seismic and aseismic weakening effects in transtension field and microstructural observations on the mechanics and architecture of a large fault zone in se tibet

discussion streamlined erosional residuals and drumlins in central british columbia canada by j donald mcclenagan 2013 geomorphology 189 41 54 abstract mcclenagan 2013 presents a model to explain streamlined erosional residuals or drumlins on uplands and lowlands in the plateau region of central british columbia canada in this discussion paper we note that mcclenagan 2013 has not adequately discussed previous relevant work in the region and we argue that additional analyses and evidence are required to substantiate this new model the hypothesis offered for the origin of the plateau landscape specifically catastrophic glaciofluvial activity differs significantly from a model based on glacial erosion and deformation that has been developed from field based research over the past six decades we discuss four critical points relating to the proposed model 1 the current geological model for the plateau region of central british columbia 2 theory of glacial dispersal 3 existing hypotheses for the formation of drumlins and other glacial landforms and 4 theoretical glacial erosion modeling we further suggest that the model cannot be substantiated without sedimentological or morphological field evidence for water bodies argued to be the source of the proposed megaflood or megafloods

holocene glaciation and climate evolution of baffin island arctic canada abstract lake sediment cores and cosmogenic exposure ce dates constrain the pattern of deglaciation and evolution of climate across baffin island since the last glacial maximum lgm ce dating of erratics demonstrates that the northeastern coastal lowlands became ice free ca 14 ka as the laurentide ice sheet lis receded from its lgm margin on the continental shelf coastal lakes in southeastern baffin island started to accumulate sediment at this time whereas initial lacustrine sedimentation was delayed by two millennia in the north reduced organic matter in lake sediment deposited during the younger dryas chron and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the lis and local mountain glaciers 9 6 ka cockburn substage a second readvance occurred just before 8 ka during a period of unusually cold summers corresponding to the 8 2 ka cold event in the greenland ice sheet most local glaciers were behind their present margins before 7 ka and in some instances much earlier although the foxe dome of the lis continued to slowly retract toward the present day barnes ice cap throughout the holocene pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka subsequently grass tundra became established followed by modern tundra vegetation ca 8 ka with subtle changes in pollen assemblages in the late holocene lake primary productivity peaked in the early holocene before terrestrial vegetation or marine surface waters reached their apparent thermal maxima lacustrine marine and glacial proxies all reflect significant late holocene cooling the onset of neoglaciation is well dated in lacustrine records at ca 6 ka with intensification after 2 5 ka the expansion of local glaciers during the little ice age represents the most extensive advance since 7 ka we suggest that the replacement of atlantic surface waters by cold low salinity arctic ocean water coupled with the steady reduction of summer insolation resulted in a significant positive sea ice feedback that produced a larger late holocene summer temperature depression over the baffin region than in the pacific sector of the arctic

sensitivity studies of northern hemisphere glaciation using an atmospheric general circulation model abstract the u k university global atmospheric modeling programme gcm is used to investigate whether the growth of northern hemisphere ice sheets could have been initiated by changes of orbital parameters and sea surface temperature two different orbital configurations corresponding to the present day and 115 kyr bp are used the reduced summer solar insulation in the northern hemisphere results in a decrease of the surface temperature by 4 to 10 c in the northern continents and to perennial snow in some high latitude regions therefore the model results support the hypothesis that a deficit of summer insulation can create conditions favorable for initiation of ice sheet growth in the northern hemisphere a decreased sea surface temperature northward of 65 n during the northern hemisphere summer may contribute to the maintenance of ice sheets a simple mixed layer ocean model coupled to the gcm indicates that the changes of sea surface temperature and extension of sea ice due to insulation changes pl

imbricate architecture of the upper paleozoic to jurassic oceanic cache creek terrane central british columbia upper paleozoic to lower jurassic oceanic rocks of the cache creek terrane near fort st james in central british columbia form a stack of thrust sheets cut by steeply dipping strike slip faults paleontologically dated upper paleozoic strata include bioclastic shallow water limestone and ribbon chert isotopically dated permian rocks consist of tonalite sills and stocks and rhyolite flows intercalated with basalt flows paleontologically dated lower mesozoic rocks include greywacke sandstone siltstone argillite ribbon chert conglomerate limestone and basalt tuff trembleur ultramafite unit of the cache creek complex in places part of an ophiolite suite forms thrust sheets and klippen that overlie lower mesozoic sedimentary rocks sedimentological lithochemical paleontological petrological and textural comparisons with other areas and established models demonstrate that cache creek terrane is an accretionary complex a structurally stacked assemblage of rocks that originated in diverse and

