timing of abrupt climate change a precise clock 1 many paleoclimatic data reveal a 1 500 year cyclicity of unknown origin a crucial question is how stable and regular this cycle is an analysis of the gisp2 ice core record from greenland reveals that abrupt climate events appear to be paced by a 1 470 year cycle with a period that is probably stable to within a few percent with 95 confidence the period is maintained to better than 12 over at least 23 cycles this highly precise clock points to an origin outside the earth system oscillatory modes within the earth system can be expected to be far more irregular in period

geochemical constraints on the laurentide ice sheet contribution to meltwater pulse 1a planktonic and benthic d 18 o records adjacent to the runoff outlets of the laurentide ice sheet lis indicate that the lis contributed to the abrupt w20 m rise in sea level w14 6 ka meltwater pulse 1a mwp 1a however the magnitude of the lis contribution still remains unresolved here i use a freshwater runoff ocean mixing model to calculate the lis meltwater required to explain the decreases in planktonic and benthic d 18 o observed during mwp 1a at the southern eastern and northern runoff

radiocarbon constraints on antarctic peninsula ice sheet retreat following the last glacial maximum lgm abstract we present marine sedimentologic and radiocarbon data for the timing of retreat of the largely marine based antarctic peninsula ice sheet since the last glacial maximum lgm our findings indicate minimum estimates of deglaciation between 18 000 and 9000 calibrated years before present cal yr bp roughly in phase with the northern hemisphere deglaciation and eustatic sea level rise our findings show this retreat occurred progressively from the outer middle and inner continental shelf regions as well as progressively from the north to the south retreat initiated on the outer shelf of the northern peninsula by 18 000 cal yr bp and continued southward by 14 000 cal yr bp on the outer shelf of marguerite bay several thousand years earlier than estimated by numeric models while individual cores yield estimates of glacial retreat that may vary up to 1100 years we note steps in the data occur at 14 000 and possibly 11 000 cal yr bp coincidental to rapidly rising eustatic sea level including the well documented melt water pulses mwp 1a and 1b these data support the hypothesis that rapidly rising sea level is associated with marine ice sheet destabilization although additional dates are necessary to substantiate this finding this study highlights problems with radiocarbon dating acid insoluble organic aio matter in proximal lateglacial sediments as well as the need for more accurate dating techniques

initiation of fennoscandian ice sheet retreat during the last deglaciation although the retreat history of the southern margin of the laurentide ice sheet during the last deglaciation has been well known for several decades1 3 and recently supported by evidence from accelerator mass spectrometer ams radiocarbon dating of meltwater in the gulf of mexico4 and the north atlantic subtropical gyre5 the retreat history of the fennoscandian ice sheet before 13kyr ago is still poorly documented from ams 14c dating and isotopic analysis of a rapidly deposited series of supra till sediments in the norwegian channel north sea we find that the southern margin of the fennoscandian ice sheet was in retreat by 15 kyr bp before present approximately 2 000 yr earlier than previously supposed oxygen isotope analyses in the channel sediments confirm earlier evidence from deep norwegian sea sediment cores for low salinity due to ice sheet discharge beginning 15 14 5 kyr bp ref 6 recent recalibration of the 14c timescale indicates that the onset of deglaciation within the norwegian sea occurred during an interval of rapidly increasing summer insolation beginning 18 000 calendar yr bp ref 7 suggesting that ice sheet retreat may have been caused by increasing insolation acting on a particularly climate sensitive ice sheet configuration fresh water and icebergs discharged into the norwegian sea at this time reached the north atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of north atlantic deep water9 10 these factors may also have helped to briefly reverse the deglaciation trend erie interstade already underway in north america

pollen taphonomy of cave sediments what does the pollen record in caves tell us about external environments and how do we assess its reliability cave sediments may contain important long term records of past environments and human activity pollen provides key evidence since it disperses widely and is relatively durable we still know relatively little about the dispersal of pollen into caves and its preservation within cave sediments compared with our relatively detailed knowledge of pollen taphonomy in other sedimentary environments pollen taphonomy in caves is dependent on a variety of transport pathways and seems to be very contingent on local circumstance the airfall component of cave pollen assemblages often seems comparable with airfall spectra in the landscape outside the cave but bees birds and bats may transport considerable quantities of pollen into caves and the entrance flora may also be significant cave sediments are rarely waterlogged and pollen within them can be subject tomicrobial and chemical degradation sedimentation in caves is often episodic with episodes of storage and deposition sometimes redeposition of sediment which means that biostratinomic preservational factors become very significant comparison with sequences outside caves is difficult because few caves are found in landscapes where there are comparable pollen records from lakes and bogs here we review the factors affecting cave pollen taphonomy and hence the reliability of palynological analysis of sediments from caves with suggestions for future investigation

stress release in exhumed intermediate and deep earthquakes determined from ultramafic pseudotachylyte stresses released by coseismic faults during subduction toward lawsonite eclogite facies conditions in the alpine subduction complex of corsica can be estimated based on the energy required to form pseudotachylyte fault veins where shear strain can be measured congruent peridotite melting at ambient conditions of 1 5 gpa and 470 c requires a temperature increase of 1280 c to 1750 c we assume that more than 95 of the work is converted to heat during faulting hence that the stress drop is nearly proportional to the amount of melting and inversely proportional to shear strain minimum estimates of released stress are typically greater than 220 mpa and as high as 580 mpa the abundance of pseudotachylyte on small faults in the studied peridotite suggests that melting is very common on intermediate and deep earthquakes and that shear heating is important for seismic faulting at depth

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

modelling the heat pulses generated on a fault plane during coseismic slip inferences from the pseudotachylites of the copanello cliffs calabria italy abstract a pseudotachylite vein network crosscutting late hercynian foliated tonalites can be observed along the copanello cliffs calabria southern italy pseudotachylites formed during the oligocene miocene at intermediate crustal levels ca 10 km they show variable thickness ranging from few mm up to 10 cm as observed in injection veins branching from the fault plane microscopic observations indicate that pseudotachylite matrix mainly consists of plagioclase an46 an58 and biotite microlites rounded clasts of quartz plagioclase or of plagioclase quartz lithic fragments are disseminated in the matrix intergranular flow and spherulitic textures are commonly observed microstructural features are consistent with rapid crystallisation from melt eds analyses of rare and tiny glass veins indicated a trachyandesite or an50 plagioclase melt composition the conditions for pseudotachylite formation were reproduced by an analytical model taking into account the heat released by friction along a horizontal fault plane during a seismic event the model is based on a three stage rupture history that includes nucleation propagation and stopping in addition by means of a numerical approach the model reproduces cooling that follows the stopping stage according to previous studies the thermal perturbation induced by fault displacement is very intense in fact temperatures exceeding the tonalite and even an50 plagioclase liquidus 1470 c are reproduced by small amount of slip 6 cm in suprahydrostatic regime on the other hand the thermal perturbation is strongly localised and of short duration peak temperatures abruptly decrease at a short distance from the fault plane typically in few millimetres in these conditions a thin film of melt can be produced therefore the presence of cm scale pseudotachylite veins can be only explained assuming an efficient and fast melt migration towards dilatant sites such as pull apart structures and injections veins results of the model may be useful to predict the thermal disturbance produced by earthquakes of low intensity

microcrystalline textures resulting from rapid crystallization in a pseudotachylite melt in a meta anorthosite the very fine grained 1 m polygonal microcrystalline texture occurring in the groundmass of pseudotachylite veins in the harris meta anorthosite and its variation with position are described and an origin by crystallization from a melt at very large undercooling suggested the intrusive nature of the veins is shown by their geometry and internal structures clasts which are almost always only plagioclase are generally concentrated towards the centres of veins flow of tens of millimetres can account for this concentration in millimetre thick veins as a result of the bagnold effect the veins are generally thin 5 m to 5 mm or more are frequently zoned and always contain transparent granules of high relief probably al rich pyroxene and opaque granules of magnetite up to a few micrometres in size the granules are either uniformly distributed in microcrystalline textures or concentrated locally giving cellular textures in some veins spherulitic or bow tie textures occur the coarsest textures are found in the centres of the thickest veins the groundmass of the pseudotachylite is never completely isotropic but consists of a mosaic of transparent plagioclase crystals decreasing in size from the centres of thick veins to less than 1 m in thin veins or in the margins of thicker veins this fine microcrystalline texture was studied by both scanning and transmission electron microscopy and consists of polyhedral crystals of regular size in the range 0 2 1 5 m which show little sign of deformation the local composition of the pseudotachylites varies little from the average compositions of the rocks in optically homogeneous veins the variation being within the compositional space defined by the minerals of the host rock this shows that homogenization of the pseudotachylite has occurred in cellular veinsdifferentiation has occurred as the compositions of the cell centres lie outside those of the minerals of the host rock this was produced by segregation of the granules pyroxene being absent from the host rock the plagioclase in the pseudotachylite is more disordered than that in the host rock all the microtextures described are absent from the associated cataclasites and cannot be due to recrystallization of a fine grained and intensely strained rock powder the physical state on and after intrusion was that of a melt and injection was followed by crystallization the melt was produced by more or less total fusion of the host rock minerals at shallow depth by heat produced during local faulting and perhaps during crack propagation the fine microcrystalline texture very closely resembles that produced during hypercooling of molten metals and alloys it thus possibly formed not by devitrification but from a melt at much greater degrees of undercooling than the spherulitic and bow tie textures

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

pseudotachylite from the main zone of the hidaka metamorphic belt hokkaido northern japan pseudotachylite veins have been found in the mylonite zone of the hidaka metamorphic belt hokkaido northern japan they are associated with faults with wnw ese to ene wsw or ne sw trends which make a conjugate set cutting foliations of the host mylonitic rocks with high obliquity the mylonitic rocks comprise greenschist facies to prehnite pumpellyite facies mineral assemblages the mode of occurrence of the pseudotachylite veins indicates that they were generated on surfaces of the faults and were intruded as injection veins along microfractures in the host rocks during brittle deformation in near surface environments an analysis of the deformational and metamorphic history of the hidaka main zone suggests that the ambient rock temperature was 200 300 c immediately before the formation of the hidaka pseudotachylite three textural types of veins are distinguished cryptocrystalline microcrystalline and glassy the cryptocrystalline or glassy type often occupies the marginal zones of the microcrystalline type veins the microcrystalline type is largely made up of quench microlites of orthopyroxene clinopyroxene biotite plagioclase and opaque minerals with small amounts of amphibole microlites the interstices of these microlites are occupied by glassy and or cryptocrystalline materials the presence of microlites and glasses in the pseudotachylite veins suggests that the pseudotachylites are the products of rapid cooling of silicate melts at depths of less than 5 km the bulk chemical composition of the pseudotachylite veins is characterized by low sio2 and a high water content and is very close to that of the host mylonitic rocks this indicates that the pseudotachylite was formed by virtual total melting of the host rocks with sufficient hydrous mineral phases local chemical variation in the glassy parts of the pseudotachylite veins may be due to either crystallization of quench microlites or the disequilibrium nature of melting of mineral fragments and incomplete mixing of the melts pyroxene microlites show a crystallization trend from hypersthene through pigeonite to subcalcic augite with unusually high al contents the presence of pigeonite and high al pyroxene microlites of hornblende and biotite microlites and rare plagioclase microlites may indicate the high temperature and high water content of the melt which formed the pseudotachylite veins the melt temperatures were estimated to be up to 1100 c using a two pyroxene geothermometer using published data relating water solubilities in high temperature andesitic magmas to pressure a depth estimate of about 4 km is inferred for the hidaka pseudotachylites evidence derived from pseudotachylites in the hidaka metamorphic belt supports the conclusion that pseudotachylite is formed by frictional melting along fault surfaces at shallow depths from rocks containing hydrous minerals

a pseudotachylyte geothermometer abstract pseudotachylytes invariably contain a conspicuous concentration of clasts and lithic fragments in their matrices which reflect brittle wear processes during frictional melting the ratio of clasts to matrix is interpreted as the ratio of wear to melt w m and measurements of this ratio show a range of 0 1 0 7 based on models of melting and wear processes it is shown that the ratio w m is independent of fault displacement stress fault area and mineralogy thermodynamic considerations indicate that w m corresponds to the thermodynamic efficiency of the conversion of work to heat and is defined as w q thigh tlow thigh where thigh refers to the melt temperature and tlow is the ambient country rock temperature this provides a simple new technique for estimating the ambient crustal temperature tcrust in degrees kelvin t crust 1 w m t melt assuming a reasonable value for the temperature of the melt estimates of country rock temperatures tcrust for pseudotachylytes from four different localities in the usa indicate a range of 123 387 c eclogite facies pseudotachylytes from western norway yield a mean country rock temperature of 658 c in good agreement with independent fe mg exchange geothermometry this new geothermometer appears to be applicable throughout the entire crust and may provide a better understanding of melting and wear processes during seismic faulting

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

fossil earthquakes recorded by pseudotachylytes in mantle peridotite from the alpine subduction complex of corsica paleo earthquakes recorded by pseudotachylytes have recently been discovered in the blueschist facies subduction complex of alpine corsica pseudotachylytes occur in ophiolite gabbro and mantle peridotite belonging to the schistes lustres of cape corse ultramafic pseudotachylyte fault and injection veins are found within well preserved peridotite lenses and are progressively hydrated together with the host rock along the margins of the lenses numerous pseudotachylytes ranging in thickness from less than 1 to 380 mm have been identified veins thicker than 3 mm may show flow banded chilled glassy margins and cores with dendritic to spherulitic quench textures the newly formed minerals are zoned olivine fo93 89 clino and ortho pyroxene with compositions indicative of high crystallization temperatures 1300 1400 8c zoned cr spinel and a glassy to micro vesicular hydrous matrix showing that frictional melts contained up to 4 water frictional heating on co seismic faults raised the temperature from ambient blueschist facies conditions 450 8c and 1 1 5 gpa to more than 1700 8c which is required for 75 disequilibrium melting of spinel peridotite at 1 5 gpa the characteristic fault vein thicknesses observed are 1 to 3 cm but several fault veins are thicker than 10 cm co seismic displacement of 1 m a stress of 300 mpa and seismic efficiency of 5 may melt ca 60 kg peridotite pr m 2 fault surface corresponding to 20 mm thick layer of ultramafic pseudotachylyte the ultramafic pseudotachylytes described here formed by disequilibrium melting of peridotite in the upper part of the alpine subduction zone if the interpretations of typical displacements of approximately 1 m are correct the most common pseudotachylyte fault veins are related to magnitude ca 7 or larger subduction earthquakes d 2005 elsevier b v all rights reserved

evidence for late pleistocene thinning of siple dome west antarctica 1 we use a two dimensional full stress thermomechanical flow band model to investigate late pleistocene and holocene histories of ice thickness and ice flow at siple dome in west antarctica measurements obtained from an ice core and borehole near the ice divide and measurements of radar detected internal stratigraphy are used as targets for modeling models that account for the climate history accumulation rate and temperature alone yield a poor match to observations histories of ice dynamics ice thickness ice divide location and ice flow enhancement also need to be included our favored model includes 350 m of thinning at siple dome between 15 000 and 14 000 years ago onset of divide flow 3000 years ago ongoing divide migration starting 2500 years ago and evolution of ice fabric over the past 30 000 years the timing of thinning is earlier than that inferred from geologic evidence from the margins but is coincident with a 20 m rise in global sea level about 14 500 years ago meltwater pulse 1a this opens the possibility that thinning was a result of increased activity of the ice streams in the late pleistocene forced by meltwater pulse 1a the contribution to meltwater pulse 1a as a result of this thinning was likely small

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

the contribution of open air sites to the environmental reconstruction of the gravettian at the basque crossroads north iberia abstract the reconstruction of the cantabrian gravettian and its palaeoenvironmental sequence is based on cave stratigraphies which generally indicate a very rigorous climate intense cold occasionally dry and other times attenuated by the humidity however as open air deposits are increasingly studied ametzagaina irikaitz and mugarduia south other situations are being detected in the gravettian with much milder conditions we can now criticise the simplistic view of the gravettian as a period governed solely by intensely cold conditions and look through the window of opportunity offered by the open air camps to observe completely different landscapes and environments consequently in the cold heinrich events caves would have been inhabited while in more temperate times such as the dansgaard oeschger cycles the habitat would have been preferentially in the open air the historiographic and methodological over emphasis on cave sites has created a mirage that is reinforced by every new study in such locations the difficulties of all kind involved in locating excavating and dating open air sites adequately has led us to believe they did not exist or their contribution was unnecessary to draw a global picture of the period the most extreme case is the flint workshop of mugarduia south navarre at over 900 m above sea level nearly 60 km from the modern coast and in a palaeobotanic environment dominated by deciduous species

origin of the first global meltwater pulse following the last glacial maximum well dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates these very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets the laurentide ice sheet is commonly targeted as the source of the first and largest of the meltwater pulses mwp ia between 14 200 12 200 14c years b p and 13 700 years ago 11 700 14c years b p in all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review only those from the gulf of mexico and the bermuda rise show evidence of low 18o values at the time of mwp ia identifying the southern laurentide ice sheet as a potential source for mwp ia we question this source for mwp ia however because 1 ice sheet models suggest that this sector of the ice sheet contributed only a fraction 10 of the sea level needed for mwp ia 2 melting this sector of the ice sheet at the necessary rate to explain mwp ia is physically implausible and 3 ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the mississippi river into the north atlantic than is recorded this leaves the antarctic ice sheet as the only other ice sheet capable of delivering enough sea level to explain mwp ia but there are currently no well dated high resolution records to document this hypothesis these conclusions suggest that reconstructions of the laurentide ice sheet in the ice 4g model which are constrained to match the sea level record may be too low for time periods younger than 15 000 years ago furthermore 18o records from the gulf of mexico show variable fluxes of meltwater from the southern margin of the laurentide ice sheet which can be traced to the opening and closing of eastward draining glacial lake outlets associated with surging ice sheet behavior these variable fluxes through eastern outlets were apparently sufficient to affect formation of north atlantic deep water thus underscoring the sensitivity of this process to changes in freshwater forcing

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

hydrothermal origin of hexagonal caal2si2o8 dmisteinbergite in a compact type a cai from the northwest africa 2086 cv3 chondrite we report an occurrence of hexagonal caal2si2o8 dmisteinbergite in a compact type a calcium aluminum rich inclusion cai from the cv3 vigarano like carbonaceous chondrite northwest africa 2086 dmisteinbergite occurs as approximately 10 m long and few micrometer thick lath shaped crystal aggregates in altered parts of the cai and is associated with secondary nepheline sodalite ti poor al diopside grossular and fe rich spinel spinel is the only primary cai mineral that retained its original o isotope composition 17o 24 17o values of melilite perovskite and al ti diopside range from 3 to 11 suggesting postcrystallization isotope exchange dmisteinbergite anorthite ti poor al diopside and ferroan olivine have 16o poor compositions 17o 3 we infer that dmisteinbergite together with the other secondary minerals formed by replacement of melilite as a result of fluid assisted thermal metamorphism experienced by the cv chondrite parent asteroid based on the textural appearance of dmisteinbergite in nwa 2086 and petrographic observations of altered cais from the allende meteorite we suggest that dmisteinbergite is a common secondary mineral in cais from the oxidized allende like cv3 chondrites that has been previously misidentified as a secondary anorthite

pseudotachylyte and the development of ultramylonite bands in the saint barthelemy massif french pyrenees abstract in mylonitic gneisses of the saint barthelemy massif in the french pyrenees evidence was found that ultramylonite bands developed by ductile deformation of pseudotachylyte in the gneiss a mylonitic shape fabric was produced by a continuous structural event during retrogression from amphibolite to upper greenschist facies decrease in temperature caused gradual hardening in the gneiss which led to the development of pseudotachylyte bands by intermittent seismic slip these acted as weak zones in which ductile deformation was concentrated a microstructure typical of ultramylonite was produced in these deformed pseudotachylyte bands

pseudotachylytes generated during seismic faulting and eclogitization of the deep crust pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust pseudotachylytes in the bergen arcs of western norway contain microlites including omphacite garnet plagioclase and quartz this eclogite facies assemblage is stable at temperatures of about 800 c and pressures of 18 to 19 kilobars corresponding to depths of 60 kilometers or more the pseudotachylytes are exposed in grenvillian granulites that locally underwent fluid induced eclogitization and corresponding volume reduction of approximately 10 percent during the caledonian continental collision the pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process

microlite morphology and chemistry in pseudotachylite from the fuyun fault zone china microlites in pseudotachylite veins from the fuyun fault zone northwest china can be divided into four morphological groups simple skeletal dendritic and spherulitic from the margin to the center of microcrystalline and microlitic pseudotachylite veins the size of single crystals or crystal fibers becomes progressively larger from a few m to as much as 15 m the morphologies of microlites vary from simple shapes such as acicular and globular forms to more complex forms such as skeletal dendritic and coarse spherulitic forms in glassy pseudotachylites only simple and fine spherulitic microlites generally smaller than 5 6 m occur these microlites have a varied mineralogy but are mainly made up of plagioclase an20 70 and alkali feldspar including sanidine and anorthoclase as well as clinopyroxene grossular garnet biotite hornblende and some magnetic minerals the biotite and hornblende microlites have a variable ti content generally higher than that of biotite and hornblende frag

a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

the sensitivity of the climate response to the magnitude and location of freshwater forcing last glacial maximum experiments abstract proxy records indicate that the locations and magnitudes of freshwater forcing to the atlantic ocean basin as iceberg discharges into the high latitude north atlantic laurentide meltwater input to the gulf of mexico or meltwater diversion to the north atlantic via the st lawrence river and other eastern outlets may have influenced the north atlantic thermohaline circulation and global climate we have performed last glacial maximum lgm simulations with the ncar community climate system model ccsm3 in which the magnitude of the freshwater forcing has been varied from 0 1 to 1 sv and inserted either into the subpolar north atlantic ocean or the gulf of mexico in these glacial freshening experiments the less dense freshwater provides a lid on the ocean water below suppressing ocean convection and interaction with the atmosphere above and reducing the atlantic meridional overturning circulation amoc this is the case whether the freshwater is added directly to the area of convection south of greenland or transported there by the subtropical and subpolar gyres when added to the gulf of mexico the amoc reduction is less for the smaller freshwater forcings but is not linear with the size of the freshwater perturbation the recovery of the amoc from a slow state is 200 years for the 0 1 sv experiment and 500 years for the 1 sv experiment for glacial climates with large northern hemisphere ice sheets and reduced greenhouse gases the cold subpolar north atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the gulf of mexico greenland temperatures cool by 6 8 c in all the experiments with little sensitivity to the magnitude location or duration of the freshwater forcing but exhibiting large seasonality sea ice is important for explaining the responses the northern hemisphere high latitudes are slow to recover antarctica and the southern ocean show a bipolar response with warming and reduced sea ice this warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing equatorward of the expanded sea ice the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar north atlantic in the tropical atlantic the recovery of the intertropical convergence zone itcz from its more southerly position during the freshwater forcing is much more rapid than the recovery of the amoc and is more related to the recovery of low latitude surface temperatures than greenland temperature or sea ice these results have implications for using proxy records as indirect measures of the amoc

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

ba ca in neogloboquadrina pachyderma as an indicator of deglacial meltwater discharge into the western arctic ocean 1 down core samples of the planktonic foraminifer neogloboquadrina pachyderma sinistral from the mendeleyev ridge in the western arctic ocean have been analyzed for ba ca and 18o the apparent distribution coefficient for n pachyderma sin is estimated at dba 0 22 0 02 a meltwater event is identified at around 11 8 14c kyr bp and is coincident with elevated ba ca ratios the barium enrichment is believed to be the result of enhanced weathering and erosion following glaciation additionally barium may have desorbed from shelf sediments as sea level rose changes in ba ca correlate with the retreat of the laurentide ice sheet and the evolution of the mackenzie river drainage basin therefore maximum ba ca in arctic surface waters at 11 8 ka may be indicative of an increase in the export of freshwater from the arctic to the north atlantic potentially contributing to the onset of the younger dryas this work suggests that ba ca in planktonic foraminifera may be a useful indicator of the timing and processes associated with deglaciation

revision of the nw laurentide ice sheet implications for paleoclimate the northeast extremity of beringia and arctic ocean sedimentation abstract for the past half century reconstructions of north american ice cover during the last glacial maximum have shown ice free land distal to the laurentide ice sheet primarily on melville and banks islands in the western canadian arctic archipelago both islands reputedly preserve at the surface multiple laurentide till sheets together with associated marine and lacustrine deposits recording as many as three pre late wisconsinan glaciations the northwest corner of banks island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation banks glaciation considered to be of matuyama age 780 ka bp inside the limit of banks glaciation younger till sheets are ascribed to the thomsen glaciation pre sangamonian and the amundsen glaciation early wisconsinan stade the view that the western canadian arctic archipelago remained largely ice free during the late wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on banks and melville islands both dated to 22 ka bp these dates imply that these islands constitute the northeast extremity of beringia a fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of banks and melville islands including new dating of glacial and marine landforms and sediments on dundas peninsula southern melville island ams 14 c dates on ice transported marine molluscs within the most extensive laurentide till yield ages of 25 49 ka bp these dates require that late wisconsinan ice advanced northwestward from visount melville sound excavating fauna spanning marine isotope stage 3 laurentide ice that crossed dundas peninsula 300 m asl coalesced with melville island ice occupying liddon gulf coalescent laurentide and melville ice continued to advance westward through m clure strait depositing granite erratics at 235 m asl that require grounded ice in m clure strait as do streamlined bedforms on the channel floor deglaciation is recorded by widespread meltwater channels that show both the initial separation of laurentide and melvile ice and the successive retreat of laurentide ice southward across dundas peninsula into viscount melville sound sedimentation from these channels deposited deltas marking deglacial marine limit forty dates on shells collected from associated glaciomarine rhythmites record near synchronous ice retreat from m clure strait and dundas peninsula to north central victoria island 11 5 ka bp along the adjacent coast of banks island deglacial shorelines also record the retreat of laurentide ice both eastward through m clure strait and southward into the island s interior the elevation and age 11 5 ka bp of deglacial marine limit there is fully compatible with the record of ice retreat on melville island the last retreat of ice from mercy bay northern banks island previously assigned to northward retreat into m clure strait during the early wisconsinan is contradicted by geomorphic evidence for southward retreat into the island s interior during the late wisconsinan this revision of the pattern and age of ice retreat across northern banks island results in a significant simplification of the previous quaternary model our observations support the amalgamation of multiple till sheets previously assigned to at least three pre late wisconsinan glaciations into the late wisconsinan this revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking erratics were also widely observed armouring meltwater channels originating on the previously proposed never glaciated landscape an extensive late wisconsinan laurentide ice sheet across the western canadian arctic is compatible with similar evidence for extensive laurentide ice entering the richardson mountains yukon farther south and with the innuitian ice sheet to the north widespread late wisconsinan ice in a region previously thought to be too arid to sustain it has important implications for paleoclimate ice sheet modelling arctic ocean ice and sediment delivery and clarifying the northeast limit of beringia

the destiny of a clast within a molten pseudotachylyte vein pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window on the other hand survivor fragmented clasts embedded in the quenched material are also very impor tant in that they provide information about the energy spent to create new fracture surfaces in this paper i study the temperature evolution of clasts subjected to the heat dissipated by a just formed molten pseudotachylyte pt vein in particular i find the analytical solutions for the temperature evolution within the pt vein the surrounding undamaged host rock and inside a clast according to the proposed model the numerical results show that the clasts tend to preferentially melt in the inner part of the pt vein i e they are completely assimilated by the pt in contrast some clasts can survive far from the pt vein center my solutions although based upon a simplified model can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the pt center the distribution of these survivor clasts follows a power law relation in terms of their radius and its features generally agree with field and laboratory observations

frictional melting processes and products in geological materials introduction and discussion this special issue is the outcome of a theme session convened by the above authors entitled frictional melting processes and products in geologic materials held at the 1990 geological society of america annual meeting in dallas texas u s a the goals of the session were threefold to bring together researchers working on various aspects of frictional melting in rock to provide a forum for the exchange of new ideas and to encourage the production of a thematic set of papers dedicated to the topic of the eight papers presented here the first two spray swanson are primarily processand mechanism oriented the next magloughlin maddock o hara deal primarily with chemical aspects of host rock pseudotachylyte relations the last three mainly provide descriptions of naturally occurring koch and masch techmer et al and artificially produced kennedy and spray friction melts natural pseudotachylytes are described from strike slip zones magloughlin swanson thrusts and their listric counterparts koch and masch techmer et al and connecting lateral ramps o hara thus it appears that there exists an association between pseudotachylyte generation and relatively long lived largedisplacement faulting and shearing the prime objective of the meeting was to promote the integration of different approaches

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

ice streaming in the laurentide ice sheet a first comparison between data calibrated numerical model output and geological evidence 1 despite the importance of rapidly flowing ice streams to ice sheet mass balance their incorporation into numerical ice sheet models is a major scientific challenge this introduces large uncertainties in model output and inhibits a more complete understanding of the role of ice streams in overall ice sheet stability recent computational advances have enabled more realistic representations of ice streaming but few studies have attempted to compare model output against known locations of ice streams this paper compares predictions of ice streaming derived from a large ensemble analysis of a glacial systems model of the laurentide ice sheet against independent geological evidence compiled from previously published studies although the precise dating of paleo ice stream locations is problematic our analysis includes comparisons at six different time steps 18 to 10 cal ka bp during deglaciation results indicate that the model is successful in predicting all of the major marine terminating ice streams but there is mixed success in simulating terrestrial ice streams in the right place and at the right time which is vital in guiding future model development the model also reveals that whilst some ice streams persist throughout deglaciation the focus of mass loss associated with ice streaming switches through time with dynamic changes in ice stream catchments and tributaries this implies that major changes in ice stream activity are to be expected in a deglaciating ice sheet with important implications for contemporary ice sheet dynamics

mineralogy and petrology of a mullite bearing pseudotachylyte constraints on the temperature of coseismic frictional fusion pseudotachylyte from the homestake shear zone central colorado contains acicular 5 10 x 100 m mullite crystals 1 5 m octahedra of magnetite and variably melted clasts of quartz in an originally molten matrix several lines of evidence support the interpretation that the pseudotachylyte represents the quenched equivalent of a molten phase derived from preferential melting of primarily biotite microcline and plagioclase and to a lesser extent quartz from the gneissic protolith the morphology of the mullite crystals which nucleate on and radiate from relic sillimanite clasts abundant magnetite octahedra scattered throughout the pseudotachylyte matrix and intergrown with mullite forming plumose quench structures partially melted relict quartz clasts the composition of the isotropic pseudotachylyte matrix and chemical gradients surrounding quartz clasts in pseudotachylyte matrix although the sample had been nearly completely molten except for 10 100 m relict quartz clasts hrtem imaging of the pseudotachylyte matrix reveals that it has devitrified the slightly birefringent matrix consists of intergrowths of submicrometer flakes of white mica microprobe analysis shows that the mullite is highly enriched in fe 8 10 wt fe 2 o 3 compared with other natural mullites hrtem and sem images reveal the presence of oriented platelets of an fe oxide phase dominantly hematite that appears to have exsolved from the mullite during cooling indicating that the limit of solid solution of fe 3 in mullite decreases with temperature the estimated melt temperature ranges from 1150 to 1200 c this interpretation is based on the fe 2 o 3 content of mullite the liquidus temperature for melts corresponding to the matrix compositions and liquidus temperatures for gneissic wall rocks which underwent complete to very high degrees of melting

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

evidence of dmisteinbergite hexagonal form of caal2si2o8 in pseudotachylyte a tool to constrain the thermal history of a seismic event the determination of the maximum temperature achieved by friction melt tmelt in pseudotachylytebearing faults is crucial to estimate earthquake source parameters e g earthquake energy budgets coseismic fault strength on a geological basis here we investigated the mineralogy of a pseudotachylyte from the gole larghe fault italian alps by using x ray powder diffraction micro raman spectroscopy and eds equipped field emission scanning electron microscopy in particular we report the presence of the hexagonal polymorph of caal2si2o8 dmisteinbergite in a pseudotachylyte published experimental work shows dmisteinbergite can crystallize at 1200 1400 c by rapid quenching therefore the presence of dmisteinbergite in pseudotachylyte could be a reliable geothermometer for friction melts for which tmelt has only as yet been estimated

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

deglacial history of the west antarctic ice sheet in the western amundsen sea embayment abstract the amundsen sea embayment ase drains approximately 35 of the west antarctic ice sheet wais and is one of the most rapidly changing parts of the cryosphere in order to predict future ice sheet behaviour modellers require long term records of ice sheet melting to constrain and build confidence in their simulations here we present detailed marine geological and radiocarbon data along three palaeo ice stream tributary troughs in the western ase to establish vital information on the timing of deglaciation of the wais since the last glacial maximum lgm we have undertaken multi proxy analyses of the cores core description shear strength x radiographs magnetic susceptibility wet bulk density total organic carbon nitrogen carbonate content and clay mineral analyses in order to 1 characterise the sedimentological facies and depositional environments and 2 identify the horizon s in each core that would yield the most reliable age for deglaciation in accordance with previous studies we identify three key facies which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments these facies are i subglacial ii proximal grounding line and iii seasonal open marine in addition we incorporate ages from other facies e g glaciomarine diamictons deposited at some distance from the grounding line such as glaciogenic debris flows and iceberg rafted diamictons and turbates into our deglacial model in total we have dated 78 samples mainly the acid insoluble organic aio fraction but also calcareous foraminifers which include 63 downcore and 15 surface samples through careful sample selection prior to dating we have established a robust deglacial chronology for this sector of the wais our data show that deglaciation of the western ase was probably underway as early as 22 351 calibrated years before present cal yr bp reaching the mid shelf by 13 837 cal yr bp and the inner shelf to within c 10 12 km of the present ice shelf front between 12 618 and 10 072 cal yr bp the deglacial steps in the western ase broadly coincide with the rapid rises in sea level associated with global meltwater pulses 1a and 1b although given the potential dating uncertainty additional more precise ages are required before these findings can be fully substantiated finally we show that the rate of ice sheet retreat increased across the deep up to1600 m basins of the inner shelf highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation

kumdykolite a high temperature feldspar from an enstatite chondrite we report the first occurrence of kumdykolite in a meteorite sahara 97072 eh3 this orthorhombic form of albite occurs in the core of a concentrically zoned metal sulfide nodule in contrast to the terrestrial kumdykolite the meteoritic sample has a domain structure that is consistent with either orthorhombic pmnn or monoclinic p21 space groups the two symmetries are indicated by the presence or lack respectively of h k 2n 1 reflections in 001 selected area electron diffraction patterns effects that likely result from different si al ordering pmnn kumdykolite has only one tetrahedral site for si and al whereas p21 kumdykolite would have three tetrahedral sites for si and one for al we propose that kumdykolite formed above 1300 k and cooled rapidly enough to preserve its unique structure apparently the cooling rate varied on the scale of nanometers allowing the local development of si al ordering

modeling the surface mass balance response of the laurentide ice sheet to bolling warming and its contribution to meltwater pulse 1a meltwater pulse mwp 1a occurred 14 5 14 ka and is the largest abrupt rise in sea level 10 20 m of sea level rise of the last deglaciation the timing of mwp 1a is coincident with or shortly follows the abrupt warming of the north atlantic region into the bolling warm period which could have triggered a large laurentide ice sheet lis contribution to mwp 1a given that outside of the arctic lis iceberg discharge probably did not increase during the bolling much of the lis mwp 1a contribution likely occurred through surface ablation here we test the response of lis surface mass balance to bolling warming by forcing a lis energy mass balance model with climate from an atmosphere ocean general circulation model our modeling approach neglects changes in lis mass from dynamics and iceberg calving allowing us to isolate the surface mass balance response model results suggest that lis surface ablation can explain much of the sea level rise just prior to mwp 1a lis surface mass balance becomes more negative in response to the bolling warming contributing an additional 2 9 1 0 m of sea level rise in 500 yr in addition to the background contribution of 4 0 0 8 m the modeled lis mwp 1a contribution is less than previous assumptions but agrees with geochemical runoff and lis area volume estimates the fraction of mwp 1a attributable to other ice sheets particularly antarctica depends on the total sea level rise that occurred during this mwp

the dynamic response of the greenland and antarctic ice sheets to multiple century climatic warming new calculations were performed to investigate the combined response of the greenland and antarctic ice sheets to a range of climatic warming scenarios over the next millennium use was made of fully dynamic 3d thermomechanic ice sheet models which were coupled to a two dimensional climate model the experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent co2 increases of two four and eight times the present 1990 a d value by the year 2130 a d and a stabilization after that the calculations brought to light that during the next century short term effect the background evolution trend would dominate the response of the antarctic ice sheet but would be negligible for the greenland ice sheet on that timescale the greenland and antarctic ice sheets would roughly balance one another for the middle scenario similar to the ipcc96 is92a scenario with respective contributions to the worldwide sea level stand on the order of about 610 cm on the longer term however both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the greenland ice sheet sensitivity experiments highlighted the role of ice dynamics and the height massbalance feedback on the results it was found that ice dynamics cannot be neglected for the greenland ice sheet not even on a century timescale but becomes only important for antarctica on the longer term the latter is related to an increased outflow of ice into the ice shelves and to the grounding line retreat of the west antarctic ice sheet which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century21 of which 60 cm would originate from the greenland ice sheet alone

late pleistocene and holocene meltwater events in the western arctic ocean accelerator mass spectrometer 14 c dated stable isotope data from neogloboquadrina pachyerma in cores raised from the mendeleyev ridge and slope provide evidence for significant influx of meltwater to the western arctic ocean during the early part of marine oxygen isotope stage 1 ois 1 and during several intervals within ois 3 the strongest ois 3 meltwater event occurred before ca 45 ka conventional radiocarbon age and was probably related to the deglaciation at the beginning of ois 3 major meltwater input to the western arctic ocean during the last deglaciation coincides closely with the maximum rate of global sea level rise as determined from the barbados sea level record demonstrating a strong link between the global record and changes in the central arctic ocean ois 2 which includes the last glacial maximum is very condensed or absent in the cores abundance and 13 c values for n pachyderma in the middle part of ois 3 are similar to modern values indicating high productivity and seasonal ice free areas along the arctic margin at that time these records indicate that the arctic ocean was a source of heat and moisture to the northern polar atmosphere during parts of ois 3

on the mineralogy of the anthropocene epoch the anthropocene epoch has been proposed as a new post holocene geological time interval a period characterized by the pervasive impact of human activities on the geological record prior to the influence of human technologies the diversity and distribution of minerals at or near earth s surface arose through physical chemical and or biological processes since the advent of human mining and manufacturing particularly since the industrial revolution of the mid eighteenth century mineral like compounds have experienced a punctuation event in diversity and distribution owing to the pervasive impact of human activities we catalog 208 mineral species approved by the international mineralogical association that occur principally or exclusively as a consequence of human processes at least three types of human activities have affected the diversity and distribution of minerals and mineral like compounds in ways that might be reflected in the worldwide stratigraphic record the most obvious influence is the widespread occurrence of synthetic mineral like compounds some of which are manufactured directly for applications e g yag crystals for lasers portland cement and others that arise indirectly e g alteration of mine tunnel walls weathering products of mine dumps and slag a second human influence on the distribution of earth s near surface minerals relates to large scale movements of rocks and sediments sites where large volumes of rocks and minerals have been removed finally humans have become relentlessly efficient in redistributing select natural minerals such as gemstones and fine mineral specimens across the globe all three influences are likely to be preserved as distinctive stratigraphic markers far into the future

the last deglaciation of the southeastern sector of the scandinavian ice sheet the scandinavian ice sheet sis was an important component of the global ice sheet system during the last glaciation but the timing of its growth to or retreat from its maximum extent remains poorly known we used 115 cosmogenic beryllium 10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice margin fluctuations of the sis between 25 000 and 12 000 years before the present the age of initial deglaciation indicates that the sis may have contributed to an abrupt rise in global sea level subsequent ice margin fluctuations identify opposite mass balance responses to north atlantic climate change indicating differing ice sheet sensitivities to mean climate state

a global perspective on last glacial maximum to holocene climate change while the abrupt climate events of the last deglaciation are well defined in ice core records from the polar regions of both hemispheres their manifestation elsewhere is less well constrained here we compile 104 high resolution paleoclimate records to characterize the timing and spatial pattern of climate change during the last deglaciation this compilation indicates relatively concurrent timing of the last glacial maximum lgm peak glacial conditions and the altithermal peak interglacial conditions in the northern 22 1 4 3 ka and 8 0 3 2 ka and southern 22 3 3 6 ka and 7 4 3 7 ka hemispheres suggesting the hemispheres were synchronized by greenhouse gases local insolation and or northern hemisphere induced ocean circulation changes the magnitude of the glacialeinterglacial temperature change increases with latitude reflecting the polar amplification of climate change with a likely minimum global mean cooling of ww4 9 c during the lgm relative to the altithermal empirical orthogonal function eof analysis of 71 records spanning 19e11 ka indicates that two modes explain 72 of deglacial climate variability eof1 61 of variance shows a globally near uniform pattern with its principal component pc1 strongly correlated with changes in atmospheric co2 e of2 11 of variance exhibits a bipolar seesaw pattern between the hemispheres with its principal component pc2 resembling changes in atlantic meridional overturning circulation strength eof analysis of 90 records from 15 to 11 ka indicates that northern and southern modes of climate variability characterize the younger dryas bolling allerod interval these modes dominate at the higher latitudes of each hemisphere and exhibit a complex interaction in the tropics the magnitude of the younger dryas climate anomaly cooler drier increases with latitude in the northern hemisphere with an opposite pattern warmer wetter in the southern hemisphere reflecting a general bipolar seesaw climate response global mean temperature decreased by w0 6 c during the younger dryas therefore our analysis supports the paradigm that while the younger dryas was a period of global climate change it was not a major global cooling event but rather a manifestation of the bipolar seesaw driven by a reduction in atlantic meridional overturning circulation strength

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects

the 8200 year b p event in the slope water system western subpolar north atlantic 1 stable isotope trace metal alkenone paleothermometry and radiocarbon methods have been applied to sediment cores in the western subpolar north atlantic between hudson strait and cape hatteras to reveal the history of climate in that region over the past 11 kyr we focus on cores from the laurentian fan which is known to have rapid and continuous accumulation of hemipelagic sediment although results among our various proxy data are not always in agreement the weight of the evidence alkenone sea surface temperature sst 18o and abundance of globigerinoides ruber indicates a continual cooling of surface waters over laurentian fan from about 18 c in the early holocene to about 8 c today alternatively mg ca data on planktonic foraminifera indicate no systematic change in holocene sst the inferred long term decrease in sst was probably driven by decreasing seasonality of northern hemisphere insolation two series of proxy data show the gradual cooling was interrupted by a two step cold pulse that began 8500 years ago and lasted about 700 years although this event is associated with the final deglaciation of hudson bay there is no 18o minimum anywhere in the labrador sea yet there is some evidence for it as far south as cape hatteras finally although the 8200 year b p event has been implicated in decreasing north atlantic ventilation and hence widespread temperature depression on land and at sea we find inconsistent evidence for a change at that time in deep ocean nutrient content at 4 km water depth

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

slip weakening distance of faults during frictional melting as inferred from experimental and natural pseudotachylytes the slip weakening distance d c over which a fault weakens during seismogenic fault motion is one of most important parameters controlling fault instability a paradox over the last decade has been the source of the large difference between laboratory measured values of d c using conventional friction experiments 10 5 10 3 m and seismically determined d c values for natural earthquakes 10 1 10 0 m d c is a difficult quantity to estimate for natural faults but this study attempts to determine the order of d c values for natural faults containing pseudotachylytes based on a comparison between experimental and natural pseudotachylytes experiments at a constant slip velocity of 0 85 m sec and a normal stress of 1 4 mpa on gabbro have revealed that the progressive growth of a molten layer causes marked slip weakening slip weakening a reduction in frictional strength with displacement and the growth of the molten layer an increase in the thickness of the molten layer with displacement are both characterized by exponential changes with nearly the same characteristic distances the comparison suggests that the order of d c can be estimated from the relationship between pseudotachylyte thickness along its generation fault and fault displacement sibson s 1975 data from the outer hebrides exhibit a similar pseudotachylyte thickness versus fault displacement curve with a characteristic distance of 0 38 m this is the same order of magnitude as seismically inferred values of d c the effect of frictional melting is a possible solution for the d c paradox although it is not the only possible solution since frictional melting along large faults is rather uncommon

origin of hydrous fluids at seismogenic depth constraints from natural and experimental fault rocks abstract fluids control the mechanical behavior of fault zones during the seismic cycle we used geochemical mineralogical microstructural hydrogen isotope compositions and fourier transform infrared ftir investigations to characterize the origin of hydrous fluids involved in ductile and brittle shear zones at the bottom of the seismogenic crust natural samples were collected from exhumed mylonitic shear zones and cataclasite pseudotachylyte bearing faults in the northern adamello italian southern alps which were active at 9 11 km depth pseudotachylytes solidified coseismic friction induced melts testify to ancient seismogenic behavior of the faults natural pseudotachylytes were compared with artificial pseudotachylytes produced in high velocity friction experiments simulating seismic slip mylonites have mineralogical elemental and hydrogen isotope compositions 80 d 78 similar to the host tonalite 77 d 73 within the analytical error of 5 cataclasites have instead mineralogical chlorite epidote k feldspar no biotite major and trace elements enrichment in k2o ba rb depletion in cao na2o sio2 and hydrogen isotope 69 d 60 compositions suggesting interactions with a crustal metamorphic fluid pseudotachylytes are composed of high temperature minerals plagioclase biotite dmisteinbergite cordierite and scapolite and have elemental compositions resulting from mixing of tonalite and cataclasite pseudotachylytes have complex microstructures including i microlitic domains with well crystallized micrometric biotite which have hydrogen isotope composition 81 d 59 similar to cataclasites and tonalite and ii cryptocrystalline domains with poorly crystallized biotite which have very high water content release water upon heating at t 50 c and have low d value 93 the hydrogen isotope composition of bulk samples is dominated by the composition of cryptocrystalline domains 103 d 88 where most of the water is hosted their hydrogen isotope composition is compatible with adsorption of present day rainfall water d 95 artificial pseudotachylytes have the same hydrogen isotope compositions of the starting tonalite 76 d 74 or cataclasite 68 d 62 with a slight decrease of the d values in some samples 85 d 81 the first ingression of a crustal metamorphic fluid occurred in cataclastic faults natural pseudotachylytes when not contaminated by present day rainfall water have a hydrogen isotope composition similar to tonalite and cataclasite as reproduced in dry high velocity friction experiments the fluids dissolved in coseismic melts are most likely derived from the breakdown of hydrous minerals of cataclasite and tonalite undergone melting and we could not identify the infiltration of an external fluid during earthquakes

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

a reevaluation of the timing and causes of high lake phases in the lake michigan basin abstract radiocarbon age control on the type glenwood calumet and toleston shoreline features and on the abandoned chicago outlet at the south end of the lake michigan basin provides a basis for reevaluating the timing and causes of high lake phases in the basin radiocarbon dates suggest that glenwood level 195 m shoreline features formed between 14 100 and 12 700 yr b p glenwood i and ii phases calumet level 189 m between 12 700 and 11 000 yr b p calumet i and ii phases and toleston level 184 5 m between 5000 and 4000 yr b p nipissing phase and that the chicago outlet was cut to its present level 180 m on bedrock while the lake was at the glenwood level this new chronology is inconsistent with j h bretz hypothesis 1951 american journal of science249 401 429 that the progressive lowering of lake level resulted from episodic down cutting of the outlet instead the changes in lake level appear to relate to changes in the amount of glacial meltwater and precipitation entering the basin we hypothesize that the glenwood phases correspond with times when discharge from the huron and erie basins also entered the lake michigan basin lake border and early port huron glacial phases the calumet phases with times when drainage was from the lake michigan basin alone late port huron and two rivers glacial phases and the nipissing phase with the postglacial middle holocene transgression caused by differential uplift in the basin estimates of relative net inputs to the basin during the glenwood calumet and nipissing lake phases are consistent with estimates of relative outputs i e discharge through the chicago outlet the magnitude of relative differences in inputs and outputs between phases is sufficient to explain lake level changes of 4 5 to 6 m

pseudotachylites in the eastern peninsular ranges of california abstract a continuous zone containing pseudotachylites in the eastern peninsular ranges of california extends over more than 15 km from deep canyon in the north to at least toro canyon in the south pseudotachylites are found in rocks of tonalitic to dioritic composition while the overall compositions of host rock and pseudotachylite veins are similar veins are characteristically enriched in fe and ti and depleted in si many veins are cataclastic and all contain fragments but a large number have a groundmass with skeletal and spherulitic microlites of calcic plagioclase an 40 50 biotite and ilmenite indicative of partial melting the pseudotachylites formed mainly during a late brittle event 56 62 ma and postdate the high strain ductile mylonitic deformation in the santa rosa mylonite zone 65 87 ma as ascertained by 40ar 39ar ages the size of veins ranges from less than 1 mm to more than 10 cm in thickness and aspect ratios display a broad log normal distribution three quarters of the veins are more or less parallel to the foliation the orientation of the veins is consistent with a top to the west displacement similar to that for the ductile mylonites from the sizes energies required for melting are estimated to range between 105 j for smaller veins and 1010 j for larger veins interestingly the energy distribution and geometry of these pseudotachylites correspond closely with energy distributions of current microseismic events along the san andreas fault at parkfield suggesting that basic mechanisms may be similar and due to intrinsic mechanical properties of rocks in particular these indicate that local stress concentrations rather than average crustal stresses are relevant for earthquakes

discovery of dmisteinbergite hexagonal caal2si2o8 in the allende meteorite a new member of refractory silicates formed in the solar nebula dmisteinbergite caal 2si 2o 8 with p6 3 mcm structure was identified in a rounded coarse grained igneous type b2 ca al rich inclusion cai stp 1 from the allende cv3 carbonaceous chondrite stp 1 belongs to a very rare type of refractory inclusions fractionation and unknown nuclear effects fun cais which experienced melt evaporation and crystallization at low total gas pressure p 1200 c region possibly near the proto sun and were subsequently radially transported away from region possibly by a disk wind the allende dmisteinbergite occurs as irregular single crystals 100 600 m in size in contact with gehlenitic melilite and al ti diopside poikilitically enclosing euhedral spinel and rare anorthite it is colorless and transparent the mean chemical composition determined by electron microprobe analysis is wt sio 2 42 6 al 2o 3 36 9 cao 20 2 mgo 0 05 sum 99 75 giving rise to an empirical formula of ca 1 01 al 1 96 si 2 02 o 8 its electron backscatter diffraction patterns are a good match to that of synthetic caal 2si 2o 8 with the p6 3 mcm structure and the unit cell a 5 10 a c 14 72 a and z 2 dmisteinbergite could have crystallized from a silicate melt at high temperature 1200 1400 c via rapid cooling dmisteinbergite in allende the first find in a meteorite is a new member of refractory silicates among the first solid materials formed in the solar nebula

retreat of the east antarctic ice sheet during the last glacial termination the east antarctic ice sheet retreated at the end of the last glacial period terrestrial and marine data suggest that the retreat began 14 000 years ago indicating that the east antarctic ice sheet probably did not contribute to meltwater pulse 1a 14 700 years ago

modeling the subglacial hydrology of the james lobe of the laurentide ice sheet to investigate the drainage conditions that might be expected to develop beneath soft bedded ice sheets we modeled the subglacial hydrology of the james lobe of the laurentide ice sheet from hudson bay to the missouri river simulations suggest the james lobe had little effect on regional groundwater flow because the poorly conductive upper cretaceous shale that occupies the upper layer of the bedrock would have functioned as a regional aquitard this implies that general northward groundwater flow out of the williston basin has likely persisted throughout the quaternary moreover the simulations indicate that the regional aquifer system could not have drained even the minimum amount of basal meltwater that might have been produced from at the glacier bed therefore excess drainage must have occurred by some sort of channelized drainage network at the ice till interface using a regional groundwater model to determine the hydraulic conductivity for an equivalent porous medium in a 1 m thick zone between the ice and underlying sediment and assuming conduit dimensions from previous theoretical work we use a theoretical karst aquifer analog as a heuristic approach to estimate the spacing of subglacial conduits that would have been required at the ice till interface to evacuate the minimum water flux results suggest that for conduits assumed to be on the order of a tenth of a meter deep and up to a meter wide inter conduit spacing must be on the order of tens hundreds of meters apart to maintain basal water pressures below the ice overburden pressure while evacuating the hypothesized minimum meltwater flux r 2007 elsevier ltd all rights reserved

first exposure ages from the amundsen sea embayment west antarctica the late quaternary context for recent thinning of pine island smith and pope glaciers dramatic changes acceleration thinning and grounding line retreat of major ice streams in the amundsen sea sector of the west antarctic ice sheet wais have been observed during the past two decades but the millennial scale context for these changes is not yet known we present the first surface exposure ages recording thinning of pine island smith and pope glaciers which all drain into the amundsen sea from these we infer progressive thinning of pine island glacier at an average rate of 3 8 0 3 cm yr 1 for at least the past 4 7 k y and of smith and pope glaciers at 2 3 0 2 cm yr 1 over the past 14 5 k y these rates are more than an order of magnitude lower than the similar to 1 6 m yr 1 recorded by satellite altimetry for pine island glacier in the period 1992 1996 similarly low long term rates 2 5 9 ern yr 1 since 10 ka have been reported farther west in the ford ranges marie byrd land but in that area the same rates of thinning continue to the present day our data provide the first evidence that puts into context recent rates of thinning of the wais in the amundsen sea embayment and demonstrates that these are unusually rapid the data also provide much needed constraints for ice sheet models which are the primary tool for predicting the future behavior of the wais and its likely contribution to sea level rise

glassy pseudotachylyte veins from the fuyun fault zone northwest china glassy pseudotachylytes occur in granitic mylonites from the fuyun fault zone northwest china powder x ray diffraction data indicate that the fine grained matrices of the fuyun pseudotachylytes vary from almost crystalline to complete glass a few to 90 wt glass powder x ray diffraction patterns also indicate that clasts in the glass type pseudotachylyte veins mostly consist of quartz grains microlites displaying quenched or rapid cooling textures vesicles and amygdules flow structures and rounded fragments are also common in the fuyun pseudotachylytes the average bulk chemical compositions of these pseudotachylytes are similar to those of the host rocks but the glass matrix has a low sio2 component which is 5 15 wt lower than that of the host rocks the pseudotachylytes contain 2 3 wt water h2o using experimental data which relate the solubility of water to pressure approximately 400 bars lithostatic pressure corresponding to approximately 1 5 km depth of pseudotachylyte formation is estimated a minimum temperature estimate of 1450 c can be estimated due to the presence of the pure sio2 glass the x ray diffraction and chemical data indicate that the fuyun pseudotachylytes formed during seismic faulting at shallow depths by selective melting under water saturated conditions rather than by total melting or by crushing of the host rocks along fault surfaces

large volumes of anhydrous pseudotachylyte in the woodroffe thrust eastern musgrave ranges australia a mylonitic thrust zone at least 1 5 km thick forms a sharp contact between granulite and amphibolite facies gneisses in the eastern musgrave ranges central australia the thrust dips gently to the south and is interpreted as an extension of the woodroffe thrust which was formed about 550 ma ago mylonites at the base of the thrust grade upwards into ultramylonites which pass abruptly into a pseudotachylyte bearing zone approximately 1 km thick containing approximately 4 of pseudotachylyte veining the orientation of the veins appears to be random pseudotachylytes occur only in the granulite facies rocks and their precursors are felsic pyroxene and or garnet granofelses rotated blocks of ultramylonite are present in some of the pseudotachylytes and some pseudotachylyte veins have been plastically deformed suggesting nearly contemporaneous semiductile and brittle behaviour the matrix of the pseudotachylyte shows spectacular examples of igneous quench microstructures especially skeletal and dendritic crystals of plagioclase and feathery pyroxene dendrites also present are glass devitrification microstructures spherulites evidence of liquid flow and partly melted residual grains with former glassy rims showing different optical properties from those of the surrounding isotropic material these features confirm that the pseudotachylyte formed by melting in anhydrous conditions the matrix of the pseudotachylyte veins is less siliceous than the host rocks owing to non equilibrium melting of pyroxene garnet and plagioclase the igneous assemblages of the melt notably the crystallization of pigeonite are consistent with rapid cooling from very high temperature 1000 c melting and quenching is probably due to very local short lived rises in temperature accompanied by dilation

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

ice sheet and solid earth influences on far field sea level histories previous predictions of sea level change subsequent to the last glacial maximum show significant systematic discrepancies between observations at tahiti huon peninsula and sunda shelf during lateglacial time 14 000 to 9000 calibrated years before the present we demonstrate that a model of glacial isostatic adjustment characterized by both a high viscosity lower mantle 4 1022 pa s and a large contribution from the antarctic ice sheet to meltwater pulse ia 15 meters eustatic equivalent resolves these discrepancies this result supports arguments that an early and rapid antarctic deglaciation contributed to a sequence of climatic events that ended the most recent glacial period of the current ice age

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

fluid inclusions in pseudotachylytes from the nojima fault japan pseudotachylytes i e rocks formed by frictional melting have been observed in the nojima fault that was penetrated by the hirabayashi borehole drilled 1 year after the 1995 hyogo ken nanbu kobe earthquake these rocks display millimeter scale banding defined by different pseudotachylyte layers the nature of unmolten crystal fragments k feldspar albite calcite and or quartz allows us to infer a minimum melting temperature of 1200 c the glass has a 8 3 volatile content and a higher cao content than that of the parent granodiorite thus suggesting that pseudotachylyte formation occurred in an already altered calcite bearing and hydrated fault zone fluid inclusions have been observed in the glass and are filled with a dense low salinity 4 3 1 2 wt eq nacl co2 h2o fluid characterized by steep isochoric curves the intersection between the isochores and the measured 24 c km geothermal gradient indicates a minimum 15 km depth for the pseudotachylyte formation such a depth suggests that an important uplift has brought the studied pseudotachylytes to their present position and that these pseudotachylytes are probably pre miocene in age the calculated thermal evolution of a typical millimeter scale pseudotachylyte layer indicates that cooling does not last more than a few seconds this indicates that related seismic processes such as deceleration of fault movement and healing of the fault were both very rapid the geometry and thermal budget of the millimeter thick pseudotachylytes suggest that seismic events of magnitude 6 to 7 are responsible for their formation

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos