high resolution numerical modeling of stress distribution in visco elasto plastic subducting slabs abstract we employ high resolution 2d thermomechanical modelling with complex elasto visco plastic rheology to analyse stresses in subducting and overriding plates the model contains a dynamic subduction channel defined as a few km thick zone of specific weak visco plastic rheology between the slab and the overriding plate our high resolution model corresponds to the zoom in of the large scale thermomechanical model of the central andes with the 4 fold resolution increase initial model configuration material temperature and stress distributions was interpolated from the parent model boundary conditions including slab pull and push velocities as well as velocity of the overriding plate were also re mapped from the large scale model we demonstrate that for shallow dipping overridden slabs the dominant stress is unbending stress at 50 100 km depth this stress reaches 1 1 5 gpa and strongly prevails over the slab bending stress near the trench which is limited by the frictional plastic yield unbending creates double 5 10 km distance between maximums compression zone in the upper part of the slab and a zone of extension some 20 30 km below pressure in these zones differs from the lithostatic pressure to as much as plus minus 0 8 gpa details of the distribution and magnitude of bending and unbending stresses in the slab are mainly controlled by the overriding velocity and direction of the slab pull force overpressure in the subduction channel in all models does not exceed 100 mpa large over and under pressures in the slab do not however lead to significant more than 10 km offsets of main dehydration reactions in crust and mantle of the slab

late weichselian and holocene sedimentary palaeoenvironment and glacial activity in the high arctic van keulenfjorden spitsbergen high arctic fjords for example van keulenfjorden on spitsbergen provide valuable palaeoenvironmental archives as they typically contain landforms and sediment sequences that document past changes in glacial activity with high temporal resolution van keulenfjorden was covered with a grounded glacier during the last glacial and it was deglaciated between c 11 8 and 11 3 cal ka bp the retreat of the ice front accelerated from approximately 80 to 190 m a during the deglaciation the maximum late holocene glacier extent occurred after surge like advances of the glacier nathorstbreen between 2790 and 2610 cal yr bp i e during a period with the coldest climatic conditions on svalbard this maximum extent was reached approximately 2600 years earlier than inferred for most fjords on svalbard suggesting that surge like glacier advances on svalbard can occur under variable climatic conditions the time interval between the advances of nathorstbreen around 2 7 ka bp was approximately 100 150 years this is comparable to the last and only historically known quiescent phase of nathorstbreen of c 120 years between the late 19th century and the most recent surge from 2003 to 2012

permafrost and climate in europe monitoring and modelling thermal geomorphological and geotechnical responses we present a review of the changing state of european permafrost within a spatial zone that includes the continuous high latitude arctic permafrost of svalbard and the discontinuous high altitude mountain permafrost of iceland fennoscandia and the alps the paper focuses on methodological developments and data collection over the last decade or so including research associated with the continent scale network of instrumented permafrost boreholes established between 1998 and 2001 under the european union pace project data indicate recent warming trends with greatest warming at higher latitudes equally important are the impacts of shorter term extreme climatic events most immediately reflected in changes in active layer thickness a large number of complex variables including altitude topography insolation and snow distribution determine permafrost temperatures the development of regionally calibrated empirical statistical models and physically based process oriented models is described and it is shown that though more complex and data dependent process oriented approaches are better suited to estimating transient effects of climate change in complex mountain topography mapping and characterisation of permafrost depth and distribution requires integrated multiple geophysical approaches and recent advances are discussed we report on recent research into ground ice formation including ice segregation within bedrock and vein ice formation within ice wedge systems the potential impacts of climate change on rock weathering permafrost creep landslides rock falls debris flows and slow mass movements are also discussed recent engineering responses to the potentially damaging effects of climate warming are outlined and risk assessment strategies to minimise geological hazards are described we conclude that forecasting changes in hazard occurrence magnitude and frequency is likely to depend on process based modelling demanding improved understanding of geomorphological process response systems and their impacts on human activity

the seasonal water temperature cycle in the arctic dicksonfjord svalbard during the holocene climate optimum derived from subfossil arctica islandica shells future climate change will have significant effects on ecosystems worldwide and on polar regions in particular hence palaeo environmental studies focussing on the last warmer than today phase i

p s velocity and vp vs ratio beneath the toba caldera complex northern sumatra from local earthquake tomography summary in this paper we investigate the crustal and uppermost mantle structure beneath toba caldera which is known as the location of one of the largest cenozoic eruptions on earth the most recent event occurred 74 000 yr bp and had a significant global impact on climate and the biosphere in this study we revise data on local seismicity in the toba area recorded by a temporary passcal network in 1995 we applied the newest version of the lotos 07 algorithm which includes absolute source location optimization of the starting 1 d velocity model and iterative tomographic inversion for 3 d seismicp s or thevp vs ratio and source parameters special attention is paid to verification of the obtained results beneath the toba caldera and other volcanoes of the arc we observe relatively moderate for volcanic areas negative p and s velocity anomalies that reach 18 per cent in the uppermost layer 10 12 per cent in the lower crust and about 7 per cent in the uppermost mantle much stronger contrasts are observed for the vp vs ratio that is a possible indicator of dominant effect of melting in origin of seismic anomalies at a depth of 5 km beneath active volcanoes we observe small patterns 7 15 km size with a high vp vs ratio that might be an image of actual magmatic chambers filled with partially molten material feeding the volcanoes in the mantle wedge we observe a vertical anomaly with low p and s velocities and a high vp vs ratio that link the cluster of events at 120 140 km depth with toba caldera this may be an image of ascending fluids and melts released from the subducted slab due to phase transitions however taking into account poor vertical resolution these results should be interpreted with prudence although the results show clear signatures that are quite typical for volcanic areas low velocity and high vp vs ratio beneath volcanoes we do not observe any specific features in seismic structure that could characterize toba as a super volcano

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

creating realistic models based on combined forward modeling and tomographic inversion of seismic profiling data amplitudes and shapes of seismic patterns derived from tomographic images often are strongly biased with respect to real structures in the earth in particular tomography usually provides continuous velocity distributions whereas major velocity changes in the earth often occur on first order interfaces we propose an approach that constructs a realistic structure of the earth that combines forward modeling and tomographic inversion fm ti using available a priori information we first construct a synthetic model with realistic patterns then we compute synthetic times and invert them using the same tomographic code and the same parameters as in the case of observed data processing we compare the reconstruction result with the tomographicimage of observed data inversion if a discrepancy is observed we correct the synthetic model and repeat the fm ti process after several trials we obtain similar results of synthetic and observed data inversion in this case the derived synthetic model adequately represents the real structure of the earth in a working scheme of this approach we three authors used two different synthetic models with a realistic setup one of us created models but the other two performed the reconstruction with no knowledge of the models we discovered that the synthetic models derived by fm ti were closer to the true model than the tomographic inversion result our reconstruction results from modeling marine data acquired in the musicians seamount province in the pacific ocean indicate the capacity and limitations of fm ti

holocene paleoclimatology of the queen elizabeth islands canadian high arctic abstract a wide variety of evidence reflecting in different ways the changing climate of the queen elizabeth islands during the holocene is reviewed all proxies pertain to summer conditions many sources of information provide weak or equivocal paleoclimatic signals but a general pattern of events can be discerned temperatures in the early to mid holocene were highest comparable with or higher than temperatures prevailing for much of this century although much evidence points to a mid holocene thermal maximum there is also considerable evidence that conditions were warmer in the early holocene possibly related to orbitally induced radiation anomalies the apparent mid holocene thermal maximum may reflect lags in the response of the environment and of some proxies in recording paleoclimatic conditions more direct indices point to warmest conditions in the early holocene before 7500 bp temperatures declined from 3000 bp culminating in exceptionally low temperatures from 100 400 bp this may have been the coldest period of the entire holocene resulting in glacier advances to post glacial maximum positions the period since 1925 has witnessed a pronounced increase in temperature leading to negative mass balances on glaciers and ice sheets throughout the archipelago this period is the warmest for at least 1000 years and perhaps for several thousand years modern climate in the queen elizabeth islands may thus be characteristic of the early to mid holocene and atypical of conditions which prevailed for much of the last few thousand years

research paperreprint of reconstruction of inflow of atlantic water to isfjorden svalbard during the holocene correlation to climate and seasonality the distribution patterns of benthic foraminifera faunas stable isotopes and ice rafted debris ird have been studied in piston core jm98 845 pc from isfjorden western svalbard to reconstruct changes in the flow of atlantic water during the holocene interglacial the paleoenvironmental conditions in isfjorden and the inflow of the atlantic water followed closely the changes in insolation with strong seasonality in the early holocene and weaker seasonality in the middle to late holocene a summer temperature maximum of the bottom water occurred in the early holocene 10 500 c 8200 years bp cooling began at 9000 years bp with stepwise coolings at c 8200 7400 and 4000 years bp the cooling correlated with an increase in ice rafting and increased influence of polar water and seasonal sea ice cover between 4000 and 2000 years bp bottom water temperatures reached a minimum after 2000 years bp episodic inflow of warmer atlantic water at the bottom of the fjord occurred and conditions became more unstable the data indicate close interaction of the flow of atlantic water with the development of the terrestrial climate and the amount of polar meltwater and sea ice

structure and tectonics of the erosional convergent margin off antofagasta north chile 23 30 s subduction erosion has dominated the evolution of the north chile convergent continental margin since at least the mesozoic we investigate the structure of the antofagasta 23 s sector of this margin along a transect using coincident wide angle and near vertical seismic profiling and gravity data a 2 d velocity field of the overriding and subducting plates was obtained using joint refraction and reflection travel time tomography a velocity derived density distribution was used to model marine gravity data and substantiate the velocity model the gravity and velocity models imply that the overriding plate is mainly made of arc type igneous basement the upper plate is constructed of two main rock bodies separated by a subhorizontal layer defined by a velocity inversion the top coincident with a reflection in near vertical seismic images the seismic boundary is interpreted as a detachment separating an upper extended domain with large scale normal faulting from a lower domain apparently undergoing a different type of deformation velocity derived porosity indicates that the front of the margin is probably fluid saturated and disaggregated by fracturation as a consequence of frontal subduction erosion fluids carried into the subduction channel within slope debris filling underthrusting grabens reduce basal friction and probably induce hydrofracturing and basal erosion along the underside of the overriding plate at depths greater than 20 km porosity and density values imply that most fluids have been exhausted and the lower part of the upper plate is structurally coherent and little fractured the change in physical properties leads to increased mechanical coupling along the plate boundary and occurs at the updip limit of the distribution of aftershocks of the 1995 antofagasta earthquake m w 8 0 defining the seismogenic zone

late weichselian and holocene sedimentary environments and ice rafting in isfjorden spitsbergen abstract multi proxy analyses of two sediment cores from central isfjorden were used to reconstruct the glacial history in central spitsbergen during the late weichselian and the holocene and to relate iceberg rafting and sea ice rafting to climatic and oceanographic changes in the north atlantic region a basal till was deposited beneath an ice stream prior to 12 700 cal years bp calendar years before the present several tidewater glaciers influenced the sedimentary environment during the younger dryas and probably already during the allerod the younger dryas cooling might be reflected by enhanced sea ice formation and suspension settling as well as reduced iceberg rafting the final deglaciation was dominated by intense iceberg rafting it terminated around 11 200 cal years bp optimum holocene climatic and oceanographic conditions with significantly reduced ice rafting occurred between c 11 200 and 9000 cal years bp ice rafting occurred almost exclusively from icebergs after 10 200 cal years bp the icebergs most probably originated from tidewater glaciers on east spitsbergen indicating the presence of a strong east west temperature gradient at this time an increase of iceberg rafting around 9000 cal years bp followed by enhanced sea ice rafting reflects the onset of a general cooling in the western barents sea svalbard region comparatively intense rafting from icebergs and sea ice between 9000 and 4000 cal years bp is related to this cooling a general reduction in ice rafting after 4000 cal years bp is most probably the result of the enhanced formation of shore fast and or more permanent sea ice cover reducing the drift of icebergs and sea ice in the fjord the results indicate that the palaeoenvironmental conditions on central spitsbergen to a large degree depended on the oceanographic conditions in the western barents sea and west off spitsbergen however climatic trends affecting greenland and the entire north atlantic region can also be identified

the recession of the inland ice margin during the holocene climatic optimum in the jakobshavn isfjord area of west greenland recent subsurface mapping of parts of the greenland inland ice margin in the region of jakobshavn isbrae indicates that the fjord system in the period of at least 2700 4700 calendar yr b p was more ice free than at present and that the front of the glacier was at least 15 km behind the present position the 14c datings of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for greenland s first settlers the sarqaq people who arrived in the region about 4000 yr ago to find hunting grounds 10 20 larger than the present

debris flow recurrence periods and multi temporal observations of colluvial fan evolution in central spitsbergen svalbard abstract fan shaped accumulations of debris flow deposits are common landforms in polar regions such as svalbard although depositional processes in these environments are of high interest to climate as well as mars analog research several parameters e g debris flow recurrence periods remain poorly constrained here we present an investigation based on remote sensing as well as in situ data of a 0 4 km2 large colluvial fan in hanaskogdalen central spitsbergen we analyzed high resolution satellite and aerial images covering five decades from 1961 to 2014 and correlated them with lichenometric dating as well as meteorological data image analyses and lichenometry deliver consistent results and show that the recurrence period of large debris flows 400 m3 is about 5 to 10 years with smaller flows averaging at two per year in the period from 2008 to 2013 while this is up to two orders of magnitude shorter than previous estimates for svalbard 80 to 500 years we found the average volume of 220 m3 per individual flow to be similar to previous estimates for the region image data also reveal that an avulsion took place between 1961 and 1976 when the active part of the fan moved from its eastern to its western portion a case study of the effects of a light rain event 5 mm day in the rainy summer of 2013 which triggered a large debris flow further shows that even light precipitation can trigger major flows this is made possible by multiple light rain events or gradual snow melt pre saturating the permafrost ground and has to be taken into account when predicting the likelihood of potentially hazardous mass wasting in polar regions furthermore our findings imply a current net deposition rate on the colluvial fan of 480 m3 year which is slightly less than the integrated net deposition rate of 576 to 720 m3 year resulting from the current fan volume divided by the 12 500 to 10 000 years since the onset of fan build up after the area s deglaciation however the actual deposition rate which should increase in a warmer climate including more rain cannot be constrained due to effects like ongoing toe cutting of the debris fan and some flows only causing internal redistributions

the island of amsterdamoya a key site for studying past climate in the arctic archipelago of svalbard abstract this paper introduces a series of articles assembled in a special issue that explore holocene climate evolution as recorded in lakes on the island of amsterdamoya on the westernmost fringe of the arctic svalbard archipelago due to its location near the interface of oceanic and atmospheric systems sourced from arctic and atlantic regions amsterdamoya is a key site for recording the terrestrial response to marine and atmospheric changes we employed multi proxy approaches on lake sediments integrating physical biogeochemical and isotopic analyses to infer past changes in temperature precipitation and glacier activity the results comprise a series of quantitative holocene length paleoclimate reconstructions that reveal different aspects of past climate change each of the four papers addresses various facets of the holocene climate history of north western svalbard including a reconstruction of the annabreen glacier based on the sedimentology of the distal glacier fed lake gjoavatnet a reconstruction of changing hydrologic conditions based on sedimentology and stratigraphy in lake hakluytvatnet reconstruction of summer temperature based on alkenone paleothermometry from lakes hakluytvatnet and hajeren and a hydrogen isotope based hydrological reconstruction from lake hakluytvatnet we also present high resolution paleomagnetic secular variation data from the same lake which document important regional magnetic field variations and demonstrate the potential for use in synchronizing holocene sedimentary records in the arctic the paleoclimate picture that emerges is one of early holocene warmth from ca 10 5 ka bp interrupted by transient cooling ca 10 8ka bp and followed by cooling that mostly manifested as two stepwise events ca 7 and 4 ka bp the past 4ka were characterized by dynamic glaciers and summer temperature fluctuations decoupled from the declining summer insolation

denudation rates in the arctic estimated from lake sediments on spitsbergen svalbard a mean holocene denudation rate of 15 mm 1000 yr is calculated for the high arctic valley linnedalen western svalbard based on estimates of the total volume of lacustrine sediments deposited in lake linnevatnet thirty six sub bottom sediment profiles and 16 sediment cores have been used to map the postglacial sediments stored in the lake these reveal a lower marine unit overlain by lacustrine sediments the base and top of the marine sediments were radiocarbon dated to around 12 300 and 9600 yr b p respectively from isopach maps of the lacustrine unit and the total sediment thickness we calculated 0 9 10 2 km3 of holocene lacustrine sediments and 20 1 10 2 km3 of marine sediments a denudation rate of 15 mm 1000 yr is calculated from the volume of the lacustrine sediments this demonstrates that fluvial erosion does not contribute significantly to the lowering of the landscape in the present climate in contrast glacial erosion rates in nearby areas on svalbard are much higher indicating that glacial erosion by warm based valley glaciers is the most important geomorphic process in the present climate three km of tertiary sediments are postulated to have been removed from central parts of svalbard our denudation rates suggest that this could not have occurred in the present interglacial type of climate we suggest that most of that was removed either in a warmer climate or by glaciers

a multi disciplinary macrofossil study of middle weichselian sediments at kobbelgard mon denmark abstract multi proxy studies of radiocarbon and luminescence dated middle weichselian sediments and allochthonous plant and animal macrofossils from kobbelgaard mon point to a lacustrine environment with shallow mesotrophic fresh water the lake was surrounded by mires rich in mosses and carex while the vegetation on the uplands was tree less and herb dominated but with scattered shrubs the climate was considerably colder than at the present day with average july temperatures around 11 c about 6 c below those for the region today probably normal for the later part of the middle weichselian the sediments contain the first remains of lemmings dicrostonyx torquatus and lemmus lemmus found in denmark

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

structure and tectonics of the central chilean margin 31 33 s implications for subduction erosion and shallow crustal seismicity the pre and current collision of the juan fernandez ridge with the central chilean margin at 31 33 s is characterized by large scale crustal thinning and long term subsidence of the submarine forearc caused by subduction erosion processes here we study the structure of the central chilean margin in the ridge trench collision zone by using wide angle and multichannel seismic data the transition from the upper to middle continental slope is defined by a trenchward dipping normal scarp with variable offsets of 500 2000 m height beneath the scarp the 2 d velocity depth models show a prominent lateral velocity contrast of 1 s 1 that propagates deep into the continental crust defining a major lateral seismic discontinuity the discontinuity is interpreted as the lithological contact between the subsided collapsed outermost forearc composed of eroded and highly fractured volcanic rocks and the seaward part of the uplifted coastal cordillera made of less fractured metamorphic igneous rocks extensional faults are abundant in the collapsed outermost forearc however landward of the continental slope scarp both extensional and compressional structures are observed along the uplifted continental shelf that forms part of the coastal cordillera particularly at the landward flank of the valparaiso forearc basin 32 33 5 s shallow crustal seismicity has been recorded in 2008 2009 forming a dense cluster of thrust events of mw 4 5 the estimated hypocentres spatially correlate with the location of the fault scarp and they highlight the upper part of the seismic crustal discontinuity

ams radiocarbon dating of organic poor lake sediment an example from linnevatnet spitsbergen svalbard ams radiocarbon dating of specific organic fractions is used to evaluate sources of errors in dating of organic poor lake sediment from linnevatnet a proglacial arctic lake dates on un differentiated bulk organic matter are much too old because of contamination from detrital coal attempts to remove coal from other organic matter were only partially successful a consequence of the wide grain size distribution of the coal even if coal contamination is fully removed the bulk of the remaining organic matter is of aquatic origin and is unsuitable for 14c dating because the lake waters are depleted in 14 c due to dissolution of carbonate minerals terrestrial plant macrofossils provide the only reliable material to date the lake sediment however this material is present in sufficient quantity for ams radiocarbon dating only in cores proximal to the main inlet streams paired dates on terrestrial plants and aquatic insects from the same core level and paired dates on modern aquatic and terrestrial vege

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

geological record of fluid flow and seismogenesis along an erosive subducting plate boundary a fossil erosive subduction channel the shear zone marking the plate boundary preserved in the northern apennines of italy is identified the fossil zone records the presence of two decollements which seem to have been simultaneously active at the top and base of the subduction channel in modern subduction zones the onset of seismic activity is believed to occur at 150 c however in the fossil channel the onset seems to have occurred at colder temperatures tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the earth s subduction zones1 2 in situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone until now a fossil erosive subduction channel the shear zone marking the plate boundary3 has not been recognized in the field so that seismic observations have provided the only information on plate boundary processes at erosive margins here we show that a fossil erosive margin is preserved in the northern apennines of italy it formed during the tertiary transition from oceanic subduction to continental collision and was preserved by the late deactivation and fossilization of the plate boundary the outcropping erosive subduction channel is 500 m thick it is representative of the first 5 km of depth with its deeper portions reaching 150 c the fossil zone records several surprises two decollements were simultaneously active at the top and base of the subduction channel both deeper basal erosion and near surface frontal erosion occurred at shallow depths extension was a key deformation component within this erosive convergent plate boundary and slip occurred without an observable fluid pressure cycle at depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast co seismic and slow inter seismic slip in the deepest portions of the outcropping subduction channel extension is finally overprinted by compressional structures in modern subduction zones the onset of seismic activity is believed to occur at 150 c but in the fossil channel the onset occurred at cooler palaeo temperatures

seismic structure of the north central chilean convergent margin subduction erosion of a paleomagmatic arc we study the erosive convergent margin of north central chile at similar to 31 degrees s by using high resolution bathymetric wide angle refraction and multichannel seismic reflection data to derive a detailed tomographic 2 d velocity depth model in the overriding plate our velocity model shows that the lowermost crustal velocities beneath the upper continental slope are 6 0 6 5km s which are interpreted as the continental basement composed by characteristic metamorphic and igneous rocks of the coastal cordillera beneath the lower and middle continental slope however the presence of a zone of reduced velocities 3 5 5 0km s is interpreted as the outermost fore arc composed of volcanic rocks hydrofractured as a result of frontal and basal erosion at the landward edge of the outermost fore arc the bathymetric and seismic data provide evidence for the presence of a prominent trenchward dipping normal scarp similar to 1km offset which overlies a strong lateral velocity contrast from similar to 5 0 to similar to 6 0km s this pronounced velocity contrast propagates deep into the continental crust and it resembles a major normal listric fault we interpret this seismic discontinuity as the volcanic continental basement contact of the submerged coastal cordillera characterized by a gravitational collapse of the outermost fore arc subduction erosion has most likely caused large scale crustal thinning and long term subsidence of the outermost fore arc

holocene multi proxy environmental reconstruction from lake hakluytvatnet amsterdamoya island svalbard 79 5 n high resolution proxy records of past climate are sparse in the arctic due to low organic production that restricts the use of radiocarbon dating and challenging logistics that make data collection difficult here we present a new lake record from lake hakluytvatnet at amsterdamoya island 79 5 n the northwesternmost island on svalbard multi proxy analyses of lake sediments in combination with geomorphological mapping reveal large environmental shifts that have taken place at amsterdamoya during the holocene a robust chronology has been established for the lake sediment core through 28 ams radiocarbon ages and this gives an exceptionally well constrained age control for a lake at this latitude the holocene was a period with large changes in the hakluytvatnet catchment and the onset of the neoglacial ca 5 ka marks the start of modern day conditions in the catchment the neoglacial is characterized by fluctuations in the minerogenic input to the lake as well as internal productivity and we suggest that these fluctuations are driven by atmospherically forced precipitation changes as well as sea ice extent modulating the amount of moisture that can reach hakluytvatnet

high latitude holocene paleosecular variation and magneto stratigraphic correlation between two lakes on spitsbergen 78 n abstract paleomagnetic signals in cores from two nearby lakes linnevatn and skardtjonn on spitsbergen 78 n record high latitude geomagnetic field variations for the last 10000 years although the paleomagnetic signal in the lake linnevatn core has probably been modified by subsampling effects application of a latitude invariant transformation procedure yields logs with directional amplitudes similar to the transformed holocene paleosecular variation master curve from the uk stratigraphic correlations based on pattern recognition suggest maximum ages of the lacustrine sediments in agreement with 14c age determinations age depth curves based on more than six magnetic datum horizons from each core reveal an abrupt increase in sedimentation rate in linnevatn from about 0 4 mm year 1 to about 0 8 mm year 1 around 2500 b p vertical inclinations in both cores between about 3500 and 6000 b p are interpreted to reflect a stationary magnetic pole in the region of the sampling sites this adds further arguments for the proposed sudden dipole shift recognized around 3500 b p in paleomagnetic records from high latitude 63 n lacustrine sediments in alaska

flora fauna and climate of scotland during the weichselian middle pleniglacial palynological macrofossil and coleopteran investigations thin lenses of organic rich material on the upper surface of a layer of glacio fluvial deposits have been studied in an open cast coal mine near sourlie western scotland radiocarbon dates on antler fragments plant debris and bulk organic matter from silt showed that the sediments accumulated between ca 33 500 and 29 000 14c yr bp during a period when this part of western scotland was free of glaciers the organic rich sediments yielded a very rich flora and fauna and in total about 160 plant taxa and 61 coleopteran taxa were recorded together with other invertebrates the sourlie flora is one of the richest late middle weichselian floras yet studied within the british isles leg bones of coelodonta antiquitatis woolly rhinoceros and rangifer tarandus reindeer were also found at the site during this period the landscape was treeless and the vegetation could be characterised as an intermediate between a low shrub tundra and sedge grass moss tundra both the flora and arthropod fauna suggest that during formation of the organic rich layers at sourlie mean july temperatures were 9 10 c the flora suggests also that at the beginning of formation of these layers minimum mean july temperatures increased from 7 to 9 10 c but later dropped again to 7 8 c a possible time correlation with one of the warmer periods of the dansgaard oeschger cycles in the stable oxygen isotope record of the greenland ice cores during this period is proposed the arthropod fauna suggests that mean january temperatures were somewhere between 34 and 11 c mean annual temperatures lay probably between 1 and 10 c which implies the possible presence of discontinuous or continuous permafrost in the area during winter a protective snow cover of varying thickness probably enabled perennial plants especially shrubs to survive

holocene glacial history of svalbard status perspectives and challenges abstract we synthesize the current understanding of glacier activity on svalbard from the end of the late pleistocene 12 000 yrs before present to the end of the little ice age c 1920 ad our glacier history is derived from the svalhola database the first compilation of holocene geochronology for svalbard and the surrounding waters including over 1 800 radiocarbon terrestrial cosmogenic nuclide and optically stimulated luminescence ages data have been categorized by geological setting uniformly re calibrated quality assessed and ultimately used to constrain glacier fluctuations deglaciation ice free conditions glacier re advances and ice marginal positions we advance existing knowledge by mapping the extent and distribution of ice cover during the holocene glacial maximum and the glacial minimum as well as present retreat rates and percentages within early holocene fjord systems throughout the holocene svalbard glaciers have responded to a varying combination of climatic environmental and dynamic driving factors which influence both the extent and behavior of ice margins we discuss the complexities of glacier systems and their dynamics in response to changes in climate this review provides a holistic state of the art of holocene glaciers on svalbard suitable for orienting future works which address gaps in our current knowledge

accretion and erosion in subduction zones the role of fluids convergence occurs today along about 60 000 km of plate boundaries parsons 1981 in this paper we consider frontal subduction which occurs along about 40 000 km of convergent plate boundaries using the kine matic solution of de mets et al 1990 and including 0 5 km 2 yr1 of marginal basin openings otsuki 1989 we find that 2 95 km 2 per year disappear in frontal subduction at an average rate of 7 3 cm yr the upper overriding plate is significantly modified not only through the addition of a large amount of magmatic material markhinin 1968 but also through tectonic processes which result either in outgrowth of the margin through addit ion of sediments silver 1969 or in recession through frontal and subcrustal erosion which appears to be linked to sediment subduction coats 1962 gilluly 1963 the various phenomena observed must in some way be related to variations in mechanical coupling between the two plates uyeda kanamori 1979 had proposed that the transition from erosion to accretion results from increasing mechanical coupling the marianas trench was presented as typical of an crosional margin and the chile trench of an accreting margin ruff kanamori 1980 and kana mori 1986 showed that the magnitude of the subduction earthquakes increases with the convergence velocity and the inverse of the age of the subducted lithosphere this correlation was qualitatively explained by the control of age on the d ip of the platc and of convergence velocity on the

hydroclimate variability of high arctic svalbard during the holocene inferred from hydrogen isotopes of leaf waxes abstract the response of the arctic hydrologic cycle to global warming includes changes in precipitation patterns and moisture availability associated with variable sea ice extent and modes of atmospheric circulation reconstructions of past hydroclimate changes help constrain the natural range of these systems identify the manners in which they respond to different forcing mechanisms and reveal their connections to other components of the climate system all of which lead to a better understanding of present and future changes here we examine hydroclimate changes during the holocene in the high arctic archipelago of svalbard by reconstructing the isotopic composition of precipitation we measured the hydrogen isotopic composition d values of leaf wax compounds n alkanes c 25 c 31 in a sediment core from lake hakluytvatnet on the island of amsterdamoya northwest spitsbergen we interpret d values of mid chain c 25 and long chain c 29 c 31 length n alkanes to represent changes in the isotopic composition of lake water and precipitation over the last 12 9 ka after deglaciation of the catchment water supply became restricted and the lake experienced significant evaporative isotopic enrichment indicating warmer conditions from 12 8 to 7 5 ka the isotope values suggest an increase in the delivery of moisture from warmer sub polar air masses between 12 8 and 9 5 ka followed by generally warm but unstable conditions between 9 5 and 7 5 ka possibly indicating a response to meltwater forcing sedimentary evidence indicates a hiatus in deposition c 7 5 5 0 ka likely as a result of desiccation of the lake at c 5 0 ka lacustrine sedimentation resumed and over the last 5 ka there was a progressive increase in the influence of polar air masses and colder conditions which culminated in an abrupt shift to colder conditions at c 1 8 ka this late holocene cooling ended c 0 18 ka when isotopic data indicate warmer conditions and greater influence of moisture derived from lower latitudes

paleoclimatic inferences from glacial fluctuations on svalbard during the last 20 000 years the climate history of western spitsbergen svalbard is deduced from variations of glaciers during the last 20 000 years a major depression of the regional equilibrium line altitude ela occurred during the late weichselian glacial maximum 18000 13000y ago when low summer temperatures may have caused year round snow accumulation on the ground this rapid expansion of the glaciers also indicates nearby moisture sources suggesting partly open conditions in the norwegian sea during the summers a rapid glacial retreat around 13 000 12 500 y bp was caused by a sudden warming during the younger dryas the ela along the extreme western coast of spitsbergen was not significantly lower than at present in contrast to fennoscandia the british isles and the alps there is no evidence for readvance of local glaciers during younger dryas on western spitsbergen this difference is attributed to a much dryer climate on spitsbergen and probably only slight changes in sea surface temperatures in addition summer melting in this high arctic area is more sensitive to orbitally increased insolation around 10 000 y bp another rapid warming occurred and during early and mid holocene the summer temperatures were significantly higher than at present a temperature decline during the late holocene caused regrowth of the glaciers which reached their maximum holocene position during the last century

nonlinear variations of the physical properties along the southern ecuador subduction channel results from depth migrated seismic data abstract we use two high quality pre stack depth migrated multichannel seismic profiles acquired to quantify physical properties variations of underthrust sediments along the first 30 km of subduction off the erosional southern ecuadorian margin seismic data show three zones along the subduction channel referred to as zones i ii and iii characterized by distinct velocity and velocity derived physical properties which are in agreement with values estimated from experimental results of deformation in granular media these three zones result from transformational changes of underthrust sediments governed by fundamentally different physical processes that control their mechanical behavior at increasing confining pressures based on our observations and its comparison with experimental results we argue that the transformations undergone by underthrust sediments as they dip into the subduction zone are the following within zone i progressively increasing velocity and decreasing velocity derived porosity indicates continuous sediment compaction which must be accompanied by effective fluid drainage along the decollement and or across the accretionary wedge the underthrust material is here unconsolidated from a mechanical point of view laboratory experiments indicate that the dominant processes at this range of pressures are grain rolling particle rotation and frictional slip at grain contacts within zone ii velocity and porosity remains constant for 16 km sis 72 and 12 km sis 18 this suggests undrained conditions resulting in growing fluid overpressure at the subduction channel grain deformation is similar to zone i within zone iii velocity increases and porosity falls rapidly indicating sediment compaction and subsequent release of over pressured fluids where grain deformation is likely to be elastic this might be the dominant process until the grains attain their crushing strength resulting in granular cataclasis and eventually in the collapse of the system we suggest that over pressured fluid release may induce hydrofracturation and it is likely to increase inter plate coupling down from zone iii

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

minimizing the edge effect in environmental reconstructions by trimming the calibration set chironomid inferred temperatures from spitsbergen a core from lake skardtjorna on western spitsbergen was analysed for subfossil chironomids with the aim of inferring past temperatures the core spans the last 1760 years and has a low concentration and low diversity of chironomids three taxa dominate the record oliveridia tricornis micropsectra radialistype and m insignilobus type the latter not previously recorded on svalbard compared with the full norwegian modern climate chironomid calibration data set skardtjorna is at the coldest end of the modern temperature gradient in an attempt to decrease potential bias caused by the numerical edge effect and to improve the taxon response functions the training set was trimmed by excluding lakes dissimilar to the study site two trimming approaches are tested in the first lakes at the warm end of the gradient are excluded in the second the calibration data set lakes are partitioned by twinspan on the basis of their modern chironomid assemblages and lakes most dissimilar to skardtjorna are exclude

holocene vegetational history and climatic change in west spitsbergen plant macrofossils from skardtjorna an arctic lake macrofossil analyses of a 335 cm long core from skardtjorna a small lake on the west coast of spitsbergen svalbard are presented the known processes of deposition of plant remains to arctic lake sediments are summarised and used in the interpretation of the vegetation history at skardtjorna the basal sediment is ams dated to 8110 110 bp the rest of the profile is dated by palaeomagnetic correlation the lowest sediments have the greatest macrofossil concentration and numbers of taxa per sample the occurrences of cassiope hypnoides and salix cf glauca before 4000 bp indicate a mean july temperature for the early holocene about 2 c higher than today comparable to the cassiope tetragona vegetation zone of the mid arctic region of the inner fjords increasing climatic severity resulted in the threshold from the cassiope to the dryas vegetation zone being passed at about 2500 bp the inferred climatic history at skardtjorna is compatible with other evidence from svalbard and elsewhere in the arctic

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

variations in temperature and extent of atlantic water in the northern north atlantic during the holocene we compare six high resolution holocene sediment cores along a s n transect on the norwegian svalbard continental margin from ca 601n to 77 41n northern north atlantic planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties including summer sea surface temperatures sst the cores are located below the axis of the norwegian current and the west spitsbergen current which today transport warm atlantic water to the arctic sediment accumulation rates are generally high at all the core sites allowing for a temporal resolution of 10 10 2 years sst is reconstructed using different types of transfer functions resulting in very similar sst trends with deviations of no more than 71 0 1 51c a transfer function based on the maximum likelihood statistical approach is found to be most relevant the reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the younger dryas preboreal transition the earliest part of the holocene was characterized by large temperature variability including the preboreal oscillations and the 8 2 k event in general the early holocene was characterized by ssts similar to those of today in the south and warmer than today in the north and a smaller s n temperature gradient 0 231c 1n compared to the present temperature gradient 0 461c 1n the southern proxy records 60 691n were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening the northern records 72 77 41n display a millennial scale change associated with reduced insolation and a gradual weakening of the north atlantic thermohaline circulation thc the observed northwards amplification of the early holocene warming is comparable to the pattern of recent global warming and future climate modelling which predicts greater warming at higher latitudes the overall trend during mid and late holocene was a cooling in the north stable or weak warming in the south and a maximum s n sst gradient of ca 0 71c 1n at 5000 cal years bp superimposed on this trend were several abrupt temperature shifts four of these shifts dated to 9000 8000 5500 3000 and 1000 and 400 cal years bp appear to be global as they correlate with periods of global climate change in general there is a good correlation between the northern north atlantic temperature records and climate records from norway and svalbard r 2007 elsevier ltd all rights reserved

on the thermal viability of dikes leaving magma chambers dikes beginning to propagate away from a magma source are thin and grow slowly and thus are susceptible to freezing a self similar solution is obtained for a dike propagating down a temperature gradient when the wallrock and magma temperatures are equal at the chamber wall the solution applies only to the special case of a single component magma intruded at the solidus temperature but provides insight into the case in which the magma temperature is above the solidus the dike propagation velocity relative to that in the absence of freezing is determined by a single dimensionless parameter for sufficiently large magma freezing chokes the dike faster than propagation can elastically widen it and the dike cannot grow if the magma intrudes at a temperature above the solidus there is some value of above which the dike will propagate a certain distance and freeze and below which it will propagate until depletion of the source or three dimensional elastic effects promote freezing for reasonable parameters this process can explain why basaltic dikes are found far from obvious source regions while granitic dikes are scarce except in the immediate vicinity of granitic plutons even if a rhyolite is 5 orders of magnitude more viscous than a basalt however this distinction can be offset if the rhyolite has an excess source pressure only 1 order of magnitude greater than that of the basalt

vegetation and climate during the weichselian early glacial and pleniglacial in the niederlausitz eastern germany macrofossil and pollen evidence cryoturbated organic beds and channel fills intercalated with sandy and gravelly fluvial units have been studied in an opencast brown coal mine near nochten niederlausitz eastern germany the fluvial aeolian sequence covers parts of the early pleni and late glacial the detailed chronology is based on 11 radiocarbon and 12 osl dates covering the period between ca 100 kyr and 11 kyr bp basal peat deposits are correlated with an early weichselian interstadial during this period boreal forests were present and minimum mean summer temperatures were 13 c early pleniglacial deposits are absent the middle and late pleniglacial environments were treeless and different types of tundra vegetation can be recognised minimum mean summer temperatures varied between 10 and 15 c vegetation and climate is reconstructed in detail for the periods around 34 38 kyr bp and 24 25 kyr bp around 34 38 ka a mixture between a low shrub tundra and a cottongrass tussock subshrub tundra was present the botanical and sedimentological data suggest that from the middle to the late pleniglacial the climate became more continental aridity and wind strength increased and the role of a protecting winter snow cover decreased a sedge grass moss tundra dominated around 24 and 25 kyr bp copyright 2001 john wiley sons ltd

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

coast formation in an arctic area due to glacier surge and retreat the hornbreen hambergbreen case from spistbergen glacierized coasts undergo faster geomorphic processes than unglaciated ones we have studied changes of the coastal area in southern svalbard with the glacier bridge between torell land and sorkapp land since the beginning of the 20th century the existence of a continuous subglacial depression beneath the hornbreen hambergbreen system has been debated since the 1960s with inconclusive results in this study we assess both the subglacial topography and the bathymetry of hornsund fjord and hambergbukta bay this included 40 km of radar surveys over the glacial system and sea depth sounding the extent of the glaciers from maps and satellite images together with digital terrain models and surface elevation data based on gps profiling were used to analyse geometry changes of the glacier surfaces the results confirm the existence a continuous subglacial depression below sea level c 40 m deep between hornsund and the barents sea the hornbreen hambergbreen system has changed in shape over the past century reflecting its dynamic origin and activity also exemplified by the sequential surges identified since 1899 there was a pre surge build up event of flatbreen causing a surge and subsequent lowering of the hornbreen hambergbreen terminus by the 1960s after the entire surface lowered albeit with a delay in the hornbreen terminal zone since the year 2000 hornbreen terminus has retreated at an average rate of 106 m a 1 50 faster than that of hambergbreen if the retreat continues at the 2000 2015 average rate the ice bridge between hornsund and hambergbukta will be broken sometime between 2055 and 2065 and the hornsund strait will separate sorkapp land from the spitsbergen island the processes and events described in this study particularly the effects of the glacier surge may provide a model for changes likely to occur in other coastal glaciated regions experiencing rapid change

reconstruction of inflow of atlantic water to isfjorden svalbard during the holocene correlation to climate and seasonality abstract the distribution patterns of benthic foraminifera faunas stable isotopes and ice rafted debris ird have been studied in piston core jm98 845 pc from isfjorden western svalbard to reconstruct changes in the flow of atlantic water during the holocene interglacial the paleoenvironmental conditions in isfjorden and the inflow of the atlantic water followed closely the changes in insolation with strong seasonality in the early holocene and weaker seasonality in the middle to late holocene a summer temperature maximum of the bottom water occurred in the early holocene 10 500 c 8200 years bp cooling began at 9000 years bp with stepwise coolings at c 8200 7400 and 4000 years bp the cooling correlated with an increase in ice rafting and increased influence of polar water and seasonal sea ice cover between 4000 and 2000 years bp bottom water temperatures reached a minimum after 2000 years bp episodic inflow of warmer atlantic water at the bottom of the fjord occurred and conditions became more unstable the data indicate close interaction of the flow of atlantic water with the development of the terrestrial climate and the amount of polar meltwater and sea ice

finding a realistic velocity distribution based on iterating forward modelling and tomographic inversion tomography is like a photograph that was taken by a camera with blurred and defective lenses that deform the shapes and colours of objects reporting quantitative parameters derived from tomographic inversion is not always adequate because tomographic results are often strongly biased to quantify the results of tomographic inversion we propose a forward modelling and tomographic inversion fm ti approach that aims to find a more realistic solution than conventional tomographic inversion the fm ti scheme is based on the assumption that if two tomograms derived from the inversion of observed and synthetic data are identical the synthetic structure may appear to be closer to the real unknown structure in the ground than the inversion result however the manual design of the synthetic velocity distribution is usually time consuming and ambiguous in this study we propose an approach that automatically searches for a probabilistic model in this approach a synthetic model is iteratively updated while taking into account the bias of the model in previous stages of the fm ti performance here we present an example of synthetic modelling and real data processing for an active source refraction data set corresponding to a marine profile across the subduction zone in chile at about 32 s latitude a key feature of the model is a low velocity channel above the subducted oceanic crust which was defined in the synthetic model and expected in the real case the conventional first arrival traveltime tomography was barely able to resolve this channel however after several iterations of the fm ti modelling we succeeded in reconstructing this channel clearly in the paper we briefly discuss the nature of this low velocity subduction channel and we compare the results with other studies

9 400 yr b p the mortality of mollusk shell mya truncata at high arctic is associated with a sudden cooling event an 118 cm long well preserved sediment profile was collected from a paleo notch formed by ocean wave action before rising to the terrace on ny alesund svalbard norway a large number of mollusk shell fragments predominantly mya truncata were found in the sediment profile ams 14c dating and stable oxygen and carbon isotope analyses were performed on the shell fragments samples the reservoir corrected radiocarbon ages averaged 9 400 yr b p which accurately dates the raised terrace and the upper marine limit after kongsfjorden was completely deglaciated the calibrated aragonite isotopic temperature equation was established for ny alesund by comparing the 18o profiles of modern mollusks as follows t c 16 26 3 68 18oaragonite pdb 18owater vsmow the reconstructed paleotemperature range was 0 52 to 4 78 c warmer than today by about 1 c which was further confirmed by reconstructed sea surface temperature sst in west svalbard moreover the mortality of mollusks was very likely caused by an abrupt cooling event at about 9 400 yr b p which was triggered by reduced insolation weakened thermohaline circulation and abruptly decreased sst more evidences for this distinct but short cooling event centered at about 9 400 yr b p were found in northern siberia north atlantic alps and eastern europe

teleseismic tomography reveals no signature of the dead sea transform in the upper mantle structure abstract we present results of a tomographic inversion of teleseismic data recorded at 48 stations of a temporary network which was installed in the area of the dead sea transform dst and operated for 1 yr in the framework of the multidisciplinary desert project the 3366 teleseismic p and pkp phases from 135 events were hand picked and corrected for surface topography and crustal thickness the inversion shows pronounced low velocity anomalies in the crust beneath the dst which are consistent with recent results from local source tomography these anomalies are likely related to the young sediments and fractured rocks in the fault zone the deeper the retrieved anomalies are quite weak most prominent is the high velocity strip like anomaly striking se nw we attribute this anomaly to the inherited heterogeneity of lithospheric structure with a possible contribution by the shallow precambrian basement east of the dst and to lower crustal heterogeneity reported in this region by other seismic studies we do not observe reliable signature of the dst in the upper mantle structure some weak indications of low velocity anomalies in the upper mantle beneath the dst may well result from the down smearing of the strong upper crustal anomalies we also see very little topography of the lithosphere asthenosphere boundary beneath the dst which would generate significant horizontal velocity variations these results are consistent with predictions from a recent thermo mechanical model of the dst our tomographic model provides some indication of hot mantle flow from the deeper upper mantle rooted in the region of the red sea however resolution tests show that this anomaly may well be beyond resolution of the model

synchronized proxy based temperature reconstructions reveal mid to late holocene climate oscillations in high arctic svalbard existing paleoclimate data are exceedingly sparse from southern spitsbergen a high arctic region predicted to experience significant environmental changes because of amplified warming we analyzed biotic and isotopic paleolimnological proxies to reconstruct past climate from a lacustrine sediment core with a basal age of 5500 a bp in southern spitsbergen 77 n we used fossil chironomidae assemblages to quantitatively reconstruct past mean july air temperatures and stable oxygen isotope values 18o of these fossils to estimate changes in mean annual air temperature these proxy records are strikingly similar and show that the coldest anomaly since the mid holocene occurred between 350 and 50 cal a bp during the little ice age whereas the warmest period in the summer temperature record occurred between 5500 5000 and 2000 cal a bp our findings indicate that the natural long term air temperature dynamics in our study area are most likely connected to solar minima and positive feedback mechanisms from sea surface temperature maxima the results also highlight that the recent temperature increase is unprecedented in its rate with a 2 c increase in the summer temperatures during the past 50 years

arctic holocene glacier fluctuations reconstructed from lake sediments at mitrahalvoya spitsbergen the arctic region has experienced a significantly larger warming during the last decades compared to the rest of the world and model simulations indicate a continued amplification of future global warming in the polar regions a better understanding of natural climate variability in the arctic is much needed to provide a better context for the observed warming trend by utilising proxy data it is possible to obtain palaeoclimatic records beyond the range of instrumental observations which increase our understanding of long term arctic climate change here a continuous record of past changes in equilibriumline altitude ela has been reconstructed for the alpine glacier karlbreen located on the northwest coast of spitsbergen 79 n based on sediment analyses from a distal glacier fed lake a multivariate statistical analysis suggests that the concentration of geochemical elements ti si and k in the lake sediments together with the physical parameter dry bulk density dbd reflect changes in the amount of inorganic detrital input to klosa which is closely linked to the size and ela of the upstream glacier karlbreen a linear regression model based on historically documented glacier extents was used to calculate continuous ela changes back to 3500 cal yr bp from about 9200 to 3500 cal yr bp the sedimentary record indicates that karlbreen was very small or had completely melted away karlbreen was probably close to its maximum holocene extent several times during the neoglacial first around 1700 cal yr bp then later at 225 and 135 cal yr bp an ice cored moraine system in front of karlbreen extends well into the main basin of klosa and it is difficult to explain how this moraine could have formed without disturbing the sedimentary record in the lake e g through slumping events the sedimentary record in klosa is continuous and undisturbed over the past 6700 years suggesting that the outermost moraine formed prior to this time and that it most likely survived the holocene thermal maximum on svalbard

late holocene glacier growth in svalbard documented by subglacial relict vegetation and living soil microbes much renewed research interest in arctic regions stems from the increasing concentration of atmospheric greenhouse gases and the alleged climatic sensitivity of high latitude areas glacier and permafrost changes are among a number of proxies used for monitoring past and present arctic climate change here we present observations on frozen in situ soil and vegetation found below cold based glacier longyearbreen 78813 n 2 km upstream from the present glacier terminus dating of the relict vegetation indicates that the glacier has increased in length from about 3 km to its present size of about 5 km during the last c 1100 years the meteorological setting of non surging longyearbreen suggests this example of late holocene glacier growth represents a widespread phenomenon in svalbard and in adjoining arctic regions in addition we use the subglacial permafrozen soil system to evaluate microbial survival capacity over considerable time periods and we present evidence for microbes having survived more than 1100 years in a subglacial permafrozen state

late weichselian environmental change in norway including svalbard a synthesis of the principal environmental changes that are inferred to have occurred in norway and svalbard fig 1 during the late glacial period 14 9 ka bp is presented the paper has three sections dealing separately with i western norway ii northern norway and iii spitsbergen svalbard the main conditions described include glacial events sea level changes vegetation history and climatic variations a summary chart of environmental reconstructions is presented for each of the three areas each including a curve of temperature reconstructions for the late glacial period these indicate some significant regional variations in contemporaneous thermal conditions during the late glacial

holocene climate and landscape evolution east of the pechora delta east european russian arctic this study presents a multiproxy record of holocene environmental change in the region east of the pechora delta a peat plateau profile ortino ii is analyzed for plant macrofossils sediment type loss on ignition and radiocarbon dating a paleosol profile ortino iii is described and radiocarbon dated a previously published peat plateau profile ortino i was analyzed for pollen and conifer stomata loss on ignition and radiocarbon dating the interpretation of the latter site is reassessed in view of new evidence spruce immigrated to the study area at about 8900 14c yr b p peatland development started at approximately the same time during the early holocene hypsithermal taiga forests occupied most of the present east european tundra and peatlands were permafrost free cooling started after 5000 14c yr b p resulting in a retreat of forests and permafrost aggradation remaining forests disappeared from the study area around 3000 14c yr b p coinciding with more permafrost aggradation the retreat of forests resulted in landscape instability and the redistribution of sand by eolian activity the displacement of the arctic forest line and permafrost zones indicates a warming of at least 2 3 c in mean july and annual temperatures during the early holocene at least two cooling periods can be recognized for the second half of the holocene starting at about 4800 and 3000 14c yr b p

holocene treeline history and climate change across northern eurasia radiocarbon dated macrofossils are used to document holocene treeline history across northern russia including siberia boreal forest development in this region commenced by 10 000 yr b p over most of russia forest advanced to or near the current arctic coastline between 9000 and 7000 yr b p and retreated to its present position by between 4000 and 3000 yr b p forest establishment and retreat was roughly synchronous across most of northern russia treeline advance on the kola peninsula however appears to have occurred later than in other regions during the period of maximum forest extension the mean july temperatures along the northern coastline of russia may have been 2 5 to 7 0 c warmer than modern the development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions including heightened summer insolation the demise of eurasian ice sheets reduced sea ice cover greater continentality with eustatically lower sea level and extreme arctic penetration of warm north atlantic waters the late holocene retreat of eurasian treeline coincides with declining summer insolation cooling arctic waters and neoglaciation

p and s velocity anomalies in the upper mantle beneath europe from tomographic inversion of isc data we present a new tomographic model for p and s velocity anomalies beneath europe 30 n 55 n 5 w 40 e extending in depth up to 700 km and constrained by inversion of data from the international seismological center isc catalogue the algorithm uses the traveltimes from events located in the study area recorded by all available worldwide stations as well as times from teleseismic events recorded by european stations the events from the isc catalogue have been relocated and combined into composite events all the traveltimes were corrected for crustal structure using the reference model eucrust 07 the resulting velocity anomalies show similar large scale patterns as observed in previous studies but have a higher resolution which allows detection of some features in more detail for example it is now possible to assess the depth extension of the small slow velocity body beneath the eifel region and eger graben the p and the s model show a good consistency in the uppermost 200 km below most of the european area and in some parts even in the deeper layers e g beneath the apennines and the hellenic arc the new model provides clear images of some principal features which were previously detected in a limited number of studies while the comparison between p and s velocity anomalies provides novel constraints to address on their nature e g the gap in the adriatic plate subducted below the central southern apennines in this paper we pay special attention to testing the reliability of the results the random noise effect is evaluated using a test with independent inversion of two data subsets with odd even events the spatial resolution is estimated using different checkerboard tests furthermore we present a synthetic model with realistic patterns which reproduces after performing forward and inverse modelling the same shape and amplitudes of the anomalies as in the case of the real data inversion in this case the parameters of the model can be used to assess the amplitudes of p and s anomalies that is critical for evaluation of other petrophysical parameters temperature density composition etc in the upper mantle 2009 the authors journal compilation 2009 ras