the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

first principles prediction of fast migration channels of potassium ions in kalsi3o8 hollandite implications for high conductivity anomalies in subduction zones materials sharing the hollandite structure were widely reported as fast ionic conductors however the ionic conductivity of kalsi3o8 hollandite k hollandite which can be formed during the subduction process has not been investigated so far here first principles calculations are used to investigate the potassium ion k transport properties in k hollandite the calculated k migration barrier energy is 0 44 ev at a pressure of 10 gpa an energy quite small to block the k migration in k hollandite channels the calculated ionic conductivity of k hollandite is highly anisotropic and depends on its concentration of k vacancies about 6 k vacancies in k hollandite can lead to a higher conductivity compared to the conductivity of hydrated wadsleyite and ringwoodite in the mantle k vacancies being commonly found in many k hollandite samples with maximum vacancies over 30 the formation of k hollandite during subduction of continental or alkali rich oceanic crust can contribute to the high conductivity anomalies observed in subduction zones

unexpected uses for obsidian experimental replication and use wear residue analyses of chopping tools abstract large flaked stemmed artefacts with a morphological resemblance to axes or adzes have been recovered from stone quarries in west new britain papua new guinea but they are made from obsidian a volcanic glass generally considered too brittle for tasks demanding tough long lasting edges such as chopping wood to evaluate the potential of obsidian for percussive woodworking 11 replica obsidian tools were used as axes and adzes although breakage was common and the tools suffered extensive edge damage they were surprisingly effective as chopping tools the patterns of use wear and residue traces on the experimental tools informed the analysis of 27 archaeological artefacts which were found to have been used as axes or adzes with the addition of sawing in a few cases as these tools have not been found outside the quarries their occurrence suggests that during this period some forms of woodworking took place only where there was an abundant supply of raw material the limited spatial distribution of obsidian chopping tools raises questions about the nature of forest clearance and woodworking in this tropical environment

modeling cultural responses to volcanic disaster in the ancient jama coaque tradition coastal ecuador a case study in cultural collapse and social resilience the cultural impacts of catastrophic late pleistocene and holocene volcanism are characteristically variable throughout the world due to a wide range of factors such as magnitude of the eruptive event proximity to the eruption the geographic and ecological settings of the eruptive footprint and relative social and political complexity of the societies affected the reasons why one society succumbs to a volcanic disaster while another may recover are complex and not subject to invariant laws likewise even in cases where recovery is possible different pathways may be followed depending on a host of contingent factors in archaeological cases it is sometimes difficult to distinguish between cultural developments that may be caused by volcanic disasters and those that are merely coincidental with these events but not all volcanic eruptions lead to cultural collapse archaeological research in the jama valley of coastal ecuador has revealed evidence of three volcanic eruptions emanating from the northern ecuadorian highlands some 200 km to the east all three of which represent major stratigraphic breaks in the regional archaeological record the third of these volcanic events now thought to have occurred at 90 ad significantly affected the muchique phase 1 chiefdoms of the jama coaque tradition that occupied much of northern manabi province and like the first two eruptive events in the formative period that led to centuries long valley abandonment this eruption also resulted in valley abandonment for several centuries but it also ushered in a new ceramic phase muchique phase 2 of the jama coaque tradition and a notable change in settlement hierarchy ceramic figural sculpture evidence for warfare agricultural intensification and diversification surplus storage facilities and new forms of political complexity and chiefly authority this paper offers a model of differential human response to catastrophic volcanism that focuses attention on human resource imbalances resulting from such events and identifies a series of contingent circumstances in which complex chiefdoms may cope and even flourish in the aftermath of disaster

a remarkable pulse of large scale volcanism on new britain island papua new guinea new studies of the deposits from the latest caldera forming eruption the dk event at dakataua volcano new britain island papua new guinea help identify an intense space time concentration of large scale volcanism during the 7th century ad on new britain radiocarbon dating of charcoal from the dk deposits yields an age of 1 383 28 bp calibration of this result gives an age in the range ad 635 670 at 1 s d at about the same time two other volcanoes on new britain rabaul and witori also produced very large eruptions very high acidity levels in ice cores from antarctica and greenland at ad 639 and ad 640 respectively may be linked to either or both of the dakataua and rabaul eruptions another ice core high acidity level at ad 692 may be associated with the witori eruption significant volcanic risk within the new britain region is indicated by its late cenozoic history of relatively frequent large scale eruptions from as many as 8 caldera systems within an arc parallel zone about 380 km long over the last 20 ka the return period for major vei 5 eruptions in this region was about 1 0 ka and individually high frequencies of major eruptive activity were experienced at witori and rabaul the relatively short return period for major eruptions in the region would tend to increase the chance that such events could cluster in time

integrating phytoliths within use wear residue studies of stone tools abstract analyses of phytolith assemblages extracted from residues on obsidian artefacts and from the surrounding soil matrix of two sites in papua new guinea address two important methodological issues first multivariate analysis of phytolith assemblages extracted from the edges of stone artefacts from soil directly in contact with the artefact and from soil derived from the same archaeological context demonstrates the integrity of phytolith residues second reconstructions of tool use based on the analysis of phytoliths are compared with results from an independent use wear residue study the interpretation of phytolith assemblage variability enhances and strengthens the use wear residue results finally integrating the phytolith data within the broader use wear residue study produces significant new findings about changes in obsidian tool use in prehistoric papua new guinea

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

continental scale deep electrical resistivity structure beneath china abstract electrical resistivity structure in the deep earth can provide important information and constraints on regional geodynamics especially in regions with complex tectonics and geodynamical processes in this study we image the electrical resistivity structure in the depth range of 350 1200 km beneath china by inverting the frequency dependent ratios of geomagnetic field components at a relatively dense network of geomagnetic observatories very long time series of hourly mean values of the three component geomagnetic field from 45 geomagnetic observatories are collected and processed to derive robust ratios of the geomagnetic components which are then converted to the apparent resistivities and impedance phases in the period range of 5 3 113 8 days and used in 1 d occam inversion with smoothing constraint and the method to obtain the electrical resistivity profiles and delta function models at individual observatories 1 d electrical resistivity models suggest that low electrical resistivity structure exists in the mantle transition zone beneath eastern china high water content in the mantle minerals due to the subduction of seismically fast pacific slab is proposed as the main reason for the low electrical resistivity beneath eastern china our results provide further evidence that the western front of the subducting pacific slab in the mantle transition zone roughly coincides with the abrupt change in the surface topography in eastern china

on the heterogeneous electrical conductivity structure of the earth s mantle with implications for transition zone water content 1 we have investigated the lateral variations in mantle electrical conductivity structure using electromagnetic sounding data for this purpose we used very long time series up to 51 years of geomagnetic observatory data at six locations encompassing different geological settings to compute response functions that cover the broadest possible frequency range 3 9 to 95 2 days furstenfeldbruck fur europe hermanus her south africa langzhou lzh china alice springs asp australia tucson tuc united states north america and honolulu hon united states north pacific we inverted the response functions beneath each observatory for a local radial conductivity profile using a stochastic sampling algorithm specifically we found significant lateral variations in conductivity throughout the mantle with resolution limited to the depth range 500 1200 km at 600 km depth conductivity varies between 0 1 and 0 4 s m and increases to 1 3 2 0 s m at 800 km depth beneath all stations except her 0 5 s m at 900 km depth conductivity increases further to 1 4 2 4 s m with her hon and asp being most conductive this trend persists to a depth of 1200 km comparison with conductivity profiles constructed from laboratory measurements of mantle mineral conductivities and models of earth s mantle composition and thermal state reveal that significant thermochemical variations are at the origin of the observed heterogeneities in mantle conductivity found here because of the somewhat large error bounds on sampled conductivity profiles and the reduced sensitivity of the electromagnetic sounding data above 500 km depth constraints on transition zone water content are less conclusive although h2o contents 0 5 wt in the midtransition zone appear less likely

were deforming subglacial beds beneath past ice sheets really widespread abstract the concept of widespread large strain deformation of subglacial unconsolidated unfrozen sediments during pleistocene glaciations has inconsistencies in the geological record numerous properties of tills and related sediments are difficult to reconcile with pervasive strains as predicted by the deforming bed theory while accepting glacier bed deformation as a geological process occurring under certain circumstances we propose that it was much less widespread than believed by some instead we believe that basal sliding and englacial transport are major ice movement and debris transport mechanisms

global induction and the spatial structure of mid latitude geomagnetic variations summary a pre requisite for more precise estimates of the electromagnetic response of the earth is a better knowledge of the origin and spatial structure of geomagnetic time variations with periods of a few hours to several years the period range from four hours to four days is particularly crucial for constraining upper mantle conductivity models but is difficult to analyse because of overlapping contributions from current systems with different spatial scales a period band centred on two days has been isolated from two years of hourly mean values recorded at up to 130 observatories plots of the coherence between pairs of records of the same component of the field at different observatories as a function of the station separation prove to be a valuable diagnostic tool they show that two groups of sources contribute to this part of the spectrum one group has a spatial scale in excess of 10 000 km dominates the geomagnetic north xm component but produces no east ym component it can be satisfactorily modelled by a p01 spherical harmonic and must be generated by fluctuations in the symmetric magnetospheric ring current the spatial coherence of the second group falls to zero in a distance of 5000 7000 km and can be predicted by a stochastic source model for which the autocovariance scale length is 7000 km the spatial structure of the two groups is further investigated using the principal component technique of egbert booker 1989 the spectrum is dominated by the largest eigenvalue and the eigenfunctions corresponding to this mode show the expected p01 source behaviour the modes which correspond to the next largest eigenvalues are organized into foci approximately 10 000 km across the vertical fields associated with these modes are of low amplitude at mid latitudes but increase steeply beyond 50d estimates of the p01 response based upon the horizontal and vertical fields recorded at a single station will be biased by the contribution from the higher order modes the magnetic observatory network is incapable of describing them properly on a global basis and only the european subarray is sufficiently dense to form locally valid response estimates

3 d modelling and analysis of dst c responses in the north pacific ocean region revisited summary during the last decade a number of one dimensional 1 d conductivity profiles have been constructed for the upper and mid mantle of the north pacific ocean region these profiles differ significantly and from our point of view it is still unclear which profile is the best candidate for the upper and mid mantle conductivity reference model for this region keeping the differences in mind and inspired by recent findings that the ocean effect is a major contributor to the anomalous behaviour of c responses up to the period of 20 days especially at coastal observatories the goal of this paper has been three fold 1 to understand on the basis of systematic model studies using 3 d ocean models which of the published 1 d upper and mid mantle profiles is in best agreement with the available observations 2 to try to reduce the misfit between the observed and modelled responses by using dense grids in modelling by considering 3 d models which include not only an inhomogeneous surface layer but also inhomogeneous deeper structures 3 to derive an alternative 1 d upper and mid mantle section for the north pacific ocean by carefully selecting the data for interpretation and by using 3 d models that are as realistic and detailed as possible in order to perform the simulations using realistic 3 d models on a routine basis a novel 3 d spherical forward solution has been elaborated in this paper the solution combines the modified iterative dissipative method with a conjugate gradient iteration and allows one to compute efficiently the electromagnetic fields in full 3 d spherical models with very high lateral contrasts of conductivity and for very dense grids during the 3 d simulations a systematic shift of observed c responses at honolulu compared with those at other observatories was detected the reason for this shift is still unclear even if a very detailed grid of 0 3 0 3 is used the 3 d simulations using a model of the inhomogeneous surface has no notable ocean effect to c responses at this site an attempt has been made to reduce the misfit between observed and modelled c responses by incorporating a 3 d model with inhomogeneous lithosphere and upper mantle however this has resulted only in a slight change in responses the main conclusion drawn from our 3 d model studies is that there exists a significant disagreement between observed and 3 d modelled c responses if the published 1 d sections with conducting uppermost 400 km are considered as the upper and mid mantle sections our 3 d simulations and reinterpretation of the data also confirm the recent finding that the upper and mid mantle beneath north pacific ocean in the depth range down to 400 km is much more resistive than hitherto assumed

three dimensional imaging of electrical conductivity in the mantle transition zone beneath the north pacific ocean by a semi global induction study abstract the three dimensional 3 d electrical conductivity distribution in and around the mantle transition zone mtz beneath the north pacific is imaged by inverting revised geomagnetic responses at 13 geomagnetic observatories and cable responses of 8 long baseline submarine cables in the area two one dimensional 1 d models representing the average structure beneath the north pacific were employed as the reference and initial models for the 3 d conductivity inversions the features in the revised semi global conductivity model in the mtz are 1 a high conductivity anomaly beneath the philippine sea 2 a high conductivity anomaly beneath the hawaiian islands and 3 a low conductivity anomaly beneath and in the vicinity of northern japan arrhenius plots of the conductivity and temperature estimated from global seismic tomography models indicate that the anomalies in the mtz beneath northern japan and most areas under hawaii can be explained mainly by the temperature effect but that the conductivity beneath the philippine sea requires an additional cause to explain the higher conductivity if the cause is the effect of water then the present result suggests high water content of 1 wt or more throughout the mtz beneath the philippine sea

