a 4500 year proxy climate record from peatlands in the north of ireland the identification of widespread summer drought phases abstract mid to late holocene high resolution testate amoebae derived water table reconstructions from two peatlands in the north of ireland are presented the proxy climate records are dated and correlated using a combination of ams 14 c dating spheroidal carbonaceous particles and tephrochronology the reconstructions start prior to the hekla 4 tephra isochron 2395 2279 bc and thus span the last 4500 years the records are compiled by the process of tuning within chronological errors standardisation and stacking comparisons are made to existing palaeoclimate records from peatlands in northern britain and ireland and the compiled lake level record for mid latitude europe four coherent dry phases are identified in the records at ca 1150 800 bc 320 bc ad 150 ad 250 470 and ad 1850 2000 recent research has shown that peat derived water table reconstructions reflect summer water deficit and therefore the dry phases are interpreted as periods with a higher frequency and or greater magnitudes of summer drought these drought phases occur during periods of relatively low 14 c production which may add support to the hypothesis of persistent solar forcing of climate change during the holocene any relationship with the north atlantic stacked drift ice record is less clear

the proportionality between relative plate velocity and seismicity in subduction zones the magnitude and rate of seismicity differ between subduction zones calculations of background seismicity rates based on a global model of subduction zone seismicity reveal a positive correlation between relative plate velocity and background seismicity yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes

middle pleistocene climate and hydrological environment at the boxgrove hominin site west sussex uk from ostracod records the sediments of the slindon formation at the junction of the chalk south downs and the west sussex coastal plain as revealed and studied at boxgrove contain evidence for early middle pleistocene environments in southern england around half a million years ago the archaeological importance of the deposits is attested to by the recovery of stone and organic tools butchered fauna and fossil hominin remains we combine palaeoecological and geochemical analyses of ostracods from the coastal plain deposits to reconstruct the climate and environment at one period of the hominin occupation the stratigraphy of our study area is indicative of a terrestrial environment surrounding a small lake or pond ostracod assemblages from the sediments indicate that the ponds were shallow but permanent and fed by groundwater and springwater however the species alone cannot confirm that these ponds were completely fresh application of mutual climatic range mcr techniques shows that summer temperatures were similar to present day values and winter temperatures were probably colder whereas mean annual air temperature was similar to present or perhaps slightly cooler trace element and strontium isotope analyses of ostracods from the sediments support the conclusion that the ponds were fed largely by fresh groundwater derived from the chalk although there may have been a minor seawater input the carbon isotope ratios of the ostracod shells are consistent with a groundwater source although they also indicate that the dissolved inorganic carbon most likely did not reach equilibrium with atmospheric carbon dioxide suggesting that the ponds had short residence time the combination of palaeotemperature estimates with oxygen isotope values from ostracod shells allowed us to reconstruct the oxygen isotope ratio of the pond water which was close to the value of early middle pleistocene precipitation at this site values were similar to present day suggesting that there may have been a change in seasonality or precipitation source since the mean air temperatures might have been lower

new insights on the tectonics along the new hebrides subduction zone based on gps results 1 at the new hebrides nh subduction zone ridges born by the subducting australia plate enter the trench and collide with the overriding margin results from gps surveys conducted on both sides of the trench and new bathymetry maps of the nh archipelago bring new light on the complex tectonics of this area convergence vectors present large variations that are not explained by australia pacific a p poles and that define four segments vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors slow convergence i e 30 40 mm yr is found at the central segment facing the d entrecasteaux ridge the southern segment moves faster than a p motion predicts 89 to 124 mm yr relatively to a western north fiji basin wnfb reference the northern and southern segments rotate in opposite directions consistently with the extension observed in the troughs east of both segments both rotations combine in central vanuatu into an eastward translation that bulldozes the central segment into the wnfb at 55 mm yr that model suggests that the motion of the central segment forced by the subduction collision of the d entrecasteaux ridge influences the motion of the adjoining segments the new caledonia archipelago is motionless with respect to the rest of the australia plate despite the incipient interaction between the loyalty ridge and the nh margin southeast of the interaction area convergence is partitioned into a 50 mm yr trench normal component accommodated at the trench and a 90 mm yr trench parallel component close to the a p convergence and presumably accommodated by a transform boundary at the rear of the nh arc

rapid forearc uplift and subsidence caused by impinging bathymetric features examples from the new hebrides and solomon arcs 1 isotopically dated corals from the central new hebrides and new georgia island group solomon islands indicate that both forearcs underwent rapid late quaternary subsidence that was abruptly replaced by hundreds of meters of uplift at rates up to 8 mm yr while total plate convergence was only a few kilometers two mechanisms that might account for these rapid reversals in vertical motion include 1 a displacement mechanism in which the forearc is displaced upward by the volume of an object passing beneath on the subducting plate as the object moves deeper and vacates the base of the forearc the forearc subsides to near its original position and 2 a crustal shortening mechanism in which the forearc thickens and uplifts because of horizontal shortening when a large object impinges on the forearc and abruptly increases interplate coupling on the shallow end of the main thrust zone rapid subsidence follows when the impinging object is broken or otherwise decoupled shallow interplate coupling becomes weak and the uplifted forearc extends and subsides the displacement mechanism surely plays a role on timescales over which plates converge tens of kilometers but it fails to explain the geographic pattern short time frame and abruptness of the change from subsidence to uplift that we observe the crustal shortening mechanism is preferred because it allows the observed abrupt uplift when an object impinges on a forearc and causes locking of a shallow segment of the interplate thrust zone

insights into subduction related uplift along the hikurangi margin new zealand using numerical modeling 1 we investigate the causes of regional uplift along the hikurangi margin north island new zealand late quaternary rock uplift rates and postglacial fluvial incision rates delineate broad changes in rock uplift pattern along the margin comparison with the neogene rock uplift rates the erosion surface on basement and the margin morphology suggests that these uplift patterns are long lived and relate to deep seated subduction processes we use two dimensional numerical finite element models to place constraints on margin geometry and uplift rates resulting from subduction processes inferred to drive regional uplift the models indicate that subduction of relatively buoyant and thick hikurangi plateau crust is the most likely mechanism for low rates 1 mm yr 1 of uplift along the entire margin sediment underplating is probably the major cause of higher rates of uplift of the central and northern axial ranges 2 4 mm yr 1 seamount subduction could account for short wavelength zones of higher uplift rate on the order of 1 mm yr 1 and could contribute to tectonic erosion which may be driving uplift in the northern margin this study shows the value of using numerical models to link regional patterns of rock uplift and surface morphology to deep seated subduction processes

marine climate variability during the last millennium the loch sunart record scotland uk abstract the first decadal scale reconstruction of british coastal temperature anomalies spanning the last millennium is presented from a sea loch fjord basin loch sunart nw scotland based on modern observation and the results of previous numerical modeling of fjord circulation benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature a significant climate transition apparently driven by large scale reorganization of northern hemisphere atmospheric circulation occurs in the record around ad 1400 an abrupt but relatively short lived climate warming occurs between ad 1540 1610 when the bottom water temperature anomalies are 1 1 c above the long term average which is warmer than most of the 20th century and the late medieval warm period a long term cooling occurs throughout the little ice age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s the warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record which ends in 2006 a replicated post ad 1900 shift in benthic foraminiferal 13 c of ca 0 6 provides evidence of the oceanic 13 c suess effect this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo proxies in the loch sunart record

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

the potential of arctica islandica growth records to reconstruct coastal climate in north west scotland uk this paper describes potential methods for reconstructing past marine environmental and climatic variability in scottish coastal waters through the investigation of annual growth increments measured from shells of the long lived marine bivalve arctica islandica l this is accomplished by using a combination of sclerochronological and dendrochronological techniques which were employed to determine the age of specimens and to create growth chronologies using negative exponential detrending methods a preliminary a islandica master chronology for the lynn of lorn scotland has been produced this chronology indicates highly suppressed growth between the mid 1940s and late 1980s the growth response of this species to the sea surface temperatures in scottish coastal waters appears to be complex most notably during recent decades when land use changes and marine aquaculture may influence shell growth at this site

first cross matched floating chronology from the marine fossil record data from growth lines of the long lived bivalve mollusc arctica islandica integrated understanding of phasings within the climate system over the last glacial cycle and at higher frequencies is inhibited because no absolute timescale for the marine environment currently exists this precludes identification of forcings and feedbacks accurate temporal calibration of the marine radiocarbon reservoir effect and the application of radiocarbon as a proxy of short timescale ocean ventilation this has prompted a search for annually banded marine proxies in the hope of establishing an accurate marine chronometer we present annual growth band series from dead collected specimens of the long lived bivalve mollusc arctica islandica from the northern north sea and demonstrate their successful cross matching with the general timescale context independently verified by radiocarbon dating though at present limited to only a few statistically cross matched series this has already generated the longest arctica chronology and the first floating chronology constructed entirely from marine fossils the record covers the period from c ad 1000 to 1400 and integrates a 267 yr series from the longest lived arctica specimen yet recorded from the north sea this breakthrough in cross matching demonstrates that arctica islandica can fulfill its potential as the tree of the sea to provide an absolute timescale for the marine environment

synchronous radiocarbon and climate shifts during the last deglaciation radiocarbon data from the cariaco basin provide calibration of the carbon 14 time scale across the period of deglaciation 15 000 to 10 000 years ago with resolution available previously only from holocene tree rings reconstructed changes in atmospheric carbon 14 are larger than previously thought with the largest change occurring simultaneously with the sudden climatic cooling of the younger dryas event carbon 14 and published beryllium 10 data together suggest that concurrent climate and carbon 14 changes were predominantly the result of abrupt shifts in deep ocean ventilation

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

late holocene land and sea level changes in the british isles implications for future sea level predictions abstract four decades of palaeosea level research in the british isles have produced a large dataset of age altitude curves of postglacial sea level changes patterns of late holocene relative sea level change reveal the persistent influence of the british irish ice sheet and the larger scandinavian ice sheet on contemporary rates of vertical land movements the shennan and horton 2002 map of late holocene relative land movements has been used in future sea level rise predictions by the united kingdom climate impact programme in their 2002 assessment ukcip02 but has been mistaken for a map of absolute land movements in this paper land motion data for britain are extracted from the shennan and horton 2002 relative sea level data and a new map of crustal land movements is presented which also includes ireland this procedure takes into account the regional 20th century sea level rise 0 14 m and the process of ocean syphoning i e a global fall in sea level of 0 3 mm yr due to gia induced ocean floor lowering and re distribution of ocean mass the calculated land motion rates also depend on the global late holocene ice equivalent sea level change given by the intergovernmental panel on climate change as 0 0 0 2 mm yr accounting for these processes reduces the misfit between geological observations of vertical land motion and those independently derived from gravity aligned global positioning system ag gps measurements and shows that ukcip02 has underestimated land subsidence in southern britain and over estimated land uplift in scotland both by 0 1 0 2 mm yr a best fit between gps and geological estimates of land movements in britain is achieved for a global long term eustatic sea level fall of ca 0 2 mm yr suggesting some global ice expansion in the late holocene rather than melt if this is correct uplift rates in scotland would be lower and subsidence rates in southern britain would be faster by 0 4 0 5 mm yr than estimated by ukcip02 more high quality late holocene relative sea level data are required to quantify vertical land motion as accurately as possible especially near large coastal population centres for input into regional scenarios of future sea level rise

quaternary science 2007 a 50 year retrospective this paper reviews 50 years of progress in understanding the recent history of the earth as contained within the stratigraphical record of the quaternary it describes some of the major technological and methodological advances that have occurred in quaternary geochronology examines the impressive range of palaeoenvironmental evidence that has been assembled from terrestrial marine and cryospheric archives assesses the progress that has been made towards an understanding of quaternary climatic variability discusses the development of numerical modelling as a basis for explaining and predicting climatic and environmental change and outlines the present status of the quaternary in relation to the geological time scale the review concludes with a consideration of the global quaternary community and the challenge for the future

recent tectonics associated with the subduction collision of the d entrecasteaux zone in the central new hebrides abstract recent data from the new hebrides vanuatu subduction zone have enabled a morphological description and tectonic interpretation to be made of the complex plate contact between the d entrecasteaux zone and the west torres massif on the one hand and the old santo malekula block on the other between latitudes 14 30 and 17 s no trench occurs owing to the presence of the old rigid santo malekula block at the edge of the overriding plate the outer limit of plate contact describes a tortuous line westward of the projected line of the adjacent trenches this may be explained by local collision of the north d entrecasteaux ridge and the south d entrecasteaux chain with the west flank of santo this collision is compensated for by lateral plastic flow of the inner wall downward into the small basins which separate the d entrecasteaux zone ridges a process which may be explained by plastic plane strain theory the westward jump of the plate contact zone here may result from pieces of the north d entrecasteaux ridge being cut off and incorporated in the frontal arc a review of the geological evidence and the shallow seismicity of the central new hebrides shows that radiant horizontal stresses resulting from this collision have generated a specific compressive stress regime which influences the whole width of the arc the resultant deformation shows a close resemblance to a theoretical strain field produced by the indentation of a long narrow plastic body cf the arc by a rigid flat die cf the d entrecasteaux zone thus the central new hebrides block is both elastically bent under vertical stresses and plastically deformed and pushed eastwards by horizontal stresses recent uplift of the eastern chain can be explained by this model in contrast at the rear of both the northern and southern sections of the arc the tectonics are mainly controlled by a tensional stress regime the strong plate interaction due to the subduction of the d entrecasteaux zone is thought to be responsible for the compressive stress regime across the central new hebrides the same cause can be invoked to account for the tensional stress regime observed in north and south new hebrides rear arc regions

centennial climate variability in the british isles during the mid late holocene abstract multi millennial climate changes were relatively minor over the mid late holocene in the british isles because orbitally forced insolation changes were smaller than those at higher latitudes centennial climate variability is thus likely to have exerted a greater influence on the environment and human society of the region proxy climate records from the british isles covering the last 4500 years are assembled and re evaluated with the aim of identifying centennial climate variability reflected by multi proxy indicators the proxies include bog oak populations peatland surface wetness flooding episodes from fluvial deposits speleothem annual band width and oxygen isotopes chironomids from lake sediments and sand and dune deposition most proxies reflect water balance rather than temperature alone and records predominantly reflect warm season climate a series of 12 key periods of enhanced precipitation evaporation p e are identified by their presence in two or more proxy records variability in p e is much greater than that shown by temperature proxies and there is no necessary association between warm cool and dry wet periods although the data for temperature are less robust than those for p e a series of key temperature changes are proposed based on speleothem 18o and chironomid inferred july temperature records relatively cool before c 3100 years bp warmer 3100 2000 years bp cool 2000 1250 cal years bp warm 1250 650 cal years bp and cool 650 cal years bp onwards some key increases in p e 2750 1650 550 cal years bp show a strong correspondence with bond cycles in ocean proxy records for increased ice rafted debris decreased summer sea surface temperatures and sometimes decreased north atlantic deep water circulation other higher frequency changes in p e are also strongly related to sst variability whilst some of the main changes to cooler ssts and increased p e are approximately coincident with reduced solar output most are not and thus must be the result of the internal dynamics of the ocean and atmosphere future work should concentrate on firmly establishing the pattern of temperature change improving chronological accuracy and precision in existing records and improving process based understanding of proxies

chironomid inferred late glacial air temperatures at whitrig bog southeast scotland this paper presents the first chironomid inferred mean july air temperature reconstruction for the late glacial in britain the reconstruction suggests that the thermal maximum occurred early in the interstadial with temperatures reaching about 12 degreesc there was then a gradual downward trend to about 11 degreesc punctuated by four distinct cold oscillations of varying intensity at the beginning of the younger dryas mean july temperatures fell to about 7 5 degreesc but gradually increased to about 9 degreesc before a rapid rise at the onset of the holocene the chironomid inferred temperature curve agrees closely both in general trends and in detail with the grip ice core oxygen isotope curve the reconstructed temperatures are 2 4 degreesc lower than coleopteran inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium line altitudes during the younger dryas copyright c 2000 john wiley sons ltd

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

automated identification location and volume estimation of rockfalls at piton de la fournaise volcano since the collapse of the dolomieu crater floor at piton de la fournaise volcano la reunion in 2007 hundreds of seismic signals generated by rockfalls have been recorded daily at the observatoire volcanologique du piton de la fournaise ovpf to study rockfall activity over a long period of time automated methods are required to process the available continuous seismic records we present a set of automated methods designed to identify locate and estimate the volume of rockfalls from their seismic signals the method used to automatically discriminate seismic signals generated by rockfalls from other common events recorded at ovpf is based on fuzzy sets and has a success rate of 92 a kurtosis based automated picking method makes it possible to precisely pick the onset time and the final time of the rockfall generated seismic signals we present methods to determine rockfall locations based on these accurate pickings and a surface wave propagation model computed for each station using a fast marching method these methods have successfully located directly observed rockfalls with an accuracy of about 100 m they also make it possible to compute the seismic energy generated by rockfalls which is then used to retrieve their volume the methods developed were applied to a data set of 12 422 rockfalls that occurred over a period extending from the collapse of the dolomieu crater floor in april 2007 to the end of the undervolc project in may 2011 to identify the most hazardous areas of the piton de la fournaise volcano summit

a quantitative look at the demise of a basaltic vent the death of kupaianaha kilauea volcano hawai i the kupaianaha vent the source of the 48th episode of the 1983 to present pu u o o kupaianaha eruption erupted nearly continuously from july 1986 until february 1992 this investigation documents the geophysical and geologic monitoring of the final 10 months of activity at the kupaianaha vent detailed very low frequency vlf electromagnetic profiles across the single lava tube transporting lava from the vent were used to determine the cross sectional area of the molten lava within the tube combined with measurements of lava velocity these data provide an estimate of the lava output of kupaianaha in addition lava temperatures calculated from analysis of quenched glass and bulk rock chemistry were obtained for samples taken from the tube at the same site the combined data set shows the lava flux from kupaianaha vent declining linearly from 250 000 m3 day in april 1991 to 54 000 m3 day by november 1991 during that time surface breakouts of lava from weak points along the tube occurred progressively closer to the vent consistent with declining efficiency in lava transport there were no significant changes in lava temperature or in bulk mgo content during this period another eruptive episode the 49th began uprift of kupaianaha on 8 november 1991 and erupted lava concurrently with kupaianaha for 18 days lava flux from kupaianaha decreased in response to this new episode but the response was delayed by approximately 1 day after 14 november 1991 lava velocities were no longer measurable in the tube because the lava stream beneath the skylight had crusted over however the vlf derived electrical conductances documented the decreasing flux of molten lava through the tube kupaianaha remained active but output continued to decrease until early february 1992 when the last active surface flows were seen in november 1991 we used the linearly decreasing effusion rate to accurately predict the date for the death of the kupaianaha vent the linear nature of the decline in lava tube conductance and the delayed and slow response of the waha ula tube conductances to the 49th eruptive episode led us to speculate that a the kupaianaha vent shut down because of a decrease in driving pressure and not because of a freeze up of the vent and b that pu u o o episode 49 and kupaianaha were fed nearly vertically from a source deep within the rift zone

accurate hypocentre determination in the seismogenic zone of the subducting nazca plate in northern chile using a combined on offshore network the coupled plate interface of subduction zones commonly called the seismogenic zone has been recognized as the origin of fatal earthquakes a subset of the after shock series of the great antofagasta thrust type event 1995 july 30 mw 8 0 has been used to study the extent of the seismogenic zone in northern chile to achieve reliable and precise hypocentre locations we applied the concept of the minimum 1 d model which incorporates iterative simultaneous inversion of velocity and hypocentre parameters the minimum 1 d model is complemented by station corrections which are influenced by near surface velocity heterogeneity and by the individual station elevations by relocating mine blasts which were not included in the inversion we obtain absolute location errors of 1 km in epicentre and 2 km in focal depth a study of the resolution parameters ale and dspr documents the importance of offshore stations on location accuracy for offshore events based on precisely determined hypo centres we calculate a depth of 46 km for the lower limit of the seismogenic zone which is in good agreement with previous studies for this area for the upper limit we found a depth of 20 km our results of an aseismic zone between the upper limit of the seismogenic zone and the surface correlates with a detachment zone proposed by other studies the results are also in agreement with thermal studies for the antofagasta forearc region

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

horizontal and vertical interseismic velocity fields in the vanuatu subduction zone from gps measurements evidence for a central vanuatu locked zone we analyzed interseismic velocity fields along the vanuatu arc subduction zone from more than 45 gps station measurements spanning 15 years convergence with respect to the australian plate ap is normal to the trench with amplitudes that vary greatly from a maximum of 170 mm a a1 at vanikoro to 27 mm a a1 facing the d entrecasteaux ridge der motions expressed relative to the pacific plate pp highlight arc segmentation both the northern and southern segments undergo back arc spreading in a roughly ne sw direction rotating anticlockwise and clockwise respectively while the central block moves eastward at a faster rate with respect to the pp than to the ap more convergence is therefore accommodated at the eastern bound of the arc than at the vanuatu trench a right lateral strike slip movement 26 1 mm a a1 along a zone normal to the trench direction n70 is necessary to accommodate the rate variation between the central and southern parts of the arc horizontal and vertical rates indicate partitioning between malekula southernmost santo and central northern santo blocks simple elastic modeling of the interseismic stage deformation gives locked zone characteristics 25 dip and 50 km width and a 54 mm a a1 long term convergence rate between the ap and the central part of the vanuatu arc from gps horizontal and vertical velocities estimated south of the der the modeling does not fit the observed velocities facing the der probably because it does not account for the inelastic deformation associated with buoyant ridge subduction and back arc thrusting

fracture strength of dry silicate rocks at high confining pressures and activity of acoustic emission abstract three dry silicate rocks gabbro dunite and eclogite were triaxially compressed up to a confining pressure of 3 gpa at room temperature these rocks exhibited brittle fracture behavior up to the highest confining pressure the change of the mechanism of fracture in the brittle region is suggested from the measurement of the compressive fracture strength and the activity of acoustic emission the existence of the high pressure brittle fracture phase is proposed the fracture strength increased with increase of confining pressure the increasing rate of strength was lowered at a value of confining pressure at about 0 8 gpa on gabbro at about 1 0 gpa on dunite and at about 1 5 gpa on eclogite at lower confining pressures than the above value the acoustic emission rate began to increase at the onset of dilatancy and increased rapidly followed by fracture as the axial stress was increased at the higher confining pressures however the acoustic emission rate did not increase rapidly before final fracture and stayed constant to the fracture the similar behavior was shown on the granite studied previously it is interesting that the frictional strength forms the boundary between low and high pressure brittle fracture phases

double seismic zone and dehydration embrittlement of the subducting slab 1 dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate depth earthquakes we explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast japan southwest japan northeast taiwan northern chile cape mendocino and eastern aleutians we calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions we then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams the depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age the dehydration loci of serpentine produce a double layered structure because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab we find that the lower plane seismicity is located at the lower dehydration loci of serpentine which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

seismicity and shallow slab geometry in the central vanuatu subduction zone the vanuatu arc in the southwest pacific ocean is one of the world s most seismically active regions with almost 39 magnitude 7 earthquakes in the past 43 years convergence rates are around 90 120 mm yr along most of the arc but drop to 25 43 mm yr in the central section probably due to the subduction of the d entrecasteaux ridge we characterize the slab geometry and tectonic state in this central section by analyzing data from a 10 month deployment of 30 seismometers over this section we located more than 30 000 events all less than magnitude 5 5 constructed an improved 1 d velocity model calculated focal mechanisms and cluster geometries and determined the 3 d geometry of the interplate seismogenic zone the seismogenic zone has a shallow bulge in front of the d entrecasteaux ridge which could be explained by the ridge s buoyancy contributing to the uplift of the fore arc islands the seismogenic zone extends to 45 km depth significantly below the 26 27 km depth of the fore arc moho indicating that the upper mantle wedge is not significantly serpentinized which is consistent with the relatively high thermal parameter of the subducting plate the maximum width of the seismogenic zone is 80 km indicating an upper earthquake magnitude limit of mw 7 85 0 4 assuming standard rupture zone aspect ratios the data also reveal a double seismic zone 20 to 30 km below the seismogenic zone which is presumably caused by flexure of the downgoing plate

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

crustal motions in great britain evidence from continuous gps absolute gravity and holocene sea level data two independent continuous global positioning system cgps processing strategies based on a double difference regional network and a globally transformed precise point positioning solution provide horizontal and vertical crustal motion estimates for great britain absolute gravity and geological information from late holocene sea level data further constrain the vertical motion estimates for 40 cgps stations we estimate station velocities and associated uncertainties using maximum likelihood estimation assuming the presence of white and coloured noise horizontal station velocity estimates agree to 1 mm yr 1 between the two cgps processing strategies and closely follow predicted plate motions residual velocities generally 1 mm yr 1 follow no regular pattern that is there is no discernible internal deformation nor any dependence on station monumentation or time series length vertical station velocity estimates for the two cgps processing strategies agree to similar to 1 mm yr 1 but show an offset of similar to 1 mm yr 1 with respect to the absolute gravity ag estimates we attribute this offset to a bias related to known issues in current cgps results and correct for it by ag alignment of our cgps estimates of vertical station velocity both cgps estimates and ag aligned cgps estimates of present day vertical crustal motions confirm the pattern of subsidence and uplift in great britain derived from holocene sea level data for the last few thousand years ongoing subsidence on shetland uplift in most areas of scotland and subsidence in large areas of england and wales

marine climate in the irish sea analysis of a 489 year marine master chronology derived from growth increments in the shell of the clam arctica islandica abstract we demonstrate here that the growth increment variability in the shell of the long lived bivalve mollusc arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important north atlantic shelf seas multi centennial up to 489 year chronologies were constructed using five detrending techniques and their characteristics compared the strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree ring chronologies the negative exponential function using truncated increment width series from which the first thirty years have been removed was chosen as the optimal detrending technique chronology indices were compared with the central england temperature record and with seawater temperature records from stations close to the study site in the irish sea statistically significant correlations were found between the chronology indices and a mean air temperature for the 14 month period beginning in the january preceding the year of growth b mean seawater temperatures for february october in the year preceding the year of growth c late summer and autumn air temperatures and sea surface temperatures for the year of growth and d the timing of the autumn decline in sst changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics

the collision zone between the north d entrecasteaux ridge and the new hebrides island arc 1 sea beam morphology and shallow structure sea beam bathymetric data closely spaced single channel seismic reflection sections and geopotential field data were collected aboard the r v j charcot over the collision zone between the north d entrecasteaux ridge ndr and the new hebrides island arc the ndr trends east at a small angle 14 to the plate convergence direction so that the ridge creeps northward along the trench at about 2 5 cm yr requiring a continual structural adjustment of the accretionary complex in this report we study the shallow structure tectonic erosion and consequent mass wasting of the accretionary complex all of which were produced by the collision of the ndr in a complex deformational environment the accretionary complex in this collision zone can be divided into northern central and southern parts the northern part of the collision zone which lies north of the leading flank of the ridge shows a lobate lower accretionary complex that is structured by east to southeast dipping thrust and reverse faults and n60 w trending strike slip faults a middle accretionary complex that bulges seaward and appears to be rotated 45 e from the regional arc trend and an upper accretionary complex that is shaped by slumps and a canyon network the central part of the collision zone which directly overlies the crest of the ridge forms a broad shallow protrusion that is bounded on its northern and southern sides by steep scarps rocks forming this protrusion have been uplifted possibly by as much as 1500 2500 m and tilted to the north causing northward block sliding along an extensional detachment surface the southern part of the collision zone which lies in the wake of the ridge is deformed by large slumps and normal faults that trend parallel to the ridge axis rocks forming this southern part collapse causing widespread mass wasting these geophysical data indicate that normal trench convergence has apparently produced only a few trench parallel structures confined to the toe of the accretionary complex whereas the along trench motion of the ndr has resulted in well developed structures that extend obliquely across the arc slope and form an asymmetric tectonic pattern the area of the accretionary complex that is disturbed by collision appears to be about twice as wide as the width of the ndr and the time required to heal the disturbance may be about 0 8 m y

are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle in a number of subduction zones earthquakes at 50 200 km depth define two dipping planes separated by 20 40 km that appear to merge downdip upper plane earthquakes are inferred to occur within the subducting oceanic crust whereas lower plane earthquakes occur in the subducting oceanic mantle beneath northeast japan the results of a new finite element heat transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle lower plane earthquakes occur at 550 800 c at 100 km depth and at 350 600 c at 160 km depth these conditions coincide with the dehydration reaction antigorite serpentine forsterite enstatite h 2 o which suggests that lower plane earthquakes may be triggered by dehydration embrittlement which in turn suggests that the subducting oceanic mantle is partially hydrated serpentinization may occur in the trench outer rise region where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere if this hypothesis is correct current subduction zone h 2 o budgets may significantly underestimate the amount of bound h 2 o entering the subduction factory

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

regional consistency in lateglacial chironomid inferred temperatures from five sites in north west england abstract high resolution lateglacial ice core records from greenland show both millennial and centennial scale change and have been used as a benchmark for lateglacial climatic stratigraphy throughout the north atlantic region and beyond in this study we assess the local reflection in north west europe of climatic events recognised in ice cores and identify differences in the climate signature between greenland uk and sites in continental europe this study uses chironomid inferred temperature analysis and loss on ignition data from five carbonate lakes in north west england to determine the pattern of lateglacial climatic change and demonstrates the reproducibility of chironomid inferred temperature reconstructions both within a catchment and from sites within a small area at both millennial and centennial scales our results show statistical similarities between sites giving a clear regional signal chironomid assemblages pick out the rapid shifts at the major event boundaries at all sites and indicate temperatures of between 12 and 13 c for the region at the beginning of greenland interstadial 1 a rapid fall of around 4 c into the younger dryas and a rise of around 5 c in the early holocene at a finer scale four centennial cooling events are identified within the interstadial together with an oscillation in the early holocene which we tentatively identify as the pre boreal event the records were analysed statistically using redundancy analysis and sequence slotting techniques differences in the impact of individual climatic events demonstrate that subtle changes in the chironomid inferred temperatures reflect the local geographical setting and morphology of the lakes with more marked impact registered in higher altitude and more wind exposed sites whilst the overall pattern of lateglacial climate can be recognised from greenland to central europe important regional differences that can be attributed to marine influence and perhaps changes in atmospheric circulation are beginning to emerge

holocene climate variability revealed by oxygen isotope analysis of sphagnum cellulose from walton moss northern england abstract stable isotope analyses of sphagnum alpha cellulose precipitation and bog water from three sites across northwestern europe raheenmore ireland walton moss northern england and dosenmoor northern germany over a total period of 26 months were used to investigate the nature of the climatic signal recorded by sphagnum moss the 18o values of modern alpha cellulose tracked precipitation more closely than bog water with a mean isotopic fractionation factor cellulose precipitation of 1 0274 0 001 1 27 sub samples of isolated sphagnum alpha cellulose were subsequently analysed from core wlm22 walton moss northern england yielding a sphagnum specific isotope record spanning the last 4300 years the palaeo record calibrated using the modern data provides evidence for large amplitude variations in the estimated oxygen isotope composition of precipitation during the mid to late holocene estimates of palaeotemperature change derived from statistical relationships between modern surface air temperatures and 18oprecipitation values for the british isles give unrealistically large variation in comparison to proxies from other archives we conclude that use of such relationships to calibrate mid latitude palaeo data must be undertaken with caution the 18o record from sphagnum cellulose was highly correlated with a palaeoecologically derived index of bog surface wetness bsw suggesting a common climatic driver

quaternary uplift astride the aseismic cocos ridge pacific coast costa rica the pacific coast of costa rica lies within the central american forearc and magmatic arc region that was created by northeastward subduction of the cocos plate beneath the caribbean plate at the middle america trench from the peninsula de nicoya south eastward toward the peninsula de osa and the peninsula de burica on the panamanian border the middle america trench loses its physiographic expression where it intersects the aseismic cocos ridge interaction between subduction of the buoyant aseismic cocos ridge and the overriding caribbean plate is invoked to explain the variation in rates of vertical crustal uplift along a coastal transect from nicoya to burica the pliocene and pleistocene stratigraphic record and holocene marine terraces and beach ridge complexes indicate that maximum rates of crustal uplift have occurred on the peninsula de osa immediately landward of the aseismic cocos ridge crustal uplift rates decrease northwest toward the peninsula de nicoya and to a lesser extent southwest toward the peninsula de burica the late quaternary stratigraphy on the peninsula de osa is subdivided into two major chronostratigraphic sequences from groupings of radiocarbon dates crustal uplift rates calculated from these sequences systematically decrease from 6 5 to 2 1 m ka north east across the peninsula deformation of the peninsula is modeled as uplifted and down to the northeast tilted fault blocks with an angular rotation rate of 0 03 to 0 06 per thousand years although less well constrained crustal uplift rates on the peninsula de nicoya 200 km to the northwest of the peninsula de osa vary from 1 m ka for pliocene and pleistocene sediments to 2 5 m ka for holocene marine terraces in the quepos region 100 km to the northwest of the peninsula de osa calculated uplift rates derived from incision of late quaternary fluvial terraces range from 0 5 to 3 0 m ka on the peninsula de burica only 60 km to the southwest of the peninsula de osa calculated uplift rates range from 4 7 m ka for a late holocene marine terrace to 1 2 m ka for post late pliocene deep sea sediments the variations in calculated uplift rates on the peninsula de osa constrain a dynamic model for subduction of the cocos ridge and the resulting uplift of the overriding caribbean plate deflection of the caribbean plate is modeled using various effective elastic thicknesses as the response of an elastic plate to the buoyant force of the subducted cocos ridge because the shape of the subducted end of the cocos ridge is unknown two scenarios are evaluated 1 a radially symmetric ridge with a slope similar to the slope of the flanks of the ridge and 2 a ridge where the subducted end was truncated by the panama fracture zone the best fit model utilizes a truncated ridge that has been subducted during the past 0 5 m y 50 km beneath the overriding caribbean plate which has an effective elastic thickness of 5 km the model predicts that the highest uplift rate should be 3 7 m ka and occur on the southwest coast of the peninsula de osa the rate of uplift slows considerably to the northeast and indicates that the peninsula de osa is tilting to the northeast which agrees with observations in that region the predicted uplift rate attributed to aseismic ridge subduction also decreases along the coast both north and south of the peninsula de osa resulting in little uplift that can be attributed to cocos ridge subduction in the northwestern portions of the peninsula de nicoya

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

megathrust earthquakes can nucleate in the forearc mantle evidence from the 2004 sumatra event current models predict that the seismogenic zone along subduction thrusts where the largest earthquakes nucleate and propagate does not extend to the forearc mantle below the crust of the upper plate stable sliding conditions have been shown to prevail there particularly along several circum pacific margins that underwent great megathrust earthquakes mw 8 5 during the twentieth century based on geophysical investigation we show that the great 2004 sumatra andaman earthquake mw 9 9 3 contradicts these models not only did it propagate downdip along the interface between the forearc mantle and the subducting plate but it actually nucleated along this reportedly aseismic part of the interplate contact petrological models can therefore underestimate the downdip extent of rupture zones to be expected in megathrust earthquakes and need to be revised to account for this observation albeit unusual

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally