variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

does mean annual insolation have the potential to change the climate long term climatic changes such as glacial interglacial cycles are usually explained in term of changes in solar energy received at the top of the atmosphere in particular daily insolation in the high northern hemisphere latitudes during summer is widely used in interpreting palaeoclimate records this insolation forcing is strongly marked by changes in precession however some climate variations are much more imprinted by changes in obliquity this was the case for sea surface temperature in the north atlantic during the eemian period as well as for the vostok ice core deuterium excess history over the last 250 ka therefore we investigate the insolation forcing in order to identify characteristics that could explain the observed climate response this is mainly the case for annual mean insolation variations simple hypotheses for how this forcing could act on climate are also suggested these being mainly related to changes in the moisture transport induced by the annual insolation gradient between low and high latitudes along these lines a simple conceptual model of annual mean temperature variations illustrates the role of annual mean insolation on climate c 2004 elsevier b v all rights reserved

sulfide mineralogy and sulfur isotope geochemistry of layered sills in the deer lake complex minnesota the deer lake complex located in north central minnesota consists of a series of layered peridotite pyroxenite gabbro sills sulfide minerals occur as fine disseminations throughout pyroxenite and gabbro units and occur more sporadically in peridotite and basal chilled margin units sulfide volume percentage rarely exceeds 0 5 a distinct zonation in sulfide mineralogy and sulfur isotopic composition characterizes the sills cobaltian pentlandite is the dominant sulfide mineral in peridotite pd units with ni enrichment most likely linked to the serpentinization process 34spd values are variable ranging from 3 5 to 2 8 sulfide assemblages in pyroxenite px and lower gabbro units consist of chalcopyrite pyrrhotite and minor pentlandite 34spx values range from 1 to 1 pyrite is the principal sulfide mineral in upper gabbro g units its origin may be related to increased f02 conditions of the remaining melt and to reaction between a s bearing volatile phase and mafic silicates 34sug values range from 1 to 3 5 sulfur isotopic values of chilled margin 2 9 and peridotite units together with the erratic spatial distribution of sulfide minerals in these zones suggests that the parent magma was not initially saturated with sulfur and that local sulfide concentrations are the result of incorporation of sulfur derived from metasedimentary country rocks sulfide saturation was more uniformly reached during pyroxenite formation with contained sulfur being of magmatic origin enrichment in 34s of pyrite from upper gabbro may be explained by buildup of isotopically heavy sulfur following a rayleigh process coupled with possible involvement of a so2 rich fluid phase during hydrothermal alteration

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

was the climate of the eemian stable a quantitative climate reconstruction from seven european pollen records the aim of the present study is to estimate the range of the climatic variability during the eemian interglacial which lasted about 10 000 years marine isotopic stage 5e the modem pollen analogue technique is applied to seven high resolution pollen records from france and poland to infer the annual precipitation and the mean temperature of the coldest month the succession of pollen taxa and the reconstructed climate can be interpreted coherently the warmest winter temperatures are centred in the first three millennia of the eemian interglacial during the mixed oak forest phase with quercus and corylus as dominant trees a rapid shift to cooler winter temperatures of about 6 degrees to 10 degrees c occurred between 4000 and 5000 years after the beginning of the eemian related to the spread of the carpinus forest this shift is more obvious for the reconstructed temperatures than for precipitation and is unique and irreversible for the whole eemian period following this climatic shift of the eemian variations of temperature and precipitation during the fast 5000 years were only slight with an amplitude of about 2 degrees to 4 degrees c and 200 to 400 mm yr the estimated temperature changes were certainly not as strong as those reconstructed for the stage 6 5e termination or the transition 5e 5d this is consistent with the constantly high ratio of tree pollen throughout the eemian indicative of a succession of temperate forest types this gradual transition between different forest landscapes can be related to intrinsic competition between the species rather than to a drastic climatic change c 1998 elsevier science b v all rights reserved

evaluating the role of climate cooling in iceberg production and the heinrich events bond et al 1 recently presented evidence for the frequent occurrence in the pleistocene epoch of periods of massive iceberg discharge into the north atlantic ocean heinrich events each lasting a few thousand years the cause of these events is uncertain but one possibility1 is repeated advances of the laurentide ice sheet during episodes of cooler climate here i examine this idea using a model of the laurentide ice sheet driven by orbitally forced variations in insolation with and without three additional 3 000 yr long cooling episodes imposed just before the occurrence of the three most recent heinrich events hi h2 and h3 in the model the cooling event preceding hi when the climate was relatively warm and deglaciation was about to begin led to increased calving but those preceding h2 and h3 which occurred during the last ice age when the climate was very cold led to reduced iceberg calving it thus seems unlikely that the heinrich events generally reflect a direct response of the laurentide ice sheet to climate cooling

weichselian palynological records from southern europe correlation and chronology abstract the high resolution independently dated palynostratigraphic record from lago grande di monticchio spanning the last 101 530 calendar years provides a basis for re evaluating the correlations between palaeoenvironmental events in europe during the last glacial as well as a means to determine their chronology the interstadial events recorded from various localities throughout europe are combined into a single scheme of correlations and a chronological framework is suggested this provides a basis for assessing the evolution of the vegetation and environmental patterns across europe during the last glacial revealing a general tendency for the latitudinal climatic gradient to have been steeper than it has been during the holocene the vegetation has also generally been subject to greater moisture deficiency either because of prevailing climatic conditions or as a reflection of the lower atmospheric concentration of co 2 the scheme of correlations is shown to be capable of being extended beyond europe not only to marine and ice core records from the north atlantic region but also to a palynological record from north west north america

how long and how stable was the last interglacial abstract surface ocean indicators in the north atlantic during marine isotope stage mis 5 correlate closely with the vegetational succession in northeastern france the melisey i silty layer which marks the end of the last interglacial biozone in la grande pile pollen record appears coeval with the polar front advance c24 registered in the core v29 191 by a sharply increased presence of ice rafted detritus and the cold water foraminifer neogloboquadrina pachyderma sinistral since this event is younger than the peak of mis 5d the last interglacial as recognized in northern france correlates not only with the mis 5e but also with a substantial part of mis 5d the last interglacial in la grande pile was twice as long as the holocene and the climate in its first half was apparently not less stable than during the current interglacial if the future natural climates were to develop as analogs of the past then the onset of the next glacial environments on land would be still many millennia ahead

the demise of the last interglacial recorded in isotopically dated speleothems from the alps abstract the transition from interglacial to glacial climate has attracted much attention in paleoclimatic research partly because orbital forcing dictates that such a return to a new ice age is inescapable albeit in the distant future only the detailed series of steps that leads to glacial inceptions remains poorly understood however and studies of past glacial inceptions are often compromised by incomplete records imprecise chronological control and or uncertainties associated with proxy transfer functions here we present results from u th dated speleothems from a cave in the austrian alps entrische kirche cave which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials the alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits we use high resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the last interglacial unprecedented in detail for central europe peak interglacial conditions are characterized by high 18 o values and high growth rates from ca 127 to 124 ka a major drop in 18 o by 3 occurred at ca 118 ka which coincided with cold event c26 in the north atlantic this isotopic shift which occurred at or close to isotopic equilibrium cannot be explained by simple uniform cooling modelling suggests that enhanced seasonality dominated by significant changes in winter precipitation are required to reconcile the isotope data with the fact that calcite deposition continued across the mis 5e d transition i e no cave freezing this period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free eventually speleothem growth terminated at ca 114 ka which is in line with widespread ice rafting in the north atlantic cold event c24 and the onset of fully stadial conditions during mis 5d

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

a late eemian aridity pulse in central europe during the last glacial inception how do ice ages begin it s an obvious question to ask as we enjoy the relative luxury of an interglacial but a hard one to answer a look at past transitions may give some clues as to how this period will one day come to an end a climate reconstruction based on sediments found beneath a lake in the eifel mountains in germany provides evidence of an extreme climate event lasting 468 years right at the end of the last interglacial dust storms aridity bushfires and the loss of trees associated with a warm climate coincided with a southward shift of the warm waters of the north atlantic drift in terms of insolation the rate of delivery of the sun s radiation to earth conditions then were similar to those we have now investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end which has been a matter of much debate see for example refs 1 2 a recent ice core from greenland demonstrates climate cooling from 122 000 years ago3 driven by orbitally controlled insolation with glacial inception at 118 000 years ago4 5 6 7 8 here we present an annually resolved layer counted record of varve thickness quartz grain size and pollen assemblages from a maar lake in the eifel germany which documents a late eemian aridity pulse lasting 468 years with dust storms aridity bushfire and a decline of thermophilous trees at the time of glacial inception we interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the north atlantic drift the ocean current that brings warm surface waters to the northern european region the late eemian aridity pulse occurred at a 65 n july insolation of 416 w m 2 close to today s value of 428 w m 2 ref 9 and may therefore be relevant for the interpretation of present day climate variability

coherent deep flow variation in the iceland and american basins during the last interglacial the first direct evidence that the deepflow speed of north atlantic deep water nadw in the south iceland and north americanbasins declined dramatically over a period of a few hundred years at about 120 000 years ago is presented the flow rate inferred from silt grain size then rose into the subsequent cool period stage 5d these changes are clear and synchronous in records from both locations these circulation events are recorded less markedly in chemical and isotopic proxies for the nutrient status of water masses the congruence of flowvariation and hydrography at the two separated sites suggests they are primarily controlled by variation in the deep thermohaline circulation

characteristics of the deep ocean carbon system during the past 150 000 years σco2 distributions deep water flow patterns and abrupt climate change abstract studies of carbon isotopes and cadmium in bottom dwelling foraminifera from ocean sediment cores have advanced our knowledge of ocean chemical distributions during the late pleistocene last glacial maximum data are consistent with a persistent high co2 state for eastern pacific deep water both tracers indicate that the mid depth north and tropical atlantic ocean almost always has lower co2 levels than those in the pacific upper waters of the last glacial maximum atlantic are more co2 depleted and deep waters are co2 enriched compared with the waters of the present in the northern indian ocean 13c and cd data are consistent with upper water co2 depletion relative to the present there is no evident proximate source of this co2 depleted water so i suggest that co2 depleted north atlantic intermediate deep water turns northward around the southern tip of africa and moves toward the equator as a western boundary current at long periods 15 000 years milankovitch cycle variability is evident in paleochemical time series but rapid millennial scale variability can be seen in cores from high accumulation rate series atlantic deep water chemical properties are seen to change in as little as a few hundred years or less an extraordinary new 52 7 m long core from the bermuda rise contains a faithful record of climate variability with century scale resolution sediment composition can be linked in detail with the isotope stage 3 interstadials recorded in greenland ice cores this new record shows at least 12 major climate fluctuations within marine isotope stage 5 about 70 000 130 000 years before the present

sudden end of an interglacial for the past 9 000 years or so the world has experienced an interglacial period with in terms of geological time an anomalously warm and stable climate but how stable are interglacials and what processes might bring them to a sudden close evidence from a 53 metre long sediment core retrieved from the bermuda rise in the western north atlantic now gives us the most detailed picture yet of events during the previous interglacial the results date the period concerned to between 129 000 and 119 000 years ago most notably however its termination seems to have been marked by a sudden reduction in the ocean conveyor circulation which today carries ocean heat north from the tropics and warms much of europe

new tephra horizons from oxygen isotope stage 5 in the north atlantic correlation potential for terrestrial marine and ice core archives abstract tephra horizons of oxygen isotope stage ois 5 age from two cores in the north atlantic have been analysed geochemically the results show that several discrete tephra horizons are present which have an icelandic provenance tephras of basaltic geochemistry dominate the sequences correlation of the cores is based on the occurrence of a basaltic tephra near the base of ois 5e a rhyolitic tephra has been discovered within ois 5e sediments in a core from the se norwegian sea which is geochemically identical to the middle eemian tephra found in several cores from the nordic seas this tephra is probably widespread and thus the potential exists for its wider detection in terrestrial sequences on mainland europe and the greenland ice cores

relation of subtropical atlantic temperature high latitude ice rafting deep water formation and european climate 130 000 60 000 years ago abstract a new high resolution record of sea surface temperature from the subtropical western north atlantic documents a series of abrupt coolings within marine isotope stage 5 which can be objectively correlated with marine core evidence for increased ice sheet discharge at subpolar latitudes and reduced north atlantic deep water formation these results indicate that ice sheet forcing of deep ocean circulation influenced surface temperatures over much of the north atlantic a proposed correlation to the pollen record of grande pile france indicates that each cold event seen in the pollen sequence has a unique counterpart in the record of subtropical ocean temperature if this correlation is correct it suggests that the warmest part of the european eemian ended suddenly in response to oceanographic changes and that the subsequent post temperate phase of the eemian extended well into the interval of ice sheet growth corresponding to marine isotope substage 5d

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate 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

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

substantial contribution to sea level rise during the last interglacial from the greenland ice sheet during the last interglacial period the eemian global sea level was at least three metres and probably more than five metres higher than at present1 2 complete melting of either the west antarctic ice sheet or the greenland ice sheet would today raise sea levels by 6 7 metres but the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the west antarctic ice sheet3 with model studies attributing only 1 2 m of sea level rise to meltwater from greenland4 5 this result was considered consistent with ice core evidence4 although earlier work had suggested a much reduced greenland ice sheet during the last interglacial period6 here we reconsider the eemian evolution of the greenland ice sheet by combining numerical modelling with insights obtained from recent central greenland ice core analyses our results suggest that the greenland ice sheet was considerably smaller and steeper during the eemian and plausibly contributed 4 5 5 m to the sea level highstand during that period we conclude that the high sea level during the last interglacial period most probably included a large contribution from greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the west antarctic ice sheet

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

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