dynamical mechanisms for african monsoon changes during the mid holocene 1 during the mid holocene about 6 ka bp the african monsoon was stronger and extended farther north than in present day climate associated with differences in orbital parameters affecting insolation earlier research suggests that land surface vegetation interaction and atmosphere ocean coupling may be important to the northward extension of the holocene monsoon rainfall but different climate models produce different results in terms of rainfall distribution this study examines the dynamical mechanisms that modulate the orbital forcing effect on the african monsoon convection a series of simulations with 6 ka bp orbital parameters modified land surface albedo that mimics grassland extending over north africa and alterations of the model dynamics are used it is found that the ventilation mechanism inflow of low moist static energy air from oceanic or poleward regions is a key process in setting the northern rainfall boundary for the african monsoon in particular advection and diffusion of less moist air oppose the increase of moisture that would be required to meet the increased convective instability criteria set by the warmer tropospheric air above the continent while changes in heat fluxes into the atmospheric column favor convection in principle the ventilation mechanism limits the poleward extent of the region that can actually convect

magnetic polarity stratigraphy of a plio pleistocene marine sequence of north island new zealand abstract thick sequences of relatively undisturbed plio pleistocene sediments in the wanganui basin north island new zealand consist of well exposed silts clayey silts sandstones rare limestones and several tephras oriented specimens were collected from a section more than 2500 m thick and palaeomagnetic measurements were made using a c demagnetisations in fields up to 35 mt with the aid of tephrochronology the age of the upper sequence is now well established and falls within the matuyama epoch the lower two thirds of the section except for the basal 500 m is predominantly normally magnetised and is interpreted as a very extended sequence of the gauss epoch the lowest 500 m then represents the gilbert epoch the plio pleistocene boundary as defined at vrica italy falls within the upper part of the section studied in the upper nukumaruan stage for the first time a reliable correlation is made with the international boundary using as intermediaries the palaeomagnetic and tephrostratigraphy of deep sea cores from the southwest pacific as a result of the high deposition rate of the order of 1 2 m ky and the apparent lack of unconformities the temporal resolution is high short lived magnetic events are detected especially in the lower matuyama and upper gauss epochs these generally correlate well with events reported from other extended sections

potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

a multi model analysis of the role of the ocean on the african and indian monsoon during the mid holocene we investigate the role of the ocean feedback on the climate in response to insolation forcing during the mid holocene 6 000 year bp using results from seven coupled ocean atmosphere general circulation models we examine how the dipole in late summer sea surface temperature sst anomalies in the tropical atlantic increases the length of the african monsoon how this dipole structure is created and maintained and how the late summer sst warming in the northwest indian ocean affects the monsoon retreat in this sector similar mechanisms are found in all of the models including a strong wind evaporation feedback and changes in the mixed layer depth that enhance the insolation forcing as well as increased ekman transport in the atlantic that sharpens the atlantic dipole pattern we also consider changes in interannual variability over west africa and the indian ocean the teleconnection between variations in sst and sahelian precipitation favor a larger impact of the atlantic dipole mode in this region in the indian ocean the strengthening of the indian dipole structure in autumn has a damping effect on the indian dipole mode at the interannual time scale

the role of oceanic forcing in mid holocene northern hemisphere climatic change previous model investigations suggested that changes in orbital forcing and feedbacks associated with northward expansion of the boreal forest were both required to explain the full magnitude of enhanced high latitude northern hemisphere summer warming at 6 ka thus implying that biospheric feedbacks decreased planetary albedo associated with forest expansion may be large in the future foley et al 1994 tempo testing earth system models with paleo observations 1996 before the magnitude of past biospheric and other feedbacks can be estimated with confidence however the role of realistic high latitude oceanic forcing i e sea surface temperature sst increases and sea ice reductions should also be considered here we review existing paleoceanographic observations that suggest portions of the north atlantic were up to 4 c warmer than today at 6 ka we then combine our estimates of mid holocene north atlantic sst and sea ice conditions with new climate model simulations to suggest that a significant portion of high latitude summer warming at 6 ka in the northern hemisphere can be accounted for by altered orbital forcing ssts and sea ice relative to today our results underscore the importance of incorporating realistic boundary conditions when using paleoenvironmental data to evaluate the climate system s sensitivity to altered forcing and suggest that high latitude oceanic feedbacks were major contributors to enhanced high latitude summer warming in the northern hemisphere at 6 ka

the holocene occurrence of reindeer on franz josef land russia reindeer are absent historically on the high arctic islands of franz josef land russia however shed antlers are common on unglaciated forelands on hooker scot keltie and alexandra land islands in the archipelago radiocarbon dating of 19 new antler remains combined with seven ages reported previously demonstrate the presence of reindeer between c 6400 and 1300 cal bp reindeer probably occupied franz josef land for much of the holocene reflecting sufficient forage associated with summer air temperatures 1 c warmer than today and retracted glaciers and snowfields a prominent neoglacial advance at c 1000 cal bp is coincident with inferred extinction of reindeer late twentieth century warming and associated glacier retraction may provide environmental conditions for the immigration of reindeer to franz josef land and other high arctic areas similar to earlier in the holocene

integrated tephrochronology and magnetostratigraphy for cyclothemic marine strata wanganui basin implications for the pliocene pleistocene boundary in new zealand abstract the middle pliocene to earliest pleistocene part of the rangitikei river section in wanganui basin contains at least six distal tephras five are rhyolitic kowhai eagle hill ohingaiti waipura and vinegar hill tephras and one is andesitic mangamako tephra all tephras occur as macroscopic layers and are enclosed within cyclothemic marine sediments that accumulated in shoreface to outer shelf water depths under conditions of oscillating sea level driven by glacio eustacy the glass and ferromagnesian compositions of the silicic tephras imply derivation from calc alkaline rhyolitic sources either or both of taupo volcanic zone and southern coromandel volcanic zone the waipuru and vinegar hill tephras have isothermal plateau fission track itpft ages of 1 87 0 15 ma and 1 75 0 13 ma respectively paleomagnetic results allow identification of i the gauss matuyama boundary located ca 70 m below the top of the mangaweka mudstone and ii the top of the olduvai subchron placed at the base of the waipuru shellbed the itpft ages of the tephras are consistent with the interpreted magnetostratigraphy and also with astronomically tuned timescales correlation of the rangitikei sequences to the odp site 846 18o record indicates that each sequence corresponds to a glacial interglacial isotope stage couplet and allows ages to be interpolated for tephras not dated directly integration of the new ages for the waipuru and vinegar hill tephras the magnetostratigraphy and the sequence correlations to the astronomically tuned oxygen isotope timescale lead us to place the pliocene pleistocene boundary as defined at the vrica stratotype at the base of the highstand systems tract siltstone of sequence 17 in the rangitikei section 60 m below the vinegar hill tephra

on the development of electron microprobe zircon fission track geochronology abstract the fission track method has been applied for decades to quantify rates and timing of processes in the shallow crust the most widely used approach the external detector method involves counting fission tracks a decay product resulting from the spontaneous fission of 238 u and a paired set of induced tracks parent proxy from the thermal neutron irradiation of 235 u we propose an alternate method of dating zircons that utilizes an electron microprobe to directly measure uranium concentration u and image the number of spontaneous fission tracks or etch figures that intersect the surface of the crystal using an electron backscatter detector the electron microprobe fission track ep ft method is used to date six zircon samples four of which are widely used as standards fish canyon tuff peach springs tuff buluk member of the bakata formation tuff tardee rhyolite mt dromedary complex hypabyssal granite and browns park formation tuff all samples yield ages that overlap within two standard deviations of published reference ages determined using other radiometric techniques i e k ar 40 ar 39 ar and u pb and also by the traditional fission track external detector method to correct for poorly constrained parameters such as the spontaneous fission decay constant weight to volume percent conversions etching efficiency and selection bias we calculate a preliminary z proportionality factor of 4469 661 1 the ep ft technique avoids the hazard and expense of thermal neutron irradiation allows simultaneous chemical compositions to be determined removes the step of counting an external detector manually and will likely allow much higher track densities to be counted than would be normally possible with optical microscopy the technique is ideal for dating moderate to high u zircons 100 ppm u

iron partitioning in a pyrolite mantle and the nature of the 410 km seismic discontinuity pyrolite1 is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the earth s mantle the main pressure induced phase transformations of the olivine component of pyrolite occur at about 13 5 gpa to and 24 gpa to mgsio3 rich perovskite magnesiowustite 2 3 which are thought to be responsible for the seismic discontinuities at 410 and 660 km depths in the mantle recent seismological studies however have demonstrated that the 410 km seismic discontinuity is sharper in some areas than that expected from the to transformation in mantle olivine with a fixed composition4 5 6 7 moreover some mineral physics studies suggest that the seismic velocity jump at the 410 km discontinuity is inconsistent with that associated with the to transformation in olivine8 9 here we present a phase equilibria study of a material having pyrolite composition at pressures of 6 16 gpa we found that the iron content in olivine changes significantly with increasing pressure as a result of the formation of a relatively iron rich majorite phase at these pressures this variation in iron content can overcome or at least reduce both of the above difficulties encountered with the pyrolite model of mantle composition by showing that the component mineral systems cannot be treated as separate

new zircon fission track ages from new zealand quaternary tephra an interlaboratory experiment and recommendations for the determination of young ages abstract fission track dating of zircons from five pleistocene tephra in the wanganui basin north island new zealand has been carried out independently in two different laboratories the results from each are statistically identical even though there were some differences in laboratory techniques the resulting ages confirm recent isothermal plateau fission track itpft ages on two of these tephra but with increased precision the weighted mean ages 1 are potaka tephra 0 97 0 04 ma 4 determinations rewa pumice 1 00 0 06 ma 3 determinations mangapipi ash 1 26 0 08 ma 2 determinations pakihikura pumice 1 66 0 07 ma 4 determinations and the vinegar hill tephra 1 73 0 08 ma 3 determinations these new results further constrain the time control in this important pleistocene section which contains many cyclothems reflecting climatic and tectonic influences this study illustrates well the pitfalls that can occur when dating such young material using single crystal techniques the difficulties of determining when etching is optimal the presence of detrital grains and their subsequent removal from the data set are described as well as a recommendation that a minimum of 15 crystals but optimally at least 20 be counted before calculating the final age it may also be necessary to plot running means of the single crystal ages to determine when the final age has been approached

indoor seismology by probing the earth s interior by using sound velocity measurements at high pressures and temperatures the adiabatic bulk ks and shear g moduli of mantle materials at high pressure and temperature can be obtained directly by measuring compressional and shear wave velocities in the laboratory with experimental techniques based on physical acoustics we present the application of the current state of the art experimental techniques by using ultrasonic interferometry in conjunction with synchrotron x radiation to study the elasticity of olivine and pyroxenes and their high pressure phases by using these updated thermoelasticity data for these phases velocity and density profiles for a pyrolite model are constructed and compared with radial seismic models we conclude that pyrolite provides an adequate explanation of the major seismic discontinuities at 410 and 660 km depths the gradient in the transition zone as well as the velocities in the lower mantle if the uncertainties in the modeling and the variations in different seismic models are considered the characteristics of the seismic scaling factors in response to thermal anomalies suggest that anticorrelations between bulk sound and shear wave velocities as well as the large positive density anomalies observed in the lower mantle cannot be explained fully without invoking chemical variations

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

potential role of vegetation feedback in the climate sensitivity of high latitude regions a case study at 6000 years b p previous climate model simulations have shown that the configuration of the earth s orbit during the early to mid holocene approximately 10 5 kyr can account for the generally warmer than present conditions experienced by the high latitudes of the northern hemisphere new simulations for 6 kyr with two atmospheric mixed layer ocean models community climate model version 1 ccm1 and global environmental and ecological simulation of interactive systems version 2 genesis 2 are presented here and compared with results from two previous simulations with genesis 1 that were obtained with and without the albedo feedback due to climate induced poleward expansion of the boreal forest the climate model results are summarized in the form of potential vegetation maps obtained with the global biome model which facilitates visual comparisons both among models and with pollen and plant macrofossil data recording shifts of the forest tundra boundary a preliminary synthesis shows that the forest limit was shifted 100 200 km north in most sectors both ccmi and genesis 2 produced a shift of this magnitude genesis 1 however produced too small a shift except when the boreal forest albedo feedback was included the feedback in this case was estimated to have amplified forest expansion by approximately 50 the forest limit changes also show meridional patterns greatest expansion in central siberia and little or none in alaska and labrador which have yet to be reproduced by models further progress in understanding of the processes involved in the response of climate and vegetation to orbital forcing will require both the deployment of coupled atmosphere biosphere ocean models and the development of more comprehensive observational data sets

holocene paleoclimate data from the arctic testing models of global climate change to evaluate the spatial variability of arctic climate change during the present interglacial cape project members compiled well dated terrestrial marine and ice core paleoenvironmental records spanning the past 10 12 thousand years ka six tundra biomes of increasing summer temperature requirements were defined based on regionally coherent pollen assemblages using a rule based approach pollen spectra were converted to tundra forest tundra or forest biomes ranked by their average growing season requirements marine sea surface reconstructions were based on proxy data following a similar rule based approach from these data based reconstructions departures in summer temperatures from modern normals were calculated in 1 ka time slices through the holocene to test predictive models data based summer temperature reconstructions were compared with general circulation model gcm simulations for 10 ka and 6 ka ago paleodata and model results both show that warming occurred earlier across beringia and asia relative to lands adjacent to the north atlantic and that late holocene cooling was most apparent in the north atlantic region however the gcm over predicts the magnitude of mid holocene warming over northern asia and underestimates the intensification of the north atlantic drift in the early holocene strong spatial variability in environmental response during the holocene despite symmetric insolation forcing suggests that any future changes whether caused by anthropogenic or natural factors are unlikely to result in a uniform change across the arctic adding additional complexity to forecasts of global impacts

comparative compressibility of hydrous wadsleyite and ringwoodite effect of h2o and implications for detecting water in the transition zone review of recent mineral physics literature shows consistent trends for the influence of fe and h2o on the bulk modulus k0 of wadsleyite and ringwoodite the major phases of earth s mantle transition zone 410 660 km however there is little consensus on the first pressure derivative k0 dk dp p 0 which ranges from about 4 to 5 across experimental studies and compositions here we demonstrate the importance of k0 in evaluating the bulk sound velocity of the transition zone in terms of water content and provide new constraints on the effect of h2o on k0 for wadsleyite and ringwoodite by conducting a comparative compressibility study in the experiment multiple crystals of hydrous fo90 wadsleyite containing 2 0 and 0 25 wt h2o were loaded into the same diamond anvil cell along with hydrous ringwoodite containing 1 4 wt h2o by measuring their pressure volume evolution simultaneously up to 32 gpa we constrain the difference in k0 independent of the pressure scale finding that h2o has no effect on k0 whereas the effect of h2o on k0 is significant the fitted k0 values of hydrous wadsleyite 0 25 and 2 0 wt h2o and hydrous ringwoodite 1 4 wt h2o examined in this study were found to be identical within uncertainty with k0 3 7 2 new secondary ion mass spectrometry measurements of the h2o content of these and previously investigated wadsleyite samples shows the bulk modulus of wadsleyite is reduced by 7 0 5 gpa wt h2o independent of fe content for upper mantle compositions because k0 is unaffected by h2o the reduction of bulk sound velocity in very hydrous regions of transition zone is expected to be on the order of 1 6 which is potentially detectible in high resolution regional seismology studies

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years

zircon fission track age for middle pleistocene rangitawa tephra new zealand stratigraphic and paleoclimatic significance rangitawa tephra is an important stratigraphic marker in mid pleistocene marine and terrestrial sequences in new zealand and adjacent ocean basins zircon fission track ages zfta on rangitawa tephra from five sites in the southern north island yield mean site ages in the range 0 34 to 0 40 ma with a weighted mean of 0 35 0 04 ma 1 on the basis of glass shard major element chemistry ferromagnesian mineralogy zfta and similarity of paleomagnetic dates of proposed tephra correlatives in deep sea cores it is concluded that rangitawa tephra represents a major eruptive event in the taupo volcanic zone most probably associated with eruption of the whakamaru group ignimbrites 0 35 0 39 ma or less likely the paeroa range group ignimbrites 0 36 0 38 ma pollen analyses from two onshore sites together with regional loess stratigraphy show that rangitawa tephra was erupted during a glacial period the zfta and previously reported oxygen isotope data from dsdp site 594 indicate that rangitawa tephra was erupted near the end of oxygen isotope stage 10

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

megalakes in the sahara a review the sahara was wetter and greener during multiple interglacial periods of the quaternary when some have suggested it featured very large mega lakes ranging in surface area from 30 000 to 350 000 km2 in this paper we review the physical and biological evidence for these large lakes especially during the african humid period ahp 11 5 ka megalake systems from around the world provide a checklist of diagnostic features such as multiple well defined shoreline benches wave rounded beach gravels where coarse material is present landscape smoothing by lacustrine sediment large scale deltaic deposits and in places tufas encrusting shorelines our survey reveals no clear evidence of these features in the sahara except in the chad basin hydrologic modeling of the proposed megalakes requires mean annual rainfall 1 2 m yr and a northward displacement of tropical rainfall belts by 1000 km such a profound displacement is not supported by other paleo climate proxies and comprehensive climate models challenging the existence of megalakes in the sahara rather than megalakes isolated wetlands and small lakes are more consistent with the sahelo sudanian paleoenvironment that prevailed in the sahara during the ahp a pale green and discontinuously wet sahara is the likelier context for human migrations out of africa during the late quaternary

vegetation succession and east asian summer monsoon changes since the last deglaciation inferred from high resolution pollen record in gonghai lake shanxi province china a cal 20 year resolution pollen record from gonghai lake presented the detailed process of mountain vegetation succession and east asian summer monsoon easm changes since the last deglaciation i

isothermal plateau fission track ages of hydrated glass shards from silicic tephra beds abstract the age of silicic tephra beds that have experienced a simple thermal history can be accurately and precisely determined by application of the isothermal plateau fission track technique to hydrated glass shards age estimates obtained by this means compare very well with those based on co existing mineral phases using the k ar 40ar 39ar external detector fission track and thermoluminescence techniques this concordance contradicts the popular belief that hydrated glass shards give unreliable ages distal tephra beds many of which are difficult to date because of their fine grainsize low abundance of crystals and common presence of detrital grains are readily dated by the isothermal plateau glass fission track method this new advance should greatly facilitate the development of detailed chronologies of tephra bearing sedimentary sequences located far from volcanic centres

chronology of pliocene and quaternary bioevents and climatic events from fission track ages on tephra beds wairarapa new zealand abstract high resolution pliocene and pleistocene sequences exposed on land in new zealand are some of the few detailed records of widepread marine bioevents and paleoclimatic changes in the southern hemisphere marine biostratigraphy calibrated in deep sea cores by paleomagnetic reversals has been the primary basis for the chronology of these sequences we have determined ages for several tephra beds which now provide an independent numerical age calibration for a well studied marine and terrestrial section in wairarapa by using the isothermal plateau fission track itpft method on volcanic glass we have overcome the problems of partial track fading and detrital mineral contamination which hindered earlier studies to reveal a new chronology extending back to nearly 5 ma our ages for the hikawera tuff 4 91 0 25 ma and spooner tuff 3 44 0 13 ma are consistent with the appearance and disappearance of many early pliocene foraminiferial species validating their age calibration in new zealand however some fossil occurrences including coccoliths differ temporally by as much as 0 55 ma perhaps due to local tectonic induced recycling four pleistocene tephra beds potaka tephra 1 00 0 03 ma kaukatea tephra 0 87 0 05 ma rangitawa tephra ca 0 35 ma and kawakawa tephra ca 0 22 ma are now recognised in the wairarapa sequence via stratigraphic and new geochemical and age data these beds allow direct correlation to other marine and terrestrial basins as well as volcanic regions in new zealand and will ultimately aid in a regional paleoenvironmental reconstruction where bioevents are absent the tephra ages indicate that the marine sediment accumulation rates varied from 90 to 250 m ma between different sections of the pliocene and reached ca 350 m ma in the last 2 4 ma when the sequence displays pronounced glacioeustatic cyclic deposition in the terrestrial realm the oldest loess in new zealand is now constrained to between 1 00 and 0 87 ma

biological oxygen productivity during the last 60 000 years from triple oxygen isotope measurements during isotope exchange between o2 and co2 in the stratosphere the relative rates of biologic o2 production and stratospheric processing determine the relationship between d 17 o and d 18 oo f o2 in the atmosphere variations of this relationship thus allow us to estimate changes in the rate of mass dependent o2 production by photosynthesis versus the rate of o2 co2 exchange in the stratosphere with about equal fractionations of d 17 o and d 18 o in this study we reconstruct total oxygen productivity for the last glacial the last glacial termination and the early holocene from the triple isotope composition of atmospheric oxygen trapped in ice cores with a box model we estimate that total biogenic productivity was only 76 83 of today for the glacial and was probably lower than today during the glacial interglacial transition and the early holocene depending on how reduced the oxygen flux from the land biosphere was during the glacial the oxygen flux from the glacial ocean biosphere was 88 140 of its present value index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4870 oceanography biological and chemical stable isotopes 1615 global change biogeochemical processes 4805 0315 atmospheric composition and structure biosphere atmosphere interactions keywords gisp2 siple ice cores oxygen isotopes past oxygen productivity stratospheric isotope exchange respiration

onshore offshore correlation of pleistocene rhyolitic eruptions from new zealand implications for tvz eruptive history and paleoenvironmental construction abstract taupo volcanic zone tvz in the north island new zealand is arguably the most active quaternary rhyolitic system in the world numerous and widespread rhyolitic tephra layers sourced from the tvz form valuable chronostratigraphic markers in onshore and offshore sedimentary sequences in deep sea cores from ocean drilling program odp leg 181 sites 1125 1124 1123 and 1122 located east of new zealand ca 100 tephra beds are recognised post dating the plio pleistocene boundary at 1 81 ma these tephras have been dated by a combination of magnetostratigraphy orbitally tuned stable isotope data and isothermal plateau fission track ages the widespread occurrence of ash offshore to the east of new zealand is favoured by the small size of new zealand the explosivity of the mainly plinian and ignimbritic eruptions and the prevailing westerly wind field although some tephras can be directly attributed to known tvz eruptions there are many more tephras represented within odp cores that have yet to be recognised in near source on land sequences this is due to proximal source area erosion and or deep burial as well as the adverse effect of vapour phase alteration and devitrification within near source welded ignimbrites despite these difficulties a number of key deep sea tephras can be reliably correlated to equivalent aged tephra exposed in uplifted marine back arc successions of wanganui basin where an excellent chronology has been developed based on magnetostratigraphy orbitally calibrated sedimentary cycles and isothermal plateau fission track ages on tephra significant pleistocene tephra markers include the kawakawa omataroa rangitawa onepuhi kaukatea kidnappers b potaka unit d ahuroa ongatiti rewa sub rewa pakihikura ototoka and table flat tephras six other tephra layers are correlated between odp core sites but have yet to be recognised within onshore records the identification of pleistocene tvz sourced tephras within the odp record and their correlation to wanganui basin and other onshore sites is a significant advance as it provides 1 an even more detailed history of the tvz than can be currently achieved from the near source record 2 a high resolution tephrochronologic framework for future onshore offshore paleoenvironmental reconstructions and 3 well dated tephra beds correlated from the offshore odp sites with astronomically tuned timescales provide an opportunity to critically evaluate the chronostratigraphic framework for onshore plio pleistocene sedimentary sequences e g wanganui basin cf naish et al 1998 quaternary science reviews 17 695 710

holocene climate and carbon cycle dynamics experiments with the green mcgill paleoclimate model 1 an inverse method is used to investigate the global carbon cycle from the early holocene 8 kyr bp to the end of the pre industrial period 0 kyr bp in an improved version of the green mcgill paleoclimate model mpm in this paper we now take into account the vegetation precipitation feedback and evaluate the terrestrial carbon cycle for the pre industrial equilibrium from our coupled transient simulation under orbital forcing reconstructed taylor dome atmospheric co2 forcing and a prescribed retreating laurentide ice sheet lis we find a decrease of 70 pgc in total carbon storage in the sahara region 15 degrees n to 30 degrees n and 15 degrees w to 50 degrees e which is caused by the desertification simulated in the green mpm the above decrease is partially compensated by an increase of 40 pgc in total carbon storage in the southern hemisphere from 8 to 2 kyr bp from an analysis of the total carbon stored under the ice sheet we can infer that this carbon has negligible impact on atmospheric co2 after 8 kyr bp from our model results we further conclude that the retreating lis together with the vegetation albedo feedback cause the global terrestrial carbon to increase from 8 to 6 kyr bp the application of the inverse method suggests that the first 10 ppmv increase in atmospheric co2 from 8 to 6 kyr bp comes from the ocean finally in the model simulations the total terrestrial carbon release from 6 to 0 kyr bp is about 68 to 95 pgc which would produce about a 5 to 7 ppmv atmospheric co2 increase based on the calculation of joos et al 2004 owing to our model limitation there is no ocean carbon cycle we cannot conclude whether the overall oceanic co2 release from 8 to 0 kyr bp is due to outgassing related to sst changes or to calcite compensation as proposed by broecker et al 2001

the greening of the mcgill paleoclimate model part ii simulation of holocene millennial scale natural climate changes various proxy data reveal that in many regions of the northern hemisphere nh the middle holocene 6 kyr bp was warmer than the early holocene 8 kyr bp as well as the later holocene up to the end of the pre industrial period 1800 ad this pattern of warming and then cooling in the nh represents the response of the climate system to changes in orbital forcing vegetation cover and the laurentide ice sheet lis during the holocene in an attempt to better understand these changes in the climate system the mcgill paleoclimate model mpm has been coupled to the dynamic global vegetation model known as vecode see part i of this two part paper and a number of sensitivity experiments have been performed with the green mpm the model results illustrate the following 1 the orbital forcing together with the vegetation albedo feedback result in the gradual cooling of global sat from about 6 kyr bp to the end of the pre industrial period 2 the disappearance of the lis over the period 8 6 kyr bp associated with vegetation albedo feedback allows the global sat to increase and reach its maximum at around 6 kyr bp 3 the northern limit of the boreal forest moves northward during the period 8 6 4 kyr bp due to the lis retreat 4 during the period 6 4 0 kyr bp the northern limit of the boreal forest moves southward about 120 km in response to the decreasing summer insolation in the nh and 5 the desertification of northern africa during the period 8 2 6 kyr bp is mainly explained by the decreasing summer monsoon precipitation

comparison of north american pollen based temperature and global lake status with cccma agcm2 output at 6 ka abstract we present new paleoclimate reconstructions for the time period of 6000 yr bp 6 ka that permit a quantitative comparison to corresponding mapped patterns of the newest version of the canadian cccma agcm2 climate model july temperature reconstructions were estimated using the modern analog technique employing fossil pollen records from the north american pollen database we present a new method of optimizing critical choices within the application of the mat through modern calibration the pattern of 6 ka temperature anomalies generated by the cccma agcm2 generally agree with those of the pollen based reconstruction particularly in the presence of a band of positive temperature anomalies across the continent from the yukon through the great lakes region and along the st lawrence this agreement suggests that both the model and data are reconstructing a contraction in the polar vortex over north america at 6 ka major areas of disagreement between the pollen based reconstruction and model simulation are also areas where the data are sparse and edge effects produce less reliable reconstructions the cccma agcm2 simulates drier conditions in a west east band stretching from alaska through the canadian prairies and midwest united states in agreement with low lake level observations at 6 ka simulated and reconstructed precipitation evaporation are also in agreement over the southwest united states with the exception of north central africa the cccma agcm2 fails to capture the northward and eastern extension of the afro asian monsoon belt at 6 ka general agreement between cccma agcm2 p e anomalies and lake status change is found throughout europe at 6 ka

elasticity of mg0 87fe0 13 2sio4 wadsleyite to 12 gpa and 1073 k abstract elasticity of mg0 87fe0 13 2sio4 wadsleyite has been measured at simultaneous high pressure and high temperature to 12 gpa and 1073 k using ultrasonic interferometry in conjunction with synchrotron x radiation the elastic moduli and their pressure and temperature derivatives are precisely determined using pressure standard free third order and fourth order finite strain equations combined with previous thermoelastic data on olivine the density velocity and acoustic impedance contrasts between and mg0 9fe0 1 2sio4 at 410 km depth are calculated along a 1673 k adiabatic geotherm both the third and fourth order finite strain equation fitting results give estimation of 33 58 olivine content in the upper mantle to account for a seismic discontinuity of 5 velocity jumps and 8 5 p wave and 11 1 s wave impedance jumps at 410 km depth

the structure and sharpness of mg fe 2sio4 phase transformations in the transition zone abstract to calculate accurately the pressure interval and mineral proportions i e yields across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non ideality of fe mg mixing in these mg fe 2 sio 4 solid solutions in order to constrain the activity composition relations that describe non ideal mixing fe mg partitioning experiments have been conducted between magnesiowustite and mg fe 2 sio 4 olivine wadsleyite and ringwoodite as a function of pressure at 1400 c using known activity composition relations for magnesiowustite the corresponding relations for the three polymorphs were determined from the partitioning data in all experiments the presence of metallic iron ensured redox conditions compatible with the earth s transition zone the non ideality of the mg fe 2 sio 4 solid solutions was found to decrease in the order w wadsleyite femg w ringwoodite femg w olivine femg these partitioning data were used along with published phase equilibria measurements for the mg 2 sio 4 and fe 2 sio 4 end member transformations to produce an internally consistent thermodynamic model for the mg 2 sio 4 fe 2 sio 4 system at 1400 c using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations by combining these results with fe mg partitioning data for garnet the widths of transition zone phase transformations in a peridotite composition were calculated the olivine to wadsleyite transformation at 1400 c in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation this transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow the entire range of estimated widths for the 410 km discontinuity 4 35 km could therefore be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and h 2 o contents the wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400 c this transformation yield was also found to be near linear

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

possible role of atmosphere biosphere interactions in triggering the last glaciation we coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system at the time of glacial inception 115 000 years ago orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present atmospheric composition oceans biosphere and cryosphere summers were however cold enough to induce major vegetation shifts in high northern latitudes southward migration of the boreal forest tundra limit helped to create favourable conditions for continental ice sheet growth with increasing snow depth and duration in labrador arctic canada and northern western fennoscandia these results support a role for biogeophysical feedback in initiating glaciations

simulated warm polar currents during the middle permian 1 during permian stage 6 wordian kazanian the pangaean supercontinent was surrounded by a superocean panthalassa an ocean general circulation model has been coupled to an atmospheric energy balance model to simulate the sensitivity of the wordian climate 265 million years ago to changes in greenhouse gas concentrations high latitude geography and earth orbital configurations the model simulates significantly different circulation features with different levels of greenhouse gas forcing ranging from a strong meridional overturning circulation in the southern hemisphere at low co2 concentration present level to more symmetric overturning circulation cells with deep water formation in polar latitudes of both hemispheres at high co2 concentration 8 times present level the simulated climate with 4 times present level co2 concentration agrees generally well with climate sensitive sediments and phytogeographic patterns the model simulates strong subtropical gyres with similarities to the modern south pacific circulation and moderate surface temperatures on the southern continent gondwana resulting from a strong poleward heat transport in the ocean an even more moderate climate is generated if high latitude land is removed from the southern continent so that ocean currents can penetrate into the polar regions of gondwana

timing of the tsergo ri landslide langtang himal determined by fission track dating of pseudotachylyte abstract fission track dating was carried out on zircon grains from pseudotachylyte associated with a late pleistocene landslide tsergo ri landslide in langtang himal nepal zircon grains were separated from an injection pipe of glassy and vesicular pseudotachylyte about 10 cm in diameter the resulting age of 51 13 ka lies between the two subpeaks 70 and 20 ka of the wurm glacial period and is concordant with the previous age estimate from geomorphological evidence i e older than 25 30 ka this is the first reliable isotopic age for a landslide generated pseudotachylyte excluding the possibility of contamination by an inherited age

the response of northern hemisphere extratropical climate and vegetation to orbitally induced changes in insolation during the last interglaciation abstract the last interglaciation substage 5e provides an opportunity to examine the effects of extreme orbital changes on regional climates we have made two atmospheric general circulation model experiments p t approximated the northern hemisphere seasonality maximum near the beginning of 5e p t approximated the minimum near the end of 5e simulated regional climate changes have been translated into biome changes using a physiologically based model of global vegetation types major climatic and vegetational changes were simulated for the northern hemisphere extratropics due to radiational effects that were both amplified and modified by atmospheric circulation changes and sea ice feedback p t showed mid continental summers up to 8 c warmer than present mid latitude winters were 2 4 c cooler than present but in the arctic summer warmth reduced sea ice extent and thickness producing winters 2 8 c warmer than present the tundra and taiga biomes were displaced poleward while warm summer steppes expanded in the mid latitudes due to drought p t showed summers up to 5 c cooler than present especially in mid latitudes sea ice and snowpack were thicker and lasted longer polar desert tundra and taiga biomes were displaced equatorward while cool summer steppes and semideserts expanded due to the cooling a slight winter warming in mid latitudes however caused warm temperate evergreen forests and scrub to expand poleward such qualitative contrasts in the direction of climate and vegetation change during 5e should be identifiable in the paleorecord

phase transformations in a harzburgite composition to 26 gpa implications for dynamical behaviour of the subducting slab abstract the mineralogy adopted by a depleted harzburgite composition has been studied over the pressure interval 5 26 gpa at temperatures of 1300 1400 c the pyroxene garnet component of the harzburgite composition harzburgite minus 82 wt olivine transforms to majorite garnet by 18 19 gpa and further disproportionates to the assemblage of garnet stishovite mg 2 sio 4 spinel above 20 gpa at still higher pressures first ilmenite 22 24 gpa and then perovskite mgsio 3 24 26 gpa are found to coexist with garnet garnet disappears at 26 gpa and almost complete transition to perovskite is achieved at this pressure the mineral proportions and density profiles in the subducting oceanic lithosphere modelled by a combination of 80 harzburgite 20 primitive morb compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km under isothermal conditions the slab has a density similar to surrounding mantle to a depth of 600 km however between 600 and 700 km the slab is up to 0 08 g cm 3 denser than surrounding mantle this is caused primarily by the higher alumina content in pyrolite as compared to harzburgite which causes the transition to perovskite in pyrolite to occur at substantially higher pressures than in harzburgite the presence of alumina also smears out the garnet perovskite transition in pyrolite over a depth interval of 50 km whereas this transformation is much sharper in the harzburgite composition calculations based on the observed phase equilibria also show that a subducted cool slab remains much denser by 0 1 0 3 g cm 3 than surrounding mantle to a depth of 700 km but possesses a density similar to surrounding mantle below this depth these results have important implications for the dynamical behaviour of slabs possessing different thermal regimes when they encounter the 670 km discontinuity and also for the nature of this discontinuity

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

upper mantle discontinuity topography from thermal and chemical heterogeneity using high resolution stacks of precursors to the seismic phase ss we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers km deep within earth beneath south america and the surrounding oceans detailed maps of phase boundary topography revealed deep 410 and 660 km discontinuities in the down dip direction of subduction inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature in some regions multiple reflections from the discontinuities were detected consistent with partial melt near 410 km depth and or additional phase changes near 660 km depth thus the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes

fission track age 400 000 yr of the rockland tephra based on inclusion of zirco grains lacking fossil fission tracks abstract a zircon fission track age of about 400 000 yr b p has been determined for the rockland tephra a widespread pyroclastic layer in northern california and western nevada new ages of zircon separates from both proximal and distal exposures of this layer range from 370 000 to 460 000 yr ages of the best material provide a narrower range from 370 000 yr for unwelded ash flow tuff to 420 000 yr for distal air fall ash that appears to be uncontaminated by clastic detritus or xenocrysts detrital or xenocrystic grains in the ash flow tuff may have been annealed during emplacement and cooling of the tuff detrital and xenocrystic zircons are identified on the basis of their physical characteristics and distinctly older ages independent stratigraphic and magnetostratigraphic data constrain the age of the rockland tephra between 300 000 and 600 000 yr a range that is compatible with the fission track age zircon grains containing no spontaneous fossil tracks are regarded as part of the normal population of comagmatic grains because maximum ages calculated for these grains form a population that mimics the distribution of ages of individual zircon grains that contain fossil tracks modal ages of both groups fall between 250 000 and 500 000 yr induced fission tracks from grains that lack fossil tracks are included in the age calculations resulting in significantly younger and more coherent dates than would result if these tracks had been omitted especially those of the finer grained distal samples

influence of insolation and glaciation on atmospheric circulation in the north atlantic sector implications of general circulation model experiments for the late quaternary climatology of europe abstract atmospheric general circulation models have been used to simulate the sensitivity of regional climates to late quaternary changes in insolation ice sheets and atmospheric co 2 model results for full glacial conditions 18 ka show the atlantic westerly jet strengthened and shifted south a corresponding southward shift of the icelandic low and a strengthening and northward shift of the subtropical anticyclone sta a glacial anticyclone developed over the european ice sheet and cold dry conditions prevailed over much of europe the full glacial climate anomaly for the north atlantic sector is explained by a combination of low atmospheric co 2 reducing global surface temperatures and circulation changes caused by the ice sheets by the early holocene 9 ka the ice sheets were much reduced while the orbital anomaly was near its maximum producing mid continental summer warming and winter cooling and a reduced latitudinal temperature gradient in the northern hemisphere in both seasons the jet and the icelandic low were displaced to north of their present position producing strong onshore flow and mild wet winters in northern europe while the sta was also shifted northwards producing offshore flow and dry summers in the same region during the late glacial transition the effects of insolation and glaciation were antagonistic for some features of the circulation and synergistic for others the model results suggest palaeoclimatic hypotheses that could be directly tested by comparison with palaeoclimatic data mapped at a synoptic scale

temperature trends during the present and last interglacial periods a multi model data comparison though primarily driven by insolation changes associated with well known variations in earth s astronomical parameters the response of the climate system during interglacials includes a diversity of feedbacks involving the atmosphere ocean sea ice vegetation and land ice a thorough multi model data comparison is essential to assess the ability of climate models to resolve interglacial temperature trends and to help in understanding the recorded climatic signal and the underlying climate dynamics we present the first multi model data comparison of transient millennial scale temperature changes through two intervals of the present interglacial pig 8 1 2 ka and the last interglacial lig 123 116 2 ka periods we include temperature trends simulated by 9 different climate models alkenone based temperature reconstructions from 117 globally distributed locations about 45 of them within the lig and 12 ice core based temperature trends from greenland and antarctica 50 of them within the lig the definitions of these specific interglacial intervals enable a consistent inter comparison of the two intervals because both are characterised by minor changes in atmospheric greenhouse gas concentrations and more importantly by insolation trends that show clear similarities our analysis shows that in general the reconstructed pig and lig northern hemisphere mid to high latitude cooling compares well with multi model mean temperature trends for the warmest months and that these cooling trends reflect a linear response to the warmest month insolation decrease over the interglacial intervals the most notable exception is the strong lig cooling trend reconstructed from greenland ice cores that is not simulated by any of the models a striking model data mismatch is found for both the pig and the lig over large parts of the mid to high latitudes of the southern hemisphere where the data depicts negative temperature trends that are not in agreement with near zero trends in the simulations in this area the positive local summer insolation trend is counteracted in climate models by an enhancement of the southern ocean summer sea ice cover and or an increase in southern ocean upwelling if the general picture emerging from reconstructions is realistic then the model data mismatch in mid and high southern hemisphere latitudes implies that none of the models is able to resolve the correct balance of these feedbacks or alternatively that interglacial southern hemisphere temperature trends are driven by mechanisms which are not included in the transient simulations such as changes in the antarctic ice sheet or meltwater induced changes in the overturning circulation

the boreal forest and the polar front the analysis presented in this paper suggests that the larger heating over the boreal forest in the spring and summer as contrasted with weaker heating over the adjacent tundra results in a preferred position of the polar front along the northern edge of the boreal forest this positioning is well documented in the literature see for example bryson 1966 barry and hare 1974 kreps and barry 1970 this heating results from the lower albedo of the boreal forest which is not compensated by an increase in transpiration even with the larger leaf area index of the forest the warmer temperatures are mixed upward by the deep boundary layer over the forest and mesoscale circulations which result from the patchiness of heating associated with the heterogeneous landscapes of the forest thus in contrast to previous assumptions in which the arctic front position in the summer determines the northern limit of the boreal tree line our study suggests the boreal forest itself significantly influences the preferred position of the front this conclusion reinforces the findings of bonan et al 1992 and foley et al 1994 on the important role of boreal forest tundra interactions with climate

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

both differential and equatorial heating contributed to african monsoon variations during the mid holocene the sahara was significantly greener 11 5 kya and during multiple earlier interglacial periods but the mechanisms related to the greening of the sahara remain uncertain as most climate models severely underestimate past wet conditions over north africa the variations in the african monsoon related to the greening of the sahara are thought to be associated with the variations in the inter hemispheric differential heating of earth caused by orbital variations however how orbital variations affect regional climate is not well understood using recent theory that relates the position of the tropical rain belt to the atmospheric energy budget we study the effect of orbital forcing during the mid holocene on the african monsoon in simulations provided by the third phase of the paleo model intercomparison project pmip3 we find that energy fluxes in the african sector are related to orbital forcing in a complex manner contrary to generally accepted theory orbital modulation of seasonal differential heating alone is shown to be a weak driver of african monsoon variations instead net atmospheric heating near the equator which modulates the intensity and extent of seasonal migrations of the tropical rain belt is an important but overlooked driver of african monsoon variations a conceptual framework that relates african monsoon variations to both equatorial and inter hemispheric differential solar heating is presented

magnetostratigraphic lithostratigraphic and tephrostratigraphic constraints on lower and middle pleistocene sea level changes wanganui basin new zealand wanganui basin north island new zealand contains a complex sedimentary record of lower and middle pleistocene sea level changes palaeomagnetic results allow identification of the matuyama brunhes transition the jaramillo subchron and the cobb mountain subchron correlations of rhyolitic tuff horizons across the basin are consistent with magnetostratigraphic correlations between sections isothermal plateau fission track itpft ages of 1 05 0 05 ma and 1 63 0 15 ma on two tuffs potaka pumice and pakihikura pumice respectively are consistent with the interpreted magnetostratigraphy and also with the astronomically tuned timescale of odp site 677 magnetostratigraphy and itpft ages allow correlation of sedimentary cycles at wanganui with odd numbered oxygen isotope stages 17 31 in deep sea cores the stratotype section for the new zealand castlecliffian stage is shown to be incomplete relative to other studied sections in the basin below stage 31 the character of the cyclothems changes at wanganui from marine dominated to a greater representation of non marine and estuarine strata this change may be partly related to a change in amplitude and frequency of climatic cycles identified in oxygen isotope records but the primary cause is likely to be increased basinal uplift

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

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

dating early and middle reid pleistocene glaciations in central yukon by tephrochronology abstract the late cenozoic deposits of central yukon contain numerous distal tephra beds derived from vents in the wrangell mountains and aleutian arc alaska peninsula region we use a few of these tephra beds to gain a better understanding on the timing of extensive pleistocene glaciations that affected this area exposures at fort selkirk show that the cordilleran ice sheet advanced close to the outer limit of glaciation about 1 5 myr ago at the midnight dome terrace near dawson city exposed outwash gravel aeolian sand and loess related to valley glaciers in the adjacent ogilvie mountains are of the same age reid glacial deposits at ash bend on the stewart river are older than oxygen isotope stage ois 6 and likely of ois 8 age that is about 250 000 yr b p supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the gulf of alaska at 1 5 and 0 25 myr b p

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

holocene paleohydrology and paleoclimate at treeline north central russia inferred from oxygen isotope records in lake sediment cellulose lake water oxygen isotope histories for three lakes in northern russia derived from the cellulose oxygen isotope stratigraphies of sediment cores provide the basis for preliminary reconstruction of holocene paleohydrology in two regions along the boreal treeline deconvolution of shifting precipitation 18o from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation the isotopic composition of paleo waters preserved in frozen peat deposits as well as other supporting paleoclimatic information these data indicate that during the early holocene when the boreal treeline advanced to the current arctic coastline conditions in the lower yenisey river region were moist compared to the present whereas greater aridity prevailed to the east near the lower lena river this longitudinal moisture gradient is consistent with the suggestion that oceanic forcing increased sea surface temperatures in the nordic seas and reduced sea ice cover was a major contributor to the development of a more maritime climate in western eurasia in addition to increased summer insolation east of the taimyr peninsula large tracts of the continental shelf exposed by glacial sea level drawdown may have suppressed maritime climatic influence in what are now coastal areas in contrast during the late holocene the two regions have apparently experienced coherent shifts in effective moisture the similarity of the records may primarily reflect reduced north atlantic influence in the nordic seas and southward retreat of coastline in eastern siberia coupled with declining summer insolation

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

impacts of snow and glaciers over tibetan plateau on holocene climate change sensitivity experiments with a coupled model of intermediate complexity 1 an earth system model of intermediate complexity has been used to investigate the sensitivity of simulated global climate to gradually increased snow and glacier cover over the tibetan plateau for the last 9000 years 9 kyr the simulations show that in the mid holocene at about 6 kyr before present bp the imposed ice sheets over the tibetan plateau induces summer precipitation decreases strongly in north africa and south asia and increases in southeast asia the response of vegetation cover to the imposed ice sheets over the tibetan plateau is not synchronous in south asia and in north africa showing an earlier and hence a more rapid decrease in vegetation cover in north africa from 9 to 6 kyr bp while it has almost no influence on that in south asia until 5 kyr bp the simulation results suggest that the snow and glacier environment over the tibetan plateau is an important factor for holocene climate variability in north africa south asia and southeast asia

reconstruction of holocene precipitation patterns in europe using pollen and lake level data abstract lake level data can be used to refine palaeoclimate reconstructions based on pollen data this approach is illustrated for the european holocene estimates of p pet precipitation minus potential evapotranspiration were first inferred from modern pollen analogues the pollen based estimates were then compared with the status of lakes within a 5 radius analogues with p pet anomalies inconsistent with the lake level changes were rejected the constrained sets of analogues were used to estimate continental scale patterns of annual mean temperature and annual precipitation at 3000 yr intervals estimated temperature anomalies differed only slightly from the unconstrained reconstructions estimated precipitation anomalies however showed improved spatial coherence and increased regional contrast and were occasionally reversed in sign the effect of the constraint was to impose a rational selection among almost equally similar modern pollen analogues with similar temperatures but widely varying moisture regimes the resulting maps showed clear spatially coherent patterns of change in precipitation as well as temperature suitable for comparison with climate model results further improvement of these maps will become possible as a more extensive coverage of lake level data is obtained

elastic properties of iron bearing wadsleyite to 17 7 gpa implications for mantle mineral models abstract the sound velocities and single crystal elastic moduli of iron bearing wadsleyite with fe fe mg molar ratio of 0 075 have been measured by brillouin scattering experiments at high pressures up to 17 7 gpa pressure derivatives for the adiabatic bulk modulus k s0 and shear modulus 0 are 4 1 1 and 1 45 4 respectively a comparison of our results with previous brillouin scattering results on the mg end member wadsleyite shows that incorporating 7 5 mol iron in wadsleyite at high pressure conditions decreases the shear moduli by 4 5 but does not have a discernable effect on the bulk modulus the effects of iron on the elastic moduli of wadsleyite at ambient pressure persist to high pressure conditions at a relatively constant level using our results on iron bearing wadsleyite at high pressure we conclude that less olivine than in the pyrolite model of mantle composition provides a satisfactory explanation for 410 km seismic discontinuity at the top of the transition zone

evaluation of coupled ocean atmosphere simulations of the mid holocene using palaeovegetation data from the northern hemisphere extratropics we have used the biome4 biogeography biochemistry model and comparison with palaeovegetation data to evaluate the response of six ocean atmosphere general circulation models to mid holocene changes in orbital forcing in the mid to high latitudes of the northern hemisphere all the models produce a a northward shift of the northern limit of boreal forest in response to simulated summer warming in high latitudes the northward shift is markedly asymmetric with larger shifts in eurasia than in north america b an expansion of xerophytic vegetation in mid continental north america and eurasia in response to increased temperatures during the growing season c a northward expansion of temperate forests in eastern north america in response to simulated winter warming the northward shift of the northern limit of boreal forest and the northward expansion of temperate forests in north america are supported by palaeovegetation data the expansion of xerophytic vegetation in mid continental north america is consistent with palaeodata although the extent may be over estimated the simulated expansion of xerophytic vegetation in eurasia is not supported by the data analysis of an asynchronous coupling of one model to an equilibrium vegetation model suggests vegetation feedback exacerbates this mid continental drying and produces conditions more unlike the observations not all features of the simulations are robust some models produce winter warming over europe while others produce winter cooling as a result some models show a northward shift of temperate forests consistent with though less marked than the expansion shown by data and others produce a reduction in temperate forests elucidation of the cause of such differences is a focus of the current phase of the palaeoclimate modelling intercomparison project

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

early to middle pleistocene tephrochronology of north island new zealand implications for volcanism tectonism and paleoenvironments thick volcaniclastic sequences of early to middle pleistocene age in southern north island new zealand contain rhyolitic tephra beds that record the early history of the taupo volcanic zone tvz at least 54 different tephra beds are recorded and their chronology is defined by glass fission track ages and paleomagnetism the tephra beds span the interval ca 2 0 0 6 ma and provide an event frequency of 1 19 k y significantly higher than the frequency of sheet forming ignimbrites preserved in the tvz at this time 1 100 k y the distal tephra beds thus provide a record of volcanism not revealed in the proximal volcanic region and suggest a major period of explosive activity at ca 1 79 1 60 ma several important marker horizons are identified pakihikura tephra 1 63 ma mangatewaiiti tephra 1 24 ma potaka tephra 1 00 ma kidnappers b tephra 1 00 ma and kaukatea tephra 0 88 ma these tephra beds allow direct correlation between 1 marine and nonmarine facies and 2 the fore arc and back arc regions of new zealand the tephra beds provide a framework for a paleoenvironmental reconstruction of the southern north island volcaniclastic transport routes from the tvz to basins in the south and southeast and through the site of present mountain ranges supplied material to a terrestrial lowland fore arc area in the interval 1 64 0 7 ma uplift and deformation since 0 7 ma have disrupted paleodrainage routes diverting them to the north and southwest

revision of the marine chronology in the wanganui basin new zealand based on the isothermal plateau fission track dating of tephra horizons abstract the occurrence of tephra horizons in basins adjacent to volcanic arcs provide an excellent opportunity for establishing a reliable chronostratigraphic framework for detailed sedimentological studies in this study three widespread and stratigraphically important rhyolitic tephra horizons interbedded in plio pleistocene strata of the wanganui basin new zealand are dated by application of the isothermal plateau fission track itpft technique to hydrated glass shards all glass samples were corrected for annealing and consequently yield reliable ages rangitawa tephra yielded statistically indistinguishable ages from three localities that are in excellent agreement with recently determined zircon fission track age estimates of ca 0 35 ma itpft ages of 1 05 0 05 and 1 63 0 15 ma for potaka pumice and pakihikura pumice respectively are considerably older than previous ft estimates but consistent with new magnetostratigraphic data that places the potaka within the jaramillo subchron and pakihikura within the matuyama chron between the cobb mountain and olduvai subchrons combining our fission track ages with the magnetostratigraphy the true age of sediments within the wanganui basin is found to be significantly underestimated sedimentation rates of between ca 680 630 m ma from 1 63 ma to 0 35 ma are calculated in the eastern part of the basin and are much lower than those calculated using the previous ft chronology this new itpft age data demonstrates that the existing plio pleistocene marine chronology in new zealand will require age revision and has important implications when considering the evolution of several other sedimentary basins in southern north island that contain the same itpft dated tephra horizons

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

zircon fission track thermochronology and applications to fault studies zircon is one of the most useful minerals used to unravel the earth s history recorded in rocks after the success of etching fission tracks in zircon fleischer et al 1964 naeser 1969 krishnaswami et al 1974 early studies focused primarily on dating young volcanic horizons for stratigraphic purposes e g naeser et al 1973 hurford et al 1976 seward 1979 gleadow 1980 kowallis et al 1986 kohn et al 1992 subsequently fission track analysis of zircon has been extensively employed along with other radiometric dating methods such as u pb and u th he techniques e g davis et al 2003 reiners 2005 to understand the thermochronology of rocks in a variety of geological settings i e thermal history analysis of basement rocks for orogenic studies e g zeilter et al 1982 hurford 1986 kamp et al 1989 sorkhabi 1993 seward and mancktelow 1994 hasebe and tagami 2001 spikings et al 2001 thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults which will be highlighted below in this present chapter the thermal sensitivity of the zircon fission track thermochronometry is reviewed in the context of laboratory and field studies then laboratory procedures of the zircon fission track analysis using the external detector method are outlined as practiced in the fission track laboratory of kyoto university for basic fundamentals of these fission track analyses including data analysis and graphical displays see the chapter by tagami and o sullivan 2005 finally as an example of recent geological applications of the technique the results of zircon fission track analysis of the nojima fault zone japan are presented these rocks were the target of systematic drilling of an active fault system using five boreholes and a trench applications to other geological settings and the