reworking of sialic crust as represented in late archean age gneisses northern labrador regionally reworked sialic crust has been recognized in the form of 2 800 m y old nebulitic rocks kiyuktok gneisses with high initial 87sr 86sr ratios 0 7081 and pb isotope ratios that suggest a history of the source back to at least 3 500 m y b p the field geochemical and isotopic data are consistent with these rocks having formed by in situ mobilization of granitic components in the 3 600 m y old uivak gneisses by the introduction of aqueous fluids some 2 800 m y ago contemporary but subordinate tonalitic granodioritic orthogneisses derived from discrete intrusive bodies have contrasting sr isotope compositions some display low initial 87sr 86sr ratios 0 7030 that suggest derivation from a source with mantlelike sr isotope composition however most of the late archean age intrusive rocks display higher initial 87sr 86sr ratios 0 7056 0 7059 recognition of these contrasting isotopic patterns suggests that processes of late archean crust formation and stabilization in the north atlantic craton were more complex than previously realized crustal reworking due to interaction of old crust with aqueous fluids must have been accompanied by the introduction of granitic melts derived by melting of ancient deep crustal rocks or contamination of juvenile granitic melts by ancient deep crustal material

u th pb ages of single zircons in archaean supracrustals from nain province labrador canada ion probe u pb dating of igneous zircons from an acid metavolcanite belonging to the nulliak supracrustal association of the saglek area northern labrador suggests an original age of 3776 8 ma 2 interpreted as the deposition age of the volcanite in accordance with the field model this is slightly but significantly older than the previously obtained ion probe u pb age of igneous zircons from the main phase of the uivak gneisses which carries inclusions of the supracrustal association a secondary event of zircon growth recorded in the metavolcanite has a maximum age of 3065 8 ma 2 a metapelite belonging to the weekes amphibolite supracrustal association of the hopedale area south of nain contains rounded low u zircons of 3258 24 ma 2 age occasional textural evidence suggests that some of these zircons are most likely detrital grains of igneous origin in which case 3258 24 ma is a minimum age of the source from which the sediment was derived and a maximum age for the deposition of

nature of mantle source contributions and the role of contamination and in situ crystallisation in the petrogenesis of proterozoic mafic dykes and flood basalts labrador proterozoic tholeiitic dyke swarms share many compositional features with and pose similar petrogenetic problems to phanerozoic continental flood basalts but there are few extrusive equivalents of such swarms the mesoproterozoic 1 27 ga harp dyke swarm in labrador is one where possible extrusive equivalents exist in the seal lake group but are slightly displaced in space and time and can probably be related by models of progressive crustal extension here we try to evaluate the roles of crystal differentiation in situ crystallisation crustal assimilation and the relative contributions of asthenosphere and lithosphere derived melts in the petrogenesis of the mafic magmas modelling of the major and trace element variations both within individual dykes and between dykes and within the lava sequence does not suggest an important role for continental crust involvement while in situ crystallisation processes could account for some of the compositional variations the most successful models invoke mixing or contamination of asthenospheric magmas with by veined material in the lower lithosphere upper asthenosphere which carries the continental characteristics the results imply an important role for hydrous phases such as phlogopite and hornblende in the sub lithosphere mantle much of the low mgo character of mafic dykes may result from significant removal of mafic phases during in situ crystallisation within the lithosphere

proxy dependence of the temporal pattern of deglacial warming in the tropical south china sea toward resolving seasonality abstract sea surface temperatures ssts reconstructed from two globigerinoides ruber white morphotypes g ruber sensu stricto s s g ruber sensu lato s l mg ca and alkenones uk 37 from core md01 2390 from the tropical south china sea scs during the last deglaciation reveal a proxy dependent discrepancy in the temporal pattern of the deglacial warming alkenone data suggest that the deglacial warming is punctuated by a decrease in temperature between 17 and 15 ka bp corroborating previously published alkenone uk 37 sst records from the southern scs within dating uncertainties this cooling is coeval with the heinrich event 1 h1 time interval in the north atlantic region underscoring the imprints of northern hemisphere forcing on tropical scs ocean temperatures the deglacial uk 37 sst minimum is also paralleled by a maximum in g ruber morphotype specific 18o g ruber mg ca sst estimates suggest a morphotype specific record of ssts during the time interval of h1 whereas g ruber s s imply a continuous warming starting around 18 ka bp without any marked response to h1 g ruber s l based mg ca sst estimates reveal a cooling around 17 15 ka bp similar to the h1 interval cooling seen in the alkenone sst record similar proxy dependent differences in deglacial surface water warming have been recorded in the eastern equatorial pacific implying a common pattern on both sides of the tropical pacific ocean we submit that this discrepancy could be due to differences in seasonality of planktonic foraminifera g ruber morphotypes and alkenone producing algae

influence of lithostatic stress on earthquake stress drops in north america abstract we estimate stress drops for earthquakes in and near the continental united states using the method of spectral ratios the ratio of acceleration spectra between collocated earthquakes recorded at a given station removes the effects of path and recording site and yields source parameters including corner frequency for and the ratio of seismic moment between the two earthquakes we determine stress drop from these parameters for 1121 earthquakes greater than m 3 in 60 earthquake clusters we find that the average brune stress drop for the few eastern united states eus tectonic mainshocks studied 2 6 36 mpa is about three times greater than that of tectonic mainshocks in the western united states wus 1 0 7 9 mpa and five times greater than mainshocks potentially induced by wastewater injection in the central united states cus 0 6 5 6 mpa eus events tend to be deeper thrusting events whereas wus events tend to be shallower but have a wide range of focal mechanisms cus events tend to be shallow with strike slip to normal faulting mechanisms with the possible exception of cus aftershocks we find that differences in stress drop among all events can be taken into account within one standard deviation of significance by differences in the shear failure stress as outlined by mohr coulomb theory the shear failure stress is a function of vertical stress or depth the fault style normal strike slip or reverse and coefficient of friction estimated here to be on average 0 64 after accounting for faulting style and depth dependence we find that the average brune stress drop is about 3 of the failure stress these results suggest that high frequency shaking hazard 1 hz from shallow induced events and aftershocks is reduced to some extent by lower stress drop however the shallow hypocenters will increase hazard within several kilometers of the source electronic supplement earthquake catalog

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

source radiation invariant property of local and near regional shear wave coda application to source scaling for the mw 5 9 wells nevada sequence 1 this study documents another unique property of local and regional shear wave coda that scattering in the earth s crust averages out source heterogeneities such as focal mechanism and directivity we consider two recent events which exhibited significant source directivity the first an mw 4 2 oakland hills california strike slip event on july 20 2007 resulted in uncharacteristically large amounts of damage in the montclair and south berkeley neighborhoods along strike and north west of the hypocenter but almost no damage to the south east the second event the mw 5 9 wells nevada dip slip event of february 21 2008 was well recorded by the earthscope transportable array usarray and determined to exhibit south west directivity we conclude with an example of corner frequency fc estimates from the wells sequence which showcase the coda s low variance and find that scaling is non self similar suggesting a change in dynamics between the mainshock and aftershocks

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

regionally adjustable generic ground motion prediction equation based on equivalent point source simulations application to central and eastern north america abstract we develop a generic ground motion prediction equation gmpe that can be adjusted for use in any region by modifying a few key model parameters the basis of the gmpe is an equivalent point source simulation model whose parameters have been calibrated to empirical data in california in such a way as to determine the decoupled effects of basic source and attenuation parameters on ground motion amplitudes we formulate the generic gmpe as a function of magnitude distance stress parameter geometrical spreading rate and anelastic attenuation this provides a fully adjustable predictive model allowing users to calibrate its parameters using observed motions in the target region we also include an empirical calibration factor to account for residual effects that are different from and or missing in simulations compared to observed motions in the target region as an example we show how the generic gmpe can be adjusted for use in central and eastern north america cena and calibrated with the next generation attenuation east database we provide median predictions of ground motions in cena for average horizontal component peak ground motions and 5 damped pseudospectral acceleration periods up to t 10 s for magnitudes m 3 8 and distances up to 600 km

climatic reconstruction in europe for 18 000 yr b p from pollen data an improved concept of the best analogs method is used to reconstruct the climate of the last glacial maximum from pollen data in europe in order to deal with the lack of perfect analogs of fossil assemblages and therefore to obtain a more accurate climate reconstruction we used a combination of pollen types grouped according to plant phenology and present climate constraints rather than pollen percentages for each individual taxon the distribution of pollen taxa into plant functional types pfts is aimed to reflect the vegetation in terms of biomes which have a wider distribution than a species the climatic variables are then calibrated on these pfts using an artificial neural network technique the use of pfts allowed us to deal with situations where pollen assemblages have only partial modern analogs the method is applied to the glacial steppic vegetation in europe using 15 pollen records north of the pyrenees alps line the reconstructed temperatures were lower than today 30 10 degrees c for the temperature of the coldest month t c and 12 3 degrees c far the annual mean t ann south of that line t c and t ann anomalies were respectively 15 5 degrees c and 10 5 degrees c the available moisture index and annual precipitation were also lower than present 60 20 north of mediterranean sea 800 100 mm for precipitation in italy and greece the available moisture was 20 lower with a precipitation anomaly of ca 600 200 mm southward the moisture index was close to that at present 20 and precipitation was lower 300 300 mm c 1998 university of washington

regression coefficients of thermal gradients in northwestern europe during the last glacial holocene transition using beetle mcr data palaeotemperature estimates obtained from 74 sites in northern europe and collectively spanning approximately the last 45 000 yr radiocarbon time scale have been compiled as a major component o

mass balance flow and subglacial processes of a modelled younger dryas ice cap in scotland we use an empirically validated high resolution three dimensional ice sheet model to investigate the mass balance regime flow mechanisms and subglacial characteristics of a simulated younger dryas stadial ice cap in scotland and compare the resulting model forecasts with geological evidence input data for the model are basal topography a temperature forcing derived from grip 18 o fluctuations and a precipitation distribution interpolated from modern data the model employs a positive degree day scheme to calculate net mass balance within a domain of 112 500 km 2 which under the imposed climate gives rise to an elongate ice cap along the axis of the western scottish highlands at its maximum the ice cap is dynamically and thermally zoned reflecting topographic and climatic con trols respectively in order to link these palaeoglaciological conditions to geological interpretations we calculate the relative balance between sliding and creep within the simulated ice cap forecast areas of the ice cap with the greatest capacity for basal erosion and predict the likely pattern of subglacial drain age we conclude that ice flow in central areas of the ice cap is largely due to internal deformation and is associated with geological evidence of landscape preservation conversely the distribution of stream lined landforms is linked to faster flowing ice whose velocity is predominantly the result of basal sliding the geometry of the main ice mass focuses subglacial erosion in the mid sections of topographic troughs and produces glaciohydraulic gradients that favour subglacial drainage through low order arterial routes

effect of precipitation seasonality on climatic sensitivity of glacier mass balance abstract numerical calculations are described aimed at evaluating the influence of precipitation seasonality and seasonality concentration on climatic sensitivity of glacier mass balance equilibrium line altitudes elas are modeled using idealized meteorological variables and then a warming test 1 c is performed which revealed that the effects of latitude and the annual precipitation amount are less than those of precipitation seasonality and its concentration calculation shows higher sensitivities for the glaciers located in a summer precipitation climate than for those located within a winter precipitation climate difference due to seasonality is enhanced with the seasonality concentration the present study suggests that the earlier parameterization of glacier mass balance with annual precipitation amount is insufficient to describe the response of glaciers to climate change distribution of precipitation seasonality and its concentration suggest that many parts of the world have a summer precipitation climate but their seasonality concentration is not significant worldwide on the other hand an extensive region of asia and part of the andes are located in the highly concentrated summer precipitation climate this suggests the high sensitivity of glacier mass balance in these regions to climate change

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

the impact of the north atlantic ocean on the younger dryas climate in northwestern and central europe the main results of multiproxy climate reconstructions for the younger dryas and experiments carried out with an atmospheric general circulation model are discussed quantitative temperature inferences for northwestern and central europe show that winter conditions were remarkably extreme with values of 20 30 c below that of today annual temperature ranges with a continental signature 30 34 c were reconstructed for the entire study area compared with today the greatest cooling was experienced in the seaboard area the comparison of the climate reconstructions and simulation experiments indicates that sea ice in the north atlantic ocean played a decisive role in the climate of the study area by cooling the surface air temperatures and by controlling the position of the storm track surface air circulation was westerly even during younger dryas winters a slight northward shift of the mean atlantic sea ice margin during winter may explain the proposed subdivision of the younger drays into a phase of maximum cold and humidity succeeded by a less cold and relatively dry phase 1998 john wiley sons ltd

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

orbital changes and climate at the 41 000 period of orbital tilt summer insolation forces a lagged response in northern ice sheets this delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics these ice driven responses lead to late phased changes in atmospheric co2 that provide positive feedback to the ice sheets and also project late 41 k forcing across the tropics and the southern hemisphere responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes at the 22 000 year precession period northern summer insolation again forces a lagged ice sheet response but with muted transfers to proximal regions and no subsequent effect on atmospheric co2 most 22 000 year greenhouse gas responses have the early phase of july insolation july forcing of monsoonal and boreal wetlands explains the early ch4 response the slightly later 22 k co2 response originates in the southern hemisphere the early 22 k ch4 and co2 responses add to insolation forcing of the ice sheets the dominant 100 000 year response of ice sheets is not externally forced nor does it result from internal resonance internal forcing appears to play at most a minor role the origin of this signal lies mainly in internal feedbacks co2 and ice albedo that drive the gradual build up of large ice sheets and then their rapid destruction ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession

ion probe u th pb zircon dating of polymetamorphic orthogneisses from northern labrador canada rounded zircons included within igneous zircons from the uivak i gneisses northern labrador have ages of up to 3863 12 ma 2 showing the former existence of rocks that predate the uivak gneisses by more than 100 ma the igneous zircons themselves have experienced varying amounts of early pb loss but age estimates based on maximum 207pb 206pb from three separate gneiss samples agree to within error at 3732 6 ma 2 which is taken as the age of emplacement of the igneous precursor to the dominant component of the uivak gneisses a new generation of zircons was formed during migmatization at ca 3620 ma the volumetrically less important lister gneiss was emplaced at 3235 8 ma 2 in the late archaean different parts of the gneiss complex were subjected to different grades of metamorphic overprinting the zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events with simultaneous recrystallization of old zircons and growth of new u poor zi

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

temperature and precipitation climate at the equilibrium line altitude of glaciers expressed by the degree day factor for melting snow several authors relate accumulation or precipitation at the glacier equilibrium line altitude ela to summer mean temperature using exponential or power law functions i analyze the accumulation temperature relation at the ela with a degree day model using data from the 1992 paper by a ohmura and others the dataset includes estimates at the ela of winter balance and of winter balance plus summer precipitation which represent respectively low and high estimates of annual accumulation which is seldom measured the ohmura dataset only lists summer mean temperature but i recover monthly temperatures for the whole year for 66 of the glaciers by assuming sinusoidal temperature variation through the year and using annual temperature range from a gridded climatology monthly degree day sums are then estimated from monthly mean temperature and summed to give annual totals so degree day factors for melting snow at the ela are obtained the degree day factors fall close to those reported in the literature for glacier snowmelt with averages of 3 5 1 4 and 4 6 1 4 mm d 1 k 1 for low and high accumulation estimates on the 66 glaciers the degree day model gives a family of accumulation temperature curves that depend upon the annual temperature range representing the contrast between maritime and continental climates

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

how extreme was northern hemisphere seasonality during the younger dryas abstract in explaining the rapid transitions associated with the younger dryas cooling a reduced meridional overturning circulation has traditionally been invoked but such a scenario has been difficult to reproduce in model studies without adding excessive amounts of freshwater to the north atlantic more recent studies challenge this view and indicate that the role of an extensive sea ice cover may have been as important in promoting abrupt climate change as reorganisations of the north atlantic ocean gildor h tziperman e 2003 sea ice switches and abrupt climate change philosophical transactions of the royal society of london series a mathematical physical and engineering sciences 361 1935 1942 based on glacier evidence from eastern greenland denton g h alley r b comer g c broecker w s 2005 the role of seasonality in abrupt climate change quaternary science reviews 24 1159 1182 suggest that the seasonal temperature amplitude increased by about 20 c during the younger dryas such a switching of seasonality lends support to the idea of a fast expanding sea ice cover because it allows for extremely cold winters that are balanced by relatively mild summers however climatic interpretations based on the geometry and length of glaciers under such conditions as in scoresby sund is not well understood and equilibrium line altitude ela estimates should therefore be regarded as tentative here we discuss the absolute seasonal amplitude during the younger dryas by taking winter precipitation into account and show that the changes in seasonality may have been limited to 10 c we propose that by reducing the seasonal response in greenland compared with western europe we better understand the hinged door modus operandi cohmap 1988 climatic changes of the last 18 000 years observations and model simulations science 241 1043 1052 of the polar front and sea ice cover where the absolute southward migration of sea ice is highest in the east atlantic region

deglacial surface circulation changes in the northeastern atlantic temperature and salinity records off nw scotland on a century scale sea surface temperature and salinity estimates reconstructed from a core collected on the barra fan northwest scotland 56 43 n 09 19 w water depth 1320 m show a series of rapid oscillations during the last deglacial period that are very similar to those observed in the 18o records from greenland ice cores these records indicate that the transport of heat and salt toward the nordic seas was highest during the bolling period this superconveyor weakened after the bolling probably as a consequence of increased meltwater flux reducing the oceanic salt content as suggested by the barbados sea level record evidence for a phase of ice rafting during the allerod is presented for the first time from this latitude in the northeast atlantic the younger dryas stadial resolved here at a century decadal scale is characterized by very rapid oscillations in temperature and salinity indicating that warm relatively saline waters repeatedly displaced cool polar waters at this latitude these observations attest to the inherent instability of the deglacial climate system

characterizing potentially induced earthquake rate changes in the brawley seismic zone southern california the brawley seismic zone bsz in the salton trough of southern california has a history of earthquake swarms and geothermal energy exploitation some earthquake rate changes may have been induced by fluid extraction and injection activity at local geothermal fields particularly at the north brawley geothermal field nbgf and at the salton sea geothermal field ssgf we explore this issue by examining earthquake rate changes and interevent distance distributions in these fields in oklahoma and arkansas where considerable wastewater injection occurs increases in background seismicity rate and aftershock productivity and decreases in interevent distance were indicative of fluid injection induced seismicity here we test if similar changes occur that may be associated with fluid injection and extraction in geothermal areas we use stochastic epidemic type aftershock sequence models to detect changes in the underlying seismogenic processes shown by statistically significant changes in the model parameters the most robust model changes in the ssgf roughly occur when large changes in net fluid production occur but a similar correlation is not seen in the nbgf also although both background seismicity rate and aftershock productivity increased for fluid injection induced earthquake rate changes in oklahoma and arkansas the background rate increases significantly in the bsz only roughly corresponding with net fluid production rate increases moreover in both fields the interevent spacing does not change significantly during active energy projects this suggests that although geothermal field activities in a tectonically active region may not significantly change the physics of earthquake interactions earthquake rates may still be driven by fluid injection or extraction rates particularly in the ssgf

the configuration sensitivity and rapid retreat of the late weichselian icelandic ice sheet abstract the fragmentary glacial geological record across the icelandic continental shelf has hampered reconstruction of the volume extent and chronology of the late weichselian ice sheet particularly in key offshore zones marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf break position in all sectors during the last glacial maximum though its precise timing and configuration remains largely unknown within this context we review the available empirical evidence and use a well constrained three dimensional thermomechanical model to investigate the drivers of an extensive late weichselian icelandic ice sheet its sensitivity to environmental forcing and phases of deglaciation our reconstruction attains the continental shelf break across all sectors with a total ice volume of 5 96 105 km3 with high precipitation rates being critical to forcing extensive ice sheet flow offshore due to its location astride an active mantle plume a relatively fast and dynamic ice sheet with a low aspect ratio is maintained our results reveal that once initial ice sheet retreat was triggered through climate warming at 21 8 ka bp marine deglaciation was rapid and accomplished in all sectors within c 5 ka at a mean rate of 71 gt of mass loss per year this rate of ice wastage is comparable to contemporary rates observed for the west antarctic ice sheet the ice sheet subsequently stabilised on shallow pinning points across the near shelf for two millennia but abrupt atmospheric warming during the bolling interstadial forced a second dramatic collapse of the ice sheet onshore with a net wastage of 221 gt a 1 over 750 years analogous to contemporary greenland rates of mass loss geothermal conditions impart a significant control on the ice sheet s transient response particularly during phases of rapid retreat insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions such as siple coast antarctica and ne greenland have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated

alpine younger dryas glaciers as palaeo precipitation gauges moraines of the younger dryas egesen stadial which are widespread features in the alps are a valuable terrestrial data source for quantitative palaeoclimatic studies the depression of the early younger dryas egesen i ela shows a distinct spatial pattern it was highest ca 450 500 m against present day in those areas which are exposed towards the west and northwest in the central more shielded valleys it was in the order of 300 m and less summer temperature depression which can be derived from the younger dryas timberline depression is in the order of 3 5 k the stochastic glacier climate model by ohmura and others 1992 which relates summer temperature and precipitation at the ela is used to infer precipitation change results are compared with those obtained from the glacial meteorological approach by kuhn 1981a both models lead to highly similar results during the early younger dryas climate in the central valleys of the alps seems to have been considerably drier than today in those areas which are open to the west and northwest precipitation seems to have been the same as today or even slightly higher these results which are based on a rather dense network of data points agree well with the results from permafrost climate studies and the more qualitative information from palaeobotanical research they also support the results from atmospheric general circulation models for the younger dryas in europe which point towards a more zonal type of circulation

surface temperature in nw europe during the younger dryas agcm simulation compared with temperature reconstructions during the younger dryas yd the climate in nw europe returned to near glacial conditions to improve our understanding of climate variability during this cold interval we compare an agcm simulation of this climate performed with the echam model with temperature reconstructions for nw europe based on geological and paleoecological records maps for the mean winter summer and annual temperature are presented the simulated winters are consistent with reconstructions in the northern part of the study area a strong deviation is noted in ireland and england where the simulation is too warm by at least 10 c it appears that the n atlantic was cooler than prescribed in the yd simulation including a southward expansion of the sea ice margin the comparison for the summer shows a too warm continental europe in the simulation supposedly these anomalously warm conditions are caused by the agcm s response to the prescribed increased summer insolation the region of maximum summer cooling is similar in both the simulation and reconstruction i e s sweden we suggest that this is due to the local cooling effect of the scandinavian ice sheet compared to the present climate a considerable increase of the annual temperature range is inferred especially for regions close to the atlantic ocean

an ice cap landsystem for palaeoglaciological reconstructions characterizing the younger dryas in western scotland abstract this paper reviews the contrasting behaviours of ice caps and icefields defines a generic landsystem model that can effectively discriminate between them and applies the model to landform sediment assemblages in an area of western scotland such a model is necessary since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry extent and dynamics of reconstructed ice masses the validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments and their inter relationships a new landsystems model is presented here in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation when applied to a 1200 km 2 area of the western scottish highlands the landsystem tool predicts 1 an extensive younger dryas ice cap with a maximum surface elevation of 900 m above sea level implying colder or wetter conditions than previously thought and 2 the survival of an independent mountain icefield in part of the area during deglaciation glaciological theory proxy palaeoenvironmental data and established glacier climate topography relationships support these predictions thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions

anomalously mild younger dryas summer conditions in southern greenland the first late glacial lake sediments found in greenland were analyzed with respect to a variety of environmental variables the analyzed sequence covers the time span between 14400 and 10500 calendar yr b p and the data imply that the conditions in southernmost greenland during the younger dryas stadial 12800 11550 calendar yr b p were characterized by an arid climate with cold winters and mild summers preceded by humid conditions with cooler summers climate models imply that such an anomaly may be explained by local climatic phenomenon caused by high insolation and fohn effects it shows that regional and local variations of younger dryas summer conditions in the north atlantic region may have been larger than previously found from proxy data and modeling experiments

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

younger dryas glacial landsystems in north west scotland an assessment of modern analogues and palaeoclimatic implications abstract by explicitly linking process to form landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record some landform characteristics however may originate by more than one process equifinality so although a particular depositional model may fit the data it is not necessarily the correct one here we critically examine the use of modern analogues to interpret glacial landforms focusing on hummocky moraine a distinctive landform association consisting of numerous sharp crested moraine mounds and ridge fragments which occurs on many valley floors in upland britain detailed studies of examples of younger dryas age in the north west highlands of scotland show that they represent ice contact fans which have been affected to varying degrees by ice push and subglacial deformation and that they formed at active oscillating ice margins the sedimentological data are inconsistent with an origin by englacial thrusting as has been proposed for similar moraines elsewhere in upland britain on the basis of morphological criteria comparison with modern glacial landsystems shows that although aspects of hummocky moraines in the study area have close modern counterparts none provides an exact analogue in all respects this may reflect the distinctive climate of western scotland during the younger dryas estimates of mean july temperatures in the younger dryas in scotland based on chironomid assemblages are c 8 c at sea level when combined with reconstructed equilibrium line altitudes for contemporaneous glaciers these estimates indicate mean annual precipitation totals in the range of 2358 337 mm yr 1 at sea level in nw scotland c 26 higher than present day values the implied heavy snowfall suggests that glaciers in western scotland during the younger dryas were of high activity type unlike modern glaciers in svalbard for example high glacier velocities and high winter precipitation would suppress permafrost development despite low mean annual temperatures the climatic environment also favoured rapid oscillations of glacier margins during both glacier build up and retreat phases climatic factors combined with the availability of large quantities of subglacial debris led to the development of distinctive glacial landsystems which may have no direct modern analogue

pleistocene ice caps on the coastal mountains of the adriatic sea ice caps once covered large areas of mount orjen 1894 m on the adriatic coast of montenegro bosnia herzegovina croatia the largest ice cap covered an area of c 165 km2 and reached a maximum ice thickness of c 450 m in some areas reaching down to 500 m above modern sea level u series dating of secondary carbonates within moraines indicates that the most extensive glaciation occurred during the middle pleistocene correlating with a major phase of glaciation in greece to the south during mis 12 c 480 430 ka later less extensive glaciations are also recorded in the cirques and valleys and correlate with glaciations during mis 6 190 130 ka and mis 5d 2 110 11 7 ka each phase of glaciation would have required large amounts of snow accumulation under modern precipitation values which at c 5000 mm are some of the highest in europe mean annual temperatures would need to be only c 5 6 c lower in order to form similar sized glaciers today a mean annual temperature depression of 12 13 c would still require 1000 mm of snow accumulation water equivalent to balance ablation suggesting sustained moisture supply during pleistocene cold stages such sustained precipitation supply during pleistocene cold stages is likely to have been facilitated by major temperature contrasts between the european landmass and the mediterranean sea which are likely to have sustained lee side vortices to the south of the alps in the gulf of genoa and adriatic sea forming weak moisture bearing depressions which tracked across the eastern adriatic coastal mountains large ice caps on the dinaric alps would have blocked the inland penetration of these depressions resulting in much drier conditions in the balkan interior creating favourable conditions for the deposition of thick accumulations of loess the last glaciers on orjen formed during the younger dryas 12 9 11 7 ka and confirm the influence of north atlantic ocean circulation on pleistocene climate change in this part of the mediterranean

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

influence of precipitation seasonality on glacier mass balance and its sensitivity to climate change numerical calculations are described aimed at evaluating the influence of precipitation seasonality summer and winter on glacier mass balance first equilibrium line altitudes elas are modeled using idealized meteorological variables modeled climatic conditions summer mean temperature and annual precipitation at the ela of glaciers located within a winter accumulation pattern confirm the observational results of earlier studies however the ela of glaciers located within a summer accumulation climate pattern locates in a colder environment than that of glaciers located within a winter accumulation climate pattern this difference is mainly due to the annual snow accumulation and the surface albedo a warming test 1k reveals higher sensitivities for the glaciers located within a summer accumulation pattern than for the glaciers located within a winter accumulation pattern in a humid environment a significant decrease in snow accumulation on the glaciers located within a summer accumulation pattern directly causes higher sensitivities in an arid environment on the other hand the decreased summer snow induces accelerated melting by lowering the surface albedo and thus increasing absorption of solar radiation on the glaciers located within a summer accumulation pattern both influences are due to significant differences in summer precipitation this study shows the importance of precipitation seasonality on the climatic sensitivity of glacier mass balance which in previous studies has been linked only with annual precipitation

finite fault slip model of the 2011 mw 5 6 prague oklahoma earthquake from regional waveforms the slip model for the 2011 mw 5 6 prague oklahoma earthquake is inferred using a linear least squares methodology waveforms of six aftershocks recorded at 21 regional stations are used as empirical green s functions egfs the solution indicates two large slip patches one located around the hypocenter with a depth range of 3 5 5 km the other located to the southwest of the epicenter with a depth range from 7 5 to 9 5 km the total moment of the solution is estimated at 3 37 1024 dyne cm mw 5 65 the peak slip and average stress drop for the source at the hypocenter are 70 cm and 90 bars respectively approximately one half the values for the mw 5 8 2011 mineral virginia earthquake the stress drop averaged over all areas of slip is 16 bars the relatively low peak slip and stress drop may indicate an induced component in the origin of the prague earthquake from deep fluid injection

sensitivity of net mass balance estimates to near surface temperature lapse rates when employing the degree day method to estimate glacier melt glacier mass balance models that employ the degree day method of melt modeling are most commonly driven by surface air temperatures that have been downscaled over the area of interest using digital elevation models and assuming a constant free air lapse rate that is often taken to be the moist adiabatic lapse rate malr 6 58 ck m 1 air temperature lapse rates measured over melting glacier surface are however consistently less steep than free air values and have been shown to vary systematically with lower tropospheric temperatures in this study the implications of including a variable near surface lapse rate in a 26 year 1980 2006 degree day model simulation of the surface mass balance of devon ice cap nunavut canada are examined and compared with estimates derived from surface air temperatures downscaled using a constant near surface lapse rate equal to the measured summer mean 4 98 ck m 1 and the malr our results show that degree day models are highly sensitive to the choice of lapse rate when compared with 23 years of surface mass balance measurements from the northwest sector of the ice cap model estimates are significantly better when surface air temperatures are downscaled using a modeled daily lapse rate rather than a constant lapse equal to either the summer mean or the malr

the devensian weichselian lateglacial palaeoenvironmental record from gransmoor east yorkshire england a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract palynological and coleopteran data are described from a section through late devensian weichselian deposits at gransmoor east yorkshire england the pollen evidence shows that following an initial open habitat episode first juniperus scrub and later betula woodland became established in the area during the lateglacial interstadial this woodland was replaced during the loch lomond younger dryas stadial by a predominatly herbaceous flora with arctic alpine steppe and halophytic elements the coleopteran evidence indicates a similar local environment and that the thermal maximum of the interstadial when mean july temperatures may well have exceeded 18 c occurred prior to the deposition of the earliest polleniferous sediments by the time of the juniperus expansion summer temperatures had fallen by 2 4 c to levels comparable with those of the present day a further temperature decline followed the expansion of betula during the later interstadial and another fall occurred at the lateglacial interstadial loch lomond stadial boundary during the loch lomond stadial mean july temperatures of 9 11 c are implied with winter temperatures as low as 15 to 20 c collectively the evidence reemphasises the point that for the first 1000 years or so of the lateglacial interstadial there was a disequilibrium between the palynological and coleopteran records in terms of climatic signal during the later interstadial however a closer relationship is apparent between both proxy data sources of particular significance in this respect is the fluctuation in reconstructed summer and winter temperatures and a rise and subsequent fall in betula pollen frequencies this may be the correlative of one of the pre younger dryas climatic oscillations recorded in other proxy data sources including palynological records from britain and eastern canada oxygen isotope traces from swiss lake sediments isotopic and electrical conductivity profiles from the greenland ice sheet and diatom and foraminiferal records in cores from the norwegian sea and the north atlantic ocean

the loch lomond readvance on the isle of mull scotland glacier reconstruction and palaeoclimatic implications geomorphological mapping of mull provides evidence for an icefield 143 km2 in area flanked by six corrie glaciers with a total area of ca 13 km2 the absence of lateglacial periglacial features shorelines and pollen sites from the area occupied by this readvance together with radiocarbon dating of shell fragments confirm that it occurred during the loch lomond younger dryas stade the thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments up valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat consistent with slow warming following the coldest part of the stade reconstructed equilibrium line altitudes elas imply vigorous snow blowing by westerly winds and are consistent with a general southwestwards decline in elas across the scottish highlands an ela of 250 m was calculated for the mull icefield using an ablation accumulation balance ratio abr approach palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ela from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ela approximates conditions at 250 m on mull during the loch lomond stade the result indicates a mean july sea level temperature of 5 7 0 5 c and a mean annual precipitation at 250 m of ca 2700 3800 mm best estimate 3200 mm indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation copyright 2002 john wiley sons ltd

younger dryas glaciers and climate in the mourne mountains northern ireland here we present evidence to suggest that the mourne mountains northern ireland were last occupied by glaciers during the younger dryas stadial the margins of these glaciers are marked by moraines chronologically constrained to the younger dryas by schmidt hammer exposure dating reconstructions indicate that these glaciers had equilibrium line altitudes elas ranging from 356 33 m a s l to 570 9 m a s l with a mean of 475 36 m a s l elas rise from west to east probably reflecting the contribution of windblown snow and ice to the accumulation of younger dryas glaciers in the western mournes taking this into consideration a mean climatic ela of 529 4 m a s l is calculated for the mountains as a whole assuming a mean annual sea level air temperature of 8 c and an annual temperature range of 34 c degree day modelling suggests that during the younger dryas accumulation at the climatic ela of glaciers in the mournes was 846 990 mm a 1 this suggests increased aridity relative to present and is consistent with other parts of nw europe where reduced precipitation alongside notable cooling is thought to reflect increased north atlantic sea ice extent during the younger dryas

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

differentiating induced and natural seismicity using space time magnitude statistics applied to the coso geothermal field a remarkable characteristic of earthquakes is their clustering in time and space displaying their self similarity it remains to be tested if natural and induced earthquakes share the same behavior we study natural and induced earthquakes comparatively in the same tectonic setting at the coso geothermal field covering the preproduction and coproduction periods from 1981 to 2013 we analyze interevent times spatial dimension and frequency size distributions for natural and induced earthquakes individually these distributions are statistically indistinguishable determining the distribution of nearest neighbor distances in a combined space time magnitude metric lets us identify clear differences between both kinds of seismicity compared to natural earthquakes induced earthquakes feature a larger population of background seismicity and nearest neighbors at large magnitude rescaled times and small magnitude rescaled distances local stress perturbations induced by field operations appear to be strong enough to drive local faults through several seismic cycles and reactivate them after time periods on the order of a year

north atlantic control on precipitation pattern in the eastern mediterranean black sea region during the last glacial based on proxy records from western black sea cores we provide a comprehensive study of climate change during the last glacial maximum and late glacial period in the black sea region for the first time we present a record of relative changes in precipitation for nw anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration the good correspondence between reconstructed rainfall intensity in nw anatolia and past western mediterranean sea surface temperatures ssts implies that during the glacial period the precipitation variability was controlled like today by mediterranean cyclonic disturbances periods of reduced precipitation correlate well with low ssts in the mediterranean related to heinrich events h1 and h2 stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater sediment source concomitant to the meltwater inflow after 16 4 cal ka bp this change implies intensification of the northern sediment source and with other records from the mediterranean region consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the european continent the early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the mediterranean region leading simultaneously to more humid conditions in central and northern europe

evolution of 3 1 and 3 0 ga volcanic belts and a new thermotectonic model for the hopedale block north atlantic craton canada a new model for evolution of the archean hopedale block based on mapping and supporting u pb geochronological and geochemical studies is highlighted by i ca 3 25 ga emplacement of igneous precursors of maggo gneiss ii g iii emplacement of the hopedale mafic dykes iv 3 1 ga deposition of hunt river volcanic rocks v ca 3 0 ga deposition of florence lake volcanic rocks vi 2 88 2 96 ga greenschist to amphibolite facies fiordian metamorphism and formation of penetrative northeast striking fiordian structures and vii emplacement of a suite of 2 89 2 83 ga tonalite to granite intrusions which partially overlap and locally postdate fiordian metamorphism and deformation the hunt river and florence lake volcanic sequences are different in age but similar in most other respects the former consists mainly of amphibolite facies mafic metavolcanic rocks and lesser amounts of komatiite flows and metasedimentary and 3105

a change in seasonality in greenland during a dansgaard oeschger warming a new sub seasonal chemical record is presented from the north greenland icecore project northgrip ice core during the onset of one of the longest and strongest interstadials of the last glacial period dansgaard oeschger event 8 approximately 38 000 years ago this is the first time that a record of such resolution has been achieved over several metres of deep glacial ice and provides a unique opportunity for using additional parameters to carry out accurate dating using annual layer counting the very high resolution chemical data were used to assess the phasing of various ions and determine changes in the seasonal strength of chemical deposition and the shape of the seasonal cycle the study shows that a change in seasonality accompanied the dramatic warming transition from stadial to interstadial conditions in greenland thickness due to the exceptionally small sample size a new cutting method using a microtome device and a low volume ion chromatography method was developed the section of ice used in this study was from the outer most part of the ice core the outer surfaces were removed using a bandsaw to prevent contamination from drilling fluid and handling a sledge microtome was then used to cut 2 mm samples using several passes of the blade to cut a succession of 40 mm shavings with no ice loss that were placed in clean coulter accuvettes for melting and then transferred into clean ion chromatography auto sampler vials for analysis powder free gloves and protective clothing were worn throughout to minimize contamination ion chromatography ic was used to determine five anions chloride cl fluoride f methanesulphonate msa nitrate no3 and sulphate so4 2 the system used was a reagent free dionex ics 2500 with a 2 mm column and a 250 ml sample loop a potassium hydroxide eluent generator cartridge egc oh was used to reduce operational errors and contamination associated with eluent preparation the flow was set to 0 25 ml min 1 with an isocratic elution of 23 mm koh four cations calcium ca 2 potassium k sodium na and magnesium mg were analyzed using a reagent free dionex ic 2000 3 mm column and 250 ml sample loop the cation system is equipped with an msa eluent generator cartridge and the method followed set the flow to 0 5 ml min 1 with an isocratic elution of 20 mm msa a sequential flow method was used to analyze both anions and cations from the same sample vial using a dionex as50 auto sampler thus minimizing sample volume requirements the sample and the anion eluent are passed from the ics 2500 system into the ic 2000 system tests of this method were made using frozen ultra pure water to show that the blanks were negligible 5 of glacial concentration levels for all ions thomas 2006

late quaternary glacier sensitivity to temperature and precipitation distribution in the southern alps of new zealand glaciers respond to climate variations and leave geomorphic evidence that represents an important terrestrial paleoclimate record however the accuracy of paleoclimate reconstructions from glacial geology is limited by the challenge of representing mountain meteorology in numerical models precipitation is usually treated in a simple manner and yet represents difficult to characterize variables such as amount distribution and phase furthermore precipitation distributions during a glacial probably differed from present day interglacial patterns we applied two models to investigate glacier sensitivity to temperature and precipitation in the eastern southern alps of new zealand a 2 d model was used to quantify variations in the length of the reconstructed glaciers resulting from plausible precipitation distributions compared to variations in length resulting from change in mean annual air temperature and precipitation amount a 1 d model was used to quantify variations in length resulting from interannual climate variability assuming that present day interglacial values represent precipitation distributions during the last glacial a range of plausible present day precipitation distributions resulted in uncertainty in the last glacial maximum length of the pukaki glacier of 17 1 km 24 and the rakaia glacier of 9 3 km 25 corresponding to a 0 5 c difference in temperature smaller changes in glacier length resulted from a 50 decrease in precipitation amount from present day values 14 and 18 and from a 50 increase in precipitation amount 5 and 9 our results demonstrate that precipitation distribution can produce considerable variation in simulated glacier extents and that reconstructions of paleoglaciers should include this uncertainty

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

mean july temperatures during the younger dryas in northwestern and central europe as inferred from climate indicator plant species abstract we estimated minimum mean july temperatures in northwestern and central europe during the younger dryas 10 950 10 15014c yr b p from distributions of climate indicator plant species which were reconstructed from 140 pollen and plant macrofossil diagrams paleobotanical records mainly from the central and eastern part of the study area show that the coldest conditions occurred early in the younger dryas before 10 55014c yr b p for this phase mean july temperatures at sea level of around 10 c are suggested for the northern part of the british isles and for ice free scandinavia we estimated a mean july temperature of 12 c for central england the netherlands and northern germany the 13 c mean july isotherm largely based on the modern distribution oftypha latifolia was most probably located in southern england belgium central germany and poland the reappearance of thermophilous elements in the records after 10 55014c yr b p suggests a summer warming at least temporarily of 1 to 2 c in the study area the reconstructed temperatures are comparable with temperature estimates based on beetle data however they appear rather high when compared with estimates based on glaciological evidence

accumulation at the equilibrium line altitude of glaciers inferred from a degree day model and tested against field observations we extrapolate temperature data from a gridded climatology to the equilibrium line altitude ela of a glacier and tune a degree day model by adjusting precipitation to give zero mass balance at the ela we verify the tuned model by comparing modelled accumulation with winter balance where this has been measured presently for 180 glaciers the modelled accumulation naturally depends upon the vertical lapse rate vlr for temperature and the degree day factor ddf for snowmelt both are somewhat uncertain in high mountain areas but modelled accumulation and measured winter balance are in reasonable agreement for most glaciers the degree day model predicts a non linear relation between accumulation and summer temperature at the ela as assumed by many workers but we find a family of curves rather than a single universal curve maritime glaciers with low annual temperature range have proportionally more accumulation than continental glaciers with high annual temperature range for a similar summer mean temperature averages of winter balance for the five main geographical regions where mass balance data are available agree well with annual accumulation from the degree day model

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

source and site response study of the 2008 mount carmel illinois earthquake abstract two separate inversions are performed using the ground motion data from the 2008 mount carmel illinois earthquake one uses aftershocks as empirical green s functions to determine a finite fault slip distribution the second uses mainshock ground motion spectra to calculate source path and site response parameters the slip inversion reveals a prominent asperity at the hypocenter with an area of approximately 6 km 2 moment of m w 5 20 and stress drop of about 100 bars considering all major and minor slip the total moment is m w 5 45 the rupture velocity is not resolvable due to the small source area after fixing the geometric spreading the source path and site parameter inversion yields a similar moment of m w 5 26 and a corner frequency of 0 89 hz which also give a stress drop of approximately 100 bars our combined geometric and anelastic attenuation function q f r b 1137 f 0 12 r 0 94 fits the regional spectral amplitudes where the data is more plentiful as well as previously derived attenuation relationships site response spectra show prominent resonant frequencies that correlate with the thickness of mississippi river sediments and mississippi embayment deposits in addition higher frequency resonance peaks are observed that most likely represent higher mode resonances and resonances from shallower structure

influence of seasonality on glacier mass balance and implications for palaeoclimate reconstructions climates inferred from former glacier geometries in some areas exhibit discrepancies with regional palaeoclimates predicted by general circulation models gcms and modelling of palaeoecological data possibly as a consequence of their differing treatments of climatic seasonality since glacier based climate reconstructions potentially offer an important tool in the calibration of gcms which themselves need validation if used to predict future climate scenarios we attempt to resolve mismatches between these techniques by 1 investigating the influence of seasonality on glacier mass balance and 2 refining the methodology used for the derivation of glacier based palaeoclimates focussing on the younger dryas stadial glaciation of scotland northeast atlantic we show that sea ice amplified seasonality led to a significantly drier climate than has been suggested by glacier based interpretations this was characterised by a relatively short ablation season and the survival of a more substantial winter snowpack we suggest that if palaeoglaciological studies were to account for changes in seasonal temperature and precipitation variability their results would agree more closely with the cold arid northeast atlantic palaeoenvironment predicted by atmospheric modelling and northwest european pollen studies and would therefore provide more accurate constraints for gcm calibration

high resolution numerical simulation of younger dryas glaciation in scotland golledge n r hubbard a sugden d e 2008 high resolution numerical simulation of younger dryas glaciation in scotland quaternary science reviews 27 9 10 888 904 sponsorship nerc

latest pleistocene glacier advances and post younger dryas rock glacier stabilization in the mt krivaň group high tatra mountains slovakia abstract the timing of glacier disappearance and rock glacier stabilization in the highest massifs of the carpathians is still poorly documented in this paper we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the tatra mountains which are the highest 2654 m a s l northernmost n 49 12 and coldest range in the carpathians on the base of morphostratigraphic principles schmidt hammer tests and glacier equilibrium line altitude ela estimation we assigned moraines and rock glaciers in the mt kriva massif sw part of high tatras to a threefold stratigraphic sequence with glacial stages advances from older to younger popradske pleso pp sucha va ecka i sv i and sucha va ecka ii sv ii landforms attributed to two younger advances sv i and sv ii were sampled for the purpose of cosmogenic 10be surface exposure dating our data show that pp and sv i glacial advances occurred during the oldest dryas climatic downturn the younger advance sv i occurred just before the bolling allerod b a warming at 14 9 0 4 ka at this time small glaciers occupied lower glacial cirques in the study area the youngest sv ii advance was characterized by rock glaciers and small debris covered glaciers confined to the highest cirques the mean exposure age of four relict rock glaciers of this stage is 11 1 0 9 ka but individual rock glacier mean ages spanned between 11 8 and 10 4 ka our research results show that the youngest moraines and rock glaciers in the tatra mountains were formed during the younger dryas yd but the final permafrost melting and rock glacier stabilization period was delayed until the early holocene but no later than 10 4 ka in high elevation cirque bottoms up to 2120 m a s l the yd glaciers and rock glaciers readvanced across land which was ice free as early as 14 8 14 2 ka thus it is likely that during the b a interphase glaciers completely disappeared in the tatra mountains the yd was the last period of glacial periglacial activity in the massif as we investigated one of the highest situated rock glaciers in the tatras up to 2220 m a s l we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe lateglacial climate conditions the lateglacial climate of the tatra mountains is discussed herein on the basis of glacier equilibrium line altitude ela estimation and the vertical distribution of rock glacier belts we argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account

high resolution simulations of the last glacial maximum climate over europe a solution to discrepancies with continental palaeoclimatic reconstructions the analyses of low resolution models simulations of the last glacial maximum lgm 21 kyr bp climate have revealed a large discrepancy between all the models and pollen based palaeoclimatic reconstructions in general the models are too warm relative to the observations especially in winter where the difference is of the order of 10 c over western europe one of the causes of this discrepancy may be related to the low spatial resolution of these models to assess the impact of using high resolution models on simulated climate sensitivity we use three approaches to obtain high resolution climate simulations over europe first an atmospheric general circulation model agcm with a stretched grid over europe second a homogeneous t106 agcm high resolution everywhere on the globe and last a limited area model lam nested in a low resolution agcm with all three methods we have performed simulations of the european climate for present and lgm conditions according to the experimental design recommended by the palaeoclimate modeling intercomparison project pmip model results have been compared with updated pollen based palaeoclimatic indicators for temperature and precipitation that were initially developed in pmip for each model a low resolution global run was also performed as expected the low resolution simulations underestimate the large cooling indicated by pollen data especially in winter despite revised slightly warmer reconstructions of the temperatures of the coldest month and show results in the range of those obtained in pmip with similar models the two high resolution agcms do not improve the temperature field and cannot account for the discrepancy between model results and data especially in winter however they are able to reproduce trends in precipitation more closely than their low resolution counterparts do but the simulated climates are still not as arid as depicted by the data conversely the lam temperature results compare well with climate reconstructions in winter but the simulated hydrological cycle is not consistent with the data finally these results are discussed in regard of other possible causes for discrepancies between models and palaeoclimatic reconstructions for the lgm european climate

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

cooling and changing seasonality in the southern alps new zealand during the antarctic cold reversal abstract a comprehensively 14c ams dated pollen and chironomid record from boundary stream tarn provides the first chironomid derived temperature reconstruction to quantify temperature change during lateglacial times 17 500 10 000 cal yr bp in the southern alps new zealand the records indicate a ca 1000 year disruption to the lateglacial warming trend and an overall cooling consistent with the antarctic cold reversal acr the main interval of chironomid inferred summer temperature depression 2 3 c lasted about 700 years during the acr following this cooling event both proxies indicate a warming step to temperatures slightly cooler than present during the younger dryas chronozone 12 900 11 500 cal yr bp these results highlight a direct linkage between antarctica and mid latitude terrestrial climate systems and the largely asynchronous nature of the interhemispheric climate system during the last glacial transition the greater magnitude of temperature changes shown by the chironomid record is attributed to the response of the proxies to differences in seasonal climate with chironomids reflecting summer temperature and vegetation more strongly controlled by duration of winter or by minimum temperatures these differences imply stronger seasonality at times during the lateglacial which may explain some of the variability between other paleoclimate records from new zealand and have wider implications for understanding differences between proxy records for abrupt climate change

a 10be chronology of lateglacial and holocene mountain glaciation in the scoresby sund region east greenland implications for seasonality during lateglacial time abstract thirty eight new cosmogenic 10 be exposure ages from the scoresby sund region of east greenland indicate that prominent moraine sets deposited by mountain glaciers date from 780 to 310 yr approximately during the little ice age from 11 660 to 10 630 yr at the end of the younger dryas cold interval or during preboreal time and from 13 010 to 11 630 yr during lateglacial time equilibrium line altitudes elas interpreted from lateglacial to early holocene moraines indicate summertime cooling between 3 9 and 6 6 c relative to today s value much less than the extreme younger dryas cooling registered by greenland ice cores mean annual temperatures of 15 c colder than today s value this apparent discrepancy between paleotemperature records supports the contention that younger dryas cooling was primarily a wintertime phenomenon 10 be ages of lateglacial and holocene moraines show that mountain glaciers during the little ice age were more extensive than at any other time since the early holocene epoch in addition 10 be ages of lateglacial moraines show extensive reworking of boulders with cosmogenic nuclides inherited from prior periods of exposure consistent with our geomorphic observations and cosmogenic exposure dating studies in other arctic regions

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

temperature gradients in northern europe during the last glacial holocene transition 14 914c kyr bp interpreted from coleopteran assemblages late glacial and early holocene climatic conditions have been reconstructed for northern europe using the mutual climatic range mcr palaeoclimate method based on fossil coleopteran assemblages altogether beetle faunas from 77 sites have been analysed ranging from ireland in the west to poland and finland in the east and mcr estimates calculated the results are plotted on 16 maps each representative of a selected time slice covering the period from 14 5 14c kyr bp to 9 0 14c kyr bp eight of the maps show the mcr estimates of tmax mean temperature of the warmest month derived from each site for which data are available while the remainder show estimated tmax isotherms interpolated from these values it can be demonstrated that at times the thermal climate was fairly uniform throughout the study area whereas at others temperature gradients were much steeper than they are in the region today there also appears to be a distinct contrast between cold periods when contours trended nw se and warmer periods when contours trend w e or even ne sw the pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying late glacial climatic events on a wide even global scale the suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived 1998 john wiley sons ltd

late holocene effective precipitation variations in the maritime regions of south west scandinavia at present the climate in south west scandinavia is predominantly controlled by westerlies carrying moist atlantic air which forms a main source of precipitation in all seasons past variations in the ratio between precipitation and evaporation effective precipitation from terrestrial sites however may indicate changes in the degree of maritime influence palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns in this study multi proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional scale variations of effective precipitation in south west sweden during the late holocene the total aeolian sediment influx into two peat bogs is used as a proxy for storm activity the frequency of storm phases increases strongly after ca 2500 cal yrs bp dry conditions occur on a regional scale around 4800 4400 2000 1700 1300 1000 700 500 and 300 100 cal yrs bp in addition a comparison to winter precipitation reconstructed from four norwegian glaciers shows similar variations during the past ca 2000 years this indicates that the climate in both regions was controlled by large scale atmospheric circulation dynamics of the north atlantic region the strong variability of effective precipitation and storm activity after ca 2500 cal yrs bp indicates a highly variable climate

spatial and temporal stress drop variations in small earthquakes near parkfield california 1 we estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the parkfield segment of the san andreas fault in central california we use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed p wave source spectra with a spatially varying empirical green s function egf our brune type stress drop estimates vary from 0 1 to over 100 mpa with a median value of 6 75 mpa which is nearly constant with moment implying self similarity over the ml 0 5 to 3 0 range of our data the corner frequency decreases for earthquakes at shallower depths consistent with slower rupture velocities and reduced shear wave velocities in local velocity models the estimated median stress drops show significant lateral variations we find lower stress drops in the middle mountain asperity and along the creeping fault section and higher stress drops in the hypocentral region of the 2004 m6 0 parkfield earthquake the main shock did not alter the overall pattern of high and low stress drop regions however a statistical test reveals areas with significant changes in computed stress drops after the main shock which we compare to estimated absolute shear stress changes from a main shock slip model by calculating t from the spectral egf ratio we also identify areas with increased attenuation after the main shock and we are able to distinguish source effects and near source attenuation effects in the spectral analysis these results are confirmed independently from spectral ratios of repeating microearthquake clusters

evolution of continental crust in southern africa abstract nd isotopic data from the zimbabwe and kaapvaal cratons and the limpopo kalahari namaqualand and damara mobile belts imply that over 50 of present day continental crust in this region had separated from the mantle by the end of the archaean and that

rupture model of the 2011 mineral virginia earthquake from teleseismic and regional waveforms 1 we independently invert teleseismic p waveforms and regional crustal phases to examine the finite fault slip model for the 2011 mw 5 8 mineral virginia earthquake theoretical and empirical green s functions are used for the teleseismic and regional models respectively both solutions show two distinct sources each about 2 km across and separated by 2 5 km the source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model both sources are centered at approximately 8 km depth in the regional model largely below the aftershock distribution in the teleseismic model the sources extend updip to approximately 6 km depth into the depth range of the aftershocks the rupture velocity is not well resolved but appears to be near 2 7 km s

deglaciation of the eurasian ice sheet complex the eurasian ice sheet complex eisc was the third largest ice mass during the last glacial maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea level lowering whilst recent terrestrial and marine empirical insights have improved understanding of the chronology pattern and rates of retreat of this vast ice sheet a concerted attempt to model the deglaciation of the eisc honouring these new constraints is conspicuously lacking here we apply a first order thermomechanical ice sheet model validated against a diverse suite of empirical data to investigate the retreat of the eisc after 23 ka bp directly extending the work of patton et al 2016 who modelled the build up to its maximum extent retreat of the ice sheet complex was highly asynchronous reflecting contrasting regional sensitivities to climate forcing oceanic influence and internal dynamics most rapid retreat was experienced across the barents sea sector after 17 8 ka bp when this marine based ice sheet disintegrated at a rate of 670 gigatonnes per year gt a 1 through enhanced calving and interior dynamic thinning driven by oceanic atmospheric warming and exacerbated by eustatic sea level rise from 14 9 to 12 9 ka bp the eisc lost on average 750 gt a 1 peaking at rates 3000 gt a 1 roughly equally partitioned between surface melt and dynamic losses and potentially contributing up to 2 5 m to global sea level rise during meltwater pulse 1a independent glacio isostatic modelling constrained by an extensive inventory of relative sea level change corroborates our ice sheet loading history of the barents sea sector subglacial conditions were predominately temperate during deglaciation with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network moreover the maximum eisc and its isostatic footprint had a profound impact on the proglacial hydrological network forming the fleuve manche mega catchment which had an area of 2 5 106 km2 and drained the present day vistula elbe rhine and thames rivers through the seine estuary during the bolling allerod oscillation after c 14 6 ka bp two major proglacial lakes formed in the baltic and white seas buffering meltwater pulses from eastern fennoscandia through to the younger dryas when these massive proglacial freshwater lakes flooded into the north atlantic ocean deglaciation temporarily abated during the younger dryas stadial at 12 9 ka bp when remnant ice across svalbard franz josef land novaya zemlya fennoscandia and scotland experienced a short lived but dynamic re advance the final stage of deglaciation converged on present day ice cover around the scandes mountains and the barents sea by 8 7 ka bp although the phase lagged isostatic recovery still continues today

the validation and sensitivity of a model of the icelandic ice sheet abstract the derivation and implementation of a three dimensional model used to investigate the last glacial maximum ice sheet across iceland by hubbard et al 2006 a modelling insight into the icelandic last glacial maximum ice sheet quaternary science reviews is described it is applied at 2 km resolution and requires boundary distributions of topography geothermal heat flux surface air temperature and mass balance calculated using a temperature index approach based on reference distributions of annual temperature and precipitation the model enables the variables of ice thickness stress strain and temperature to evolve freely through time and caters for the coupling of thermally triggered basal sliding with non local dynamics through the computation of longitudinal stresses it is driven through perturbations in sea level and annual precipitation and temperature a series of contemporary experiments are initiated to validate the model against the present ice cover across iceland forcing the model from ice free conditions with the 1961 1990 reference climatology yields a good simulation of all the ice masses except for vatnajokull where the model falls well short of its present margins however an experiment forced from ice free conditions for 1000 years with a 2 c cooling perturbation followed by 100 years of reference climatology yields a good simulation of vatnajokull in addition to other ice masses implying that it is a remnant icecap inherited from the little ice age and perpetuated through strong ice elevation mass balance coupling an ensemble of experiments are initiated to investigate the sensitivity of the optimum lgm model isolated in hubbard et al 2006 ice sheet volume and aspect ratio but not area are found to be sensitive to basal boundary conditions in particular to the choice of sliding parameter and the applied geothermal conditions due to strong topographic control in particular the configuration of offshore bathymetry and shelf break ice sheet volume and area is sensitive to the calving parameter and sea level change however an asymmetrical response indicates that the ice sheet is effectively decoupled from further climatic deterioration once it advances to the continental shelf break these experiments imply that there is little latitude in the selection of model parameters which yields an ice sheet compatible with the available evidence and that the optimum lgm experiment represents a sound result by inference at least 63 of the optimum lgm ice sheet was grounded below sea level implying potential instability with the onset of deglaciation

loch lomond stadial glaciers in north harris outer hebrides north west scotland glacier reconstruction and palaeoclimatic implications abstract geomorphological mapping of north harris provides evidence for the former existence of 10 glaciers with a total area of ca 35 km2 a loch lomond younger dryas stadial age ca 12 9 11 5 kyr bp for this glacial episode is inferred from glacier configuration landsystems dominated by hummocky recessional moraines and relationships with lateglacial periglacial phenomena equilibrium line altitudes elas of 150 289 m were calculated for individual glaciers ela variability mainly reflects differences in snow contributing area the area weighted mean ela 204 m is consistent with a northwards decline in elas along the western seaboard of the british isles of 69 5 m 100 km 1 equivalent to a northwards ablation season temperature decrease of 0 42 c 100 km 1 this latitudinal temperature gradient implies a mean july sea level temperature of ca 7 2 c for the coldest part of the stade roughly 6 c lower than at present sea level precipitation at the time of the lls glacial maximum is inferred to have been between ca 1970 200 and 2350 200 mm yr 1 implying that lls precipitation was up to 25 greater than now patterns of recessional moraines indicate that the glaciers remained close to climatic equilibrium as they retreated to their sources though moraine belts implying near stationary or readvancing ice margins on flat valley floors are separated by moraine free zones indicating uninterrupted retreat calculation of elas for residual glaciers in former source areas suggests that summer warming of 1 0 c would have resulted in shrinkage of the glaciers to their sources

rb sr geochronology of the archaean maggo gneiss from the hopedale block nain province labrador the maggo gneiss a typical grey gneiss from the hopedale block of coastal labrador southern nain province preserves structures of two major archaean tectonothermal events the hopedalian and the younger fiordian rb sr whole rock analyses of four suites representing the hopedalian event 3140 95 ma 1 3125 43 ma 3028 199 ma and 3025 163 ma fall within the early middle archaean and represent a period of cratonization of the hopedale block two suites with a younger fiordian structural fabric 2899 116 ma and 2804 100 ma fall within the late middle archaean and are interpreted as dating a period of reworking that locally reset the rb sr isotopic systematics of the maggo gneiss fiordian ages were also determined from four suites 2927 50 ma 2884 86 ma 2854 83 ma and 2764 89 ma that do not display the fiordian structural fabric indicating that chemical and mechanical components of the fiordian event did not occur simultaneously age determinations of the fiordian do not dat

comparison of direct and coda wave stress drop measurements for the wells nevada earthquake sequence 1 i calculate the corner frequencies and stress drops of the seven largest earthquakes m4 6 in the wells nevada sequence 2008 using both coda and direct waves i use spectral ratio empirical green s function egf and methods to investigate whether differences and uncertainties in the analyses could affect the calculated source parameters i find that the source spectral ratios from the coda and direct s waves are similar for the same pairs of earthquakes but that the source spectra and corresponding source parameters depend systematically on whether the earthquake of interest is the larger or smaller within the spectral ratio mayeda and malagnini 2009a calculated coda spectral ratios between the m6 main shock and six large aftershocks m 4 and performed a combined inversion to calculate source parameters they found that the main shock had a higher stress drop than the large aftershocks i model the identical spectral ratios individually in the manner that i use for direct waves i find that the choice of source model and fitting procedure produces significant random scatter but no systematic biases i calculate direct wave ratios for the same earthquake pairs and find higher variability but no systematic difference in the results lastly i use m2 8 3 2 aftershocks as egfs for the large aftershocks these spectral ratios yield significantly higher corner frequencies and stress drops for the large aftershocks than when the same earthquakes are the denominator in ratios with the main shock to improve the quality of egf analyses i propose strict objective criteria for acceptance of a spectral ratio fit 1 observable source pulse 2 the amplitude ratio of the low to high frequency limits of the fit is at least 5 and 3 the corner frequency only varies by 50 when the variance is within 5 of the minimum

an abrupt wind shift in western europe at the onset of the younger dryas cold period the younger dryas cold reversal during the last glacial termination is one of the most abrupt climate change events observed in the northern hemisphere analyses of varved lake sediments from western germany suggest that storminess in the north atlantic region increased within a single year at this time providing a mechanistic link between a decrease in the meridional overturning circulation and western european cooling the younger dryas cooling 12 700 years ago is one of the most abrupt climate changes observed in northern hemisphere palaeoclimate records1 2 3 4 annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes as the seasonal deposition responds immediately to climate and the varve counts provide an accurate estimate of the timing of the change here we present sub annual records of varve microfacies and geochemistry from lake meerfelder maar in western germany providing one of the best dated records of this climate transition5 our data indicate an abrupt increase in storminess during the autumn to spring seasons occurring from one year to the next at 12 679 yr bp broadly coincident with other changes in this region we suggest that this shift in wind strength represents an abrupt change in the north atlantic westerlies towards a stronger and more zonal jet changes in meridional overturning circulation alone cannot fully explain the changes in european climate6 7 we suggest the observed wind shift provides the mechanism for the strong temporal link between north atlantic ocean overturning circulation and european climate during deglaciation

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

application of a degree day model to reconstruct pleistocene glacial climates there is empirical evidence of a nonlinear relation between annual precipitation or accumulation and summer mean temperature at the equilibrium line altitude ela on glaciers around the world the degree day model gives a similar relation between accumulation and summer temperature although instead of a single universal curve there is a family of curves depending upon the annual temperature range furthermore the degree day model also gives nonlinear relations between accumulation and annual mean temperature thus estimations of accumulation can be made from both summer and annual temperatures at the ela of former reconstructed glaciers such as those in greece this is particularly useful since these climatic variables have major implications for biological proxies such as vegetation history indicated in the pollen record and for periglacial proxies such as permafrost distributions indicated in the geomorphological record the close relationship between glaciers and climate provides one of the most precise methods for reconstructing former climates and offers considerable potential for resolving our understanding of pleistocene cold stage climates

u pb ages of single zircons within upernavik metasedimentary rocks and regional implications for the tectonic evolution of the archaean nain province labrador detrital zircons and their postdepositional overgrowths from three units of the upernavik supracrustal association in the northern saglek block of the archaean nain province have been dated with the ion microprobe shrimp in one unit from the granulite facies area in inner saglek fiord the zircon population is dominated by early archaean grains thought to be derived from the uivak gneisses recrystallization and growth of new zircon within this metasediment took place during granulite facies metamorphism at 2761 12 ma 2 which is also a younger limit on the age of deposition in a second unit from the amphibolite facies area in outer saglek fiord detrital zircons have predominantly mid and late archaean ages the mid archaean zircons are comparable in age to the 3235 ma lister gneisses the ages of the late archaean detrital zircons 2800 2960 ma do not correspond to any known rock complex in the saglek block but plutonic rocks associated or correlative with the ca 2840 ma kanairiktok plut

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time

climate patterns during former periods of mountain glaciation in britain and ireland inferences from the cirque record we map glacial cirques and analyse spatial variability in their altitude and aspect to derive a long term time integrated perspective on climate patterns during former periods of mountain glaciation likely spanning multiple quaternary glaciations in britain and ireland the data reveal that although air temperatures were important exposure to moisture bearing air masses was the key factor in regulating sites of former mountain glacier formation and indicate that during such periods moisture supply was largely controlled by north atlantic westerlies with notable inland precipitation gradients precipitation decreasing inland similar to present day in places trends in cirque altitude may also reflect regional differences in the extent of cirque deepening controlled by the dimensions and dynamics of the glaciers that came to occupy them specifically comparatively deep cirques in coastal locations may reflect the former presence of dynamic fed by moisture from the north atlantic but comparatively small glaciers largely confined to their cirques by contrast decreasing cirque depth further inland may reflect the former presence of larger and or less dynamic ice masses occupying comparatively continental climatic conditions