oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

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

ice rafting from the british irish ice sheet since the earliest pleistocene 2 6 million years ago implications for long term mid latitudinal ice sheet growth in the north atlantic region abstract the plio pleistocene intensification of northern hemisphere continental ice sheet development is known to have profoundly affected the global climate system evidence for early continental glaciation is preserved in sediments throughout the north atlantic ocean where ice rafted detritus ird layers attest to the calving of sediment loaded icebergs from circum atlantic ice sheets so far early pleistocene ird deposition has been attributed to the presence of high latitudinal ice sheets whereas the existence and extent of ice accumulation in more temperate mid latitudinal regions remains enigmatic here we present results from the multiproxy provenance analysis of a unique pleistocene holocene ird sequence from the irish ne atlantic continental margin there the challenger coral carbonate mound iodp expedition 307 site u1317 preserved an early pleistocene record of 16 distinctive ird events deposited between ca 2 6 and 1 7 ma strong and complex ird signals are also identified during the mid pleistocene climate transition ca 1 2 to 0 65 ma and throughout the middle late pleistocene interval radiogenic isotope source fingerprinting in combination with coarse lithic component analysis indicates a dominant sediment source in the nearby british irish isles even for the oldest early pleistocene ird deposits hence our findings demonstrate for the first time repeated and substantial i e marine terminating ice accumulation on the british irish isles since the beginning of the pleistocene contemporaneous expansion of both high and mid latitudinal ice sheets in the north atlantic region is therefore implied at the onset of the pleistocene moreover it suggests the recurrent establishment of climatically favourable conditions for ice sheet inception growth and instability in mid latitudinal regions even in the earliest stages of northern hemisphere glacial expansion and in an obliquity driven climate system

model for the combined flow origin of hummocky cross stratification many shallow marine sandstones are characterized by gently dipping trough cross stratification there appear to be significant similarities between this low angle cross stratification and typical hummocky cross stratification and it is proposed that much of what is currently recognized as hummocky cross stratification is related to low relief megaripple bed forms that are equilibrium structures for fine grained sand under combined wave surge and unidirectional currents the geometry that obtains when these bed forms migrate is low angle trough cross stratification high rates of sedimentation from incipient suspension and limited lateral migration of individual bed forms promote preservation of convex upward depositional surfaces hummocks between troughs highly unsteady flow leads to abundant internal scour and drape surfaces neither random scour and drape nor oscillatory currents seem sufficient to generate hummocky bed forms

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

paleotectonic significance of the quartzite of the sauratown mountains window north carolina recent mapping within the metamorphic core of the southern appalachians has led to the identification of several internal basement massifs interpreted to be windows that expose parautochthonous basement beneath the main thrust sheet one such internal massif is exposed within the inner piedmont of north carolina by the sauratown mountain window and is overlain by a cover sequence of arkose schist and quartzite detailed examination of the primary cross stratification types preserved within the quartzite at pilot mountain indicates that deposition took place in several marine environments ranging from foreshore to inner shelf deposits of similar origin within the early cambrian north american passive margin sediments appear to thin west to east from 80 m at the chilhowee group type locality at chilhowee mountain 300 km west southwest of pilot mountain to 40 m within the unaka belt 150 km west of pilot mountain the quartzite at pilot mountain is more than 45 m thick and therefore does not appear to represent a distal part of this passive margin sequence alternatively two paleotectonic interpretations seem plausible 1 quartzites of the sauratown mountains window north carolina represent late proterozoic tallulah falls ashe formation equivalent deposition along a sea floor high associated with the rifted basement terrane during the rift phase prior to the opening of iapetus or 2 quartzites of the sauratown mountains window north carolina represent latest proterozoic to early cambrian chilhowee group time equivalent deposition on an isolated rifted continental fragment during the drift phase of the north american iapetus margin evolution

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

high heat flux on ancient mars evidence from rift flank uplift at coracis fossae 1 we have identified flexural uplift at the flanks of the coracis fossae rift valley modeling the topography the elastic thickness is constrained to 10 3 12 5 km the corresponding mechanical thickness and thermal gradient are 15 19 km and 27 33 k km 1 respectively the time of rifting is dated by evaluating the crater size frequency distribution of key surface units related to the rifting thus the heat flux between 3 5 and 3 9 ga is calculated to be 54 66 mw m 2 furthermore the stresses supported by the rift bounding faults are estimated to be below 5 mpa we speculate that this weakness may be connected to the presence of water below the surface

three dimensional normal faulting models of the valles marineris mars and geodynamic implications inversion of martian topography using a three dimensional boundary element model permits revised estimates of fault dip angle depth of faulting paleogeothermal gradient and extensional strain in the valles marineris region the major normal faults dip at 40 55 to depths of 60 75 km with comparatively small footwall uplifts 500 m for throws to 10 km implying that paleogeothermal gradients during faulting were 10 k km 1 or less assuming relatively rapid strain rates appropriate to the extending martian crust accumulation of dip slip offsets along the main normal faults likely was associated with anticlinal flexure and deformation of preexisting strata within the troughs the magnitudes of the predicted vertical and horizontal displacements outside the troughs as well as extensional strains are spatially variable depending on both cross and along strike position relative to the troughs the predicted displacements and strains attain maximum values at the troughs and decay to background values at cross strike distances of 250 km corresponding to 3 4 times the depth of faulting with an average province wide strain of 4 15 by implication the aggregate strain field surrounding tharsis is a highly variable spatial and temporal composite of the inhomogeneous strain fields each associated and scaling in size with an individual graben from the smallest structures through the largest valles marineris troughs

linear and non linear response of late neogene glacial cycles to obliquity forcing and implications for the milankovitch theory constraints are given for the geometry and time lags of the prominent obliquity paced glacial stages 100 98 and 96 which mark a major phase in northern hemisphere nh glaciations during the late pliocene 2 56 2 4 ma ago for this purpose a high resolution benthic 18o record was constructed from the astronomically tuned mediterranean odp site 967 and decomposed into an ice volume and an annual nh 40 80 n temperature component using an inverse modelling approach our results indicate that the dominant 41 ky component in 18o lags obliquity by 6 5 0 6 ky which approximates late pleistocene estimates maximum minimum ice volume growth occurred in phase with obliquity minima maxima which invoked low high total summer energy conditions that reduced increased ice sheet ablation sea level dropped 60 70 m during full glacial conditions similar to late pleistocene ice core and marine 18o records our late pliocene 18o record reveals significant power at 28 ky which appear to be bound to the major glacial terminations we argue that this beat most likely reflects the sum frequency of the 41 ky prime and its multiples of 82 and 123 ky supporting the theory that the late neogene glacial cycles are primarily determined by the linear and non linear response mechanisms of the ice sheets to the obliquity forcing evidence for such a scenario may come from the alignment between the devils hole 18o chronology and the sum of the filtered linear and non linear obliquity related components of late pleistocene climate records suggesting that the 28 ky beat is intrinsic to the climate system or at least an important constituent of the annual high latitude nh temperature changes that have set the stage for the geometry of the glacial interglacial variability throughout the course of the pliocene and pleistocene

mechanical modeling of thrust faults in the thaumasia region mars and implications for the noachian heat flux abstract insight into the state of the early martian lithosphere is gained by modeling the topography above surface breaking thrust faults in the southern thaumasia region crater counts of key surface units associated with the faulting indicate a scarp emplacement in the late noachian early hesperian periods between 4 0 and 3 7 gyr the seismogenic layer thickness at the time of faulting is constrained to 27 35 km and 21 28 km for the two scarps investigated implying paleo geothermal gradients of 12 18 and 15 23 k km 1 corresponding to heat flows of 24 36 and 30 46 mw m 2 the heat flow values obtained in this study are considerably lower than those derived from rift flank uplift at the close by coracis fossae for a similar time period indicating that surface heat flow is a strong function of regional setting if viewed as representative for magmatically active and inactive regions the thermal gradients at rifts and scarps span the range of admissible global mean values this implies d t d z 17 32 k km 1 with the true value probably being closer to the lower bound

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

primary production in the arabian sea during the last 135 000 years abstract variations in primary productivity pp have been reconstructed in eutrophic mesotrophic and oligotrophic parts of the arabian sea over the past 135 000 years applying principal component analysis and transfer function to planktic foraminiferal assemblages temporal variation in paleoproductivity is most pronounced in the mesotrophic northern nast site and oligotrophic eastern east site arabian sea and comparatively weak in the western eutrophic geob 3011 1 site in the upwelling area off oman higher pp during interglacials 250 320 g c m 2 year 1 than during cold stages 210 270 g c m 2 year 1 at geob 3011 1 could have been caused by a strengthened upwelling during intensified summer monsoons and increased wind velocities at nast during interglacials pp is estimated to exceed 250 g c m 2 year 1 and during glacials to be as low as 140 180 g c m 2 year 1 these fluctuations may result from a 1 varying impact of filaments that are associated to the oman coastal upwelling and 2 from open ocean upwelling associated to the findlater jet at east highest productivity of about 380 g c m 2 year 1 is documented for the transition from isotope stage 5 to 4 we suggest that during isotope stages 2 4 5 2 the transition 5 4 and the end of stage 6 deep mixing of surface waters was caused by moderate to strong winter monsoons and induced an injection of nutrients into the euphotic layer leading to enhanced primary production the deepening of the mixed layer during these intervals is confirmed by an increased concentration of deep dwelling planktic foraminiferal species a high productivity event in stage 3 displayed by estimated pp values and by planktic foraminifera and radiolaria flux and accumulation rate likely resulted from a combination of intensified sw monsoons with moderate to strong ne monsoons differential response of globigerina bulloides globigerinita glutinata and mixed layer species to the availability of food is suited to subdivide productivity regimes on a temporal and spatial scale

surface water temperature salinity and density changes in the northeast atlantic during the last 45 000 years heinrich events deep water formation and climatic rebounds we developed a new method to calculate sea surface salinities sss and densities ssd from planktonic foraminiferal 18o and sea surface temperatures sst as determined from planktonic foraminiferal species abundances sst sss and ssd records were calculated for the last 45 000 years for biogeochemical oceanic flux study bofs cores 5k and 8k recovered from the northeast atlantic the strongest feature is the dramatic drop in all three parameters during the heinrich ice rafting events we modelled the possibility of deepwater formation in die northeast atlantic from the ssd records by assuming that the surface waters at our sites cooled as they flowed further north comparison with modelled north atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45 000 and 30 000 14c years b p interrupted by iceberg meltwater input of heinrich event 3 and 4 at 27 000 and 38 000 14c years b p and during the holocene no amount of cooling in the northeast atlantic between 30 000 and 13 000 years could cause deep water to form because of the low salinities resulting from the high meltwater inputs from icebergs our records indicate that after each heinrich event there were periods of climatic rebound with milder conditions persisting for up to 2000 years as indicated by the presence of warmer and more saline water masses after these warm periods conditions returned to average glacial levels these short term cold and warm episodes in the northeast atlantic are superimposed on the general trend towards colder conditions of the last glacial maximum lgm heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the fennoscandian ice sheet we propose that meltwater input of heinrich event 1 significantly reduced north atlantic deep water formation reducing the heat exchange between the low and high latitudes thus delaying deglaciation by about 1500 radiocarbon years 2000 calendar years

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

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

modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle contribution to the change of seawater d 18 o dw between the last glacial maximum lgm and the holocene and to evaluate the effect of nonequilibrium isotopic composition of the nais on the relationship between ice volume variations and the ocean isotopic enrichment the enrichment due to the nais at the lgm was 0 63 corresponding to 60 of the lgm sea level lowstand and to a mean d 18 o of the nais of approximately 31 the modeled nais volume variations and the induced dw changes over the past 120 000 years indicated no significant time lag the inaccuracy associated with linearly inferring ice volume variations from dw changes was generally less than 10 citation sima a a paul m schulz and j oerlemans 2006 modeling the oxygen isotopic composition of the north american ice sheet and its effect on the isotopic composition of the ocean during the last glacial cycle geophys res lett 33 l15706 doi 10 1029 2006gl026923

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

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

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

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

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

salinity changes in the north west pacific ocean during the late pliocene early quaternary from 2 73 ma to 2 52 ma recent research has increasingly advocated a role for the north pacific ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record here a diatom 18o record is presented from ocean drilling program site 882 over the pliocene quaternary boundary from 2 73 ma to 2 52 ma mis g6 mis 99 large changes in 18odiatom of c 4 from 2 73 ma onwards are documented to occur on a timeframe broadly coinciding with glacial interglacial cycles these changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the north pacific basin and the bering sea despite these inputs and associated change in surface water salinity on the basis of existing opal and uk37 temperature data and new modelled water column densities no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2 73 ma the permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial interglacial cycles that followed the onset of major northern hemisphere glaciation by inhibiting deep water upwelling and ventilation of co2 to the atmosphere

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

features of ice rafted debris ird at iodp site u1312 and their palaeoenvironmental implications during the last 2 6 myr abstract in this paper we build an age model by tuning the g ruber 18o curve to the lr04 stack and u1308 benthic 18o curve with the aid of the high resolution lightness parameter l which mirrors the marine oxygen isotope stages and we analyse the major palaeoenvironmental events indicated by different proxies particularly the 250 m fraction and the 150 250 m fraction of ice rafted debris ird at iodp site u1312 in general the input of ird at site u1312 can be divided into two stages in stage 1 ranging from 2 6 ma to 1 ma the number of lithic grains was small the frequency of ice rafting events was low and the components were diverse and mainly comprised quartz feldspar and clasts in stage 2 ranging from 1 ma to the present the number and frequency of lithic grains considerably increased and were accompanied by detrital carbonate additions derived from the hudson strait after 650 ka regarding the ird features in the study area the distinctive layers are as follows ird did not occur until 2 52 ma at site u1312 implying that icebergs discharged by the northern hemisphere glaciers bearing lithic grains were involved in pelagic sedimentation for the first time interestingly a monotonic component of debris magnetite with some ilmenite and quartz was observed in a single layer at approximately 1 4 ma the source of this component may simply be the erosion of volcanic formations in iceland during the glacial period detrital carbonate played an important role in the ird component after 650 ka and the input and frequency of ird increased dramatically revealing glacier enhancements and the instability of the laurentide ice sheet the ird characteristics at site u1312 during mis 22 mis 12 and mis 6 were different from those at other sites near the ird belt and may be closely related to the european ice sheets during mis 10 8 the input of ird was high the dominant warm species g ruber was too rare for the isotope test to be conducted and the abundance of planktonic foraminifera severely declined which may indicate that extreme conditions occurred at site u1312 during this interval

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

deciphering the palaeoecology of late pliocene and early pleistocene dinoflagellate cysts abstract in an attempt to document the palaeoecological affinities of individual extant and extinct dinoflagellate cysts late pliocene and early pleistocene dinoflagellate cyst assemblages have been compared with geochemical data from the same samples mg ca ratios of globigerina bulloides were measured to estimate the spring summer sea surface temperatures from four north atlantic iodp dsdp sites currently our pliocene pleistocene database contains 204 dinoflagellate cyst samples calibrated to geochemical data this palaeo database is compared with modern north atlantic and global datasets the focus lies in the quantitative relationship between mg ca based i e spring summer sea surface temperatures sstmg ca and dinoflagellate cyst distributions in general extant species are shown to have comparable spring summer sst ranges in the past sstmg ca and today sst from world ocean atlas 2005 locarnini et al 2006 demonstrating that our new approach is valid for inferring spring summer sst ranges for extinct species for example habibacysta tectata represents sstmg ca values between 10 and 15 c when it exceeds 30 of the assemblage and invertocysta lacrymosa exceeds 15 when sstmg ca values are between 18 6 and 23 5 c however comparing pliocene and pleistocene sstmg ca values with present day summer values for the extant impagidinium pallidum suggests a greater tolerance of higher temperatures in the past this species occupies more than 5 of the assemblage at sstmg ca values of 11 6 17 9 c in the pliocene and pleistocene whereas present day summer ssts are around 1 7 to 6 9 c this observation questions the value of impagidinium pallidum as reliable indicator of cold waters in older deposits and may explain its bipolar distribution

