sedimentology of quaternary perched springline and paludal tufas criteria for recognition with examples from guadalajara province spain outcrop scale geometries and bed relationships of ambient temperature freshwater carbonates are poorly understood because many described tufas have been dismantled by erosion and present only part of a particular depositional model at the field scale four end member models encompass the tufa continuum 1 perched springline 2 paludal 3 fluvial and 4 lacustrine tufas individual bed types can occur with variable dominance within several of these models but one or more beds are characteristically dominant only within a single tufa model so it can be differentiated from relatively isolated outcrop fragments two models perched springline tufas and paludal tufas are known in outline only in the literature despite being present within the quaternary deposits of most karstic regions perched springline tufas generally form lobate fan shaped mound morphologies on hillslopes and develop from single or multiple spring resurgences mature deposits show a subhorizontal top and a steep face on the downflow side the steep outer zones of tufa mounds may be developed into cascades with moss curtains or can be dominated by shallow rimstone pools according to face angle tufa deposits lying downslope of the mounds are usually detrital in nature especially if some dismantling of the mound has occurred the relatively thin subhorizontal lobe top deposits commonly contain organic rich deposits paludal tufas develop predominantly in waterlogged valley bottom situations where line sourced waters emerge from valley side and bottom aquifers lime mud precipitation predominates in these sites mud is deposited as subhorizontal laminites that thin towards the valley axis and downstream of resurgences tufa spring mounds may form where lesser volumes of water are involved individual tussocks phytoherm cushions of grasses and rushes are the most diagnostic feature of the model but sapropels and peats may be intercalated diagenesis in both models is rapid lithification of individual beds is virtually instantaneous and always occurs before the decay of the associated living vegetation the resulting highly porous and permeable fabrics remain fresh in holocene tufas but aggrading neomorphism and partial spar infill of vegetation moulds is common in older deposits dissolution in many perched springline tufas is small scale many large cavities are primary but with later coatings of speleothems early removal of organics from paludal tufas is responsible for autobrecciation and differential compaction

climate logging with a new rapid optical technique at siple dome the dust logger design is based on a decade of experience in the use of light sources to measure optical properties of deep antarctic ice light is emitted at the top of the instrument by side directed leds scattered or absorbed by dust in the ice surrounding the borehole and collected in a downhole pointing photomultiplier tube pmt a meter below with this method the ice is sampled at ambient pressure in a much larger volume than is the case in a core study and the entire length can be logged in one day in ice in which scattering is dominated by bubbles the absorption from dust impurities is perceived as a drop in signal whereas in bubble free ice the scattering from dust increases the light collected we report on results obtained in siple dome hole a in december 2000 the instrument measured increases in dust concentration extending over many meters during glacial maxima as well as narrow spikes due to 1 cm thick ash and dust bands of volcanic origin monte carlo simulation is employed to clarify data analysis and predict the capabilities of future designs

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

high resolution ammonium ice core record covering a complete glacial interglacial cycle high resolution ammonium measurements were performed along the greenland ice core program grip deep ice core covering a complete climatic cycle no overall anthropogenic increase is observed over the last 300 years however springtime concentrations have roughly doubled since 1950 biomass burning is estimated to be a major source for ammonia emissions for preindustrial times it contributes between 10 to 40 to the total ammonium deposited on the central greenland ice sheet during the holocene no correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern north america which is considered to be the main source area for ammonium deposited on the central greenland ice sheet this suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core if unchanged meteorological conditions are assumed for the holocene as indicated by the 18o ice record a decreasing biomass burning activity toward present time can be derived from the ammonium ice record soil and vegetation emissions are responsible for the ammonium background concentrations in the ice the record therefore may be used to trace back the biomass history of the north american continent a pronounced decreasing trend in background ammonium is found during the holocene reflecting decreasing temperature and therefore lower nh3 emissions in the source region variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength which can be related to the extent of the laurentide ice sheet the data suggest that the laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

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

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

volcanic ash from the 1362 a d oraefajokull eruption iceland in the greenland ice sheet a continuous record of electrical conductivity measurements ecm was made on site during the drilling of a 200 m ice core at summit greenland and was used to identify horizons in the ice that might be linked to volcanic eruptions in one detailed section that we studied a large peak in the number of particles two orders of magnitude above the background was measured the particle peak was not associated with an ecm peak however the particles were identified as volcanic ash on the basis of both particle morphology and chemical composition the ash composition suggests an explosive rhyolitic eruption and is believed to have originatedfrom oraefajokull in iceland in 1362 a d

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

high precision dating of volcanic events a d 1301 1995 using ice cores from law dome antarctica a record of volcanic activity over the period a d 1301 1995 has been extracted from three law dome ice cores east antarctica the record dating is unambiguous at the annual level from a d 1807 to 1995 and has an uncertainty of 1 year at a d 1301 signals from 20 eruptions are preserved in the record including those of two unknown eruptions with acid deposition beginning in a d 1810 8 and a d 1685 8 the beginning of the ice core signal from the a d 1815 tambora eruption is observed in the austral summer of a d 1816 1817 the mean observed stratospheric transport and deposition time to law dome from the eruption site is 1 5 years 0 6 years from 11 well dated eruptions the largest eruption observed in the law dome record has its maximum in a d 1460 with volcanic sulfate deposition beginning in the austral winter of a d 1459 this event is also observed in other ice core records and is attributed to the volcano kuwae with an eruption date in the range a d 1455 9 1459 9 if all sources of error are considered this is at least three years later than the date previously ascribed by dendrochronological and historical studies

sulphate record from a northeast greenland ice core over the last 1200 years based on continuous flow analysis a 150 m deep ice core from the low accumulation area of northeast greenland was analyzed for sulphate calcium sodium and electrolytical meltwater conductivity at a depth resolution of approximately 1 cm by continuous flow analysis cfa the calcium and sodium profiles are used to establish a relatively precise ice core chronology by annual layer counting back to ad 830 inspection of the novel cfa method for sulphate revealed relative errors typically around 15 but at least 20 ng g 1 for concentrations 5130 ng g 1 and a current detection limit for routine ice core analyses of 40 ng g 1 annual sulphate peaks are shown to occur over almost the entire core with only a small shift in seasonality between the modern and pre industrial sections inspection of volcanic horizons allowed more accurate timing of these peaks and clear identification of calcium rich events disregarding clear volcanic peaks significant long term changes of sulphate are only seen over the industrial period however a higher frequency of important volcanic inputs was identified around ad 1200

synchronization of the ngrip grip and gisp2 ice cores across mis 2 and palaeoclimatic implications abstract we here present a synchronization of the ngrip grip and gisp2 ice cores based mainly on volcanic events over the period 14 9 32 45 ka b2k before ad 2000 corresponding to marine isotope stage 2 mis 2 and the end of mis 3 the matching provides a basis for applying the recent ngrip based greenland ice core chronology 2005 gicc05 time scale to the grip and gisp2 ice cores thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores based on the matching a period of anomalous high accumulation rates in the gisp2 ice core is detected within the period 16 5 18 3 ka b2k the 18 o and ca 2 profiles of the three cores are presented on the common gicc05 time scale and generally show excellent agreement across the stadial interstadial transitions and across the two characteristic dust events in greenland stadial 3 however large differences between the 18 o and ca 2 profiles of the three cores are seen in the same period as the 7 9 increase in the gisp2 accumulation rate we conclude that changes of the atmospheric circulation are likely to have occurred in this period altering the spatial gradients in greenland and resulting in larger variations between the records

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

comparison of holocene electrical records from dome c and vostok antarctica as part of the european project for ice coring in antarctica a new deep ice core is being drilled at dome c two electrical methods have been used on the core drilled so far a new design of electrical conductivity method ecm instrument and a traditional dielectric profiler the two profiles are very similar in both peaks and background consistent with acidity being the dominant influence on both in this part of the record the dome c records have been compared to ecm records from vostok and a tentative match has been made between them this suggests a long term average ratio of accumulation rate of 1 36 between this dome c core and vostok and that the dome c core analyzed so far to 358 m probably includes the very end of the glacial holocene transition

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

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 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

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

volcanic ash layers from the last glacial termination in the ngrip ice core the tephrochronological record of the 1400 1640 m depth 10 000 16 000 calendar ice core years before present of the ngrip ice core has been established by particle screening of selected samples ash was identified in 20 samples correlation with ice marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the saksunarvatn ash and the vedde ash ash zone 1 major element chemistry of the remaining identified ash layers mainly points towards an icelandic origin this tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the last glacial termination within the north atlantic region as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation copyright 2005 john wiley sons ltd

anomalous concentrations of seismically triggered rock falls in pacoima canyon are they caused by highly susceptible slopes or local amplification of seismic shaking anomalously high concentrations of rock falls were triggered in pacoima canyon los angeles california during the 1994 northridge earthquake similar concentrations were also documented from the 1971 san fernando earthquake using an engineering rock mass classification that evaluates the susceptibility of rock slopes to seismic failure based on the fracture properties of a rock mass in terms of a numerical q value that describes rock quality the rock slopes in pacoima canyon were compared with rock slopes in surrounding areas where topography and lithology are similar but rock fall concentrations from the earthquakes were much lower a statistical comparison of q values from five sites surrounding pacoima canyon indicates that seismic susceptibilities are similar to those within pacoima canyon differences in the characteristics of rock slopes between these sites are not sufficient to account for the relatively high concentrations of rock falls within pacoima canyon as compared to low concentrations elsewhere by eliminating susceptibility differences as a cause the most likely explanation for the differences in rock fall concentrations is anomalously high shaking levels in pacoima canyon possibly resulting from topographic amplification within the canyon manuscript received 21 may 2001

a comparison of the volcanic records over the past 4000 years from the greenland ice core project and dye 3 greenland ice cores since 1980 the electrical conductivity method ecm has been used to infer volcanic acid signals in greenland ice cores the method reveals the great majority of major volcanic eruptions including several known from historic records subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition i e the concentration of the volcanic acids h2so4 hci and hf plus e g the nonvolcanically derived hno3 while ecm data are available from a large number of shallow depth greenland ice cores covering the past 500 1500 years only the greenland ice core project grip greenland ice sheet project 2 gisp2 and dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in greenland ice cores representing several thousand years comparison of the volcanic signals registered in the grip and gisp2 cores will be presented elsewhere the latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature snow accumulation and chemical composition of the air here we present a comparison between the major volcanic signals over the past 4000 years in the grip core from central greenland and the dye 3 core from se greenland in order to investigate the depositional differences many of the major signals are detected in both cores but some of the differences in the records can be used to infer the latitudinal band of some eruption sites furthermore the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed

electrical measurements on the greenland ice sheet project 2 core the greenland ice sheet project 2 gisp2 electrical conductivity measurement ecm record is an indication of the concentration of h in the core the ecm detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting volcanic eruptions that produce acidic aerosols are recorded in the ecm record evidence of biomass burning is detected by the ecm because fire related ammonium emissions neutralize the acids in the core rapid climate transitions associated with the younger dryas and dansgaard oeschger interstadial events alter the concentration of alkaline dust and are detected by the ecm the ecm has been used to develop stratigraphic ties between the gisp2 and the greenland ice core project cores users of the data should be aware of some instrument related artifacts in the ecm record

biomass burning recorded in the gisp2 ice core a record from eastern canada combustion byproducts from biomass burning are preserved in annually stratified layers in the greenland ice sheet electrical conductivity ecm and ammonium records from the gisp2 ice core in central greenland have been used to develop a 6000 year record of biomass burning although there is some uncer tainty regarding the source area for the combustion byproducts it is likely that the majority of the material originates in eastern canada time periods of high biomass burning activity occurred in 0 150 bp 350 750 bp and 5000 to 6000 bp the period 1150 3250 bp is characterized by moderately elevated levels of biomass burning activity these periods are associated with drier conditions the 5000 to 6000 bp period of high biomass burning activity may also be related to forest successional sequences following the removal of the laurentide ice sheet this paper explains how ice cores can be used to develop records of biomass burning and offers suggestions for future studies

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

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

an inter hemispheric volcanic time marker in ice cores from greenland and antarctica a strong volcanic acid signal is clearly registered using an acidity measuring technique in the a d 1259 ice layer in four different greenland ice cores camp century milcent crete and dye 3 this signal is similar in amplitude to the laki iceland a d 1783 volcanic event as recorded in the central and south greenland ice cores measurement of ice layers from corresponding age levels in antarctic ice cores byrd station south pole and j 9 on the ross ice shelf provides similar strong acid signals there is no historical record of a significant volcanic eruption for the period around a d 1260 in the northern hemisphere subsequent chemical analyses of all a d 1259 ice layers show similar compositions we suggest that the a d 1259 signals registered in both greenland and antarctica were caused by the same volcanic disturbance and that its epicenter was located at the earth s equatorial zone which enabled global distribution of the acid gases these results indicate that inter hemispheric dating of ice sheets is possible by the chemical identification of major eruptive volcanic events in the equatorial zone