does an asymmetric thermohaline ice sheet oscillator drive 100 000 yr glacial cycles a hypothesis is presented that late quaternary 100 000 yr glacial cycles are driven by an asymmetric thermohaline ice sheet oscillator that emerged in the global climate system 650 000 950 000 yr ago perhaps when the main source of northern hemisphere deep water production shifted south from the arctic into the nordic seas it is hypothesised that the asymmetry is due to the increasing difficulty after 950 000 years ago of resetting an interglacial mode of the critical nordic limb of the salinity conveyor once it switches off and an ensuing iceberg flux enters the areas of downwelling a possible reason for both a southward shift and the resulting asymmetry is uplift of the greenland scotland submarine ridge from activity of the iceland mantle plume in this hypothesis an individual 100 000 yr glacial cycle begins when the northernmost limb of the salinity conveyor in the nordic seas is curtailed or even switched off perhaps due to the growing strength of competing antarctic bottom water aabw generated by interglacial recession of the west antarctic ice sheet wais from the west antarctic rift system such recession produces southern marginal seas where dense shelf water can collect and overflow into the abyss when northern ice sheets nucleated by this circulation switch develop marine components that calve icebergs into the nordic seas the salinity conveyor can no longer revert to an interglacial mode from orbital forcing as it did prior to 950 000 yr ago in order to reset an interglacial circulation mode of the conveyor ice sheets must continue to grow for 100 000 years until they capture enough excess volume to produce a gravitational collapse of marine based components so massive that all grounded ice is flushed from north atlantic continental shelves the outburst of icebergs produced by this collapse cripples the glacial mode of overturning in the northern north atlantic once this collapse ends however the nordic seas become nearly free of icebergs for the first time in 100 000 years because of the depletion of adjacent marine based components as a consequence north atlantic salinity increases rapidly switching the conveyor into a vigorous interglacial mode of operation and hence terminating the glacial cycle by lowering sea level the prolonged growth of northern hemisphere ice sheets during each 100 000 yr cycle drives antarctic grounding lines seaward across continental shelves squeezing off the source of densified shelf waters that feed aabw sea level rise and increased basal melting however caused by the subsequent collapse of northern ice sheets and the reintroduction of north atlantic deep water into the southern ocean reverses the process forcing retreat of antarctic grounding lines from their advanced last glacial maximum positions this retreat opens marginal seas for renewed formation of dense shelf water by expanding marginal seas and hence the source of dense shelf water ongoing recession of the wais strengthens aabw during the course of an interglaciation eventually forcing a thermohaline circulation switch in the nordic seas and initiating yet another 100 000 yr glacial cycle the 100 000 yr duration of each cycle is set by two factors inertia is built into the system by the long time required for ice sheets to grow to the excess volume necessary for a marine collapse that resets the salinity conveyor into an interglacial mode eccentricity driven changes in the amplitude of the precession or tropical half precession signal give rise to warming events that trigger such a collapse of excess ice about each 100 000 yr

are we studying deformed rocks in the right sections best practices in the kinematic analysis of 3d deformation zones abstract a standard procedure in kinematic analyses of deformed rocks is studying samples only on the foliation perpendicular lineation parallel section based on the assumption that the rotational component of deformation is restricted to that plane the theoretical background for this procedure is that deformation is plane strain which is often useful but fails to account for all relevant features observed in many natural cases more general 3d kinematic models reproduce several of these features and help to better understand 3d deformation likely predominant in nature so they are a more appropriate starting point for deformation zone analysis theoretical and natural 3d deformation examples suggest that the section with highest degree of asymmetry the vorticity normal section vns and the corresponding vorticity vector are independent from the finite strain fabric and thus may present varied orientations with respect to the tectonic foliation and lineation the vns orientation depends on the kinematics resulting from boundary conditions whereas the strain fabric orientation also depends on accumulated strain the orientation of the vns is itself an essential element of shear zone kinematics hence it cannot be pre assumed but must be determined independently

biogenic silica record of the lake baikal response to climatic forcing during the brunhes abstract this work presents a detailed orbitally tuned biogenic silica record of continental paleoclimate change during the brunhes chron the brunhes matuyama boundary lies within the warm isotopic stage 19 in baikal and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record the high amplitude and resolution of climatically driven changes in biosi content in lake baikal sediments permits tuning of almost every precessional cycle during the brunhes and reveals the structure of interglacial stages for example the last three interglacial stages mis 5 7 and 9 clearly consist of five substages a b c d e corresponding to precessional insolation peaks abrupt and intense regional glaciations in siberia during substages 5d and 7d were driven by extreme insolation minima during substage 9d cooling was more gradual in response to more moderate forcing the impact of strong glaciation is also observed in the middle of stage 15 where full glacial conditions appear to have lasted for over 30 000 yr during substages 15d 15c and 15b marine oxygen isotopic stage 11 appears to be the warmest period during the brunhes in the lake baikal record with at least three substages a new hypothesis is presented regarding the response of the lake baikal biosi record to insolation forcing based on the mechanism controlling modern diatom blooms biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column this mechanism is also sensitive to short term sub milankovich cooling events such as the mid eemian cooling the montaigu event during substage 5c and a cooling which appears to be analogous to the montaigu event during substage 9c the continuity of the lake baikal paleoclimate record its sensitivity to orbital forcing and its high resolution make it an excellent candidate for a new paleoclimatic stratotype section for continental asia

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

vegetation and climate dynamics during the holocene and eemian interglacials derived from lake baikal pollen records abstract the last interglacial li and holocene changes in annual precipitation p ann the mean temperature of the warmest t w and coldest t c month and the moisture index were reconstructed from continuous pollen records from lake baikal the holocene core 52 31 n 106 09 e presented in this study was recovered from a depth of 355 m in the 25 km wide underwater buguldeika saddle separating the southern sub basin of lake baikal from its central sub basin the biome reconstruction shows that tundra and steppe biomes have highest scores during ca 15 000 13 300 cal years b p and that taiga becomes a dominant vegetation type after ca 13 300 cal years b p our quantitative reconstruction indicates an onset of relatively warm and wet conditions soon after ca 10 000 cal years b p the warmest and wettest climate with t w 16 c p ann 480 mm and 0 9 1 has been reconstructed for ca 9000 7000 cal years b p in the lake baikal region this interval is characterized by the appearance and spread of hunter communities kitoi culture consistently a hiatus in the regional archaeological record 4900 4200 years b c or 6850 6150 cal years b p coincides with the interval of a major climate deterioration which followed the climatic optimum an attempt to find a relationship between the archaeological record and a spread of steppe and meadow communities in the lake baikal region demonstrates that despite a long habitation of the area the human impact on vegetation was local rather than regional and likely did not affect the pollen record from lake baikal the reconstructed peaks in the steppe biome scores during the last 9000 years are consistent with short one to five hundred year episodes of weak pacific summer monsoon supporting our interpretation that the holocene vegetation changes around lake baikal are associated with large scale circulation processes controlling regional water balance rather than with human activities thus our study proves the suitability of lake baikal pollen data for the reconstruction of natural vegetation and climate dynamics through the whole period from the onset of the li to the present comparison of the recent and the last interglacial suggests that the holocene climatic optimum was less pronounced e g lower summer and winter temperatures and annual precipitation sums than that of the li on the other hand pollen records demonstrate that the holocene forest phase already lasts some thousand years longer than that of the li the interglacial vegetation dynamics derived from the lake baikal pollen records can be satisfactorily explained by reconstructed changes in summer and winter temperatures and in available moisture the interglacial vegetation around lake baikal is dominated by the boreal forests which are associated with a generally warm and wet climate the high sea level associated with decreased ice volume appears to have had a greater impact on the siberian environments during the last and the recent interglacial than the direct effect of lower than present winter insolation reconstructed changes in the winter temperature correlate well with changes in the sea level and global ice volume while the summer temperatures derived from the lake baikal pollen records track changes in the summer insolation

weathering and evolution of soils formed on granitic glacial deposits results from chronosequences of swiss alpine environments abstract two soil chronosequences of mountainous ecosystems in switzerland served as the basis to calculate the accumulation of soil organic matter transformation of pedogenic fe and al and net losses of the main elements ca mg k na fe al mn and si by means of mass balance calculations elemental losses due to deglaciation and exposure to the weathering environment were calculated these mass balance calculations indicate that extensive mineral weathering resulted in significant leaching losses of si major base cations and al particularly from the upper horizons the losses are especially pronounced in the early stages of soil formation in most cases the exponential decay model incorporating an asymptotic or logarithmic regression model seems to provide a good description of weathering the greatest changes in the soil chemistry of these alpine soils on granitic host material occurred within the first 3000 4000 years of soil development later the weathering rates decreased rapidly and the overall depletion of elements nearly reached an asymptote we also found that the mean ratio of al t fe d al d fe t of the fine earth of the a e and b horizons is closely linked to the duration of soil development a very rapid decrease of this ratio also occurred at the beginning of soil evolution in order to reach asymptotic values after about 3000 years consequently this ratio could be a good indicator of the age of alpine soils furthermore there is a close relationship between the mass of organic c or n in the whole profile and the soil age the older the soil the higher the corresponding mass per unit area the chronofunctions presented give a first attempt of the chemical soil evolution in the alps however only little data has been available up until now regarding alpine soils and this fact inhibits a more detailed observation of the changes that have occurred over a period of 2000 8000 years of soil formation under similar climatic conditions

high resolution record of climate stability in france during the last interglacial period the last interglacial period 127 110 kyr ago has been considered to be an analogue to the present interglacial period the holocene which may help us to understand present climate evolution but whereas holocene climate has been essentially stable in europe variability in climate during the last interglacial period has remained unresolved because climate reconstructions from ice cores1 2 continental records3 4 and marine sediment cores5 6 give conflicting results for this period7 here we present a high resolution multi proxy lacustrine record of climate change during the last interglacial period based on oxygen isotopes in diatom silica diatom assemblages and pollen climate transfer functions from the ribains maar in france contrary to a previous study8 our data do not show a cold event interrupting the warm interglacial climate instead we find an early temperature maximum with a transition to a colder climate about halfway through the sequence the end of the interglacial period is clearly marked by an abrupt change in all proxy records our study confirms that in southwestern europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate

the determination of true shear senses from the deflection of passive markers in shear zones the sense of movement in shear zones can often be determined from the reorientation of pre existing planar or linear features within the zone this cannot always be done simply by examining the change in strike or trend of these features sometimes these will show the opposite sense of rotation to the true sense of shear in the zone this is illustrated for a generalized oblique slip zone using the deflection method9 described here the true movement sense can be deduced from the apparent rotation the emphasis being on a three dimensional approach consideration of the movement on a large scale shear zone the laxford front underlines the importance of being aware of this aspect of shear zone geometry the method may be applied to brittle fault offsets as well as to deflections in ductile shear zones

the paleoclimatology of lake baikal a diatom synthesis and prospectus abstract the paleoclimatic archive held in lake baikal sediments is of significant importance given the lake s position in one of the world s most continental regions where there are few continuous high quality records spanning the quaternary here i review diatom and associated biogenic silica records from lake baikal sediments and provide a paleoclimatic synthesis of changes at various timescales over the quaternary i initially highlight major climatic and hydrological aspects of lake baikal as understanding the contemporary system both regionally and within the lake are fundamental to understanding past change interpreted from the sedimentary archive in this respect special attention is given to factors that can affect the integrity of the diatom record most notably dissolution processes these mechanisms are likely to have had a relatively greater impact on the preservation of diatom valves during glacial periods because of overall lower diatom productivity lower diatom numbers and relative increased dissolution during cold periods explains the lack of diatoms and low biogenic silica concentrations found in the lake sediments during glacial periods the biogenic record highlights the nature of the 100 ka cycle especially during the last 800 ka although there is also a strong precessional component further work is needed to reassess biological responses in lake baikal with respect to different orbital forcing mechanisms together with their impacts on evolution and speciation of diatoms the biological record from lake baikal confirms that the last interglacial in central asia lasted approximately 10 5 ka productivity in the lake as inferred from diatom biovolume accumulation rates exhibits millennial scale variability with the occurrence of centennial scale reductions in diatom biomass throughout the last interglacial period the most severe reduction in diatom biomass at c 120 ka bp is concurrent with millennial scale cooling in the north atlantic region links to changes in north atlantic ocean thermohaline circulation via teleconnections are also evident in the nature of the abrupt ecological changes in the lake throughout the last 60 ka linked to ice rafting into the north atlantic otherwise known as heinrich events new robust radiocarbon chronologies for sediments deposited during the late glacial and holocene in lake baikal allow detailed multi decadal records to be constructed for the last 14 000 years cooling events associated with millennial scale cycles are also apparent in the lake baikal record and both the diatom record and oxygen isotope record of the diatom silica highlight that biological responses to these abrupt events are almost simultaneous comparisons made between lake baikal records with others worldwide highlights that many of the holocene cooling events are associated with melt water outburst from the laurentide ice sheet and changes in solar insolation during the last 1000 years snow cover on lake baikal has been inferred from past diatom assemblages and is closely linked to weakening of the north atlantic oscillation allowing increasing intensity of the siberian high to develop and during the 17th and 18th centuries in the last 150 years diatom species have been shown to be sensitive indicators of recent warming however impacts from future global warming will be complex and are likely to impact not only on the balance between endemic and cosmopolitan diatoms throughout the lake but on the balance between siliceous and non siliceous algae and sources of primary productivity

structure of the penultimate deglaciation along the california margin and implications for milankovitch theory the detailed structure and timing of the penultimate deglaciation are insufficiently defined yet critical for understanding mechanisms responsible for abrupt climate change here we present oxygen isotope records from planktonic and benthic foraminifera at unprecedented resolution encompassing late marine oxygen isotope stage mis 6 and termination ii ca 150 120 ka from the santa barbara basin supported by additional southern california margin records a region highly sensitive to millennial scale climate oscillations during the last deglaciation these records reveal millennial and centennial scale climate variability throughout the interval including an interstadial immediately preceding the deglaciation a brief warm event near the beginning of termination ii and a bolling allerod younger dryas like climate oscillation midway through the deglaciation recognition of these events in an oxygen isotope record from a 230th dated stalagmite allows the adoption of this radiometric chronology for the california margin records this chronology supports the milankovitch theory of deglaciation the suborbital history of climate variability during termination ii may account for records of early deglaciation

interpretation of si concentrations in lake sediments three case studies the biogenic si concentration in a sediment can be determined as the non detrital si concentration by normalization of the total si concentration with al this procedure is based upon the assumptions that 1 that al exists predominantly in detrital i e minerogenic particles and 2 that biogenic si mainly diatom frustules is the dominating non detrital si phase this paper focuses on the reasons for the variations of the non detrital si concentration in these lake sediments data from three lakes are presented representing three principally different cases regarding the si concentration the processes controlling the concentrations of detrital and non detrital si are discussed

the dilemma of asymmetric porphyroclast systems and sense of shear abstract asymmetric porphyroclast systems have long been used as independent shear sense indicators based on their clast tail asymmetry and or stair stepping tail geometry over the last two decades advances in exploring the mechanical behavior of rigid clasts in a viscous flow has shed new light on understanding the formation of porphyroclast systems embedded in noncoaxial viscous flow and subsequently quantifying many aspects of flow kinematics using examples from naturally deformed rocks combined with results from recent advances our study indicates that 1 in general only porphyroclast systems composed of equant shaped clasts can be treated as independent shear sense indicators 2 special attention should be given to type porphyroclast systems composed of high angle intermediate aspect ratio clasts which may contain meaningful information on bulk flow kinematics 3 bookshelf structures cannot serve as independent shear sense indicators multi criteria and thorough three dimensional shape analyses are suggested for a proper interpretation of flow kinematics in ductile shear zones

