modelling glacial climatic millennial scale variability related to changes in the atlantic meridional overturning circulation a review abstract since the discovery of glacial abrupt variability in greenland and the north atlantic about two decades ago its modelling remains a conceptual and technical challenge while the global climatic signature of heinrich events can reasonably be ascribed to the fresh water discharge related to the massive iceberg armadas released by the laurentide ice sheet in the north atlantic the existence of such a triggering mechanism is elusive as far as dansgaard oeschger type variability is concerned even if other mechanisms have been proposed the majority of modelling attempts to better understand glacial climate variability has assumed it to be linked to abrupt variations in the atlantic meridional overturning circulation amoc in this review we introduce the rationale behind this approach i e the possible existence of several deep ocean circulation equilibria associated with distinct climate signatures we then review the published fresh water hosing experiments and the mechanisms at work to explain the climate differences related to the different amoc states most of these works have been performed under pre industrial boundary conditions the few hosing experiments run under glacial conditions show that the sensitivity of the climate system to fresh water hosing is very dependent on the background climate state in order to rigourously compare several types of experiments equilibrium runs vs transient runs with pre industrial vs glacial boundary conditions we present experiments especially run for this review with two climate models of intermediate complexity uvic and loveclim although there are similarities between the responses simulated by these models there are also many differences which would benefit being compared to reconstructions such as those presented in this special issue however a strict comparison will require to consider boundary conditions as realistic as possible for marine isotopic stage 3 modelling glacial variability to compare model results with paleoclimatic data remains a big challenge

millennial scale variations in western sierra nevada precipitation during the last glacial cycle mis 4 3 transition abstract dansgaard oeschger d o cycles had far reaching effects on northern hemisphere and tropical climate systems during the last glacial period yet the climatic response to d o cycles in western north america is controversial especially prior to 55 ka we document changes in precipitation along the western slope of the central sierra nevada during early marine oxygen isotope stages mis 3 and 4 55 67 ka from a u series dated speleothem record from mclean s cave the timing of our multi proxy geochemical dataset is coeval with d o interstadials 15 18 and stadials including heinrich event 6 the mclean s cave stalagmite indicates warmer and drier conditions during greenland interstadials giss 15 18 signified by elevated 18o 13c reflectance and trace element concentrations and less radiogenic 87sr 86sr our record extends evidence of a strong linkage between high latitude warming and reduced precipitation in western north america to early mis 3 and mis 4 this record shows that the linkage persists in diverse global climate states and documents the nature of the climatic response in central california to heinrich event 6

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

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

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

high latitude forcing of the south american summer monsoon during the last glacial the climate of the last glacial period 10 000 to 110 000 years ago was characterized by rapid millennial scale climate fluctuations termed dansgaard oeschger d o and heinrich events we present results from a speleothem derived proxy of the south american summer monsoon sasm from 16 000 to 50 000 years ago that demonstrate the occurrence of d o cycles and heinrich events this tropical southern hemisphere monsoon reconstruction illustrates an antiphase relationship to northern hemisphere monsoon intensity at the millennial scale our results also show an influence of antarctic millennial scale climate fluctuations on the sasm this high resolution precisely dated tropical precipitation record can be used to establish the timing of climate events in the high latitudes of the northern and southern hemispheres

annual trace element variations in a holocene speleothem high resolution secondary ionization mass spectrometry sims analysis along the growth axis of a holocene speleothem from northern scotland reveals high frequency oscillations and longer term trends in mg ca sr ca and ba ca at the scale of the high frequency oscillations mg ca and sr ca display a well defined anticorrelation while sr ca and ba ca are positively correlated imaging of elemental ratios in two dimensions reveals that the high frequency signal is well preserved and laterally continuous across the sample tims 230th ages and annual ultraviolet luminescence banding provide chronological control and demonstrate that the high frequency cyclicity is annual trace element variations in speleothem calcite are a reflection of hydrochemical processes in the unsaturated zone overlying the cave supply effects and partitioning at the water calcite interface mg partitioning between water and calcite is temperature dependent calculations suggest that the annual mg ca oscillations may be caused by seasonal temperature changes however the longer timescale variations in mg ca are too great to be explained by this mechanism seasonal variations in water residence time in the unsaturated zone which reflect effective precipitation provide a more probable explanation for the observed annual oscillations and also explain the inverse relationship between mg ca and sr ca this record suggests that trace elements in speleothems have the potential to provide the high resolution insights into interannual palaeoclimatic variability required for assessment of general circulation models

wisconsin glaciation of the sierra nevada 79 000 15 000 yr b p as recorded by rock flour in sediments of owens lake california chemical analyses of the clay sized fractions of 564 continuous sediment samples 200 yr resolution from composite core ol90 92 allow quantification of an abundance of glacial rock flour rock flour produced during glacier advances is represented by clay sized plagioclase k feldspar and biotite in homogeneous internal composition the abundance of rock flour is deemed proportional to the intensity of glacies advances age control for the composite section is provided by combining previously published radiocarbon dates on organics u th dates on ostracode shells and u th dates on saline minerals from nearby searles lake correlated to ol92 by pollen the rock flour record displays three levels of variability 1 a dominant one of about 20 000 yr related to summer insolation and precipitation 2 an intermediate one of 3000 5000 yr perhaps related to north atlantic heinrich events and 3 a minor one of 1000 2000 yr perhaps related to north atlantic thermohaline driven air temperature variation

quaternary geological mapping of the lowlands of the netherlands a 21st century perspective old borehole descriptions modern lithostratigraphical classification and geostatistics have been combined in recent geological mapping in the netherlands recent developments in geostatistics and the increased computing capacity of personal computers enable three dimensional geological mapping based on already available data the data originate from a mapping programme at the scale of 1 50 000 that was started in the 1950s by the national geological survey rijks geologische dienst although started on a lithostratigraphical basis the increased use of radiocarbon dates since the 1950s influenced the map legend the map units were largely defined by age boundaries that were supposed to coincide with transgressions and regressions more recent research revealed that not only sea level but also regional basin topography sediment supply and regional neo tectonics are important factors controlling coastal development the netherlands institute of applied geoscience tno national geological survey the successor of the rijks geologische dienst recently redefined the classification of holocene coastal and alluvial deposits in a purely lithostratigraphical way the old borehole descriptions contain purely lithological descriptions as well as interpretations that were derived from those descriptions the larger part of the originally defined map units represents boundaries that characterise a change in lithology by returning to the original lithological descriptions the borehole data and the geological maps are applicable in the new lithostratigraphical framework they are now used in modern three dimensional geological mapping modelling of the subsurface these models are very useful for applied geological research 2004 elsevier ltd and inqua all rights reserved

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

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

high resolution climate simulation of the last glacial maximum the climate of the last glacial maximum lgm is simulated with a high resolution atmospheric general circulation model the ncar ccm3 at spectral truncation of t170 corresponding to a grid cell size of roughly 75 km the purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography the lgm simulations were forced with modified climap sea ice distribution and sea surface temperatures sst reduced by 1 c ice sheet topography reduced co2 and 21 000 bp orbital parameters the high resolution model captures modern climate reasonably well in particular the distribution of heavy precipitation in the tropical pacific for the ice age case surface temperature simulated by the high resolution model agrees better with those of proxy estimates than does the low resolution model despite the fact that tropical ssts were only 2 1 c less than the control run there are many lowland tropical land areas 4 6 c colder than present comparison of t170 model results with the best constrained proxy temperature estimates noble gas concentrations in groundwater now yield no significant differences between model and observations there are also significant upland temperature changes in the best resolved tropical mountain belt the andes we provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells a longstanding model data discrepancy therefore appears to be resolved without invoking any unusual model physics the response of the asian summer monsoon can also be more clearly linked to local geography in the high resolution model than in the low resolution model this distinction should enable more confident validation of climate proxy data with the high resolution model elsewhere an inferred salinity increase in the subtropical north atlantic may have significant implications for ocean circulation changes during the lgm a large part of the amazon and congo basins are simulated to be substantially drier in the ice age consistent with many but not all paleo data these results suggest that there are considerable benefits derived from high resolution model regarding regional climate responses and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent

north pacific climate response to freshwater forcing in the subarctic north atlantic oceanic and atmospheric pathways abstract sudden changes of the atlantic meridional overturning circulation amoc are believed to have caused large abrupt climate changes over many parts of the globe during the last glacial and deglacial period this study investigates the mechanisms by which a large freshwater input to the subarctic north atlantic and an attendant rapid weakening of the amoc influence north pacific climate by analyzing four different ocean atmosphere coupled general circulation models gcms under present day or preindustrial boundary conditions when the coupled gcms are forced with a 1 sv sv 106 m3 s 1 freshwater flux anomaly in the subarctic north atlantic the amoc nearly shuts down and the north atlantic cools significantly the south atlantic warms slightly shifting the atlantic intertropical convergence zone southward in addition to this atlantic ocean atmosphere response all of the models exhibit cooling of the north pacific especially along the oceanic frontal zone consistent with paleoclimate recons

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

testing feldspar and quartz luminescence dating of sandy loess sediments from the doroshivtsy site ukraine against radiocarbon dating abstract post infrared infrared stimulated luminescence pirir dating has reactivated the use of feldspar minerals to date pleistocene deposits we compared pirir stimulation measured at 290 c pirir290 of coarse grain feldspar 100 200 m and optically stimulated luminescence osl of coarse grain quartz 100 150 m with radiocarbon dating the samples were taken from the lower part of the doroshivtsy sandy loess sequence which contains gravettian artefact layers the site is one of the very few sections in europe that provides a high resolution sedimentary record including prehistoric finds of the last glacial cycle s cooling maximum field observation indicated that the deposits in the lower part of the loess section were redeposited we applied early background subtraction for equivalent dose estimation of the quartz samples the comparison of late background and early background subtraction revealed late background subtraction to be less suitable for estimating the net osl signal of the quartz samples although the pirir290 signal resets slowly we chose this stimulation for feldspar dating because the pirir290 signal is the most stable infrared simulated luminescence irsl signal the section was convenient for testing two different luminescence techniques because a potential influence of partial bleaching can be uncovered by independent age control the osl signal of quartz and the pirir290 signal of potassium feldspar bleach at different rates but this had little influence because the coincident dating results confirmed complete resetting of both luminescence signals prior to deposition moreover the quartz feldspar and radiocarbon ages were within the time range of the gravettian period in ukraine 22 28 ka

climate and hydrology of the last interglaciation mis 5 in owens basin california isotopic and geochemical evidence from core ol 92 abstract 18 o 13 c total organic carbon total inorganic carbon and acid leachable li mg and sr concentrations on 443 samples from 32 to 83 m depth in owens lake core ol 92 were analyzed to study the climatic and hydrological conditions between 60 and 155 ka with a resolution of 200 a the multi proxy data show that owens lake overflowed during wet cold conditions of marine isotope stages mis 4 5b and 6 and was closed during the dry warm conditions of mis 5a c and e the lake partially overflowed during mis 5d our age model places the mis 4 5 boundary at ca 72 5 ka and the mis 5 6 boundary termination ii at ca 140 ka agreeing with the devils hole chronology the diametrical precipitation intensities between the great basin cold wet and eastern china cold dry on milankovitch time scales imply a climatic teleconnection across the pacific it also probably reflects the effect of high latitude ice sheets on the southward shifts of both the summer monsoon frontal zone in eastern asia and the polar jet stream in western north america during glacial periods

variability in the mean latitude of the atlantic intertropical convergence zone as recorded by riverine input of sediments to the cariaco basin venezuela abstract changes in the strength and position of the intertropical convergence zone itcz are an important component of climate variability in the tropical atlantic the cariaco basin located on the northern margin of venezuela is sensitive to tropical atlantic climate change and its sediments provide a record of past itcz behavior today the cariaco basin experiences two distinct seasons that reflect the annual migration of the atlantic itcz between january and march when the itcz lies south of the equator northeasterly trade winds sit directly over cariaco basin and strong coastal upwelling and dry conditions dominate beginning in june july as the itcz moves north local rainfall reaches a maximum and the upwelling diminishes or disappears here we summarize new and previously published data on the river derived terrigenous fraction of cariaco basin sediments as well as comparisons to other paleoclimate records which together suggest a coherent climatologic response in the tropical atlantic triggered by a pattern of itcz migration that mimics the seasonal cycle during periods of cooler north atlantic ssts on time scales ranging from the little ice age to the younger dryas to the cold stadials of the last glacial decreased detrital delivery to cariaco basin from local rivers suggests a southward shift in the mean latitudinal position of the itcz during warm interstadials and periods of holocene and deglacial warmth northward shifts in itcz position and its belt of convective rainfall are inferred from increased detrital delivery to the basin whether the rapid shifts in itcz position and precipitation recorded by cariaco basin sediments and other regional records reflect a response to forcing originating in the high latitude atlantic or to forcing potentially sourced in the tropics is a key question yet to be fully answered

late pleistocene vegetation of kings canyon sierra nevada california seven packrat midden samples make possible a comparison between the modern and late pleistocene vegetation in kings canyon on the western side of the southern sierra nevada one modern sample contains macrofossils and pollen derived from the present day oak chaparral vegetation macrofossils from the six late pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers juniperus occidentalis pinus cf ponderosa and p monophylla the pollen spectra of these pleistocene middens are dominated by pinus sp taxodiaceae cupressaceae taxaceae tct and artemisia sp mesophytic conifers are represented by low macrofossil concentrations sequoiadendron giganteum is represented by a few pollen grains in the full glacial edaphic control and snow dispersal are the most likely causes of these mixed assemblages the dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the sierra nevada these assemblages suggest that late wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values this conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late wisconsin the records in these middens also suggest that s giganteum grew at lower elevations along the western side of the range and that p monophylla was more widely distributed in cismontane california during the pleistocene

lacustrine cave carbonates novel archives of paleohydrologic change in the bonneville basin utah usa records of past changes in lake levels and lake water isotopic composition in closed basins provide key insights into past variations in the hydrological cycle however these records are often limited by dating precision and temporal resolution here we present data from lacustrine cave carbonates a previously unexplored class of carbonates that comprise a promising new archive of past hydrologic changes in the bonneville basin of the northeastern great basin usa these dense carbonates precipitated within caves crevices and other protected spaces flooded by lake bonneville during its highstand in the last glacial period we report on deposits in cathedral and craners caves located 50 km apart at similar elevations approximately 100 m above the modern great salt lake and almost 200 m below lake bonneville s highstand shoreline carbonates from the two caves show similar chronologies mineralogical transitions isotopic compositions and uranium concentrations these findings suggest that lacustrine cave carbonates record changes in lake level and in the isotopic composition and chemistry of lake water importantly the deposits can be precisely dated by u th methods providing the first records of lake bonneville s water balance changes tied to precise u th ages close agreement between paired u th and calibrated 14 c ages in the deposits suggests a minimal o200 a carbon reservoir effect in the lake and allows 14 c dating to be used for age control in portions of the deposits less suitable for u th dating we use ages for the onset and cessation of lacustrine cave carbonate deposition to offer new constraints on past changes in lake level and the carbonate saturation state of lake water we also present precisely dated high resolution oxygen and uranium isotope records from the deposits within a first phase of deposition reflecting the lake s transgression between 26 and 18 ka our isotopic data suggest a large influx of freshwater during heinrich stadial 2 a hiatus in deposition beginning at 18 270 3 ka may be the result of freshening related to the lake s overflow calcite deposition resumes at cathedral cave at 16 470 2 ka suggesting that basin overflow had ceased by this time and that the lake s calcite saturation state had increased andd 18 o values increase markedly after 15 9 ka consistent with drying at this time these data imply that the lake s deglacial regression began well before the bolling warming cessation of this second phase of deposition at 14 770 2 ka coincident with the bolling warming may reflect the lake s drop below cathedral cave s elevation a final stage of aragonite deposition between 13 8 and 13 6 ka differs from the underlying facies and may not reflect deposition from lake waters filling the cave

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

sub millennial variability of asian monsoon intensity during the early mis 3 and its analogue to the ice age terminations abstract although the initiation and continuation of orbital and millennial climate transitions were reported to be roughly similar little is yet known about the extent to which their sequences of climate events are linked together in the same physical processes here we present a stalagmite isotope record from wulu cave southwestern china based on 1200 oxygen isotope data and 15 230 th ages registering a detailed history of the asian monsoon am from 61 3 to 50 5 ka bp with an average resolution of 12 yr two replicated high resolution calcite 18 o profiles show four millennial scale strong summer monsoon events analogous in timing and structure to chinese interstadials a 17 a 14 cis a 17 a 14 as recorded elsewhere in china and greenland interstadials 17 14 gis 17 14 these events exhibit two distinct phases consistent with multi decadal centennial shifts in greenland temperature and storminess this relationship reveals a tight coupling between high and low latitude climates at sub millennial scales implying a role for westerly winds in linking greenland temperature and the am around the marine isotope stage mis 4 3 boundary successive am events resemble but in higher frequency structure of the bolling younger dryas yd surrounding termination i along with evidence from similar shifts in bipolar temperature and atmospheric ch 4 we suggest that the recurrence of similar climate structure worldwide is likely caused by changes in atlantic meridional overturning circulation amoc at various timescales under thresholds of global ice volume boundaries as predicted by the bipolar seesaw model

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

regional climate variability and ecosystem responses to the last deglaciation in the northern hemisphere from stable isotope data and calcite fabrics in two northern adriatic stalagmites abstract geochemical and physical changes along the growth axis of speleothems are controlled by climate as well as the dynamics of the host karst system discriminating between the two is one of the major challenges in assembling robust cave palaeoclimate records overcoming this dilemma may be achieved by investigating multiple properties from two or more speleothems from the same cave spanning the same time interval in this study we use high resolution stable oxygen and carbon isotope 13c and 18o morphological and petrographic data from two calcite stalagmites sv1 and sv7 from grotta savi italy to help constraining the regional climate conditions during the younger dryas the new sv1 record spanning 15 3 9 4 ka builds on a previously published low resolution stable isotope time series it is anchored by 22 new u th ages and lamina counting yielding a refined age model that supersedes the previous one the sv7 record is anchored by 8 u th ages and spans 13 1 10 5 ka partially overlapping the sv1 record together the morphological and geochemical characteristics of sv1 and sv7 allow us to identify site specific processes driving the isotopic variations this enables us to explore the degree of complacency in speleothems whereby periodically a speleothem is insensitive to recording a climate signal due to aquifer hydrology and network evolution the model suggests that 18o is a proxy for the infiltration amount that reaches the site of deposition which in the case of sv7 was buffered by the aquifer hydrology the interpretation of 13c in both stalagmites is more complex being influenced by both temperature and hydrology only a comparison of the two stalagmite records allows us to recognise a decoupling between the effects of hydrology and temperature according to our interpretation the most distinctive climate information of the younger dryas was the high hydrological variability with phases dominated by seasonal infiltration within an overall cooling trend our record also reveals a significant early holocene climate anomaly centred at 10 4 ka whose magnitude was possibly amplified by local synoptic conditions our research demonstrates the importance of investigating several complementary proxies particularly from morphologically diverse stalagmites when monitoring data are not available fabric and lamina thickness can be fundamental to unravelling the dominant control of hydrology or temperature on stable isotopes

palaeo climate reconstruction from stable isotope variations in speleothems a review abstract speleothems are now regarded as valuable archives of climatic conditions on the continents offering a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores they are ideal materials for precise u series dating yielding ages in calendar years thereby circumventing the radiocarbon calibration problems associated with most other continental records stable isotope studies in speleothems have shifted away from attempting to provide palaeo temperature reconstructions to the attainable goal of providing precise estimates for the timing and duration of major o isotope defined climatic events characterised by high signal to noise ratios e g glacial interglacial transitions dansgaard oeschger oscillations the 8200 year event unlike the marine records speleothem data sets are not tuned and their independent chronology offers opportunities to critically assess leads and lags in the climate system that in turn can provide important insights into forcing and feedback mechanisms improved procedures for the extraction and measurement of stable isotope ratios in fluid inclusions trapped in speleothems are likely to provide in the near future a much enhanced basis for the quantitative interpretation of o isotope ratios in speleothem calcite the latter developments open up once again the tantalising prospect of palaeo temperature estimates but more importantly perhaps provide a direct test for a new generation of general circulation models whose hydrological cycles will incorporate the water isotopes the literature is reviewed briefly to provide for the reader a sense of the current state of the art and to provide some pointers for future research directions

moisture variability in the southwestern united states linked to abrupt glacial climate change the atmospheric response to millennial scale circulation changes in the north atlantic ocean during the last glacial period has been difficult to constrain cave deposits from southwestern north america reveal that atmospheric moisture in this region increased in response to slowdowns of the atlantic meridional overturning circulation

late pleistocene california droughts during deglaciation and arctic warming abstract recent studies document the synchronous nature of shifts in north atlantic regional climate the intensity of the east asian monsoon and productivity and precipitation in the cariaco basin during the last glacial and deglacial period yet questions remain as to what climate mechanisms influenced continental regions far removed from the north atlantic and beyond the direct influence of the inter tropical convergence zone here we present u series calibrated stable isotopic and trace element time series for a speleothem from moaning cave on the western slope of the central sierra nevada california that documents changes in precipitation that are approximately coeval with greenland temperature changes for the period 16 5 to 8 8 ka from 16 5 to 10 6 ka the moaning cave stalagmite proxies record drier and possibly warmer conditions signified by elevated 18 o 13 c mg sr and ba and more radiogenic 87 sr 86 sr during northern hemisphere warm periods bolling early and late allerod and wetter and possibly colder conditions during northern hemisphere cool periods older dryas inter allerod cold period and younger dryas moaning cave stable isotope records indicate that wet conditions persisted in this area well beyond 11 5 ka suggesting the effects of the younger dryas event may have been longer lived in the western sierra nevada than in greenland however a shifting drip center and corresponding change in seepage water routing may have influenced the trace element records between 10 6 and 9 6 ka linkages between northern high latitude climate and precipitation in the sierra nevada suggested here could indicate that under conditions of continued global warming this drought prone region may experience a reduction in pacific sourced moisture

variable north pacific influence on drought in southwestern north america since ad 854 over the twentieth century droughts in southwestern north america have been linked to sea surface temperature variability in the north pacific ocean speleothem data from southern california suggest that links between the north pacific and drought were less pronounced during the past millennium

stalagmite stable isotope record of recent tropical cyclone events we present a 23 yr stalagmite record 1977 2000 of oxygen isotope variation associated with 11 tropical cyclones tcs from actun tunichil muknal cave in central belize high resolution microsampling yielded a record of monthly to weekly temporal resolution that contains abrupt decreases negative excursions in calcite 18 o values that correspond with recent tc rain events nearby a logistic discriminant model reliably identifi ed tc proxy signals using the measurable parameters 18 o and 13 c values and single point changes in 18 o value the logistic model cor rectly identifi ed 80 of excursions as tc events and incorrectly classifi ed only 1 of nearly 1200 nonstorm sampling points in addition to enabling high resolution tc frequency reconstruction this geologic proxy also provides information about the intensity of individual tcs a multiple regression predicted tc intensity r 2 0 465 p 0 034 using sampling frequency and excursion amplitude consistent with previous low resolution studies we found that the decadal average 18 o value was lower during the 1990s when several tcs produced rainfall in the area but higher during the 1980s when only one tc struck longer accurately dated high resolution speleo them stable isotope records may be a useful new tool for paleotempestology to clarify associa tions between highly variable tc activity and the dynamic range of quaternary climate

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

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

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka