climate volcanism feedback and the toba eruption of 74 000 years ago abstract a general feedback between volcanism and climate at times of transition in the quaternary climate record is suggested exemplified by events accompanying the toba eruption 74 000 yr ago the largest known late quaternary explosive volcanic eruption the toba paroxysm occurred during the 18o stage 5a 4 transition a period of rapid ice growth and falling global sea level which may have been a factor in creating stresses that triggered the volcanic event toba is estimated to have produced between 1015 and 1016 g of fine ash and sulfur gases lofted in co ignimbrite ash clouds to heights of at least 32 5 km which may have led to dense stratospheric dust and sulfuric acid aerosol clouds these conditions could have created a brief dramatic cooling or volcanic winter followed by estimated annual northern hemisphere surface temperature decreases of 3 to 5 c caused by the longer lived aerosols summer temperature decreases of 10 c at high northern latitudes adjacent to regions already covered by snow and ice might have increased snow cover and sea ice extent accelerating the global cooling already in progress evidence for such climate volcanic feedback following milankovitch periodicities is found at several climatic transitions

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

newly discovered eastern dispersal of the youngest toba tuff volcanic glasses with minor mafic mineral fragments such as biotite and hornblende found in deep sea sediments of the south china sea basin scsb have been clearly identified as eruptive products of the youngest toba tuff ytt northern sumatra indonesia the tephra layer occurs between marine oxygen isotopic event 5 1 79 3 ka and event 4 22 64 1 ka with an interpolated age of 74 0 ka which is in good consistence with previous radiometric dating 73 75 ka and ice core dating 71 5 ka of the ytt the tephra consists predominantly of bubble wall shards with minor elongated vesicles of pumice fragments geochemical characteristics of the tephra such as high total alkali content high 87 sr 86 sr ratio and uniformity of their compositions all suggest that the recovered tephra is of the youngest toba tuff this finding supports an extended dispersal of coarse 63 mm glass shards over 1500 km northeast of the toba caldera a direction opposite to what previously conceived while providing a better documentation of the distribution extent of the toba ash this report points to the need to reestimating the eruptive volume of the ytt and re evaluating its environmental impact q 2000 elsevier science b v all rights reserved

the role of microphysical and chemical processes in prolonging the climate forcing of the toba eruption the mega eruption of toba sumatra occurred around 73 ka ago during the onset of a glaciation of the late quaternary this coincidence combined with the unprecedented amount of sulphur released by this volcano has led to the hypothesis that toba sulphate aerosols caused a transient surface cooling which may have contributed to a shift of the climate system because of the self limiting effect of gravitational sedimentation the climatic impact of extremely large sulphur injections into the stratosphere are thought to be rather limited here we present model calculations combining microphysical and chemical feedbacks which show that the eruption could instead have led to the formation of a long lasting volcanic aerosol layer although the concentrations of radiatively active species such as o3 or so2 could also have been considerably perturbed the resulting forcings should have only slightly moderated the aerosol cooling effect during the first few years following the eruption according to our results extremely high stratospheric sulphur loading could lead to a more prolonged effect on the climate than previously assumed

major element geochemistry of glass shards and minerals of the youngest toba tephra in the southwestern south china sea an ash layer newly discovered in core md01 2393 from the southwestern south china sea has been studied in order to characterize its major element features the layer 4 0 cm thick light grayish and silt size occurs right at the marine isotope stage 4 5 transition ca 74 kyr ago the morphology and geochemistry of glass shards combined with oxygen isotope and carbonate stratigraphy confirm the youngest toba eruption in northern sumatra as the origin of the ash layer major element data on mineral crystals i e biotite plagioclase and hornblende from the ash layer suggest that biotite is phenocrystic while hornblende and some plagioclase are xenocrystic implying that these xenocrysts were incorporated into the youngest toba magma before the eruption q 2005 elsevier ltd all rights reserved

recent and holocene climate change controls on vegetation and carbon accumulation in alaskan coastal muskegs abstract pollen spore macrofossil and carbon data from a peatland near cordova alaska reveal insights into the climate vegetation carbon interactions from the initiation of the holocene c the last 11 5 ka to the present 1 ka 1000 calibrated years before present where 0 1950 ce the holocene period is characterized by early deposition of gyttja in a pond environment with aquatics such as nuphar polysepalum and potamogeton and a significant regional presence of alnus crispa subsp sinuata carbon accumulation 50 g m 2 a was high for a short interval in the early holocene when sphagnum peat accumulated but was followed by a major decline to 13 g m 2 a from 7 to 3 7 ka when cyperaceae and ericads such as rhododendron formerly ledum groenlandicum expanded this shift to sedge growth is representative of many peatlands throughout the south central region of alaska and indicates a drier more evaporative environment with a large decline in carbon storage the subsequent return to sphagnum peat after 4 ka in the neoglacial represents a widespread shift to moister cooler conditions which favored a resurgence of ericads such as andromeda polifolia and increased carbon accumulation rate the sustained alnus expansion visible in the top 10 cm of the peat profile is correlative with glacial retreat and warming of the region in the last century and suggests this colonization will continue as temperature increases and ice melts

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

a millennial scale u37k sea surface temperature record from the south china sea 8 n over the last 150 kyr monsoon and sea level influence we report 150 kyr records of u37 sea surface temperature sst and carbonate content with 150 200 year sampling resolution from the southern south china sea scs in the northern margin of the western pacific warm pool wpwp using images core md972151 the glacial interglacial sst change is about 5 c for termination ii 23 5 to 28 5 c and 4 c for termination i 24 to 28 c the simultaneous rise of sea level and u37 sst during termination i suggests that sea level change has played an important role in the scs sst variability by influencing the exchange of tropical ocean warm surface water with the scs through the sunda shelf region sill depth 30 50 m when sea level drop was less than 30 m relative to today s md972151 sst was constantly above 27 c a situation which occurred during mis 5e part of mis5c and 5a and over the last 11 kyr sea level change was also the main control on carbonate content in the scs this was lower during low sea level stands due to the dilution effect of enhanced terrigenous inputs within the limitations of our age model millennial scale sst oscillations 1 5 c over a few hundred years occurred frequently during the entire glacial period correlating reasonably well with the hulu monsoon record from eastern china and the dansgaard oeschger d o cycles recorded for high latitude regions in the northern hemisphere such correlations suggest a possible teleconnection between higher latitude atmospheric forcing and low latitude climate oscillations in the western pacific tropical region via the asian monsoon system carbonate content also reveals millennial scale oscillations during the glacial period with higher content correlated with higher sst millennial scale fluctuations of sst and carbonate contents at this low latitude scs provide additional evidence that high frequency climate changes are global phenomena

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

mass transport in european cretaceous chalk fabric criteria for its recognition although it is a pelagic sediment fine grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units numerous occurrences of allochthonous chalk have been reported in recent years having been recognized by large scale bedding features seen in outcrop smaller scale internal features such as contorted laminae and larger features such as smeared burrows and imbricated flint nodules attest to a significant amount of soft sediment deformation and synsedimentary slumping in european chalk sections of late cretaceous age truly autochthonous chalks contain complex tiered ichnofabrics and in some cases exhibit a diagenetic nodular fabric that is undisturbed by transport in some situations such as stagnant water conditions autochthonous chalks may exhibit primary lamination although this is very uncommon in european chalk sequences different types of redepositional processes produce an array of varied allochthonous fabrics glide and slump units for example contain internal deformational features produced during sliding ooze flow causes plastic deformation of chalk units internally as well as externally resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric such as a conglomerate composed of detrital chalk clasts in this paper typical macroscopic sedimentary fabric types are illustrated and the means of identifying them are discussed in terms of bioturbation features in situ diagenetic nodules versus detrital clasts physical deformation structures and development of flints

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

sea surface temperature estimates for the tropical western pacific during the last glaciation and their implications for the pacific warm pool twenty deep sea sediment cores from the western pacific between 30 n and 30 s provide evidence of sea surface temperature sst changes throughout the tropics and subtropics glacial ssts were estimated using the modern analog technique mat applied to planktonic foraminifers and planktonic foraminiferal 18o changes we used 18o to identify the last glacial maximum the mat method differs from the traditional transfer function approach in that it utilizes a global coretop database and estimates paleotemperature by finding analogs from the modern coretop samples in addition the mat approach appears to be less susceptible than the transfer function technique to biases introduced by carbonate dissolution our results indicate that tropical ssts differed by less than 2 c from present away from the tropics 30 n and 30 s ssts were at least 3 c cooler our results differ from those of previous studies in the western pacific by using a set of well preserved high sedimentation rate cores from shallow regions the results of this study clearly indicate that a western pacific warm pool existed during the last glacial maximum lgm providing a heat and moisture source for a walker circulation cell similar to that of today we propose that a steeper lapse rate existed during the last glacial maximum and that this can explain at least part of the discrepancy between marine and terrestrial temperature estimates adjacent to new guinea for the lgm

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

16 c rapid temperature variation in central greenland 70 000 years ago variations in the29n2 28n2 ratio of air bubbles trapped in polar ice cores and their relation to variations of the 18o 16o of the ice allow past surface temperature variations and ice age gas age differences to be determined high resolution measurements of29n2 28n2 in dansgaard oeschger event 19 around 70 000 years before the present in ice from central greenland show that at the beginning of the event the ice age gas age difference was 1090 100 years with the use of a combined firn densification temperature and gas diffusion model the 18oice temperature coefficient was determined to be 0 42 0 05 per mil per kelvin this coefficient implies a mean surface temperature change of 16 0 kelvin between 14 3 and 18 1 kelvin which differs substantially from values derived from borehole temperatures and modern spatial 18oice surface temperature correlations

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

compositions of foraminifera rich turbidite sediments from the shenhu area on the northern slope of the south china sea implication for the presence of deep water bottom currents abstract the sediments in gravity core dh 1 collected from shenhu area on the northern slope of the south china sea are composed of two dark grey clay silt layers a1 and a3 and two foraminifera rich layers a2 and a4 a1 is the top layer and a4 is the bottom layer major and trace metal contents along with grain size and mineralogic data suggest that these silt layers represent background hemipelagic sedimentation unlike silt layers the intervening foraminifera rich layera4 exhibits a fining upward trend is distal turbidite grain size cm diagram and the sharp contacts between the foraminifera rich layer a2 and the upper and lower layers suggest layer a2 is the result of depositional interaction between turbidite and bottom currents ams 14c dating of planktonic foraminifera indicate the age of the turbidite in a2 is between15 3 ka and 22 6 ka we hypothesize that turbidite formation in this period was related to the increase supply of terrigenous matter since the last glacial maximum the rapid deposition of each turbidite led to reduced rates of oxygen diffusion into the sediment allowing anoxic conditions develop in sediments and fostering u enrichment 3 1 g g in foraminifera rich layer a4b in contrast decrease concentration of u and u mo ratios in foraminifera rich layera2 which is possibly due to u remobilization as a consequence of downward penetration of the oxidation front from the oxygen rich bottom currents these new data suggest that authigenic u was quite sensitive to the inflow of bottom currents and u mo ratios may indicate the depositional environmental change in relation to the bottom current action on the turbidite

cooling of the south china sea by the toba eruption and correlation with other climate proxies 71 000 years ago the toba tephra layer has been identified in core md972151 in the southern south china sea scs northeast of the indonesia toba caldera this affords us an opportunity to directly determine a 1 c cooling for ca 1 kyr on the scs following the toba eruption 71 ka during the marine isotope stage 5a 4 transition using century scale sea surface temperature records this cooling event in the scs is well correlated with several coeval proxies such as increased east asia winter monsoon intensity increased ice rafted detritus in the north pacific ocean sediments and decreased 18 o in greenland ice core such correlation suggests a climate change where cold climate signals originated in the northern hemisphere ice sheets transferred southward by the winter monsoon and cooled the scs

a 263 year record of summer temperature for northern quebec reconstructed from tree ring data and evidence of a major climatic shift in the early 1800 s abstract tree ring data are used to reconstruct 263 years of summer temperatures at a site located near the northern tree line in central western quebec a chronology comprising 20 ring density time series is used in conjunction with a chronology comprising 20 ring width time series in the regression analyses the increased precision of the temperature estimates obtained by using density data as an additional proxy time series places the reconstruction and its interpretation on a firmer basis than it is when only ring width data are used the results are considerably improved over the use of either tree ring parameter alone the temperature reconstruction reflects a major cooling event in the early nineteenth century comparisons with other temperature and proxy data series support the idea of a global cooling event with a persistence of the cool period of about three decades in high latitude north america and of much shorter duration in other regions of the world volcanic activity in the early 1800 s is suggested as partially responsible for the cooling event but is considered inadequate as cause for the extended period of low temperatures in the locale of this reconstruction

toba ash layers in the south china sea evidence of contrasting wind directions during eruption ca 74 ka two cores from the southern south china sea contain discrete ash layers that mainly consist of rhyolithic glass shards on the basis of the specmap time scale the ash layers were dated to ca 74 ka the age of the youngest toba eruption in northern sumatra this link is supported by the chemical composition of the glass which is distinct from volcanic glass supplied from the philippines and the northern south china sea but is almost identical with the chemistry of the toba ash the youngest toba ash layers in the south china sea expand the previously known ash fall zone over more than 1800 km to the east the dispersal of ashes from sumatra in both western and eastern directions indicates two contrasting wind directions and suggests that 1 the toba eruption probably happened during the southeast asian summer monsoon season and 2 the volume of erupted magma was larger than previously interpreted

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr