on the 1470 year pacing of dansgaard oeschger warm events 1 the oxygen isotope record from the greenland ice sheet project 2 gisp2 ice core was reanalyzed in the frequency and time domains the prominent 1470 year spectral peak which has been associated with the occurrence of dansgaard oeschger interstadial events is solely caused by dansgaard oeschger events 5 6 and 7 this result emphasizes the nonstationary character of the oxygen isotope time series nevertheless a fundamental pacing period of 1470 years seems to control the timing of the onset of the dansgaard oeschger events a trapezoidal time series model is introduced which provides a template for the pacing of the dansgaard oeschger events statistical analysis indicates only a 3 probability that the number of matches between observed and template derived onsets of dansgaard oeschger events between 13 and 46 kyr b p resulted by chance during this interval the spacing of the dansgaard oeschger onsets varied by 20 around the fundamental 1470 year period and multiples thereof the pacing seems unaffected by variations in the strength of north atlantic deep water formation suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period

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

conceptual model for millennial climate variability a possible combined solar thermohaline circulation origin for the 1 500 year cycle dansgaard oeschger and heinrich events are the most pronounced climatic changes over the last 120 000 years although many of their properties were derived from climate reconstructions the associated physical mechanisms are not yet fully understood these events are paced by a 1 500 year periodicity whose origin remains unclear in a conceptual model approach we show that this millennial variability can originate from rectification of an external solar forcing and suggest that the thermohaline circulation through a threshold response could be the rectifier we argue that internal threshold response of the thermohaline circulation thc to solar forcing is more likely to produce the observed do cycles than amplification of weak direct 1 500 year forcing of unknown origin by thc one consequence of our concept is that the millennial variability is viewed as a derived mode without physical processes on its characteristic time scale rather the mode results from the linear representation in the fourier space of nonlinearly transformed fundamental modes

signature of magnetic enhancement in a loessic soil in nebraska united states of america our study of a loessic soil profile from east central nebraska shows that the a horizons of the modern soil are characterized by higher concentrations of fine grained b0 1 am magnetic minerals this pedogenic magnetic component leads to higher values of concentration dependent parameters such as magnetic susceptibility v isothermal remanent magnetization irm and anhysteretic remanent magnetization arm combined with increases in frequency dependent susceptibility vfd and arm irm ratios hysteresis properties are relatively insensitive towards the presence of this pedogenic magnetic component the magnetic properties of the soil profile are dominated by ferrimagnetic magnetite or maghemite analyses of bsoftq irm sirm and bhardq irm hirm however do show that approximately 80 90 of the remanence carrying magnetic component exists in the form of hematite or goethite and that the magnetically enhanced horizons are enriched in both ferri and antiferromagnetic minerals the pedogenic magnetic component is most likely caused by the conversion of paramagnetic iron bearing minerals to ferriand antiferromagnetic minerals soil compaction lessivage or decalcification cannot explain the observed magnetic soil properties magnetic analyses of loess paleosol sequences from the midwestern united states may yield valuable information about regional variability of paleoclimate based on the fine grained nature of the pedogenic magnetic component we expect grain size dependent proxies arm arm irm vfd to yield better paleoclimatic information than low field magnetic susceptibility used in previous analyses d 2004 elsevier b v all rights reserved

paleoclimatic forcing of magnetic susceptibility variations in alaskan loess during the late quaternary visual matches and statistical tests suggest correlations between marine isotope curves retrodictive solar insolation at lat 65 n and magnetic susceptibility profiles through late quaternary age alaskan loess sections the susceptibility changes largely appear to reflect variability in magnetite content due to climatically controlled changes in wind intensity and competence magnetic susceptibility profiles through massive loess can provide stratigraphic context for intercalated paleosols and tephras a prominent paleosol correlated with marine isotope stage 5 occurs several metres above the old crow ash in loess sections indicating that this important tephra is older than suggested by thermoluminescence dates and may have been deposited ca 215 25 ka

loess deposits from the tajik depression central asia magnetic properties and paleoclimate abstract continuous accumulation of dust during the quaternary has formed widespread loess deposits in southern tajikistan the magnetic susceptibility variations of these aeolian sediments have recorded the paleoclimatic fluctuations in a similar direct and complete way to the well studied sediments from the central loess plateau in china 11 susceptibility measurements were carried out in situ at intervals of 10 cm along seven partly overlapping sections in the loess paleosol sequence of karamaidan ca 100 km east of dushanbe nearly 250 oriented samples were taken for rock magnetic investigations careful field observation revealed a total actual loess thickness of ca 100 m for a composite profile with thirteen intervening pedocomplexes pc standard demagnetization techniques yielded a characteristic component of natural remanent magnetization nrm which was used to obtain a well defined magnetostratigraphy the section covers a total timespan of approximately 1 m y including the brunhes and the youngest part of the matuyama polarity chron the susceptibility variations correlate excellently with those of the chinese loess record at xifeng 22 although minor differences in the relative amplitude of the susceptibility signal occur close correlation with the astronomically tuned oxygen isotope record 26 enables refined dating of the loess sequence at karamaidan and demonstrates the global significance of the recorded paleoclimatic variations especially with respect to paleoprecipitation on land during the quaternary

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

interhemispheric space time attributes of the dansgaard oeschger oscillations between 100 and 0 ka the persistence stability and interhemispheric phasing of the dansgaard oeschger do climate oscillation over the last glacial period 0 100 ka has been evaluated in oxygen isotope records of three polar ice cores grip gisp2 and byrd station and a midlatitude deep sea core from the north atlantic ocean md95 2042 the results show that do oscillations in atmospheric conditions occurred in both northern and southern polar ice records although in the southern records the oscillations had at most only ca one tenth the power of those in the north the do oscillations first appeared duringmarine isotope stage mis 4 and the average spectral power of the northern hemisphere do oscillations increased markedly during mis 3 30 38 ka the do mode in the gisp2 record is confined to the frequency band 1 1 59 kyr to 1 1 37 kyr but in the grip record the mode exhibits strong frequency splittingover a band that is wider by ca 50 time frequency analysis shows that in grip the do mode underg oes a frequency modulation that is phase locked with the earth s obliquity cycle this modulation does not appear in nearby gisp2 in the north atlantic marine record do oscillations behaved somewhat differently appearingsporadically duringmis 5 and 4 the planktonic do oscillations increased in spectral power duringmis 3 leadingpeak power in the gisp2 record by ca 3 kyr do oscillations were relatively stable in all five records duringmis 3 they could not be detected unequivocally in any of the records duringthe holocene 0 11 ka at other times the do mode in all of the records was amplitude modulated by earth s orbital parameters finally interhemispheric phasingof do oscillations over 10 90 ka was assessed between the byrd station and gisp2 records and between the benthic and planktonic records of core md95 2042 coherency studies reveal an apparent time lead of byrd do oscillations over gisp2 by 384770 yr 2s level and of the north atlantic benthic over planktonic do oscillations by 208733 yr this apparent time lead of the southern over the northern temperature proxies is likely the consequence of the distinctive harmonic shapes affecting the northern rectangular vs southern triangular do oscillations the actual northern southern relationship as suggested by modelling and other recent data studies is most probably in simple antiphase cross phase of 1801 r 2002 published by elsevier science ltd

direct estimates of pedogenic magnetite as a tool to reconstruct past climates from buried soils 1 variations in magnetic properties of buried soils can be used to reconstruct past climatic conditions during paleosol formation most methods however are based on comparisons between the magnetically enriched upper soil horizons and the magnetically unaltered parent material in thin loess paleosol sequences such a comparison can be problematic because all horizons soil and underlying loess may be affected to varying degrees by pedogenesis we propose two direct estimates of pedogenic magnetite based on the analysis of anhysteretic remanent magnetization ratios carm isothermal remanent magnetization and coercivity distributions these estimates are independent of any information regarding the parent material and are possible if pedogenic minerals have similar magnetic properties throughout the study region this condition seems to be met throughout the midwestern united states and a few loessic soils elsewhere the remanence carrying part of pedogenic magnetite is composed of single domain particles with consistent well constrained magnetic properties these particles are extremely well dispersed in the soil matrix as indicated by the absence of noticeable magnetostatic interaction effects our analyses of over 70 modern loessic soil profiles demonstrate that the abundance of pedogenic magnetite correlates well with modern climate and that the method is suited for reconstruction of past climates from paleosols

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

responses of the okhotsk sea environment and sedimentology to global climate changes at the orbital and millennial scale during the last 350 kyr abstract we measured productivity proxies chlorin carbonate and organic carbon opal and biogenic ba content and lithophysical proxies magnetic susceptibility water content density and coarse sediment fraction in sediment of central okhotsk sea core pc 7r the age model covering the last 350 kyr of this core was constructed by correlating the dated series of relative paleointensity lows recognized in geomagnetic intensity records marine isotope stage mis boundaries determined in broad variations of the lithophysical and productivity proxies and tephrochronology the orbital changes of the lithophysical and productivity proxy stacks lag behind northern hemisphere summer radiation by approximately 6 3 and 5 9 kyr respectively this lag is consistent with a milankovich model of climate control by solar radiation through the northern ice sheet volume and sea surface and surrounding land responses which are fast compared with sedimentological evidence productivity proxies of the okhotsk sea also demonstrate 52 abrupt pronounced productivity minima associated with regional climate coolings during the last 350 kyr which present useful indicators of millennial scale climate changes in this marginal sea based on the postulated synchronicity of dansgaard oeschger cycles in the northern hemisphere and the established simultaneity of 11 okhotsk sea coolings in the last 77 kyr with abrupt severe cold events in the greenland ice core and north atlantic heinrich events all of these may be regarded as heinrich equivalent event anomalies the okhotsk sea events have their counterparts in the records of north atlantic sediments the greenland ice sheet east asia summer monsoon and the antarctic ice sheet probably the arctic oscillation was the main factor determining orbital and millennial climate oscillations in the high latitude northern hemisphere including the okhotsk sea region

magnetic indicator of global paleoclimate cycles in siberian loess paleosol sequences abstract the loess paleosol sequences of china siberia alaska and many other regions along with lake sediments and glaciers provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years the frequency dependence fd of magnetic susceptibility ms in such sequences has become the leading parameter for analyzing climatic change and milankovitch astronomical periodicity in siberian sequences it is always higher in soil horizons than in loess the enhanced fd parameter in soils is associated with ferromagnetic minerals mostly magnetite produced during pedogenesis the ms and fd parameters of 670 samples from five sections in siberia are reported here inter section correlation is used to produce a combined fd time series for the studied sections chronological control is established by absolute dating and stratigraphic correlation spectral analysis of the fd time series reveals the presence of milankovitch signals at 100 kyr eccentricity 40 kyr obliquity and 23 kyr precession and demonstrates that siberian loess paleosol sequences are excellent continental recorders of long term paleoclimatic changes this suggests that the fd parameter can potentially be used more widely for evaluation of climate periodicity in loess paleosol sequences in other parts of the world

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

how abundant is pedogenic magnetite abundance and grain size estimates for loessic soils based on rock magnetic analyses 1 the upper soil horizons of many modern and ancient soils are enriched in fine grained pedogenic ferrimagnetic minerals we use three grain size and concentration dependent proxies anhysteretic remanent magnetization isothermal remanent magnetization ratios coercivity spectra derived from alternating field demagnetization of saturation isothermal remanent magnetization and hysteresis properties to quantify the abundance and grain size of the pedogenic magnetic component our analyses of modern loessic soils from the midwestern united states show that relatively small additions 2 10 vol of the total ferrimagnetic component of fine grained coarse superparamagnetic to fine pseudosingle domain magnetite or maghemite are sufficient to explain the changes in concentration and grain size dependent properties observed in the upper soil horizons furthermore the pedogenic components of all studied sites display a narrow range of magnetic properties which argues for a common origin of these particles over a wide range of climatic conditions

origin of millennial scale climate signals in the subtropical north atlantic we present a high resolution planktonic foraminiferal stable isotope record globigerinoides ruber spanning marine oxygen isotope stages miss 6 through 8 in the northwestern subtropical atlantic ocean ocean drilling program leg 172 site 1059 the record fills a gap to produce an about 1 3 myr long continuous time series of high frequency 1 12 kyr surface ocean hydrography the first of this kind we test the hypothesis that the suborbital climate signals i e half and quarter precession cycles are linked to precession forcing in tropical latitudes semiprecession cycles present between 0 and 320 ka are of the right periodicity to relate to the dominant precession forcing 23 kyr these cycles are evident as double peaks within the given precession framework and there is good match in the amplitude modulation of the filter output and the 18o time series quarter precession cycles dominate the suborbital spectra between 320 ka and 1 3 ma periodicities are close to those expected from the harmonics of the dominant precession peaks in the 18o record but present in the time series only intermittently and their amplitude modulation does not match that of the primary precession period thus only the half precession cycles evidence a response to low latitude insolation such as that introduced by insolation maxima at the equinoxes or solstices during the course of a precession cycle additionally we find well defined rapid 1 5 2 kyr variations across the first of the interglacial maxima of mis 7 adding to evidence of non ice sheet related forcing factors in driving climate instabilities

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

magnetic enhancement in wildfire affected soil and its potential for sediment source ascription intense rainfall following wildfire can cause substantial soil and sediment redistribution with concern for the increasing magnitude and frequency of wildfire events research needs to focus on hydrogeomorphological impacts of fire particularly downstream fluxes of sediment and nutrients here we investigate variation in magnetic enhancement of soil by fire in burnt eucalypt forest slopes to explore its potential as a post fire sediment tracer low frequency magnetic susceptibility values lf of 10 m material sourced from burnt slopes c 8 0 10 4 10 6 m3 kg 1 are an order of magnitude greater than those of 10 m material derived from long unburnt areas 0 8 10 6 m3 kg 1 susceptibility of anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm values are similarly enhanced signatures are strongly influenced by soil and sediment particle size and storage of previously burnt material in footslope areas whilst observations indicate that signatures based on magnetic enhancement show promise for post fire sediment tracing problems arise with the lack of dimensionality in such data magnetic grain size indicators fd arm sirm and fd arm offer further discrimination of source material but cannot be included in numerical unmixing models owing to non linear additivity this leads to complications in quantitatively ascribing downstream sediment to source areas of contrasting burn severity since sources represent numerical multiples of each other indicating the need to involve additional indicators such as geochemical evidence to allow a more robust discrimination copyright 2005 john wiley sons ltd

a quantitative model of magnetic enhancement in loessic soils we present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils the model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores the rate at which this occurs depends on the frequency of drying wetting cycles and on the average moisture of the soil both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production which is proportional to a new parameter called magnetite enhancement proxy mep our model is tested by comparing mep calculated for known present day climates with the magnetic enhancement of modern soils the magnetic enhancement factor defined as the ratio between a given magnetic enhancement parameter and mep is expected to be a site independent constant we show that magnetic enhancement differences between soils from the chinese loess plateau and from midwestern u s are explained by our model which yields similar magnetic enhancement factors for the two regions our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate

mechanisms of abrupt climate change of the last glacial period 1 more than a decade ago ice core records from greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales since their discovery there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the north atlantic region and also to reveal the mechanisms that were responsible for them in this paper we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms three different mechanisms are then reviewed ocean thermohaline circulation sea ice feedbacks and tropical processes each mechanism is tested for its ability to explain the key features of the observations particularly with regard to the abruptness millennial recurrence and geographical extent of the observed changes it is found that each of these mechanisms has explanatory strengths and weaknesses and key areas in which progress could be made in improving the understanding of their long term behavior both from observational and modeling approaches are suggested finally it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes as well as the potential for feedbacks between them some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given

modes of global climate variability during marine isotope stage 3 60 26 ka recent analysis of 38 globally distributed paleoclimatic records covering marine isotope stage 3 mis 3 60 26 ka demonstrated that the two leading empirical orthogonal functions eofs explaining the data are the greenland ice core signal northern signal and the antarctic ice core signal southern signal here singular spectral analysis ssa is used to show that millennial scale variability of each of these two leading eofs is characterized by two independent modes the two modes of each eof share similar relative distributions of variance identical spectra and where each mode has spectral power coherency spectra which are significantly above the null hypothesis level at 95 confidence the only difference between the modes of the northern and southern signals is that they are phase shifted the phasing and long response time of the low frequency mode combined with its relationship to atmospheric co2 and sea level are consistent with coupled changes in the ocean ice sheets atmosphere and carbon cycle whereas the phasing and short response time of the high frequency mode are consistent with an atmospheric transmission likely induced by changes in hemispheric sea ice distributions and attendant feedbacks

linking co2 degassing in active fault zones to long term changes in water balance and surface water circulation an example from sw turkey abstract calcite veins are commonly found at shallow depth a few metres below the surface in damage zones of active normal fault systems in southwest turkey although earlier studies demonstrated the link between the vein formation and seismicity the association of near surface carbonate precipitation with climate driven hydrological conditions water table amount of precipitation and evaporation and water discharge is poorly understood in this study using the u th dating method we investigate the timing of vein formation and the interrelationship between tectonic and climatic related hydrological processes carbonate precipitation is interpreted to occur as a result of sudden pressure drops and co2 release after earthquake induced fracturing vein formation mostly occurred during glacial periods which coincide with slow growth rates and higher oxygen isotope values of speleothems from the eastern mediterranean region we relate these episodes to reduced winter rainfall due to the decrease in westerly flow in sw turkey these somewhat drier conditions influenced the chemical composition of circulating water creating conditions conducive to carbonate precipitation and sealing of damage zones these conditions also facilitated co2 accumulation and overpressure build up in the rupture zones failure of the faults resulted in the release of large volumes of co2 rich fluids and the generation of shallow carbonate veins it is proposed that during phases of increased winter rainfall co2 is advected to the surface and discharged as passive degassing when meteoric water circulation is enhanced while regional tectonics is the ultimate driver of fault activity and fracture formation climate driven near surface hydrological changes may have played an important role in modulating co2 rich fluid circulation and surface discharge

quantifying the periodicity of heinrich and dansgaard oeschger events during marine oxygen isotope stage 3 article i nfo data from multiple ice and sediment cores in the north atlantic show that marine oxygen isotope stage 3 mis 3 was characterized by recurring millennial scale variations in climate but the periodic behavior of the well known millennial scale variations heinrich events and dansgaard oeschger events is uncertain we use oxygen isotope values from the greenland ice sheet project 2 gisp2 and north greenland ice core project ngrip ice cores and estimated sea surface temperature derived from a bermuda rise marine sediment core as climate proxies to assess the periodic behavior of heinrich events and dansgaard oeschger events using lomb scargle spectral decomposition and continuous time autoregressive models we find that continuous time autoregressive models produce less variable estimates of periodicity for heinrich events than lomb scargle methods heinrich events during mis 3 are periodic with an estimated periodicity of 6 29 6 49 ka in the gisp 2 ice core 6 71 6 76 ka in the marine sediment core and 7 89 8 23 ka in the ngrip core there is insufficient evidence from these data to conclude that dansgaard oeschger events ex hibit a single periodicity during mis 3 we also find that the periodic behavior of millennial scale variations depends on the observational time frame

paleoenvironmental dynamics of low order paleovalleys in the late quaternary palmas cacador summit surface southern brazil abstract the quaternary dynamics of landscapes in the subtropical continental region of brazil is not still well understood pedostratigraphic records of low order paleovalleys paleovalley heads and 1st and 2nd order paleovalleys of the palmas cacador summit surface serve as important resources for the identification of landscape component responses relief soil sediment and vegetation of plateau areas of southern brazil in the light of environmental changes driven by climatic variations of the late quaternary we integrated litho pedo allo and chronostratigraphic descriptions with carbon stable isotope analysis phytoliths indices and 14c and osl dating we found that at 44 86 ky bp there was a change in the hydrodynamics of 2nd order perennial channels humid climate controlled possibly by tectonics at 28 35 to 23 69 to 28 ky bp regressive pedogenesis in dry climate began with a predominance of erosion by overland flows at 2 60 to 23 69 ky bp full regressive pedogenesis occurred under a continuous climate regime of drier characteristics punctuated by millenary climatic fluctuations to a wetter regime of between 4 60 and 19 77 ky bp echoing the results postulated by the knox s model during this period the most pronounced modifications to the landscape were made with a change in vegetation from campo cerrado to campo limpo with changes in erosion patterns caused first by overland flows and then earthflows debris flows and with the gradual silting filling and burying of gullies valley heads and 1st and 2nd order valley bases since 2 60 ky bp the area returned to a predominance of progressive pedogenesis in wet and cold climates finally we found that at the local scale low order basins

heinrich events sediments a history of terminology and recommendations for future usage abstract we document the history of terms used to describe heinrich h layers and events and which mark major glaciological iceberg discharge events in the north atlantic we argue that the usage heinrich layer heinrich zone or heinrich event should be restricted to only those sediments that can be ascribed to an origin from the hudson strait ice stream and the laurentide ice sheet we also argue that the commonplace understanding of these events as dominated by massive iceberg discharges fails to include the earlier well documented evidence that these events were also massive meltwater events linked to deposition along the north atlantic mid ocean channel namoc in the labrador sea we make five recommendations for future usage of heinrich events which include restricting the usage to those events that can be mineralogically geochemically linked to hudson strait abandoning the term heinrich stadial and promote local terminology for ice rafted events that may be correlated or not with hudson strait heinrich events based on calibrated radiocarbon dates or other appropriate chronological markers

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

rock magnetic chemical and bacterial community analysis of a modern soil from nebraska abstract detailed rock magnetic and bacterial community analyses have been conducted on a 2 2 m long soil profile developed over loess in nebraska results show magnetic enhancement in the a horizon of the soil profile in part due to increased concentration of pedogenic superparamagnetic sp ferrimagnetic minerals i e magnetite maghemite the magnetic enhancement correlates well with higher microbial biomass and lower iron hydroxide concentrations here determined using a goethite specific magnetic method therefore supporting the idea of bacterially mediated topsoil magnetite formation through iron reduction of iron hydroxides cultivation independent bacterial community analysis biased towards the geobacteraceae common dissimilatory iron reducing bacteria failed to show the involvement of this phylogenetic group in sp magnetite formation at this site although preliminary in nature our failure to implicate dissimilatory geobacteraceae with magnetic enhancement in modern nebraskan soil and dearing et al dearing hannam anderson wellington geophysical journal international 144 2001 183 196 earlier failure to detect magnetotactic bacteria in enhanced british soils points to the need to focus further multidisciplinary investigations on the possible roles of other dissimilatory iron reducing bacteria in contributing to magnetic enhancement many authors have produced strong circumstantial evidence of a microbial role in causing magnetic enhancement in topsoils of temperate climate zones yet a precise role of specific cultured microbes in enhancing soil magnetism is still lacking

tipping points early warning and wishful thinking 1 the causes for and possible predictions of rapid climate changes are poorly understood the most pronounced changes observed beside the glacial terminations are the dansgaard oeschger events present day general circulation climate models simulating glacial conditions are not capable of reproducing these rapid shifts it is thus not known if they are due to bifurcations in the structural stability of the climate or if they are induced by stochastic fluctuations by analyzing a high resolution ice core record we exclude the bifurcation scenario which strongly suggests that they are noise induced and thus have very limited predictability

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

establishing fire incidence in temperate soils using magnetic measurements abstract natural unburnt topsoil samples from the cotswolds region of england and samples from archaeological contexts in the uk and hungary some of which are known to have been affected by burning have been used to identify a distinctive magnetic signature linked to the effects of fire on magnetic properties a combination of bulk low field lf and frequency dependent fd magnetic susceptibility and normalized anhysteretic remanent magnetization arm measurements have been used on both unburnt and experimentally burnt samples from the cotswolds and on the archaeological samples complementary determinations were made for both sets of samples of the maximum potential susceptibility max and hence percentage fractional conversion conv which provides independent evidence of burning the results show that the ferrimagnetic mineral assemblages produced as a result of fire have a significantly finer grain size than those arising from weathering and soil formation alone burning thus gives rise to a distinctive envelope of values on a bilogarithmic plot of arm fd versus arm lf such a diagram provides a convenient basis for identifying magnetic signatures in soils archaeological materials and palaeosols that have arisen mainly through burning

magnetic stratigraphy of chinese loess as a record of natural fires magnetic susceptibility records of paleosols and loess show high correlation with oxygen isotope stratigraphy of ocean sediments kukla 1987 providing a global paleoclimatic record different models have been put forth to explain the nature and cause of susceptibility variations but consensus has not yet been achieved our low temperature studies reveal a secondary magnetite component in paleosols that is characterized by a higher verwey transition 115k than that for the magnetite 100 k in unaltered loess the same shift in the verwey transition can be achieved by heating and cooling loess samples this is consistent with a new hypothesis that the magnetic signal from paleosols may be produced by natural fires in the past natural fire intensity is sensitive to the amount of annual precipitation so that increased fire induced susceptibilities should reflect an increase in the humidity of regional climate

