geometry of subducted plates and island arcs viewed as a buckling problem during subduction a plate9s leading edge is forced to squeeze into a smaller total width than it occupied at the surface yet the plate resists change of dimension in its own plane a possible outcome is that the plate buckles as it descends at a depth of 500 km the amplitude of buckling could be as much as one tenth the wavelength and dip angles for a plate descending at 45 on average could range from 35 to 55 observed plate geometries though not ideally regular are compatible with these suggestions before being subducted a lithosphere plate is convex upward at all points whereas to buckle it must become convex downward in a series of plunging synclines the pop through is most likely to occur after the leading edge has descended about 100 km at the moment of pop through the subduction hinge line changes from being smooth to being a series of arcs and cusps back arc spreading associated with the change can be 150 km or more in the arc embayments but should be zero opposite the cusps where a compressive regime is sustained in the pop through event elastic strain energy is released and the associated back arc spreading should be a comparatively sudden event on a geologic time scale

late holocene and younger dryas glaciers in the northern cairngorm mountains scotland we present 17 cosmogenic 10be ages of glacial deposits in coire an lochain cairngorm mountains which demonstrate that glacial and nival deposits cover a longer timescale than previously recognis

tracking slabs beneath northwestern pacific subduction zones article i nfo article history this study uses the amplitudes of bottom side reflected shear waves to constrain the morphology and dynam ics of subducted oceanic lithosphere beneath northwestern pacific subduction zones across honshu arc the 410 and 660 km seismic discontinuities are detected at the respective depths of 395 5 and 685 5 km within the wadati benioff zone their topographies are negatively correlated along slab dip showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone the base of the upper mantle shows broad depressions as well as localized zones of shallow average depths be neath korea and northeast china the 15 km peak to peak topography west of the wadati benioff zones suggests that the stagnant part of the subducted pacific plate is not as flat as previously suggested eastward slab pile up is also possible at the base of the upper mantle across southern kuril arc the shear wave reflec tion coefficients of major olivine phase boundaries fall below 5 within the wadati benioff zone the appar ent reflection gaps and the spatial connection between a strong reflector at 900 km depth may imply 1 possible compositional variations at the top and bottom of the transition zone and 2 substantial mass heat flux across the 660 km seismic discontinuity we also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths the depths and strengths of these reflectors are highly variable be tween honshu and southern kuril islands

glacier reconstruction and mass balance modelling as a geomorphic and palaeoclimatic tool the reconstruction of former mountain glaciers has long been used to examine the implications of rapid climate shifts for example at the last glacial interglacial transition and for evaluating asynchronous behaviour of mountain glaciers compared with mid latitude ice sheets during the late quaternary glacier reconstruction has also been used as a source of palaeoclimatic information based on the recognition of empirical relationships between glaciers and climate this paper reviews the application and implications of a recently revised method of glacier reconstruction carr and coleman 2007 based around glaciological principles of mass balance this study examines how this approach can be used to test geomorphological interpretations of former mountain glaciation and also to infer precipitation fields at sites of former glaciation sites of younger dryas niche and icefield glaciation in the british isles demonstrate how this method can verify interpretations of marginal glaciation and begin to understand the different behaviour of outlet glaciers within the same environmental regime examination of a site of former niche glaciation in southern africa demonstrates how glacier reconstruction may be used to infer annual and seasonal precipitation values and strongly supports the idea that winter precipitation in lesotho and se south africa was substantially greater than present day values during the last glacial cycle copyright 2010 john wiley sons ltd

shortening of an overriding plate and its implications for slip on a subduction thrust central hikurangi margin new zealand 1 at subduction plate boundaries strains accumulate within the overriding plate in response to motion of the down going plate to a first approximation margin normal interplate slip and shortening in the overriding plate sum to the total plate convergence therefore margin normal interplate slip can be estimated by measuring shortening in the overriding plate and total plate convergence here we quantify margin normal interplate slip by measuring shortening of the upper plate along a profile which extends up to 480 km across and approximately normal to the central hikurangi margin new zealand long term deformation is estimated for periods of millions of years using data from seismic reflection lines and cross sections while contemporary strain rates are derived from global positioning system gps geodetic velocities these data permit comparison of plate convergence rates determined by seafloor spreading data with the rates of contraction over short 7 years and long 2 5 and 5 myr periods of time on this part of the plate boundary total margin normal shortening in the overriding plate over the last 5 myr was 9 28 km and accounts for 6 19 of the total convergence 145 160 km at rates of 2 6 mm yr the remaining 80 or more of plate convergence has been accommodated by slip on the subduction thrust gps contraction along approximately the same profile indicates 14 16 mm yr of contemporary shortening across the terrestrial part of the upper plate which is approximately modeled by 80 interplate coupling on the subduction interface down to depths of 30 km the contrasting proportions of inferred interplate coupling for contemporary and geological data sets are consistent with stick slip behavior on the plate interface and with slip being principally achieved during intermittent large earthquakes the general shapes of short and long term shortening profiles are similar and suggest that the highest strains occur at or immediately east of the mohaka fault these strain profiles are consistent with a model where high strains in the upper plate are concentrated near the down dip end of the contemporary locked zone on the plate interface this model requires that the down dip end of the interseismic locked zone has on average been approximately stable over a period of at least 2 5 5 myr

towards a climate event stratigraphy for new zealand over the past 30 000 years nz intimate project it is widely recognised that the acquisition of high resolution palaeoclimate records from southern mid latitude sites is essential for establishing a coherent picture of inter hemispheric climate change and for better understanding of the role of antarctic climate dynamics in the global climate system new zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the southern hemisphere westerly circulation zone a critical transition zone between subtropical and antarctic influences new zealand has mountainous axial ranges that amplify the climate signals and consequently the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions since 1995 intimate has through a series of international workshops sought ways to improve procedures for establishing the precise ages of climate events and to correlate them with high precision for the last 30 000 calendar years the nz intimate project commenced in late 2003 and has involved virtually the entire new zealand palaeoclimate community its aim is to develop an event stratigraphy for the new zealand region over the past 30 000 years and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from northern hemisphere records e g last glacial maximum lgm termination i younger dryas an initial outcome of nz intimate has been the identification of a series of well dated high resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal yr bp to the present day high resolution records for the last glacial coldest period lgcp including the lgm sensu stricto and last glacial interglacial transition lgit from auckland maars kaipo and otamangakau wetlands on eastern and central north island marine core md97 2121 east of southern north island speleothems on northwest south island okarito wetland on southwestern south island are presented discontinuous fragmentary records comprising compilations of glacial sequences fluvial sequences loess accumulation and aeolian quartz accumulation in an andesitic terrain are described comparisons with ice core records from antarctica epica dome c and greenland gisp2 are discussed a major advantage immediately evident from these records apart from the speleothem record is that they are linked precisely by one or more tephra layers based on these new zealand terrestrial and marine records a reasonably coherent regionally applicable sequence of climatically linked stratigraphic events over the past 30 000 cal yr is emerging three major climate events are recognised 1 lgcp beginning at ca 28 000 cal yr bp ending at termination i ca 18 000 cal yr bp and including a warmer and more variable phase between ca 27 000 and 21 000 cal yr bp 2 lgit between ca 18 000 and 11 600 cal yr bp including a lateglacial warm period from ca 14 800 to 13 500 cal yr bp and a lateglacial climate reversal between ca 13 500 and 11 600 cal yr bp and 3 holocene interglacial conditions with two phases of greatest warmth between ca 11 600 and 10 800 cal yr bp and from ca 6 800 to 6 500 cal yr bp some key boundaries coincide with volcanic tephras copyright 2007 john wiley sons ltd

a composite pollen based stratotype for inter regional evaluation of climatic events in new zealand over the past 30 000 years nz intimate project abstract our review of paleoclimate information for new zealand pertaining to the past 30 000 years has identified a general sequence of climatic events spanning the onset of cold conditions marking the final phase of the last glaciation through to the emergence to full interglacial conditions in the early holocene in order to facilitate more detailed assessments of climate variability and any leads or lags in the timing of climate changes across the region a composite stratotype is proposed for new zealand the stratotype is based on terrestrial stratigraphic records and is intended to provide a standard reference for the intercomparison and evaluation of climate proxy records we nominate a specific stratigraphic type record for each climatic event using either natural exposure or drill core stratigraphic sections type records were selected on the basis of having very good numerical age control and a clear proxy record in all cases the main proxy of the type record is subfossil pollen the type record for the period from ca 30 to ca 18 calendar kiloyears bp cal ka bp is designated in lake bed sediments from a small morainic kettle lake galway tarn in western south island the galway tarn type record spans a period of full glacial conditions last glacial coldest period lgcp within the otira glaciation and includes three cold stadials separated by two cool interstadials the type record for the emergence from glacial conditions following the termination of the last glaciation post termination amelioration is in a core of lake sediments from a maar pukaki volcanic crater in auckland northern north island and spans from ca 18 to 15 64 0 41 cal ka bp the type record for the lateglacial period is an exposure of interbedded peat and mud at montane kaipo bog eastern north island in this high resolution type record an initial mild period was succeeded at 13 74 0 13 cal ka bp by a cooler period which after 12 55 0 14 cal ka bp gave way to a progressive ascent to full interglacial conditions that were achieved by 11 88 0 18 cal ka bp although a type section is not formally designated for the holocene interglacial 11 88 0 18 cal ka bp to the present day the sedimentary record of lake maratoto on the waikato lowlands northwestern north island is identified as a prospective type section pending the integration and updating of existing stratigraphic and proxy datasets and age models the type records are interconnected by one or more dated tephra layers the ages of which are derived from bayesian depositional modelling and oxcal based calibrations using the intcal09 dataset along with the type sections and the lake maratoto record important well dated terrestrial reference records are provided for each climate event climate proxies from these reference records include pollen flora stable isotopes from speleothems beetle and chironomid fauna and glacier moraines the regional composite stratotype provides a benchmark against which to compare other records and proxies based on the composite stratotype we provide an updated climate event stratigraphic classification for the new zealand region the stratotype and event classification are not intended to act as definitive statements of paleoclimate history for the new zealand region but rather provide a firm baseline against which to compare other records including those from the marine realm

a long late quaternary record from lake poukawa hawke s bay new zealand abstract the lake poukawa basin is a large co seismic depression located at 20 m above mean sea level in hawke s bay in eastern north island new zealand we present a detailed environmental history of the basin for the last c 60 ka based on analyses of the top 105 m of a 200 m core record dating control is provided by radiocarbon optically stimulated luminescence osl and u th disequilibrium ages the chronology is supported by nine tephras of inferred age including marker tephras kawakawa 22 590 230 yr bp at 18 25 m core datum tahuna c 35 43 ka at 33 1 m core datum and rotoehu 45 50 ka at 39 1 m core datum disagreements between some of the older tephra ages and the numerical ages from the osl and u th dating mean that more than one age model can be applied three major lithostratigraphic units are identified a basal calcareous silt with lignitic peats between 105 28 and 98 58 m of marine oxygen isotope stage mis 3 age an extended sequence of detrital shelly sands and silts between 98 58 and 8 m of mis 3 and 2 age and a holocene peat unit mis 1 from 8 to 0 m alternatively but less likely the basal unit may represent stage mis 5a and the detrital shelly sands would then contain an amalgam of mis 4 3 and 2 deposits we propose a notably moist phase represented by the peat which our numerical dating model places near the start of isotope stage 3 this suggests the existence of mild conditions during an interstadial in central new zealand at c 55 50 ka when a podocarp beech broadleaf forest of near interglacial affinity surrounded the basin the interstadial is marked by both lake and peat formation in the basin after 50 ka a thermal decline set in though the climate remained moist initially under these conditions the poukawa basin was rapidly infilled by alluvial fan deposits from the surrounding hills the floor of the basin was occupied by grasses and sedges responding to both the highly disturbed environment and swampy conditions in the basin after the deposition of the rotoehu ash effective precipitation declined markedly and woody shrubs expanded across the previously swampy basin floor the data suggest an apparent thermal decline of c 6 7 c for much of mis 2 and the latter half of mis 3 the holocene was marked by the establishment of fen and lake environments on the basin floor prior to human disturbance podocarp broadleaf forest surrounded the basin

glacial cirques as palaeoenvironmental indicators their potential and limitations abstract glacial cirques are armchair shaped erosional hollows typified by steep headwalls and often overdeepened floors they reflect former regions of glacier initiation and their distribution is therefore linked to palaeoclimate because of this association cirques can be analysed for the information they provide about past environments an approach that has a strong heritage and has seen resurgence over recent years this paper provides a critical assessment of what cirques can tell us about past environments and considers their reliability as palaeoenvironmental proxies specific focus is placed on information that can be obtained from consideration of cirque distribution aspect altitude and morphometry the paper highlights the fact that cirques potentially provide information about the style duration and intensity of former glaciation as well as information about past temperatures precipitation gradients cloud cover and wind directions in all cirques are considered a valuable source of palaeoenvironmental information if used judiciously particularly as they are ubiquitous within formerly glaciated mountain ranges globally thus making regional or even global scale studies possible furthermore cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking

spherical shell tectonics buckling of subducting lithosphere abstract the lithospheric plate is a spherical shell rather than a plane plate a spherical shell must buckle when it is bent inward we examined the possibility of lithospheric buckling upon subduction the lithosphere with its subducted portion is simulated by a hemispherical elastic shell bent inward at its circumferential edge by a uniform radial load the buoyancy force acting on the lithosphere seaward of the trench is simulated by clamping the shell along a parallel the deformable portion between the loaded and clamped edges corresponds to the subducting slab of lithosphere buckling analyses were made using the techniques of a linear stability analysis and a finite element method the wavelength of buckling depends on the thickness of the shell and the length of its deformable portion a longer wavelength is associated with a thicker shell and a longer deformable portion by scaling the shell thickness and the length of the deformable portion to the elastic thickness of lithosphere and the length of subducting slab respectively the wavelength of buckling can be compared favourably to the length of one unit of arcuate trench in a chain like continuation of island arcs the load to be applied for initiation of buckling is called the critical load a lower critical load is associated with a thinner shell with a longer deformable portion the excess weight of subducting slab provides a load large enough to initiate lithospheric buckling at a relatively early stage of subduction radial displacement of the circumferential edge at the critical state is an order of magnitude smaller than the depth of the leading edge of the wadati benioff zone indicating that most of the present subducting lithospheres are under a postbuckling state undulation of the shell in the postbuckling state is not purely sinusoidal but a successive continuation of arcs with cusps in between invoking the continuation of arcuate deep sea trenches with cusps at their junctions the cuspate feature of island arc chains is thus a natural consequence of lithospheric buckling and does not require any such irregularities as seamounts colliding with a trench collision of seamounts however can aid buckling greatly if they are aligned along a trench at an interval not very different from the inherent buckling wavelength

a 2 d numerical model of snow ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features abstract standard methods of interpreting the paleoclimates recorded in alpine glacial geomorphic features rely on estimates of paleoglacier shape commonly assume that relationships between mass balance gradient and equilibrium line altitude of modern glaciers apply equally well to glaciers of in many cases dramatically different climates and do not account for the varying influence of topography on glacial extent while those methods may be adequate for many studies there are an increasing number of areas in which that level of analysis does not match the level of detail of the glacial chronologies being developed as an alternative we present a physically based 2 d glacier model that can be used to determine steady state glacier shapes and distributions for a wide range of climatic conditions the model requires only a modest amount of data beyond that which would be required for simpler methods and includes a relatively accurate representation of the effects of topography on the largest component of the surface energy balance shortwave radiation it calculates 2 d in the horizontal plane distribution of snow accumulation using a surface mass and energy balance approach and calculates the resultant glacier shapes with a 2 d flow model in addition to offering a potentially more accurate reconstruction of paleoclimatic conditions the model provides a means of performing detailed sensitivity analysis establishing relationships between similar deposits in basins of different shape and aspect and of predicting glacier shape terminus position in areas not yet explored

thermochronology constraints for the propagation sequence of the south pyrenean basement thrust system france spain 1 in this work we combined apatite fission track and biotite k feldspar 40ar 39ar ages with tectonic data in the west central part of the axial zone of the pyrenees we discuss the exhumation ages and rates of the neouvielle bordere louron and bielsa variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the pyrenean orogenic prism the 40ar 39ar ages on k feldspars from the neouvielle massif sample nv7 seem to indicate tectonic movements on the eaux chaudes thrust during the early middle eocene fission track results suggest that the exhumation of the neouvielle massif occurred around 35 ma and exhumation of the bordere louron massif around 32 ma in relation to thrusting on the gavarnie thrust the bielsa massif was exhumed from around 19 ma by out of sequence movements on the bielsa thrust we thus show that whereas most of the pyrenean basement thrust faults here the eaux chaudes gavarnie and guarga thrusts were active in sequence toward the southern foreland from the early eocene to the earliest miocene some of them here the bielsa thrust were activated out of sequence in the hinterland later than the generally accepted aquitanian age for the end of the pyrenean compression finally the apatite fission track modeling indicate a last cooling episode starting around 5 ma which is most certainly related to the pliocene reexcavation of the southern and northern flanks of the pyrenees

significance of snowblow in the generation of loch lomond stadial younger dryas glaciers in the western pennines northern england geomorphological mapping has identified the former existence of five cirque glaciers that formed during the loch lomond stadial in the western pennines northern england landforms in mallerstang which previously have been interpreted as moraine ridges are shown to be better explained as large complex landslides reconstruction of these former glaciers has allowed the calculation of the former equilibrium line altitudes ela by a number of different methods values for the ela show a range across the area from 311 m to 608 m od but with low values 311 m and 428 m for the two western glaciers these are explained by the existence of large plateau areas adjacent to the former glaciers which contributed additional mass to the glaciers by snowblow on to the glacier surfaces delimitation of the potential snowblow area for each glacier shows that it has a distinct orientation with the western sector 225 315 being statistically significant with the ela indicating the importance of winds from this direction in determining the existence of these palaeoglaciers the significance of snowblow for the generation of small glaciers in marginal areas means that such local factors must be investigated before regional firn line trends are determined in former glaciated areas

first cosmogenic 10be constraints on lgm glaciation on new zealand s north island park valley tararua range we report the first direct ages for late quaternary glaciation on the north island of new zealand mt ruapehu the volcanic massif in the north island s centre is currently glaciated and probably sustained glaciers throughout the late quaternary yet no numeric ages have been reported for glacial advances anywhere on the north island here we describe cosmogenic 10be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the tararua range part of the axial ranges of the north island results indicate that a limited valley glaciation occurred culminating in recession at the end of the last glacial coldest period lgcp ca 18 ka this provides an initial age for deglaciation on the north island during the last glacial interglacial transition lgit it appears that glaciation occurred in response to an equilibrium line altitude ela lowering of 1400 m below the present day mean summer freezing level ages for glaciation in the tararua range correspond closely to exposure ages for the last glacial maximum lgm from the lateral moraines of cascade valley in the south island and in cobb valley in northern south island the corollary is that glaciation in the tararua range coincided with the phase of maximum cooling during mis 2 prior to the antarctic cold reversal acr during the lgcp copyright 2008 john wiley sons ltd

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau southern alps of new zealand abstract determining whether glaciers registered the classic last glacial maximum lgm 26 500 19 000 yrs ago coevally between the hemispheres can help to discriminate among hypothesized drivers of ice age climate here we present a record of glacier behavior from the southern alps of new zealand during the local lgm llgm we used 10 be surface exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well preserved terminal moraines deposited during the llgm near lake ohau on central south island we then used a glaciological model to estimate a llgm glacier snowline and atmospheric temperature from the ohau glacier record seventy three 10 be surface exposure ages place culminations of terminal moraine construction and hence completions of glacier advances to positions outboard of present day lake ohau at 138 600 10 600 yrs 32 520 970 yrs ago 27 400 1300 yrs ago 22 510 660 yrs ago and 18 220 500 yrs ago recessional moraines document glacier recession into the lake ohau trough by 17 690 350 yrs ago exposure of an ice molded bedrock bench located inboard of the innermost llgm moraines by 17 380 510 yrs ago indicates that the ice tongue had receded about 40 of its overall length by that time comparing our chronology with distances of retreat suggests that the ohau glacier terminus receded at a mean net rate of about 77 m yr 1 and its surface lowered by 200 m between 17 690 and 17 380 yrs ago a long term continuation of ice retreat in the ohau glacier catchment is implied by moraine records at the head of irishman stream valley a tributary of the ohau glacier valley the irishman stream cirque glacier advanced to produce a set of lateglacial moraines at 13 000 500 yrs ago implying that the cirque glacier was less extensive prior to that advance we employed a glaciological model fit to these mapped and dated llgm moraines to derive snowline elevations and temperature parameters from the ohau glacier record the modeling experiments indicate that a snowline lowering of 920 50 m and temperature depression of 6 25 0 5 c below modern values allows for the ohau glacier to grow to an equilibrium position within the lgm moraine belt taken together with a glaciological simulation reported from the irishman stream valley snowlines and temperatures increased by at least 520 m and 3 6 c respectively between 18 000 and 13 000 yrs ago climate parameters derived from the ohau glacier reconstruction are similar to those derived from glacier records from patagonia to air temperature indicators from antarctica as well as to sea surface temperature and stratification signatures of the southern ocean we think that the best explanation for the observed southern llgm is that southern winter duration modulated southern ocean sea ice which in turn influenced southern ocean stratification and made the surface ocean cooler orbitally induced cooling of the southern ocean provides an explanation for the llgm in the southern alps having been coincident with the northern lgm we argue further that the global effect of north atlantic stadials led to disturbance of southern ocean stratification southward shifts of the subtropical front and retreat of southern alps glaciers collapse of southern ocean stratification during heinrich stadial 1 along with attendant sea surface warming triggered the onset of the last glacial termination in the southern alps of new zealand

a cosmogenic 3he chronology of late quaternary glacier fluctuations in north island new zealand 39 s abstract mountain glaciers advance and retreat primarily in response to changes in climate establishing the timing and magnitude of mountain glacier fluctuations from geological records can thus help to identify the drivers and mechanisms of past climate change in this study we use cosmogenic 3 he surface exposure dating and tephrochronology to constrain the timing of past glaciation on tongariro massif in central north island new zealand 39 s exposure ages from moraine boulders show that valley glaciation persisted between c 30 18 ka which coincides with the global last glacial maximum reinterpretation of moraine tephrostratigraphy using major element geochemistry analysis shows that ice retreat and climatic amelioration at the last glacial termination was well underway prior to 14 ka the equilibrium line altitude in central north island during the last glacial maximum was c 1400 1550 m above sea level which is c 930 1080 m lower than present considering the uncertainties in the glacial reconstruction and temperature lapse rates we estimate that this equilibrium line altitude lowering equates to a temperature depression of 5 6 1 1 c relative to present our mapping and surface exposure dating also show evidence for an earlier period of glaciation of similar magnitude to the last glacial maximum which culminated prior to 57 ka probably during marine isotope stage 4 good agreement between the timing and magnitude of glacier fluctuations in central north island and the southern alps indicate a response to a common climatic forcing during the last glacial cycle

state of stress within a bending spherical shell and its implications for subducting lithosphere summary the state of stress within a bending spherical shell has some special features that are caused by sphericity while most lithospheres are more like spherical shells than flat plates our ideas of the state of stress have been dominated by flat plate models as a consequence we might be missing some important aspects of the state of stress within subducting lithospheres in order to examine this problem we analyse spherical shell bending problems from basic equations we present two approaches to solve sphericalshell bending problems one by the variational approach which is suitable for globalscale problems and the other by the asymptotic equation which is valid to first order in h r where h is the thickness of the lithosphere and r is its curvature radius i e under the assumption of small curvature the form of the equation for displacement shows that wavelengths of deformation are determined by the spherical elastic evect and the gravitational buoyancy evect for which only the latter evect is included in the usual flat plate formulations in the case of the earth the buoyancy force is dominant and consequently spherical evects are suppressed to a large extent this explains why flat plate models have been successful for earth s lithospheric problems on the other hand the state of stress shows interesting spherical evects while bending fibre stress along the subduction zone is always important bending stress along the trench strike direction can also be important in particular when the subduction zone arc is small numerical results also indicate that compressive normal stress along the trench strike direction is important when a subduction zone arc is large these two stresses the bending stress and the compressive normal stress both along the trench strike direction may have important implications for intraplate earthquakes at subduction zones

mean annual temperature in new zealand during the last glacial maximum derived from dissolved noble gases in groundwater abstract this study presents a reconstruction of mean annual surface temperature in new zealand over the last glacial period using groundwater noble gas paleothermometry low resolution 14c derived mean recharge ages of groundwater from the deep moutere deep wairau and taranaki aquifers range from roughly 41 500 yr to present including the last glacial maximum lgm modeled noble gas temperatures of probable glacial age samples range from roughly 3 7 6 2 c cooler than present we present an error weighted mean cooling of 4 6 0 5 c relative to present during last glacial period the screened depth intervals of some wells sampled in this study allow for a degree of mixing during extraction between groundwater layers of different recharge age mixing with modern groundwater may slightly elevate the noble gas temperatures ngts of glacial age samples while making them appear substantially younger given the uncertainty in dating we cannot rule out a larger lgm temperature depression of up to 6 c the 4 6 c cooling estimate agrees with a number of terrestrial paleoclimate reconstructions near the study area as well as the majority of nearby paleoceanographic temperature studies

the influence of sub glacial bed evolution on ice extent a model based evaluation of the last glacial maximum pukaki glacier new zealand abstract a potential complication in using glacier extent to estimate paleoclimatic conditions is the influence of glacier bed evolution on changes in ice extent over time here we examine this issue through model based reconstructions of the last glacial maximum lgm pukaki glacier southern alps new zealand whose lgm extents are exceptionally well defined by lateral and terminal moraines using the well dated moraine limits as an empirical constraint on maximum ice extents we employ a one dimensional glacier flowline model driven by a mass balance model in order to evaluate the influence of climate and glacier bed profile on the extent of the lgm pukaki glacier the lgm glacier bed is buried by lateglacial and post glacial sediment so we calculate bed profiles using a modified version of the one dimensional model and available geologic constraints a best fit to the moraine record occurs with a lgm temperature of 7 8 c cooler than present with precipitation ranging from 80 to 100 of present levels modeling of the bed profile evolution indicates that bed changes alone could account for kilometer scale changes in glacier width and length

mismatch of glacier extent and summer insolation in southern hemisphere mid latitudes here we address a long standing puzzle of ice age climate called the fly in the ointment of the milankovitch theory using geomorphic mapping and 10be surface exposure dating we show that five moraine belts were formed during maxima of the last ice age by the pukaki glacier in new zealand s southern alps they afford ages of 41 76 1 09 ka 35 50 1 26 ka 27 17 0 68 ka 20 27 0 60 ka and 18 29 0 49 ka these five maxima spanned an entire precessional cycle in summer insolation intensity at the latitude of the southern alps a similar mismatch between summer insolation and glacier extent also characterized the chilean lake district in the mid latitudes of south america thus in apparent contrast to northern ice sheets linked by milankovitch to summer insolation at 65 n latitude the behavior of southern mid latitude glaciers was not tied to local summer insolation intensity instead glacier extent between 41 76 ka and 18 29 ka as well as during the last termination was aligned with southern ocean surface temperature and with atmospheric carbon dioxide

glacial geomorphological mapping a review of approaches and frameworks for best practice geomorphological mapping is a well established method for examining earth surface processes and landscape evolution in a range of environmental contexts in glacial research it provides crucial data for a wide range of process oriented studies and palaeoglaciological reconstructions in the latter case providing an essential geomorphological framework for establishing glacial chronologies in recent decades there have been significant developments in remote sensing and geographical information systems gis with a plethora of high quality remotely sensed datasets now often freely available most recently the emergence of unmanned aerial vehicle uav technology has allowed sub decimetre scale aerial images and digital elevation models dems to be obtained traditional field mapping methods still have an important role in glacial geomorphology particularly in cirque glacier valley glacier and icefield ice cap outlet settings field mapping is also used in ice sheet settings but often takes the form of necessarily highly selective ground truthing of remote mapping given the increasing abundance of datasets and methods available for mapping effective approaches are necessary to enable assimilation of data and ensure robustness this paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available with a focus on their applicability in particular glacial settings we distinguish two overarching work streams that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes i mapping of ice sheet geomorphological imprints using a combined remote sensing approach with some field checking where feasible and ii mapping of alpine and plateau style ice mass cirque glacier valley glacier icefield and ice cap geomorphological imprints using remote sensing and considerable field mapping key challenges to accurate and robust geomorphological mapping are highlighted often necessitating compromises and pragmatic solutions the importance of combining multiple datasets and or mapping approaches is emphasised akin to multi proxy approaches used in many earth science disciplines based on our review we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment comparison and integration of geomorphological data these will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions finally we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and or sedimentological evidence and that such data should ideally be collected as part of a holistic assessment of the overall glacier system

an improved technique for the reconstruction of former glacier mass balance and dynamics abstract the recognition of past glacier extent and dynamics is a fundamental aspect of investigations of the climatic sensitivity of glaciers especially when examining short lived climate events such as the younger dryas or little ice age existing approaches to the reconstruction of glacier form and dynamics depend on speculative reasoning of key glacier dynamic parameters including the role of basal slip and subglacial deformation in glacier mass transfer this study reviews approaches to glacier reconstruction derivation of former glacier equilibrium line altitudes ela s and estimation of mass balance and dynamics concluding that most reconstructions of glacier mass balance are compromised by a lack of glaciological considerations an alternative approach to glacier reconstruction is presented demonstrated and discussed by which an empirical relationship between ablation gradient and mass loss at the ela is used to derive mass balance mass flux through the ela and average balance velocity at the ela this glaciological approach is applied to four reconstructed glaciers to test previous interpretations that each reflects younger dryas glaciation in the uk the study concludes that this approach provides a more robust technique for reconstructing former glacier dynamics and may be applied to test geomorphological interpretations of former mountain glaciation

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

flexural response of the oceanic lithosphere at an arc arc junction implication for the subduction of aseismic ridges abstract the deformation of the oceanic lithosphere subducting at the junction of two trenches is studied by means of a three dimensional finite element analysis results show that the existence of a junction i e a change in trend of the trench axis yields a specific shape of the outer topographic rise in a convex junction area such as the japan and kuril trenches the topographic bulge presents a dome whereas in a concave junction area such as the java and sumatra trenches this bulge is less pronounced these theoretical results are confirmed by the bathymetry seaward of the junctions of the japan and kuril trenches and of the peru chile trench moreover the existence of the abnormal topographic dome in front of a convex junction contributes to the creation of normal faults which help the subduction of seamounts or of other bathymetric features in such areas

cenozoic plate tectonic history of the northern venezuela trinidad area geological and geophysical data coupled with recent plate tectonic reconstructions suggest that the cenozoic geologic history of the northern venezuela trinidad area has been dominated by strike slip displacement of discrete crustal blocks allochthonous terranes within the area include metavolcanic rocks of the cretaceous villa de cura group and metamorphic rocks of the precambrian to cretaceous cordillera de la costa a relatively competent crustal block margarita block is defined by an outline around the metamorphic basement of margarita island the araya paria peninsula the northern range of trinidad and tobago island reconstruction of the margarita block to its original position requires at least partial closure of the falcon basin closure of the bonaire and cariaco basins and restoration of about 50 km of motion on both the oca and bocono faults post middle eocene eastward translation of the caribbean plate caused eastward motion of the margarita block a minor change in relative plate motion during the late oligocene or early miocene produced a right step in the moron fault forming the cariaco pull apart basin and el pilar fault zone maximum offset on el pilar fault is estimated to be no more than 125 km though displacement along the entire fault zone may have been greater transpressional stresses between the caribbean plate and northern south america caused folding of the serrania del interior of venezuela and the central range of trinidad eastward migration of transpressional stresses at the southeastern corner of the caribbean south american plate boundary is being accommodated by formation of oblique thrusts transpressive anticlines and downwarping of the crust bouguer gravity data suggest that jurassic aged atlantic oceanic crust is being depressed as the caribbean plate expands into the demerara plateau area this study suggests that the faults and transtensional transpressional compressional structures identified in this study are the result of stresses produced during the large eastward translation of the caribbean plate since the paleocene and are not the product of a shear couple

last glacial maximum climate in new zealand inferred from a modelled southern alps icefield abstract we present a simulation of the new zealand southern alps icefield at the last glacial maximum lgm c 30 000 20 000 calendar years ago ka in an attempt to constrain the climate of that period we use a 500 m resolution ice sheet model parameterised using empirical glaciological climatological and geological data specific to the model domain to simulate the entire southern alps icefield we find that an lgm cooling of at least 6 6 5 c is necessary to bring about valley glaciers that extend beyond the mountains however climate topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain and in order to remain within geologically reconstructed lgm limits we find that the lgm cooling was most likely associated with a precipitation regime up to 25 drier than today wetter than present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence these results perhaps indicate that either the westerly air masses affecting new zealand during the lgm were drier than today or that they were weaker or zonally displaced with respect to present

a 28 000 7600 cal yr bp pollen record of vegetation and climate change from pukaki crater northern new zealand a pollen record of vegetation and climate change representing the interval ca 28 000 7600 cal yr bp was obtained from a 52 5 m sediment core taken from a volcanic explosion crater at present sea level in auckland new zealand 36 59 s this provides one of the few continuous terrestrial records covering marine isotope stage 2 and part of stage 1 from the mid latitudes of the southern hemisphere chronology of the record is underpinned by eight distal taupo volcanic zone rhyolitic tephra of known age augmented by thirteen ams radiocarbon dates the last glacial maximum cooling extended from at least c 28 000 cal yr bp to ca 18 000 cal yr bp when vegetation apparently consisted of patches of beech dominated forest embedded within shrubland and grassland forest patches were probably larger or more widespread than those in central north island to the south but less extensive than further to the north in northland climate warming commenced ca 18 000 cal yr bp marked by the replacement of beech by conifers and angiosperms and by the expansion of forest at the expense of shrubland and grassland no clear late glacial climatic reversal is evident at this site early holocene forest is characterised by the replacement of the dominant forest tree prumnopitys taxifolia by dacrydium cupressinum following breach of the crater rim ca 7600 cal yr bp by rising sea level the maar was rapidly infilled with marine sediments over a period of ca 1000 years

the volcanic history of ruapehu during the past 2 millennia based on the record of tufa trig tephras tufa trig formation comprises a sequence of at least 19 andesitic tephras erupted from mt ruapehu tongariro volcanic centre new zealand tephras of tufa trig formation are the most recent eruptives from ruapehu dated between ca 1850 years b p and the present members of the formation show restricted dispersals principally to the east of mt ruapehu volumes calculated for the most widespread members are all less than 0 1 km3 compared with other mt ruapehu eruptives tufa trig formation tephras represent small eruptions that have contributed little tephra to the ring plain they do however show a greater frequency of eruption with one event occurring on average every 100 years tufa trig formation members tf3 tf18 are black to dark grey vitric coarse ash and lapilli grade tephras which mantle the relief they contain juvenile vitric particles which exhibit varying degrees of vesicularity together with free crystals of pyroxene and feldspar and few lithic fragments several morphological types of vitric pyroclasts are recognised in these tephras the dominant type being of equant blocky morphology with fracture bound surfaces type 1 morphology field characteristics tephra distributions and the morphologies and textures of constituent pyroclasts suggest that these members tf3 tf18 are the products of small volume hydrovolcanic eruptions resulting from the interaction of fresh magma and meteoric water we propose that a source of this water was an ancestral crater lake which formed within the late holocene ca 3000 years b p the morphological compositional and chemical major element characteristics of three tufa trig formation tephras are compared with those of two new tephras erupted from ruapehu volcano during the october 1995 eruptions which comprise part of a newly defined member tf19 of tufa trig formation the comparisons support our interpretation that the majority of the tufa trig formation tephras are primarily the products of hydrovolcanic eruptions other members of the formation tf1 and tf2 are coarse grained scoriaceous tephras and are interpreted to be the products of strombolian events

cosmogenic 10be and 26al exposure ages of moraines in the rakaia valley new zealand and the nature of the last termination in new zealand glacial systems new zealand glaciers reached their last glacial maximum position at or before 25 ka and as early as 23 ka commenced a slow and continual retreat new cosmogenic exposure ages and field mapping from the rakaia valley in the south island suggest that extensive ice survived well into the latter half of the last glacial interglacial transition 18 11 ka with the post 15 ka period inferred to have near holocene climate conditions based on ecological proxy data by as late as 15 5 ka glacier termini had retreated as little as 5 10 km from glacial maximum positions numerous minor ice still stand positions and oscillations are recognized but the record specifically excludes evidence for either a major climatic amelioration at 15 16 ka or a significant glacial re advance during the antarctic cold reversal acr or the younger dryas yd we conclude that the currently widespread interpretation of an episodic new zealand glacial record since the lgm is an artifact of valley dependent retreat processes pro glacial lake formation and local site conditions combined to give an apparent but misleading picture of glacial retreat punctuated by major climatically driven re advances copyright 2010 elsevier b v all rights reserved

abrupt millennial scale changes in intensity of southern hemisphere westerly winds during marine isotope stages 2 4 the strength of mid southern latitude westerly atmospheric circulation plays an important role in global climate due to a lack of long continuous high resolution paleoclimate archives from mid southern latitudes it remains unclear what factors control changes in its intensity and how past changes affected the climates of landmasses in their path here we show growth rate and stable isotope 18 o 13 c profiles from a south island new zealand stalagmite hw3 that permit centennial scale investigation of southern hemisphere westerly paleointensity between 73 and 11 ka correlation between hw3 growth rate and isotope profiles suggests sensitivity to changes in annual precipitation a factor controlled by westerly intensity low growth rates and relatively enriched isotope ratios define long term trends in hw3 supporting existing evidence that weaker westerlies predominated during the last glacial period abrupt millennial scale events occur frequently such that the hw3 record resembles greenland ice core stable isotope profiles furthermore nearly synchronous timing of nine prominent wet and cool intervals with heinrich events supports studies showing that increased westerly intensity is closely linked to north atlantic cooling as well as heinrich events the hw3 profiles also show an antarctic cold reversal like event during deglaciation advocating for a bipolar seesaw of global climate at that time

continental underplating model for the rise of the tibetan plateau abstract subduction of continental lithosphere entrained in an oceanic plate for distances of several hundred kilometers can lead to continental underplating whereby the continental crust with or without its lithospheric mantle is detached at depth from the main part of the sinking slab and rises buoyantly beneath the overriding plate the rising continental material causes first extension in the overriding plate as the asthenosphere flows laterally and later rapid isostatic uplift when it reaches the base of the overriding lithosphere this continental underplating model is applied to the geology of the tibetan region and the following stages are identified 100 ma to 50 ma oceanic subduction leading to continental collision 50 ma to 20 ma pause in convergence with possible delamination of indian crust 20 ma to 5 ma continental subduction initially at an angle of 30 of indian lithosphere along the main central thrust 5 ma to 2 ma rise of the continental lithosphere displacing the asthenosphere beneath tibet and causing widespread graben formation 2 ma to present contact between the underplating indian continental lithosphere and the overlying asian crust leading to rapid rise of the surface altitude by 3 4 km present day convergence between india and tibet albeit at a rate much less than the total india eurasia convergence continues as continental underthrusting

three dimensional model of the cascadia subduction zone using earthquake hypocenters western washington abstract the identification of seismically active fault planes is important for assessment of earthquake potential as well as development of neotectonic models and analysis of stress systems for a region an automated set of computer programs seispln has been developed for the identification of three dimensional 3 d alignments of seismic hypocenters the seispln technique is based on rotating a 3 d elongate grid system through the hypocenter distribution the number of events in each cell is tabulated and those cells which contain statistically significant numbers of events are considered to be potential fault surfaces a multiple linear regression is applied to the set of hypocenters in each delineated cell to model the 3 d geometry of each of the inferred fault surfaces we applied the technique to earthquakes located by the washington regional seismic network to separate the seismic events associated with the subducted juan de fuca jdf plate from events in the overlying crust a total of 259 jdf associated events were delineated and the resulting 3 d models of the jdf slab beneath washington reveal a complex combination of arching and flattening also a steep orientation for the slab is observed beneath the southern portion of the washington cascades while a much shallower orientation is inferred beneath the northern cascades

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

reconstruction and paleoclimatic significance of late quaternary glaciers in the tararua range north island new zealand abstract reconstructed mountain glaciers are routinely used as a proxy for climate in the search for evidence of interhemispheric climate fluctuations during the quaternary in new zealand valley glaciers at the last glacial maximum lgm extended from an ice sheet centred on new zealand s southern alps to below present day sea level in contrast evidence of lgm glacial activity on the north island is rare here a glacioclimatic reconstruction is presented of two former glaciers in the tararua range 41 s in the southern north island at mt aston an isolated cirque basin contains landform evidence of a marginal niche glacier at park valley the lateral moraine of a larger cirque glacier has yielded published cosmogenic isotope ages the paleoglacier reconstruction shows that paleoequilibrium line altitudes increased northwards across new zealand during the local lgm hence at this latitude only topography 1200 m above present day sea level was of sufficient elevation to allow small glaciers to form the mt aston glacier covered only 0 18 km2 with an equilibrium line altitude ela of c 1287 m above present sea level a mean ela glacier thickness of c 25 m gives a basal shear stress at the ela of c 100 kpa 1 with a mean summer december january february djf temperature at the ela of no lower than 5 5 c below present below which precipitation would have been insufficient to support the reconstructed glacier implied lgm paleo temperatures from both the ela reconstruction and the glaciological reconstruction broadly accord with other paleo temperature proxies from the north island park valley glacier covered c 0 45 km2 with an ela of c 1270 m and a mean ela basal shear stress of 65 kpa its balance discharge was 9 greater than at mt aston it appears to have been glaciologically viable across a wide range of paleotemperatures thus the more marginal glacier is a more useful paleoclimatic indicator because it places a maximum limit on lgm temperature depression which the larger glacier does not elas of both glaciers closely approximate the regional lgm ela trend surface the paleo glacier reconstructions imply that together with temperature driving lgm paleo ela depression changes in south westerly airflow over new zealand bringing moisture laden but cool air maximized snowfall and minimised winter melt the corollary is that patterns of quaternary glacier fluctuations may be interpreted as responses at least in part to precipitation driven changes and secondly north island glaciation was probably more extensive than previously assumed

sea surface temperatures of southern midlatitudes 0 160 kyr b p 1 late quaternary climate fluctuated between extremes of glaciations lasting 90 kyr on average and interglacial episodes lasting 10 kyr still largely unknown are the spatial and temporal evolution of these global climate states with vigorous debate still underway on the mechanisms responsible for glacial inceptions and terminations though it is widely believed that the southern hemisphere oceans play a central role in global climate changes few paleoclimate records exist from there here we present three new alkenone derived sst records from the midlatitude southern hemisphere spanning the last 160 kyr a full glacial interglacial cycle our subtropical sst records from the last glacial period are characterized by 1 warming 47 23 kyr b p when high latitudes in both hemispheres cooled and 2 milder temperatures during the penultimate glacial period than during the last glacial interval these sst features are found to be of tropical to subtropical wide extent implying increased thermal gradients at times of high latitude ice sheet growth this has implications for the vigor of atmospheric and upper ocean circulation and the transport of heat and moisture to the poles that may have been instrumental in the growth and maintenance of polar ice sheets during glacial periods

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

spherical shell tectonics on the buckling of the lithosphere at subduction zones abstract the buckling phenomena of the subducting lithosphere due to the sphericity of the earth are studied by a nonlinear finite element method fem and the effects of geometrical nonlinearity are examined the subduction of the lithosphere is modelled by a hemispherical shell squeezed at its circumferential edge in scaling the geometry of the subducting lithosphere two parameters are employed one is the thickness of the hemispherical shell i e the thickness of the lithosphere and the other is the length of its deformable portion i e the length of the descending slab to simulate the bending of the lithosphere at the trench uniform inward load is applied to the free circumferential edge of the deformable portion which corresponds to the leading edge of the subducting lithosphere at the opposite edge of the deformable portion i e at the trench a built in boundary condition is imposed no displacements and no rotations are allowed with a load greater than some critical value the deformable portion of the shell buckles and undulates azimuthally the investigation of this buckling phenomenon can be summarized as follows 1 1 buckling with a shorter wavelength is associated with a thinner and shorter shell mechanical irregularities simulating lithospheric tearing or seamount collision do not alter the buckling wavelength very much after appropriate scaling the lengths of subduction zones coincide with the buckling wavelength calculated by f e m 2 2 sharp cusps pointing outward from the shell appear during the postbuckling undulation without any irregularities in shell property and in the applied load the shape of this cuspidal undulation is quite similar to that actually observed at an arc arc junction 3 3 buckling can take place in the stress environment likely to exist in the earth these results strongly suggest that the arcuate shapes of subduction zones are in fact generated by buckling of the subducting lithosphere

evaluation of lateglacial temperatures in the southern alps of new zealand based on glacier modelling at irishman stream ben ohau range abstract climate proxy records from the middle to high latitude southern hemisphere indicate that a lateglacial 15 000 11 500 years ago climate reversal approximately coeval with the antarctic cold reversal acr interrupted a warming trend during deglaciation in new zealand some palaeoclimate proxy records indicate a cool episode during the acr ca 14 500 12 500 years ago while others do not express a significant change in climate recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers we use a coupled energy balance and ice flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of irishman stream a high elevation catchment in the southern alps first a suite of steady state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well dated lateglacial moraine crests second time dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record steady state experiments using an optimal parameter set demonstrate that the conditions under which the 13 000 year old moraine formed were 2 3 3 2 c colder than present with the range in temperature corresponding to a 20 variance in precipitation relative to the present day this reconstructed climate change relative to the present day corresponds to an equilibrium line altitude of ca 2000 40 m above sea level asl which is ca 400 m lower than present time dependent simulations of glacier length produce ice advance to within 100 m of the 13 000 year old terminal moraine indicating that the chironomid based temperature forcing and moraine record provide consistent information about past climate our results together with other climate proxy reconstructions from pollen records and marine sediment cores support the notion that temperatures during the acr in new zealand were 2 3 c cooler than today

climate sensitivity of a high precipitation glacier in new zealand the sensitivity of glaciers to climatic change is key information in assessing the response and sea level implications of projected future warming new zealand glaciers are important globally as an example of how maritime glaciers will contribute to sea level rise a spatially distributed energy balance model is applied to brewster glacier new zealand in order to calculate glacier mass balance run off and sensitivity to climate change the model successfully simulates four annual mass balance cycles close to half 52 of the energy available for melt on the glacier is supplied by turbulent heat fluxes with radiation less important except during the winter model sensitivity to temperature change is one of the largest reported on earth at 2 0 m w e a 1 8c 1 in contrast a 50 change in precipitation is required to offset the mass balance change resulting from a 18c temperature change meltwater run off sensitivity is also very high increasing 60 with a 18c warming the extreme sensitivity of mass balance to temperature change suggests that significant ice loss will occur with even moderate climate warming

crust and upper mantle structure of a continental backarc central north island new zealand summary near vertical and wide angle seismic data provide evidence for a gradational crust mantle boundary in a depth range of 15 20 km beneath the central volcanic region cvr new zealand this volcanic area includes the taupo volcanic zone and is a direct extension of tonga kermadec oceanic backarc spreading into continental lithosphere long range seismic refraction data show velocities of 6 km s 1 and less within the top 15 km of the crust of the cvr at a depth of 15 km compressional seismic velocities increase to 6 8 km s 1 and then to 7 4 0 2 km s 1 at 20 km depth these 7 4 km s 1 seismic wave speeds are interpreted as anomalous upper mantle as beneath this level passive seismic studies show similar pn wave speeds that increase slowly to 7 8 km s 1 at about 80 km deep we interpret rocks between 15 and 20 km to be a layer of new crust formed by underplating the strongest reflection observed and what might also be interpreted as a reflection moho is from the top of the proposed underplated layer at 15 km depth at 20 km depth no such distinct reflection is observed rather wide angle reflection data show a continuum of low level reflectivity between 15 and at least 35 km depth indicating some heterogeneity and or structure within the lower crust and upper mantle thus the transition from lower crust to upper mantle is broad and a conventional reflection moho does not exist beneath the cvr buoyancy force calculations based on rock uplift for the central north island indicate that the subjacent mantle to a depth of 80 100 km is 70 kg m 3 or 2 per cent less dense than normal mantle best estimates attribute half of this density anomaly to the effects of increased temperature with additional contributions from partial melt 1 2 per cent and melt residuum

the timing and cause of glacial advances in the southern mid latitudes during the last glacial cycle based on a synthesis of exposure ages from patagonia and new zealand abstract glacier advances in the southern mid latitudes during the last glacial cycle ca 110 10 ka were controlled by changes in temperature and precipitation linked to several important ocean climate systems as such the timing of glacial advance and retreat can yield important insights into the mechanisms of southern hemisphere climate change this is particularly important given that several recent studies have demonstrated significant glacial advances prior to the global last glacial maximum glgm in patagonia and new zealand the cause of which are uncertain the recent increase in chronological studies in these regions offers the opportunity to compare regional trends in glacial activity here we compile the first consistent 10be exposure dating chronologies for patagonia and new zealand to highlight the broad pattern of mid latitude glacial activity over the last glacial cycle our results show that advances or still stands culminated at 26 27 ka 18 19 ka and 13 14 ka in both patagonia and new zealand and were broadly synchronous but with an offset between regions of up to 900 years that cannot be explained by age calculation or physically plausible erosion differences furthermore there is evidence in both regions for glacial advances culminating from at least 45 ka during the latter half of marine isotope stage mis 3 glacial activity prior to the glgm differed from the large northern hemisphere ice sheets likely due to favourable southern hemisphere conditions during late mis 3 summer insolation reached a minimum seasonality was reduced winter duration was increasing and sea ice had expanded significantly inducing stratification of the ocean and triggering northward migration of oceanic fronts and the southern westerly winds glacial advances in patagonia and new zealand during the glgm were probably primed by underlying orbital parameters however the precise timing is likely to have been intrinsically linked to migration of the coupled ocean atmosphere system which may account for the small offset between patagonia and new zealand due to differences in oceanic frontal migration during deglaciation advances or still stands occurred in both regions during the southern antarctic cold reversal ca 14 5 12 9 ka rather than the northern younger dryas ca 12 9 11 7 ka our findings suggest that major rearrangements of the southern hemisphere climate system occurred at various times during the last glacial cycle with associated impacts on the position and intensity of the southern westerly winds and oceanic fronts as well as wind driven upwelling and degassing of the deep southern ocean thus reconstructing the timing of glacial advance retreat using our compilation is a powerful way to understand the mechanisms of past interhemispheric climate change

palaeoclimatic reconstruction from loch lomond readvance glaciers in the west drumochter hills scotland geomorphological mapping in the west drumochter hills provides evidence of a readvance of locally nourished glaciers during the loch lomond younger dryas stade in the form of an icefield 67 7 km2 in area drained by outlet glaciers the icefield limits accord broadly with those proposed by sissons 1980 but all geomorphic stratigraphic and sedimentological evidence conflicts with a recent proposal that the landforms in the area reflect southwestwards retreat of the last ice sheet up valley continuity of recessional moraines indicates that the ice remained active and close to climatic equilibrium during the earlier stages of glacier retreat consistent with slow warming following the coldest part of the stade the pattern of equilibrium line altitudes elas across the icefield is consistent with transfer of snow by westerly and southerly winds the ela of the reconstructed icefield as a whole is 622 629 m although this figure is likely to be lower than the regional climatic ela because the icefield probably received additional snow blown from adjacent plateau surfaces and slopes inclusion of potential snow blow areas in the ela calculation yields a value of 648 656 m the climatic ela is therefore likely to have lain between 622 and 656 m mean june to august temperature at the ela based on chironomid assemblages at two sites falls within the range 4 0 0 7 c empirical relationships between temperature and precipitation at modern glacier elas indicate that mean annual precipitation map at the ela was 1977 464 mm statistically indistinguishable from modern values comparison with precipitation values calculated for the isle of mull on the west coast suggest that the precipitation gradient across the central highlands of scotland was steeper during the loch lomond stade than at present probably as the result of efficient scavenging of precipitation from westerly airflows by the west highland icefield copyright 2005 john wiley sons ltd

the relationship between plate curvature and elastic plate thickness a study of the peru chile trench the age of the nazca plate where it enters the peru and northern chile trenches varies from 30 ma in the north to 45 ma in the south as its dip beneath the south american continent steepens from 13 to 30 if the elastic thickness te of oceanic lithosphere depends only on its age and therefore thermal state we would expect that te determined from fitting the flexure of the lithosphere over the outer rise as revealed in the depth geoid and gravity anomalies would increase from the peru trench in the north to the northern chile trench further south we find that the opposite is true the lithosphere appears suffer outboard of the peru trench than it does offshore chile to explain deflections of the lithosphere seaward of peru the isotherm controlling the elastic ductile transition must be near 800 c providing the thermal structure of the plate is that predicted by the standard thermal plate model because the decrease in plate stiffness to the south is correlated with an increase of plate curvature over the outer rise and outer trench wall we interpret our result in terms of inelastic yielding of the oceanic lithosphere when bent to high strains the magnitude of the reduction in strength however suggests that the standard oceanic yield strength envelope underestimates the amount of failure for lithosphere bent to high strains unless the stress field off northern chile is characterized by 100 mpa level tension the more highly bent segment of subducting lithosphere at this trench also dips at a steeper angle at greater depth beneath the continent but detailed analysis of plate geometry does not support a relationship between slab dip as determined by earthquake hypocenters and elastic behavior over the outer rise

the southernmost quaternary niche glacier system in great britain until recently the scientific consensus has been that the uplands of south west britain remained unglaciated throughout the quaternary with glacial ice sheet limits lying to the north of the south west peninsula however recent work has shown that small glaciers and ice caps existed in the uplands of exmoor and dartmoor during the late quaternary demonstrating that the consensus of an unglaciated south west britain requires considerable revision here we report geomorphological and sedimentary evidence supported by glacier climate modelling for a quaternary niche glacier from west cornwall south west england this niche glacier represents the southernmost such system from mainland great britain and provides evidence for the presence of extra glacial niche glaciers probably during the last glacial maximum of the devensian glaciation and well outside the limits of the main british irish ice sheet

bending of spherical lithosphere axisymmetric case summary effects of sphericity are commonly ignored in the lithospheric bending problem in order to examine its effects i solve a simple axisymmetric spherical shell model the full solution and the asymptotic solution are derived from the basic equations and their relationship to the flat plate solution is examined for displacement effects of sphericity are small and use of the flat plate solution produces results that are numerically indistinguishable from those of the spherical solution the most significant effect of sphericity appears in the stress in particular the normal stress along the strike direction of the trench this stress is approximately given by eu r where e is young s modulus u is the vertical deformation of the shell and r is its radius of curvature if the shell lithosphere is bent downwards and reaches 30 km this stress can become about 5 kbar in the earth while plastic behaviour may set in under such high pressure conditions and analysis beyond elasticity theory may be required sphericity may be a cause of large compressive stress in the trench strike direction this stress may play an important role in forming the overall shape of the earth s subduction zones

recognition and paleoclimatic implications of late holocene glaciation on mt taranaki north island new zealand evidence for the timings of inter hemispheric climate fluctuations during the holocene is important with mountain glacier moraine systems routinely used as a proxy for climate in new zealand such evidence for glacier expansion during the late holocene is fragmentary and is limited to glaciers in a narrow zone within the southern alps here we present the first evidence for late holocene glacier expansion on the north island of new zealand in the form of two unconsolidated debris ridges on the south side of the stratovolcano mt taranaki mt egmont at 1920 m a s l the two ridges are aligned north south along the western and eastern sides of a small basin rangitoto flat which is formed between the main taranaki cone to the north and the parasitic cone of fanthams peak to the south the approximate age of the ridges is constrained by dated eruptive events and the relationship between ridge locations and the spatial positioning of adjacent volcanic landforms we propose the ridges formed as two l