bounded influence magnetotelluric response function estimation author posting blackwell 2004 this article is posted here by permission of blackwell for personal use not for redistribution the definitive version was published in geophysical journal international 157 2004 988 1006 doi 10 1111 j 1365 246x 2004 02203 x

how a wet tropical rainforest copes with repeated volcanic destruction the holocene period for the province of west new britain papua new guinea is characterised by periodic catastrophic volcanism the region is mantled in dense wet tropical rainforest and has been occupied by people since the pleistocene analyses of peat from two nearby sites within a lowland rainforest environment provide us with a macro level landscape account of the periodic destruction and recovery of the coastal forests during seven periods of volcanic activity in the latter part 2900 yr ago to present of the holocene radiocarbon dating shows the very close correlation of the peat and tephra layers at both sites yet the pollen analysis reveals different vegetation communities these initial results allow us to begin identifying the processes of recovery and to recognise different ecological pressures placed on vegetation at these neighbouring sites evidence of hydrological changes are observed beginning with a marine incursion recorded at garu site 3 1360 14 c yr b p the distinct differences in the vegetation re establishment and community regeneration rates suggest the greater level of disturbance at garu site 1 could be related to the depth of the ashfall although the proximity of a known human settlement may also be a contributing factor of note palynologically we found that the fern spore flora is particularly rich and believe it will be useful for ecological interpretation d 2005 university of washington all rights reserved

starch grains and environmental reconstruction a modern test case from west new britain papua new guinea the analysis of starch grains preserved in sediments as a technique for palaeoenvironmental reconstruction is an important new technique but the limits of inference using this methodology still need to be assessed a morphological classification of starches extracted from topsoils collected from a range of modern environments in the humid tropical region of papua new guinea was therefore conducted to see if discrimination among plots with different vegetation could be achieved using an assemblage based approach starch grains initially classified into morphological categories and re organized into groups according to size shape frequency distributions were grouped using principal components analysis the results correctly identified different types of human land use and provided good discrimination between gardens and forest these preliminary results show that past human land use can be satisfactorily reconstructed using multivariate analysis of starch grain assemblages with only data on size and morphology to characterize the grains the findings of the starch study compared favourably with a phytolith analysis of material from the same locations although the two microfossils target different plant groups whereas phytoliths discriminate among different levels of disturbance starch grains can add information about specific site function an important consideration especially for regions where plant staples are typically high starch producers combining starch grains and phytoliths in future studies will enhance the accuracy of palaeoenvironmental reconstructions

on the vertical gradient and associated heterogeneity in mantle electrical conductivity abstract equivalent scalar magnetotelluric response functions obtained from the robust analysis of geomagnetic field daily mean values at 16 magnetic observatories have been systematically inverted data from these sites were found to contain sufficient one dimensional 1 d data consistent with required source field assumptions for meaningful interpretation and were also found to have acceptably well bounded response function confidence limits previous work is reviewed which indicates that significant lateral heterogeneity in mantle conductivity structure is required by the data and that most of these data are adequately modeled by a series of simple two layered earth models with a conductivity jump at depths of 500 1000 km regional variations in upper mantle conductivity have previously been suggested by systematic inversion using the h algorithm these features are examined in the restricted model space of conductance delta functions the statistical significance of these variations is also investigated new evidence is found here for the coast effect at very long periods as well as related evidence for the presence of electrically conductive zones in the upper mantle beneath the pacific ocean semi norm minimization inversion techniques are applied to directly place strong constraints on the sharpness of the vertical conductivity gradient in the mid mantle the mid mantle conductivity jump is required to be abrupt with values beneath this mid mantle transition zone of o 1 s m 1 at all sites

mantle transition zone beneath a normal seafloor in the northwestern pacific electrical conductivity seismic thickness and water content abstract we conducted a joint electromagnetic em and seismic experiment to reveal the mantle structure beneath a normal seafloor at 130 145 ma in the northwestern pacific where the seafloor is relatively flat and the underlying mantle is expected to be normal free from tectonic perturbations in the experiment we deployed state of the art instruments in two arrays from 2010 2015 here we report the result of analyses of the em and seismic data for investigating the mantle transition zone mtz structure the em data analysis revealed that an electrical conductivity structure below both arrays was approximated by an average 1 d model of the north pacific and showed a possible downward increase in conductivity at the top of the mtz from the p wave receiver function analysis perturbations in the mtz thickness from a global average were estimated to be 20 km and 2 km below the northern and southern arrays respectively from which temperature profiles in the mtz below these two arrays were then estimated we jointly interpreted the profiles of electrical conductivity and thus estimated temperature with reference to the experimental values of the effects of water on the electrical conductivities of mtz minerals wadsleyite and ringwoodite from mineral physics the upper bound of the water content below the northern array was determined to be 0 4 wt or 0 04 wt depending on different results of mineral physics and that below the southern array was determined to be slightly smaller the lower bound of the water content was not constrained by our data our results indicate that the mtz beneath the normal seafloor in the northwestern pacific is drier than subduction zones and may be a water poor region in a plum pudding mantle model

