the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

multidecadal oceanographic changes in the western pacific detected through high resolution bomb derived radiocarbon measurements on corals high resolution measurements of radiocarbon 14c in corals can be used to reconstruct past variability in ocean conditions here we report seasonal 14c changes in coral from ishigaki island japan and compare with previously reported data from palau and guam our data clearly indicate a significant increase in 14c from 1947 to 1998 related to atmospheric nuclear bomb testing the three early 14c spikes related to the atmospheric nuclear bomb tests in the us proving grounds at bikini and enewerak atoll conducted in 1954 1956 and 1958 were detected from the ishigaki coral after 1976 variability in the mindanao dome region related to north equatorial current nec bifurcation latitude migration affected the 14c difference between palau and guam whereas the difference between ishigaki and guam was not correlated with the bifurcation latitude the 14c difference between ishigaki and guam may be due to mesoscale eddies in the kuroshio area on the decadal scale the northward shift of nec bifurcation latitude after 1976 the year as known as pacific decadal oscillation regime shift from negative to positive was concurrent with the abundant westward propagating mesoscale eddies in the subtropical countercurrent region and stronger kuroshio transport off the east taiwan which may be represented by a smaller 14c difference between ishigaki and guam after 1976

dynamical excitation of the tropical pacific ocean and enso variability by little ice age cooling tropical pacific ocean dynamics during the medieval climate anomaly mca and the little ice age lia are poorly characterized due to a lack of evidence from the eastern equatorial pacific we reconstructed sea surface temperature el nino southern oscillation enso activity and the tropical pacific zonal gradient for the past millennium from galapagos ocean sediments we document a mid millennium shift mms in ocean atmosphere circulation around 1500 1650 ce from a state with dampened enso and strong zonal gradient to one with amplified enso and weak gradient the mms coincided with the deepest lia cooling and was probably caused by a southward shift of the intertropical convergence zone the peak of the mca 900 1150 ce was a warm period in the eastern pacific contradicting the paradigm of a persistent la nina pattern

anisotropic zonation in the lithosphere of central north america influence of a strong cratonic lithosphere on the mid continent rift we present shear wave splitting analyses of sks and skks waves recorded at sixteen superior province rifting earthscope experiment spree seismic stations on the north shore of lake superior as well as fifteen selected earthscope transportable array instruments south of the lake these instruments bracket the mid continent rift mcr and sample the superior penokean yavapai and mazatzal tectonic provinces the data set can be explained by a single layer of anisotropic fabric which we interpret to be dominated by a lithospheric contribution the fast s polarization directions are consistently ene wsw but the split time varies greatly across the study area showing strong anisotropy up to 1 48 s in the western superior moderate anisotropy in the eastern superior and moderate to low anisotropy in the terranes south of lake superior we locate two localized zones of very low split time 0 6 s adjacent to the mcr one in the nipigon embayment an mcr related magmatic feature immediately north of lake superior and the other adjacent to the eastern end of the lake at the southern end of the kapuskasing structural zone ksz both low splitting zones are adjacent to sharp bends in the mcr axis we interpret these two zones along with a low velocity linear feature imaged by a previous tomographic study beneath minnesota and the dakotas as failed lithospheric branches of the mcr given that all three of these branches failed to propagate into the superior province lithosphere we propose that the sharp bend of the mcr through lake superior is a consequence of the high mechanical strength of the superior lithosphere ca 1 1 ga

evidence for two zones of debris entrainment beneath the greenland ice sheet investigation of the ice debris and stable isotope characteristics of basal ice exposed at the margin of the greenland ice sheet provides a means of testing and refining models of ice sheet erosion and deposition the basal ice exposed at the ice sheet margin gives evidence of the processes operating at the bed at different locations which can be used to constrain theoretical models predicting varying basal conditions1 2 improved understanding of the effects of isotope fractionation in hydrogen and oxygen caused by freezing processes at the bed which modify the isotope characteristics of the basal ice layers enables us to report evidence of two separate zones of debris entrainment beneath the ice sheet

results and implications of seismic performance studies for duncan dam screening level studies indicated large zones of the foundation soil beneath duncan dam could be triggered to liquefy under the design earthquake resulting in flow slides that could lead to breaching of the dam in these studies estimates of the key soil parameters were obtained from an indirect procedure using penetration tests and seed s chart which is based on field experience during past earthquakes together with empirical correction factors for high confining stress and static bias this is state of the practice procedure in north america and is used because of the difficulty in retrieving and testing undisturbed samples of sand with the high confining stresses present at the site the indirect approach gave very low values of the key liquefaction properties of the soil and the use of such low values in analyses indicated that major and costly remedial measures were required thus a more direct approach was undertaken this involved both direct and semidirect determination of the key soil parame

radiocarbon and stable isotopes in palmyra corals during the past century abstract annual samples from two palmyra atoll corals porites lutea that lived during the past 110 years were analyzed for radiocarbon 14 c and 18 o the 14 c values decreased 7 6 from 1896 to 1953 similar to other coral records from the tropical and subtropical pacific 14 c values rose from 60 to 110 by 1980 due to the input of bomb radiocarbon from the atmosphere elevated 14 c values were observed for the mid to late 1950s suggesting early input of bomb radiocarbon possibly from the largest marshall islands bomb tests in 1954 secondary aragonite precipitation was identified in a portion of one core using scanning electron microscopy and x radiography and was responsible for high 18 o and 13 c values and a correlation between them the 14 c results were more resistant to alteration except when contamination was from the bomb era 1956

interpretation of in situ test results from the canlex sites one of the primary objectives of the canadian liquefaction experiment canlex project was to evaluate in situ testing techniques and existing interpretation methods as part of the overall goal to

soil parameters for deformation analysis of sand masses meaningful stress and deformation analysis of soil structures requires an adequate stress strain law herein are presented guidelines for selection of parameters for a simple incremental hyperbolic stress strain law for sand based upon a tangent stiffness that varies with stress level the parameters are obtained from an examination of laboratory and field measurements available in the literature and are presented in terms of both penetration value and relative density the laboratory results indicate the importance of first time or primary loading versus repeated loading on modulus values back analysis of field observations for monotonic loading conditions indicates that primary loading modulus values obtained from triaxial tests are appropriate at low relative density whereas perhaps higher values in the repeated loading range are appropriate at high relative densities key words sand deformation analysis hyperbolic tangent stiffness modulus relative density monotonic loading repeated loading

radiocarbon as a thermocline proxy for the eastern equatorial pacific an ocean model is used to test the idea that sea surface delta 14 c behaves as a thermocline proxy in the eastern equatorial pacific the orca2 model which includes delta 14 c as a passive tracer has been forced with reanalysis fluxes over 1948 1999 and the output is compared with a previously reported galapagos delta 14 c record the model reproduces the abrupt increase in the seasonally minimum delta 14 c in 1976 77 found in the data this increase is associated with neither a shift of thermocline depth over the nino3 region nor a change in the relative proportion of northern southern source waters rather it is due to a decrease in the sub antarctic mode water samw component of the upwelling water thereby representing a decrease in entrainment of water from below the base of the directly ventilated thermocline

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

oceanic climate and circulation changes during the past four centuries from radiocarbon in corals we analyzed radiocarbon in annual coral bands from the galapagos islands in the tropical east pacific to understand natural variability of past ocean circulation associated with climate change variability was observed on el nino timescales 3 7 years as well as at decadal and multi decadal periods low radiocarbon levels persisted for ten years during the early 1600s and for sixteen years during the early 1800s both coincident with periods of high volcanic aerosol loading in the atmosphere from massive eruptions intensification of tropical circulation at this time may be linked to climatically controlled changes in the structure of the tropical thermocline that is responsible for delivering cool upwelled waters to the tropical east pacific

intrusion of ice into porous media by regelation a mechanism of sediment entrainment by glaciers unlithified sediment at glacier beds should be entrained in ice as a result of melting above individual grains and refreezing below grains regelation to test this hypothesis a device that simulates subglacial conditions was used to push ice downward through idealized and natural porous media in contact with a flat bed ice regelated toward the bed at speeds proportional to the gradient in ice pressure across the thickness of particles ice temperatures responded predictably to changes in driving stress and demonstrated that the ice particle mixtures were at or very near the pressure melting temperature a theory of pore ice motion by regelation predicted the measured speed usually to within a factor of two although at low driving stresses the speed was less than the predicted value by as much as a factor of five the low speeds were probably caused by imperfect temperature control that resulted either in heat loss from the ice particle mixtures or in slightly subfreezing pore ice temperatures that were not detected by thermistors ice should intrude the pores of underlying sediment to a steady depth at which the downward regelation speed equals the rate of basal melting departures from the steady state should cause release of debris from ice or further entrainment an approximate calculation of the steady intrusion depth yields values comparable to typical thicknesses of debris in basal ice a few centimeters to more than a meter intrusion of sediment by regelation is consistent with the isotopic composition of debris bearing ice if melting exceeds refreezing

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

radiocarbon variability in the western equatorial pacific inferred from a high resolution coral record from nauru island we have generated a high resolution coral delta sup 14 c record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical pacific prebomb 1947 endash 1956 delta sup 14 c values average minus 63 per thousand and have a total range of 30 per thousand values begin to increase in 1957 reaching a maximum of 137 per thousand in mid 1983 large interannual variability of up to 80 per thousand closely follows the el ni tilde n o southern oscillation enso during each enso warm phase delta sup 14 c values begin to increase reflecting the reduction of low sup 14 c water upwelling in the east and the invasion of subtropical water into the western equatorial tropical pacific maximum delta sup 14 c values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical pacific whereas the rapid return to more negative delta sup 14 c is in phase with eastern pacific enso indices the highest amplitude excursions occur during the 1965 1966 and 1972 1973 events when the sup 14 c contrast is highest between the eastern pacific and subtropics the 1982 1983 el ni tilde n o although a larger enso event has a lower delta sup 14 c amplitude reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in delta sup 14 c betweenmore thermocline and subtropical surface waters at that time this coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in pacific shallow circulation over interannual and decadal timescales copyright 1998 american geophysical union less

on the isotopic composition in δd and δ18o of water and ice during freezing experiments on progressive unidirectional freezing are coi1 ducted to determine rhe evol ution in 00 and 51 bo of successive water samples and ice layers ta ken during the course of freezing r es ults indicate t hal lhi s evoluti on takes pl ace in a bd bibo diagram a long a strai ght line wi th a characteri sti c slope this slope different from that due to the precip itation effec t gives a finger print of the occurrence of a freezing or of a melt ing refreez ing process in the stud ied reservoir residual water was sampled at the beginning of the experiment after 40 80 85 90 and 95 of the material had frozen when the freezing process was complete the ice core was recovered and sectioned the samples covered the freezing ranges from 0 to 10 10 to 20 20 to 50 50 to 60 60 to 70 70 to 80

canlex full scale experiment and modelling a major aim of the canadian liquefaction experiment canlex was to verify analysis procedures for pre dicting liquefaction phenomena towards this purpose two loading events were carried out a field event comprising a clay embankment built over a loose sand foundation layer and a centrifuge test performed on a model of a sand em bankment structure both the field event and the centrifuge model were planned so as to induce a static liquefaction failure and were instrumented to observe their response in terms of displacement and pore pressure the fundamental mechanical characteristics of the foundation layer were determined from laboratory element tests triaxial and simple shear these tests formed the basis for the stress strain modelling used in the numerical analyses two fundamentally different modelling techniques were used one involved a fully coupled plasticity model and the other involved a model based on a collapse surface approach the model and prototype structures were then analyzed and the predicted results in terms of displacements and pore pressures were compared with the measured values the results from both approaches were found to be in reasonable agreement with the measurements provided allowance was made for direc tion of loading and drainage effects were accounted for resume un but principal du canadian liquefaction experiment canlex etait de verifier les procedures d analyse pour predire les phenomenes de liquefaction a cette fin deux cas de chargement ont ete realises un chargement sur le terrain comprenant la construction d un remblai d argile sur une couche de fondation de sable meuble et un essai au centrifuge realise sur un modele d une structure de remblai de sable tant le remblai sur le terrain que le modele dans le centrifuge ont ete planifies de facon a induire une rupture par liquefaction statique et ont ete instrumentes pour ob server leurs reponses en termes de deplacement et de pression interstitielle les caracteristiques mecaniques

basal glacier ice and massive ground ice different scientists same science whilst glaciologists and permafrost researchers investigate ice bodies using similar techniques there has been surprisingly little collaboration between the two communities this paper examines the potential benefits of interdisciplinary research into the formation of basal ice beneath glaciers and the origin of massive ice in glaciated permafrost regions active collaboration in these areas has already improved our understanding of the formation of basal ice beneath cold based glaciers the critical role played by basal freezing in controlling the dynamic behaviour of stagnating ice streams and the significance of glacier permafrost interactions at the margins of pleistocene ice sheets however in order to promote future collaboration certain obstacles need to be overcome the contrasting ice classification schemes employed by glaciologists and permafrost scientists for example need to be unified in order to allow detailed comparisons of ice rich sequences in both environments this could in turn enable exciting research advances most notably by facilitating the identification of preserved remnants of pleistocene ice sheets within permafrost regions that provide a potentially invaluable and currently largely untapped source of palaeoglaciological information

the canadian liquefaction experiment an overview the canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the canadian liquefaction experiment canlex the main objective of the project was to study the phenomenon of soil liquefaction which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations in many areas of canada large structures are constructed on or comprise sandy soils e g some major hydroelectricity earth dams and many tailings impoundments in the mining industry the behaviour of loose sandy soils can be difficult to predict but can have a significant financial impact on these types of engineering structures consequently the intent of the canlex project was to improve the overall understanding of soil liquefaction this paper provides an overview of the canlex project outlining the project objectives major achievements and conclusions four companion papers describe different aspects of the pr

abrupt shift in subsurface temperatures in the tropical pacific associated with changes in el nino radiocarbon 14c content of surface waters inferred from a coral record from the galapagos islands increased abruptly during the upwelling season july through september after the el nino event of 1976 sea surface temperatures ssts associated with the upwelling season also shifted after 1976 the synchroneity of the shift in both 14c and sst implies that the vertical thermal structure of the eastern tropical pacific changed in 1976 this change may be responsible for the increase in frequency and intensity of el nino events since 1976

radiocarbon in annual coral rings from the eastern tropical pacific ocean sixty radiocarbon measurements were performed on aragonite from annually banded corals collected from three sites in the galapagos islands preanthropogenic 14c values of coral that grew around a d 1930 averaged 70 this is substantially lower than average values previously reported 51 for corals from florida and belize in the western north atlantic ocean a decrease of 6 was noticed in coral that grew from 1930 to 1954 this decrease could be interpreted as a suess effect in surface ocean water the 100 increase in 14c for coral that grew from 1954 to 1973 is the result of bomb produced 14c that was introduced to the surface ocean waters the 14c levels in corals that grew during el nino years were considerably higher than those for normal years these higher values are attributed to the absence of up welling at the equator during el nino events

blast densification multi instrumented case history a comprehensive blast densification field study was conducted at a test site in south carolina to densify a loose soil layer at a depth between z 8 13 m the study included extensive laboratory and field characterizations and four carefully monitored blast events results revealed that densification is not an instantaneous phenomenon underlying time dependent processes involve resedimentation drainage of excess pore pressure as the granular skeleton deforms and the effective stress recovers and secondary settlement effects which do not involve excess pore pressure dissipation the degree of densification decreased in successive blasting events and the soil gradually evolved toward an asymptotical terminal density associated with blast densification the blasting sequence and detonation delays appeared to have a minor effect on shear induced movements the increase in penetration resistance manifested 2 years after four blasting drainage events instead surface settlement using standard surveying te

ventilation time scales of the north atlantic subtropical cell revealed by coral radiocarbon from the cape verde islands we present coral and sclerosponge based reconstructions of the 14c content in north atlantic dissolved inorganic carbon dic during the last 100 years from the subtropical cells stcs these waters are sensitive to the dynamics of the shallow overturning meridional circulation that transports heat and water masses from the subtropics to the tropics we use these records to investigate the circulation patterns of the off equatorial upwelling regions of the stcs which are not well understood coral and sclerosponge skeletons provide long time series of ocean dic 14c content a tracer of oceanic circulation effectively extending the observational record back in time sclerosponge data from the bahamas were used to extend the existing subtropical 14c time series to the 21st century coral 14c data from the cape verde islands 1890 2002 captured the 14c signature of water brought to the surface in the off equatorial regions of the stc present near the west african coast we observe a unique postbomb trend at cape verde that is similar to the upwelling regions in the pacific and we interpret this trend as the result of the slow penetration of bomb 14c into the interior ocean as part of the stc circulation using a multibox mixing model we constrain the time history of bomb 14c in the eastern tropical atlantic and we estimate a 20 year time scale for ventilation of the thermocline in this area of the ocean the similarity between the atlantic and pacific 14c based records of upwelling suggests that both are caused by bomb 14c penetration rather than more complex explanations that invoke changes in thermocline depth e g related to el nino southern oscillation variability or changes in the strength of the subtropical cells our results offer constraints for models of tropical ocean circulation and anthropogenic co2 uptake that attempt to reproduce the characteristics of the shallow wind driven circulation in the atlantic

transverse englacial debris rich ice bands at kviarjokull southeast iceland thick exposures of debris rich ice at various icelandic glaciers are central to the debate over the prevalence of glacial sediment transfer by glaciohydraulic supercooling we present physical analyses of ice and debris at kviarjokull a temperate glacier in southeast iceland with a terminal glacier bed overdeepening where stratified debris rich ice forms up to metre thick transverse englacial bands our results are not consistent with debris rich ice formation predominantly by supercooling because 1 137cs was absent from sediment filtered from debris rich ice 2 isotopic analysis d and 18o demonstrated no clear pattern of isotopic enrichment of debris rich ice with respect to englacial ice and 3 melt out debris from debris rich ice included large striated clasts from both fluvial and basal sources we support transverse englacial debris rich ice band formation by the thickening and elevation of basal materials in a region of longitudinally compressive ice flow situated between the reverse slope of the overdeepening and the base of an ice fall debris band form and distribution are likely to be controlled by thrusting along transverse englacial foliae associated with the formation of band ogives on the glacier surface

analysis of canlex liquefaction embankments prototype and centrifuge models un objectif principal du projet canadien d etude de la liquefaction canadian liquefaction experiment canlex etait de verifier les procedures d analyse pour la prediction des phenomenes de liquefaction a cette fin deux cas de chargement ont ete realises un chargement sur le terrain comprenant un remblai construit sur une couche de fondation de sable l che et un essai au centrifuge realise sur un modele de la structure prototype tant l essai sur le terrain que l essai au centrifuge ont ete planifies de facon a induire une rupture par liquefaction statique les caracteristiques mecaniques fondamentales de la couche de fondation ont ete determinees dans des essais en laboratoire sur des elements triaxiaux et cisaillement simple ces caracteristiques ont ete d abord obtenues sur un element en utilisant un modele de comportement contrainte deformation elasto plastique le prototype et les structures a l echelle ont alors ete modelises comme un ensemble de tels elements le drainage etait un facteur tres important durant le chargement et etait directement incorpore dans la procedure de l analyse les resultats predits concordent bien tant avec l essai au centrifuge qu avec les mesures sur le terrain

cold temperate transition surface and permafrost base cts pb as an environmental axis in glacier permafrost relationship based on research carried out on the storglaciaren and its forefield northern sweden here we present empirical ground penetrating radar gpr and electroresistivity tomography data ert to verify the cold temperate transition surface permafrost base cts pb axis theoretical model the data were collected from storglaciaren in tarfala northern sweden and its forefield the gpr results show a material relation between the glacial ice and the sediments incorporated in the glacier and a geophysical relation between the cold ice and the temperate ice layers clearly identifying lateral glacier margins is difficult as periglacial and glacial environments frequently overlap in this case we identified areas showing permafrost aggradation already under the glacier particularly where the cts is replaced by the pb surface this structure appears as a result of the influence of a cold climate over both the glacial and periglacial environments the results show how these surfaces form a specific continuous environmental axis thus both glacial and periglacial areas can be treated uniformly as a specific continuum in the geophysical sense similarly other examples previously described also allow identifying a continuation of permafrost from the periglacial environment onto the glacial base in addition the ert results show the presence of double layered periglacial permafrost possibly suggesting a past climatic fluctuation in the study area

reduced deep ocean ventilation in the southern pacific ocean during the last glaciation persisted into the deglaciation abstract marine radiocarbon 14c is widely used to trace ocean circulation and the 14c levels of interior ocean water masses can provide insight into atmosphere ocean exchange of co2 the since the last glaciation using tephras as stratigraphic tie points with which to estimate past atmospheric 14c we reconstructed a series of deep radiocarbon ages for several time slices from the last glaciation through the deglaciation and holocene in the southwestern pacific glacial ventilation ages were much greater in magnitude than modern and had a strong mid depth 14c minimum centered on 2500 m glacial radiocarbon ages of intermediate depth waters 600 1200 m were 800 to 1600 14c years about twice modern and persisted through the early deglaciation notably in the glaciation shallower depths were significantly more enriched in 14c than waters between 1600 and 3800 m which were 4000 to 6200 14c years or about 3 5 times older than modern abyssal waters deeper than 4000 m were also more 14c rich than the overlying deep water with radiocarbon ages of 1800 2300 14c years this was similar to modern values in the early deglaciation 14c depleted waters were flushed from shallower depths first and replaced with progressively younger waters such that by 18 ka the deep to intermediate age difference was reduced by half and by 14 ka a modern type 14c profile for deep ocean water masses was in place our results 1 confirm a deep 14c depleted water mass during the lgm and early deglaciation and 2 constrain the extent of this old water in the southern pacific as between 1600 m and 3800 m the availability of atmospheric ages from tephras reveals that the presence of older surface reservoir ages in the glaciation caused the estimation of ventilation ages from simple benthic planktonic offsets to significantly underestimate the depletion of 14c in deep waters this may have had a role in masking the large change in reservoir ages since the glaciation when using benthic planktonic reservoir age estimates