magnetostratigraphic results from impact crater lake el gygytgyn northeastern siberia a 300 kyr long high resolution terrestrial palaeoclimatic record from the arctic summary a 12 7 m long sedimentary record recovered from lake el gygytgyn located in a meteorite impact crater created 3 6 ma in late cretaceous igneous rocks on chukotka peninsula northeast siberia has been analysed for its palaeo and rock magnetic properties continuous high resolution 1 mm measurements of magnetic susceptibility yielded successions of pronounced lows and highs analyses of the rock magnetic properties by low and high temperature runs of magnetic susceptibility determination of hysteresis parameters as well as irm acquisition experiments yielded a dominance of psd pseudo single domain magnetite in intervals of high magnetic susceptibility whereas due to selective magnetite dissolution associated with anoxic lake water and or pore water conditions during times of enhanced deposition of organic matter haematite dominates within low susceptibility intervals in terms of mass percentage here however magnetic properties are still dominated by magnetite five ams accelerator mass spectromentry 14 c ages eight irsl infrared stimulated luminescense ages together with preliminary pollen data suggest that variations in magnetite content reflect climatic variability of the last 300 ka with low high susceptibilities representing cold warm climates this pattern caused by a complex system of deposition preservation or decomposition of organic matter and or magnetic minerals in turn can be correlated in detail to global climate archives such as the oxygen isotope records from greenland ice cores and marine sediments respectively thus the sedimentary sequence recovered from lake el gygytgyn represents the longest continuous terrestrial climate record now available from the arctic

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

ice complex permafrost of mis5 age in the dmitry laptev strait coastal region east siberian arctic ice complex deposits locally known as the buchchagy ice complex are exposed at both coasts of the east siberian dmitry laptev strait and preserved below the yedoma ice complex that formed during mis3 and mis2 marine isotope stage and lateglacial holocene thermokarst deposits mis1 radioisotope disequilibria 230th u of peaty horizons date the buchchagy ice complex deposition to 126 16 13 kyr and 117 19 14 kyr until 98 5 kyr and 89 5 kyr the deposit is characterised by poorlysorted medium to coarse silts with cryogenic structures of horizontal ice bands lens like and lenslike reticulated segregation ice two peaty horizons within the buchchagy ice complex and syngenetic ice wedges 2e4 m wide up to 10 m high are striking the isotopic composition d18o dd of buchchagy ice wedge ice indicates winter conditions colder than during the mis3 interstadial and warmer than during mis2 stadial and similar atmospheric winter moisture sources as during the mis2 stadial buchchagy ice complex pollen spectra reveal tundra steppe vegetation and harsher summer conditions than during the mis3 interstadial and rather similar vegetation as during the mis2 stadial short term climatic variability during mis5 is reflected in the record even though the regional chronostratigraphic relationship of the buchchagy ice complex to the last interglacial remains unclear because numerical dating is widely lacking the present study indicates permafrost ice complex formation during mis5 sensu lato and its preservation afterwards palaeoenvironmental insights into past climate and the periglacial landscape dynamics of arctic lowlands in eastern siberia are deduced from the record

quartz content and the quartz to plagioclase ratio determined by x ray diffraction a proxy for ice rafting in the northern north atlantic many paleoceanographic reconstructions of the glacial north atlantic include estimates of iceberg discharge which are based on the variable abundance of ice rafted detritus ird in deep sea sediments ird abundance is most often determined by the mechanical separation and painstaking counting of terrigenous particles larger than a specified threshold grain size typically 150 mum here we present a new proxy for ird based on x ray diffraction xrd analysis of bulk sediments this approach complements results obtained from standard techniques while offering several distinct advantages in addition to the rapid production of objective data xrd measurements on bulk sediments are sensitive to a broader and more characteristic grain size range than counts of individual coarse lithic fragments the technique is demonstrated in a study of 12 sediment cores from the north atlantic bulk quartz content and the quartz to plagioclase ratio exhibit peak to peak correspondence to manual counting results which verifies the identification of large ird influxes the xrd data also reveal variations between the manually identified peaks suggesting increased sensitivity to low level distal or sea ice sources of ird a saw tooth pattern emerges in many ird events which supports a link between ice rafting and atmospheric temperature changes over greenland and providing further evidence of the influence of climate on iceberg discharges c 2003 elsevier b v all rights reserved less

geochemical control of magnetite dissolution in subarctic lake sediments and the implications for environmental magnetism geochemical and mineral magnetic studies of lake sediments from the karsa valley in north sweden demonstrate that down core variations in magnetic properties have been determined by post depositional magnetite dissolution rather than by sediment source changes a low sediment accumulation rate during times of climatic amelioration combined with a higher organic carbon content produced intense reducing conditions with almost complete magnetite loss an increase in the sedimentation rate and a reduction in the organic carbon content primarily due to glacier reformation allowed magnetite preservation thus the mineral magnetic profiles record lake sediment palaeoredox conditions brought about by climate change this new interpretation of mineral magnetic transformations in freshwater sediments may have far reaching implications for other mineral magnetic studies concerned with the alternation between glacial stadial and interglacial interstadial episodes during the quaternary period

paleoenvironmental record in lake baikal sediments environmental changes in the last 160 ky measurement of magnetic susceptibility ms and diffuse reflectance spectra drs were used to construct environmental proxies in a 6 5 m section of the sediment core ver98 1 13 from the academician ridge lake baikal the interpretation of ms and drs was supported by x ray diffraction and microparticle voltammetry to identify the main fe bearing minerals the record of the relative paleointensity of the earth s magnetic field was used to construct an age model showing the core interval covers the last 160 ky the time resolution of the record was 1 ky the main environmental changes were recognized by a combination of drs and ms records and compared to marine isotopic stages in addition to the diatom record from 120 to 60 ky bp so as to demonstrate the importance of these inorganic proxies as paleoenvironmental records a dramatic climatic deterioration between 66 and 60 ky bp was probably preceded by a dry intermediate stage between 77 and 66 ky bp the drs based proxies of fe ii fe iii ratios in the mineral assemblage ms and or diatom records clearly reveal 1 2 ky long environmental extremes at 110 103 90 85 77 61 54 36 27 23 and 19 ky bp the majority of these extremes were contemporaneous with discharges of north atlantic and arctic ocean icebergs heinrich events documenting a teleconnection between the north atlantic ocean and east central siberia these sharp changes coincided with a major transition to the colder climatic stages of the last 100 ky d 2006 published by elsevier b v

rotating micro structures in antarctic cold basal ice implications for glacier flow and its interpretation structural analyses were conducted in the basal zone of an antarctic glacier the studied basal ice sequence was retrieved from a 20 m long subglacial tunnel dug at the margin of the glacier and is at the temperature of 17 c for the first time rotating clast systems embedded within debris rich ice were thin sectioned using specially designed cutting techniques the observed structures reflect the occurrence of pervasive shearing at the base of the glacier and can be used as shear sense indicators in addition some of these structures provide evidence for the presence of thin liquid films at the time of formation despite the marked freezing temperature of the ice it is showed here that cautious analysis of deformation structures present in debris bearing ice may bring insights not only into the flow dynamics of the embedding matrix but also into the behaviour of the interstitial fluid network at the base of cold glaciers and ice sheets

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

orbital forcing of continental climate during the pleistocene a complete astronomically tuned climatic record from lake baikal se siberia abstract a new composite bdp 96 biogenic silica record over the entire pleistocene was generated by splicing bdp 96 1 and bdp 96 2 drill cores from lake baikal crosschecked against a similar record from a nearby bdp 98 drill core a new astronomically tuned age model is proposed based on correlating peak biogenic silica responses with the timing of september perihelia this target is derived from analysis of regional climate proxy responses during the holocene the last interglacial and around paleomagnetic reversals by resolving virtually every precessional cycle during the pleistocene the new age model represents a major improvement compared with previously reported lake baikal timescales the astronomically tuned ages of the pleistocene paleomagnetic reversals are consistent with published dates the minimal tuning approach we used precession only has also aligned high signal power in a narrow obliquity band confirming the strong presence of orbital forcing there are also strong ca 100 ka scale cycles but these are not aligned with the orbital eccentricity despite the location of lake baikal in a continental interior that is highly sensitive to insolation forcing the tuned biogenic silica record reveals a consistent phase difference of 32 ca 4 ka relative to insolation in the obliquity band an inherent lag embedded in a continental proxy record not driven by global ice volume is an intriguing finding another new observation is that long term changes in sedimentation rates in lake baikal appear to be related to the amplitude of orbital forcing both amplitudes and sedimentation rates undergo significant changes during mis 24 mis 19 interval corresponding to the middle pleistocene transition with potential for linking continental and marine climato stratigraphies the new baikal record serves a new benchmark correlation target in continental eurasia as an alternative to june 65 n insolation and odp correlated timescales

origin and dynamics of fe and mn sedimentary layers in lake baikal remobilization and accumulation of iron and manganese were measured by porewater and sediment core analyses at six contrasting sedimentary environments of lake baikal with bulk sedimentation rates varying between 0 8 and 0 02 mm year 1 the results allow for the distinction between two types of fe and mn diagenesis in areas of relatively high sedimentation and in regions of low sedimentation rates in the first case only small fe mn enrichments near the sediment water interface were observed in the central and southern basins at the high sediment flux area near the selenga delta and in maloe more strait massive sedimentary layers enriched in fe and mn were found within the upper 15 25 cm of the sediments exclusively in northern baikal and in the underwater academician ridge which are characterized by low sedimentation rates and deep sulfate penetration depths in the porewaters the mn content in the enriched layers ranged from 10 5 mol cm 2 at the sites near the selenga delta up to 10 2 mol cm 2 at academician ridge the accumulation times for the enriched fe mn layers calculated from the size of the fe and mn oxide pools and the diffusive fluxes into the enriched zones also varied by a factor of 1000 they ranged from a few years near the selenga delta to several thousand years for the sites at academician ridge and northern baikal these values were generally congruent with the sediment age of the accumulation zones calculated from sedimentation rates these findings have significant implications for paleolimnological studies iron and manganese dynamics at sites with high sedimentation rates is dominated by allochthonous input which is only partially dissolved close to the sediment surface in contrast the massive fe mn sedimentary layers at sites of slow sedimentation are of autochthonous origin slow dissolution and reprecipitation maintain their constant position with respect to the sediment surface and prevent burial as long as the sedimentation regime remains constant buried fe mn sedimentary layers widespread in lake baikal may therefore serve as general indicators for low sedimentation rates and as specific proxies for sudden changes in the sediment regime d 2004 elsevier b v all rights reserved

structure and emplacement of granite plutons in the paleoproterozoic crust of eastern burkina faso rheological implications the fada n gourma area in burkina faso is underlain by paleoproterozoic rocks that make the northeastern west african craton this region is composed of ne trending volcano sedimentary belts and foliated tonalites affected by several shear zones a generation of younger 2100 ma old non foliated biotite bearing granites intrudes the former rock units we have investigated the younger granite pluton of kouare that was previously considered as forming a single body with the pluton of satenga to the west a pluton which likely belongs to the 20 ma more recent tenkodogo yamba batholith magnetic fabric measurements have been combined with microstructural observations and the analysis of field and aeromagnetic data the granite encloses angular enclaves of the host tonalites magmatic microstructures are preserved inside the pluton and solid state high temperature deformation features are ubiquitous at its periphery the presence of steeply plunging lineations in the pluton of kouare and its adjacent host rocks suggests that large volumes of granitic magmas became crystallized while they were ascending through the crust that was softened and steepened close to the contact around kouare the foliation in the host tonalites conforms with a map scale z shaped fold in between nne trending shear zones implying a bulk clockwise rotation of the material contained in between the shear zones including the emplacing pluton regionally the fada n gourma area is concluded to result from nw shortening associated with transcurrent shearing and vertical transfer of granitic magmas this study concludes that the 2200 myears old juvenile crust of burkina faso was brittle before the intrusion of the biotite granites became softened close to them and that gravity driven and regional scale wrench tectonics were active together

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

conflicting shear sense indicators in shear zones the problem of non ideal sections abstract deflection of pre existing planar structures such as foliations or veins by ductile shear zones is geometrically very similar to the curvature of newly developed shear zone restricted foliations in zones that cut a rock with a random fabric sense of curvature of shear zone restricted foliations can be used to determine shear sense but the deflection of pre existing planar structures is less reliable two examples are presented of shear zones in australia where both types of structures seem to represent conflicting shear sense this conflict can be attributed to a geometrical effect which causes deflection of older structures in an opposite direction to shear sense on outcrop surfaces oblique to the displacement vector if the orientation of the displacement vector cannot be accurately determined in shear zones e g because of limited outcrop or unclear lineations most shear sense indicators can still be used to determine shear sense but pre existing planar structures are notoriously unreliable

evidence for last interglacial chronology and environmental change from southern europe establishing phase relationships between earth system components during periods of rapid global change is vital to understanding the underlying processes it requires records of each component with independent and accurate chronologies until now no continental record extending from the present to the penultimate glacial had such a chronology to our knowledge here we present such a record from the annually laminated sediments of lago grande di monticchio southern italy using this record we determine the duration 17 70 0 20 ka and age of onset 127 20 1 60 ka b p of the last interglacial as reflected by terrestrial ecosystems this record also reveals that the transitions at the beginning and end of the interglacial spanned only 100 and 150 years respectively comparison with records of other earth system components reveals complex leads and lags during the penultimate deglaciation phase relationships are similar to those during the most recent deglaciation peaks in antarctic warming and atmospheric methane both leading northern hemisphere terrestrial warming it is notable however that there is no evidence at monticchio of a younger dryas like oscillation during the penultimate deglaciation warming into the first major interstadial event after the last interglacial is characterized by markedly different phase relationships to those of the deglaciations warming at monticchio coinciding with antarctic warming and leading the atmospheric methane increase diachroneity is seen at the end of the interglacial several global proxies indicate progressive cooling after 115 ka b p whereas the main terrestrial response in the mediterranean region is abrupt and occurs at 109 50 1 40 ka b p

an outline of shear sense analysis in high grade rocks ductile shear zones are important in tectonic reconstructions as a source of information on the relative motion of large crustal blocks or plates in the geological past methods to interpret fabric in ductile shear zones were mostly developed for low grade rocks where overprinting relations are usually well preserved however high grade shear zones are common and dominate in many precambrian terrains high grade shear zones should be analysed in a different way from low grade zones the plane on which shear sense markers should be observed the vorticity profile plane is more difficult to find than in low grade shear zones the most reliable shear sense markers in high grade shear zones are shear bands mineral fish mantled porphyroclasts sigmoids and asymmetric boudins 2006 published by elsevier b v on behalf of international association for gondwana research

single layer folding in simple shear abstract despite the common occurrence of simple shear deformation laboratory and numerical simulations of folding have so far been almost exclusively in pure shear here we present a series of finite element simulations of single layer folding in simple shear up to high shear strains 4 and up to 75 shortening of the folding layer in the simulations we vary the viscosity contrast between layer and its surroundings 25 100 the stress exponent 1 or 3 and the kinematics of deformation pure versus simple shear in simple shear fold trains do not show a clear asymmetry axial planes form perpendicular to the developing fold train and rotate along with the fold train differences in geometries between folds formed in simple and pure shear folds are thus difficult to distinguish visually with simple shear folds slightly more irregular and with more variable axial plane orientation than in pure shear asymmetric refraction of an axial planar cleavage is a clearer indication of folding in simple shear the main effect of an increase in stress exponent is an increase in effective viscosity contrast with only a secondary effect on fold geometry naturally folded aplite dykes in a granodiorite are found in a shear zone in roses ne spain comparison of the folded dykes with our numerical simulations indicates a viscosity contrast of around 25 and a stress exponent of 3 the natural folds confirm that at this moderate viscosity contrast a significant amount of shortening 20 30 is achieved by layer thickening instead of folding

fabrics and geochronology of the wushan ductile shear zone tectonic implications for the shangdan suture zone in the qinling orogen central china abstract the ductile shearing along the shangdan suture zone during the paleozoic time is a key to understand the collisional deformation and tectonic regime of amalgamation between the north china block and the south china blocks the wushan ductile shear zone a branch of the shangdan suture records mylonitic deformation that affected granitic and felsic rocks outcropping in an over 1 km wide belt in the western qinling orogenic belt shear sense indicators and kinematic vorticity number 0 79 0 99 of the mylonites reveal a dextral shear deformation the quartz c axis fabrics indicate activation of combined basal a and rhomb a slip prism a slip and prism c slip the dynamic recrystallization of quartz is accommodated by combined subgrain rotation and grain boundary migration these characteristics suggest that the mylonites experienced ductile shear deformation under amphibolite facies conditions at temperatures of 500 650 c zircons from granitic mylonite yield a u pb age of 910 4 8 ma which represents the formation age of the protolith of the mylonite the ductile shear zone was intruded by a granitic dyke which yields a zircon u pb age of 403 3 5 ma constraining the minimum age of the ductile shear deformation together with regional geology and available geochronological data these structural characteristics and ages indicate that the wushan ductile shear zone was formed by dextral shearing following the n s shortening as a result of collision between the north china and south china blocks along the shangdan suture

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

timing and duration of last interglacial conditions in europe a chronicle of a changing chronology abstract estimates of the length of the last interglacial in europe conventionally defined by the presence of forest as inferred from pollen diagrams have varied considerably here an account of recent developments largely instigated by a paper by kukla et al 1997 is presented these include the emergence of new records with improved chronologies and a re evaluation of previous assumptions of synchroneity between marine and terrestrial stage boundaries and also between northern and southern european changes the current scheme proposes that the onset of the last interglacial in europe started well into mis 5e after deglaciation was complete and was coincident with a rise to peak sea surface temperatures however the timing of the end of the last interglacial between northern and southern europe appears to have diverged considerably in the north the elimination of forest occurred ca 115 ka near the time of the mis 5e 5d transition while in the south tree populations persisted into the interval of global ice growth until the onset of significant ice rafting ca 110 ka this significant n s diachroneity may be a reflection of the effects of different bioclimatic parameters limiting tree growth in the two areas these developments highlight the problems of correlating records of different proxies and from different geographical regions

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

high resolution palynological record off the iberian margin direct land sea correlation for the last interglacial complex abstract we present high resolution pollen dinocyst and isotopic data for the last interglacial complex from marine core md952042 southwestern margin of the iberian peninsula 37 48 n 10 10 w 3148 m direct land sea correlation from this core indicates that during this period north atlantic sea surface temperatures were in phase with iberian climate our palynological analysis suggests a younger dryas like event at the marine isotope stage mis 6 5 transition the analysis also indicates that the eemian spans from the lightest isotopic values of mis 5e ca 126 ky bp to the heavier isotopic values towards the mis 5e 5d transition therefore the eemian is not entirely equivalent to mis 5e pollen analysis identifies four climatic phases of low amplitude during the eemian a mediterranean climate in southwestern europe is gradually replaced by oceanic conditions the middle of the eemian is characterized by an increase in precipitation on the land and ocean associated with a slight cooling this seems to be the result of a displacement of the polar front as far south as southern europe during this period after the eemian three relatively short climatic phases on land melisey i st germain ia and montaigu cold event occurred contemporaneously with three shifts of sea surface temperatures the montaigu event first identified in terrestrial pollen sequences is therefore also recorded in core md952042 on the basis of pollen dinocyst and planktonic isotopic data our results also show that the warm periods of mis 5 are not characterized by similar climatic conditions on land

mid mantle seismic anisotropy beneath southwestern pacific subduction systems and implications for mid mantle deformation abstract observations of seismic anisotropy can offer relatively direct constraints on patterns of mantle deformation but most studies have focused on the upper mantle while much of the lower mantle is thought to be isotropic several recent studies have found evidence for anisotropy in the transition zone and uppermost lower mantle the mid mantle particularly in the vicinity of subducting slabs here we investigate anisotropy at mid mantle depths in the tonga kermadec sumatra new britain new hebrides and philippines subduction zones using the source side shear wave splitting technique we measure splitting of direct teleseismic s phases originating from deep events 300 km that have been corrected for the effect of upper mantle anisotropy beneath the seismic stations we find evidence for considerable anisotropy at mid mantle depths in all subduction systems studied with delay times averaging 1 0 1 5 s several measurements originating from depths greater than 600 km exhibit delay times greater than 1 s suggesting a significant contribution from anisotropy in the uppermost lower mantle we combine our results with those documented in previous studies into a quasi global set of source side shear wave splitting measurements that reflect mid mantle anisotropy we document significant variability in the dominant fast directions both within and among individual subduction systems suggesting different deformation geometries among different subduction systems as further constraints on the elasticity and deformation of mid mantle minerals become available our dataset can be used to constrain patterns of mid mantle flow associated with subduction

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

the stability and the abrupt ending of the last interglaciation in southeastern siberia abstract paleoproductivity records from lake baikal indicate that the last interglaciation in southeastern siberia lasted ca 12 000 yr from 127 000 to 115 000 yr b p was punctuated by a climatic oscillation about 120 000 yr ago and ended abruptly with a rapid onset of regional glaciation during marine isotope substage mis 5d the siberian equivalent of the mis 5e 5d transition appears to lead the post eemian cold pulses in europe and in the central north atlantic by 5000 to 8000 yr the baikal record also registers a pronounced cold event during early mis 5c which correlates with the montaigu event in pollen records from france in siberia the climatic deterioration during the mis 5d was a full scale glacial pulse unlike the short moderate cooling during the montaigu event

climatic variability during the last interglacial inferred from geochemical proxies in the lake el gygytgyn sediment record the last interglacial period lip is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios despite this there is still debate over the nature duration and frequency of climatic changes during this period one particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives especially within the arctic a key region for global climate change research in this paper geochemical records from lake el gygytgyn north eastern russia are used to infer past climatic changes during the lip from within the high arctic with a sampling resolution of 20 90 years these records offer the potential for detailed high resolution palaeoclimate reconstruction this study shows that the lip commenced in central chukotka 129 thousand years ago ka with the warmest climatic conditions occurring between 128 and 127 ka before being interrupted by a short lived cold reversal mild climatic conditions then persisted until 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation a further climatic deterioration at 118 ka marks the return to glacial conditions this study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions thus providing the potential to identify signals related to environmental change within the catchment we also demonstrate the importance of considering how changes in sedimentation rate influence proxy records in order to develop robust palaeoenvironmental reconstructions

sense and non sense of shear reloaded abstract this paper reviews the geometrical and mechanical evolution of selected groups of kinematic indicators that are frequently used for inferring large scale geodynamics but are prone to ambiguous shear sense interpretations i flanking folds and shear bands are complex structures because under general shear conditions co rotating secondary shear zones can experience either syn or antithetic slip leading to extensional or contractional offsets on the other hand counter rotating secondary shear zones can exhibit either extensional or contractional offsets but always experience synthetic slip ii boudinaged layers may display both syn and antithetic offset across the interboudin surfaces in addition to the flow type the initial orientation of interboudin surfaces strongly influences the sense of slip under coaxial flow conditions and with high strength contrast between the boudinaged layer and the matrix domains of layer oblique parallel interboudin surfaces can form by chance and their local occurrence may hence lead to misinterpretations of shear zone kinematics in particular if the number of observable boudins is small if the viscosity contrast between the boudinaged layer and the matrix is low domino boudins may strongly deform internally during shearing so that in contrast to flanking structures antithetic slip along interboudin surface may lead to a marked normal drag resulting in shear band boudinage geometries that appear to have formed during flow with an opposite shear sense iii winged inclusions are pinch and swell shaped objects rotating into the shear direction after several revolutions these structures can resemble b type clasts or clasts with stair stepping that formed during shear flow with the opposite shear sense in this paper new and published examples of these ambiguous shear sense indicators are discussed and interpreted we give some guidelines for the correct interpretation of these structures with the caveat that if marker lines and their deflections are not well preserved these shear sense criteria are not always reliable kinematic indicators

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

zooming on northern cap de creus shear zones abstract the northern cap de creus shear belt provides fine examples of shear zones developed at different scales in rocks bearing pre existing penetrative foliations the shear zones developed under retrograde metamorphic conditions and they are preferentially located in crystalline schists lower grade metasedimentary rocks accommodated deformation by folding the shear zones are linked in an anastomosing framework with self similar properties they are interpreted to have formed as the result of a progressive wrench dominated deformation affecting anisotropic rocks a progressive non coaxial deformation regime is considered responsible for the development of the complex kinematic pattern wherein shear zones with opposite senses of shear may come to lie in close parallelism in such a framework individual shear zones are characterised by marked strain gradients not only across the shear zone but also along it these features together with the geometrical analysis of shear zone marginal domains indicate that these structures developed with a component of shortening across the shear zones the shear zones are interpreted to have nucleated as buckling instabilities that gradually evolved to become shear zones approaching the simple shear model microstructural and quartz c axis fabric analyses indicate that shear zone formation is associated with strong strain partitioning on all scales

precise dating of dansgaard oeschger climate oscillations in western europe from stalagmite data the signature of dansgaard oeschger events millennial scale abrupt climate oscillations during the last glacial period is well established in ice cores and marine records but the effects of such events in continental settings are not as clear and their absolute chronology is uncertain beyond the limit of 14 c dating and annual layer counting for marine records and ice cores respectively here we present carbon and oxygen isotope records from a stalagmite collected in southwest france which have been precisely dated using 234u 230th ratios we find rapid climate oscillations coincident with the established dansgaard oeschger events between 83 000 and 32 000 years ago in both isotope records the oxygen isotope signature is similar to a record from soreq cave israel and deep sea records indicating the large spatial scale of the climate oscillations the signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western europe an important site in human cultural evolution we also find evidence for a long phase of extremely cold climate in southwest france between 61 2 0 6 and 67 4 0 9 kyr ago

evolution and demise of the last interglacial warmth in the subpolar north atlantic detailed faunal isotopic and lithic marine records provide new insight into the stability and climate progression of the last interglacial period marine isotope stage mis 5 which peaked approximately 125 000 years ago in the eastern subpolar north atlantic at the latitude of ireland interglacial warmth of the ice volume minimum of substage 5e mis 5e lasted 10 000 years 10 ka and its demise occurred in two cooling steps the first cooling step marked the end of the climatic optimum which was 2 3 ka long minor ice rafting accompanied each cooling step the second larger step encompassing cold events c26 and c25 was previously identified in the northwestern atlantic approximately 41c of cooling occurred between peak interglacial warmth and c25 and the region experienced an additional temporary cooling of at least 1 21c during c24 a cooling event associated with widespread ice rafting in the north atlantic beginning with c24 mis 5 was characterized by oscillations of at least 1 21c superimposed on a generally cool baseline the results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought the finding that the eastern subpolar north atlantic cooled significantly before c24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions our results also demonstrate a close association between modest ice rafting cooling and deep ocean circulation even during the peak of mis 5e and in the earliest stages of ice growth

shear zone related folds folds in ductile shear zones are common structures that have a variety of origins these can be pre existing folds that become modified or folds developed during the shearing event among the syn shearing folds a second subdivision is based on the relative age of the folded surface which can be pre existing or newly formed during the shearing event in each of the three categories final fold geometry and orientation show complex relationships with the kinematic frame the final fold geometry depends on the vorticity within the shear zone the rheology and the initial orientation of the folded surface relative to the kinematic framework it follows that folds are complex structures difficult to use as kinematic indicators however in shear zones where undeformed wall rocks with pre shear structures are accessible and where kinematics can be well established folds can provide a valuable natural means to understand the initiation and evolution of structures under non coaxial regimes we point to the need of discriminating among different plausible categories based on the nature of the folded surface and on the inherent structural features of each category q 2004 elsevier ltd all rights reserved