can milankovitch orbital variations initiate the growth of ice sheets in a general circulation model the goddard institute for space studies climate model is used to investigate whether the growth of ice sheets could have been initiated by solar insolation variations three different orbital configurations are used corresponding to 116 and 106 kyr b p and a modified insolation field with greater reductions in summer insolation at high northern latitudes the time periods chosen are those in which geophysical evidence suggests ice sheets may have been growing rapidly the reduced summer insolation field characteristic of all the experiments is thought to be a necessary condition for allowing snow to last through the summer and ice sheets to build the results show that the model fails to maintain snow cover through the summer at locations of suspected initiation of the major ice sheets despite the reduced summer and fall insolation when 10 m thick ice was inserted in all locations where continental ice sheets existed during the last glacial maximum the model failed to maintain it as well producing energy and mass imbalances which would remove the ice within 5 years only when the ocean surface temperatures were adjusted to their peak ice age values was the model able to keep any of the additional ice and then only in a very restricted region of northern baffin island the experiments indicate there is a wide discrepancy between the model s response to milankovitch perturbations and the geophysical evidence of ice sheet initiation as the model failed to grow or sustain low altitude ice during the time of high latitude maximum solar radiation reduction 120 110 kyr b p it is unlikely it could have done so at any other time within the last several hundred thousand years if the model results are correct it indicates that the growth of ice occurred in an extremely ablative environment and thus demanded some complicated strategy or else some other climate forcing occurred in addition to the orbital variation influence and co2 reduction which would imply we do not really understand the cause of the ice ages and the milankovitch connection if the model is not nearly sensitive enough to climate forcing it could have implications for projections of future climate change

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

detrital transport of metals by glaciers an example from the pinchi mine central british columbia abundant cinnabar hgs mineralization is associated with the pinchi fault in central british columbia two formerly producing mercury mines have been developed on this fault pinchi and bralorne takla the mercury content of till a sediment type directly deposited by glaciers in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock and the direction of ice flow cinnabar bearing bedrock was eroded by glaciers transported in the direction of ice flow and deposited down ice from its source an example of such a dispersal train is documented for the pinchi mine area where mercury ore was transported over a distance of 12 km as measured in the clay sized fraction 3 3 of this same sediment antimony chromium and nickel dispersal trains were also detected in the region these data indicate that natural glacial processes can result in the mobilization of metals in the surficial environment a factor which has to be considered at mine sites in glaciated terrain where mine reclamation and remediation measures are now required

abrupt holocene climate change as an important factor for human migration in west greenland west greenland has had multiple episodes of human colonization and cultural transitions over the past 4 500 y however the explanations for these large scale human migrations are varied including climatic factors resistance to adaptation economic marginalization mercantile exploration and hostile neighborhood interactions evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of holocene temperature derived from ice cores atop the greenland ice sheet here we present high resolution records of temperature over the past 5 600 y based on alkenone unsaturation in sediments of two lakes in west greenland we find that major temperature changes in the past 4 500 y occurred abruptly within decades and were coeval in timing with the archaeological records of settlement and abandonment of the saqqaq dorset and norse cultures which suggests that abrupt temperature changes profoundly impacted human civilization in the region temperature variations in west greenland display an antiphased relationship to temperature changes in ireland over centennial to millennial timescales resembling the interannual to multidecadal temperature seesaw associated with the north atlantic oscillation

transient simulation of the last glacial inception part ii sensitivity and feedback analysis the sensitivity of the last glacial inception around 115 kyr bp 115 000 years before present to different feedback mechanisms has been analysed by using the earth system model of intermediate complexity climber 2 climber 2 includes dynamic modules of the atmosphere ocean terrestrial biosphere and inland ice the last of which was added recently by utilising the three dimensonal polythermal icesheet model sicopolis we performed a set of transient experiments starting at the middle of the eemiam interglacial and ran the model for 26 000 years with timedependent orbital forcing and observed changes in atmospheric co 2 concentration co2 forcing the role of vegetation and ocean feedback co 2 forcing mineral dust thermohaline circulation and orbital insolation are closely investigated in our model glacial inception as a bifurcation in the climate system appears in nearly all sensitivity runs including a run with constant atmospheric co 2 concentration of 280 ppmv a typical interglacial value and simulations with prescribed present day seasurface temperatures or vegetation cover although the rate of the ice sheets growth is smaller than in the case of the fully in teractive model only if we run the fully interactive model with constant present day insolation and apply present day co 2 forcing does no glacial inception appear at all this implies that within our model the orbital forcing alone is sufficient to trigger the interglacial glacial transition while vegetation ocean and atmospheric co2 concentration only provide additional although important positive feedbacks in addition we found that possible reorganisations of the thermohaline circulation influence the distribution of inland ice

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

on the causes of glacial inception at 116 kabp to explore processes involved in glacial inception at 116 kabp the response of an atmospheric general circulation model agcm to changes in lower boundary conditions is investigated two 116 kabp experiments are conducted to examine the importance of sea surface conditions sea surface temperature and sea ice distribution one with the present day sea surface conditions and the other with 116 kabp sea surface conditions these two different sea surface conditions are obtained from simulations using an earth system climate model of intermediate complexity perennial snow cover occurred over the canadian archipelago under 116 kabp orbital and co2 forcing with present day warm sea surface conditions and further expanded over northeastern canada when 116 kabp cool sea surface conditions were applied the net positive accumulation in northeastern canada with little in alaska is in good agreement with geological records two additional 116 kabp experiments are conducted to examine the combined importance of sea surface conditions and land surface conditions vegetation one with the present day sea surface and modified land surface conditions and the other with 116 kabp sea surface and modified land surface conditions modifying vegetation based on cooling during summer induced by 116 kabp sea surface conditions leads to much larger areas of perennial snow cover only when 116 kabp sea surface conditions are applied is a realistic global net snow accumulation rate obtained contrary to the earlier ice age hypothesis our results suggest that the capturing of glacial inception at 116 kabp requires the use of cooler sea surface conditions than those of the present climate also the large impact of vegetation change on climate suggests that the inclusion of the vegetation feedback is important for model validation at least in this particular period of earth history

glacial inception on baffin island the role of insolation meteorology and topography abstractgeologic evidence suggests that the last glacial inception 115 kya occurred within the mountains of baffin island global climate models gcms have difficulty simulating this climate transition likely because of their coarse horizontal resolution that smooths topography and necessitates the use of cumulus parameterizations a regional configuration of the weather research and forecasting wrf model is used to simulate the small scale topographic and cloud processes neglected by gcms and the sensitivity of the region to milankovitch forcing topography and meteorology is tested it is found that ice growth is possible with 115 kya insolation realistic topography and slightly colder than average meteorology represented by specific years within the past three decades the simulation with low gcm like topography shows a negative surface mass balance even with the relevant orbital parameter configuration demonstrating the criticality of realistic topography the downslope growth of the ice

rapid neoglaciation on ellesmere island promoted by enhanced summer snowfall in a transient climate model simulation of the middle late holocene arctic neoglaciation following the holocene thermal maximum is an important feature of late holocene climate we investigated this phenomenon using a transient 6000 year simulation with the cesm ca

high arctic holocene temperature record from the agassiz ice cap and greenland ice sheet evolution we present a revised and extended high arctic air temperature reconstruction from a single proxy that spans the past 12 000 y up to 2009 ce our reconstruction from the agassiz ice cap ellesmere island canada indicates an earlier and warmer holocene thermal maximum with early holocene temperatures that are 4 5 c warmer compared with a previous reconstruction and regularly exceed contemporary values for a period of 3 000 y our results show that air temperatures in this region are now at their warmest in the past 6 800 7 800 y and that the recent rate of temperature change is unprecedented over the entire holocene the warmer early holocene inferred from the agassiz ice core leads to an estimated 1 km of ice thinning in northwest greenland during the early holocene using the camp century ice core ice modeling results show that this large thinning is consistent with our air temperature reconstruction the modeling results also demonstrate the broader significance of the enhanced warming with a retreat of the northern ice margin behind its present position in the mid holocene and a 25 increase in total greenland ice sheet mass loss 1 4 m sea level equivalent during the last deglaciation both of which have implications for interpreting geodetic measurements of land uplift and gravity changes in northern greenland

geological survey of canada s contributions to understanding the composition of glacial sediments drift compositional studies were initiated at the geological survey of canada gsc in the mid 1960 s in projects that drew heavily on the technology and approaches developed in fennoscandia over the previous century as this research progressed and expanded in the 1970 s its fennoscandian character diminished and like the geochemical exploration research program that it closely paralleled drift prospecting began to acquire a distinctly canadian character imposed by the geographical and logistical constraints of climate and asymmetric population distribution gsc research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering because glacial sediments are generated largely by crushing and abrasion their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness this s

true to milankovitch glacial inception in the new community climate system model the equilibrium solution of a fully coupled general circulation model with present day orbital forcing is compared to the solution of the same model with the orbital forcing from 115 000 years ago the difference in snow accumulation between these two simulations has a pattern and a magnitude comparable to the ones inferred from reconstructions for the last glacial inception this is a major improvement over previous similar studies and the increased realism is attributed to the higher spatial resolution in the atmospheric model which allows for a more accurate representation of the orography of northern canada and siberia the analysis of the atmospheric heat budget reveals that as postulated by milankovitch s hypothesis the only necessary positive feedback is the snow albedo feedback which is initiated by reduced melting of snow and sea ice in the summer however this positive feedback is almost fully compensated by an increased meridionalheat transportin theatmosphereandareducedconcentrationoflow arcticclouds in contrasttosimilar previous studies the ocean heat transport remains largely unchanged this stability of the northern north atlanticcirculation is explainedby the regulatingeffect of thefreshwaterimportthroughthe naresstrait and northwest passage and the spiciness import by the north atlantic current

stochastic atmospheric forcing as a cause of greenland climate transitions abstractan unforced simulation of the community climate system model version 4 ccsm4 is found to have greenland warming and cooling events that resemble dansgaard oeschger cycles in pattern and magnitude with the caveat that only three transitions were available to be analyzed it is found that the transitions are triggered by stochastic atmospheric forcing the atmospheric anomalies change the strength of the subpolar gyre leading to a change in labrador sea sea ice concentration and meridional heat transport the changed climate state is maintained over centuries through the feedback between sea ice and sea level pressure in the north atlantic indications that the initial atmospheric pressure anomalies are preceded by precipitation anomalies in the western pacific warm pool are discussed the full evolution of the anomalous climate state depends crucially on the climatic background state

a holocene ice core pollen record from ellesmere island nunavut canada abstract a holocene record of pollen deposition was obtained from an ice core drilled through the agassiz ice cap the pollen records long range atmospheric transport to the ice cap pollen concentrations were highest in the early holocene 15 grains l decreased in the mid holocene 6 grains l and increased in the late holocene 9 grains l in the early holocene the higher concentration of tree pollen at a time when large parts of canada were still ice covered and when forest was generally farther away implies that atmospheric circulation was stronger than at present following deglaciation as vegetation migrated north in central and eastern canada sources of pollen were closer to the agassiz ice cap however the concentration of tree pollen decreased on the ice cap this was followed by several relatively rapid changes after 3500 yr ago until ca 3500 yr ago the pollen concentration curves resembled the ice core 18 o and summer melt layer curves both regarded as temperature proxies

a millennial scale record of arctic ocean sea ice variability and the demise of the ellesmere island ice shelves 1 sea ice ice shelves at the apex of north america 80 n constitute the oldest sea ice in the northern hemisphere we document the establishment and subsequent stability of the ward hunt ice shelf and multiyear landfast sea ice in adjacent fiords using 69 radiocarbon dates obtained on holocene driftwood deposited prior to coastal blockage these dates 47 of which are new record a hiatus in driftwood deposition beginning 5500 cal yr bp marking the inception of widespread multiyear landfast sea ice across northern ellesmere island this chronology together with historical observations of ice shelf breakup 1950 to present provides the only millennial scale record of arctic ocean sea ice variability to which the past three decades of satellite surveillance can be compared removal of the remaining ice shelves would be unprecedented in the last 5500 years this highlights the impact of ongoing 20th and 21st century climate warming that continues to break up the remaining ice shelves and soon may cause historically ice filled fiords nearby to open seasonally

40ar 39ar geochronometry of pseudotachylytes by vacuum encapsulation north cascade mountains washington usa to determine a reliable means of dating pseudotachylytes we obtained total gas ages plateau ages and argon retention ages on samples from the north cascade mountains washington quartz ampoule vacuum encapsulation analysis of small grains a few milligrams from six samples allowed evaluation of 39 ar loss through recoil during irradiation and laser ablation on four samples allowed textural control in microlitic samples recoil loss 39 ar ranges from 0 2 to 8 4 the total gas ages incorporating this 39 ar are inconsistent but retention ages are much more internally consistent and within analytical error they match or nearly match plateau ages from most of the microlitic samples at 54 55 ma samples analyzed by laser ablation suggest one episode of faulting and pseudotachylyte formation at 55 59 ma and an earlier episode at ca 80 ma the partly glassy pseudotachylyte yielded laser ablation total gas and retention ages of ca 65 ma the microlitic pseudotachylytes indicate formation close to 55 ma with possible older faulting and pseudotachylyte formation at ca 81 84 ma the good consistency among the retention ages the laser ages with highest precision and especially the plateau dates combined with the ages falling within the anticipated time span provides confidence in the geologic reality of the ages nevertheless it is clear that large clasts and crystal fragments within these particular veins did not completely degas or may have an anomalous inherited radiogenic 40 ar component

introduction to the special issue of canadian journal of earth sciences the nechako natmap project of the central canadian cordillera the canadian cordillera in central british columbia has seen the mesozoic subduction of an oceanic terrane the amalgamation of volcanic arc terranes continued intermittent mesozoic compression and magmatism and tertiary wrenching extension and magmatism except in its northernmost mountain ranges the area is extensively cov ered in glacial drift and thin veneers of tertiary volcanic rocks in 1994 a group of scientists and technologists be lieved they could understand that cover see through it and discover the components of that collision and extensional orogen they would apply modern techniques of isotopic and paleontological geochronology lake sediment till and plant geochemistry detailed gravity magnetic radiometric paleomagnetic and electromagnetic surveys and isotopic and trace element lithochemistry as they conducted extensive bedrock and surficial mapping this special issue summa rizes a cross section of the scientific contributions derived from that mapping conducted under the auspices of the nechako natmap project it demonstrates the absolute necessity of applying modern isotopic and paleontologic geo chronology to understand the phanerozoic geology of the cordillera it emphasizes the necessity of detailed aeromag netic surveys 500 m or less line spacing in looking through covered terranes at anything more than 1 250 000 scale and it shows the immense utility of applying various geochemical techniques to solve geological problems and estab lish baselines for future research and economic development bedrock and surficial mapping in the central cordillera using these and other techniques have established the nature and timing of mesozoic crustal growth tertiary crustal thinning and the associated formation of mineral deposits

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

quantifying ice sheet feedbacks during the last glacial inception 1 the last glacial inception 116 ky ago has long been used to test the sensitivity of climate models to insolation from these simulations atmospheric oceanic and vegetation feedbacks have been shown to amplify the initial insolation signal into a rapid growth of ice sheets over the northern hemisphere however due to the lack of comprehensive atmosphere ocean vegetation northern hemisphere ice sheet models the impact of all these feedbacks acting concurrently has not yet been evaluated here we present the results from such a model which simulates significant ice sheet growth over north america but none over eurasia our analyses focus on the different behaviours over these regions and the quantification of the ice sheet feedbacks on climate

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

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

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

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

neoglacial ice expansion and late holocene cold based ice cap dynamics on cumberland peninsula baffin island arctic canada abstract radiocarbon dating of fossil flora and fauna collected along receding cold based ice caps and cold based sections of polythermal glaciers on cumberland peninsula reveal insights into neoglacial ice expansion and late holocene ice dynamics the taphonomic advantages of subfossilized moss were exploited to precisely document regional expansions of ice caps through the late holocene when compared with climate proxies and records of volcanic eruptions the moss radiocarbon age distributions indicate i onset of neoglaciation shortly after 5 ka concomitant with increased sea ice cover ii intensification of ice expansion between 1 9 and 1 1 ka followed by halt of ice growth or ice recession during the medieval warm period and iii renewed ice expansion after 0 8 ka in response to cooling related to a combination of large volcanic eruptions and low solar activity overall the observations support a model of near instantaneous glacial response to regional climate controls and that these responses were synchronous throughout eastern canadian arctic and possibly eastern greenland