did large ice caps persist on low ground in north west scotland during the lateglacial interstade recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north west scotland throughout the lateglacial interstade greenland interstade 1 ca 14 7 12 9 ka and that glacier ice was much more extensive in this area during the older dryas chronozone ca 14 0 ka than during the younger dryas stade ca 12 9 11 7 ka we have recalibrated the same exposure age data using locally derived 10be production rates this increases the original mean ages by 6 5 12 implying moraine deposition between ca 14 3 and ca 15 1 ka and we infer a most probable age of ca 14 7 ka based on palaeoclimatic considerations the internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin the wester ross readvance pollen stratigraphic evidence from a lateglacial site at loch droma on the present drainage divide demonstrates deglaciation before ca 14 0 ka and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade ca 14 7 14 0 ka this inference appears consistent with lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in scotland between 14 and 13 ka that large active glaciers probably survived throughout the lateglacial interstade and that ice extent was greater during the older dryas period than during the younger dryas stade copyright 2011 john wiley sons ltd

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

centennial scale variability of the british ice sheet implications for climate forcing and atlantic meridional overturning circulation during the last deglaciation evidence from paleoclimatic archives suggests that earth s climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean s thermohaline circulation but the driving mechanism remains to be identified here we use multidecadal marine records of faunal oxygen isotope and sediment proxies from the northeast atlantic proximal to the western margins of the last glacial british ice sheet bis to document the coupling between ice sheet dynamics ocean circulation and insolation changes the core data reveal successions of short lived 80 100 years high amplitude ice rafted debris ird events that were initiated up to 2000 years before the deposition of detrital carbonate during heinrich events he 1 and 2 progressive disintegration of the bis 19 16 kyr before present b p occurred in response to abrupt ocean climate warmings that impinged on the northeast atlantic during the early deglaciation peak ird deposition recurs at 180 220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves the early deglaciation culminated in a major meltwater pulse at 16 3 kyr b p followed by another discharge associated with he1 some 300 years after we conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the bis and possibly other margins of the eurasian ice sheet massive but short lived meltwater surges influenced the atlantic meridional overturning circulation thereby contributing to north atlantic climate variability and bipolar climatic asymmetry

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

pattern style and timing of british irish ice sheet retreat shetland and northern north sea sector the offshore sector around shetland remains one of the least well studied parts of the former british irish ice sheet with several long standing scientific issues unresolved these key issues include i the dominance of a locally sourced shetland ice cap vs an invasive fennoscandian ice sheet ii the flow configuration and style of glaciation at the last glacial maximum i e terrestrial vs marine glaciation iii the nature of confluence between the british irish and fennoscandian ice sheets iv the cause style and rate of ice sheet separation and v the wider implications of ice sheet uncoupling on the tempo of subsequent deglaciation as part of the britice chrono project we present new geological seabed cores geomorphological marine geophysical and geochronological data from the northernmost sector of the last british irish ice sheet north of 59 5 n to address these questions the study area covers ca 95 000 km2 an area approximately the size of ireland and includes the islands of shetland and the surrounding continental shelf some of the continental slope and the western margin of the norwegian channel we collect and analyse data from onshore in shetland and along key transects offshore to establish the most coherent picture so far of former ice sheet deglaciation in this important sector alongside new seabed mapping and quaternary sediment analysis we use a multi proxy suite of new isotopic age assessments including 32 cosmogenic nuclide exposure ages from glacially transported boulders and 35 radiocarbon dates from deglacial marine sediments to develop a synoptic sector wide reconstruction combining strong onshore and offshore geological evidence with bayesian chronosequence modelling the results show widespread and significant spatial fluctuations in size shape and flow configuration of an ice sheet ice cap centred on or to the east of the orkney shetland platform between 30 and 15 ka bp at its maximum extent ca 26 25 ka bp this ice sheet was coalescent with the fennoscandian ice sheet to the east between 25 and 23 ka bp the ice sheet in this sector underwent a significant size reduction from ca 85 000 to 50 000 km2 accompanied by several ice margin oscillations soon after connection was lost with the fennoscandian ice sheet and a marine corridor opened to the east of shetland this triggered initial and unstable re growth of a glaciologically independent shetland ice cap ca 21 20 ka bp with a strong east west asymmetry with respect to topography ice mass growth was followed by rapid collapse from an area of ca 45 000 km2 to ca 15 000 km2 between 19 and 18 ka bp stabilizing at ca 2000 km2 by 17 ka bp final deglaciation of shetland occurred ca 17 15 ka bp and may have involved one or more subsidiary ice centres on now submerged parts of the continental shelf we suggest that the unusually dynamic behaviour of the northernmost sector of the british irish ice sheet between 21 and 18 ka bp characterized by numerous extensive ice sheet ice mass readvances rapid loss and flow redistributions was driven by significant changes in ice mass geometry ice divide location and calving flux as the glaciologically independent ice cap adjusted to new boundary conditions we propose that this dynamism was forced to a large degree by internal glaciological factors specific to the strongly marine influenced shetland ice cap

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

changes in north atlantic deep water formation associated with the dansgaard oeschger temperature oscillations 60 10 ka we closely comparedhigh resolution d 13 c records of benthic foraminifera cibicides wuellerstorfi a proxy for deep water ventilation with the dansgaard oeschger temperature oscillations our results reveal different perturbations of deep water formation in the north atlantic ocean associated with the millennial scale climate oscillations during the last glacial period the cooling episodes associated with the drastic heinrich events are related to large reductions of deep water formation and a northward migration of 13 c depleted southern source deep waters to 621n in the north atlantic ocean the inter heinrich events which are correlatedto the other coldstad ials are markedby significant changes of sea surface temperature aroundthe rockall plateau variations in the flux of icebergs to the north atlantic ocean but are not associated with such important reduction of deep water formation if changes in the thermohaline circulation thc are associatedwith these millennial scale climatic oscillation they affect only the deeper water masses below 2000 m of the north atlantic ocean we thus show that equivalent degree of cooling over greenland is obtained with different perturbations of deep water formation our results either question the role of the thc as the unique explanation for these millennial scale climate oscillations or call upon an amplifying mechanism not yet taken into account r 2002 elsevier science ltd all rights reserved

implications of 36cl exposure ages from skye northwest scotland for the timing of ice stream deglaciation and deglacial ice dynamics geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change this paper presents new 36cl cosmic ray exposure dating from boulders located on two moraines glen brittle and loch scavaig in southern skye northwest scotland ages from the glen brittle moraines constrain deglaciation of a major marine terminating ice stream the barra donegal ice stream that drained the former british irish ice sheet depending on choice of production method and scaling model this occurred 19 9 1 5 17 6 1 3 ka ago we compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence another small section of moraine the scavaig moraine is traced offshore through multibeam swath bathymetry and interpreted as delimiting a later stillstand readvance stage following ice stream deglaciation additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16 3 1 3 15 2 0 9 ka ago when calculated using the most up to date scaling scheme this time of deposition is within uncertainty the same as the timing of a widely identified readvance the wester ross readvance observed elsewhere in northwest scotland this extends the area over which this readvance has potentially occurred reinforcing the view that it was climatically forced

ice caps existed throughout the lateglacial interstadial in northern scotland we constrain in detail fluctuations of two former ice caps in nw scotland with multibeam seabed surveys geomorphological mapping and cosmogenic 10 be isotope analyses we map a continuous sequence of 40 recessional moraines stretching from 10 km offshore to the wester ross mountains surface exposure ages from boulders on moraine ridges in assynt and the summer isles region show that substantial dynamic ice caps existed in nw scotland between 13 and 14 ka bp we interpret this as strong evidence that large active glaciers probably survived throughout the lateglacial interstadial and that during the older dryas period ca 14 ka bp ice caps in nw scotland were thicker and considerably more extensive than in the subsequent younger dryas stadial by inference we suggest that lateglacial ice cap oscillations in scotland reflect the complex interplay between changing temperature and precipitation regimes during this climatically unstable period ca 15 11 ka bp natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

ice sheet action versus reaction distinguishing between heinrich events and dansgaard oeschger cycles in the north atlantic 1 glaciers and ice sheets play an active role in the climate system and the global hydrological cycle the stability of continental ice sheets must be better understood for assessments of future sea level rise and to uncover the causes of millennial scale climate variability that characterized the last glacial period ice rafted debris ird in the midlatitude oceans and subpolar seas tells of widespread calving of icebergs from the northern hemisphere ice sheets during the last glacial period but the climatic implications of this ird are unclear does the sediment record indicate repeated dynamical collapse of the ice sheets with ice sheets actively forcing the climate system alternatively were ice sheet margins simply advancing and retreating in response to climate vacillations on the basis of simulations of iceberg delivery to the ocean during the last glacial cycle we argue that the marine record exemplifies both of these phenomena heinrich events were clearly episodes of internal dynamical instability of the laurentide ice sheet while millennial scale ird is more simply interpreted as a response of the circum atlantic ice sheets to dansgaard oeschger climate cycles ice sheets in different coastal regions respond differently to climate fluctuations but overall iceberg fluxes increase in cold periods peaking within a few centuries of climatic cooling regions with relatively warm wet climates scandinavia western north america and svalbard are the most sensitive to millennial climate variability with rapid response times and large millennial variability in iceberg fluxes

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

iceberg rafted tephra as a potential tool for the reconstruction of ice sheet processes and ocean surface circulation in the glacial north atlantic ice rafted tephra deposits of marine isotope stage 6 mis 6 age from site u 1304 on the gardar drift north atlantic were examined for their shard size distribution and major element composition the heterogeneous composition large shard sizes and association with ice rafted debris ird indicate that these late mis 6 deposits were transported by iceberg rafting from iceland to site u 1304 comparison of individual shard geochemistry with the geochemistry of holocene volcanic systems from iceland allows the identification of different potential volcanic source regions this detailed geochemical analysis when combined with icelandic ice sheet iis flow models for the last glacial maximum lgm suggests that the iis had calving margins to both the north and south during the late mis 6 and that icebergs could have been transported to the site u 1304 by following surface ocean circulation patterns similar to those that prevailed during the lgm we demonstrate that the descriptive concept of icelandic glass in the characterization of tephra components within north atlantic ird can be significantly improved through quantitative characterization and that such data hold the potential to help constrain surface ocean circulation models while also potentially yielding new information about the iis during earlier glacial periods supplementary material statistical tests major element concentrations of analysed shards primary and secondary standards are available at http www geolsoc org uk sup18716

oscillating retreat of the last british irish ice sheet on the continental shelf offshore galway bay western ireland during the last glacial maximum the british irish ice sheet extended across the continental shelf offshore of galway bay western ireland and reached a maximum westward extent on the porcupine bank new marine geophysical data sediment cores and radiocarbon dates are used to constrain the style and timing of ice sheet retreat across the mid to inner shelf radiocarbon dated shell fragments in subglacial till on the mid shelf constrains ice advance to after 26 4 ka bp initial retreat was underway before 24 4 ka bp significantly earlier than previous reconstructions grounding line retreat was accompanied by stillstands and or localised readvances of the grounding line a large composite mid shelf grounding zone complex marks a major grounding line position with the ice grounded and the margin oscillating at this position by and probably after 23 ka bp the continental shelf was ice free by 17 1 cal ka bp but the ice sheet may have retained a marine margin until c 15 3 ka bp retreat occurred in a glacimarine setting and the ice sheet was fringed by a floating ice shelf collectively this evidence indicates a dynamic and oscillatory marine terminating ice sheet offshore of western ireland during the last deglaciation

sea surface temperatures did not control the first occurrence of hudson strait heinrich events during mis 16 1 hudson strait hs heinrich events ice rafting events in the north atlantic originating from the laurentide ice sheet lis are among the most dramatic examples of millennial scale climate variability and have a large influence on global climate however it is debated as to whether the occurrence of hs heinrich events in the eastern north atlantic in the geological record depends on greater ice discharge or simply from the longer survival of icebergs in cold waters using sediments from integrated ocean drilling program iodp site u1313 in the north atlantic spanning the period between 960 and 320 ka we show that sea surface temperatures ssts did not control the first occurrence of hs heinrich like events in the sedimentary record using mineralogy and organic geochemistry to determine the characteristics of ice rafting debris ird we detect the first hs heinrich like event in our record around 643 ka marine isotope stage mis 16 which is similar as previously reported for site u1308 however the accompanying high resolution alkenone based sst record demonstrates that the first hs heinrich like event did not coincide with low ssts thus the hs heinrich like events do indicate enhanced ice discharge from the lis at the end of the mid pleistocene transition not simply the survivability of icebergs due to cold conditions in the north atlantic

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

deglacial surface circulation changes in the northeastern atlantic temperature and salinity records off nw scotland on a century scale sea surface temperature and salinity estimates reconstructed from a core collected on the barra fan northwest scotland 56 43 n 09 19 w water depth 1320 m show a series of rapid oscillations during the last deglacial period that are very similar to those observed in the 18o records from greenland ice cores these records indicate that the transport of heat and salt toward the nordic seas was highest during the bolling period this superconveyor weakened after the bolling probably as a consequence of increased meltwater flux reducing the oceanic salt content as suggested by the barbados sea level record evidence for a phase of ice rafting during the allerod is presented for the first time from this latitude in the northeast atlantic the younger dryas stadial resolved here at a century decadal scale is characterized by very rapid oscillations in temperature and salinity indicating that warm relatively saline waters repeatedly displaced cool polar waters at this latitude these observations attest to the inherent instability of the deglacial climate system

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

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

cosmogenic exposure age constraints on deglaciation and flow behaviour of a marine based ice stream in western scotland 21 16 ka understanding how marine based ice streams operated during episodes of deglaciation requires geochronological data that constrain both timing of deglaciation and changes in their flow behaviour such as that from unconstrained ice streaming to topographically restricted flow we present seventeen new 10be exposure ages from glacial boulders and bedrock at sites in western scotland within the area drained by the hebrides ice stream a marine based ice stream that drained a large proportion of the former british irish ice sheet exposure ages from tiree constrain deglaciation of a topographic high within the central zone of the ice stream from which convergent flowsets were produced during ice streaming these ages thus constrain thinning of the hebrides ice stream which on the basis of supporting information we infer to represent cessation of ice streaming at 20 6 1 2 ka 3 4 ka earlier than previously inferred a period of more topographically restricted flow produced flow indicators superimposed on those relating to full ice stream conditions and exposure ages from up stream of these constrain deglaciation to 17 5 1 0 ka complete deglaciation of the marine sector of the hebrides ice stream occurred by 17 16 ka at which time the ice margin was located near the present coastline exposure ages from the southernmost outer hebrides mingulay and barra indicate deglaciation at 18 9 1 0 and 17 1 1 0 ka respectively demonstrating that an independent ice cap persisted on the southern outer hebrides for 3 4 ka after initial ice stream deglaciation this suggests that deglaciation of the hebrides ice stream was focused along major submarine troughs collectively our data constrain initial deglaciation and changes in flow regime of the hebrides ice stream final deglaciation of its marine sector and deglaciation of the southern portion of the independent outer hebrides ice cap providing chronological constraints on future numerical reconstructions of this key sector of the former british irish ice sheet

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

magnetic characterisation and correlation of a younger dryas tephra in north atlantic marine sediments a technique for identifying non visible basaltic tephra rich horizons of younger dryas yd greenland stadial gs 1 age in northeast atlantic sediments using rapid non destructive magnetic measurements is presented three high resolution marine sediment cores have been studied in an e w transect across the hebridean margin st kilda basin md95 2007 barra fan md95 2006 and rockall trough md04 2822 magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments in all three cores an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard 250 m counts which can be constrained to the early part of the yd gs1 based on faunal climate proxies electron microprobe analyses of the magnetically distinct basaltic tephra interval in all three cores displays the same major element geochemistry as published for the vedde basaltic i tab 1 i e sourced from the icelandic volcano katla the identification of transitional alkalic basaltic tephras within marine sediments could potentially be facilitated by magnetic analysis as a useful chronostratigraphic screening tool copyright 2009 john wiley sons ltd

devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last british irish ice sheet this contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last british irish ice sheet a task undertaken as part of a larger community based project britice chrono that aims to improve understanding of the ice sheet s deglacial evolution as accurate reconstructions depend on the quality of the available data some form of assessment is needed of the reliability and suitability of each given age s in our dataset we outline the background considerations that informed the quality assurance procedures devised given our specific research question we describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty when these criteria were applied to an existing database of all geochronological data relating to the last british irish ice sheet they resulted in a significant reduction in data considered suitable for synthesis the assessed data set was used to test a bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

northern hemisphere forcing of southern hemisphere climate during the last deglaciation changes in ocean circulation are the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature milankovitch theory which was developed to explain the relationship between earth s movement and the climate holds that glacial cycles are ultimately controlled by variations in northern hemisphere summer insolation exposure to the sun s rays spectral analyses of palaeoclimate records support this theory but a mechanistic test has been elusive other lines of evidence also show that climate changes in the southern hemisphere may have led those in the northern hemisphere casting doubt on the main theory here feng he and colleagues use a coupled ocean atmosphere model to show that the last deglaciation was indeed triggered by northern hemisphere insolation changes amplified by albedo co2 and ocean circulation changes according to the milankovitch theory changes in summer insolation in the high latitude northern hemisphere caused glacial cycles through their impact on ice sheet mass balance1 statistical analyses of long climate records supported this theory but they also posed a substantial challenge by showing that changes in southern hemisphere climate were in phase with or led those in the north2 although an orbitally forced northern hemisphere signal may have been transmitted to the southern hemisphere3 insolation forcing can also directly influence local southern hemisphere climate potentially intensified by sea ice feedback4 5 6 suggesting that the hemispheres may have responded independently to different aspects of orbital forcing signal processing of climate records cannot distinguish between these conditions however because the proposed insolation forcings share essentially identical variability7 here we use transient simulations with a coupled atmosphere ocean general circulation model to identify the impacts of forcing from changes in orbits atmospheric co2 concentration ice sheets and the atlantic meridional overturning circulation amoc on hemispheric temperatures during the first half of the last deglaciation 22 14 3 kyr bp although based on a single model our transient simulation with only orbital changes supports the milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid latitude to high latitude northern hemisphere and by terrestrial snow albedo feedback the simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the southern hemisphere in deglacial proxy records8 9 amoc changes associated with an orbitally induced retreat of northern hemisphere ice sheets10 is the most plausible explanation for the early southern hemisphere deglacial warming and its lead over northern hemisphere temperature the ensuing rise in atmospheric co2 concentration provided the critical feedback on global deglaciation9 11

growth dynamics and deglaciation of the last british irish ice sheet the deep sea ice rafted detritus record the evolution and dynamics of the last british irish ice sheet biis have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data this reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary in order to enhance biis reconstruction we present a compilation of new and previously published ice rafted detritus ird flux and concentration data from high resolution sediment cores recovered from the ne atlantic deep sea continental slope adjacent to the last biis these cores are situated adjacent to the full latitudinal extent of the last biis and cover marine isotope stages mis 2 and 3 age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera neogloboquadrina pachyderma sinistral nps to the greenland gisp2 ice core record multiple ird fingerprinting techniques indicate that at the selected locations most ird are sourced from adjacent biis ice streams except in the centre of heinrich h layers in which ird shows a prominent laurentide ice sheet provenance ird flux data are interpreted with reference to a conceptual model explaining the relations between flux north atlantic hydrography and ice dynamics both positive and rapid negative mass balance can cause increases and prominent peaks in ird flux first order interpretation of the ird record indicates the timing of the presence of the biis with an actively calving marine margin the records show a coherent latitudinal but partly phased signal during mis 3 and 2 published data indicate that the last biis initiated during the mis 5 4 cooling transition renewed growth just before h5 46 ka was succeeded by very strong millennial scale variability apparently corresponding with dansgaard oeschger do cycles closely coupled to millennial scale climate variability in the north atlantic region involving latitudinal migration of the north atlantic polar front this indicates that the previously defined precursor events are not uniquely associated with h events but are part of the millennial scale variability major growth of the ice sheet occurred after 29 ka with the barra ice stream attaining a shelf edge position and generating turbiditic flows on the barra donegal fan at 27 ka the ice sheet reached its maximum extent at h2 24 ka earlier than interpreted in previous studies rapid retreat initially characterised by peak ird flux during greenland interstadial 2 23 ka was followed by readvance between 22 and 16 ka readvance during h1 was only characterised by biis ice streams draining central dome s of the ice sheet and was followed by rapid deglaciation and ice exhaustion the evidence for a calving margin and ird supply from the biis during greenland stadial 1 younger dryas event is equivocal the timing of the initiation maximum extent deglacial and readvance phases of the biis interpreted from the ird flux record is strongly supported by recent independent data from both the irish sea and north sea sectors of the ice sheet

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

british ice sheet dynamics inferred from north atlantic ice rafted debris records spanning the last 175 000 years sediment core md04 2822 from the rockall trough northeast atlantic provides lithological evidence for the expansion of the british ice sheet bis onto the hebridean margin during both the penultimate marine isotope stage mis 6 wolstonian saalian and last glaciation devensian weichselian a composite chronology is constructed using i the benthic foraminiferal oxygen isotope record matched to an orbitally tuned stacked record of global ice volume specmap ii the synchronisation of the planktonic foraminiferal neogloboquadrina pachyderma sinistral and itrax xrf ca records to the greenland ice core ngrip back to ca 123 ka and iii the synchronisation of the same n pachyderma sinistral and itrax xrf ca records to the atmospheric methane record of the antarctic ice core epica dome c beyond 123 ka the first offshore evidence for the expansion of the last bis within mis 4 is presented suggesting extensive glaciation of northwestern britain during the devensian weichselian as early as 70 ka the proximity of this long sediment core to the glaciated margin of northwestern scotland makes it ideal to capture the ice rafted debris ird signal of the bis for the last 175 ka via a continuous flux record of ird british geological survey nerc 2009 all rights reserved

a new concept for the paleoceanographic evolution of heinrich event 1 in the north atlantic new records of planktonic foraminiferal 18o and lithic and foraminiferal counts from eirik drift are combined with published data from the nordic seas and the ice rafted debris ird belt to portray a sequence of events through heinrich event 1 h1 these events progressed from an onset of meltwater release at not vert similar19 ka bp through the conventional h1 ird deposition phase in the ird belt starting from not vert similar17 5 ka bp to a final phase between 16 5 and not vert similar15 ka bp that was characterised by a pooling of freshwater in the nordic seas which we suggest was hyperpycnally injected into that basin after not vert similar15 ka bp this freshwater was purged from the nordic seas into the north atlantic which preconditioned the nordic seas for convective deep water formation this allowed an abrupt re start of north atlantic deep water nadw formation in the nordic seas at the bolling warming 14 6 ka bp in contrast to previous estimates for the duration of h1 i e 1000 years to only a century or two the total combined composite h1 signal presented here had a duration of over 4000 yrs not vert similar19 14 6 ka bp which spanned the entire period of nadw collapse it appears that deep water formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead the location of meltwater injections may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

a pb isotope tracer of ocean ice sheet interaction the record from the ne atlantic during the last glacial interglacial cycle abstract ice sheet ocean interactions are both a response to climate forcing and a source of climate feedback releasing freshwater to the surface ocean and influencing climate and atmospheric co2 through changes in ocean circulation documenting the outcomes of these interactions for recent glacial cycles is important given current and future scenarios of polar ice retreat however this is currently hampered by lack of accurate constraints on ice sheet development and demise marine sedimentary pb isotope records have potential to investigate these aspects of ice sheet feedbacks at high temporal resolution because of the sensitivity of the pb isotope composition to continental weathering intensity and solute flux here we present a pb isotope record sourced from the femn oxyhydroxide fraction in marine sediments from odp site 980 on feni drift 2168 mbsl rockall trough ne atlantic spanning the last 43 ka the location of site 980 at the northern edge of the british irish ice sheet biis makes it well placed to monitor changes in biis development as it responded to migration of the polar front during the last glacial interglacial cycle the data reveal millennial scale cyclicity in pb isotope composition reminiscent of dansgaard oeschger cycles from the start of the record until heinrich event 2 43 24 ka characterised by extreme shifts to radiogenic compositions i e variation in 206pb 204pb from 18 9 to 20 5 the period 24 17 5 ka is also characterised by exceptionally radiogenic and highly variable pb isotope compositions associated with the rapid and repeated expansion and collapse of the biis the presence of such radiogenic pb isotope compositions during periods of maximum ice sheet activity support interpretation of the subglacial environment as an active weathering environment contributing to biogeochemical cycles through the transport vectors of meltwater release and debris laden ice calving

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

freshwater influx hydrographic reorganization and the dispersal of ice rafted detritus in the sub polar north atlantic ocean during the last deglaciation a sediment core from the north east north atlantic contains high resolution co registered foraminiferal 18o and ice rafted detritus ird records for the last deglaciation these reveal a distinct ice rafting event that occurred at the time of greenland interstade 1d gi 1d a feature also seen in other high resolution cores from the north atlantic the occurrence of a geographically widespread peak in ird at ice distal sites at a time when increased freshwater flux to the surface ocean is inferred to have caused rapid cooling suggests a mechanistic link between the processes analogous to the younger dryas gs 1 cooling episode the general absence of ird at southern locations at other times during gi 1 when the flux of icebergs from surviving ice sheets to northern locations continued suggests that the gi 1d ird peak represents a time of hyrdrographic reorganization which changed ird dispersal while numerous studies have suggested freshwater flux as a major driver of rapid climate oscillations observed around the north atlantic during the last deglaciation the evidence presented here both supports that mechanism and highlights the potential for rapid and major reorganization of the north atlantic s surface hydrography to explain changes in ird flux independently of ice sheet calving dynamics

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

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

late devensian and flandrian palaeoenvironmental changes on the scottish continental shelf west of the outer hebrides examination of two radiocarbon dated vibrocores taken from south of st kilda at a water depth of about 155 m a short distance within the maximum position of the late devensian dimlington stadial ice sheet suggests that the st kilda basin became free of glacier ice after 15250 yr bp sedimentation in a shallow low energy high arctic muddy environment continued until after 13500 yr bp there followed a higher energy temperate episode during which water depths were roughly about 40 m this is correlated with the latter part of the windermere interstadial and with the warmer interval known in shallow scottish seas about or a little before 11 000 yr bp the loch lomond younger dryas stadial is marked in the vibrocores by the return of muddy sediments and a cold water fauna relatively shallow water conditions seem to have persisted into the earliest flandrian when the water depth was still roughly 60 m corresponding to a sea level in the area 90 100 m below present it is suggested that pack ice was widespread in the northeast atlantic before the windermere interstadial and also during the loch lomond stadial when it transported shards of icelandic volcanic ash into the st kilda basin estimates of sea surface temperature for the last part of the windermere interstadial are close to those derived from the deep sea record for the same period

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

eastward moving 2 4 day waves in the winter antarctic mesosphere the structure of short period 2 4 days planetary waves in the antarctic mesosphere has been determined from ground based wind measurements at the south pole observations are made with a fabry perot spectrometer fps to determine the meridional wind component of oh tracer molecules azimuth scanning of the fps shows that the observed modes are of zonal wavenumber one as expected at the rotation pole in the neutral atmosphere at scott base 78 s observations are made with an mf spaced antenna mode mesospheric wind profiler radar the vertical structure of the waves at altitudes of 80 100 km shows a phase variation corresponding to a vertical wavelength of more than 100 km the observed periods support previous interpretations based on satellite observations and barotropic instability models of modes associated with the 4 day wave

modeling the surface mass balance response of the laurentide ice sheet to bolling warming and its contribution to meltwater pulse 1a meltwater pulse mwp 1a occurred 14 5 14 ka and is the largest abrupt rise in sea level 10 20 m of sea level rise of the last deglaciation the timing of mwp 1a is coincident with or shortly follows the abrupt warming of the north atlantic region into the bolling warm period which could have triggered a large laurentide ice sheet lis contribution to mwp 1a given that outside of the arctic lis iceberg discharge probably did not increase during the bolling much of the lis mwp 1a contribution likely occurred through surface ablation here we test the response of lis surface mass balance to bolling warming by forcing a lis energy mass balance model with climate from an atmosphere ocean general circulation model our modeling approach neglects changes in lis mass from dynamics and iceberg calving allowing us to isolate the surface mass balance response model results suggest that lis surface ablation can explain much of the sea level rise just prior to mwp 1a lis surface mass balance becomes more negative in response to the bolling warming contributing an additional 2 9 1 0 m of sea level rise in 500 yr in addition to the background contribution of 4 0 0 8 m the modeled lis mwp 1a contribution is less than previous assumptions but agrees with geochemical runoff and lis area volume estimates the fraction of mwp 1a attributable to other ice sheets particularly antarctica depends on the total sea level rise that occurred during this mwp

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

the relationship of heinrich events and their european precursors over the past 60 ka bp a multi proxy ice rafted debris provenance study in the north east atlantic high resolution multi proxy records of ice rafted debris ird flux and provenance in the ne atlantic detail the development variability and decline of marine margins of the last glacial circum north atlantic ice sheets coupled lithological identification sr and nd isotopic composition and 40ar 39ar ages of individual hornblende grains reduce ambiguity as to ird potential source region allowing clear differentiation between laurentide lis icelandic and british bis ice sheet sources the icelandic and bis are collectively referred to as the nw european ice sheet nweis a step wise increase in the flux of ird to the core site at 26 5 ka bp documents bis advance and glaciation of ireland millennial scale variability of the bis at a 2 ka periodicity is inferred through clusters of pulsed ird fluxes throughout the late glacial 26 5 10 ka bp combination of these european ird events and the 7 ka periodicity of lis instability is thought to account for quasi synchronicity of the nweis and lis ird pulses at heinrich event h 2 and h1 previously suggested to represent the possible involvement of the nweis in the initiation of h events furthermore the lack of extensive nweis marine margin is inferred prior to h3 31 5 ka bp such that no european precursor event is associated with either h5 or h4 this suggests that precursor events were not directly implicated in the collapse of the lis and the persistent instabilities of the bis that are clustered at a 2 ka periodicity are incompatible with the concept that both h events and their precursors are independent responses to a common underlying trigger

tracing time in the ocean a brief review of chronological constraints 60 8 kyr on north atlantic marine event based stratigraphies abstract well resolved event based stratigraphies in marine sediments spanning a significant portion of the last glacial period 60 8 kyr provide a unique opportunity for time stratigraphic correlation in the north atlantic region here we review the current methods available to chronologically constrain these event based stratigraphies highlighting in particular the value of tephrochronology as an independent tool to validate correlations between records while the intimate protocols lowe et al 2008 blockley et al 2011 are equally applicable to marine and terrestrial records spatially and temporally variable marine radiocarbon reservoir age effects mres provide a challenge to using marine radiocarbon in the former as an independent chronostratigraphic tool despite the inherent uncertainties associated with tuning we conclude that the mid points of the common abrupt warming transitions associated with the well defined millennial scale climate oscillations the dansgaard oeschger d o cycles observed in the oxygen isotopes of the greenland ice cores and north atlantic sea surface temperature sst records currently provide the most robust correlation tie points from which to derive age control in this invited intimate special issue article we propose a new protocol for establishing marine event based chronostratigraphies in the north atlantic region and focus on areas of chronological potential in palaeoceanographic research

ch4 and co2 emissions from mud volcanoes on the southern margin of the junggar basin nw china origin output and relation to regional tectonics

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

on the timing and mechanism of millennial scale climate variability during the last glacial cycle the demonstration that natural climate variability during the last glacial cycle shifted rapidly between remarkable extremes has dramatically revised the understanding of climate change to further advance our understanding research continues into the timings geographic distribution and nature of the millennial scale climate extremes and into the mechanisms for intra and inter hemispheric transmission of variability through the climate ocean system complementing the traditional definition of the timings of millennial scale climate variability from ice core 18o records we here further narrow down the temporal constraints by determining statistically significant anomalies in the major ion series of the gisp2 ice core this exercise offers an objective definition of the timing of climatic anomalies in northern hemisphere palaeoclimate proxy records of the last 110 000 years that significantly improves the potential for inter calibration of ice core tuned chronostratigraphies we then present a process oriented synthesis of proxy records from the northern hemisphere this leads to a conclusion that the dansgaard oeschger d o style fluctuations in these records are virtually in phase since all fall within a clear atmospheric pattern of concerted relative dominance shifts between polar westerly dominated winter type conditions and tropical monsoon dominated summer type conditions finally we speculate on a monsoon related mechanism that could help explain the anomalously long duration of d o interstadials 12 8 and 1 which coincided with cooling trends in antarctic records

first results from the meteor radar at south pole a large 12 hour oscillation with zonal wavenumber one the first mesopause region ca 92 5 km wind measurements from the meteor radar at amundsen scott station at south pole are described measurements are made along four orthogonal azimuth directions approximately 2 from the geographic south pole a large 20 ms 1 oscillation in the northward wind is observed with 12 hour period and zonal wavenumber one a similar wave was observed during august 1 13 1992 at south pole by hernandez et al 1993 using optical methods the predominant semidiurnal tide in the atmosphere is migrating with the apparent motion of the sun with s 2 the s 1 oscillation is interpreted here to result from the nonlinear interaction between the migrating semidiurnal tide and a stationary wave with s 1 the present mechanism represents an alternative to the gravity wave driven pseudotide theory put forth by walterscheid et al 1986 to explain the occurrence of unexpectedly large semidiurnal tidal oscillations at high latitudes

freshwater input and abrupt deglacial climate change in the north atlantic greenland ice core records indicate that the last deglaciation 7 21 ka was punctuated by numerous abrupt climate reversals involving temperature changes of up to 5 10oc within decades however the cause behind many of these events is uncertain a likely candidate may have been the input of deglacial meltwater from the laurentide ice sheet lis to the high latitude north atlantic which disrupted ocean circulation and triggered cooling yet the direct evidence of meltwater input for many of these event has so far remained undetected in this study we use the geochemistry paired mg ca 18 o of planktonic foraminifera from a sediment core south of iceland to reconstruct the input of freshwater to the northern north atlantic during abrupt deglacial climate change our record can be placed on the same timescale as ice cores and therefore provides a direct comparison between the timing of freshwater input and climate variability meltwater events coincide with the onset of numerous cold intervals including the older dryas 14 0 ka two events during the allerod at 13 1 and 13 6 ka the younger dryas 12 9 ka and the 8 2 ka event supporting a causal link between these abrupt climate changes and meltwater input during the bolling allerod warm interval we find that periods of warming are associated with an increased meltwater flux to the northern north atlantic which in turn induces abrupt cooling a cessation in meltwater input and eventual climate recovery this implies that feedback between climate and meltwater input produced a highly variable climate a comparison to published data sets suggests that this feedback likely included fluctuations in the southern margin of the lis causing rerouting of lis meltwater between southern and eastern drainage outlets as proposed by clark et al science 2001 v293 283 287

impact of floods versus routing events on the thermohaline circulation 1 the last deglaciation was interrupted by three major cooling events the younger dryas the preboreal oscillation and the 8 2 ka cold event as the laurentide ice sheet retreated different outlets from lake agassiz became available causing the proglacial lake to drain to a new level in a rather short timescale flood and divert continental runoff over hundreds of years routing here we use an earth system model to investigate the impact of floods short term high amplitude versus routing events long term low amplitude on the thermohaline circulation and the resulting climate change we show that the initial outbursts of freshwater are not strong enough to influence large scale climate and can therefore not be the cause of millennial scale climate variability however routing events have the potential of weakening the thermohaline circulation and therefore causing a cool event in the northern hemisphere

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

vulnerability of the cordilleran ice sheet to iceberg calving during late quaternary rapid climate change events 1 we present the first high resolution record of iceberg calving on the continental slope of vancouver island british columbia md02 2496 48 58n 127 02w 1243 m water depth through the last glacial from the cordilleran ice sheet cis these previously unknown ice rafted debris ird events representing significant retreat of the western margin of the cis out of marine waters show little correspondence with local climate change high resolution radiocarbon dating indicates that the younger ird events coincide with global radiocarbon age plateaus that allow direct correlation with distal climate records where the same plateaus have been identified the coincidence of episodic shedding of ird from the cis with north atlantic climate events i e north atlantic deep water shutdown and heinrich events begs the question what drove cis destabilization forcing appears to be external to cis dynamics perhaps resulting from either eustatic sea level rise or episodes of atmospheric warming over the north american continent

large scale waves in the upper mesosphere at antarctic high latitudes upper mesosphere combined optical measurements of wind and temperature fields at amundsen scott station south pole and wind radar measurements at scott base 78 s 167 e show the presence of large scale waves in this region of the atmosphere at amundsen scott the largest amplitude wave observed with sub diurnal periodicity appears with a frequency near 2 4 day 10 1 hour period with a westward phase progression of wavenumber one the presence of a wave with this periodicity is confirmed by the observations at scott base the combination of the experimentally found period phase progression associated small temperature oscillations and theoretical considerations lead to the interpretation of this wave as a lamb wave the present combination of spatially resolved optical measurements and radar measurements illustrates the value of multiple station and multiple technique observations in elucidating the upper mesosphere dynamical state as well as the properties of the waves propagating through the medium where the observations are being made

simultaneous mesospheric wind measurements near south pole by optical and meteor radar methods simultaneous and co located measurements of mesospheric winds near south pole by high resolution optical and meteor radar methods show that these two methods determine very similar motions at slightly different heights of observation the measured atmospheric motions by the two techniques show that a the mean wind during 12 days in june 1995 was found to have a 7 m s amplitude flowing towards the 5 e longitude direction the latter direction is different from the 30e direction found earlier during august 1991 and 1992 b the observed dominant oscillations in the wind at both heights of observation are those of zonal wavenumber one character westward phase propagation was determined for the observed short period 0 hours oscillations and eastward phase propagation for the longer period 3 days oscillations respectively because of the neighboring heights of observation by the optical and meteor radar methods the in situ vertical wavelengths of propagation of the observed waves have been determined to be greater than 100 km for the 10 hr oscillations and near 65 km for the longer period oscillations with this new information we are able to independently establish the earlier assignment of the nearly 10 hr oscillations as the different meridional modes of a zonal wavenumber one lamb wave the determined vertical wavelength and eastward phase progression of the longer periodicity waves indicate these oscillations are likely to be the gravest inertio gravity wave which has the appropriate equivalent depths at these periods of oscillation the simultaneous absence of statistically significant kinetic temperature and optical tracer emission rate oscillations at the frequencies corresponding to the wind motions provides independent support to the earlier deductions on the ability of the atmosphere near the rotational poles to support only certain zonal character oscillations

extent and retreat history of the barra fan ice stream offshore western scotland and northern ireland during the last glaciation abstract during the last glacial maximum lgm the marine terminating barra fan ice stream bfis a major conduit of the british irish ice sheet biis drained much of western scotland and northwest ireland with ice streaming onto the continental shelf of the malin sea the extent and retreat history of this ice stream across the shelf until now is not well known in particular geochronological constraints on the history of this ice stream have thus far been restricted to deep sea cores or terrestrial cosmogenic nuclide dating onshore with ages across the shelf absent to understand the possible external forcing factors acting on this marine terminating ice stream during retreat improved geochronological constraint on its deglaciation is necessary here we present new geophysical data marine sediment cores and over forty radiocarbon dates to provide important constraints on maximum extent of the bfis as well as the timing and pattern of retreat back across the malin shelf dated moraines and grounding zone wedges gzw seen in seafloor sub bottom profiles provide evidence that the bfis reached the malin shelf edge during the lgm and was at its maximum extent around 26 7 ka bp the presence of two sets of gzws suggests that the style of retreat was episodic the new radiocarbon chronology shows that retreat from the shelf edge was underway by 25 9 ka bp with the majority of the continental shelf ice free by 23 2 ka bp and that glacimarine conditions were present in the sea of hebrides by 20 2 ka bp at the latest collectively these results indicate that the majority of the malin shelf was free of grounded ice by 21 5 20 ka bp which is up to 4000 years earlier than previously reconstructed we attribute this early deglaciation to high relative sea level caused by glacial isostatic depression when the biis reached its maximum extent promoting ice shelf and grounding line instability two deep troughs forming reverse bed slopes aided the continued retreat of the bfis this suggests that local ice loading and bed morphology can be significant controls on the destabilisation of a marine terminating ice stream and can override the influence of ocean and atmospheric temperatures

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

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume