modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

global atmospheric teleconnections during dansgaard oeschger events during the last glacial period the north atlantic region experienced a series of dansgaard oeschger cycles in which climate abruptly alternated between warm and cold periods corresponding variations in antarctic surface temperature were out of phase with their northern hemisphere counterparts the temperature relationship between the hemispheres is commonly attributed to an interhemispheric redistribution of heat by the ocean overturning circulation changes in ocean heat transport should be accompanied by changes in atmospheric circulation to satisfy global energy budget constraints although changes in tropical atmospheric circulation linked to abrupt events in the northern hemisphere are well documented evidence for predicted changes in the southern hemisphere s atmospheric circulation during dansgaard oeschger cycles is lacking here we use a high resolution deuterium excess record from west antarctica to show that the latitude of the mean moisture source for antarctic precipitation changed in phase with abrupt shifts in northern hemisphere climate and significantly before antarctic temperature change this provides direct evidence that southern hemisphere mid latitude storm tracks shifted within decades of abrupt changes in the north atlantic in parallel with meridional migrations of the intertropical convergence zone we conclude that both oceanic and atmospheric processes operating on different timescales link the hemispheres during abrupt climate change abrupt glacial climate changes were slowly communicated between hemispheres by oceanic heat transport ice core data point to more rapid atmospheric teleconnections linking the north atlantic tropics and southern storm track

millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

timing and structure of mega sacz events during heinrich stadial 1 a substantial strengthening of the south american monsoon system sams during heinrich stadials hs points toward decreased cross equatorial heat transport as the main driver of monsoonal hydroclimate variability at millennial time scales in order to better constrain the exact timing and internal structure of hs1 over tropical south america we assessed two precisely dated speleothem records from central eastern and northeastern brazil in combination with two marine records of terrestrial organic and inorganic matter input into the western equatorial atlantic during hs1 we recognize at least two events of widespread intensification of the sams across the entire region influenced by the south atlantic convergence zone sacz at 16 11 14 69 kyr b p and 18 1 16 66 kyr b p labeled as hs1a and hs1c respectively separated by a dry excursion from 16 66 to 16 11 kyr b p hs1b in view of the spatial structure of precipitation anomalies the widespread increase of monsoon precipitation over the sacz domain was termed mega sacz

a review of the bipolar see saw from synchronized and high resolution ice core water stable isotope records from greenland and east antarctica numerous ice core records are now available that cover the last glacial cycle both in greenland and in antarctica recent developments in coherent ice core chronologies now enable us to depict with a precision of a few centuries the relationship between climate records in greenland and antarctica over the millennial scale variability of the last glacial period stacks of greenland and antarctic water isotopic records nicely illustrate a seesaw pattern with the abrupt warming in greenland being concomitant with the beginning of the cooling in antarctica at the antarctic isotopic maximum aim in addition from the precise estimate of chronological error bars and additional high resolution measurements performed on the edc and taldice ice cores we show that the seesaw pattern does not explain the regional variability in antarctic records with clear two step structures occurring during the warming phase of aim 8 and 12 our antarctic high resolution data also suggest possible teleconnections between changes in low latitude atmospheric circulation and antarctic without any greenland temperature fingerprint

millennial scale variability in antarctic ice sheet discharge during the last deglaciation two well dated high resolution records of iceberg rafted debris are presented that document variability in antarctic ice sheet discharge during the last deglaciation global sea levels have risen by more than 100 metres since the last glacial maximum around 20 000 years ago with several meltwater pulses of several metres or more in the most dramatic of these meltwater pulse 1a sea level rose by about 16 metres at 14 600 years ago this magnitude of sea level rise strongly suggests major antarctica contributions but to date there has been no firm physical evidence now michael weber and colleagues present a record of iceberg rafted debris from the scotia sea and show clear signals of pulsed iceberg release from antarctica as early as 19 000 years ago the largest iceberg release occurred during meltwater pulse 1a providing the long sought confirmation of antarctic contributions to this major jump in sea level rise our understanding of the deglacial evolution of the antarctic ice sheet ais following the last glacial maximum 26 000 19 000 years ago 1 is based largely on a few well dated but temporally and geographically restricted terrestrial and shallow marine sequences2 3 4 this sparseness limits our understanding of the dominant feedbacks between the ais southern hemisphere climate and global sea level marine records of iceberg rafted debris ibrd provide a nearly continuous signal of ice sheet dynamics and variability ibrd records from the north atlantic ocean have been widely used to reconstruct variability in northern hemisphere ice sheets5 but comparable records from the southern ocean of the ais are lacking because of the low resolution and large dating uncertainties in existing sediment cores here we present two well dated high resolution ibrd records that capture a spatially integrated signal of ais variability during the last deglaciation we document eight events of increased iceberg flux from various parts of the ais between 20 000 and 9 000 years ago in marked contrast to previous scenarios which identified the main ais retreat as occurring after meltwater pulse 1a3 6 7 8 and continuing into the late holocene epoch the highest ibrd flux occurred 14 600 years ago providing the first direct evidence for an antarctic contribution to meltwater pulse 1a climate model simulations with ais freshwater forcing identify a positive feedback between poleward transport of circumpolar deep water subsurface warming and ais melt suggesting that small perturbations to the ice sheet can be substantially enhanced providing a possible mechanism for rapid sea level rise

a great basin wide dry episode during the first half of the mystery interval the existence of the big dry event from 14 9 to 13 8 14 c kyrs in the lake estancia new mexico record suggests that the deglacial mystery interval 14 5 12 4 14 c kyrs has two distinct hydrologic parts in the western usa during the first great basin lake estancia shrank in size and during the second great basin lake lahontan reached its largest size it is tempting to postulate that the transition between these two parts of the mystery interval were triggered by the ird event recorded off portugal at about 13 8 14 c kyrs which post dates heinrich event 1 by about 1 5 kyrs this twofold division is consistent with the record from hulu cave china in which the initiation of the weak monsoon event occurs in the middle of the mystery interval at 16 1 kyrs i e about 13 8 14 c kyrs

discussion on dating the late precambrian volcanicity of england and wales whilst new data constraining the evolution of the avalonian superterrane in southern britain are most welcome the conclusion that compston et al 2002 draw from this data raise some points that merit comment firstly the conclusion that the new age data for the arfon group enables a redefining of the sarn complex terrane affinity is questioned in particular the statement it also now seems unlikely that the sarn complex should be compared with the padarn area as the parwyd gneiss has yielded a rb sr date of 542 17 ma beckinsale et al 1984 this is not now regarded as the age of the amphibolite facies metamorphism horak et al 1996 but must indicate a considerable retrogression event in the gneissose basement in late precambrian cambrian time does not appear to have any relevance to any of the data presented the parwyd gneiss is represented by a single exposure of retrogressed garnet amphibolite and felsic gneiss which lies entirely within the ll n shear zone although previously included within the sarn complex recent work has defined this as a separate unit of uncertain affinity e g gibbons horak 1990 gibbons mccarroll 1993 in contrast to the gneisses the sarn complex is a poorly exposed heterogeneous plutonic complex of which the most northwestern margin has been involved in ductile and brittle deformation the rb sr isotopic data age for the parwyd gneisses has no bearing on the affinity or age of the sarn complex and furthermore the published u pb age of 615 2 ma for a gabbro not granite as stated by compston et al 2002 from the complex horak

menai strait fault system an early caledonian terrane boundary in north wales a steep fault system runs parallel to the menai strait which separates anglesey from the mainland of north wales the menai strait fault system is interpreted as a major terrane boundary along which terrane docking took place during the late precambrian or earliest cambrian the evidence is based on 1 marked geologic dissimilarities exhibited by the pre late early cambrian basement to these terranes and 2 the existence of early major ductile shear zones within the fault system rocks as varied as blueschists low grade melange and shallow level granitic complexes were juxtaposed along these steep shear zones prior to the eruption of ash flow tuffs and deposition of upper lower cambrian marine sediments in the welsh basin since the amalgamation of the anglesey area with the avalonian terrane then a part of gondwana frequent phanerozoic reactivation of the resulting composite terrane boundary has been restricted to mostly dip slip fault movements

ice shelf collapse from subsurface warming as a trigger for heinrich events episodic iceberg discharge events from the hudson strait ice stream hsis of the laurentide ice sheet referred to as heinrich events are commonly attributed to internal ice sheet instabilities but their systematic occurrence at the culmination of a large reduction in the atlantic meridional overturning circulation amoc indicates a climate control we report mg ca data on benthic foraminifera from an intermediate depth site in the northwest atlantic and results from a climate model simulation that reveal basin wide subsurface warming at the same time as large reductions in the amoc with temperature increasing by approximately 2 c over a 1 2 kyr interval prior to a heinrich event in simulations with an ocean model coupled to a thermodynamically active ice shelf the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the hsis by a factor of approximately 6 by analogy with recent observations in antarctica the resulting ice shelf loss and attendant hsis acceleration would produce a heinrich event

high precision u th dating of the rock paintings at mt huashan guangxi southern china the rock art and the associated natural scenery at 38 sites located in the zuojiang river valley in the southwest of guangxi zhuang autonomous region southern china were inscribed recently on unesco s world heritage list the painted panel at the site of mt huashan is probably the largest known rock art panel in the world consisting of approximately 1900 identifiable figures and occupying an area of approximately 8000 m 2 to determine a precise age on the rock art at mt huashan 56 secondary carbonate layers above and below the paintings were studied for their mineralogy oxygen and carbon isotopic compositions and dated by the 230 th u method the 230 th u dating results demonstrate that ages of the rock paintings can be bracketed between 1856 16 and 1728 41yr bp corresponding to the middle to the end of the eastern han dynasty ad 25 to 220 the results imply that the rock painting practices at mt huashan probably lasted more than a century and the zuojiang rock art is younger than that at baiyunwan and cangyuan in yunnan province by 1 to 10 centuries

lower palaeozoic and precambrian igneous rocks from eastern england and their bearing on late ordovician closure of the tornquist sea constraints from u pb and nd isotopes the u pb isotope ages and nd isotope characteristics of asuite of igneous rocks from the basement of eastern england show that ordovician calc alkaline igneous rocks are tectonically interleaved with late precambrian volcanic rocks distinct from precambrian rocks exposed in southern britain new u pb ages for the north creake tuff zircon 449 13 ma moorby microgranite zircon 457 20 ma and the nuneaton lamprophyre zircon and baddeleyite 442 3 ma confirm the presence ofan ordovician magmatic arc tectonically interleaved precambrian volcanic rocks within this arc are verified by new u pb zircon ages for tuffs at glinton 612 21 ma and orton 616 6 ma initial end values for these basement rocks range from 4 to 6 consistent with generation of both c 615 ma and c 450 ma groups of rocksin continental arc settings the u pb and sm nd isotope data support arguments for an ordovician fold thrust belt extending from england to belgium and that the ordovician calc alkaline rocks formed in response to subductionof tornquist sea oceanic crust beneath avalonia

upper crustal recycling in southern britain evidence from nd and sr isotopes analyses of representative rocks from southern britain are used to examine in detail the evolution of this segment of continental crust the vast majority of late precambrian basement rocks have unradiogenic 87sr 86sr ratios and model tdmnd ages of 1 3 ga although locally the rosslare complex and rushton schists have model tdmnd ages 1 7 ga identifying for the first time an old component in the basement of southern britain following the closure of the iapetus ocean sediments exhibit a progressive increase in model tdmnd ages 1 35 ga in the lower palaeozoic to 1 75 ga in the jurassic this variation demonstrates the southerly transport of detritus tdmnd 2 0 ga from the mixed archaean proterozoic terrains of northern europe and america the granitoids have significantly higher end than those of contemporaneous sediments and thus yield a different nd isotope evolution curve when considered in isolation the majority of rocks analysed have model tdmsr ages in the range 1 2 to 0 46 ga with youngest sediments generally recording the lowest model ages therefore with time the sediments record a striking increase in the ratio of model nd to model sr age the data suggest that the rb sr ratios of the crustal rocks is increased by a factor of approximately 2 every 900 ma implying that on average the british upper crust was reworked by erosion and sedimentation every 600 ma

antarctic link with east asian summer monsoon variability during the heinrich stadial bolling interstadial transition abstract previous research has shown a strong persistence for direct teleconnections between the east asian summer monsoon easm and high northern latitude climate variability during the last glacial and deglaciation in particular between monsoon weakening and a reduced atlantic meridional overturning circulation amoc however less attention has been paid to easm strengthening as the amoc was reinvigorated following peak northern hemisphere nh cooling moreover climate model simulations have suggested a strong role for antarctic meltwater discharge in modulating northward heat transport and hence nh warming yet the degree to which southern hemisphere sh climate anomalies impacted the asian monsoon region is still unclear here we present a new stalagmite oxygen isotope record from the easm affected region of central china which documents two prominent stages of increased 18 o depleted moisture delivery to the region through the transition from heinrich stadial 1 hs1 to the bolling allerod b a interstadial this is in general agreement with the other monsoonal records from both nh and sh mid to low latitudes through novel comparisons with a recent iceberg rafted debris ird record from the southern ocean we propose that the two stage easm intensification observed in our speleothem records were linked with two massive antarctic icesheet discharge aid events at 16 0 ka and 14 7 ka immediately following the peak hs1 stadial event notably the large increase in easm intensity at the beginning of the hs1 b a transition 16 ka is relatively muted in the nh higher latitudes and better aligns with the changes observed in the sh indicating the antarctic and southern ocean perturbations could have an active role in driving the initial easm strengthening at this time indeed antarctic freshwater input to the southern ocean during these aid events would have cooled the surrounding surface waters and caused an expansion of sea ice restricting the southern extent of the sh westerlies moreover increased meltwater flux during ird events would have freshened antarctic intermediate water leading to the increased formation of north atlantic deep water and enhanced north atlantic subsurface heat release and causing a strengthening of the amoc during the hs1 bolling transition the result of this sequence of events would have been warming in the north atlantic whilst at the same time cooling in the antarctic the ensuing interhemispheric temperature gradient would have acted to push the itcz northward weakening the australian indonesian summer monsoon aism whilst intensifying the easm

mean global ocean temperatures during the last glacial transition little is known about the ocean temperature s long term response to climate perturbations owing to limited observations and a lack of robust reconstructions although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now its role in a century and beyond is uncertain here using noble gases trapped in ice cores we show that the mean global ocean temperature increased by 2 57 0 24 degrees celsius over the last glacial transition 20 000 to 10 000 years ago our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean in contrast to the depth region organism and season specific estimates provided by other methods we find that the mean global ocean temperature is closely correlated with antarctic temperature and has no lead or lag with atmospheric co2 thereby confirming the important role of southern hemisphere climate in global climate trends we also reveal an enigmatic 700 year warming during the early younger dryas period about 12 000 years ago that surpasses estimates of modern ocean heat uptake

deglacial variability of antarctic intermediate water penetration into the north atlantic from authigenic neodymium isotope ratios 1 understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with atlantic meridional overturning circulation variability across abrupt climate events however the links between intermediate water circulation and abrupt climate events such as the younger dryas yd and heinrich event 1 h1 are still poorly constrained here we reconstruct changes in antarctic intermediate water aaiw circulation in the subtropical north atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the florida straits our authigenic nd isotope records suggest that there was little to no penetration of aaiw into the subtropical north atlantic during the yd and h1 variations in the northward penetration of aaiw into the florida straits documented in our authigenic nd isotope record are synchronous with multiple climatic archives including the greenland ice core 18o record the cariaco basin atmosphere 14c reconstruction the bermuda rise sedimentary pa th record and nutrient and stable isotope data from the tropical north atlantic the synchroneity of our nd records with multiple climatic archives suggests a tight connection between aaiw variability and high latitude north atlantic climate change

the age of blueschist metamorphism in anglesey north wales evidence from 40ar 39ar mineral dates of the penmynydd schists the 9penmynydd9 schists of se anglesey include several high p low t lithologies including 1 metasedimentary quartz phengite schist and 2 mafic blueschist with barroisite crossite assemblages that appear to have developed from an earlier actinolitic greenschist facies protolith one phengite and three amphibole concentrates have been analysed by incremental release 40 ar 39 ar dating methods and display discordant age spectra with anomalously young apparent ages recorded in low t increments ages increase systematically throughout intermediate t portions of the analyses to define high t plateaux of c 550 560 ma barroisite crossite rich concentrates and c 580 590 ma actinolite rich concentrate the phengite concentrate also displays an internally discordant spectrum with intermediate t increments defining ages similar to those recorded by barroisite crossite and high t increments giving ages similar to those of actinolite the amphibole and phengite ages are interpreted as dating post metamorphic cooling following a regional low p ml greenschist metamorphism c 580 590 ma and a high p m2 metamorphism c 550 560 ma 40 ar 39 ar ages suggest multiple metamorphism of oceanic crust before the arrival of the blueschist terrane and its accretion to the late precambrian basement of southern britain immediately prior to development of the welsh basin an age of c 550 560 ma for blueschist metamorphism on anglesey provides a likely maximum age for ignimbrites within the pre late lower cambrian arfon group exposed in nw wales

what do benthic δ13c and δ18o data tell us about atlantic circulation during heinrich stadial 1 approximately synchronous with the onset of heinrich stadial 1 hs1 13c decreased throughout most of the upper 1000 2500 m atlantic and at some deeper north atlantic sites this early deglacial 13c decrease has been alternatively attributed to a reduced fraction of high 13c north atlantic deep water nadw or to a decrease in the nadw 13c source value here we present new benthic 18o and 13c records from three relatively shallow 1450 1650 m subpolar northeast atlantic cores with published data from other cores these data form a depth transect 1200 3900 m in the subpolar northeast atlantic we compare last glacial maximum lgm and hs1 data from this transect with data from a depth transect of cores from the brazil margin the largest lgm to hs1 decreases in both benthic 13c and 18o occurred in upper waters containing the highest nadw fraction during the lgm we show that the 13c decrease can be explained entirely by a lower nadw 13c source value entirely by a decrease in the proportion of nadw relative to southern ocean water or by a combination of these mechanisms however building on insights from model simulations we hypothesize that reduced ventilation due to a weakened but still active atlantic meridional overturning circulation also contributed to the low 13c values in the upper north atlantic we suggest that the benthic 18o gradients above 2300 m at both core transects indicate the depth to which heat and north atlantic deglacial freshwater had mixed into the subsurface ocean by early hs1

punctuated asm strengthening in late heinrich stadial from speleothem records southern china the dynamical adjustment process dap is a requisite for climate system to arrange for a new equilibrium state to evaluate the detailed structure of dap during heinrich stadial hs high resolution speleothem based asian summer monsoon asm variability was reconstructed separately covering hss 5 to 1 in these calcite 18o records a gradual increase of asm intensity is evident in each mid hs followed by a centennial scale asm stability lasting on average 590 years during late hs at this time 18o values decrease by 1 about 50 of the total hs compared with maximum values in early hs this structure of monsoonal hs in speleothem records is not reflected in temperature variations at the greenland but is well mirrored in middle to low latitudes within the northern hemisphere and even southern oceanic records it suggests that southern and low latitude climate conditions are likely important for the termination of hs thus a dap of about 400 600 years is a precondition for the asm sub system to prepare for a new equilibrium

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

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

basic mechanism for abrupt monsoon transitions abstract monsoon systems influence the livelihood of hundreds of millions of people during the holocene and last glacial period rainfall in india and china has undergone strong and abrupt changes though details of monsoon circulations are complicated observations reveal a defining moisture advection feedback that dominates the seasonal heat balance and might act as an internal amplifier leading to abrupt changes in response to relatively weak external perturbations here we present a minimal conceptual model capturing this positive feedback the basic equations motivated by observed relations yield a threshold behavior robust with respect to addition of other physical processes below this threshold in net radiative influx r c no conventional monsoon can develop above r c two stable regimes exist we identify a nondimensional parameter l that defines the threshold and makes monsoon systems comparable with respect to the character of their abrupt transition this dynamic similitude may be helpful in understanding past and future variations in monsoon circulation within the restrictions of the model we compute r c for current monsoon systems in india china the bay of bengal west africa north america and australia where moisture advection is the main driver of the circulation

high resolution stalagmite δ18o records of asian monsoon changes in central and southern china spanning the mis 3 2 transition abstract high resolution oxygen isotope records of three stalagmites from sanbao central china wulu southern china and dashibao southern china caves based on 876 oxygen isotope measurements and 25 precise 230 th dates provide a detailed asian monsoon am history from 32 5 to 20 8 ka b p spanning the shift between marine isotope stages 3 and 2 the calcite 18 o records although geographically widespread about 1000 km between them including the previously reported hulu record are similar in timing shape and amplitude these observations support the idea that changes in speleothem 18 o largely represent variations of precipitation isotopic composition associated with large scale summer monsoon circulation over a large portion of china these profiles show four centennial to millennial scale strong summer monsoon events analogous in timing and structure to greenland interstadials 5 through 3 gis 5 3 chronology of the events refines the hulu record and broadly supports the ngrip gicc05 timescale five weak monsoon events are identified at 31 2 30 1 28 1 25 7 and 24 2 ka b p all of which correspond to stadial events in greenland the 30 1 and 24 2 ka events correlate with heinrich stadials 3 and 2 furthermore these events correlate to warm episodes in antarctic ice cores indicating that the climatic response to north atlantic cooling is similar in china and in antarctica but in an opposite sense these observations are consistent with the bi polar seesaw hypothesis the strong coupling between am circulation and climate at both high latitudes at the centennial scale indicates that atmospheric circulation changes are important in transmitting abrupt climate signals globally

rb sr whole rock isochron ages δ18o values and geochemical data for the sarn igneous complex and the parwyd gneisses of the mona complex of llŷn n wales the mona complex exposed on the ll n peninsula includes the sarn complex which is a suite of variably deformed plutonic igneous rocks originally mapped partly as gneisses ranging from gabbro to granite and an inlier of high grade paragneisses geochemical data for samples from the sarn complex may be divided into two distinct populations the rb sr data for samples from these geochemical groups define significantly different ages the older age 549 19 ma initial 87 sr 86 sr 0 7096 3 is identified as the age of intrusion in late precambrian to cambrian times while a younger age of 458 16 ma may approximate to the age of a resetting event the parwyd paragneisses yield an rb sr whole rock isochron age of 542 17 ma concordant with the age of intrusion of the sarn complex with an initial 87 sr 86 sr of 0 7069 4 for the sarn complex 18 o values range from 9 5 to 12 0 per mil smow and in the parwyd metasediments from 9 4 to 13 3 per mil we conclude that the earliest magmatism and metamorphism in the mona complex of ll n occurred during late precambrian to cambrian times broadly contemporaneous with similar events in anglesey the high initial 87 sr 86 sr and high 18 o values for the sarn complex are most simply interpreted as reflecting either a crustal source region or incorporation of a significant proportion of crustal material such as the parwyd gneisses into a mantle derived magma

synchronization of north pacific and greenland climates preceded abrupt deglacial warming some proposed mechanisms for transmission of major climate change events between the north pacific and north atlantic predict opposing patterns of variations others suggest synchronization resolving this conflict has implications for regulation of poleward heat transport and global climate change new multidecadal resolution foraminiferal oxygen isotope records from the gulf of alaska goa reveal sudden shifts between intervals of synchroneity and asynchroneity with the north greenland ice core project ngrip 18 o record over the past 18 000 years synchronization of these regions occurred 15 500 to 11 000 years ago just prior to and throughout the most abrupt climate transitions of the last 20 000 years suggesting that dynamic coupling of north pacific and north atlantic climates may lead to critical transitions in earth s climate system

onset of deglacial warming in west antarctica driven by local orbital forcing an annually resolved ice core record from west antarctica indicates that warming driven by local insolation resulting from sea ice decline began in that region about 2 000 years before warming in east antarctica reconciling two alternative explanations for deglacial warming in the southern hemisphere

anatomy of heinrich layer 1 and its role in the last deglaciation this research used data acquired at the xrf core scanner lab at the marum center for marine environmental sciences university of bremen germany this research used samples provided by the international ocean discovery program iodp funding for this research was provided by the uk natural environmental research council nerc to hodell the nerc radiocarbon facility supported two radiocarbon dates and wally broecker generously supported the remainder with funding from the comer family foundation research by rodriguez tovar and dorador was financed by project cgl2015 66835 p b m acknowledges support from the csic ramon y cajal postdoctoral programme ryc 2013 14073 j f e would like to acknowledge funding under erc advanced grant 320750 nanopaleomagnetism

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

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

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

avalonian magmatism and terrane linkage new isotopic data from the precambrian of north wales new u pb isotope data from the precambrian sarn igneous complex of north wales establishes that calc alkaline plutonic rocks of the same age occur on either side of the menai strait fault system zircon fractions from the sarn igneous complex gabbro give a near concordant u pb age of 615 2 ma which is interpreted as the first accurate age of igneous crystallization and supersedes previous dating attempts using the rb sr method the new u pb age is the same within error as recent zircon dates obtained from the arfon group ignimbrites along strike from the sarn igneous complex and from the coedana complex granite on anglesey these data emphasize the importance of what appears to have been the major phase of calc alkaline magmatism at 630 600 ma recognizable along the avalonian arc in britain newfoundland and elsewhere despite the similar ages and tectonic setting of the coedana and sarn plutonic rocks however they remain petrogenetically and geochemically distinct and are not directly linked as part of the same igneous complex instead the coedana complex granite is interpreted as having been generated in the avalonian arc during a widespread magmatic event that is also recorded in britain not only by the sarn igneous complex and arfon group but by volcanic and plutonic rocks in central england investigation of granite clasts in the gwna group melange monian supergroup on anglesey failed to produce zircons adequate for dating purposes but revealed rb sr whole rock geochemical and petrographic characteristics similar to the nearby coedana complex and suggest linkage between fault bounded 9monian9 terranes on anglesey in the light of these new data rocks on either side of the menai strait terrane boundary are interpreted as belonging to the same arc system that was dismembered dispersed and laterally duplicated by transcurrent faulting after late precambrian magmatism

late cenozoic phosphogenesis on the western shelf of south africa in the vicinity of the cape canyon abstract the strontium isotope 87 sr 86 sr composition of phosphorite carbonate fluorapatite cemented grains pcg phosphate cemented limestone pcl skeletal phosphorite grains spg and biogenic calcite mollusc shell benthic foraminifera and echinoid spines from sediment on the outer continental shelf in the vicinity of the cape canyon ranges from 0 707981 to 0 709167 and corresponds to an age range of late early oligocene to late pleistocene most biogenic carbonate sr ages agree with biostratigraphic ages but some samples contain significantly older and reworked robust 250 m benthic foraminifera although the sr ages of biogenic and phosphorite grains indicate that sedimentation was fairly continuous most sediment is reworked with only lower miocene upper pliocene and upper pleistocene successions generally preserved in the study area the initial phosphogenic episode from the latest oligocene to early early miocene 21 26 ma was the largest with additional phosphogenic episodes in the late early miocene 16 19 ma and middle miocene 10 15 ma most phosphorite occurs as pcg that formed during marine transgressions and highstands from the late oligocene warming event until the mid miocene climatic optimum a period of episodic antarctic glaciation and several positive marine 13 c excursions upper oligocene to lower miocene pcg have been extensively reworked and are associated with major erosional unconformities pcg vary from peloidal sands to gravel mollusc moulds and contain variable amounts of quartz glauconite and pyrite inclusions pcl formed from 9 to 17 ma by cementation and replacement of older calcareous sediment during the middle to late miocene marine regression phosphorite as well as associated glauconite and pyrite indicate that periods of rapid accumulation of organic rich terrigenous muds derived from the focusing of the suspended load of rivers and organic matter produced in areas of coastal upwelling have occurred episodically on the margin since the late oligocene the relative paucity of phosphorite younger than the middle miocene may result from frequent erosional events as documented by pronounced unconformities on the shelf that reflect lowered eustatic sea level tectonic uplift and high frequency high amplitude quaternary sea level fluctuations

similarities and dissimilarities between the last two deglaciations and interglaciations in the north atlantic region abstract sea surface temperatures ssts recorded by alkenones and oxygen isotopes in the alboran basin are used here to describe at an unprecedented fine temporal resolution the present interglaciation pig initiated at 11 7 ka bp the last interglaciation lig onset approximately at 129 ka and respective deglaciations similarities and dissimilarities in the progression of these periods are reviewed in comparison with ice cores and stalagmites cold spells coeval with the heinrich events h described in the north atlantic include multi decadal scale oscillations not previously obvious up to 4 c in less than eight centuries within the stadials associated with h1 and h11 ca 133 ka and 17 ka respectively these abrupt oscillations precede the accumulation of organic rich layers deposited when perihelion moves from alignment with nh spring equinox to the summer solstice a reference for deglaciations events observed during the last deglaciation at 17 ka 14 8 ka and 11 7 ka are reminiscent of events occurred during the penultimate deglaciation at ca 136 ka 132 ka and 129 ka respectively the sst trend during the pig is no more than 2 c from 20 c to 18 c up to 0 2 c ka the trend is steeper during the lig i e up to a 5 c change from the early interglaciation to immediately before the glacial inception from 23 c to 18 c up to 0 4 c ka events are superimposed upon a long term trend towards colder ssts beginning with sst maxima followed by temperate periods until perihelion aligned with the nh autumn equinox before ca 5 3 ka for the pig and 121 ka for the lig a cold spell of around eight centuries at 2 8 ka during the pig was possibly mimicked during the lig at ca 118 ka by a sst fall of around 1 c in a millennium these events led interglacial sst to stabilise at around 18 c the glacial inception barely evident at the beginning ca 115 ka north atlantic event c25 after perihelion passage in the nh winter solstice culminated with a sst drop of at least 2 c in two millennia event c24 ca 111 ka the little ice age 0 7 ka also occurred after the latest perihelion passage in the nh winter solstice and could be an example of how a glacial pre inception event following an interglaciation might be

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

links between tropical rainfall and north atlantic climate during the last glacial period the last glacial period was marked by dramatic climate fluctuations sediment records from the cariaco basin and the arabian sea suggest that cooling in the north atlantic region was tightly coupled with a southward displacement of the intertropical convergence zone and a weakening of the indian summer monsoon

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

a high resolution monsoon record of millennial scale oscillations during late mis 3 from wulu cave south west china a speleothem record from south western china characterizes in detail the millennial scale changes in asian monsoon am intensity from 39 3 to 28 7 ka the calcite 18o profile with an average resolution of 8 years shows several strong monsoon events concurrent with greenland interstadials gis 8 4 to gain a systematic perspective of am millennial scale variability the new and previously reported data from the same cave are combined showing that am variation exhibits a broad similarity with greenland ice 18o records and with antarctica but in an opposite sense for the interval that encompasses gis 5 and gis 4 1 however our stalagmite 18o record depicts a sustained strong monsoon with no distinctive oscillation between these interstadials another prominent characteristic in our record is a gradual transition into chinese interstadial cis 8 which is well constrained by an annually laminated sequence we find that an initial rise in monsoon intensity lasting a few centuries significantly precedes the abrupt onset of cis 8 in the am realm this suggests that atmospheric moisture and heat transport are probably capable of inducing abrupt climate change when a rapid reorganization of ocean atmosphere circulations passes a tipping point

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

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation

hydrographic changes in the tropical and extratropical pacific during the last deglaciation fine scale paired mg ca 18o profiles globigerinoides ruber white sensu lato from the san lazaro basin slb at 25 n in the northeast pacific reveal a transition from a predominant presence of tropical subtropical waters during the last glacial termination t1 to an increasing influence of fresh and cold california current waters toward the holocene changing atmospheric circulation patterns over the northeast pacific in step with the demise of the northern hemisphere ice sheets and or with a shift from el nino to la nina like conditions toward the holocene are prime candidates to explain this water mass change 18osw ivc increases of 0 5 0 7 during the younger dryas yd and heinrich stadial 1 hs1 at the slb are observed in a number of 18osw ivc records from the tropical pacific more directly influenced by changes in the position of the intertropical convergence zone itcz conditioning by itcz migration of the tropical pacific ocean towards salinity increase during yd and hs1 and the subsequent advection of those water masses as far north as 25 n likely accounted for the reconstructed hydrographical changes at the slb a larger influence of tropical water masses as far north as 25 n plausibly contributed to changes in the atmospheric moisture transports to western north america and affected the regional hydrological cycle across t1 finally the fine scale resolution of our 18osw ivc record allows pinpointing a shift from relative salty to fresh surface conditions at 16 2 ka signaling that the two phase structure of hs1 is plausibly a ubiquitous feature of the northern tropical to extratropical ocean atmosphere dynamics