geological modelling from field data and geological knowledge part ii modelling validation using gravity and magnetic data inversion the analysis of multiple data sets is required to select a realistic 3d geological model among an infinite number of possibilities an inverse method that aims at describing the 3d geometry of geological objects is presented the method takes into account the geology and the physical properties of rocks while respecting the topological properties of an a priori model the a priori model is built from the geological data set and its geometry is largely dependent upon assumptions about inaccessible geology at depth this method referred to as total litho inversion is a generalized 3d inversion that results in quantifying the lithology and the distribution of rock property in a probabilistic way its application is demonstrated through i a simple synthetic case and ii the relative distribution characterization of granites and diorites in an orogenic domain

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

a centennial scale record of vegetation and climate variability from 312 to 240 ka marine isotope stages 9c a 8 and 7e from tenaghi philippon ne greece abstract based on a new centennial scale resolution pollen record from the terrestrial site of tenaghi philippon ne greece we report a series of high amplitude millennial scale forest expansion events during the interval from 312 to 240 ka equivalent to isotopic substages c a of marine isotope stage mis 9 mis 8 and the onset of mis 7e pollen based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the mediterranean region long term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages early middle and late analogous to the glacial substages of the last climatic cycle within this framework forest expansion events occurred during the early glacial equivalent to mis 9c a and the later part of the middle glacial mid to late mis 8 but are absent from the early part of the middle glacial early mis 8 forest expansion events are also detected during the lateglacial and onset of mis 7 associated with a millennial scale climate oscillation across the glacial interglacial transition i e termination iii t iii a peak for peak match between forest expansion events and antarctic temperature maxima suggests interhemispheric coupling of millennial scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see saw the resolution of our record mean 290 yr also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events and highlights differences in the characteristics of early and middle glacial interstadials saw tooth vs plateau profile these differences point to an influence of long term boundary conditions especially global ice volume on the characteristics of millennial scale events

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

enhanced marine productivity off western north america during warm climate intervals of the past 52 k y studies of the santa barbara basin off the coast of california have linked changes in its bottom water oxygen content to millennial scale climate changes as recorded by the oxygen isotope composition of greenland ice through the use of detailed records from a sediment core collected off the magdalena margin of baja california mexico we demonstrate that this teleconnection predominantly arose from changes in marine productivity rather than changes in ventilation of the north pacific as was originally proposed

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

persistent transport barrier on the west florida shelf 1 analysis of drifter trajectories in the gulf of mexico has revealed the existence of a region on the southern portion of the west florida shelf wfs that is not visited by drifters that are released outside of the region this socalled forbidden zone fz suggests the existence of a persistent cross shelf transport barrier on the southern portion of the wfs in this letter a year long record of surface currents produced by a hybrid coordinate ocean model simulation of the wfs is used to compute lagrangian coherent structures lcss which reveal the presence of a persistent cross shelf transport barrier in approximately the same location as the boundary of the fz the location of the cross shelf transport barrier undergoes a seasonal oscillation being closer to the coast in the summer than in the winter a month long record of surface currents inferred from high frequency hf radar measurements in a roughly 60 km 80 km region on the wfs off tampa bay is also used to compute lcss and these also reveal the presence of transient transport barriers while the hf radarderived transport barriers cannot be unambiguously linked to the boundary of the fz this analysis does demonstrate the feasibility of monitoring transport barriers on the wfs using a hf radar based measurement system the implications of a persistent cross shelf transport barrier on the wfs for the development of harmful algal blooms on the shoreward side of the barrier are considered citation olascoaga m j i i rypina m g brown f j

southern ocean seasonal temperature and subtropical front movement on the south tasman rise in the late quaternary 1 the subtropical front stf marking the northern boundary of the southern ocean has a steep gradient in sea surface temperature sst of approximately 4c over 0 5 of latitude presently in the region south of tasmania the stf lies nominally at 47s in the summer and 45s in the winter we present here sst reconstructions in a latitudinal transect of cores across the south tasman rise southeast of australia during the late quaternary sst reconstructions are based on two paleotemperature proxies alkenones and faunal assemblages which are used to assess past changes in sst in spring and summer the north south alignment in core locations allows reconstruction of movement of the stf over the last 100 ka surface water temperatures during the last glaciation in this region were 4c colder than today additional temperature changes greater in magnitude than 4c seen in individual cores can be attributed to changes in the water mass overlying the core site caused by the movement of the front across that location during the penultimate interglacial sst was 2c warmer and the stf was largely positioned south of 47s movement of the stf to the north occurred during cool climate periods such as the last marine isotope stages 3 and 4 in the last glaciation the front was at its farthest north position becoming pinned against the tasmanian landmass it moved south by 4 latitude to 47s in summer during the deglaciation but remained north of 45s in spring throughout the early deglaciation after 11 ka b p inferred invigoration of the east australia current appears to have pushed the stf seasonally south of the east tasman plateau until after 6 ka b p when it achieved its present configuration

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

long term sea surface temperature and climate change in the australian new zealand region 1 we compile and compare data for the last 150 000 years from four deep sea cores in the midlatitude zone of the southern hemisphere we recalculate sea surface temperature estimates derived from foraminifera and compare these with estimates derived from alkenones and magnesium calcium ratios in foraminiferal carbonate and with accompanying sedimentological and pollen records on a common absolute timescale using a stack of the highest resolution records we find that first order climate change occurs in concert with changes in insolation in the northern hemisphere glacier extent and inferred vegetation changes in australia and new zealand vary in tandem with sea surface temperatures signifying close links between oceanic and terrestrial temperature in the southern ocean rapid temperature change of the order of 6 c occurs within a few centuries and appears to have played an important role in midlatitude climate change sea surface temperature changes over longer periods closely match proxy temperature records from antarctic ice cores warm events correlate with antarctic events a1 a4 and appear to occur just before dansgaard oeschger events 8 12 14 and 17 in greenland

sensitivity of southern hemisphere circulation to lgm and 4 co2 climates 1 this paper investigates the effect of last glacial maximum lgm versus high co2 world boundary condition on the southern hemisphere atmospheric circulation in particular on the strength and latitudinal position of the near surface southern westerly winds sww pmip2 and pmip3 experiments as well as the abrupt 4 co2 simulations from cmip5 were analyzed robust findings include poleward expansion of the mean meridional circulation mmc and intensified and poleward shifted sww in the 4 co2 simulations consistent with recent observations and 21st century climate change projections and for the lgm stronger and southward shifted northern hemisphere mmc and weakened southern hadley cell however six of the eight lgm simulations show a decrease in the sww the other two models simulate the opposite a critical difference between the models is strong coupling between sea ice extent surface temperature gradients sww and ferrel cell in the two models with stronger and poleward shifted sww

correlated millennial scale changes in surface hydrography and terrigenous sediment yield inferred from last glacial marine deposits off northeastern brazil abstract the stable isotope composition of planktonic foraminifera correlates with evidence for pulses of terrigenous sediment in a sediment core from the upper continental slope off northeastern brazil stable oxygen isotope records of the planktonic foraminiferal speciesglobigerinoides sacculiferandglobigerinoides ruber pink reveal sub milankovitch changes in sea surface hydrography during the last 85 000 yr warming of the surface water coincided with terrigenous sedimentation pulses that are inferred from high xrf intensities of ti and fe and which suggest humid conditions in northeast brazil these tropical signals correlate with climatic oscillations recorded in greenland ice cores dansgaard oeschger cycles and in sediment cores from the north atlantic heinrich events trade winds may have caused changes in the north brazil current that altered heat and salt flux into the north atlantic thus affecting the growth and decay of the large glacial ice sheets

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

the impact of the north atlantic ocean on the younger dryas climate in northwestern and central europe the main results of multiproxy climate reconstructions for the younger dryas and experiments carried out with an atmospheric general circulation model are discussed quantitative temperature inferences for northwestern and central europe show that winter conditions were remarkably extreme with values of 20 30 c below that of today annual temperature ranges with a continental signature 30 34 c were reconstructed for the entire study area compared with today the greatest cooling was experienced in the seaboard area the comparison of the climate reconstructions and simulation experiments indicates that sea ice in the north atlantic ocean played a decisive role in the climate of the study area by cooling the surface air temperatures and by controlling the position of the storm track surface air circulation was westerly even during younger dryas winters a slight northward shift of the mean atlantic sea ice margin during winter may explain the proposed subdivision of the younger drays into a phase of maximum cold and humidity succeeded by a less cold and relatively dry phase 1998 john wiley sons ltd

numerical modeling of a highly explosive source in an elastic brittle rock mass a highly explosive source is input in an elastic brittle rock mass and the resulting near source complexities are considered this study is undertaken with a three dimensional numerical model similar to the discrete element method this model can simulate the creation of the damage zone with the associated block motions as well as the elastic wave propagation free field ground motion data are recorded to determine the reduced displacement potential rdp in a fully elastic numerical model as expected the rdp computation corresponds to the analytical one dimensional problem of a spherically symmetric explosive source acting in a homogeneous elastic medium when fracturing occurs during the creation of the damage zone block motions are observed and the rdp computations are affected for an ideal system which conserves energy the potential elastic energy is converted to kinetic energy during the fracturing process resulting in an apparent rdp which is larger than in the homogeneous elastic case this three dimensional approach is undeniably advantageous where a global description of the heterogenous effects of block motions and the continuous aspects of wave propagation are considered simultaneously