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

the effects of wildfires on the magnetic properties of soils in the everglades we present results of a rock magnetic study of soils that were affected by wildfires that burned portions of the everglades in the spring of 2008 soils at sites that were extensively burned exhibit a pronounced surface magnetic enhancement effect with magnetizations of surface samples up to 16 times greater than that observed at depth 7 cm at these sites the increase in magnetization results from an increased abundance of a low coercivity phase maghemite that occurs at the expense of the abundance of a high coercivity phase goethite these results indicate that fire induced heating caused goethite in the surface soils to convert into a more magnetic low coercivity phase such as maghemite goethite is an excellent adsorber of phosphorus and therefore we hypothesize that the destruction of goethite as a result of burning may have important implications for phosphorus cycling in the everglades ecosystem copyright 2010 john wiley sons ltd

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

stochastic resonance in the north atlantic large abrupt changes between warm and cold modes of north atlantic climate exhibit spectral power at 1500 years yet some climatic changes were linked to outburst floods and other events that are unlikely to have been truly periodic we hypothesize that a weak periodic forcing has combined with noise from ice sheet related events to cause the observed mode switches this stochastic resonance hypothesis predicts a recurrence pattern between warmings that is distinct from the predictions of simple periodic and stochastic models and at least some other models the ice isotopic data from central greenland ice cores are consistent with the stochastic resonance hypothesis but not with other models we have tested we thus support arguments for the existence of a periodicity of 1500 years in the north atlantic climate system and for the importance of ice sheet events in forcing north atlantic changes

a synchronized dating of three greenland ice cores throughout the holocene as part of the effort to create the new greenland ice core chronology 2005 gicc05 a synchronized stratigraphical timescale for the holocene parts of the dye 3 grip and ngrip ice cores is made by using volcanic reference horizons in electri cal conductivity measurements to match the cores the main annual layer counting is carried out on the most suited records only exploit ing that the three ice cores have been drilled at locations with different climatic con ditions and differences in ice flow however supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the valid ity of the match after the verification the main dating is transferred to all records us ing the volcanic reference horizons as tie points an assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores the data used for the main annual layer counting of the past 7900 years are the dye 3 grip and ngrip stable isotope records as the high accumulation rate at the dye 3 drill site makes the seasonal cycle in the dye 3 stable isotopes very resistant to firn diffusion an effort has been made to extend the dye 3 holocene record the new syn chronized dating relies heavily on this record of 75 000 stable isotope samples the dat ing of the early holocene consists of an already established part of gicc05 for grip and ngrip which has now been transferred to the dye 3 core gicc05 dates the younger dryas termination as defined from deuterium excess to 11 703 b2k 130 years earlier than the previous grip dating

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

a two parameter stochastic process for dansgaard oeschger events 1 various climatic processes are thought to evolve as rapid shift like events which points at the presence of nonlinear dynamics time series analysis of nonlinear processes however is not trivial for example because of the difficulty in coming up with a realistic random process as a viable null hypothesis in this methodology paper we construct a basic two parameter process of shift like excursions in an excitable system with a threshold we demonstrate that this stochastic process in comparison with a specific one parameter process can better reproduce main features of the waiting time histogram of abrupt glacial climate events the dansgaard oeschger events as seen in two paleoclimatic proxy records the north greenland ice core project ngrip ice core and the sofular stalagmite 18o records we use the two parameter process to test some arguments that were proposed in the ongoing discussion of a possible solar role in triggering dansgaard oeschger events using our approach we suggest for future studies to generate time series of random events which can serve as a more plausible null hypothesis for monte carlo based statistical tests on the regularity of shift like processes such as dansgaard oeschger events

surface and deep ocean variability in the northern sargasso sea during marine isotope stage 3 new geochemical proxy data from bermuda rise piston cores reveal ocean and climate conditions in the northern sargasso sea during marine isotope stage 3 using 18o on the planktonic foraminifer globigerinoides ruber we can correlate explicitly with every stadial interstadial change in greenland ice between 32 and 58 ka these data suggest repetitive changes of 4 c in the annual average sea surface temperature sst with maximum cooling comparable to or greater than sst during glacial maximum conditions the extent of sst depression is about the same for typical stadial events and for heinrich events 4 and 5 which we have identified on the bermuda rise by traces of ice rafting benthic foraminiferal 13c decreases during every stadial event consistent with reduced production of the deepest component of north atlantic deep water and shoaling of its interface with antarctic bottom water this interpretation is supported by benthic cd ca data from the climate cycle associated with interstadial 8

the recurrence time of dansgaard oeschger events and limits on the possible periodic component abstract by comparing the high resolution isotopic records from the greenland ice core project grip and the north greenland ice core project ngrip ice cores the common climate signal in the records has been approximately separated from local noise from this an objective criterion for defining dansgaard oeschger do events is achieved the analysis identifies several additional short lasting events increasing the total number of do events to 27 in the period 12 90 kyr before present bp the quasi regular occurrence of the do events could indicate a stochastic or coherent resonance mechanism governing their origin from the distribution of waiting times a statistical upper bound on the strength of a possible periodic forcing is obtained this finding indicates that the climate shifts are purely noise driven with no underlying periodicity

the greenland ice core chronology 2005 15 42 ka part 1 constructing the time scale the greenland ice core chronology 2005 gicc05 is extended back to 42 ka b2k before 2000 ad i e to the end of greenland stadial 11 the chronology is based on independent multi parameter counting of annual layers using comprehensive high resolution measurements available from the north greenland ice core project ngrip these are measurements of visual stratigraphy conductivity of the solid ice electrolytical melt water conductivity and the concentration of na c a 2 s o 4 n o 3 n h 4 a n uncertainty estimate of the time scale is obtained from identification of uncertain annual layers which are counted as 0 570 5 years the sum of the uncertain annual layers the so called maximum counting error of the presented chronology ranges from 4 in the warm interstadial periods to 7 in the cold stadials the annual accumulation rates of the stadials and interstadials are on average one third and half of the present day values respectively and the onset of the greenland interstadials 2 3 and 8 based on 20 year averaged d 18 o

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

high resolution record of the environmental response to climatic variations during the last interglacial glacial cycle in central europe the loess palaeosol sequence of dolni věstonice czech republic abstract high resolution multidisciplinary investigation of key european loess palaeosols profiles have demonstrated that loess sequences result from rapid and cyclic aeolian sedimentation which is reflected in variations of loess grain size indexes and correlated with greenland ice core dust records this correlation suggests a global connection between north atlantic and west european air masses herein we present a revised stratigraphy and a continuous high resolution record of grain size magnetic susceptibility and organic carbon 13c of the famous of dolni vestonice dv loess sequence in the moravian region of the czech republic a new set of quartz osl ages provides a reliable and accurate chronology of the sequence s main pedosedimentary events the grain size record shows strongly contrasting variations with numerous abrupt coarse grained events especially in the upper part of the sequence between ca 20 30 ka this time period is also characterised by a progressive coarsening of the loess deposits as already observed in other western european sequences the base of the dv sequence exhibits an exceptionally well preserved soil complex composed of three chernozem soil horizons and 5 aeolian silt layers marker silts this complex is at present the most complete record of environmental variations and dust deposition in the european loess belt for the weichselian early glacial period spanning about 110 to 70 ka allowing correlations with various global palaeoclimatic records osl ages combined with sedimentological and palaeopedological observations lead to the conclusion that this soil complex recorded all of the main climatic events expressed in the north grip record from greenland interstadials gis 25 to 19

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

subtropical north atlantic temperatures 60 000 to 30 000 years ago a reconstruction of sea surface temperature based on alkenone unsaturation ratios in sediments of the bermuda rise provides a detailed record of subtropical climate from 60 000 to 30 000 years ago northern sargasso sea temperatures changed repeatedly by 2 to 5 c covarying with high latitude temperatures that were previously inferred from greenland ice cores the largest temperature increases were comparable in magnitude to the full glacial holocene warming at the site abrupt cold reversals of 3 to 5 c lasting less than 250 years occurred during the onset of two such events greenland interstadials 8 and 12 suggesting that the largest most rapid warmings were especially unstable