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

facies architecture within a regional glaciolacustrine basin copper river alaska abstract this paper defines the principal architectural elements present within the pleistocene glaciolacustrine basin fill of the copper river basin in alaska the copper river drains an intermontane basin via a single deeply incised trench through the chugach mountains to the gulf of alaska this trench was blocked by ice during the last glacial cycle and a large ice dammed lake referred to as lake atna filled much of the copper basin facies analysis within the basin floor allows a series of associations to be defined consistent with the basinward transport of sediment deposited along calving ice margins and at the basin edge basinward transport involves a continuum of gravity driven processes including slumping cohesive debris flow hyperconcentrated concentrated density flows and turbidity currents this basinward transport results in the deposition of a series of subaqueous fans of which two main types are recognised 1 large stratified basin floor fans which extend over at least 5 km and are exposed in the basin centre these fans are composed of multiple lobes incised by large mega channels giving fan architectures that are dominated by horizontal strata and large cross cutting channel fills individual lobes and channel fills consist of combinations of diamict derived from iceberg rainout and the ice marginal release of subglacial sediment multiple units of fining upward gravels which grade vertically into parallel laminated and rippled fine sands and silts deposited by a range of density flows and currents derived from the subaqueous discharge of meltwater and rhythmites grading vertically into diamicts deposited from a range of sediment density flows re mobilising sediment deposited by either iceberg rainout or the ice marginal release of sediment 2 small complex proximal fans which extend over less than 2 km and are exposed in the southern part of the basin these fans are composed of coalescing and prograding lobes of diamict and gravel deposited both directly by subaqueous meltwater and from sediment density flows these lobes are cross cut by a range of sand and gravel filled troughs and channels cut by subaqueous outwash and either overlie or are overlain by horizontal sheets of gravel and diamict deposited from a range of sediment density flows the fans are therefore characterised by a complex and laterally variable facies architecture water depth proglacial topography stability of meltwater portals and sediment supply may all be important in determining the type of subaqueous fan present at any one location we suggest that the copper river basin fill is dominated by packages of sediment containing multiple subaqueous fans with individual fans separated by units of diamict each sediment package is in turn separated from the next by a palaeo landsurface shaped by interstadial interglacial fluvial processes and by volcanic debris flows

interactions between human activity volcanic eruptions and vegetation during the holocene at garua and numundo west new britain png this paper reviews recent fossil phytolith analysis from wet tropical west new britain papua new guinea the holocene vegetation has been influenced by spatially and temporally diverse patterns of both prehistoric human settlement and catastrophic volcanic events we have hypothesized different landscape responses and recovery pathways to events during the last six millennia phytolith sequences on the coastal lowlands the willaumez peninsula and nearby island of garua provide details of vegetational change and human interactions at different landscape scales since c 5900 cal yr b p during this period four major volcanic eruptions c 5900 3600 1700 and 1400 cal yr b p have disrupted the landscape the evidence provides detailed descriptions of temporal and spatial patterning in the impacts and changes in the vegetation in particular vegetation responded differently from one event to another reflecting both forest recovery from seed bank and shooting and the influence of prehistoric people on recovering vegetation furthermore after some events landscape recovery was moderately uniform while after others there was considerable landscape partitioning although these differences largely relate to airfall tephra type distribution and magnitude the partitioning is more strongly influenced by human activity

remote sensing of hydrogen in earth s mantle hydrogen1 in earth s interior is known to play a key role in a number of processes consequently inferring the distribution of hydrogen is a critical step in our study of dynamics and evolution of earth usually hydrogen distribution is inferred from two types of samples at the surface first a magma may contain hydrogen water and under some conditions the water content of the magma can be quenched upon cooling in these cases measurements of the water content of the magma provide us with some constraints on the hydrogen water content of the source region if we know the partitioning of hydrogen between magmas and the source rocks and the degree of melting second hydrogen content of some xenoliths transported by magma can be measured they provide a direct clue as to the hydrogen content in a region from which a xenolith has been carried however these direct petrologic approaches have two major problems firstly the sampling is limited by the distribution of volcanoes and even if there are volcanoes that carry rocks from earth s interior the depth extent that volcanoes sample rocks is limited usually 200 km secondly there is no guarantee that the hydrogen content that one measures on these samples actually represents the hydrogen content in a region where these samples came from for example hydrogen is known to diffuse very easily so hydrogen dissolved in minerals could diffuse out during the transport of a rock or conversely a piece of rock may acquire extra hydrogen during its ascent also hydrogen atoms dissolved in minerals may precipitate in the mineral to form fluid inclusions or micro scale hydrous minerals in summary the direct method to infer the distribution of hydrogen from rock samples has major limitations and an alternative approach i e remote sensing hydrogen content from geophysical

till as a glacial tectomict its internal architecture and the development of a typing method for till differentiation abstract till has been studied for over a century yet still a clear understanding of the mechanics of deposition and or emplacement of till eludes us tills in the past have been generally subdivided into sediments formed in various sub environments of the glacial system as such it has been generally agreed that tills can be separated in terms of these types based on various attributes such as clast fabric increasingly such separation into various sub types of till has become however highly debatable and tenuous based upon the use of micromorphology and a greater in depth appreciation of the internal architecture of till it has become apparent that previously established classifications of till are erroneous micromorphology reveals that deposition and or emplacement of tills is a complex tectonic process such that lodgement melt out and flow tills as previously defined do not appear to exist rather a new term better describes tills as glacial tectomicts by using micromorphology in establishing the presence of sets of microstructures a statistical method is introduced that permits differentiation of tills from other diamictons the implications for this new understanding of tills allied to statistical typing is considerable in terms of till formation glacial stratigraphy and understanding glacial environments in terms of stress histories porewater transmission subglacial deformation mechanics till rheological phase changes and the timeline of till formation

electrical conductivity imaging of the philippine sea upper mantle using seafloor magnetotelluric data abstract we performed a three year seafloor electromagnetic survey in the philippine sea including the western edge of the pacific ocean to image electrical features of a deep mantle slab stagnating in the transition zone and the surrounding mantle in three dimensions 3 d the project iterated one year deployment of ocean bottom electromagnetometers obems using a total of 37 instruments installed at 18 sites the data obtained have been analyzed in the order of their recovery based on a magnetotelluric mt method in this study we attempt to obtain a one dimensional 1 d electrical conductivity model beneath the philippine sea and the pacific region separately that can be used as a reference model in the first step toward the 3 d analysis the resultant 1 d models show three main features 1 the conductivity in the shallower 200 km of the upper mantle depths of the two regions contrasts sharply which is qualitatively consistent with the large difference in lithospheric age 2 the conductivity at 200 300 km depth in both regions is more or less the same at approximately 0 3 s m 1 3 the conductivity just below 400 km depth is higher for the philippine sea mantle than for the pacific mantle the conductivity structure can be interpreted in terms of the thermal structure mantle hydration and existence of partial melt using experimental results for the conductivity of mantle minerals if the conductivity is interpreted simply as the effect of temperature the mantle beneath the philippine sea could be hotter than the dry solidus of mantle peridotite and thus partially molten however beneath the pacific region the present analysis suggests that the partial melting is not required under the assumed peridotitic composition even if we consider mantle hydration

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

global 3 d imaging of mantle conductivity based on inversion of observatory c responses ii data analysis and results summary the global 3 d electrical conductivity distribution in the mantle in the depth range between 400 and 1600 km is imaged by inverting c responses estimated on a global net of geomagnetic observatories very long time series up to 51 years 1957 2007 of hourly means of three components of the geomagnetic field from 281 geomagnetic observatories are collected and analysed special attention is given to data processing in order to obtain unbiased c responses with trustworthy estimates of experimental errors in the period range from 2 9 to 104 2 d after careful inspection of the obtained c responses the data from 119 observatories are chosen for the further analysis squared coherency is used as a main quality indicator to detect and then to exclude from consideration observatories with a large noise to signal ratio during this analysis we found that along with the c responses from high latitude observatories geomagnetic latitudes higher than 58 the c responses from all low latitude observatories geomagnetic latitudes below 11 also have very low squared coherencies and thus cannot be used for global induction studies we found that the c responses from the selected 119 mid latitude observatories show a huge variability both in real and imaginary parts and we investigated to what extent the ocean effect can explain such a scatter by performing the systematic model calculations we conclude that 1 the variability due to the ocean effect is substantial especially at shorter periods and it is seen for periods up to 40 d or so 2 the imaginary part of the c responses is to a larger extent influenced by the oceans 3 two types of anomalous c response behaviour associated with the ocean effect can be distinguished 4 to accurately reproduce the ocean effect a lateral resolution of 1 1 of the conductance distribution is needed and 5 the ocean effect alone does not explain the whole variability of the observed c responses we also detected that part of the variability in the real part of the c responses is due to the auroral effect in addition we discovered that the auroral effect in the c responses reveals strong longitudinal variability at least in the northern hemisphere europe appears to be the region with smallest degree of distortion compared with north america and northern asia we found that the imaginary part of the c responses is weakly affected by the auroral source thus confirming the fact that in the considered period range the electromagnetic em induction from the auroral electrojet is small assuming weak dependence of the auroral signals on the earth s conductivity at considered periods and longitudinal variability of the auroral effect we developed a scheme to correct the experimental c responses for this effect with these developments and findings in mind we performed a number of regularized 3 d inversions of our experimental data in order to detect robust features in the recovered 3 d conductivity images although differing in details all our 3 d inversions reveal a substantial level of lateral heterogeneity in the mantle at the depths between 410 and 1600 km conductivity values vary laterally by more than one order of magnitude between resistive and conductive regions the maximum lateral variations of the conductivity have been detected in the layer at depths between 670 and 900 km by comparing our global 3 d results with the results of independent global and semi global 3 d conductivity studies we conclude that 3 d conductivity mantle models produced so far are preliminary as different groups obtain disparate results thus complicating quantitative comparison with seismic tomography or and geodynamic models in spite of this our 3 d em study and most other 3 d em studies reveal at least two robust features reduced conductivity beneath southern europe and northern africa and enhanced conductivity in northeastern china

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

changes in the west antarctic ice sheet since 1963 from declassified satellite photography comparison of declassified satellite photography taken in 1963 with more recent satellite imagery reveals that large changes have occurred in the region where an active ice stream enters the ross ice shelf ice stream b has widened by 4 kilometers at a rate much faster than suggested by models and has decreased in speed by 50 percent the ice ridge between ice streams b and c has eroded 14 kilometers these changes along with changes in the crevassing around crary ice rise imply that this region s velocity field shifted during this century

tearing of stagnant slab subducted slabs of oceanic lithosphere below the western pacific tend to be stagnant in the transition zone with poorly known mechanical properties typical examples are the izu bonin and japan slabs that meet each other to form a cusplike junction beneath southwest japan here we show that these two slabs are torn apart at their junction when they bend to flatten over the 660 kilometer discontinuity as is expected from a simple geometric argument we present three lines of evidence for this ongoing slab tear

a major ice drainage pathway of the last british irish ice sheet the tyne gap northern england the tyne gap is a wide pass situated between the scottish southern uplands and the english pennines that connects western and eastern england it was a major ice flow drainage pathway of the last british irish ice sheet this study presents new glacial geomorphological and sedimentological data from the tyne gap region that has allowed detailed reconstructions of palaeo ice flow dynamics during the late devensian marine isotope stage 2 mapped lineations reveal a complex palimpsest pattern which shows that ice flow was subject to multiple switches in direction these are summarised into three major ice flow phases stage i was characterised by convergent lake district and scottish ice that flowed east through the tyne gap as a topographically controlled ice stream this ice stream was identified from glacial geomorphological evidence in the form of convergent bedforms streamlined subglacial bedforms and evidence for deformable bed conditions stage ii involved northerly migration of the solway firth ice divide back into the southern uplands causing the easterly flow of ice to be weakened and resulting in southeasterly flow of ice down the north tyne valley and stage iii was characterised by strong drawdown of ice into the irish sea ice basin thus starving the tyne gap of ice and causing progressive ice sheet retreat westwards back across the watershed prior to ice stagnation copyright 2009 john wiley sons ltd

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

radiocarbon constraints on the age of the maximum advance of the british irish ice sheet in the celtic sea reconstructions of the british irish ice sheet biis during the last glacial maximum lgm in the celtic sea and southern ireland have been hampered by a paucity of well dated stratigraphic records as a result the timing of the last advance of the largest outlet of the biis the irish sea ice stream to its maximum limit in the celtic sea has been variously proposed as being pre last glaciation early devensian and lgm the irish sea till was deposited by the irish sea ice stream during its last advance into the celtic sea we present 26 stratigraphically well constrained new ams radiocarbon dates on glacially transported marine shells from the irish sea till in southern ireland which constrain the maximum age of this advance the youngest of these dates indicate that the biis advanced to its overall maximum limit in the celtic sea after 26 000 20 000 14c yr bp thus during the last glaciation the most extensive phase of biis growth therefore appears to have occurred during the lgm at least along the celtic sea and irish margins these data further demonstrate that the uppermost inland glacial tills from the area of supposed older drift in southern ireland a region previously regarded as having been unglaciated during the lgm also date from the last glaciation thus most of southern ireland was ice covered at the lgm advance of the biis to its maximum southern limit in the celtic sea may have been a short lived glaciodynamic response facilitated by subglacial bed conditions rather than a steady state response to climate forcing alone

a geophysical perspective on mantle water content and melting inverting electromagnetic sounding data using laboratory based electrical conductivity profiles abstract this paper applies electromagnetic sounding methods for earth s mantle to constrain its thermal state chemical composition and water content we consider long period inductive response functions in the form of c responses from four stations distributed across the earth europe north america asia and australia covering a period range from 3 9 to 95 2 days and sensitivity to 1200 km depth we invert c responses directly for thermo chemical state using a self consistent thermodynamic method that computes phase equilibria as functions of pressure temperature and composition in the na 2 o cao feo mgo al 2 o 3 sio 2 model system computed mineral modes are combined with recent laboratory based electrical conductivity models from independent experimental research groups yoshino 2010 and karato 2011 to compute bulk conductivity structure beneath each of the four stations from which c responses are estimated to reliably allocate water between the various mineral phases we include laboratory measured water partition coefficients for major upper mantle and transition zone minerals this scheme is interfaced with a sampling based algorithm to solve the resulting non linear inverse problem this approach has two advantages 1 it anchors temperatures composition electrical conductivities and discontinuities that are in laboratory based forward models and 2 at the same time it permits the use of geophysical inverse methods to optimize conductivity profiles to match geophysical data the results show lateral variations in upper mantle temperatures beneath the four stations that appear to persist throughout the upper mantle and parts of the transition zone calculated mantle temperatures at 410 and 660 km depth lie in the range 1250 1650 c and 1500 1750 c respectively and generally agree with the experimentally determined temperatures at which the measured phase reactions olivine spinel and spinel ferropericlase perovskite occur the retrieved conductivity structures beneath the various stations tend to follow trends observed for temperature with the strongest lateral variations in the uppermost mantle for depths 300 km conductivities appear to depend less on the particular conductivity database conductivities at 410 km and at 660 km depth are found to agree overall with purely geophysically derived global and semi global one dimensional conductivity models both electrical conductivity databases point to 2 o in the upper mantle for transition zone minerals results from the laboratory database of yoshino 2010 suggest that a much higher water content up to 2 wt h 2 o is required than in the other database karato 2011 which favors a relatively dry transition zone 2 o incorporating laboratory measurements of hydrous silicate melting relations and available conductivity data allows us to consider the possibility of hydration melting and a high conductivity melt layer above the 410 km discontinuity the latter appears to be 1 regionally localized and 2 principally a feature from the yoshino 2010 database further there is evidence of lateral heterogeneity the mantle beneath southwestern north america and central china appears wetter than that beneath central europe or australia

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

natural and human impacts in a 35 000 year vegetation history in central new britain papua new guinea abstract phytoliths and micro charcoal from the yombon airstrip archaeological site in central new britain papua new guinea provide the longest vegetation history record yet available for the new guinea islands the record begins about 35 kya with the first evidence for human presence at the site and with the exception of the last glacial maximum period is continuous to the present three other sites provide supplementary evidence including plant macro remains from the early holocene onwards the record is punctuated by a series of volcanic events which are reflected in the vegetation record by alternating frequencies of closed forest and regrowth elements micro charcoal is present from the oldest levels and fluctuates in frequency throughout the sequence increasing substantially from the terminal pleistocene early holocene onwards this coincides with the first appearance of panicoid grasses and a range of potential cultivars including bananas and saccharum increased levels of burning coinciding with the appearance of potential plant cultivars may indicate shifts in plant food production leading to cultivation from the early holocene onwards this compares favourably with previously reported evidence from garua island off the north coast of new britain the combination of trends in burning vegetation clearance and appearance of potential cultivars on new britain appears to parallel changes in the papua new guinea highlands at a similar time and suggests regional similarities in subsistence and vegetation management practices from before the lgm onwards further studies are needed to clarify the timing and extent of these shifts across the region and to provide a vegetation picture for the period before human colonisation of new britain

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

the volcanic environment for 40 000 years of human occupation on the willaumez isthmus west new britain papua new guinea abstract the stratigraphic sequence of 22 tephra beds and their associated paleosols at two sites selected from our studies in west new britain papua new guinea provide the essential environmental background for understanding human responses to c 40 ka years of volcanic activity lithology grain size and mineralogy of the tephras interpreted for the first time elucidate the varying volcanic provenance especially of the pleistocene beds and the environmental conditions which former inhabitants experienced this sequence provides an important long term record of how humans coped with volcanic adversity in papua new guinea the stratigraphic record contains abundant evidence for human settlement during the intervals between volcanic eruptions following plinian and subplinian eruptions people abandoned the region for significant periods of time in some cases these cataclysmic events caused major cultural disasters characterised by local population extinction and loss of some significant types of cultural behaviour despite the punctuated record of settlement and changes in material culture over the long term human populations found effective ways to maintain themselves within an active volcanic environment key responses included persistence of mobile and flexible settlement patterns planned and staged uses of raw materials social exchange and increasing levels of landscape management

social resilience and long term adaptation to volcanic disasters the archaeology of continuity and innovation in the willaumez peninsula papua new guinea abstract a review of archaeological research on the impacts of multiple volcanic events in the willaumez peninsula papua new guinea during the past 40 000 years demonstrates that disaster studies in archaeology would benefit from considering resilience and innovation in addition to the more common emphasis on vulnerability often glossed as collapse when analytical time frames are extended beyond the immediate environmental impacts continuity in cultural practices is often observed the long term exchange of obsidian in the willaumez peninsula may have been adaptive because the resulting social ties enabled impacted populations to find refuge with other communities in contrast a series of novelties were much less resilient a hypothetical reconstruction of cultural responses to the high magnitude w k2 volcanic event is used to illustrate how disasters can provide opportunities for innovative behavior leading to culture change

supercritical fluid in the mantle transition zone deduced from h d interdiffusion of wadsleyite abstract knowledge of the distribution of water in the earth s mantle is key to understanding the mantle convection and geochemical evolution of the earth as wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge where descending slab stagnates at the transition zone however there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite here we report the hydrogen self diffusion coefficient obtained from h d interdiffusion experiments in wadsleyite single crystal couples our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone in contrast the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales this phenomenon provides an alternative explanation for both the high conductivity and seismic velocity anomalies observed in the mantle wedge at the transition zone depth

a joint interpretation of electromagnetic and seismic tomography models suggests the mantle transition zone below europe is dry abstract the three dimensional 3d electrical conductivity distribution in the mantle transition zone mtz below europe is resolved by directly inverting geomagnetic response functions from 12 selected european observatories comparison of the conductivity image with the results of global seismic tomography reveals a good correlation between low conductivity and high velocity anomalies at depths of 400 700 km beneath the mediterranean subduction zone in central europe interpretation of the 3d conductivity model combined with seismic tomography indicates that the european mtz is drier than the mtz beneath the western pacific subduction zone even though the subducted slab material is stagnating similarly in both regions

palynomorph evidence for tropical climate stability in the gulf of papua papua new guinea over the latest marine transgression and highstand 14 500 years bp to today abstract three sediment cores mv 41 mv 46 and md 50 from the gulf of papua gop papua new guinea were analyzed to assess changes in climatic oceanographic and sedimentological conditions over the last 14 5 kyr palynomorphs which were isolated from sediment core samples were collected at approximately 0 5 m intervals using a strong acid and oxidant md 50 non oxidant mv 41 mv 46 procedure radiocarbon 14c stable isotope geochronology magnetic susceptibility stable isotope analysis md 50 only oxygen 18 18o and carbon 13 13c and clay mineral maturity analysis were also completed for each core palynological data indicate that climatic conditions at sea level have remained warm wet and stable for the past 14 5 kyr with sea surface temperatures in the gop above 14 c potential decreases in vegetative cover marked the younger dryas interval 12 5 11 5 kyr bp as indicated by reduced pollen and spore recovery the end of the latest marine transgression and the subsequent return to eustatic sea level highstand is clearly delineated by increases in marine palynomorph recovery and decreases in mangrove pollen at approximately 5 kyr bp an increase in seasonality and potential el nino southern oscillation variability is observed in md 50 s oxygen isotope results at 5 kyr bp this is not supported by the palynomorph record likely because of the sampling interval and dilution by tropical pollen flora which indicates stable climatic conditions throughout the last 14 5 kyr sediment transport pathways in the gop remained fairly constant throughout the time interval which is supported by the lack of major changes in palynomorph assemblage composition

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

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

megagrooves and streamlined bedrock in nw scotland the role of ice streams in landscape evolution abstract new multibeam bathymetry data onshore high resolution elevation data nextmap and fieldwork in the ullapool area of nw scotland reveal large scale megagrooves and streamlined bedrock forms in a well defined 20 km wide zone the landsystem is typical of a coherent flow corridor within a grounded ice sheet on bedrock dominated terrain we describe the morphology of the large scale features discuss their likely formation and consider the wider implications for ice sheet dynamics based on the strongly convergent bedform distribution the presence of megagrooves and highly elongate bedrock forms we interpret the erosional landscape to be the signature of a fast flowing tributary that once fed the the minch palaeo ice stream a major artery of the last british irish ice sheet the exact genesis of bedrock megagrooves remains uncertain although focused subglacial abrasion is likely to have carved most of the shallow strongly parallel features whilst glacial meltwater may have carved or modified others bedform morphometry is used to discriminate zones reflecting the degree of glacial streamlining elongation ratios 5 1 we interpret these zones to represent the transition from potentially cold based slow ice sheet flow to warm based fast flow based on these results and the presence of ribbed moraines we suggest a bedform continuum model for onset zones of palaeo ice streams on rigid beds rapid spatial bedform evolution is suggested to reflect an increase in subglacial erosive power that may be diagnostic of palaeo ice sheet thermal boundaries i e from cold to warm based and is also consistent with the expected downstream increase in ice velocity within an ice stream onset zone finally this study speculates on the role played by basal meltwater in ice stream initiation and the role of ice streams and their tributaries in landscape evolution

holocene explosive eruptions of witori and dakataua caldera volcanoes in west new britain papua new guinea abstract witori and dakataua caldera volcanoes have been very active in the middle to late holocene using tephrochronology this paper establishes the chronostratigraphy of these eruptions and their magnitude and the frequency of explosive volcanism at witori and dakataua after a long dormancy witori started explosive activity at ca 5600 conventional radiocarbon years bp producing in the next 4500 years five major tephra layers w k1 to w k4 w g with veis of 5 to 6 after the w g eruption at around 1200 bp the activity decreased in magnitude but increased in frequency with some eruptions forming central cones the major eruption of dakataua began with alternating ejections of phreatomagmatic ashfalls and plinian deposits followed by the cataclysmic eruption resulting in lithic rich pyroclastic flows ca 1100 1200 bp the major tephra layers cover extensive areas in west new britain due to their large volumes and the prevailing easterly winds providing valuable time markers for establishing holocene chronology the largest eruption the w k2 event of ca 3300 bp shaped much of the present landscape with an extensive area significantly devastated by tephra falls and pyroclastic flows obsidian and other artefacts buried by the tephras indicate that the area was repeatedly occupied the major tephra events formed new coastal plains favourable for human occupation

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

trans pacific temperature field in the mantle transition region derived from seismic and electromagnetic tomography abstract the trans pacific temperature field for the depth range 350 850 km was inferred from global seismic tomography and semi global electromagnetic tomography the seismic tomography incorporated millions of reported first arrival times and 7000 pp p differential travel times measured on broadband seismograms the electromagnetic tomography used voltage data from trans pacific submarine cables and magnetic field data from circum pacific geomagnetic observatories the resultant p wave velocity anomalies and electrical conductivity anomalies were converted to temperature anomalies using a proposed conversion formula and experimental results for mantle minerals respectively these conversions show consistently high temperature anomalies of 200 300 k in the mantle transition region beneath the hawaiian hotspot at subduction zones where slab related cold anomalies and wedge mantle related hot anomalies are likely to coexist in close proximity the seismic and electromagnetic tomography did not always give consistent features in part because of the preferred sensitivity of electromagnetic tomography to hot anomalies low temperature anomalies of 200 300 k associated with subducted slabs are clearly resolved in the seismic tomography but are less apparent in the electromagnetic tomography the high temperature anomaly in the intervening zone between the mariana and philippine slabs is very pronounced in the electromagnetic tomography but is marginal in the seismic tomography

the 3d electromagnetic response of the earth to ring current and auroral oval excitation summary we report on a new compilation of functions representing the geoelectromagnetic response of the earth s mantle the c response functions and newly defined d response functions the latter of which constitutes a sensitive indicator of lateral heterogeneities in conductivity were estimated for periods from 5 to 106 7 days the spatial coverage and statistical quality of these response function estimates were improved over previous compilations in part by making use of a newly assembled global catalogue of magnetic observatory hourly mean values and by applying a statistically robust form of empirical orthogonal function eof analysis the eof results suggest that for periods longer than 5 days the geomagnetic field variation can be represented predominantly by a single eigenmode we have identified that the primarysource fields of the dominant mode consist of two current systems in the same direction an equatorial ring current in the magnetosphere and two conjugate auroral oval ring currents in the ionosphere the influence of the auroral current system is seen at surprisingly low latitudes 40 and 50 for the vertical and northern components respectively which results in non negligible bias on the conventional c response at high latitudes a preliminary correction of the auroral current effect has been made on the c and d responses obtained for data from 55 and 52 observatories respectively at latitudes from 60 to 60 we also present a set of approximate equivalent internal mantle electrical current distributions that prove a useful indicator of the presence of deep earth heterogeneities these new sets of electromagnetic information will increase the resolving power of 3d distribution of electrical conductivity in the earth s mantle

assessing the effects of volcanic disasters on human settlement in the willaumez peninsula papua new guinea a bayesian approach to radiocarbon calibration bayesian statistical approaches to calibrating radiocarbon determinations can make a significant con tribution to disaster studies by adding precision to the dating of both the environmental forcing agent and the consequent human responses an archaeological case study in the willaumez peninsula region of new britain papua new guinea uses radiocarbon dating to examine the chronology of five major volcanic events and the timing and nature of recolonization the results demonstrate the general applicability of bayesian based approaches for building a sound tephrochronology and for evaluating the impacts of volcanic hazards on human history

stagnation of ice stream c west antarctica by water piracy the dynamic behavior of the west antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea level rise attention is focused on the fast moving and rapidly responding ice streams that drain the ice sheet one of these ice stream c largely stopped about a century ago and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice sheet here new data are presented indicating that the slowdown of the ice stream is restricted to its lower part and occurred because of loss of lubrication on localized sticky spots at the bed of the ice stream the increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream b together with slow drawdown of the ice sheet rather than from any general stabilizing feedbacks

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

abraded rock landforms whalebacks developed under ice streams in mountain areas like many mountain ranges the coast mountains of british columbia canada have undergone both local and ice sheet glaciation effects of ice sheets are concentrated along major valleys and on adjacent spurs and passes which carried strong flows of diffluent ice the major valleys are broad glacial troughs with frequent rock basins their slopes are broken into rounded steep sided bosses whalebacks abraded on all sides they are of the order of 100 m to 1 km long and 10 m high in the southern coast mountains the distribution of these whalebacks is consistent with a proposed pattern of former ice streams 1 0 2 1 km thick within the cordilleran ice sheet they are best developed where geological structures parallel the valley and thus the former ice flow direction but they are found on a range of lithologies and some are transverse to structure the whalebacks provide an impression of glacial streamlining and occasionally grade into rock drumlins roches moutonnees are rare in the major troughs it is hypothesised that these whalebacks and rock drumlins develop under ice streams of greenland or east antarctic type sliding rapidly over bedrock and exploiting rock weaknesses to produce streamlined features lee slopes are abraded when thick ice suppresses bed separation even with rapid flow basal ice of low viscosity would aid this suppression water pressures under the ice streams may have remained high so that lee side plucking was rare such plucking is most likely where pressure fluctuates dramatically and especially when lee cavities under active ice reach atmospheric pressure

volcanic disasters and agricultural intensification a case study from the willaumez peninsula papua new guinea abstract environments characterized by frequent volcanic activity provide an excellent opportunity to observe interactions between human land use and ecosystem succession as they unfold over time a case study tracing the history of re colonisation by humans and plants following a series of volcanic disasters during the past 40 000 years in the willaumez peninsula papua new guinea investigates the utility of denevan s models describing variation in the intensity of agricultural practices in wet tropical rainforest environments prior to the introduction of metal tools the archaeological and environmental data obtained to date show that people may have taken advantage of the effects of volcanic activity to establish relatively permanent gardens and therefore avoid the costs associated with shifting cultivation archaeological and plant microfossil data show that humans have been interfering with normal vegetation succession from at least the late pleistocene when long term base camps were established that some patches were used intensively from the early holocene and that groups may have been forced to increase the levels of disturbance after the end of a long period of high magnitude volcanic eruptions

the palaeoglaciology of the central sector of the british and irish ice sheet reconciling glacial geomorphology and preliminary ice sheet modelling digital elevation models of the area around the solway lowlands reveal complex subglacial bedform imprints relating the central sector of the lgm british and irish ice sheet drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time these are summarised in four major flow phases in the region phase i flow was from a dominant scottish dispersal centre which transported criffel granite erratics to the eden valley and forced lake district ice eastwards over the pennines at stainmore phase ii involved easterly flow of lake district and scottish ice through the tyne gap and stainmore gap with an ice divide located over the solway firth phase iii was a dominant westerly flow from upland dispersal centres into the solway lowlands and along the solway firth due to draw down of ice into the irish sea basin phase iv was characterised by unconstrained advance of scottish ice across the solway firth forcing of a numerical model of ice sheet inception and decay by the greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle the model indicates that after fluctuations of smaller radially flowing ice caps prior to 30 ka bp the ice sheet grows to produce an elongate triangular shaped dome over nw england and sw scotland at the lgm at 19 5 ka bp recession after 18 5 ka bp displays a complex pattern of significant ice flow directional switches over relatively short timescales complementing the geomorphologically based assessments of palaeo ice dynamics the palaeoglaciological implications of this combined geomorphic and modelling approach are that a the central sector of the biis was as a major dispersal centre for only ca 2 5 ka after the lgm b the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides c subglacial streamlining of flow sets was completed over short phases of fast flow activity with some flow reversals taking place in less than 300 years

high temperature anomalies oceanward of subducting slabs at the 410 km discontinuity abstract our p wave whole mantle tomography revealed a low velocity region oceanward of the northern honshu slab of the pacific plate at depths around the 410 km seismic discontinuity resolution tests and scrutiny of the traveltime residuals for the ray paths passing through the low velocity region indicate that this anomaly is a resolvable feature and not an artifact due to the strong slab anomalies the existence of the slow anomalies is also supported by the analysis of the p wave records from the j array a large aperture seismic array in japan for a bonin earthquake the p arrivals to northern honshu at epicentral distances of 13 20 are strongly triplicated because of the 410 km discontinuity the later arrivals along the retrograde branch where ray paths pass through the low velocity region are anomalously slow comparison of the observed and synthetic waveforms indicates not only slow anomalies but also depression of the 410 km discontinuity this depression represents the direct evidence for the low velocity zone of primarily thermal origin an excess temperature of 200 k and the associated fractional melt of less than 1 can explain both the results of the tomographic and waveform analyses