did large ice caps persist on low ground in north west scotland during the lateglacial interstade recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north west scotland throughout the lateglacial interstade greenland interstade 1 ca 14 7 12 9 ka and that glacier ice was much more extensive in this area during the older dryas chronozone ca 14 0 ka than during the younger dryas stade ca 12 9 11 7 ka we have recalibrated the same exposure age data using locally derived 10be production rates this increases the original mean ages by 6 5 12 implying moraine deposition between ca 14 3 and ca 15 1 ka and we infer a most probable age of ca 14 7 ka based on palaeoclimatic considerations the internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin the wester ross readvance pollen stratigraphic evidence from a lateglacial site at loch droma on the present drainage divide demonstrates deglaciation before ca 14 0 ka and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade ca 14 7 14 0 ka this inference appears consistent with lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in scotland between 14 and 13 ka that large active glaciers probably survived throughout the lateglacial interstade and that ice extent was greater during the older dryas period than during the younger dryas stade copyright 2011 john wiley sons ltd

a revised chronology for the growth and demise of loch lomond readvance younger dryas ice lobes in the lochaber area scotland abstract we present a revised varve chronology for the duration of ice dammed lakes that formed in the lochaber district scotland during the loch lomond younger dryas stadial we analysed new varved sequences and combined them with existing varve records to develop the lochaber master varve chronology 2019 lmvc19 published here for the first time it spans an interval of 518 18 vyrs and is considered more secure than its predecessors because i it is anchored by a more robust record of the vedde ash which is dated to 12 043 43 cal yr bp and ii it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently dated non varved records obtained from neighbouring sites the new results indicate that the lochaber ice dammed lakes existed between 12 135 and 11 618 61 cal yr bp but the pattern of glacier advance that led to lake formation was more complex than previously assumed with some ice fronts reaching their maximal positions 300 years before others initiation of ice retreat at 11 800 cal yr bp appears to have coincided with a rise of 2 c in mean july temperatures inferred from chironomid data obtained from the abernethy forest site in the eastern highlands this local climatic shift is thought to have been a delayed response by up to 335 years to a mid stadial northward migration of the north atlantic polar front the delay probably due to the influence of the sw highland icefield subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of 3 c at the start of the early holocene final drainage of the lake system occurred 190 years after the initiation of ice retreat while it took a further 200 years for the ice to vacate the rannoch plateau a nearby upland glacial source

ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data long period global scale electromagnetic induction studies of deep earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure we describe approaches to inverting for both the external sources and three dimensional 3 d conductivity variations and apply these methods to long period t 1 2 days geomagnetic observatory data our scheme involves three steps 1 observatory data from 60 years only partly overlapping and with many large gaps are reduced and merged into dominant spatial modes using a scheme based on frequency domain principal components 2 resulting modes are inverted for corresponding external source spatial structure using a simplified conductivity model with radial variations overlain by a two dimensional thin sheet the source inversion is regularized using a physically based source covariance generated through superposition of correlated tilted zonal quasi dipole current loops representing ionospheric source complexity smoothed by earth rotation free parameters in the source covariance model are tuned by a leave one out cross validation scheme 3 the estimated data modes are inverted for 3 d earth conductivity assuming the source excitation estimated in step 2 together these developments constitute key components in a practical scheme for simultaneous inversion of the catalogue of historical and modern observatory data for external source spatial structure and 3 d earth conductivity

distinguishing between water column and sedimentary denitrification in the santa barbara basin using the stable isotopes of nitrate 1 below its sill depth the santa barbara basin sbb is commonly suboxic o2 3 m with only brief periods of ventilation associated with development of suboxia the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate indicating that a substantial fraction of the nitrate supplied to the basin is removed by denitrification coincident with the decrease in nitrate concentration across the redoxcline the interface between oxic and suboxic waters within the sbb there is an increase in the 15n 14n of that nitrate as would be anticipated from the isotopic fractionation associated with denitrification however the increase in 15n 14n of nitrate is much smaller than occurs in the open eastern tropical north pacific etnp for a comparable amount of nitrate loss both the concentrations of n species within the basin and measurements of nitrate 18o 16o suggest that the lower than expected 15n enrichment in the suboxic sbb involves denitrification rather than being due to some unknown source of low 15n 14n n to the deep sbb calculations with a range of models of nitrate supply and consumption indicate that the degree of nitrate consumption in the basin is too small for differences in water circulation to explain the isotopic differences between the santa barbara basin and the open etnp previous studies indicate that the isotope effect of sedimentary denitrification is negligible due to nitrate diffusion in sediment pore waters thus we infer that the small magnitude of the isotopic enrichment of sbb water column nitrate is due to the importance of sedimentary denitrification within the basin assuming that water column and sedimentary denitrification have isotope effects of 25 and 1 5 per mil respectively our results suggest that sedimentary denitrification accounts for more than 75 of the nitrate loss within the suboxic sbb

electric currents in the ocean induced by the geomagnetic sq field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the geomagnetic sq field are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the simulation results show that the induced currents have maximum intensity in the northern pacific ocean at 22 hr ut and enhance the total induced fields by about 60 per cent even when the external current vortex is located above the eurasian continent the internal current vortex is enhanced by about 10 per cent by the existence of the ocean next we have checked the effects of the electric currents in the ocean on the estimation of the mantle conductivity and found that ignoring the currents induced in the shell gives a less conductive and shallower estimation of the mantle conductor furthermore an apparent dependence of the conductivity on the depth appears because of the effects of the currents induced in the shell even if the mantle is a uniform conductor the conductivity and depth are estimated to be 0 1 sm 1 and 500km respectively from the data analysis for the 1 day period variation field of the p12 mode if the effects of the currents in the shell are ignored but it should be 1s m 1 and 780 km if the effects are considered

rapid localized glacio isostatic uplift at glen roy scotland many studies involving measurement of the altitudes of fossil marine and lacustrine shorelines have demonstrated glacioisostatic tilting particularly in north america fennoscandia and the british isles such studies are normally illustrated by height distance diagrams in which fossil shorelines are portrayed as straight lines in some studies the shoreline relation diagram is used to analyse and illustrate the altitudinal data1 3 before constructing such a diagram it is assumed that a simple pattern of glacioisostatic uplift has prevailed warping of shorelines as opposed to uniform tilting has been inferred in north america4 6 on the other hand harme7 envisaged block movements in fennoscandia sauramo8 also proposed dislocations but his interpretation was rejected by hyyppa9 more recently the concept of the scandinavian shield as a stable area has been dismissed10 11 here we provide evidence from scotland for shoreline dislocation by differential movement of blocks of the earth s crust

rock slope failure in the british mountains abstract in this first full review of extant quaternary rock slope failure rsf in the british mountains we provide a near complete inventory of 1082 sites 40 being rock slope deformations 40 arrested rockslides and 20 rock avalanches current rsf activity is negligible and this relict population is predominantly paraglacial with a parafluvial minority its spatial distribution is perplexing with rsf density varying greatly both regionally and locally in the scottish highlands eight main clusters account for 76 of rsf area in 15 of the montane area local concentrations occur in all the british ranges across high and low relief in core and peripheral locations and on varied geological and glaciological domains as conversely do extensive areas of sparsity even in similar lithologies generic interpretations are thus precluded geology is only a secondary control an association with concentrated erosion of bedrock ceb is proposed as a driver of intensified slope stresses ceb is most evident at those glacial breaches of main divides where the most vigorous recent incision is inferred and also in some trough heads a clear association between rsfs and these late developing breaches is demonstrated in the highlands in 42 localities with sparsity away from them it is also seen in seven lake district localities glaciological models identify ice sheet volatility capable of driving breach ramification high magnitude paleoseismic events are generally unlikely to have provoked rsf clusters a few candidates are considered rsf has been underrated as an agent of mountain landscape evolution in britain its spatio temporal incidence may assist in calibrating regional ice sheet models and in assessing climate change impacts we argue that the ceb rsf association has global relevance in identifying primary drivers of mass movement in bedrock

a new varve sequence from windermere uk records rapid ice retreat prior to the lateglacial interstadial gi 1 abstract annually laminated sediments varves provide excellent temporal resolution to study rapid environmental change but are rare in the early part of the last termination 19 11 7 ka bp we present a new 400 varve year vyr varve sequence in two floating parts from windermere a lake at the southern margin of the mountains of northwest england this sequence records the final retreat of the windermere glacier at the southern edge of the lake district ice cap during the transition from heinrich stadial 1 18 14 7 ka bp into the lateglacial interstadial 14 7 12 9 ka bp laminated sediments from four lake cores from windermere s northern and southern basins were investigated and shown to be varved these sequences are integrated with seismic reflection evidence to reconstruct south to north deglaciation seismic and sedimentological evidence is consistent with gradual stepped ice retreat along the entire southern basin and into the northern basin between 255 and 700 vyr prior to the appearance of significant biota in the sediment that heralded the lateglacial interstadial and had retreated past a recessional moraine rm8 in the northern basin by 121 vyr prior to the interstadial the lateglacial interstadial age of this biota bearing unit was confirmed by 14c dating including one date from the northernmost core of 13 5 cal ka bp a change in mineralogy in all four cores as the glacier retreated north of the dent group the northernmost source of calcareous bedrock and a decrease in coarse grains in the varves shows that the ice had retreated along the entire north basin at 70 vyr prior to the lateglacial interstadial the estimated retreat rate is 70 114 m yr 1 although buried de geer moraines if annual may indicate retreat of 120 m yr 1 with a 3 year stillstand at a recessional moraine halfway along the basin the glacier then retreated north of the lake basin becoming land terminating and retreating at 92 5 49 m yr 1 the northernmost core has a varve sequence ending at least 111 vyr after the other core chronologies due to the increased proximity to remnant ice in the catchment uplands into the early lateglacial interstadial we show that almost all of the glacier retreat in the windermere catchment occurred before the abrupt warming at the onset of the lateglacial interstadial in keeping with similar findings from around the irish sea basin and suggesting a similar retreat timescale for other radial valley glaciers of the lake district ice cap the seismic and core evidence also show the potential for a much longer varve chronology extending at least 400 and potentially over 1000 vyr further back into heinrich stadial 1 18 14 7 ka bp suggesting that glacier retreat in the windermere valley initiated at least before 15 5 ka bp and perhaps 16 ka bp

a lateglacial 10be production rate from glacial lake shorelines in scotland the identification of tephra within varved deposits of a former ice dammed lake that existed in scotland during the younger dryas provides an opportunity to calibrate 10be production rates using previously published 10be concentrations from the lake shoreline and independently derived ages for the tephras derived from the greenland ice core records the best estimate ages of the tephras yield indistinguishable 10be production rate values for spallation with an average value of 4 26 0 21 atoms g 1 a 1 using the lm scaling scheme these values are in best agreement with the most proximal reference 10be production rate from norway

tidal signals in ocean bottom magnetic measurements of the northwestern pacific observation versus prediction summary motional induction in the ocean by tides has long been observed by both land and satellite measurements of magnetic fields while these signals are weak 10 nt when compared to the main magnetic field their persistent nature makes them important for consideration during geomagnetic field modelling previous studies have reported several discrepancies between observations and numerical predictions of the tidal magnetic signals and those studies were inconclusive of the source of the error we address this issue by 1 analysing magnetometer data from ocean bottom stations where the low noise and high signal environment is most suitable for detecting the weak tidal magnetic signals 2 by numerically predicting the magnetic field with a spatial resolution that is 16 times higher than the previous studies and 3 by using four different models of upper mantle conductivity we use vector magnetic data from six ocean bottom electromagnetic obem stations located in the northwestern pacific ocean the obem tidal amplitudes were derived using an iteratively re weighted leastsquares irls method and by limiting the analysis of lunar semidiurnal m2 lunar elliptic semidinurnal n2 anddiurnal o1 tidalmodestothenight time usinga3 delectromagnetic induction solver and the tpx07 2 tidal model we predict the tidal magnetic signal we use earth models with non uniform oceans and four 1 d mantle sections underneath taken from kuvshinov and olsen shimizu et al and baba et al to compare the effect of upper mantle conductivity we find that in general the predictions and observations match within 10 70percent across all the stations for each of the tidal modes the median normalized percent difference npd between observed and predicted amplitudes for the tidal modes m2 n2 and o1were15percent 47percentand98percent respectively forallthestationsandmodels at the majority of stations and for each of the tidal modes the higher resolution 0 25 0 25 modelling gave amplitudes consistently closer to the observations than the lower resolution 1 1 modelling the difference in lithospheric resistance east and west of the izu bonin trench system seems to be affecting the model response and observations in the o1 tidal mode this response is not seen in the m2 and n2 modes thereby indicating that the o1 mode is more sensitive to lithospheric resistance

a comparison of micro ct and thin section analysis of lateglacial glaciolacustrine varves from glen roy scotland abstract despite the prevalence of thin section analysis in studies of quaternary sediments there are limitations associated with the production of thin sections sediment modification and the inherently 2d view that a thin section affords non destructive and rapid scanning technologies such as x ray computed microtomography ct enable material samples to be visualised and analysed in 3d in a quaternary context however such techniques are in their infancy this paper assesses the optimum approach to ct analysis of quaternary sediments applying the method on lateglacial glaciolacustrine varves from glen roy scotland scan datasets are examined at each stage of the thin section process and comparisons are made between 2d ct images and thin sections for the recognition of 2d sediment features with further appraisal of 3d models to identify 3d sediment structures comparable sediment features are observed in 2d ct images and thin sections however the ct imaging resolution determines the precision of microfacies descriptions additional 3d structures are distinguished from volumetric models that are otherwise impossible to identify in thin section slides these 3d structures can locally alter sediment properties e g layer thickness as seen in 2d thin sections and or digital images although such variation cannot be detected with these media it has been demonstrated that clear benefits exist in understanding the 3d structure of quaternary sediments both prior to thin sectioning to avoid complicating e g deformation structures and after thin sectioning to establish the complex 3d context of 2d datasets it is recommended that ct and thin section techniques are applied in parallel in future studies which will profit from the integration of true 3d data it is also advised that samples are scanned soon after field sampling due to the significant modification of in situ sediment structures that can occur during thin section processing

lateglacial calendar year chronology based on annually laminated sediments from lake meerfelder maar germany abstract annually laminated sediments from lake meerfelder maar mfm in the eifel germany provide an independent calendar year timescale for the last glacial interglacial transition changes in varve thickness and varve facies reflect significant environment variations during this period the general micro facies pattern confirms that diatomaceous organic varves are favoured during warm climatic phases while cold periods generate higher allochthonous sediment fluxes an exception is the significant increase in diatom blooms at the beginning of the younger dryas six lateglacial biozones have been defined by litt and stebich quaternary international 1999 the sediment record comprises two tephra layers as chronomarkers the laacher see tephra 12 880 varve years bp is a continent wide correlation horizon while the ulmener maar tephra provides regional chronological links the beginning of the lateglacial warming is dated at 14 450 varve years vyrs bp which is regarded as the minimum age three abrupt cold spells interrupted the lateglacial interstadial at 13 800 vyrs bp oldest dryas 13 540 vyrs bp older dryas and 12 680 vyrs bp younger dryas the oldest dryas 130 years and the older dryas 190 years were rather short while the younger dryas lasted much longer 1090 years the mfm chronology was compared with ice core timescales from gisp2 and grip there is a good agreement between these timescales with the grip model age ss09 providing the best match to the mfm chronology

palaeoseismic liquefaction event in late quaternary lake sediment at glen roy scotland late quaternary lake sediment deposits from a former ice dammed lake at glen roy scotland contain deformation structures indicative of liquefaction the distribution of deformation styles reflects a concentric pattern of the degree of liquefaction a possible fault rupture and several landslides are also observed in the central area the liquefaction structures the zonation of the sediment deformation and the association of deformation with landsliding can most simply be interpreted in terms of ground shaking during a major earthquake occurring at the end of the last glacial episode in scotland c 10 000 bp

micromorphology and petrography of late weichselian glaciolacustrine varves in southeastern sweden abstract the purpose of this investigation is to describe and interpret the sedimentology and petrography of late weichselian varves in southeastern sweden in order to determine their nature and origin it is focused on the microscopic evidence for glaciolacustrine varve sedimentation in the baltic ice lake and the possibilities of making a detailed facies classification of the sediments in an area with an established varve chronology the material examined was cores taken from five representative localities in an area below the highest shoreline of the baltic ice lake in the provinces of skane and blekinge i e below an altitude of 55 65 m the investigations included chemical analyses xrd microscopy polarized and sem edx investigations of the summer and winter layers of the varves the results of the chemical clay mineralogy xrd and microscopic examinations of the bedrock and mineral fragments indicate that the material in the different facies of the varved clay is mainly produced by moderate alteration and erosion from the local bedrock of predominantly granitoid rocks and of residual kaoline deposits it is possible to distinguish microscopic evidence of four varve types differing in texture depending on the water depth and how close to the ice the different facies were deposited i e if they were deposited proximally distally or extramarginally in relation to the ice margin it is also possible to relate these differences to changes in the palaeoclimate during the deglaciation of the area in the bolling and older dryas chronozones

electric currents in the ocean induced by a model dst field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the external dst fields are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the effect of the ocean on the dst field is smaller than that on the geomagnetic sq field however fairly strong currents are induced is the antarctic ocean and these currents partly explain the anomalous behaviour of the geomagnetic response observed at hermanus especially for the variations of periods of less than two days

a 2000 year record of solar forcing on varved lake sediment in eastern finland abstract a high resolution study was performed on varved sediments from lake lehmilampi in eastern finland varve data was collected by digital image analysis using standard 1 8 mm thick samples impregnated in epoxy and x rayed climatic variability is imprinted on varve properties varve thickness and accumulation of mineral and organic matter during the last 2000 years the cumulative counting error of the varve record is estimated as 2 3 qualitative comparison of varve parameters and residual 14c constructed from tree rings revealed close correspondence between the two records suggesting solar forcing on lake sedimentation classical climatic periods of the last millennia medieval climate anomaly 1060 1280 in the varve record and little ice age cooler phases culminating in 1340 1465 1545 1680 1850 and also in 1930 in the varve record are clearly evident in the varve record at present the physical link between solar activity levels and lake sedimentation has not been established

a younger dryas plateau icefield in the monadhliath scotland and implications for regional palaeoclimate a record of younger dryas glaciation in scotland is well established however the role of the monadhliath a significant plateau area extending over 840 km2 in central scotland has never been investigated systematically we present the first systematic glacial geomorphological mapping across the whole region which has led to the identification of hitherto unrecorded glacial and associated landforms the spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield in addition a clear morphostratigraphical signature provides a strong indication that the icefield dates to the younger dryas 12 9 11 7 ka which is supported by numerical ages in the southeast of the study area based on the geomorphological evidence and 2d glacier surface profile modelling a 280 km2 icefield is reconstructed a novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude ela and palaeoprecipitation calculations resulting in greater overall data confidence compared to traditional reconstruction methods the ela for the whole icefield is calculated to be 714 25 m whilst the elas of individual outlet glaciers range from 560 m in the west to 816 m in the east demonstrating a significant w e precipitation gradient across the region during the younger dryas these elas compare well with those calculated for younger dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for scotland during this time whilst the total amount of precipitation calculated from these elas is highly dependent on the method used irrespective of this the study suggests a more arid younger dryas climate in the region compared to the present day

establishing tephrostratigraphic frameworks to aid the study of abrupt climatic and glacial transitions a case study of the last glacial interglacial transition in the british isles c 16 8 ka bp abstract distally dispersed tephra layers have become an important tool in the investigation of palaeoenvironmental and archaeological records across the globe they offer possibilities for the synchronisation and improved chronological control in those records to which they can be traced and hence contribute to an improved understanding of the pattern and timing of environmental and archaeological change during periods of rapid climatic adjustment however their use as robust isochronous markers for synchronising records is frequently compromised by uncertainties relating to stratigraphical context precise chronology and chemical composition here we collate and review the tephrostratigraphical information dating to the last glacial interglacial transition lgit c 16 8 ka bp in the british isles based on published and unpublished records obtained from 54 sites based on details of their stratigraphic position chronology and chemical composition we propose that 26 individual eruption events may be represented in this collective record which spans the lgit the great majority of these eruptives can be traced in origin to iceland but we also report on the recent discoveries of ultra distal tephra from the north american cascades range including for the first time the mount st helens j tephra at a site in southern ireland these particular ultra distal discoveries have resulted from a reinterpretation of older data demonstrating the potential importance of unknown analyses in older tephra datasets the outcome of this review is a comprehensive but provisional tephrostratigraphic framework for the lgit in the british isles which helps to focus future research on parts of the scheme that are in need of further development or testing the results therefore make an important contribution to the wider european tephrostratigraphic framework while adding new discoveries of transcontinental isochronous tephra markers

local time stacking of geomagnetic solar daily variations 1 regular geomagnetic solar daily variations the sq signal is used in electromagnetic induction studies to investigate the electrical conductivity structure of earth s upper mantle traditionally sq induction studies employ observatory magnetic data from a few quiet days in which the overprint on the regular sq ionospheric current vortices from various irregular disturbances is minimal active days are typically discarded a procedure which results in a gappy time series that is difficult to analyze furthermore the quiet day selection is largely arbitrary since daily geomagnetic activity levels range continuously from very quiet to very active this fact precludes the establishment of rigorous quiet active thresholds the average local time variation on active days resembles typical quiet day variations except for a multiplicative scaling factor a multiyear stack of yearlong geomagnetic time series aligned with respect to local time incorporates regular active days while greatly attenuating the effects of irregular geomagnetic disturbances external and internal current systems that rise and fall in step with the sun s transit across the sky above an observatory contribute coherently to the local time stack all other current systems are incoherent and tend to stack out an exact 1 year long stack preserves the seasonal variation the resulting stacked time series contains no gaps is dominated by regular solar daily variations and can be used for improved sq induction studies and comprehensive geomagnetic field modeling hourly geomagnetic values from niemegk boulder mbour and meanook observatories between 1970 and 2002 along with the ap index are used in this study

recent warming in a 500 year palaeotemperature record from varved sediments upper soper lake baffin island canada laminated sediments from upper soper lake on southern baffin island provide a new 500 year record of temperature change in the arctic radiometric dating using 210pb and pu shows that the light and dark coloured laminae couplets are annually deposited varves dark laminae thickness is strongly correlated to average june temperature from kimmirut r 0 82 reflecting the influence of temperature on snowmelt and fluxes of runoff and suspended sediment this relationship allowed the construction of a palaeotemperature record that documents large amplitude interannual to decadal variability superimposed on distinct century scale trends including 2 c average warming and maximum temperatures during the 1900s similar patterns of change are seen in individual and regionally averaged palaeotemperature records from around the circum arctic upper soper lake records temperatures rates of change and variance during the twentieth century that are all anomal ously high within the context of the last 500 years and outside the observed range of natural variability comparisons of upper soper lake and arctic average palaeotemperature to proxy records of hypothesized forcing mechanisms suggest that the recent warming trend is mostly due to anthropogenic emissions of atmos pheric greenhouse gases the magnitude of the warming and decade scale variability throughout the records however indicate that natural forcing mechanisms such as changing solar irradiance and volcanic activity as well as positive feedbacks within the arctic environment also play an important role

controlled source electromagnetic sounding of the oceanic lithosphere the attenuation of ionospheric signals in the frequency range 0 06 24 hz by sea water effectively precludes using the magnetotel luric method to study the electrical structure of the upper oceanic lithosphere we have carried out a dipole dipole electromagnetic sounding in the north pacific by injecting electromagnetic signals into the ocean and sea bed the crust at the site is 25 myr old and has a thin sediment cover the technique similar to that used in earlier work1 2 involves dragging a horizontal dipole antenna along the sea floor the electric fields that propagated through the resistive basement were detected by seafloor receivers at ranges of 10 65 km as the ambient electric field is very small varying from 10 18 v2 m 2 hz 1 at 0 1 hz to 10 24 v2 m2 hz 1 above 1 hz ref 3 the controlled source signals could be easily monitored our data are consistent with a simple one dimensional earth model consisting of a 3 7 km thick crustal layer of moderate conductivity 0 001 s m 1 underlain by a thicker region of very low conductivity 2 10 5 s m 1 the results suggest an upper mantle water content of at most 0 1 by volume

on induction effects of geomagnetic daily variations from equatorial electrojet and solar quiet sources at low and middle latitudes 1 we investigate the spatiotemporal behavior of the magnetic vertical component z of the daily ionospheric current systems the equatorial electrojet eej and solar quiet sq variations considering induction in the mantle and oceans the inducing eej and sq current systems are provided by the comprehensive model of sabaka et al 2004 the three dimensional 3 d conductivity model of the earth includes oceans of laterally variable conductance and a spherical conductor 1 d underneath our model studies demonstrate that induction effects in z due to the eej are negligible everywhere inland for all local times at champ altitude 400 km the magnetic signal induced by eej above the oceans does not exceed 2 5 of the external field during local noon this in particular means that considering the induction effects is not necessary when modeling the eej current strength from inland surface magnetic measurements and or satellite data as expected induction in the oceans strongly affects the sq field the model studies show that the anomalous induction effect defined as the difference between results obtained with 1 d and 3 d conductivity models of sq is substantial at champ altitude comprising 50 of the total field it is therefore necessary to consider induction in the oceans when modeling sq variations for both ground based and satellite data finally we demonstrate that the anomalous behavior of the daily variations in z at south indian sites namely a large positive prenoon peak can be explained by 3 d induction of the sq variations with no contribution from the eej

anomaly of the geomagnetic sq variation in japan effect from 3 d subterranean structure or the ocean effect summary many years ago rikitake et al described the anomalous behaviour of the vertical component z of the geomagnetic solar quiet sq daily variation field at observatories in central and northern japan namely about 2 hr shift of the local noontime peak towards morning hours they suggested that this anomaly is associated with the anomalous distribution of electrical conductivity in the mantle beneath central japan although a few works have been done to confirm or argue this explanation no clear answer has been obtained so far the goal of this work is to understand the nature of this anomaly using our 3 d forward solution the conductivity model of the earth includes oceans of laterally variable conductance and conducting mantle either spherically symmetric or 3 d underneath data from six japanese observatories at four seasons for two different years of the solar cycle are analysed as an inducing ionospheric sq current system we use those provided by the comprehensive model cm4 of sabaka et al our analysis clearly demonstrates that 3 d induction in the ocean is responsible for the anomalous behaviour of z daily variations in this region we also show that the effects from a suite of 3 d mantle models that include mantle wedge and subducting slab are minor compared with the ocean effect

high resolution chronology for deglaciation of the patagonian ice sheet at lago buenos aires 46 5 s revealed through varve chronology and bayesian age modelling abstract glaciolacustrine varves offer the potential to construct continuous annually resolved chronologies for ice sheet deglaciation and improved understanding of glacier retreat dynamics this paper investigates laminated glaciolacustrine sediments deposited around the waning margins of the patagonian ice sheet following the local last glacial maximum lgm detailed macro and microfacies analyses confirm an annual varve structure within these sediments the correlation of annual layers varves across five sites in eastern lago buenos aires yields a 994 36 varve year vyr chronology and thickness record the floating chronology has been anchored to the calendar year timescale through identification of the ho tephra 17 378 118 cal a bp in the varve sequences using a bayesian age model to integrate the new varve chronology with published moraine ages the onset of deglaciation at 46 5 s is dated to 18 086 214 cal a bp new age estimates for deglacial events are combined with high resolution analysis of varve thickness trends and new lithostratigraphic data on ice margin position s to reconstruct ice margin retreat rates for the earliest ca 1000 years of ice sheet demise glacier retreat rates were moderate 5 3 10 3 m yr 1 until 17 322 115 cal a bp but subsequently accelerated 15 4 18 0 m yr 1 sustained influxes of ice rafted debris ird after 17 145 122 cal a bp suggest retreat rates were enhanced by calving after ice contracted into deeper lake waters ice persisted in eastern lago buenos aires until at least 16 934 116 cal a bp after which the glacier started to retreat towards the patagonian mountains

on the timing of retreat of the loch lomond younger dryas readvance icefield in the sw scottish highlands and its wider significance abstract it has long been assumed that the last glacier expansion in the scottish highlands the loch lomond readvance llr resulted from a cold reversal that was broadly coeval with the younger dryas episode this view has recently been challenged with the suggestion that glacier ice had disappeared from rannoch moor one of the main ice accumulation centres in the sw scottish highlands by as early as 12 5 ka i e within the first half of the younger dryas here we present new radiocarbon tephrostratigraphical and pollen stratigraphical evidence from one of the key sites on rannoch moor the results of an experiment designed to test this hypothesis our results not only contradict that concept but are fully compatible with other evidence from the sw scottish highlands that suggests that the llr glaciers in this area continued to expand until towards the end of the younger dryas period and may have persisted in some places after the onset of the holocene we consider the possible reasons for this marked divergence in chronology a matter that is crucial to resolve because the precise timing of the demise of the llr glaciers has important palaeoclimatic and other implications in the wider context we also draw attention to problems with the general use of the term younger dryas and why we regard the greenland stratotype unit and term greenland stadial 1 gs 1 a more secure stratigraphic comparator

differential glacio isostatic uplift of crustal blocks at glen roy scotland abstract detailed measurements of the altitudes of the shorelines of former ice dammed lakes in glen roy and vicinity in the scottish highlands prove erroneous the conventional view that former shorelines in areas affected by glacio isostatic uplift are uniformly tilted and or gently warped the measurements demonstrate differential uplift of blocks of the earth s crust the surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4 6 m km and are tilted in different directions in three areas 0 7 2 0 km long shorelines are distorted by crustal movements all these areas have landslides attributed to earthquakes that accompanied the release of stress in the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area and a fault scarp was produced possibly these local distortions accompanied catastrophic lake drainage by jokulhlaup analogous to crustal movements associated with man made lakes a relationship between crustal movement and the limit of a glacial advance is demonstrated these findings have implications for other parts of the world affected by glacioisostatic uplift

electromagnetic induction in a spherical earth with non uniform oceans and continents in electric contact with the underlying medium ii bimodal global geomagnetic sounding of the lithosphere summary the vertical electric currents flowing between the inhomogeneous surface layer and the conductive layers of the earth s mantle are substantially dependent upon the transverse resistivity of the earth s crust and upper mantle although these currents do not contribute straightforwardly to a surface magnetic field they change the vortex sub surface currents which contribute to it thus there exists an indirect influence of leakage currents upon the magnetic field this makes it possible to evaluate resistance of the high ohmic layers which could not be evaluated if the earth was laterally homogeneous and only the induction mode of the field was induced this paper presents the first results of the bimodal sounding based on s variation data an estimate of the lithosphere s transverse resistance t 3 x lo9 51 m2 has been obtained

land ice teleconnections of cold climatic periods during the last glacial interglacial transition independent calendar year chronologies are a basic requirement for the establishment of high resolution land ice teleconnections the annually laminated meerfelder maar record provides both an independent chronology established by varve counting and high resolution lithological proxy data for the period of the last glacial interglacial transition these data reveal a series of four periods of climatic deterioration coinciding with negative isotopic deviations in the grip record signal thus demonstrating the synchronicity of environment changes in western germany and temperature shifts in greenland the terrestrial data supports a further sub division of the event stratigraphy based on the grip core by introducing the cold event gi 1c2 between 13 500 and 13 400 calendar years bp multiproxy analyses reveal that the environmental response at meerfelder maar was not linear throughout the lateglacial but was modified by local processes a change in the response of the lake environment to climate deterioration was observed during sub stage gi 1b gerzensee oscillation the only event with gradual rather than abrupt transitions the two fold character of the younger dryas as seen in the grip record is more pronounced in the meerfelder maar record this lithological signal occurred with a delay of 60 years to the grip signal and has been linked to a shift in the catchment it is proposed that the trigger for this shift was a trend towards a more humid second half of the younger dryas

evidence for the presence of the vedde ash in central europe abstract as part of ongoing research to find distal tephra two lacustrine cores were analysed for the presence of volcanic ash layers not visible to the naked eye soppensee in switzerland and rotmeer in southern germany the laacher see tephra 12 900 ka bp is present as a visible layer in both sites in both cores we found a discrete tephra horizon with similar morphologies in the middle of the biostratigraphic units equivalent to the younger dryas stadial the vitreous components of these two tephra layers are geochemically identical comparison of the geochemical stratigraphical and chronological data from both sites strongly suggest that the tephra can be attributed to the icelandic vedde ash a widely distributed horizon found throughout the north atlantic and northern europe our results indicate that a precise and direct correlation between the greenland ice cores and central european sequences is now possible based on a co located tephra layer this means that there is now the potential to independently test climate synchronicity between greenland and europe as far south as the alps

cosmogenic nuclide exposure ages from the parallel roads of glen roy scotland the parallel roads of glen roy scotland are the shorelines of former ice dammed lakes created by the last glaciers to occupy the area we use surface exposure dating with cosmic ray produced 10be in quartz to provide the first numerical age control on the timing of formation of one of one of these shorelines and depositional features in glen roy four bedrock samples from the surface of the 325 m parallel road yielded a mean formation age of ca 11 5 11 9 ka this age range confirms the long held view that the parallel roads are loch lomond stadial ca 12 9 11 5 ka features the age range reflects variation in currently available cosmogenic nuclide scaling schemes and the related 10be production rates two samples from the surface of the turret fan indicate that the 260 m lake drained before ca 10 7 11 0 ka while two samples from the brunachan fan suggest that subaerial sedimentation occurred after ca 9 7 9 9 ka copyright 2009 john wiley sons ltd

induction in arbitrarily shaped oceans vi oceans of variable depth we present calculations of t he electric currents induced in a model ocean by the 24 hr sq variation the model has realistic bathymetry and represents a further step of a consistent approach to oceanic induction in which we have introduced various complexities in order of priority the solution obtained is compared with our previously published results for the case of an ocean of realistic shape and uniform depth it is found that the major shelf seas considerably modify the pattern of elect ric current circu lation in the oceans of the southern hemisphere the consistent nature of the method of matched outer and inner expansions which we have used is also discussed it seems probable that other methods not limited to finding an outer solution and consequently more complicated will at best only produce an outer solution since in practice the relatively coarse mesh necessarily used in the computation of realistic global problems precludes a fine resolution of the coastal bathymetry finally the meaning of the internal and external legendre coefficients and their relationship to sq over the oceans is briefly discussed

a spatially restricted younger dryas plateau icefield in the gaick scotland reconstruction and palaeoclimatic implications considerable research has been conducted in scotland to reconstruct younger dryas glaciers and palaeoclimatic conditions but our understanding remains incomplete in this contribution we examine the gaick a dissected plateau that extends over 520 km 2 in the central grampians scotland the extent and style of younger dryas glaciation in the gaick has been repeatedly contested although a model of extensive plateau icefield glaciation has become generally accepted this is despite well documented issues with key elements of the plateau icefield reconstruction we synthesise the results of recent geomorphological mapping in the gaick and recognise a distinct morphostratigraphic signature in the upper parts of the western catchments this differs markedly from sediment landform associations in other parts of the area and we argue this provides a strong indication of spatially restricted younger dryas 12 9 11 7 ka glaciation in the gaick our interpretation is independently supported by glacierisation threshold analysis which implies that the eastern gaick was unable to nourish younger dryas ice we therefore contest the accepted paradigm of extensive younger dryas glaciation in this area based on the geomorphological evidence and glacier surface profile modelling we reconstruct a 42 km 2 plateau icefield that yields an equilibrium line altitude of 751 46 m using this value a sea level precipitation value of 826 331 mm a 1 is inferred for the younger dryas which suggests considerably drier conditions than at present using recalculated glacier derived precipitation estimates from scotland we present regional climate analysis that corroborates arguments for a strong west east precipitation gradient across scotland

century scale variability in late summer rainfall events recorded over seven centuries in subannually laminated lacustrine sediments white pass british columbia formation of annually laminated sediments in summit lake white pass british columbia is controlled by runoff generated by snowpack and glacier melt and major rainfall events the 700 yr varve record is divided into two subannual series early and late based on sedimentological criteria and sedimentary structures within each varve a comparison of recent subannual laminae with nearby meteorological records supports the interpretation they are formed by river discharge events generated by major snow and glacier melt events and large late summer rainfall events a significant correlation exists between the late subannual thickness series and the size of the largest rainfall events in late summer the long record indicates there was an abrupt increase in the thickness and frequency of major rainfall induced sedimentary events at the end of the seventeenth century in addition the frequency of laminae generated by early runoff events also increased however early subannual varve thickness component remains statistically the same as the thickness prior to the end of the seventeenth century this suggests the change in varve thickness at this time is due to increases in major late summer rainfall frequency rather than increased sediment availability caused by regional little ice age glacier advances

seismic and electromagnetic evidence of dehydration as a free water source in the reactivated crust according to recent estimates the continental mid crust contains 35 40 per cent amphibolites heating of the crust by an underlying mantle plume for example beneath continental rifts high plateaus and areas of intraplate volcanic activity releases water dehydration of amphibole bearing rocks at depths of 20 40 km occurs mainly in the temperature range 650 700 c and this releases about 0 4 wt per cent of water seismic tomography studies of the crust in the kirgyz tien shan range where the age of the tectonic activity is less than 30 ma revealed a low velocity zone in the mid crust the velocity of p waves was 0 4 km s 1 lower than in normal crust mt sounding data in the region show the existence of a low resistivity layer with an average resistivity of about 25 m at the depth of the low velocity layer the spatial correlation of the observed anomalous layers and calculated effect of fluid phase on seismic and electric parameters of rocks suggests the presence of aqueous fluids released by the heating of the mid crust

iceberg drop dump and grounding structures from pleistocene glacio lacustrine sediments scotland abstract dropstone dump and grounding structures resulting from the melt out of debris contained in floating and grounded icebergs are described from a pleistocene ice marginal glacio lacustrine sequence in scotland dropstones display bending penetration rucking and complete rupture of stratum occurring beneath them and onlap above them with the degree of deformation varying as a function of the size shape and axial disposition of the clast and of the sediment type into which they fell dump structures are conical mounds of gravel or diamict formed by the break up and overturning of dirt laden icebergs and the consequent release of large quantities of debris to the lake floor grounding structures are caused by the grounding of icebergs the down warping of underlying lake floor se iment and the subsequent in situ melt out of contained debris to form isolated troughs of diamict

reconstruction of loch lomond stadial younger dryas glaciers on ben more coigach north west scotland and implications for reconstructing palaeoclimate using small ice masses a significant inventory of evidence exists for loch lomond stadial lls younger dryas glaciation in scotland with recent work focused on satellite icefields however studies of more marginal settings are important for assessing the influence of topoclimatic factors on glacier functioning and crucially the impact of these on glacier derived palaeoclimatic reconstructions we present systematic assessments of snowblow and avalanching contributions informed by modern analogues and test these using the first detailed palaeoglaciological reconstructions of three corrie glaciers on ben more coigach north west scotland based on morphostratigraphic principles and lithostratigraphic evidence from the region these have been attributed to the lls with the reconstructions yielding an average equilibrium line altitude ela of 328 16 m a glacier derived sea level equivalent precipitation value of 1903 178 mm a 1 is inferred for the lls suggesting wetter conditions than currently and contradicting assertions of a more arid lls climate comparison with published palaeoprecipitation estimates indicates ben more coigach does not conform to expected regional precipitation gradients we argue that these discrepancies reflect topographically enhanced snow accumulation which lowered the ela from the true climatic ela this highlights the importance of assessing the influence of topoclimatic factors when applying small glaciers in palaeoclimatic reconstructions

correlation and synchronisation of lateglacial continental sequences in northern central europe based on annually laminated lacustrine sediments abstract the present study focusses on correlation and synchronisation of weichselian lateglacial varved lake sediments from western germany meerfelder maar eifel region northern germany hamelsee lower saxony central poland lake go ci a z and eastern poland lake perespilno by using varve chronology tephrochronology palynostratigraphy and stable isotopes comparison of the several independent time scales shows that biotic and abiotic parameters respond abruptly and quasi synchronously within the errors of the different chronologies during the younger dryas preboreal transition moreover there is a consensus about the length of the younger dryas cold stage of 1100 1150 varve years in the allerod the prominent laacher see tephra 12 880 varve years bp can be used to fix floating varve chronologies the relative duration of this biozone has been determined in meerfelder maar and hamelsee at between 625 and 670 varve years in the meerfelder maar a combination of continuous varve counting and biostratigraphy has been possible for the almost entire lateglacial the comparison between continental limnic sequences and greenland ice core records should be made on the basis of independent chronologies in both archives it is more practicable to develop regional stratotypes on the continental regions instead of simply using ice cores as stratotypes for the lateglacial for terrestrial european records in this respect annually laminated lacustrine sequences have a great potential

a semi global reference model for electrical conductivity in the mid mantle beneath the north pacific region 1 one dimensional electrical conductivity structure in the mid mantle of the one fourth of the earth beneath the north pacific ocean was obtained by a semi global electromagnetic induction study electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account as a most preferred model a smooth conductivity depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km

the micromorphology of glaciolacustrine varve sediments and their use for reconstructing palaeoglaciological and palaeoenvironmental change abstract former glaciolacustrine systems are an important archive of palaeoglaciological palaeoenvironmental and palaeoclimatic change the annually laminated varved sediments that under certain conditions accumulate in former glacial lakes offer a rare opportunity to reconstruct such changes e g glacier advance and retreat cycles glacier ablation trends permafrost melt nival events at annual or even sub annual temporal resolution data of this kind are desirable for their ability to guide and test numerical model simulations of glacier dynamics and palaeoclimatic change that occur over rapid time intervals with implications for predicting future glacier response to climatic change or the effects of weather and climate events on lake sedimentation the most valuable records preserved in glaciolacustrine systems are continuous varved sequences formed in the distal parts of glacial lakes where microscale lamination structures can accumulate relatively undisturbed technological advances in the last few decades have enabled improved characterisation of glaciolacustrine varve microfacies and the precise measurement of varve thickness at the micrometre scale however unlike in cognate fields e g soil science protocols for the robust and consistent description and interpretation of glaciolacustrine varve sediments are lacking to fill this gap and to provide a resource for future studies of glaciolacustrine varved sediments this paper reviews the processes of sedimentation in glacial lake basins and presents the defining microfacies characteristics of glacial varves using a descriptive protocol that uses consistent examination of grain size sorting structure nature of contacts development of plasmic fabrics and features such as dropgrains and intraclasts within individual laminations these lamination types are then combined into lamination sets whose structures can be interpreted as glaciolacustrine varves within this framework we define five principal assemblages of glaciolacustrine varve microfacies which if clearly identified in palaeoglaciolacustrine settings enable more detailed palaeoenvironmental interpretations to be made finally we discuss the utility and complexities of reconstructing the evolution of former glacial lake systems using varve microfacies and thickness datasets

recent fault movement and palaeoseismicity in western scotland abstract field study at two locations in western scotland is described and gives evidence for fault movement and seismic activity during the late and post glacial epochs the evidence comprises levelling survey of raised marine shorelines remote sensing study of lineaments radiocarbon dating of quaternary sediment and detailed field examination of faults and fault gouge material vertical fault displacements of up to 3 m are observed on a c 10 500 year old raised marine shoreline on the isle of mull and repeated predominantly lateral movement is observed on a prominent 14 km long fault lineament active since ice retreat and as recently as c 2000 yrs b p the fault movements are located close to the edge of the area formerly covered by the loch lomond readvance ice cap 11 000 10 000 yrs b p they are considered to have been caused by rapid rates of isostatic rebound soon after deglaciation

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

revised 1 d mantle electrical conductivity structure beneath the north pacific summary the 1 d electrical conductivity model in the mid mantle beneath the northern pacific was revised in order to discuss the mean state of the mantle and to obtain a credible starting model for 3 d inversions semi global geomagnetic depth sounding gds responses obtained at 13 stations and submarine cable magnetotelluric mt responses for eight cables in a period range of 1 7 113 d were used to obtain the revised structure it is well known that surface conductivity heterogeneity due to the ocean land conductivity contrast has a large influence on the responses up to a period of 20 d the effect of surface ocean land distribution was removed by performing 3 d electromagnetic induction modelling including a surface conductivity heterogeneity distribution laid above a 1 d mantle structure the corrected responses were averaged in the logarithmic space and the resulting responses quasi 1 d response were inverted to obtain 1 d conductivity models correction of the surface heterogeneity effect requires a 1 d conductivity model and the 1 d model must be similar to the resultant 1 d model for a consistent correction we attained this by making iterations of the surface layer correction and 1 d inversion synthetic tests revealed that the iterative scheme could recover the supposed structure even for a 3 d heterogeneous mantle since electromagnetic sounding is not sensitive to the presence of a sharp discontinuity we examined three different cases of conductivity variation with depth 1 a model with no discontinuity 2 a model with two jumps at 400 and 650 km depths and 3 a model with three jumps at 400 500 and 650 km depths the conductivity of the two jump model in the transition zone is higher than the experimentally determined conductivity of dry wadsleyite and ringwoodite if the difference is entirely due to the effect of water in the transition zone then the conductivity is consistent with a water content in the region of 0 5 wt per cent however if an additional discontinuity of electrical conductivity is allowed at the 500 km depth the obtained conductivity for the upper 100 km of the transition zone is lower and can be explained by a less water content 0 1 wt per cent in wadsleyite

evidence for phase locked changes in climate between scotland and greenland during gs 1 younger dryas using micromorphology of glaciolacustrine varves from glen roy there is a current need to develop annual decadal chronologies from periods of rapid climate change in order to understand the rate and timing of climate events and identify how other proxies either lead or lag this climate forcing annually laminated or varved sediments are key proxies for understanding environmental change at such a scale this paper presents the results of microscale analysis of glaciolacustrine varve sediments from scotland and develops a new index called varve group which ranks the number of pulses of sediment observed in the summer component of the varve the varve group index is compared with data from the greenland ice core record and correspondence can be observed between the oxygen isotope records from greenland during the latter part of gs 1 and the 515 year lochaber varve group index the processes that control the number of sediment pulses into the lake basin are discussed and we examine how these factors might control both the isotopic composition of the ice cores and varve group formation it is proposed that the position of the sea ice in the north atlantic may provide such a mechanism

a 750 yr record of autumn snowfall and temperature variability and winter storminess recorded in the varved sediments of bear lake devon island arctic canada abstract the varve record from high arctic proglacial bear lake reveals a regionally coherent hydroclimatic signal as well as complexities due to changing hydroclimatic and limnologic conditions varve formation is strongly dependent on underflows that exhibit variability in strength during the past 750 yr periods with reduced underflow sedimentation and accumulation rates fail to produce varves in the distal part of the lake isolated coarse silt and sand grains occur in 80 of the varves and are interpreted to be niveo aeolian in origin coarse 500 m sand grains deposited on the lake ice by strong winter winds are notably less common since a d 1850 likely due to reduced storminess regression of the varve thickness record with meteorological records indicates high correlations with autumn september and october temperatures and total monthly snowfall these correlations are best at times when underflow activity is sufficiently strong to produce varves throughout the lake the close association with warmer temperatures and snow bearing synoptic systems moving north in baffin bay suggests that the primary climate signal in the varves is varying autumn snow pack that controls nival discharge in the following year the similarity between the other records of melt season temperature and sea ice cover and the bear lake record suggests that summer and autumn conditions were generally similar across the baffin bay region through much of the last millennium

high primary productivity and nitrogen cycling after the paleoproterozoic phosphogenic event in the aravalli supergroup india the causes of atmospheric oxygenation in the paleoproterozoic are multifaceted yet poorly understood an increase in the level of primary productivity however may have been an important factor in producing large amounts of oxygen in the atmosphere a likely environmental consequence of atmospheric oxygenation is an increased abundance of seawater nitrate which would have resulted in a fundamental change from the archean nitrogen cycle in this study we investigate these questions using the carbon and nitrogen isotope compositions of carbonaceous shales from the paleoproterozoic aravalli supergroup india the shales occur stratigraphically above one of the oldest phosphogenic events that took place around 2 0 ga shales in the phosphate domain of the jhamarkotra formation from the lower aravalli group have distinct characteristics from coeval shales in the non phosphate domain carbonaceous shales of the phosphate domain contain relatively high v and u th typical of oxygen deficient environments these shales also have a high organic content of up to 14 wt generally homogeneous 13 corg values around 29 c nwr up to 360 and a large range of 15

electromagnetic induction in the oceans and the anomalous behaviour of coastal c responses for periods up to 20 days 1 electromagnetic transfer functions at coastal sites are known to be strongly distorted by the conductivity of the seawater this ocean effect is generally considered to be small for periods greater than a few days we revise this statement by detailed and systematic model studies in the period range from 1 to 64 days with subsequent comparison of the modelled and observed electromagnetic responses the conductivity model consists of a radial symmetric 1 d section that is overlaid by a thin spherical surface shell the conductance of which is compiled using the noaa etopo topography bathymetry and map of sediment thicknesses the simulations were performed for spatial resolutions of the surface shell of 5 5 2 2 and 1 1 respectively and for two continental and oceanic underlying 1 d conductivity models the inducing source is described by the spherical harmonic p10 in dipole coordinates comparisons are made for the coastal geomagnetic observatories apia hermanus kakioka kanoya and simosato where an anomalous behaviour of the local response has been previously detected from the comparison of observed and modelled responses we conclude that peculiarities in the observed coastal responses in the period range from 1 to 20 days can be explained to a large amount by induction in the oceans we show that correction for the ocean effect results in responses that are much better interpretable by 1 d conductivity models compared to the uncorrected responses

middle and late pleistocene glacial lakes of lowland britain and the southern north sea basin focusing on lowland britain and the southern north sea basin this article reviews the sedimentary and geomorphic evidence for the main glacial lakes inferred during the middle and late pleistocene and evaluates their impacts on drainage basin development glacial lakes are best known from glaciations during marine isotope stages mis 12 6 and 2 although glacial lakes have also been inferred during mis 10 and 4 some lakes for example bosworth low level humber and the lakes of the eastern fenland margin are reconstructed from unequivocal sedimentary evidence including rhythmites and subaqueous outwash whereas others lakes for example lapworth and fenland are inferred mostly from erosional features and remain to be substantiated the largest known glacial lake developed in the southern north sea basin between an ice sheet to the north and a chalk bedrock ridge in the strait of dover area first during the anglian elsterian glaciation of mis 12 and again during the late wolstonian late saalian drenthe glaciation of mis 6 the palaeohydological impacts of lake drainage are thought to include cutting of the strait of dover as a result of catastrophic drainage from the north sea lake during mis 12 incision of a number of gorges and river valleys in england and diversion or even reversal of major rivers such as the thames and the proto soar avon system recently varve chronologies have been correlated with the greenland ice core record although caution is needed to discriminate between varves and non annual rhythmites future work on pleistocene glacial lakes needs to test chronologies of lake development by luminescence dating of glaciolacustrine sediments deposited in non ice proximal locations 1 fine grained rainout deposits and 2 wave rippled sands deposited in shallow water and to model the impacts of glacial isostasy in order to reconstruct lake extents all of this work should be based on the rigorous application of sedimentology to interpret sedimentary facies and depositional environments

10000 years of interannual sedimentation recorded in the lake nautajarvi finland clastic organic varves abstract physical properties of varves formed over the last ca 10 000 years from lake nautajarvi central southern finland provide a potential proxy record of winter precipitation and temperature via catchment runoff and erosion the seasonal scale varved data indicate that the winter severity and duration of summer growing season has changed considerably during the holocene in southern central finland periods of increased catchment erosion occurred at 7590 7530 bc 7450 7400 bc 7220 7110 bc 7000 6000 bc 5400 5200 bc 4400 4000 bc 2700 2400 bc ca 1500 bc to ad 500 and 1400 ad onwards the observed changes are likely related to severe winters conditions with high net accumulation of snow between ca 7500 bc and ad 300 whereas ad 300 onwards an increasing agricultural input is seen in the varve and pollen data periods that can be interpreted as indicating attenuated spring floods caused by milder and wetter winters appeared around 7000 bc and ad 1000 ad 1200 the latter corresponding with the last historically recorded warm interval in europe known as the medieval climate anomaly

testing the fidelity of sediment chronology comparison of varve and paleomagnetic results from holocene lake sediments from central finland abstract a careful construction of independent varve and paleomagnetic chronologies from three varved lake sediment records from central finland resulted in detailed and continuous age depth profiles cumulative varve calculation errors were estimated to be 3 for lake alimmainen savijarvi 10 295 340 varve years and 1 for lakes nautajarvi 9898 97 varve years and korttajarvi 9590 103 varve years paleomagnetic secular variation psv curves demonstrate good consistency between these sites and within a margin of varve chronology error they show similar declination and inclination features commonly described in the uk and sweden the timing of psv patterns from finnish varved sites agree well with uk curves between the present and 2000 bc and in pre 6000 bc deposits and with swedish data between the present and 5000 bc combined inclination records from three independently dated finnish varved sites possess an opportunity for accurate paleomagnetic comparisons within the margin of varve chronology errors and throughout the last 10 000 years

varve formation and the climatic record in an alpine proglacial lake calibrating annually laminated sediments against hydrological and meteorological data processes leading to the formation of varves in proglacial oeschinensee switzerland are investigated the aim is to calibrate annually laminated sediments of the last three decades against hydrological and meteorological instrumental data results from water samples and sediment traps show that the suspended sediment in the lake is mainly distributed by underflows during the time of the largest sediment input from may to mid august this leads to the deposition of the basal silt layers of the varves settling of fine grained suspension from interflows dominates sedimentation between august and october forming the final layer of fine grained material at the end of the annual deposition cycle the median grain size at the top of the varves is always below 5 m and thus defines the varve boundaries varve thickness is a function of the annual discharge of suspended load from the catchment this is supported by evidence from hydrological and meteorological data compiled for a glaciated catchment loetschen

a varve record of increased little ice age rainfall associated with volcanic activity arctic archipelago canada varved sediments from nicolay lake canadian high arctic record major summer rainfall events over the last five centuries increased incidences of summer rainfall occurred during the coldest periods of the little ice age and were strongly clustered in the years immediately following major volcanic events compari son of the summer rainfall and proxy air temperature records thus provides a fuller understanding of the nature and causes of natural climate variability in the arctic study of the synoptic conditions associated with the two most recent large summer rainfall events suggests that they are associated with the incursion of cold low pressure systems from the arctic ocean basin volcanic activity may produce atmospheric conditions more conducive to the formation of such low pressure systems which generate rainfall at low elevations and summer snowfall at higher elevations thus explaining the correlation between rainfall and summer snow accumulation recorded in ice cores from high elevation ice caps

the electrical conductivity of the oceanic upper mantle summary previous inversions of sea floor magnetotelluric mt sounding data have predicted upper mantle electrical conductivities which are more than an order of magnitude higher than laboratory measurements of the conductivity of olivine would suggest and controlled source field electromagnetic csem soundings require a lithospheric mantle conductivity of 3 x lop5 sm which is so low that the electromagnetic em coast effect would produce more anisotropy in mt soundings than is observed we address these issues by constructing an olivine mantle model for conductivity and examining the inversion of mt data from three sea floor sites and show that the incompatibilities can be largely resolved if the effects of oceans and coastlines are considered our mantle model is based on recent measurements of olivine conductivity the conductivity of tholeiite melt a thermal model for the upper mantle based on lithospheric cooling and the temperature of a a 3 olivine transition the pyrolite model of mantle petrology and conductivities derived from csem sounding we propose archie s law with exponent 2 and interconnected tubes as realistic lower and upper bounds for the effect of partial melt on rock conductivity and archie s law with exponent 1 5 as the preferred estimate the 1 d forward response of this model is not compatible with observed sea floor mt data three data sets presented by oldenburg 1981 pass a test for one dimensionality based on the size of the residuals when fit with parker s d algorithm but two of the three soundings fail a test for independence of residuals we also find that the presence of the upper mantle high conductivity zone previously inferred from these data is highly dependent on data misfit and not required when the misfit criterion is relaxed a reasonable amount re inversions of the mt data produce models which are incompatible with our petrological model of mantle conductivity however by adding an ocean with various coastlines of simple geometry to our petrological model and solving the forward 3 d problem using thin sheet analysis we predict mt responses which are distorted in a manner that is remarkably similar to the observed data

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

the effect of the oceans and sedimentary cover on global magnetovariational field distribution electromagnetic fields excited by long period geomagnetic variations were calculated for spherical earth models with the realistic inhomogeneous surface layer calculations were also carried out for the model with the double inhomogeneous layer the modelling results did not display the same level of distortions which had been observed experimentally the revealed contradiction may be explained by a possible existence of significant inhomogeneities in the earth mantle

on the electrical conductivity of the mid mantle ii delineation of heterogeneity by application of extremal inverse solutions summary long period equivalent scalar magnetotelluric impedance functions from 22 magnetic observatories distributed over the earth s surface are inverted to test the hypothesis that there exists significant lateral heterogeneity in the electrical conductivity structure of the mid mantle limited spaces of extremal models are examined and strict bounds are placed on the range of permissible models joint d inversion of combined response functions from observatory pairs proves the requirement for global heterogeneity while exploration of h layered earth model space suggests systematic regional heterogeneity indicating that enhanced upper mantle conductivity is found within the pacific basin and baikal rift zone and is absent elsewhere the results of these extremal inverse solutions are compared with the backus gilbert like schmucker inversion and a heuristic inversion

correlation of swedish glacial varves with the greenland grip oxygen isotope record a mean varve thickness curve has been constructed for a part of the swedish varve chronology from the northwestern baltic proper the mean varve thickness curve has been correlated with the delta 1

global earth structure inference and assessment summary a suite of compressional and shear phase arrival times p s pp pcp ss scs pkpab pkpbc pkpdf sksac and two sets of differential times ss s410s ss s660s are used to infer lateral variations in p and s velocity structure in the entire earth crust mantle and core volumetric heterogeneity is parametrized by 22 depth layers each of which is subdivided into a grid of cells in addition to volumetric hetero geneity we determine topography on the major internal velocity discontinuities station corrections event relocation parameters and inner core anisotropy a total of 96 300 unknowns the model parameters are estimated using an iterative lanczos algorithm to obtain a partial singular value decomposition a total of 5000 lanczos values and vectors are used to construct model parameter estimates as well as measures of model parameter resolution and covariance the lanczos resolution estimates provide lower bounds on conventional svd based measures throughout most of the mantle we find that regions beneath the continents particularly in the northern hemisphere are well resolved with the exception of africa velocity variations are moderately well resolved in that portion of the outer core lying beneath the continents velocity heterogeneity is poorly resolved in the inner core where cell dimensions are small and deviations in velocity heterogeneity trade off with variations in anisotropy variations in the uppermost mantle 2 3 per cent are correlated with surface tectonics while at greater depths high velocity variations coincide with regions of past and present subduction the high velocity anomalies extend into the lower mantle although with a reduced amplitude 0 5 1 0 per cent until the lowest mantle 2 5 per cent at the base of the outer core a large scale pattern of heterogeneity 0 8 per cent is observed slower at the poles in the inner core we infer a peak anisotropy of 2 3 per cent which varies laterally and with depth however the magnitude and distribution of the anisotropy trades off strongly with velocity heterogeneity

in situ cosmogenic exposure ages from the isle of skye northwest scotland implications for the timing of deglaciation and readvance from 15 to 11 ka we present 10 in situ cosmogenic exposure ages from two moraines on the isle of skye the strollamus medial moraine was deposited during deglaciation of the devensian ice sheet and yields a mean exposure age from five samples of 14 3 0 9 ka the moraine age indicates that a significant ice mass existed on skye at the time of a regional readvance recorded in wester ross northwest scotland taken at face value the ages suggest that deglaciation did not occur until well into greenland interstade 1 the slapin moraine represents the local limit of the loch lomond readvance llr and yields a mean exposure age from five samples of 11 5 0 7 ka which is consistent with deposition relating to the llr these ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end this scenario is considered unlikely given the nature of the climate during this period which leads us to call for a locally calibrated production rate copyright 2011 john wiley sons ltd

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

a new microstructural mapping methodology for the identification analysis and interpretation of polyphase deformation within subglacial sediments although integrated clast macro and microfabric studies have been used to provide evidence of palaeo ice flow directions to discriminate between diamictons deposited in differing sedimentary environments and to model the response of tills to subglacial deformation such studies have typically only examined the bulk fabric developed within the diamicton largely ignoring the potential for several phases of fabric development within these typically polydeformed deposits we present a new graphical method for the identification description and analysis of clast microfabrics in polydeformed tills this method utilises high resolution digital scans of orientated thin sections imported into a standard computer graphics package to measure the orientation of long axes of detrital skeleton grains included within the till these data are then used to identify the main clast microfabrics present within the till allowing the delineation of clast microfabric domains in which elongate grains share a similar preferred orientation this process leads to the identification characterisation and most importantly the interrelationships between the various generations of microfabrics the relationships between these clast microfabrics and other microstructures e g plasmic fabrics turbate structures shears folds faults etc can also be examined providing a detailed microfabric microstructural map of the thin section clast long axis orientation data collected for different parts of a thin section are plotted on a series of rose diagrams allowing the variation in clast microfabric orientation to be displayed graphically a new set of terminology for the description of clast microfabrics in tills which is based upon the system used by metamorphic petrologists is also presented three case studies of the fabrics present within subglacial sediments of pleistocene age as well as the present are used as examples of how to apply this methodology

deglaciation chronology of the galloway hills ice centre southwest scotland during the last glacial maximum the galloway hills in southwest scotland acted as a major centre of ice dispersion within the last british irish ice sheet biis six new or recalibrated 10be exposure ages for samples obtained from boulders near the former ice divide yielded uncertainty weighted mean ages of 15 15 0 72 ka lm scaling or 15 33 0 74 ka du scaling these ages indicate that the former ice dome centred over the galloway hills had almost or completely disappeared by ca 15 ka imply prior deglaciation of all of southwest scotland and refute suggestions that ice cover persisted in this area during the lateglacial interstade they strongly support recent models advocating extensive deglaciation of all areas occupied by the last biis apart from the scottish highlands prior to warming at the onset of the lateglacial interstade ca 14 7 ka three samples obtained from boulders on a large latero terminal moraine tauchers moraine near the former ice divide yielded a weighted mean age of 11 91 0 77 ka lm scaling or 12 01 0 78 ka du scaling confirming that the moraine is of loch lomond younger dryas stadial age and suggesting that the moraine was deposited 200 500 years before the end of the stade copyright 2013 john wiley sons ltd

annually resolved events of younger dryas glaciation in lochaber glen roy and glen spean western scottish highlands this paper presents the results of micromorphological analysis of laminated sediments that accumulated in ice dammed lakes in lochaber glen roy and vicinity during the younger dryas loch lomond stadial these lakes were responsible for the formation of the famous parallel roads of glen roy agassiz 1840 prominent shorelines cut into the valley sides of glen roy and adjacent valleys annually deposited varved layers which can be distinguished from other rhythmites by micromorphological examination have enabled the construction of a varve chronology which underpins the glacial history of the region the duration of the lake stands and rates of ice margin advance and retreat the lake system existed for a total of 515 a during a rise in lake levels the lowermost 260 m middle 325 m and highest 350 m lakes existed for minimal periods of 191 112 and 116 a respectively and the fall of lake levels from 350 m to 260 m took 95 years ice advance rates of between 13 4 and 41 9 m a 1 are inferred while ice retreat is estimated to have been 38 5 m a 1 a provisional correlation between the lochaber varve and grip ice core records suggests that the lakes started to form at ca 12 165 a bp in turn implying that the loch lomond readvance limits in this area were not achieved until late in the younger dryas interval a conclusion which does not accord with that based on numerical model simulations copyright 2010 john wiley sons ltd

global induction by sq and dst sources in the presence of oceans bimodal solutions for non uniform spherical surface shells above radially symmetric earth models in comparison to observations summary we pursue in this paper the following goals 1 detailed study of the ocean eiect on geomagnetic elds excited by sq and dst sources in spherical earth models the investigated period range is from 6 hr to 10 days oceans and continents form a thin shell of variable conductance above a layered deep structure allowing for leakage currents from and into the shell 2 development of an interpretation scheme for the estimation of the resistivity ol of the lithosphere 3 application of this scheme to estimate ol from a comparison of calculated and observed sq harmonics at coastal sites we conduct a number of model calculations with simpli ed hemispherical shells and with realistic shells for the world s oceans and continents deriving their variable conductance from the ocean depth at sea and assuming a uniform value of 400 s on land with inclusion of continental shelfs from these model studies we draw the following conclusions 1 variations of o l in the uppermost 100 km of the deep structure signi cantly change the vertical magnetic surface eld z near oceans 2 ocean eiects in the horizontal magnetic surface elds x and y are quite negligible on land for sq therefore radially symmetric earth models can be used to determine the external sq source eld from a spherical harmonic analysis of x and y on land 3 with realistic shell models it is possible to reproduce the anomalous coast eiect in z of sq a two step interpretation scheme is presented to estimate the resistivity ol of the lithosphere in step 1 we determine the spherical harmonic coe cients of the external sq source eld using the observed sq variations in x and y and a presumed earth model of uniform shell conductance to separate their external and internal parts in step 2 we derive model elds with various trial values of ol for a realistic surface shell excited by the external source eld from step1 we choose the most likely value of ol that for which the rms mis t between observed and calculated z variations is smallest ourobservational data are the rst four sq harmonics of the four equinoctial months of 1964 as derived from the mean daily variations of quiet days at 76 observatories z observations at 12 coastal observatories lead us to the conclusion that a global estimate of lithospheric resistivity ol is of the order of 10 000 m

glaciation of scotland during the younger dryas stadial a review considerable research effort in recent years has refined our knowledge of the landforms and sedimentary sequences generated by glaciers of the last cold episode in scotland the younger dryas and the chronology of their formation these recent advances have benefited from new technologies such as high resolution digital terrain models numerical ice sheet simulations and cosmic ray surface exposure dating this review presents a summary of recent younger dryas research in scotland particularly focusing on studies from the last two decades the findings of these investigations are compared with those of earlier workers and critically are appraised in terms of their relevance to five key aspects of younger dryas glaciation growth of the ice cap its geometry dynamics mode of decay and likely stadial climate minor differences aside the consensus view appears to favour a relatively thick but areally restricted central ice cap surrounded by satellite ice fields at its centre the ice cap was probably thickest during the first 500 years of the stadial after which it most likely thinned as the climate became increasingly arid outlet glaciers were dynamic only in marginal areas where they produced abundant moraine sequences during deglaciation but throughout much of the stadial central areas of the ice cap effected only minimal landscape modification deglaciation took place by active retreat under a rapidly warming climate overall the stadial was dominated by much colder and drier conditions than present and probably experi enced greater intra annual temperature ranges copyright 2009 john wiley sons ltd