timing of massive fleuve manche discharges over the last 350 kyr insights into the european ice sheet oscillations and the european drainage network from mis 10 to 2 continuous high resolution mass accumulation rates mar and x ray fluorescence xrf measurements from marine sediment records in the bay of biscay ne atlantic have allowed the determination of the timing and the amplitude of the fleuve manche channel river discharges during glacial stages mis 10 mis 8 mis 6 and mis 4 2 these results have yielded detailed insight into the middle and late pleistocene glaciations in europe and the drainage network of the western and central european rivers over the last 350 kyr this study provides clear evidence that the fleuve manche connected the southern north sea basin with the bay of biscay during each glacial period and reveals that fleuve manche activity during the glaciations mis 10 and mis 8 was significantly less than during mis 6 and mis 2 we correlate the significant fleuve manche activity detected during mis 6 and mis 2 with the extensive saalian drenthe substage and the weichselian glaciations respectively confirming that the major elsterian glaciation precedes the glacial mis 10 in detail massive fleuve manche discharges occurred at ca 155 ka mid mis 6 and during termination i while no significant discharges are found during termination ii it is assumed that a substantial retreat of the european ice sheet at ca 155 kyr followed by the formation of ice free conditions between the british isles and scandinavia until termination ii allowed meltwater to flow northwards through the north sea basin during the second part of the mis 6 we assume that this glacial pattern corresponds to the warthe substage glacial maximum therefore indicating that the data presented here equates to the drenthe and the warthe glacial advances at ca 175 160 ka and ca 150 140 ka respectively finally the correlation of our records with odp site 980 reveals that massive fleuve manche discharges related to partial or complete melting of the european ice masses were synchronous with strong decreases in both the rate of deep water formation and the strength of the atlantic thermohaline circulation fleuve manche discharges over the last 350 kyr probably participated with other meltwater sources in the collapse of the thermohaline circulation by freshening the northern atlantic surface water

strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation the climate of the last glacial period was extremely variable characterized by abrupt warming events in the northern hemisphere accompanied by slower temperature changes in antarctica and variations of global sea level it is generally accepted that this millennial scale climate variability was caused by abrupt changes in the ocean thermohaline circulation here we use a coupled ocean atmosphere sea ice model to show that freshwater discharge into the north atlantic ocean in addition to a reduction of the thermohaline circulation has a direct effect on southern ocean temperature the related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical north atlantic caused by a fast wave adjustment process we present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of greenland and antarctic temperature changes the slow changes in antarctic temperature and its similarity to sea level as well as a possible time lag of sea level with respect to antarctic temperature during marine isotope stage 3

modulation of the bipolar seesaw in the southeast pacific during termination 1 the termination of the last ice age termination 1 t1 is crucial for our understanding of global climate change and for the validation of climate models there are still a number of open questions regarding for example the exact timing and the mechanisms involved in the initiation of deglaciation and the subsequent interhemispheric pattern of the warming our study is based on a well dated and high resolution alkenone based sea surface temperature sst record from the se pacific off southern chile ocean drilling project site 1233 showing that deglacial warming at the northern margin of the antarctic circumpolar current system acc began shortly after 19 000 years bp 19 kyr bp the timing is largely consistent with antarctic ice core records but the initial warming in the se pacific is more abrupt suggesting a direct and immediate response to the slowdown of the atlantic thermohaline circulation through the bipolar seesaw mechanism this response requires a rapid transfer of the atlantic signal to the se pacific without involving the thermal inertia of the southern ocean that may contribute to the substantially more gradual deglacial temperature rise seen in antarctic ice cores a very plausible mechanism for this rapid transfer is a seesawinduced change of the coupled ocean atmosphere system of the acc and the southern westerly wind belt in addition modelling results suggest that insolation changes and the deglacial co2 rise induced a substantial sst increase at our site location but with a gradual warming structure the similarity of the two step rise in our proxy ssts and co2 over t1 strongly demands for a forcing mechanism influencing both temperature and co2 as ssts at our coring site are particularly sensitive to latitudinal shifts of the acc southern westerly wind belt system we conclude that such latitudinal shifts may substantially affect the upwelling of deepwater masses in the southern ocean and thus the release of co2 to the atmosphere as suggested by the conceptual model of toggweiler j r rusell j l carson s r 2006 midlatitude westerlies atmospheric co2 and climate change during ice ages

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

climate variability and ice sheet dynamics during the last three glaciations a composite north atlantic record from dsdp site 609 and iodp site u1308 spans the past 300 000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations hematite stained grains exhibit similar repetitive down core variations within the marine isotope stage mis 8 and 4 2 intervals but little cyclic variability within the mis 6 section there is also no petrologic evidence in terms of detrital carbonate rich heinrich layers for surging of the laurentide ice sheet through the hudson strait during mis 6 rather very high background concentration of iceberg rafted debris ird indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events such as expanded sea ice over deepwater formation sites altered sub tropical precipitation patterns and antarctic warming during high orbital precession and low 65 n summer insolation appear related to high abundance of icelandic glass shards and southward sea ice expansion differing european and north american ice sheet configurations perhaps aided by larger variations in eccentricity leading to cooler summers may have contributed to the relative stability of the laurentide ice sheet in the hudson strait region during mis 6

a continuous record of vegetation fire regime and climatic changes in northwestern patagonia spanning the last 25 000 years abstract we present a high resolution precisely dated terrestrial paleovegetation paleoclimate record from lago pichilaguna northwestern patagonia 40 44 s which spans continuously from the last glacial maximum lgm to the present we find abundant and continuous presence of arboreal pollen chiefly nothofagus during the lgm accompanied by other trees shrubs and alpine herbs these results suggest subantarctic parkland and or scattered woodlands under a cold and hyperhumid climate during the lgm 25 000 17 800 cal yr bp with expansion of nothofagus under relatively warm interstadial conditions between 25 000 and 19 200 cal yr bp this was followed by cooling and a precipitation increase between 19 200 and 17 800 cal yr bp which was contemporaneous with the youngest lgm advance of andean glaciers in the region and maximum influence of the southern westerly wind sww the last glacial termination t1 started at 17 800 cal yr bp and featured the spread of thermophilous trees and ferns characteristic of north patagonian rainforests along with lake level lowering these results suggest a warm pulse and southward shift of the sww concurrent with a rapid collapse of andean glacier lobes subsequent changes led to the establishment of closed canopy rainforests under peak interstadial warmth between 16 000 and 15 000 cal yr bp we detect a shift to cold wet conditions during the antarctic cold reversal 14 800 12 700 cal yr bp and a precipitation decline during younger dryas time followed by maximum temperature relatively lower lake level and minimum sww influence between 11 300 and 7700 cal yr bp precipitation then rose punctuated by centennial scale variations since 6200 cal yr bp chilean european deforestation and spread of invasive exotic species started at 350 cal yr bp aided by fire we conclude that temperate rainforests have persisted with little interruption since t1 with major changes in floristic composition driven by climate change and fires rainforest composition and heterogeneity declined in response to chilean european disturbance during the 1600s and intensified since the 1800s these events constitute the fastest largest magnitude vegetation changes of the last 25 000 years

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

a bi polar signal recorded in the western tropical pacific northern and southern hemisphere climate records from the pacific warm pool during the last ice age abstract western tropical pacific sea surface temperatures and pacific deep water temperatures during marine isotope stage 3 have been reconstructed from the 18o and mg ca of planktonic and benthic foraminifera from marion dufresne core md98 2181 this 36 m marine core was collected at 6 3 n from a water depth of 2114 m with sediment accumulation rates of up to 80 cm ky it provides a decadally resolved history of ocean variability during the last glacial period surface temperatures and salinities at this site varied in close association with millennial scale atmospheric temperature swings at high northern latitudes as reflected in the gisp2 ice core at times of colder atmospheric temperatures over greenland the western pacific was more saline and summer season ssts were 2 c colder these millennial scale changes within the tropics are attributed to a southward displacement of the summer season itcz in response to steeper meridional temperature gradients within the pacific the benthic 18o record from md98 2181 documents upper pacific deep water temperature and salinity variability benthic 18o variations of 0 3 0 5 during mis 3 indicate deep waters within the pacific were varying by 1 1 5 c with the possibility that some of the variability was due to changing salinity and minor glacial eustatic changes the observed deep water variability correlates to changes in antarctic surface temperatures and thus reflects changes in southern ocean temperatures at the site of pacific deep water formation the combined planktonic and benthic records from md98 2181 thus provide a northern and southern hemispheric climate record of anti phased variability during mis 3 as has been inferred previously from ice core records furthermore the deep sea temperature excursions appear to have led millennial variations in atmospheric co2 as recorded in the edml ice core by 1 kyr

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

last glacial pollen climate reconstructions from northland new zealand despite wide ranging interest in the vegetation and climate of northland new zealand during the last glacial cycle the region and timeframe lack quantitative climate reconstructions while land based pollen records have tended to be poorly dated and fragmentary the region is also important for geochronology due to the co occurrence of the rotoehu tephra a widely dispersed isochron near the current limits of radiocarbon dating and extensive subfossil wood remains of agathis australis with strong dendrochronological and dendroclimatological potential we present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid northland 35 s all containing rotoehu tephra that collectively span the last 70 ka the phases and amplitude of temperature changes broadly align with those reported from elsewhere in new zealand and with marine isotope climate stratigraphic records including maximum temperature depression of 6 8 c during the last glacial maximum we argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt the northern margins of which extend to the region today correspondence between the northland temperature shifts and atmospheric co2 supports the model of ocean atmosphere co2 flux modulated by latitudinal migration of the southern westerlies copyright 2017 john wiley sons ltd

simulation of glacial interglacial cycles by simple relaxation models consistency with observational results the model of paillard and parrenin earth planet sci lett 227 263 271 2004 was modified to obtain a closer fit to 18o and co2 time series for the last 800 kyr the model performance can be improved if its co2 sensitivity to i65 insolation is eliminated and if different response times are assumed for ablation accumulation of ice correlations between simulated and experimental time series for co2 and ice volume v increase from 0 59 and 0 63 to 0 79 and 0 88 respectively according to these models terminations are produced by i65 amplification through co2 t and t co2 feedbacks in synergy with an extra co2 contribution from the deep ocean this contribution is strongly dependent on ice sheet extent and ice volume or alternatively co2 concentration which is a good proxy of antarctic temperature but is insensitive to southern ocean so insolation on 21 february i60 change of deep so state may be the order parameter for nonlinear deglacial changes according to these models 100 kyr periodicity of glacial cycles arises from the characteristic time of antarctic ice sheet advance to the continental slope

a cosmogenic 3he chronology of late quaternary glacier fluctuations in north island new zealand 39 s abstract mountain glaciers advance and retreat primarily in response to changes in climate establishing the timing and magnitude of mountain glacier fluctuations from geological records can thus help to identify the drivers and mechanisms of past climate change in this study we use cosmogenic 3 he surface exposure dating and tephrochronology to constrain the timing of past glaciation on tongariro massif in central north island new zealand 39 s exposure ages from moraine boulders show that valley glaciation persisted between c 30 18 ka which coincides with the global last glacial maximum reinterpretation of moraine tephrostratigraphy using major element geochemistry analysis shows that ice retreat and climatic amelioration at the last glacial termination was well underway prior to 14 ka the equilibrium line altitude in central north island during the last glacial maximum was c 1400 1550 m above sea level which is c 930 1080 m lower than present considering the uncertainties in the glacial reconstruction and temperature lapse rates we estimate that this equilibrium line altitude lowering equates to a temperature depression of 5 6 1 1 c relative to present our mapping and surface exposure dating also show evidence for an earlier period of glaciation of similar magnitude to the last glacial maximum which culminated prior to 57 ka probably during marine isotope stage 4 good agreement between the timing and magnitude of glacier fluctuations in central north island and the southern alps indicate a response to a common climatic forcing during the last glacial cycle

a cosmogenic 10be chronology for the local last glacial maximum and termination in the cordillera oriental southern peruvian andes implications for the tropical role in global climate abstract resolving patterns of tropical climate variability during and since the last glacial maximum lgm is fundamental to assessing the role of the tropics in global change both on ice age and sub millennial timescales here we present a10be moraine chronology from the cordillera carabaya 14 3 s a sub range of the cordillera oriental in southern peru covering the lgm and the first half of the last glacial termination additionally we recalculate existing 10be ages using a new tropical high altitude production rate in order to put our record into broader spatial context our results indicate that glaciers deposited a series of moraines during marine isotope stage 2 broadly synchronous with global glacier maxima but that maximum glacier extent may have occurred prior to stage 2 thereafter atmospheric warming drove widespread deglaciation of the cordillera carabaya a subsequent glacier resurgence culminated at 16 100 yrs followed by a second period of glacier recession together the observed deglaciation corresponds to heinrich stadial 1 hs1 18 000 14 600 yrs during which pluvial lakes on the adjacent peruvian bolivian altiplano rose to their highest levels of the late pleistocene as a consequence of southward displacement of the inter tropical convergence zone and intensification of the south american summer monsoon deglaciation in the cordillera carabaya also coincided with the retreat of higher latitude mountain glaciers in the southern hemisphere our findings suggest that hs1 was characterised by atmospheric warming and indicate that deglaciation of the southern peruvian andes was driven by rising temperatures despite increased precipitation recalculated 10be data from other tropical andean sites support this model finally we suggest that the broadly uniform response during the lgm and termination of the glaciers examined here involved equatorial pacific sea surface temperature anomalies and propose a framework for testing the viability of this conceptual model

radiocarbon chronology of the late glacial puerto bandera moraines southern patagonian icefield argentina abstract we report radiocarbon dates that constrain the timing of the deposition of the late glacial puerto bandera moraine system alongside the western reaches of lago argentino adjacent to the southern patagonian icefield close maximum limiting radiocarbon ages n 11 for glacier advance into the outer moraines with a mean value of 11 100 60 14 c yrs bp 12 990 80 cal yrs bp were obtained from wood in deformation soft till exposed beneath flow and lodgment till in bahia del quemado on the northeast side of brazo norte north branch of western lago argentino other exposures of this basal deformation till in bahia del quemado reveal incorporated clasts of peat along with larger inclusions of deformed glaciofluvial and lacustrine deposits radiocarbon dates of wood included in these reworked peat clasts range from 11 450 45 14 c yrs bp to 13 450 150 14 c yrs bp 13 315 60 to 16 440 340 cal yrs bp the implication is that during this interval glacier fronts were situated inboard of the puerto bandera moraines with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the puerto bandera advance minimum limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the puerto bandera moraines glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to 10 750 75 14 c yrs bp 12 660 70 cal yrs bp east of brazo rico 10 550 55 14 c yrs bp 12 490 80 cal yrs bp in peninsula avellaneda and 10 400 50 14 c yrs bp 12 280 110 cal yrs bp in bahia catalana in addition a radiocarbon date indicates that by 10 350 45 14 c yrs bp 12 220 110 cal yrs bp the brazo norte lobe or former upsala glacier had receded well up the northern branch of lago argentino to a position behind the herminita moraines furthermore glacier termini had receded to just outboard of the outer holocene moraines at lago frias and lago pearson anita prior to 10 400 40 14 c yrs bp 12 270 100 cal yrs bp and 9040 45 14 c yrs bp 10 210 50 cal yrs bp respectively the most extensive recession registered during the early holocene was in agassiz este valley where the upsala glacier had pulled back behind the outer holocene moraine reaching close to the present day glacier terminus before 8290 40 14 c yrs bp 9300 80 cal yrs bp the radiocarbon dated fluctuations of the lago argentino glacier in late glacial time given here are in accord with changes in ocean mixed layer properties predominately temperature derived from the isotopic record given here of odp core 1233 taken a short distance off shore of the chilean lake district it also matches recently published chronologies of late glacial moraines in the southern alps of new zealand on the opposite side of the pacific ocean from lago argentino finally the timing of the late glacial reversal of the lago argentino glacier fits the most recent chronology for the culmination of the antarctic cold reversal acr in the deuterium record of the epica dome c ice core from high on the east antarctic plateau therefore we conclude that the climate signature of the acr was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe

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

glacial terminations as southern warmings without northern control the timing and mechanisms of the transition from a glacial to an interglacial state are controversial an analysis of antarctic ice core records indicates that glacial terminations may begin as millennial scale warmings in the southern hemisphere that unlike previous events are not reversed by abrupt warming in the northern hemisphere

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

antarctic deglacial pattern in a 30 kyr record of sea surface temperature offshore south australia 1 comparison of ice cores from greenland and antarctica shows an asynchronous two step warming at these high latitudes during the last termination however the question whether this asynchrony extends to lower latitudes is unclear mainly due to the scarcity of paleorecords from the southern hemisphere new data from a marine core collected off south australia 36s allows a detailed reconstruction of sea surface temperatures over the last termination this confirms the existence of an antarctic type deglacial pattern and shows no indication of cooling associated with the northern hemisphere yd event the sst record also provides a new comparison with the more extensive paleoclimatic data available from continental australia this shows a strong climatic link between onshore and offshore records for australia and to southern hemisphere paleorecords we also show a progressive sst drop over the last 6 5 kyr not seen before for the australian region citation calvo e c pelejero p de deckker and g a logan 2007 antarctic deglacial pattern in a 30 kyr record of sea surface temperature offshore south australia geophys res lett 34 l13707 doi 10 1029 2007gl029937

revised deglaciation history of the pietrele stânisoara glacial complex retezat mts southern carpathians romania abstract although geomorphological evidences of quaternary glaciations of the southern carpathians were extensively studied and discussed the limited number of chronological studies resulted in poor and controversial knowledge on the age of glaciations and deglaciation of the area we use new and recalculated in situ produced 10be surface exposure ages of glacial landforms to shed light on the age of the maximum glacial extent and the glacier oscillations during the last deglaciation process on the northern side of the retezat mountains according to our data the maximum ice extent documented by preserved moraines occurred around 21 0 1 5 0 8 ka coincident with the global last glacial maximum lgm the deglaciation process during the lateglacial was characterized by two glacial advances at 18 6 0 8 0 9 and 16 3 0 6 0 6 ka inferred stabilization date of the penultimate glacial stage at 15 2 0 8 0 7 ka was closely followed by the abrupt warming at the onset of the bolling allerod documented by a local chironomid based temperature reconstruction the last small glacier advance was dated to 13 5 0 4 0 5 ka these recessional readvance phases agree with other european glacial chronologies

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

reconstructing the antarctic ice sheet at the last glacial maximum abstract a reconstruction of the antarctic ice sheet at the last glacial maximum lgm constrained by geologic data shows expansion across continental shelves accompanied by little inland change this added peripheral ice volume contributed 14 m to the lowering of eustatic sea level at the lgm of the total expansion one third took place in east antarctica and two thirds in west antarctica

the role of eddies in the southern ocean temperature response to the southern annular mode the role of eddies in modulating the southern ocean response to the southern annular mode sam is examined usinganoceanmodelrunatmultipleresolutionsfromcoarsetoeddyresolving thehigh resolution versionsof the model showan increase in eddy kinetic energy that peaks 2 3 yr after a positive anomalyin the sam index previous work has shown that the instantaneous temperature response to the sam is characterized by predominant cooling south of 458s and warming to the north at all resolutions the model captures this temperatureresponse this responseis also evidentin the coarse resolution implementation of the model with no eddy mixing parameterization showing that eddiesdo not play an important role in the instantaneous response on the longer time scales an intensification of the mesoscale eddy field occurs which causes enhanced poleward heat flux and drives warming south of the oceanic polar front this warming is of greater magnitude and occurs for a longer period than the initial cooling response the results demonstrate that this warming is surface intensified and strongest in the mixed layer non eddy resolving models are unable to capturethedelayededdy driventemperatureresponsetothesam theauthorsthereforequestiontheability

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

itcz rather than enso signature for abrupt climate changes across the tropical pacific latitudinal movements of the intertropical convergence zone itcz analogous to its present day seasonal shifts and el nino southern oscillation enso type variability both potentially impacted rainfall changes at the millennial timescale during the last glacial period in this study we compare tropical pacific sedimentary records of paleoprecipitation to decipher which climate mechanism was responsible for the past rainfall changes we find that latitudinal movements of the itcz are consistent with the observed rainfall patterns challenging the enso hypothesis for explaining the rapid rainfall changes at low latitudes the itcz related mechanism appears to reflect large scale atmospheric rearrangements over the tropical belt with a pronounced heinrich dansgaard oeschger signature this observation is coherent with the simulated tropical rainfall anomalies induced by a weakening of the atlantic thermohaline circulation in modeling experiments c 2009 university of washington published by elsevier inc all rights reserved

variable winter moisture in the southwestern united states linked to rapid glacial climate shifts the last glacial period was characterized by large rapid climate fluctuations an analysis of a speleothem from new mexico shows that the coldest conditions over greenland coincide with increased winter precipitation in the southwestern united states which can be attributed to a southward displacement of the polar jet stream and the north american storm track

wet to dry climatic trend in north western iberia within heinrich events abstract the direct sea land correlation applied to core md99 2331 retrieved from the north western iberian margin shows a two phase pattern within heinrich events 4 2 and 1 in the ocean and in the adjacent landmasses changes between wet cold and dry cool conditions in the iberian peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the atlantic meridional overturning circulation here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the md99 2331 record and other available palaeoclimate sequences from the north atlantic region 18 75 n and 0 75 w the climatic asymmetry observed between mid and subtropical eastern north atlantic latitudes wet dry and the blake outer ridge dry wet during h4 h2 and h1 can be explained by changes in the position of the atlantic jet stream during the first phase of h4 h2 and h1 the atlantic jet stream was located further south following the southward displacement of the oceanic thermal front as far south as 35 37 n on the contrary during the second phase of h4 h2 and h1 the jet stream was located further north following the northward displacement of this thermal front as far north as 42 n from the atmospheric point of view these two phases are reminiscent of the present day negative and positive prevailing modes of the north atlantic oscillation nao respectively but high resolution studies of additional north atlantic key sites and climate simulations are needed to confirm the hypothesis of a nao like mechanism operating on millennial timescales

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

northern hemisphere forcing of climatic cycles in antarctica over the past 360 000 years the milankovitch theory of climate change proposes that glacial interglacial cycles are driven by changes in summer insolation at high northern latitudes the timing of climate change in the southern hemisphere at glacial interglacial transitions which are known as terminations relative to variations in summer insolation in the northern hemisphere is an important test of this hypothesis so far it has only been possible to apply this test to the most recent termination because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined here we present a new chronology of antarctic climate change over the past 360 000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the dome fuji and vostok ice cores this ratio is a proxy for local summer insolation5 and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter the accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation our results indicate that orbital scale antarctic climate change lags northern hemisphere insolation by a few millennia and that the increases in antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of northern hemisphere summer insolation these results support the milankovitch theory that northern hemisphere summer insolation triggered the last four deglaciations

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

an isotopic and modelling study of flow paths and storage in quaternary calcarenite sw australia implications for speleothem paleoclimate records abstract we investigated the distinctive shallow sub surface hydrology of the southwest western australia swwa dune calcarenite using observed rainfall and rainfall 18 o soil moisture cave drip rate and dripwater 18 o over a six year period august 2005 march 2012 a lumped parameter hydrological model is developed to describe water fluxes and drip 18 o comparison of observed data and model output allow us to assess the critical non climatic karst hydrological processes that modify the precipitation 18 o signal and discuss the implications for speleothem paleoclimate records from this cave and those with a similar karst setting our findings include evidence of multiple reservoirs characterised by distinct 18 o values and recharge responses low and high flow sites dripwaters exhibit 18 o variations in wet versus dry years at low flow sites receiving diffuse seepage from the epikarst with an attenuated isotopic composition that approximates mean rainfall recharge from high magnitude rain events is stored in a secondary reservoir which is associated with high flow dripwater that is 1 lower than our monitored low flow sites 18 o one drip site is characterised by mixed flow behaviour and exhibits a non linear threshold response after the cessation of drainage from a secondary reservoir following a record dry year 2006 additionally our results yield a better understanding of the vadose zone hydrology and dripwater characteristics in quaternary age dune limestones we show that flow to our monitored sites is dominated by diffuse flow with inferred transit times of less than one year diffuse flow appears to follow vertical preferential paths through the limestone reflecting differences in permeability and deep recharge into the host rock

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

climatic patterns in equatorial and southern africa from 30 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract as part of a wider study of last glacial and deglacial climates in the southern hemisphere continents we here review terrestrial and near shore marine records from equatorial and southern africa between 30 000 and 10 000 years ago 30 10 ka this time interval covers the lead up to the last glacial maximum lgm 21 2 ka the lgm proper and the ensuing deglacial records selected for review needed to meet three requirements continuity or near continuity over the period a well established chronology and at least one but preferably several unambiguous proxy ies we aim to show how regional climates of the sub continent have responded to orbital forcing as opposed to other global glacial interglacial boundary conditions and how they are related to high latitude climates sea and land surface conditions positions of the intertropical convergence zone itcz and of the westerly belt evidence of past climates derived from many independent proxies is given from west to southwest africa moisture from the atlantic ocean then from equatorial east africa to the southern subtropical summer rainfall domain moisture mainly from the indian ocean the lgm was cooler than today and generally drier in the tropics north of 8 9 s glacial to holocene increase in monsoonal precipitation primarily related to orbitally induced summer insolation in the northern hemisphere occurred by steps of increasing amplitude 17 16 14 5 11 5 ka major wet dry spells coincide with abrupt warm cold events in high northern latitudes and related itcz migrations in the southern tropics the main post glacial increase in tropical rainfall generally appears more gradual and in phase with antarctic warming data suggest a restricted northward migration of the itcz and concentration of tropical rainfall well south of the equator during the lgm and the younger dryas drier glacial conditions prevailed in southeastern africa while parts of southwestern africa point to enhanced humidity during the lgm suggesting that the winter westerly belt was either stronger than today or displaced further north possibly as a result of more extensive antarctic sea ice inferred african climatic fluctuations show the competing influences of tropical and high latitude climates of both hemispheres and suggest changes in both meridional and zonal circulation modes this review also reveals major geographical and methodological gaps and a number of unresolved issues providing pointers for future research

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

possible evidence for wet heinrich phases in tropical ne australia the lynch s crater deposit unarguably one of the most significant paleoclimatological discoveries of the last two decades has been that of abrupt climate events dansgaard oeschger cycles and heinrich events most evidence for these events has originated from the high latitude northern hemisphere with few records documenting the response of the low latitude southern hemisphere here we present new data from lynch s crater a unique terrestrial record from ne australia that may show evidence for southward propagations of the intertropical convergence zone itcz during abrupt climate perturbations as a result of alteration of the low latitude air masses proxies for precipitation wetness indicate enhanced rainfall in the region during heinrich events h events 1 3 and the 8 2 ka northern hemisphere cold event a fully coupled atmosphere ocean climate model simulating a 1 sv freshwater influx to the north atlantic ocean produces a scenario which agrees with the climate changes shown by the lynch s crater record the model shows precipitation anomalies that include a southward migration of the itcz and a zonal shift in mid latitude storm tracks over the southern hemisphere equatorial region these data indicate large scale shifts of the austral summer itcz position that is known to control monsoonal precipitation in ne australia this terrestrial record from australia may demonstrate the involvement of the tropical western pacific ocean in itcz migrations during abrupt climate events of the last glacial period defining such past migrations offers insight into the importance and role of the equatorial region in global climate dynamics

increasing australian indonesian monsoon rainfall linked to early holocene sea level rise the australian indonesian summer monsoon affects rainfall variability across the indo pacific region reconstructions of monsoon strength from stalagmites show that precipitation increased from 11 000 to 7 000 years ago as rising global sea level caused the flooding of the indonesian continental shelf the australian indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical indo pacific region it has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1 2 3 but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult owing to the lack of high resolution records of past monsoon behaviour here we present a precisely dated reconstruction of monsoon rainfall over the past 12 000 years based on oxygen isotope measurements from two stalagmites collected in southeast indonesia we show that the summer monsoon precipitation increased during the younger dryas cooling event when atlantic meridional overturning circulation was relatively weak4 monsoon precipitation intensified even more rapidly from 11 000 to 7 000 years ago when the indonesian continental shelf was flooded by global sea level rise5 6 7 we suggest that the intensification during the younger dryas cooling was caused by enhanced winter monsoon outflow from asia and a related southward migration of the intertropical convergence zone8 however the early holocene intensification of monsoon precipitation was driven by sea level rise which increased the supply of moisture to the indonesian archipelago

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

lack of bipolar see saw in response to southern ocean wind reduction 1 a cessation of the atlantic meridional overturning circulation amoc significantly reduces northward oceanic heat transport in response to anomalous freshwater flux this leads to the classic bipolar see saw pattern of northern cooling and southern warming in surface air and ocean temperatures by contrast as shown here in a coupled climate model both northern and southern cooling are observed for an amoc reduction in response to reduced wind stress in the southern ocean so for very weak so wind stress not only the overturning circulation collapses but sea ice export from the so is strongly reduced consequently sea ice extent and albedo increase in this region the resulting cooling overcompensates the warming by the reduced northward heat transport the effect depends continuously on changes in wind stress and is reversed for increased winds it may have consequences for abrupt climate change the last deglaciation and climate sensitivity to increasing atmospheric co2 concentration

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

carbonate deposition pyramid lake subbasin nevada 2 lake levels and polar jet stream positions reconstructed from radiocarbon ages and elevations of carbonates tufas deposited in the lahontan basin most of the tufas in the pyramid lake subbasin were deposited within the last 35 000 yr including most of the mound tufas that border the existing lake many of the older tufas 21 000 yr b p contained in the mounds were formed in association with ground water discharge the radiocarbon 14c ages of the older tufas represent maximum estimates of the time of their formation lake lahontan experienced large and abrupt rises in level at 22 000 15 000 and 11 000 yr b p and three abrupt recessions in level at 16 000 13 600 and 10 000 yr b p the lake level rises that were initiated at 23 500 and 15 500 yr b p are believed to indicate the passage of the polar jet stream over the lahontan basin during expansion of the laurentide ice sheet the jet stream moved south across the basin and during the contraction of the ice sheet the jet stream moved north across the basin the bulk of the carbonate contained in the mound tufas was deposited during the last major lake cycle 23 500 12 000 yr b p indicating that ground and surface water discharges increased at 23 500 and decreased at 12 000 yr b p a lake level oscillation that occurred between 11 000 and 10 000 yr b p is represented by a 2 cm thick layer of dense laminated tufa that occurs at and below 1180 m in the low elevation tufa mounds and at 1205 m in the winnemucca lake subbasin