved to c 8 10 samples per year are used to reconstruct relative changes in greenland air temperature and past changes in sea surface tem perature across the western north atlantic the data show that sea surface temperatures during the late thirteenth century and the majority of the fourteenth century were characterized by relatively high amplitude warming and cooling events these changes preceded a marked reduction in the amplitude of the sea surface temperature changes c 30 40 years before the well known change in northern hemisphere tropospheric circulation characterized by a marked increase in regional storminess that started between c ad 1400 and 1420 the time interval between ad 1270 and 1450 also appears over greenland to have fea tured several short lived phases of marked air temperature lowering that were rarely ever equalled during succeeding centuries we believe that the climate changes described here are of considerable importance in understanding climate dynamics of the north atlantic region since they took place at a time when the north atlantic oscillation nao may have been weak the results also show that the marked change in atmospheric circulation coincident with a significant increase in north atlantic storminess at c ad 1400 1420 possibly the biggest such change in the holocene took place after the strong perturbations in north atlantic sea surface temperature both warming and cooling described here as well as after several episodes of air temperature lowering over greenland

scheck breccias from devonian reef complexes of canning basin western australia abstract late frasnian and early famennian marginal slope deposits of the canning basin reef complexes include distinctive red open framework breccias characterized by red micritic clasts cemented by white calcite spar they closely resemble the adneter scheck breccias in the jurassic adnet limestone of the austrian alps scheck breccias from the canning basin are largely confined to red stromatolitic and terrigenous marginal slope sediments having depositional slopes of 10 14 which were deposited in water depths of some tens to hundreds of meters individual breccias beds are strongly lensoid with concave locally scoured bases they are between 10 and 100 cm 4 and 39 in thick and are composed predominantly of irregular red micritic clasts reworked from associated nodular limestones breccias are clast supported and may be inverse to normally graded normally graded or massive the proposed depositional mechanism began with slumping of muddy sediment containing abundant early cemented nodules this initiated bimodal density modified grain flows nodules were supported by dispersive forces and deposited by frictional freezing as the depositional slope decreased producing clast supported graded sequences the finer sand and mud fractions continued downslope as turbidity currents leaving behind minor perched mud trapped in the open framework breccias early cementation by radiaxial calcite prevented further sediment infilling these devonian scheck breccias are characteristic components of condensed sequences as shown by conodont dating they represent infrequent events only about one bed of breccia was deposited for every 10 m 33 ft of section in about 300 000 years over a vertical section of about 200 m 660 ft end of article last page 495

climate response to large high latitude and low latitude volcanic eruptions in the community climate system model 1 explosive volcanism is known to be a leading natural cause of climate change the second half of the 13th century was likely the most volcanically perturbed half century of the last 2000 years although none of the major 13th century eruptions have been clearly attributed to specific volcanoes this period was in general a time of transition from the relatively warm medieval period to the colder little ice age but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism this context motivates our investigation of the climate system sensitivity to high and low latitude volcanism using the fully coupled ncar community climate system model ccsm3 we evaluate two sets of ensemble simulations each containing four volcanic pulses with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid high latitudes of both the northern and southern hemispheres the short term direct radiative impacts of tropical and high latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea ice concentration in northern hemisphere nh winter a main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern eurasia furthermore both ensembles show significant reductions in global precipitation especially in the summer monsoon regions the most important long term impact is the cooling of the high latitude nh produced by multiple tropical eruptions suggesting that positive feedbacks associated with ice and snow cover could lead to long term climate cooling in the arctic

magnetostratigraphy late devonian iridium anomaly and impact hypotheses paleomagnetism sedimentology and fine scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the late devonian of western australia thermal demagnetization experiments were carried out on 93 specimens of marginal slope limestone form the northern canning basin samples are from a condensed sequence of deep water 100 m frutexites microstromatolites frutexites is a shrublike cyanobacterial organism that probably precipitated hematite or a metastable precursor from sea water when plotted within the microstratigraphic framework for the study area the observed characteristic directions from the sampled interval 14 5 cm thick are in five discrete layer parallel normal and reversed polarity zones the measured northeast southwest declinations and shallow inclinations probably record late devonian magnetostratigraphy on a centimetre scale the frutexites bed studied there occurs close to the frasnian famennian late devonian boundary a time of mass extinction of a wide variety of marine organisms throughout the world anomalously high iridium concentrations observed in the frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact this study concludes that iridium which is present over the span of five layer parallel magnetic reversals was concentrated over a long period of time by biologic processes thus the canning basin iridium anomalymore may be unrelated to meteorite impact less

paleomagnetism of the upper devonian reef complexes canning basin western australia paleomagnetism of the upper devonian reef complexes in the canning basin western australia was reinvestigated with a primary aim of testing its magnetization age samples were collected from back reef and reefal limestones basinal red beds syndepositional allochthonous blocks and sediment infillings in syndepositional cracks and voids a characteristic remanence similar to that identified in a previous study was found in six autochthonous sites in outcrop and four diamond drill cores with a mean direction of declination d 27 5 inclination i 19 9 half angle of 95 confidence cone 95 15 2 the primary origin of this remanence was demonstrated by both a syndepositional breccia test and an allochthonous block test the corresponding late devonian pole position 62 0 s 23 2 e with half angle of 95 confidence cone a95 14 6 overlaps with the previously reported paleopole from this reef complex and other late devonian paleopoles from australia the evidence indicates that the spread of late middle to early carboniferous paleopoles from australia is caused by a phase of rapid apparent polar wander rather than the tectonic discordance of southeastern australia in relation to the craton

tephrochronology of the siple dome ice core west antarctica correlations and sources abstract a total of 24 tephra bearing volcanic layers have been recognized between 550 and 987 m depth in the siple dome a sdm a ice core in addition to a number already recognized tephra in the upper 550 m dunbar et al 2003 kurbatov et al 2006 the uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time stratigraphic markers in the ice core despite the very fine grain size of these tephra mostly less than 20 microns robust geochemical compositions were determined by electron microprobe analysis the source volcanoes for these tephra layers are largely found within the antarctic plate statistical geochemical correlations tie nine of the tephra layers to known eruptions from mt berlin a west antarctic volcano that has been very active for the past 100 000 years previous correlations were made to an eruption of mt takahe another west antarctic volcano and one to mt hudson located in south america kurbatov et al 2006 the lowest tephra layer in the ice core located at 986 21 m depth is correlated to a source eruption with an age of 118 1 1 3 ka suggesting a chronological pinning point for the lower ice an episode of anomalously high volcanic activity in the ice in the sdm a core between 18 and 35 ka gow and meese 2007 appears to be related to eruptive activity of mt berlin volcano at least some of the tephra layers found in the sdm a core appear to be the result of very explosive eruptions that spread ash across large parts of west antarctica off the west antarctic coast as well as also being recognized in east antarctica basile et al 2001 narcisi et al 2005 narcisi et al 2006 some of these layers would be expected to should be found in other deep antarctic ice cores particularly ones drilled in west antarctica providing correlative markers between different cores the analysis of the tephra layers in the siple dome core along with other antarctic cores provides a timing framework for the relatively proximal antarctic and south american volcanic eruptive events allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

evidence from sulfate mass independent oxygen isotopic compositions of dramatic changes in atmospheric oxidation following massive volcanic eruptions 1 oxygen isotopic ratio measurements 17o and 18o of background and volcanic sulfate preserved in south pole snow and ice were used to investigate the impact on the oxidation state of the atmosphere by explosive volcanic eruptions by comparing different paleovolcanic events we observe a difference in the so2 oxidation pathway between moderate tens of teragrams tg of so2 and massive hundreds of tg eruptions both isotopic data and numerical simulations suggest the shutdown of stratospheric oh chemistry and the opening of unaccounted oxidation channels for so2 such as the reaction with o 3p atoms when hundreds of tg of so2 are injected into the stratosphere it is very likely that oxidation rates and pathways and concentrations of most traces gases are also dramatically affected with potentially important implications for climate forcing

accumulation rates in dronning maud land antarctica as revealed by dielectric profiling measurements of shallow firn cores the european programme for ice coring in antarctica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land antarctica the german glaciological programme during the 1997 98 field season was carried out along a 1200 km traverse on amundsenisen and involved sampling the snow cover in pits and by shallow firn cores this paper focuses on the accumulation studies the cores were dated by dielectric profiling and continuous flow analysis distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time scale the eruptions of krakatoa tambora an unknown volcano kuwae and el chichon are well documented in the ice variations of the accumulation rates over different times were inferred from the depth time scales a composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records according to this accumulation rates decreased in the 19th century and increased in the 20th century the recent values are by no means extraordinary as they do not exceed the values at the beginning of the 19th century variations in accumulation rates are most probably linked to temperature variations indicated in 18o records from amundsenisen

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

syn deformational remanent magnetization of the mount eclipse sandstone central australia summary the palaeomagnetism of the latest devonian early carboniferous mount eclipse sandstone in central australia reveals samples from 16 out of 31 sites having a consistent hightemperature component of natural remanent magnetization site mean directions from the two limbs of the most detailed studied syncline attain their best grouping after 75 per cent of unfolding and further unfolding causes a cross over feature mineralogical studies using microscope and electron microprobe show that this remanance is most likely to be carried by secondary haematite formed by alteration of fe rich minerals during the midcarboniferous deformation four different models are examined to reconstruct the palaeohorizontal for the syn deformational remanence the best estimate of the palaeomagnetic south pole position is lat 33 8 s and long 121 2 e dp 19 2 drn 19 7 close to australia this result indicates a rapid polanvard movement of eastern gondwanaland during the first half of the carboniferous we also suggest that the widespread alice springs orogeny related overprints in central australia were acquired during the beginning of the main phase of deformation in the mid carboniferous

linearity spectrum analysis of multi component magnetizations and its application to some igneous rocks from south eastern australia summary a method that enables the objective resolution of almost parallel multi component magnetizations is described and demonstrated a feature distinguishing this method from others is its simultaneous analysis of demagnetization data from a group of specimens rather than the analysis of data from one specimen at a time the only prerequisite is that the specimens are derived from a homogeneous source thus for a formation carrying a simple single component magnetization all specimens from the formation may be simultaneously reduced for a more complicated two component magnetization it is shown that only specimens from a particular site can be considered homogeneous and for a complex three component system each sample often requires undivided attention thus the workload is proportionally increased to achieve analyses of comparable reliability from data of variable quality new pole positions from mesozoic intrusions of the sydney basin nsw are from the marsden park breccia pipe 48 s 127 e a95 6 the st marys breccia pipe 46 s 150 e a95 8 the prospect dolerite 60 s 142 e a95 13 and 53 s 180 e a95 6 and from the dundas breccia pipe 58 s 162 e a95 36 and 31 s 195 e a95 16 the last two formations possess multi component magnetizations these pole positions are consistent with previous results from south eastern australia

paleomagnetic results indicate pre permian counter clockwise rotation of the southern tamworth belt southern new england orogen australia 1 visean ignimbrites from three fault bounded blocks within the southern tamworth belt southern new england orogen australia retain a prefolding high temperature component of remanence carried mainly by magnetite paleomagnetic data indicate that the southern tamworth belt occupied low to moderate paleolatitudes during the early carboniferous normal and reversed polarities with low to moderate inclinations suggest that the steep reverse polarity latest carboniferous to earliest permian overprint is absent from the high temperature component data set the mean characteristic remanence direction of three early to middle visean ignimbrite flows 32 sites from the rouchel block is declination dec 154 2 and inclination inc 38 8 95 12 5 k 98 8 which corresponds to a paleo south pole at latitude 64 9 s longitude 258 1 e dp 5 5 dm 9 2 where dp is the angular length of the semiaxis of the ellipse of confidence of the calculated paleopole that lies along the pole to site great circle and dm is the angular length of the semiaxis perpendicular to dp six middle to late visean ignimbrite flows 29 sites from the gresford block retain a mean remanence of dec 159 6 and inc 54 1 95 13 7 k 24 7 corresponding to a paleo south pole at latitude 72 8 s longitude 228 4 e dp 13 4 dm 19 2 despite widespread overprinting throughout much of the myall block reliable information was obtained from three late visean ignimbrite flows five sites with a mean direction of dec 118 1 and inc 42 5 95 12 0 k 41 6 from which a paleo south pole of latitude 35 7 s longitude 233 4 e dp 9 1 dm 14 7 is calculated the calculated paleo south poles do not fall on the early carboniferous segment of the published apparent polar wander path for australia and suggest that the southern tamworth belt has undergone significant counter clockwise rotation relative to cratonic australia inferred rotations for the rouchel gresford and myall blocks are approximately 80 80 and 120 respectively stratigraphic and geological evidence suggest rotation took place between the mid namurian and latest carboniferous and is thought to have resulted from sinistral strike slip during compression at the eastern margin of australia

volcanism and the greenland ice cores the tephra record abstract in recent years increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the greenland ice cores this renewal has occurred in tandem with the development of continuous flow analysis techniques which provide high resolution volcanic aerosol records these chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high precision ice core timescale thus allowing ages to be assigned to volcanic events tephra horizons of glass shards in the ice cores play a critical role for 1 testing and building chronological frameworks for the ice cores and other sequences 2 synchronising disparate palaeoclimatic sequences and testing phase relationships 3 atmospheric pathway reconstruction and 4 verifying the source of volcanic aerosol peaks here we review the results of over 25 years of research into tephra horizons in the grip gisp2 and ngrip cores we provide high precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the greenland ice sheet and identified in the cores there is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far however this synthesis highlights the critical role of the greenland ice cores firstly in the reconstruction of the history of icelandic volcanic eruptions and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to north atlantic marine sequences other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as north america to resolve the debate surrounding the thera eruption and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

on the age vs depth and optical clarity of deep ice at south pole the first four strings of phototubes for the amanda high energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the south pole during the 1995 96 season an addit

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

do volcanic eruptions enhance or diminish net primary production evidence from tree rings 1 low growth rates of atmospheric co2 were observed following the 1991 pinatubo luzon volcanic eruption one hypothesis for this co2 anomaly is that since diffuse light is more efficiently used by forests than direct light the increase in the diffuse fraction of sunlight due to scattering by volcanic sulfur aerosol in the years following the eruption substantially increased forest net primary production npp however other observations suggest a decrease in northern forest npp because of the cooler conditions following the eruption here we used a global database of dated tree ring widths which correlate with forest npp to test this hypothesis ice core records of sulfur deposition allowed us to identify the timing and magnitude of 23 pinatubo scale eruptions since 1000 ce we found a significant decrease in ring width for trees in middle to high northern latitudes north of 45 n following eruption sulfur peaks decreases in tree ring widths were in the range of 2 8 and persisted for 8 years following sulfur peaks with minima at around 4 6 years ring width changes at lower latitudes in the northern hemisphere 30 n to 45 n and in the southern hemisphere 30 s to 56 s were not significant in the tropics 30 n to 30 s the paucity of tree ring records did not permit the evaluation of npp changes given that elevated aerosol levels and summer cooling last only 2 3 years after an eruption the persistence of declines in northern tree growth for up to 8 years after eruptions implies some additional mechanism that links these shorter lived global eruption effects to sustained changes in tree physiology biogeochemistry or microclimate at least for this sample of trees the beneficial effect of aerosol light scattering appears to be entirely offset by the deleterious effect of eruption induced climate change

sulfate source inventories from a svalbard ice core record spanning the industrial revolution 1 the 800 year sulfate record from lomonosovfonna was analyzed by a novel multiple linear regression algorithm that attempts to explain sulfate variability in terms of other chemical species measured in the core and sulfur emission inventories we use three statistical approaches to determine sulfate sources we examine trends using singular spectrum analysis with confidence intervals finding clear evidence that anthropogenic sources are important but not dominant we use cross wavelet coherence to examine significant multidecadal covariance in terrestrial sulfate but our main tool is multiple regression analysis of the sulfate dependency on other ions and anthropogenic emission inventories models are fitted in a moving time window of typically 50 years length explaining 80 of the sulfate variance a suite of model predictors are examined and the variation in relative magnitudes of the model coefficients along the core can be used to infer variations in the strength of various sulfate sources we observe large changes in sulfate sources at the end of the little ice age associated with changes in barents sea marine productivity changes in north atlantic sulfate input and a long lasting period of disturbance caused by the large laki volcanic eruption modeling sulfur emission inventories shows that western europe contributes about 15 of the sulfate budget with essentially no input from other regions in contrast with predictions from global circulation models incorporating sulfur chemistry multidecadal cycles are mainly confined to the little ice age and most likely associated with increased storminess and enhanced deposition of both marine aerosol and biogenic sulfate from the atlantic ocean the model residuals do not show a normal distribution but display very large spikes unexpectedly those significant at the 99 level can be closely matched to major volcanic eruptions using independent dating methods the 20th century sulfate in the core is inventoried as sea salt 15 terrestrial 10 volcanic 5 10 western european anthropogenic 10 25 barents sea biogenic 20 40 and atlantic biogenic 10 15

holocene eruptive activity of el chichon volcano chiapas mexico geologic and radiometric age data indicate that el chichon was frequently and violently active during the holocene including eruptive episodes about 600 1250 and 1700 years ago and several undated older eruptions these episodes involving explosive eruptions of sulfur rich magma and associated dome growth processes were apparently separated by intervals of approximately 350 to 650 years some of el chichon s eruptions may correlate with unusual atmospheric phenomena around a d 1300 and possibly a d 623

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

palaeomagnetism of the brewer conglomerate in central australia and fast movement of gondwanaland during the late devonian summary palaeomagnetic analysis of 11 diamond drill cores from the late devonian brewer conglomerate in the northeastern part of the amadeus basin central australia yields three magnetic components a drilling induced remanence c1 acquired during the industrial drilling process a mid to late carboniferous syndeformational overprint c2 acquired during the alice springs orogeny and a primary remanence c3 c3 passes a fold test and gives a latest devonian pole bc at 47 1ds 041 0de with a95 6 4d the revised apwp for gondwanaland requires west gondwanaland to drift across the south pole during the late devonian with a speed of 20cm yr 1 while east gondwanaland remained at low latitude positions it is suggested that fast plate movement occurred far more often during the palaeozoic than has previously been thought

dating the siple dome antarctica ice core by manual and computer interpretation of annual layering the holocene portion of the siple dome antarctica ice core was dated by interpreting the electrical visual and chemical properties of the core the data were interpreted manuallyandwith acomputeralgorithm the algorithm interpretation was adjusted to be consistent with atmospheric methane stratigraphic ties to the gisp2 greenland ice sheet project 2 ice core 10 be stratigraphic ties to the dendrochronology 14 c recordandthedatedvolcanic stratigraphy thealgorithm interpretation ismorecon sistent andbetter quantifiedthanthe tedious and subjective manual interpretation

palaeomagnetism of red beds of the late devonian worange point formation se australia summary gently folded strata of the late devonian merrimbula group along the south coast of new south wales are similar to numerous deposits of late devonian to early carboniferous subaerial to shallow marine quartzose sandstone that are known as the lambie facies of se australia because the lambie sands overlap the early palaeozoic tectonic elements of the lachlan fold belt large displacement since the late devonian of any lachlan terranes with respect to interior australia is precluded we collected oriented core samples from 37 sites primarily in reddish quartzose litharenites of the worange point formation the remanent magnetization is carried by haematite incremental thermal demagnetization reveals a dominant well defined steep upward north component of magnetization that post dates the mid carboniferous folding the south pole position 146 4 e 68 6 s ag5 3 1 derived from the overprinted specimens is close to both the late carboniferous and mid cretaceous reference poles as well as the spin axis of today the overprint is attributed to both viscous partial thermoremanent and chemical remanent magnetization vptrm and crm its exclusively normal polarity is consistent with a mid cretaceous acquisition perhaps related to the rifting of the se australian margin a characteristic component of magnetization is isolated between 660 and 680 c in 30 per cent of the samples although a regional fold test of the overall result is inconclusive because the directions of characteristic magnetization are generally close to the axes of folding two sets of samples from opposite limbs of a local syncline pass a fold test at 90 per cent confidence indicating a pre folding origin of the remanence the presence of both polarities in thin horizons some of which are palaeosols and diagenetic haematite associated with incipient cleavage formed in an early stage of deformation before folding indicates that the acquisition of remanent magnetization occurred over a protracted period an analysis that combines great circle demagnetization paths and set points facilitates the incorporation of more data but gives a biassed result although normal and reverse polarity subsets are roughly antipodal residual post folding components cause the normal subset to fail a fold test a south pole position 19 7 e7 70 8 s ag5 7 1 is derived from the specimens with characteristic component of reverse polarity in which the isolation of a characteristic component is clear the pole position is close to that of a previous palaeomagnetic study from a widely separated occurrence of lambie facies sediments both results are applicable not only to the lachlan fold belt but also to the rest of australia and gondwana as a whole the position of the two poles derived from the lambie facies overlap assemblage in the lachlan fold belt supports the interpretation that the progression

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

pre and post folding magnetizations from the early devonian snowy river volcanics and buchan caves limestone victoria summary multicomponent magnetizations of the snowy river volcanics have been resolved into pre folding dec 340 1 inc 59 2 and post folding dec 10 5 inc 72 3 elements the former is attributed to initial cooling of the volcanics while the latter is probably related to the waning stages of the deformational episode which was presumably accompanied by cooling we argue that the pole position from the pre folding magnetizations lat 74 3 s long 222 7 e represents the australian palaeopole for the early devonian a reassessment of other australian pole positions determined from rocks of about this age suggests that remagnetization during the carboniferous may be common interpretation of the pole path prior to the devonian is equivocal and awaits further study the post folding magnetizations from the volcanics are similar in stability and direction to those from the buchan caves limestone dec 27 8 inc 75 6 which appears to be completely remagnetized the age of this remagnetizing event appears to be mid carboniferous if our interpretation of the pole path for this time is correct it is noted that a much unappreciated attribute of the fold test lies with identifying not just the relative age of magnetization but also the palaeohorizontal only when the palaeohorizontal is established can the calculation of a palaeopole be justified

volcanic ash layers from the last glacial termination in the ngrip ice core the tephrochronological record of the 1400 1640 m depth 10 000 16 000 calendar ice core years before present of the ngrip ice core has been established by particle screening of selected samples ash was identified in 20 samples correlation with ice marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the saksunarvatn ash and the vedde ash ash zone 1 major element chemistry of the remaining identified ash layers mainly points towards an icelandic origin this tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the last glacial termination within the north atlantic region as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation copyright 2005 john wiley sons ltd

composition and sources of atmospheric dusts in snow at 3200 meters in the st elias range southeastern alaska usa abstract dusts in snow from the accumulation zone in the st elias range appear from their chemical compositions to have come from terranes of rocks of ferromagnesian composition these dusts with respect to their composition and to the moderate degree of variation that occurs through a depositional year are similar those deposited in greenland the high portion of the st elias range is isolated from dominance by any local dust source terranes because of altitude and the extent of the surrounding glacierized and snow covered region in greenland the altitude is typically lower but local sources are even less likely to dominate the character of the dusts deposited into the ice record there the similar compositions and moderate compositional variations of dusts from these two places bear on the question of whether the dusts that are transported over long distances by the atmosphere under modern and glacial period conditions are uniform and representative of a broad regional or even hemispheric background dust the dusts in the snow were measured by means of a suite of major minor and trace rock forming metals chosen to give information about rock types their constituent minerals degree of degradation weathering and energies of atmospheric uptake from source the variations in amounts of rock dust through the year in the st elias range snowpack have no time stratigraphic correspondence to the also large variations in concentrations of other species that are not constituents of rock derived dusts such the anions chloride sulfate and nitrate the highs and lows of the two types of materials are apparently completely independent the structure revealed by the moderately fine scale sampling of the present study 10 increments y serves as a background for the interpretation of analysis of ice core samples in which annual layers may be too compressed to permit analysis of sub annual samples

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

impact of known local and tropical volcanic eruptions of the past millennium on the wais divide microparticle record 1 we present a new method for inferring the relative location low versus high southern latitude and therefore the potential climatic impact of past eruptions based on the particle size distribution psd of micrometer sized ash measured continuously in the west antarctic ice sheet wais divide ice core we find that particles from a high southern latitude eruption buckle island antarctica 1839 common era c e have a psd with mode diameter 5 m coarser than the background dust mode 5 1 m while ash particles originating from stratospheric tropical eruptions including tambora 1815 c e kuwae 1458 c e and unknown 1258 c e have psds with mode diameters 0 6 1 5 m finer than the background in addition volcanic ash particles from global scale eruptions are deposited 3 6 months earlier and over a shorter time interval than sulfate aerosols we hypothesize that this phasing is driven by differences in atmospheric processing and aerosol particle transport and deposition

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

glacio chemical study spanning the past 2 kyr on three ice cores from dronning maud land antarctica 2 seasonally resolved chemical records the ammonium calcium and sodium concentrations from three intermediate depth ice cores drilled in the area of dronning maud land east antarctica have been investigated since all measurements were performed by a high resolution continuous flow analysis system for the first time seasonal signals of chemical trace species could be obtained from the interior of central antarctica over a period of approximately 2 millennia although the elevation as well as the accumulation rate differ between the drilling sites similar values were obtained by comparing mean concentrations spanning the last 900 years however a distinct lack of intersite correlation was found on decadal timescales despite a noticeable accumulation change apparent in one core no significant concentration change of all three species has occurred all the measured ions show clear seasonal signals over the whole records while the sea salt related component sodium peaks simultaneously with calcium the maximum ammonium concentration occurs in the snow with a time lag of 2 months after the sea salt peak more than 60 of the calcium concentration can be attributed to an ocean source elevated sodium concentrations were found within this millennium compared to mean values of the whole records but the spatially varying shape of the increase suggests that a possible climatic signal is biased by local deposition effects

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

paleomagnetism of the hervey group central new south wales and its tectonic implications paleomagnetic work on the hervey group in southeast australia reveals a predeformational magnetization as suggested by the retention of a predeformational compaction produced magnetic fabric and the effect of deformation on both the magnetic fabric and the direction of the magnetic remanence in cleaved rocks the formation mean direction d 29 2 i 19 3 with 95 15 5 gives a latest devonian early carboniferous palaeomagnetic pole at 54 4 s 24 1 e with dp 8 4 dm 16 2 comparing this pole with existing poles from australia and north america it is suggested that 1 the lachlan fold belt of southeast australia has been part of cratonic australia since at least the late devonian and consequently the late palaeozoic palaeomagnetic data from the lfb may be applied to the whole of gondwanaland 2 cratonic australia and the new england fold belt were all in an equatorial position during the early carboniferous 3 there was probably a rapid anticlockwise rotation of gondwanaland during the late devonian around an axis close to australia 4 a v shaped ocean existed between laurussia and the northern margin of western gondwanaland during the late devonian early carboniferous the appalachian hercynian orogenic belt is probably the result of the closure of this ocean

prefolding and premegakinking magnetizations from the devonian comerong volcanics new south wales australia and their bearing on the gondwana pole path palaeomagnetic results from the late middle to early late devonian comerong volcanics in the budawang synclinorium lachlan fold belt lfb new south wales australia satisfy a fold test and support the hypothesis that foliated parts of the lfb have been folded by megakinks during the terminal mid carboniferous orogenic phase the preferred pole position is at 76 9 s 330 7 e a95 7 2 allowing calibration of the australian pole path at around 370 ma ago an alterative pole position at 71 3 s 283 1 e same a95 takes into account a possible rotation of the megakinked terrane by 15 clockwise with respect to the australian craton although there are still problems unravelling previously published results from silurian rocks in the lfb both because of unreliability and uncertainty as to where the lfb crustal units lay in relation to the australian craton there is no geological reason to suspect any large relative movement between the lfb and the craton since the middle devonian and thus the comerong volcanics pole position is representative of the late devonian for australia the new pole requires reassessment of many other poles that have previously been accepted as representing the siluro devonian for australia and gondwanaland we present reasons for believing that the magnetization or remagnetization of many rock units e g mereenie sandstone and mulga downs group australia and the gneigura supergroup africa was later than sedimentation probably during widespread early carboniferous deformation another rock unit msissi norite africa could be of early carboniferous rather than late devonian age

statistical extraction of volcanic sulphate from nonpolar ice cores 1 ice cores from outside the greenland and antarctic ice sheets are difficult to date because of seasonal melting and multiple sources terrestrial marine biogenic and anthropogenic of sulfates deposited onto the ice here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space we verify the method with a well dated section of the belukha ice core from central eurasia there are excellent matches to volcanoes in the preindustrial and clear extraction of volcanic peaks in the post 1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition we then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from svalbard and a core from mount everest volcanic sulfate is 5 of the sulfate budget in every core and differences in eruption signals extracted reflect the large differences in environment between western northern and central regions of svalbard the lomonosovfonna and vestfonna cores span about the last 1000 years with good extraction of volcanic signals while holtedahlfonna which extends to about ad1700 appears to lack a clear record the mount everest core allows clean volcanic signal extraction and the core extends back to about ad700 slightly older than a previous flow model has suggested the method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

an inter hemispheric volcanic time marker in ice cores from greenland and antarctica a strong volcanic acid signal is clearly registered using an acidity measuring technique in the a d 1259 ice layer in four different greenland ice cores camp century milcent crete and dye 3 this signal is similar in amplitude to the laki iceland a d 1783 volcanic event as recorded in the central and south greenland ice cores measurement of ice layers from corresponding age levels in antarctic ice cores byrd station south pole and j 9 on the ross ice shelf provides similar strong acid signals there is no historical record of a significant volcanic eruption for the period around a d 1260 in the northern hemisphere subsequent chemical analyses of all a d 1259 ice layers show similar compositions we suggest that the a d 1259 signals registered in both greenland and antarctica were caused by the same volcanic disturbance and that its epicenter was located at the earth s equatorial zone which enabled global distribution of the acid gases these results indicate that inter hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

australian palaeozoic palaeomagnetism and tectonics ii a revised apparent polar wander path and palaeogeography abstract new palaeomagnetic data from mid to late palaeozoic rocks in australia have enabled us to revise the palaeozoic apparent polar wander path apwp this modified australian apwp is supported by data from other parts of gondwanaland the palaeomagnetic poles indicate that during the early and mid palaeozoic australia underwent rapid rotation first clockwise during the mid ordovician to the early silurian then counterclockwise from the mid silurian until the end of the devonian while it remained at low to equatorial latitudes this was succeeded by a rapid southward movement during mid carboniferous times the implications of the palaeomagnetic data for the tectonic relationship between the lachlan fold belt lfb and cratonic australia are consistent with the tectonic evidence that the lfb has been in place since the mid devonian

dynamics of the major plinian eruption of samalas in 1257 a d lombok indonesia the 1257 a d caldera forming eruption of samalas lombok indonesia was recently associated with the largest sulphate spike of the last 2 ky recorded in polar ice cores it is suspected to have impacted climate both locally and at a global scale extensive fieldwork coupled with sedimentological geochemical and physical analyses of eruptive products enabled us to provide new constraints on the stratigraphy and eruptive dynamics this four phase continuous eruption produced a total of 33 40 km3 dense rock equivalent dre of deposits consisting of i 7 9 km3 dre of pumiceous plinian fall products ii 16 km3 dre of pyroclastic density current deposits pdc and iii 8 9 km3 dre of co pdc ash that settled over the surrounding islands and was identified as far as 660 km from the source on the flanks of merapi volcano central java widespread accretionary lapilli rich deposits provide evidence of the occurrence of a violent phreatomagmatic phase during the eruption with a peak mass eruption rate of 4 6 108 kg s a maximum plume height of 43 km and a dispersal index of 110 500 km2 the 1257 a d eruption stands as the most powerful eruption of the last millennium eruption dynamics are consistent with an efficient dispersal of sulphur rich aerosols across the globe remarkable reproducibility of trace element analysis on a few milligrammes of pumiceous tephra provides unequivocal evidence for the geochemical correlation of 1257 a d proximal reference products with distal tephra identified on surrounding islands hence we identify and characterise a new prominent inter regional chronostratigraphic tephra marker

late quaternary icelandic tephras in ireland and great britain detection characterization and usefulness microscopic studies of late quaternary tephras from iceland yield a detailed tephrochronology in deposits of the british isles where the quantities of volcanic glass employed are much less than those used to construct almost any other late quatemary tephrochronology we summarize improved methods of isolating extremely sparse glass shards for light microscope and electron microprobe analysis and provide major element geochemistry for 20 volcanic glass layers detected in ireland including those which comprise an outline historic tephrochronology for ireland the paper highlights possible limitations of chronology construction when attempting to separate dated tephras whose major element geochemistries are almost identical tephras in other parts of the british isles and europe are used with those in ireland to demonstrate further applications of tephrochronology especially for dating deposits where other dating methods e g radiocarbon have proved difficult

reassessment of crete greenland ice core acidity volcanism link to climate change previous comparisons of the crete greenland ice core acidity record with climate variations of the last 1 400 years suggested that changes in volcanism may have significantly influenced climate on this time scale however the ice core acidity record consists of volcanically induced spikes superimposed on a background acidity of nonvolcanic origin that varied significantly in amplitude herein the authors produce a record of crete volcanism based solely on an objective definition of individual volcanic events in the ice core record there are 92 acidity peaks in the 1 420 year record since at least 26 of the post 1 600 eruptions are of local icelandic origin they estimate a mean recurrence interval of 20 8 years for hemispheric scale eruptions rich in sulphate on decadal time scales volcanism has varied by a factor of three four over the last 1 400 years however the climate volcanism correlation is considerably less impressive r minus 0 23 than previously concluded r minus 0 52 the good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant little ice age increase the background increase may reflect changes in ocean productivity 24 refs 5 figs 1 tab

the effects of wind on δ 18o and accumulation give an inferred record of seasonal δ amplitude from the agassiz ice cap ellesmere island canada