magnetic parameter variations in the chaona loess paleosol sequences in the central chinese loess plateau and their significance for the middle pleistocene climate transition abstract a high resolution rock magnetic investigation was performed on the chaona quaternary loess paleosol sequences in the central chinese loess plateau based on a newly developed independent unturned time scale and magnetic records we reconstructed the history of the east asia monsoons during the last 3 ma and explored the middle pleistocene climate transition mpt rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity lower magnetic susceptibility ms and that the paleosol layers are characterized by relatively high ms saturation magnetization and remanent saturation magnetization spectrum analyses indicate that there are various periods in addition to orbital periodicities according to the onset and stable appearance of 100 kyr period we consider that the mpt recorded in this section began at 1 26 ma and was completed by 0 53 ma which differs from previous investigations based on orbitally tuned time scales the forcing mechanism for the mpt was more complicated than just the orbital forcing we conclude that the rapid uplift of the tibetan plateau may have played an important role in the shift of periodicities during the middle pleistocene

regional warming pliocene 3 ma paleoclimate of europe and the mediterranean the paleoclimate of the middle pliocene ca 3 ma was generally warmer than present particularly at middle to high latitudes it has been suggested that this period may represent an analogue for future climate change mechanisms that have been proposed to account for this warming are enhanced thermohaline circulation and or greater concentrations of co 2 in the atmosphere we present new climate model simulations supported by geological data that suggest that in the european and mediterranean region the climate was warmer by 5 c wetter by 400 1000 mm yr and less seasonal than present modeling results suggest that an intensification of the icelandic low pressure system and the azores high pressure system occurred during the middle pliocene as a direct result of higher annual sea surface temperatures and reduced ice cover in the northern hemisphere this change increased the surface pressure gradient over the region and strengthened annual westerly wind velocity by 4 m s 1 associated increases in wind stress by 20 n m 2 over the north atlantic ocean may have enhanced the flow of surface currents such as the gulf stream and north atlantic current which in turn would have sustained the higher sea surface temperatures these changes to the regional climate system would have driven greater atmospheric and oceanic transport of heat from equatorial regions to the north atlantic ocean particularly during winter such conditions are proposed as a likely cause of the warming indicated for europe and the mediterranean ca 3 ma

strengthening of north american dust sources during the late pliocene 2 7 ma here we present orbitally resolved records of terrestrial higher plant leaf wax input to the north atlantic over the last 3 5 ma based on the accumulation of long chain n alkanes and n alkanl 1 ols at iodp site u1313 these lipids are a major component of dust even in remote ocean areas and have a predominantly aeolian origin in distal marine sediments our results demonstrate that around 2 7 million years ago ma coinciding with the intensification of the northern hemisphere glaciation nhg the aeolian input of terrestrial material to the north atlantic increased drastically since then during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials the close correspondence between aeolian input to the north atlantic and other dust records indicates a globally uniform response of dust sources to quaternary climate variability although the amplitude of variation differs among areas we argue that the increased aeolian input at site u1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in north america and the associated strengthening of glaciogenic dust sources evolutional spectral analyses of the n alkane records were therefore used to determine the dominant astronomical forcing in north american ice sheet advances these results demonstrate that during the early pleistocene north american ice sheet dynamics responded predominantly to variations in obliquity 41 ka which argues against previous suggestions of precession related variations in northern hemisphere ice sheets during the early pleistocene

flux and provenance of ice rafted debris in the earliest pleistocene sub polar north atlantic ocean comparable to the last glacial maximum relatively little is known in detail about the locations of the early pleistocene ice sheets responsible for ice rafted debris ird inputs to the sub polar north atlantic ocean during intensification of northern hemisphere glaciation inhg to shed new light on this problem we present the first combined in depth analysis of ird flux and geochemical provenance of individual sand sized ird deposited in the sub polar north atlantic ocean during the earliest large amplitude pleistocene glacial marine isotope stage mis 100 2 52 ma arguably the key glacial during inhg ird provenance is assessed using laser ablation lead pb isotope analyses of single feldspar grains we find that the pb isotope composition 206pb 204pb 207pb 204pb and 208pb 204pb of individual ice rafted 150 m feldspars deposited at dsdp site 611a odp site 981 and iodp site u1308 during mis 100 records a shift from predominantly archaean aged circum north atlantic ocean continental sources during early glacial ice rafting events to dominantly palaeozoic and proterozoic aged sources during full glacial conditions the distribution of feldspars in pb pb space for full glacial mis 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial ird belt at iodp dsdp site u1308 609 during ambient non heinrich event ice rafting episodes of mis 2 23 8 ka than that documented for mis 5d 106 ka comparison of our early pleistocene and last glacial cycle datasets suggests that mis 100 was characterised by abundant iceberg calving from large ice sheets on multiple continents in the high northern latitudes not just on greenland

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

modelling greenland ice sheet inception and sustainability during the late pliocene understanding the evolution and dynamics of ice sheet growth during past warm periods is a very important topic considering the potential total removal of the greenland ice sheet in this regard one key event is the full glaciation of greenland that occurred at the end of the pliocene warm period which remains partially unexplained previous modelling studies succeeded in reproducing this full glaciation either by imposing an unrealistically low co2 value or by imposing a partial ice sheet over the surface of greenland although they highlight some fundamental mechanisms none of these studies are fully satisfactory because they do not reflect realistic conditions occurring during the late pliocene through a series of simulations with the ipsl cm5a coupled climate model used to force the grisli ice sheet model we show that a drop in co2 levels does not lead to an abrupt inception of the greenland ice sheet high ablation rates in central and northern greenland combined with low accumulation prevent such an abrupt inception ice sheet inception occurs when low summer insolation and co2 levels below modern values are combined the greenland ice sheet being restricted to the southeast region where high topography favours this build up this ice sheet experiences only partial melting during summer insolation maxima combined with high co2 levels further growth of the ice sheet with recoupling experiments is important at 360 and 280 ppm during insolation minima thus the full glaciation at 2 6 ma could be the result of a cumulative build up of the greenland ice sheet over several orbital cycles leading to progressively more intense glaciations during low summer insolation periods although this result could be a shortcoming of the modelling framework itself the gradual glacial inception interpreted from the oxygen isotope record could support our scenario

a low threshold for north atlantic ice rafting from low slung slippery late pliocene ice sheets 1 suborbital variability in late pleistocene records of ice rafted debris and sea surface temperature in the north atlantic ocean appears most extreme during times of enlarged ice sheets with a well constrained benthic oxygen isotope defined ice volume threshold 18ot for the 100 ka inter glacial world information on climate instability for the earlier pleistocene and late pliocene is more fragmentary and or of much lower temporal resolution but the data available suggest similar behavior with 18ot remaining more or less constant over the past 3000 ka this finding is puzzling because it implies that ice rafting is highly sensitive to ice volume on short suborbital glacial interglacial time scales but not to the long term changes in ice sheet composition associated with intensification of northern hemisphere glaciation nhg here we report new high resolution records of stable isotope change and ice rafting in the north atlantic at integrated ocean drilling program site u1308 reoccupation of deep sea drilling project site 609 during two glacials key to intensification of nhg marine isotope stages g4 2640 ka and 100 2520 ka we find a pattern of suborbital ice rafting events showing clear evidence of threshold behavior however contrary to previous reports we find that 18ot for the late pliocene is up to 0 45 vienna peedee belemnite vpdb lower than for the late pleistocene using published plio pleistocene global sea level records we evaluate different potential explanations for this finding we conclude that the observed pliocene pleistocene offset in 18ot is attributable to the existence of low slung pliocene ice sheets that flowed more readily than their late pleistocene counterparts associated with a smaller contemporaneous continental ice volume and less isotopically depleted ice

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

stepwise expansion of desert environment across northern china in the past 3 5 ma and implications for monsoon evolution abstract a systematic study of the last glacial cycle along three transects across the chinese loess plateau shows that sand sized particle content within loess decreases rapidly from north to south and that markedly high sand particle contents in loess horizons occur only in the northern part of the plateau this suggests that variation in the sand sized particle fraction within loess near the desert margin is closely linked to migration of the southern desert border in northern china where sand grains move mainly in saltation or modified saltation mode near the ground surface as desert margin shift is essentially controlled by the amount of monsoon precipitation the sand sized particle content within loess near desert margin is regarded as a new and readily applied proxy for variations in the strength of the east asian summer monsoon a continuous record of sand content in loess along the loess desert transitional zone shows that the mu us desert migrated southward at 2 6 1 2 0 7 and 0 2 ma suggesting a stepwise weakening of the east asian summer monsoon during the past 3 5 ma this evolutionary pattern is significantly different from that previously inferred from loess magnetic susceptibility records a widely used monsoon proxy our results further suggest that changes in global ice volume may have been an essential factor in controlling plio pleistocene monsoon evolution and that the anticipated future melting of polar ice cover may lead to a northward migration of the monsoon rainfall belt in northern china

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

seasonal production patterns of planktonic foraminifera in the ne atlantic ocean implications for paleotemperature and hydrographic reconstructions 1 sediment trap samples from omex 2 49 n 13 w provide a continuous record of the seasonal succession of planktonic foraminifera in the midlatitude north atlantic and reveal a complex relationship between periods of production and specific hydrographic conditions neogloboquadrina pachyderma dextral coiling d globigerina bulloides and globorotalia inflata are found in great numbers during both the spring and summer seasons whereas globigerina quinqueloba globorotalia hirsuta globorotalia scitula and globigerinita glutinata are associated predominantly with the increase in productivity during the spring bloom globigerinella aequilateralis orbulina universa and globigerinoides sacculifer are restricted to late summer conditions following the establishment of a warm well stratified surface ocean an annually integrated fauna from the sediment trap comprising 13 000 individuals is used to evaluate the accuracy of five faunal based statistical methods of paleotemperature estimation all of the temperature reconstruction techniques produce estimates of 16 c and 11 c for summer and winter surface temperature respectively which are in excellent agreement with regional hydrographic data and suggest that the sediment trap assemblage is well represented in the core top faunas analysis of the key species that dominate the omex 2 sediment trap fauna g bulloides g inflata and n pachyderma d based on 18o derived temperatures from north atlantic core top samples suggests that seasonal variations in planktonic foraminiferal production are nonuniform across the midlatitudes and that this is likely to complicate reconstructing past seasonal hydrographic dynamics using these taxa

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

onset of hudson strait heinrich events in the eastern north atlantic at the end of the middle pleistocene transition 640 ka 1 heinrich events are well documented for the last glaciation but little is known about their occurrence in older glacial periods of the pleistocene here we report scanning xrf and bulk carbonate 18o results from integrated ocean drilling program site u1308 reoccupation of deep sea drilling project site 609 that are used to develop proxy records of ice rafted detritus ird for the last 1 4 ma ca sr is used as an indicator of ird layers that are rich in detrital carbonate i e heinrich layers whereas si sr reflects layers that are poor in biogenic carbonate and relatively rich in detrital silicate minerals a pronounced change occurred in the composition and frequency of ird at 640 ka during marine isotope stage mis 16 coinciding with the end of the middle pleistocene transition at this time hudson strait heinrich layers suddenly appeared in the sedimentary record of site u1308 and the dominant period of the si sr proxy shifted from 41 ka prior to 640 ka to 100 ka afterward the onset of heinrich layers during mis 16 represents either the initiation of surging of the laurentide ice sheet lis off hudson strait or the first time icebergs produced by this process survived the transport to site u1308 we speculate that ice volume i e thickness and duration surpassed a critical threshold during mis 16 and activated the dynamical processes responsible for lis instability in the region of hudson strait we also observe a strong coupling between ird proxies and benthic 13c variation at site u1308 throughout the pleistocene supporting a link between iceberg discharge and weakening of thermohaline circulation in the north atlantic

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

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

mg ca ratios of two globigerinoides ruber white morphotypes implications for reconstructing past tropical subtropical surface water conditions 1 tests of the planktonic foraminifer globigerinoides ruber white d orbigny have become a standard tool for reconstructing past oceanic environments paleoceanographers often utilize the mg ca ratios of the foraminiferal tests for reconstructing low latitude ocean glacial interglacial changes in sea surface temperatures sst we report herein a comparison of mg ca measurements on sample pairs n 20 of two g ruber white morphotypes g ruber sensu stricto s s and g ruber sensu lato s l from surface and downcore samples of the western pacific and indian oceans g ruber s s refers to specimens with spherical chambers sitting symmetrically over previous sutures with a wide high arched aperture whereas g ruber s l refers to a more compact test with a diminutive final chamber and small aperture the g ruber s s specimens generally show significantly higher mg ca ratios compared to g ruber s l our results from the mg ca ratio analysis suggest that g ruber s l specimens precipitated their shells in slightly colder surface waters than g ruber s s specimens this conclusion is supported by the differences in 18o and 13c values between the two morphotypes although it is still unclear if these two morphotypes represent phenotypic variants or sibling species our findings seem to support the hypothesis of depth and or seasonal allopatry within a single morphospecies

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

pliocene shallow water paleoceanography of the north atlantic ocean based on marine ostracodes abstract middle pliocene marine ostracodes from coastal and shelf deposits of north and central america and iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the western boundary current system including the gulf loop current florida current gulf stream and north atlantic drift factor analytic transfer functions provided pliocene august and february bottom water temperatures of eight regions from the tropics to the subfrigid the results indicate 1 meridional temperature gradients in the western north atlantic were less steep during the pliocene than either today or during late pleistocene isotope stage 5e 2 tropical and subtropical shelf waters during the middle pliocene were as warm as or slightly cooler than today 3 slightly cooler water was on the outer shelf off the southeastern and mid atlantic coast of the u s possibly due to summer upwelling of gulf stream water 4 the shelf north of cape hatteras north carolina may have been influenced by warm water incursions from the western edge of the gulf stream especially in summer 5 the northeast branch of the north atlantic drift brought warm water to northern iceland between 4 and 3 ma evidence from the iceland record indicates that cold east greenland current water did not affect coastal iceland between 4 and 3 ma 6 middle pliocene north atlantic circulation may have been intensified transporting more heat from the tropics to the arctic than it does today

late pliocene vegetation and climate of the lake baikal region southern east siberia reconstructed from palynological data abstract palynomorphs from a palaeomagnetically dated late pliocene sediment core 3 6 2 35 ma reflect highly variable climatic conditions and repeated expansion of steppe and boreo alpine vegetation mixed coniferous forests picea tsuga pinus with associated broadleaved taxa quercus corylus ulmus tilia were affected by dry and cold intervals already between 3 48 and 3 39 ma peak records of non arboreal pollen types and spores including subarctic boreo alpine selaginella selaginoides evidence advances of open vegetation which can be correlated to glacial marine oxygen isotope stages a cooling trend occurred from 3 15 ma to 2 5 ma documented by cold dry intervals and increased fluctuations of picea and pinus around 3 2 9 ma the palaeoclimate variation pattern shifted towards cold dry and warm moist oscillations cooling strengthened after 2 89 ma and severely restricted tsuga development cool and oligotrophic limnic conditions are documented by abundant gonyaulax dinoflagellate cysts in the interval 2 65 2 57 ma due to decreasing precipitation extensive areas with open steppe and rock steppe vegetation became permanently established after 2 62 ma dry conditions became a dominant environmental factor in the baikal region coeval in time with the red clay loess shift in northern china this climatic transition can be explained as a consequence of major intensification of northern hemisphere glaciation around 2 75 ma evidenced by marine records of ice rafted debris

closure of the panama seaway during the pliocene implications for climate and northern hemisphere glaciation the panama hypothesis states that the gradual closure of the panama seaway between 13 million years ago 13 ma and 2 6 ma led to decreased mixing of atlantic and pacific water masses the formation of north atlantic deep water and strengthening of the atlantic thermohaline circulation increased temperatures and evaporation in the north atlantic increased precipitation in northern hemisphere nh high latitudes culminating in the intensification of northern hemisphere glaciation nhg during the pliocene 3 2 2 7 ma here we test this hypothesis using a fully coupled fully dynamic ocean atmosphere general circulation model gcm with boundary conditions specific to the pliocene and a high resolution dynamic ice sheet model we carry out two gcm simulations with closed and open panama seaways and use the simulated climatologies to force the ice sheet model we find that the models support the panama hypothesis in as much as the closure of the seaway results in a more intense atlantic thermohaline circulation enhanced precipitation over greenland and north america and ultimately larger ice sheets however the volume difference between the ice sheets in the closed and open configurations is small equivalent to about 5 cm of sea level we conclude that although the closure of the panama seaway may have slightly enhanced or advanced the onset of nhg it was not a major forcing mechanism future work must fully couple the ice sheet model and gcm and investigate the role of orbital and co2 effects in controlling nhg

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

middle pliocene sea surface temperatures a global reconstruction identification and analyses of pliocene marine microfossils from 64 globally distributed stratigraphic sequences have been used to produce a middle pliocene sea surface temperature reconstruction of the earth this reconstruction shows little or no change from current conditions in low latitude regions and significant warming of the ocean surface at mid and higher latitudes of both hemispheres this pattern of warming is consistent with terrestrial records and suggests a combination of enhanced meridional ocean heat transport and enhanced greenhouse effect were responsible for the middle pliocene warmth

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

increased seasonality during the intensification of northern hemisphere glaciation at the pliocene pleistocene boundary 2 6 ma abstract near the pliocene pleistocene neogene quaternary boundary during marine isotope stage mis 104 at around 2 6 ma the intensification of northern hemisphere glaciation inhg was marked by a southward shift of the north atlantic current and arctic front and a concurrent drop in sea surface temperature sst in the mid latitudes of the north atlantic here we evaluate two mg ca based sea surface temperature reconstructions for the 2 78 2 52 ma interval using the planktonic foraminifera globigerina bulloides and globigerinoides ruber white sensu stricto as the biotic carriers sstbul and sstrub and a reconstruction based on the alkenone saturation index sstalk the mg ca based sst estimates begin to diverge from one another significantly during mis g3 2 66 ma culminating during mis 104 2 60 ma and remaining distinctly different for the remaining 80 kyr of the studied interval the magnitude of this divergence sstrub bul is caused mainly by a decrease in sstbul with sstrub remaining relatively constant we attribute this difference to a drop in sst during the early spring blooming season of g bulloides that was less pronounced during the late summer blooming season of g ruber using sstrub bul as a seasonality indicator we show that seasonality increased significantly owing to a drop in early spring temperatures from mis 104 onwards and peaked during glacial episodes maximum seasonality occurred during mis 104 in coincidence with a major expansion of the circum atlantic ice sheets particularly the north american ice sheet this expansion appears to have had a critical influence on global climate and especially seasonality

evolution of mediterranean sea surface temperatures 3 5 1 5 ma regional and hemispheric influences abstract we present a composite time series of mediterranean sea surface temperature sst and marine biomarker accumulation for the time span from 3 5 to 1 525 ma based on alkenone unsaturation and concentration from hemipelagic sediments outcropping in southern italy and sicily paleotemperature data define three regimes a late pliocene climate on average 4 5 c warmer than modern a latest pliocene to early pleistocene onset of 41 kyr cycles and a major increase in the range of glacial interglacial temperature change at 1 84 ma that shortly precedes the former definition of the plio pleistocene boundary in the crotone sequence pliocene sea surface temperature sst cycles are dominated by precession with a 1 5 c range obliquity related rhythms influence sst significantly shortly after 2 8 ma equivalent to mis g10 and dominate after 2 51 ma equivalent to mis 100 however little if any long term cooling occurred on an interglacial basis until after 1 85 ma alkenone concentrations provide a good proxy for the accumulation of marine organic matter and primarily reflect regional hydrology organic sedimentation including the formation of layers highly enriched in organic matter sapropels was paced throughout by precessional variations despite changes in both average regional temperature and the shift in temperature variance to the 41 kyr obliquity cycle in the latest pliocene and early pleistocene our reconstruction therefore highlights the intermingling of both hemispheric wide changes in temperature and regional variations in the hydrological cycle that combined to force major evolutionary changes in the fauna and flora of northern africa and the southern mediterranean in late pliocene to mid pleistocene time

late pliocene early pleistocene 100 ka problem 1 little is known about the 100 ka ice volume cycles immediately before 1 ma except that they are coherent with the 100 ka eccentricity cycles here we show that ice volume and ocean circulation change global carbon mass balance are phase locked and highly coupled regarding amplitude envelopes at the 100 ka band but neither is phase locked to and amplitude coupled to the 100 ka eccentricity orbital forcing signal between 3 1 ma we describe this phasing and amplitude mismatch at the 100 ka band between 3 1 ma between eccentricity forcing and paleo ice volume records as the late pliocene early pleistocene 100 ka problem a free 100 ka oscillation internal to our climate system especially those related to oscillations of atmospheric co2 concentration operating on an earth characterized by a high inertia deep thermohaline ocean that can store carbon and heat might hold the key for the late pliocene early pleistocene 100 ka problem

a short circuit in thermohaline circulation a cause for northern hemisphere glaciation the cause of northern hemisphere glaciation about 3 million years ago remains uncertain closing the panamanian isthmus increased thermohaline circulation and enhanced moisture supply to high latitudes but the accompanying heat would have inhibited ice growth one possible solution is that enhanced moisture transported to eurasia also enhanced freshwater delivery to the arctic via siberian rivers freshwater input to the arctic would facilitate sea ice formation increase the albedo and isolate the high heat capacity of the ocean from the atmosphere it would also act as a negative feedback on the efficiency of the conveyor belt heat pump

an updated astronomical timescale for the plio pleistocene deposits from south china sea and new insights into asian monsoon evolution abstract here we present an improved astronomical timescale since 5 ma as recorded in the odp site 1143 in the southern south china sea using a recently published asian summer monsoon record hematite to goethite content ratio hm gt and a parallel benthic 18o record correlation of the benthic 18o record to the stack of 57 globally distributed benthic 18o records lr04 stack and the hm gt curve to the 65 n summer insolation curve is a particularly useful approach to obtain refined timescales hence it constitutes the basis for our effort our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the odp site 1143 this updated timescale further enables a detailed study of the orbital variability of low latitude asian summer monsoon throughout the plio pleistocene comparison of the hm gt record with the 18o record from the same core reveals that the oscillations of low latitude asian summer monsoon over orbital scales differed considerably from the glacial interglacial climate cycles the popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low latitude asia in low latitude asia some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages vice versa some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages the well known mid pleistocene transition mpt is only identified in the benthic 18o record but not in the hm gt record from the same core this suggests that the mpt may be a feature of high and middle latitude climates possibly determined by high latitude ice sheet dynamics for low latitude monsoonal climate its orbital scale variations respond more directly to insolation and are little influenced by high latitude processes thus the mpt is likely not recorded in addition the hm gt record suggests that low latitude asian summer monsoon intensity has a long term decreasing trend since 2 8 ma with increased oscillation amplitude this long term variability is presumably linked to the northern hemisphere glaciation since then

pliocene climate and seasonality in north atlantic shelf seas this paper reviews north atlantic shelf seas palaeoclimate during the interval 4 3 ma prior to and incorporating the mid pliocene warm period ca 3 29 2 97 ma fossil assemblages and stable isotope data demonstrate northwards extension of subtropical faunas along the coast of the carolinas virginia yorktown and duplin formations relative to the present day suggesting a more vigorous florida current with reduced seasonality and warm water extending north of cape hatteras reconstructed annual range for virginia 12 30 c this interpretation supports conceptual models of increased meridional heat transport for the pliocene sea temperatures for florida lower pinecrest beds were similar to or slightly cooler than summers 25 27 c today and were probably influenced by seasonal upwelling of cold deep water reduced seasonality is also apparent in the coralline crag formation of the southern north sea with ostracods suggesting winter sea temperatures of 10 c modern 4 c however estimates from pliocene bivalves 3 6 16 6 c are similar to or cooler than the present day this mixed signal is problematic given warmer seas in the carolinas virginia and climate model and oceanographic data that show warmer seas in the mid pliocene eastern north atlantic this may be because the coralline crag formation was deposited prior to peak mid pliocene warmth

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

late pliocene changes in the north atlantic current article i nfo during the late pliocene global climate changed drastically as the northern hemisphere glaciation nhg intensified it remains poorly understood how the north atlantic current nac changed in strength and position during this time interval such changes may alter the amount of northward heat transport and therefore have a large impact on climate in the circum north atlantic region and the growth of northern hemisphere ice sheets using the alkenone biomarker we reconstructed orbitally resolved sea surface temperature sst and productivity records at integrated ocean drilling project iodp expedition 306 site u1313 during the late pliocene and early pleistocene 3 68 2 45 million years ago ma before 3 1 ma ssts in the mid latitude north atlantic were up to 6 c higher than the present and surface water productivity was low indicating that an intense nac transported warm nutrient poor surface waters northwards starting at 3 1 ma surface water characteristics changed drastically as the nhg intensified during glacial periods at the end of the late pliocene and beginning of the pleistocene ssts decreased and surface water productivity in the mid latitude north atlantic increased reflecting a weakened influence of the nac at our site at the same time the increase in surface productivity suggests that the arctic front af reached down into the mid latitudes we propose that during the intensification of the nhg the nac had an almost pure west to east flow direction in glacials and did not penetrate into the higher latitudes the diminished northward heat transport would have led to a cooling of the higher latitudes which may have encouraged the growth of large continental ice sheets in the northern hemisphere

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

seven million years of wind and precipitation variability on the chinese loess plateau abstract recent studies of the eolian deposits in northern china have extended the east asian monsoon history back to the early miocene however the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the pleistocene epoch remain poorly constrained mainly due to uncertainties in the interpretation of proxy indices generated from the mio pliocene red clay sequences here we reconstruct east asian monsoon oscillations over the past 7 ma using magnetic susceptibility and carbonate content as summer monsoon precipitation proxies and quartz grain size as a winter monsoon wind intensity index our results suggest that precipitation and wind intensity exhibited significant orbital scale variations prior to 4 2 ma followed by slightly damped variability between 4 2 and 2 75 ma subsequently east asian monsoon circulation experienced two large shifts at about 2 75 and 1 25 ma characterized by stepwise strengthening of glacial wind and interglacial precipitation a remarkable change in east asian monsoon seasonality occurred around 3 15 2 75 ma prior to 3 15 ma strong winds were positively correlated with high effective precipitation whereas after 2 75 ma strong winds were negatively correlated with heavy precipitation this shift was probably induced by a change from an insolation forced system to one strongly influenced by the combined effects of the phased uplift of the himalaya tibetan plateau and the simultaneous development of the northern hemisphere ice sheets

climate sensitivity to continental ice sheet size and configuration abstract a version of the ncar community climate model ccm has been used to carry out a study of climate sensitivity to the size and distribution of continental ice sheets by comparing two perpetual season fixed sea surface temperature sst winter simulations of the climate at a glacial maximum the two simulations differ only in the size and configuration of the continental ice sheet boundary conditions these conditions represent minimum and maximum ice sheet extent for a glacial maximum as presently constrained by the geologic evidence all other boundary conditions are as specified by climap 1981 for winter surface conditions during the last glacial maximum lgm the ice sheets specified by climap 1981 used by many previous researchers to simulate ice age climate conditions are intermediate in size between the minimum and maximum ice sheets used for the simulations described here the maximum case simulation resulted in unexpected positive temperature anomalies over the northern hemisphere

isotopic signals in two morphotypes of globigerinoides ruber white from the south china sea implications for monsoon climate change during the last glacial cycle abstract based on the study of surface and downcore sediment samples from the south china sea scs two morphotypes of globigerinoides ruber white have been differentiated by taxonomic criteria at species and or subspecies level and also by their stable isotopic compositions of oxygen and carbon the two morphotypes g ruber sensu stricto s s and g ruber sensu lato s l represent two groups with different depth habitats with g ruber s s living in the upper 30 m of the water column and g ruber s l living at depths below 30 m the different depth habitats are indicated by the comparison between the present oceanographic data and isotopic signals of the two morphotypes in the surface sediment from the scs application of this information to a hemipelagic sediment core in the northern scs shows that drastic changes existed in the morphotypes isotopic records during the last glacial cycle the isotope difference between the two morphotypes diminished during 18 o stage 2 especially during the last glacial maximum it is inferred that this is the result of intensified monsoon winds which caused mixing of the upper layer of the water column during stage 2 the proportion of g ruber s l increased which is interpreted as a result of the increased productivity due to mixing of the subsurface nutrient rich water into the surface layer

atmospheric co2 decline during the pliocene intensification of northern hemisphere glaciations 1 several hypotheses have been put forward to explain the onset of intensive glaciations on greenland scandinavia and north america during the pliocene epoch between 3 6 and 2 7 million years ago ma a decrease in atmospheric co2 may have played a role during the onset of glaciations but other tectonic and oceanic events occurring at the same time may have played a part as well here we present detailed atmospheric co2 estimates from boron isotopes in planktic foraminifer shells spanning 4 6 2 0 ma maximal pliocene atmospheric co2 estimates gradually declined from values around 410 atm to early pleistocene values of 300 atm at 2 0 ma after the onset of large scale ice sheets in the northern hemisphere maximal pco2 estimates were still at 2 5 ma 90 atm higher than values characteristic of the early pleistocene interglacials by contrast pliocene minimal atmospheric co2 gradually decreased from 310 to 245 atm at 3 2 ma coinciding with the start of transient glaciations on greenland values characteristic of early pleistocene glacial atmospheric co2 of 200 atm were abruptly reached after 2 7 ma during the late pliocene transition this trend is consistent with the suggestion that ocean stratification and iron fertilization increased after 2 7 ma in the north pacific and southern ocean and may have led to increased glacial co2 storage in the oceanic abyss after 2 7 ma onward

seasonality intensification and long term winter cooling as a part of the late pliocene climate development abstract a mutual climatic range method is applied to the mediterranean marine pollen record of semaforo vrica section calabria italy covering the period from 2 46 ma to 2 11 ma the method yields detailed information on summer annual and winter temperatures and on precipitation during the nine obliquity and precession controlled glacial periods marine isotope stages 96 to 80 and eight interglacial periods marine isotope stages 95 to 81 characterising this time interval the reconstruction reveals higher temperatures of at least 2 8 c in mean annual and 2 2 c in winter temperatures and 500 mm in precipitation during the interglacials as compared to the present day climate in the study area during the glacials temperatures are generally lower as compared to the present day climate in the region but precipitation is equivalent along the consecutive interglacials a trend toward a reduction in annual and winter temperatures by more than 2 3 c and toward a higher seasonality is observed along the consecutive glacials a trend toward a strong reduction in all temperature parameters of at least 1 6 c is reconstructed climatic amplitudes of interglacial glacial transitions increase from the older to the younger cycles for summer and annual temperatures the cross spectral analyses suggest obliquity related warm humid cold dry interglacial glacial cycles which are superimposed by precession related warm dry cold humid cycles a time displacement in the development of temperatures and precipitation is indicated for the obliquity band by temperatures generally leading precipitation change at 4 kyr and on the precession band of 9 6 kyr in maximum

sea surface temperature variability during the last glacial interglacial cycle assessing the magnitude and pattern of climate change in the north atlantic abstract sea surface temperature and salinity estimates reconstructed using planktonic foraminiferal abundance and 18o records from core su90 03 40 n 32 w 2475 m water depth reveal large climatic fluctuations linked to major instabilities in northern hemisphere ice sheets over the last 150 000 years episodes of enhanced ice rafted detritus ird input were accompanied by discrete temperature minima representing coolings of between 4 and 8 c and reductions in surface salinity of up to 2 5 3 5 several additional cooling episodes of a similar magnitude were documented during intervals of low ird input that appear to be synchronous within the limits of dating with ice rafting events spatially confined to higher latitudes accelerator mass spectrometer 14c dates for heinrich events h1 14 2 ka h2 21 4 ka h3 26 7 ka h4 34 8 ka h5 47 2 ka obtained from core su90 03 agree well with other published age estimates and suggest a contemporaneous pattern of climate change throughout the north atlantic during the last glacial period this interpretation is supported by a comparison of ird and palaeotemperature records from dsdp site 609 and core su90 03 which clearly shows that the major climatic fluctuations identified at high latitudes were transmitted toward the subtropics however 14c dates suggest that ice rafting episodes may be diachronous to some extent the northward migration of the polar front after the h1 event at 40 n in the mid atlantic occurred at 14 ka approximately 500 years earlier than along the portuguese margin where the southerly advection of polar waters persisted within eastern boundary current system

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

plio pleistocene ice volume antarctic climate and the global δ18o record we propose that from 3 to 1 million years ago ice volume changes occurred in both the northern and southern hemispheres each controlled by local summer insolation because earth9s orbital precession is out of phase between hemispheres 23 000 year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean 18 o or sea level leaving the in phase obliquity 41 000 years component of insolation to dominate those records only a modest ice mass change in antarctica is required to effectively cancel out a much larger northern ice volume signal at the mid pleistocene transition we propose that marine based ice sheet margins replaced terrestrial ice margins around the perimeter of east antarctica resulting in a shift to in phase behavior of northern and southern ice sheets as well as the strengthening of 23 000 year cyclicity in the marine 18 o record

subtropical iceberg scours and meltwater routing in the deglacial western north atlantic during the last deglaciation northern hemisphere ice sheets discharged ice and meltwater seafloor scours and numerical modelling suggest that freshwater and icebergs from the laurentide ice sheet reached the subtropical north atlantic

paleomagnetic evidence for multiple late pliocene early pleistocene glaciations in the klondike area yukon territory the late pliocene early pleistocene terraces of the klondike area provide a conformal record of sedimentation which marks the transition from preglacial to glacial conditions and is one of the most complete records of glaciation and interglaciation in the northern cordillera preglacial sedimentation is recorded in the lower white channel gravel that contains a reverse normal polarity sequence a re aggradation of the nonglaciated valleys of the goldfields in response to late pliocene cooling is recorded by the upper white channel gravel which is characterized by a dominant normal polarity with a lower reversal likely associated with the first ice wedge casts klondike gravel interfingers with upper white channel and is normally magnetized indicating an equivalent magnetostratigraphic unit this glaciofluvial gravel provides evidence of extra basinal clasts marking a major reorganization of drainage associated with the first advance of the cordilleran ice sheet in western yukon territory correlated

millennial scale climate variability in the subpolar north atlantic ocean during the late pliocene 1 large amplitude millennial scale climate oscillations have been identified in late pleistocene climate archives from around the world these oscillations appear to be of larger amplitude during times of enlarged ice sheets this observation suggests the existence of a relationship between large amplitude millennial variations in climate and extreme glacial conditions and therefore that the emergence of millennial scale climate variability may be linked to the pliocene intensification of northern hemisphere glaciation inhg here we test this hypothesis using new late pliocene high resolution 400 year records of ice rafted debris deposition and stable isotopes in planktic foraminiferal calcite globigerinoides ruber generated from integrated ocean drilling program site u1313 in the subpolar north atlantic a reoccupation of the classic deep sea drilling project site 607 our records span marine oxygen isotope stages mis 103 95 2600 to 2400 ka the first interval during inhg 3 5 to 2 5 ma in which large amplitude glacial interglacial cycles and inferred sea level changes occur our records reveal small amplitude variability at periodicities of 1 8 to 6 2 kyr that prevails regardless of inter glacial state with no significant amplification during the glacials mis 100 98 and 96 these findings imply that the threshold for the amplification of such variability to the proportions seen in the marine archive of the last glacial was not crossed during the late pliocene and in view of all available data likely not until the mid pleistocene transition

the atmospheric winter circulation during the younger dryas stadial in the atlantic european sector the younger dryas yd stadial signified an interruption of the warming during the transition from the last glacial to the present interglacial the mechanism responsible for this cooling is still uncertain so valuable information concerning climate variability can be obtained by numerical simulation of the yd climate we performed four experiments on the younger dryas climate with the hamburg atmospheric general circulation model here we use the results of these experiments which differed in prescribed boundary conditions to characterize the atmospheric winter circulation during the yd stadial in the north atlantic european sector the 10 year means of the following variables are presented sea level pressure 500 hpa geopotential heights and 200 hpa winds in addition we used daily values to calculate an index to assess the occurrence of blocking and strong zonal flow and to compute storm tracks our results show that the yd cooling in europe was present with a strong and stable westerly circulation without blocking this is in conflict with an earlier study suggesting frequent easterly winds over nw europe in our experiments the sea ice cover in the north atlantic ocean was the crucial factor forcing this specific yd circulation moreover the jet stream over the north atlantic was strengthened considerably causing an enhanced cyclonic activity over the eurasian continent the yd winter circulation was different from the circulation found in most simulation studies on the last glacial maximum since no glacial anticyclones were present and no split of the jet stream occurred

the isotopic signature of planktonic foraminifera from ne atlantic surface sediments implications for the reconstruction of past oceanic conditions the stable isotope compositions of the planktonic foraminifera globigerina bulloides globigerinoides ruber white and pink varieties globigerinoides trilobus globorotalia inflata and globorotalia truncatulinoides right and left coiling types were examined as recorders of north atlantic surface water properties based on 40 box core surface sediments between 60 and 30 n while g ruber white and pink varieties and g trilobus mainly reflect summer surface water conditions in their oxygen isotope composition g bulloides reflects temperatures of the northward migrating spring bloom february march in the south to may june in the north our data show that g bulloides cannot be regarded as an indicator for summer temperatures as deduced from duplessy et al s data gt inflata and gt truncatulinoides right and left coiling build their shells in the coldest waters compared with the other species and reflect temperatures between 100 and 400 m water depth the difference in oxygen isotope composition between g bulloides and g inflata serves as a proxy for water mass stratification g bulloides is the only species that gives a distinct pattern in its carbon isotopic composition showing a high correlation with the surface water phosphate values along the transect and may serve as a proxy for palaeonutrients and or productivity

surface temperatures of the mid pliocene north atlantic ocean implications for future climate the mid pliocene is the most recent interval in the earth s history to have experienced warming of the magnitude predicted for the second half of the twenty first century and is therefore a possible analogue for future climate conditions with continents basically in their current positions and atmospheric co2 similar to early twenty first century values the cause of mid pliocene warmth remains elusive understanding the behaviour of the north atlantic ocean during the mid pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change under the framework of the pliocene research interpretation and synoptic mapping prism sea surface reconstruction we synthesize mid pliocene north atlantic studies by prism members and others describing each region of the north atlantic in terms of palaeoceanography we then relate mid pliocene sea surface conditions to expectations of future warming the results of the data and climate model comparisons suggest that the north atlantic is more sensitive to climate change than is suggested by climate model simulations raising the concern that estimates of future climate change are conservative

holocene and eemian sea surface temperature trends as revealed by alkenone and mg ca paleothermometry in this study we review a global set of alkenone and foraminiferal mg ca derived sea surface temperatures sst records from the holocene and compare them with a suite of published eemian sst records based on the same approach for the holocene the alkenone sst records belong to the actualized ghost database kim j h schneider r r 2004 ghost global database for alkenone derived holocene sea surface temperature records available from http www pangaea de projects ghost while the mg ca derived sst database represents a new compilation the actualized ghost database not only confirms the sst changes previously described but also documents the holocene temperature evolution in new oceanic regions such as the northwestern atlantic the eastern equatorial pacific and the southern ocean a comparison of holocene sst records stemming front the two commonly applied paleothermometry methods reveals contrasting sometimes divergent sst evolution particularly at low latitudes where sst records are abundant enough to infer systematic discrepancies at a regional scale opposite sst trends at particular locations could be explained by out of phase trends in seasonal insolation during the holocene this hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms as a simple test for this hypothesis eemian sst records are considered because the holocene and eemian time periods experienced comparable changes in orbital configurations but had a higher magnitude in insolation variance during the eemian for several regions sst changes during both interglacials were of a similar sign but with higher magnitudes during the eemian as compared to the holocene this observation suggests that the ecological mechanism shaping sst trends during the holocene was comparable during the penultimate interglacial period although this ecology hypothesis fails to explain all of the available results we argue that any other mechanism would fail to satisfactorily explain the observed sst discrepancies among proxies c 2010 elsevier ltd all rights reserved

global calibration of ecological models for planktic foraminifera from coretop carbonate oxygen 18 abstract a global dataset of coretop planktic foraminiferal 18oc is combined with a global database of seawater 18ow observations and ocean climatologies to determine robust optimum parameters for an ecological model for six commonly measured species and varieties these parameters consist of the temperature ranges optimum temperatures depth habitat and the amount of secondary calcification for globigerinoides ruber white g ruber pink neogloboquadrina pachyderma l n pachyderma r globigerinoides sacculifer and globigerina bulloides this approach produces ecological models and temperature ranges consistent with previous work and manages to reproduce the coretop oxygen 18 carbonate values remarkably well the standard error of modelled values of coretop calcite globally and for all species is 0 53 compared to an error of 1 2 when assuming annual average mixed layer equilibrium calcite

micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene the middle pliocene approximately 3 million years ago has been identified as the last time the earth was significantly warmer than it was during the last interglacial and holocene a quantitative micropaleontological paleotemperature transect from equator to high latitudes in the north atlantic indicates that middle pliocene warmth involved increased meridional oceanic heat transport

interannual variability of planktic foraminiferal populations and test flux in the eastern north atlantic ocean jgofs planktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties between water masses and after periodical changes and episodic events e g reproduction storms distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data in this paper we discuss the short term impacts on interannual flux rates based on data from opening closing net hauls obtained between the ocean surface and 500 m water depth data were recorded during april may june and august at around 47 n 20 w biotrans in 1988 1989 1990 1992 1993 and during may 1989 and 1992 at 57 n 20 22 w species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column in addition species assemblages 100 m are almost indistinguishable from assemblages that are 125 m in test size the standing stock of planktic foraminifers at biotrans can vary by more than one order of magnitude over different years however species assemblages may be similar when comparing corresponding seasons early summer assemblages june are distinctly different from late summer assemblages august significant variations in the species composition during spring april may are independent of the mixed layer depth spring assemblages are characterized by high numbers of globigerinita glutinata in particular day to day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations this appears to be independent of the reproduction cycle species assemblages at 47 n and 57 n are similar during spring although surface water temperatures and salinities differ by up to 10 c and 0 7 psu we suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations a quasi annual periodicity in flux levels and substantial differences in timing and magnitude of peak fluxes at the biotrans station the average annual planktic foraminiferal caco 3 fluxes at 100 and 500 m depth are estimated to be 22 4 and 10 0 g m 2 yr 1 respectively

late pliocene to early pleistocene changes in the north atlantic current and suborbital scale sea surface temperature variability the strength and latitudinal position of the north atlantic current nac determines the position of the arctic front and heat transport to the high northern latitudes with potentially important consequences for northern hemisphere glaciation a southward shift in the nac and reduced poleward heat transport is hypothesized to have triggered the last major climate transition in earth s history late pliocene intensification of northern hemisphere glaciation inhg in turn inhg is hypothesized to have led to the amplification of climate variability on suborbital time scales to date however only a handful of adequately resolved records are available to test these two hypotheses here we present a new late pliocene to earliest pleistocene record from integrated ocean drilling program site u1313 north atlantic 41 n 2 9 to 2 4 ma we use mg ca derived paleotemperature records in planktic foraminiferal calcite to investigate changes in summer sea surface temperatures sst on orbital and suborbital time scales our results call into question the suggestion that significant weakening and or southward shift of the nac served as a trigger for northern hemisphere cooling and intensified continental ice sheet growth across inhg in contrast to the late pleistocene during inhg we find that the position of the nac and arctic front probably lay well to the north of site u1313 and that the amplitude of suborbital sst variability did not change on glacial interglacial time scales conservative estimates of late pliocene to earliest pleistocene interglacial summer ssts in our record are up to 3 c warmer than present while glacial summer ssts are only 2 c to 3 c cooler in fact our interglacial summer ssts are remarkably similar to those of the mid pliocene our findings indicate that inhg must have involved amplifying feedback mechanisms that are tightly coupled to ice sheet growth but that these processes were insufficiently developed by the late pliocene earliest pleistocene to have triggered large amplitude changes in suborbital climate in the midlatitude north atlantic

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

subpolar link to the emergence of the modern equatorial pacific cold tongue the cold upwelling tongue of the eastern equatorial pacific is a central energetic feature of the ocean dominating both the mean state and temporal variability of climate in the tropics and beyond recent evidence for the development of the modern cold tongue during the pliocene pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline we have found that the sub antarctic and sub arctic regions underwent substantial cooling nearly synchronous to the cold tongue development thereby providing support for this hypothesis in addition we show that sub antarctic climate changed in its response to earth s orbital variations from a subtropical to a subpolar pattern as expected if cooling shrank the warm water sphere of the ocean and thus contracted the subtropical gyres

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

high amplitude variations in north atlantic sea surface temperature during the early pliocene warm period 1 we provide the first continuous orbital resolution sea surface temperature sst record from the high latitude north atlantic a region critical to understanding the origin of the plio pleistocene ice ages and proximal to regions that became frequently glaciated after 2 7 ma we analyzed sediments from ocean drilling program site 982 over the last 4 ma for their alkenone unsaturation index and compared this surface water signal to a benthic 18o record obtained from the same section we find that while ocean surface temperatures were significantly warmer 6 c than modern temperatures during the early pliocene they were also as variable as those during the late pleistocene a surprising result in light of the subdued variance of oxygen isotopic time series during the interval of 3 5 ma we propose two possible explanations for the high orbital scale sst variability observed either that a strong high latitude feedback mechanism not involving large continental ice sheets alternately cooled and warmed a broad region of the northern high latitudes or that by virtue of its location near the northern margin of the north atlantic drift the site was unusually sensitive to obliquity driven climate shifts on supraorbital time scales a strong sustained cooling of north atlantic ssts 4 5 c occurred from 3 5 to 2 5 ma and was followed by an interval of more modest cooling an additional 1 5 c from 2 5 ma to the present evolutionary orbital scale phase relationships between north atlantic sst and benthic 18o show that sst began to lead 18o significantly coincident with the onset of strong cooling at site 982 3 5 ma we speculate that these changes were related to the growth and subsequent persistence of a greenland ice sheet of approximately modern size through interglacial states

vegetation cover in a warmer world simulated using a dynamic global vegetation model for the mid pliocene in this study we employ the triffid top down representation of interactive flora and foliage including dynamics dynamic global vegetation model dgvm and the hadley centre atmospheric general circulation model version 3 hadam3 gcm to investigate vegetation distributions and climate vegetation feedbacks during the mid pliocene and examine the implications of these results for the origins of hominid bipedalism the triffid model outputs support extant palaeoenvironmental reconstructions for the mid pliocene provided by the prism group pliocene research interpretations and synoptic mapping compared to the pre industrial triffid simulates a significant increase in forest cover during the mid pliocene composed of needle leaf trees in the higher latitudes of the northern hemisphere and broad leaf trees in other regions needle leaf trees extend from the arctic coast into the northern mid latitudes the fractional coverage of bare soil declines in north africa the arabian peninsula australia and southern south america a pattern that is consistent with prism s assertion of less extensive arid deserts a significant increase in the fractional coverage of both broad leaf trees in africa and south america in the mid pliocene scenario is not indicative of a major expansion of tropical rainforests rather it represents an expansion of general woodland type habitats the principal impact of using a dgvm on the gcm predicted climatology for the mid pliocene is to reduce minimum and maximum temperature extremes thus reducing the seasonality of temperature over wide regions the predicted pliocene expansion in broad leaf trees in africa is difficult to reconcile with the savannah hypothesis for the evolution of hominid bipedalism rather the results lend credence to an alternative hypothesis which suggests that bipedalism evolved in wooded to forested ecosystems and was for several million years linked to arborealism

primary signal ecological and environmental factors report from working group 2 alkenone based proxies are routinely used for paleoceanographic and climatologic reconstructions despite the fact that their calibration to environmental parameters is still a matter of debate significant differences are observed among culture calibrations using different strains of alkenone producers between regional field calibrations within the euphotic zone and between water column and core top based calibrations the reasons for these discrepancies are not well understood and call for further evaluation the possibility is raised that several aspects of genetics physiology and ecology of alkenone producing haptophytes may be responsible and suggestions of future research are proposed

palynological evidence for a southward shift of the north atlantic current at 2 6 ma during the intensification of late cenozoic northern hemisphere glaciation the position of the north atlantic current nac during the intensification of northern hemisphere glaciation inhg has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a 260 kyr interval straddling the base of the quaternary system from two sites eastern north atlantic deep sea drilling project site 610 in the path of the present nac and central north atlantic integrated ocean drilling program site u1313 in the subtropical gyre stable isotope and foraminiferal mg ca analyses confirm cooling near the marine isotope stage mis g7 g6 transition 2 74 ma however a continued dominance of the dinoflagellate cyst operculodinium centrocarpum sensu wall and dale 1966 indicates an active nac in the eastern north atlantic for a further 140 kyr at mis 104 2 60 ma a profound dinoflagellate cyst assemblage turnover indicates nac shutdown in the eastern north atlantic implying elevated atmospheric pressure over the arctic and a resulting shift in the westerlies that would have driven the nac these findings challenge recent suggestions that there was no significant southward shift of the nac or the arctic front during inhg and reveal a fundamental climatic reorganization near the base of the quaternary

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

an astronomically tuned 8 1 ma eolian record from the chinese loess plateau and its implication on the evolution of asian monsoon the chinese loess paleosol sequences have led to a great understanding of the evolution of the east asian monsoon eam in the quaternary however evolution of the eam in the late miocene and pliocene is quite blurry hindering our understanding of the mechanisms driving the eam thus we obtained high resolution grain size records of 8 1 ma from the thickest eolian red clay sequence at chaona on the chinese central loess plateau and astronomically tuned the grain size records to the orbital variation with a time resolution of 1 5 ka to 5 8 ka the variability of coarse size fraction a recognized proxy for the east asian winter monsoon eawm indicates a persistent but stepwise intensification of the eawm at ca 5 5 ma 3 6 ma 2 6 ma and 1 ma filtering of this proxy record at 100 41 and 21 ka bands was conducted to trace the evolution of the eawm in a frequency domain over 8 1 ma temporal variations of these three cycles show a remarkable simultaneous enhancement at ca 5 5 ma indicating a synchronous intensification of high and low latitude signals in the eawm record we suggest that the closure of panama seaway to form the north atlantic thermohaline circulation and the high latitude cooling during this time might collectively trigger such a response copyright 2011 by the american geophysical union

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

intensification of the walker and hadley atmospheric circulations during the pliocene pleistocene climate transition when comparing new sea surface temperature sst records between the western and eastern equatorial pacific spanning the last 3 2 ma we found that the zonal temperature gradient over the entire tropical pacific irreversibly increased by 3 to 4 degrees c from 2 2 to 2 0 ma here we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal walker circulation wc during the early pleistocene evidence from other oceanic areas also suggests a strengthening in the meridional hadley circulation hc during the same time period therefore we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the plio pleistocene transition and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm sphere associated with a prominent increase in the pole to equator temperature gradient our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes since the onset of extensive northern hemisphere glaciation nhg occurred similar to 2 75 ma ago in the late pliocene instead the development of a stronger atmospheric circulation similar to 2 2 2 0 ma ago could have significantly contributed to the plio pleistocene climate cooling c 2010 elsevier b v all rights reserved

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

early pleistocene glacial cycles and the integrated summer insolation forcing long term variations in northern hemisphere summer insolation are generally thought to control glaciation but the intensity of summer insolation is primarily controlled by 20 000 year cycles in the precession of the equinoxes whereas early pleistocene glacial cycles occur at 40 000 year intervals matching the period of changes in earth s obliquity the resolution of this 40 000 year problem is that glaciers are sensitive to insolation integrated over the duration of the summer the integrated summer insolation is primarily controlled by obliquity and not precession because by kepler s second law the duration of the summer is inversely proportional to earth s distance from the sun

plio pleistocene climate sensitivity evaluated using high resolution co2 records theory and climate modelling suggest that the sensitivity of earth s climate to changes in radiative forcing could depend on the background climate however palaeoclimate data have thus far been insufficient to provide a conclusive test of this prediction here we present atmospheric carbon dioxide co2 reconstructions based on multi site boron isotope records from the late pliocene epoch 3 3 to 2 3 million years ago we find that earth s climate sensitivity to co2 based radiative forcing earth system sensitivity was half as strong during the warm pliocene as during the cold late pleistocene epoch 0 8 to 0 01 million years ago we attribute this difference to the radiative impacts of continental ice volume changes the ice albedo feedback during the late pleistocene because equilibrium climate sensitivity is identical for the two intervals when we account for such impacts using sea level reconstructions we conclude that on a global scale no unexpected climate feedbacks operated during the warm pliocene and that predictions of equilibrium climate sensitivity excluding long term ice albedo feedbacks for our pliocene like future with co2 levels up to maximum pliocene levels of 450 parts per million are well described by the currently accepted range of an increase of 1 5 k to 4 5 k per doubling of co2

reevaluation of mid pliocene north atlantic sea surface temperatures 1 multiproxy temperature estimation requires careful attention to biological chemical physical temporal and calibration differences of each proxy and paleothermometry method we evaluated mid pliocene sea surface temperature sst estimates from multiple proxies at deep sea drilling project holes 552a 609b 607 and 606 transecting the north atlantic drift sst estimates derived from faunal assemblages foraminifer mg ca and alkenone unsaturation indices showed strong agreement at holes 552a 607 and 606 once differences in calibration depth and seasonality were addressed abundant extinct species and or an unrecognized productivity signal in the faunal assemblage at hole 609b resulted in exaggerated faunal based sst estimates but did not affect alkenone derived or mg ca derived estimates multiproxy mid pliocene north atlantic sst estimates corroborate previous studies documenting high latitude mid pliocene warmth and refine previous faunal based estimates affected by environmental factors other than temperature multiproxy investigations will aid sst estimation in high latitude areas sensitive to climate change and currently underrepresented in sst reconstructions

cold water coral carbonate mounds as unique palaeo archives the plio pleistocene challenger mound record ne atlantic through the interplay of a stabilising cold water coral framework and a dynamic sedimentary environment cold water coral carbonate mounds create distinctive centres of bio geological accumulation in often complex continental margin settings the iodp expedition 307 drilling of the challenger mound eastern porcupine seabight ne atlantic not only retrieved the first complete developmental history of a coral carbonate mound it also exposed a unique early pleistocene sedimentary sequence of exceptional resolution along the mid latitudinal ne atlantic margin in this study a comprehensive assessment of the challenger mound as an archive of quaternary palaeo environmental change and long term coral carbonate mound development is presented new and existing environmental proxy records including clay mineralogy planktonic foraminifer and calcareous nannofossil biostratigraphy and assemblage counts planktonic foraminifer oxygen isotopes and siliciclastic particle size are thereby discussed within a refined chronostratigraphic and climatic context overall the development of the challenger mound shows a strong affinity to the plio pleistocene evolution of the northern hemisphere climate system albeit not being completely in phase with it the two major oceanographic and climatic transitions of the plio pleistocene the late pliocene early pleistocene intensification of continental ice sheet development and the mid pleistocene transition to the more extremely variable and more extensively glaciated late quaternary mark two major thresholds in challenger mound development its late pliocene 2 74 ma origin and its middle late pleistocene to recent decline distinct surface water perturbations i e water mass polar front migrations productivity changes melt water pulses are identified throughout the sequence which can be linked to the intensity and extent of ice development on the nearby british irish isles since the earliest pleistocene glaciation induced shifts in surface water primary productivity are thereby proposed to fundamentally control cold water coral growth which in turn influences on mound sediment accumulation and hence coral carbonate mound development throughout the pleistocene as local factors such as proximal ice sheet dynamics and on mound changes in cold water coral density significantly affected the development of the challenger mound they can potentially explain the nature of its palaeo record and its offsets with the periodicities of global climate variability on the other hand owing to this unique setting a regionally exceptional high resolution palaeo record of early pleistocene ca 2 6 to 2 1 ma environmental change including early british irish ice sheet development broadly in phase with the 41 ka paced global climate system is preserved in the lower challenger mound all in all the challenger mound record highlights the wider relevance of coral carbonate mound archives and their potential to capture unique records from dynamic continental margin environments

an alternative suggestion for the pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of north atlantic ocean ice rafted debris abstract the onset of abundant ice rafted debris ird deposition in the nordic seas and subpolar north atlantic ocean 2 72 millions of years ago ma is thought to record the pliocene onset of major northern hemisphere glaciation nhg due to a synchronous advance of north american laurentide scandinavian and greenland ice sheets to their marine calving margins during marine isotope stage mis g6 numerous marine and terrestrial records from the nordic seas region indicate that extensive ice sheets on greenland and scandinavia increased ird inputs to these seas from 2 72 ma the timing of ice sheet expansion on north america as tracked by ird deposition in the subpolar north atlantic ocean however is less clear because both europe and north america are potential sources for icebergs in this region moreover cosmogenic dating of terrestrial tills on north america indicate that the laurentide ice sheet did not extend to 39 n until 2 4 0 14 ma at least 180 ka after the onset of major ird deposition at 2 72 ma to address this problem we present the first detailed analysis of the geochemical provenance of individual sand sized ird deposited in the subpolar north atlantic ocean between mis g6 and 100 2 72 2 52 ma ird provenance is assessed using laser ablation lead pb isotope analyses of single ice rafted 150 m feldspar grains to track when an ice rafting setting consistent with major nhg first occurred in the north atlantic ocean during the pliocene intensification of nhg inhg we investigate when the pb isotope composition 206pb 204pb 207pb 204pb 208pb 204pb of feldspars deposited at dsdp site 611 first resembles that determined for ird deposited at this site during mis 100 2 52 ma the oldest glacial for which there exists convincing evidence for widespread glaciation of north america whilst quaternary magnitude ird fluxes exist at site 611 during glacials from 2 72 ma we find that the provenance of this ird is not constant instead we find that the pb isotope composition of ird at our study site is not consistent with major nhg until mis g2 2 64 ma we hypothesise that ird deposition in the north atlantic ocean prior to mis g2 was dominated by iceberg calving from greenland and scandinavia we further suggest that the grounding line of continental ice on northeast america may not have extended onto the continental shelf and calved significant numbers of icebergs to the north atlantic ocean during glacials until 2 64 ma

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes

assessing divergent sst behavior during the last 21 ka derived from alkenones and g ruber mg ca in the equatorial pacific equatorial pacific sst reconstructions derived from mg ca ratios in planktonic foraminifera globigerinoides ruber and from alkenone producing coccolithophorids record different trends throughout the holocene and the last deglaciation we set forth the hypothesis that their diverging behavior may be related to different seasonal sensitivities which result from the annually varying production rates of alkenone producing coccolithophorids and of g ruber using a series of transient paleoclimate model simulations forced with the time varying forcing history over the last 21 ka a good qualitative agreement is found between simulated boreal winter temperatures and alkenone sst reconstructions as well as between simulated boreal summer temperatures and reconstructed mg ca based sst variations pronounced features in the reconstructions that can be readily explained by the conjectured seasonal biases include the mismatch in middle to late holocene temperature trends and the different onsets of deglacial climate change in the eastern equatorial pacific the analysis presented here further suggests that through combinations of mg ca and alkenone sst reconstructions information can be gained on annual mean temperature changes and the amplitude of the seasonal cycle in sst our study concludes by discussing potential weaknesses of the proposed model derived seasonal bias interpretation of tropical pacific sst proxies in terms of present day core top data sediment trap studies and satellite based observations of chlorophyll

thermal expansion of wadsleyite ringwoodite hydrous wadsleyite and hydrous ringwoodite abstract the thermal expansions of wadsleyite ringwoodite hydrous wadsleyite and hydrous ringwoodite have been determined by high temperature powder x ray diffraction at ambient pressure wadsleyite and ringwoodite persist up to 700 c and their thermal expansion coefficients are measured as 34 0 5 10 6 and 30 7 6 10 6 k 1 respectively values that are slightly larger than those measured by j phys earth 27 1979 53 j phys earth 28 1980 273 hydrous wadsleyite and hydrous ringwoodite were dehydrated at 450 and 400 c respectively below their dehydration temperatures their thermal expansion coefficients are 30 1 14 10 6 and 27 3 9 10 6 k 1 respectively which are slightly lower than those of their anhydrous forms using the present results combined with the previous thermoelastic data the seismic velocity contrast at the 410 km discontinuity has been calculated for both dry and wet mantle if a pyrolite composition is assumed a hydrous mantle transition zone better explains seismic constraints