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

constraints on the ocean oxygen isotopic enrichment between the last glacial maximum and the holocene paleoceanographic implications abstract we review the various methods which have been applied to estimate the change of seawater 18 o w between the last glacial maximum lgm and the holocene the most accurate constraints on these estimates are provided by the measurement of pore waters 18 o and by high resolution records of benthic foraminifer 18 o in the high latitude oceans of both hemispheres they show that the 18 o of seawater in the deep ocean during the lgm was 1 05 0 20 heavier than today with significant regional variations constraints resulting from ice sheet models are less accurate because both the volume and isotopic composition of each ice sheet are still poorly known the amplitude of the benthic 18 o change between the lgm and the holocene together with the 18 o and 13 c values of the benthic foraminifera genus cibicides during the lgm show that the southern ocean deep waters were extremely cold close to the freezing point during this time deep waters of the south atlantic and the pacific oceans were at least 1 3 c warmer than those of the southern ocean overall the glacial deep ocean below 2500 m was characterized by extremely cold temperatures everywhere lower than 0 c 18 o values of benthic foraminifer from the north atlantic are highly variable this variability suggests that deep atlantic waters were not homogeneous probably because they resulted from the sinking of different surface water masses at various locations during winter the deep waters in the north atlantic were at most 2 c warmer than in southern ocean alternatively they could have been nearer the freezing point with a 18 o value lighter than the mean ocean water brine formation during winter would preserve such light 18 o values of the northern north atlantic surface water

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

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

iron fertilisation and biogeochemical cycles in the sub arctic northwest pacific during the late pliocene intensification of northern hemisphere glaciation abstract increases in the low field mass specific magnetic susceptibility dropstones and the terrigenous sediment component from ocean drilling program odp site 882 45 n have been interpreted to indicate a major onset of ice rafting to the sub arctic northwest pacific ocean during marine isotope stage mis g6 from 2 75 ma in contrast studies of the terrigenous content of sediments cored downwind of odp site 882 indicate that dust and disseminated volcanic ash deposition in the sub arctic pacific increased markedly during mis g6 to investigate the relative contribution of dust volcanic ash and ice rafting to the pliocene increase we present new high resolution environmental magnetic and ice rafted debris records from odp sites 882 and 885 our results demonstrate that the increase at both sites across mis g6 is predominantly controlled by a previously overlooked mixture of aeolian dust and volcanic ash our findings call into question the reliability of as a proxy for ice rafting to the north pacific they also highlight a previously undocumented link between iron fertilisation and biogeochemical cycling in the north pacific at a key stage during intensification of late pliocene northern hemisphere glaciation

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

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

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

a new sea level record for the neogene quaternary boundary reveals transition to a more stable east antarctic ice sheet sea level rise resulting from the instability of polar continental ice sheets represents a major socioeconomic hazard arising from an thropogenic warming but the response of the largest component of earth s cryosphere the east antarctic ice sheet eais to global warming is poorly understood here we present a detailed record of north atlantic deep ocean temperature global sea level and ice volume change for 2 75 to 2 4 ma ago when atmospheric partial pressure of carbon dioxide pco2 ranged from present day 400 parts per million volume ppmv to preindustrial 280 ppmv values our data reveal clear glacial interglacial cy cles in global ice volume and sea level largely driven by the growth and decay of ice sheets in the northern hemisphere yet sea level values during marine isotope stage mis 101 2 55 ma also sig nal substantial melting of the eais and peak sea levels during mis g7 2 75 ma and perhaps mis g1 2 63 ma are also sugges tive of eais instability during the succeeding glacial interglacial cycles mis 100 to 95 sea levels were distinctly lower than before strongly suggesting a link between greater stability of the eais and increased land ice volumes in the northern hemisphere we propose that lower sea levels driven by ice sheet growth in the northern hemisphere decreased eais susceptibility to ocean melt ing our findings have implications for future eais vulnerability to a rapidly warming world

millennial scale climate change and oceanic processes in the late pliocene and early pleistocene we generated 200 500 year resolution records of oceanic processes in the north atlantic ocean drilling program site 983 60 24 n 23 38 w 1983 meters water depth for intervals in the latest pliocene 1 86 1 93 ma and the earliest pleistocene 1 75 1 83 ma in order to examine the linkages between millennial scale variations in the ocean and background glacial interglacial climate change within glacial intervals we find evidence for variations similar to those observed in the late pleistocene we find discrete ice rafted debris ird events that reoccur every 2 5 kyr these events are preceded by a short cooling and accompanied by a reorganization of glacial deep waters the timing of ird events in the late pliocene and early pleistocene intervals is similar to that of dansgaard oeschger cycles but we find no ird events comparable in timing to late pleistocene heinrich events although interglacial intervals are much more stable we do find evidence for low amplitude variations in deep water properties that reoccur every 2 kyr within interglacial intervals the similarity between our late pliocene early pleistocene records and late pleistocene records implies that the mechanism driving millennial scale variations cannot be uniquely attributed to the strongly nonlinear linkage between climate and insolation and the large ice sheets of the late pleistocene

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

the pacemaker always rings twice we generated new long high resolution climate proxy records from deep sea drilling project dsdp sites 607 and 609 in the subpolar north atlantic over the interval 225 970 ka which have pronounced variability at periods f 1 7 kyr variance in our north atlantic climate proxy records is shown using bispectral and cross bispectral methods to be explainable as harmonics and or combination tones of orbital scale climatic variability of the north atlantic region itself thus the timing and amplitude of high frequency climate change in the north atlantic region appears to be a nonlinear function of variations in high latitude climate at milankovitch frequencies

wally was right predictive ability of the north atlantic conveyor belt hypothesis for abrupt climate change linked abrupt changes of north atlantic deep water formation north atlantic sea ice extent and widespread climate occurred repeatedly during the last ice age cycle and beyond in response to changing freshwater fluxes and perhaps other causes this paradigm developed and championed especially by w s broecker has repeatedly proven to be successfully predictive as well as explanatory with high confidence much work remains to fully understand what happened and to assess possible implications for the future but the foundations for this work are remarkably solid

late cenozoic sea level and the rise of modern rimmed atolls this paper is not subject to u s copyright the definitive version was published in palaeogeography palaeoclimatology palaeoecology 451 2016 73 83 doi 10 1016 j palaeo 2016 03 018

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

southern greenland glaciation and western boundary undercurrent evolution recorded on eirik drift during the late pliocene intensification of northern hemisphere glaciation abstract we present new sedimentological and environmental magnetic records spanning 3 2 2 2 ma during the intensification of northern hemisphere glaciation from north atlantic integrated ocean drilling program site u1307 on eirik drift our new datasets and their high fidelity age control demonstrate that while inland glaciers and potentially also at times restricted iceberg calving margins have likely existed on southern greenland since at least 3 2 ma persistent and extensive iceberg calving glacial margins were only established in this region at 2 72 ma 300 kyr later than in northeastern and eastern greenland despite a dramatic increase in greenland sourced ice rafted debris deposition on eirik drift at this time contemporaneous changes in the bulk magnetic properties of site u1307 sediments and a reduction in sediment accumulation rates suggest a decrease in the delivery of greenland sourced glaciofluvial silt to our study site we attribute these changes to a shift in depositional regime from bottom current dominated to glacial ird dominated between 2 9 and 2 7 ma in response to a change in the depth of the flow path of the western boundary undercurrent relative to our study site

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 brevard zone in south carolina and adjacent areas an alleghanian orogen scale dextral shear zone reactivated as a thrust fault the displacement history of the brevard zone a linear orogen scale structure in the metamorphic core of the southern appalachians has been controversial geological and seismic data indicate that the brevard zone and the taconic acadian metamorphic rocks in which it resides are contained in a huge crystalline thrust sheet that overlies relatively unmetamorphosed platform sedimentary rocks along a major alleghanian thrust fault along a 100 km segment in south carolina and adjacent states the brevard zone contains three separate structural features all of which dip moderately se 1 the narrow rosman fault which contain tectonic breccia and slices of the buried platform sedimentary rocks 2 the brevard mylonite zone which contains mylonitic rocks that extend about 3 km on either side of the rosman fault and exhibits shear sense criteria which consistently indicate dextral strike slip 3 the brevard fault zone se of the rosman fault which contains stratified metamorphic rocks that are repeated

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

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

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

north atlantic midlatitude surface circulation changes through the plio pleistocene intensification of northern hemisphere glaciation the north atlantic current nac transports warm salty water to high northern latitudes with important repercussions for ocean circulation and global climate a southward displacement of the nac and subarctic front which separate subpolar and subtropical water masses is widely suggested for the last glacial maximum lgm and may have acted as a positive feedback in glacial expansion at this time however the role of the nac during the intensification of northern hemisphere glaciation inhg at 3 5 to 2 5 ma is less clear here we present new records from integrated ocean drilling program site u1313 41 n spanning 2 8 2 4 ma to trace the influence of subarctic front waters above this mid latitude site we reconstruct surface and permanent pycnocline temperatures and seawater 18 o using paired mg ca 18 o measurements on the planktic foraminifers globigerinoides ruber and globorotalia crassaformis and determine abundances of the subpolar foraminifer neogloboquadrina atlantica we find that the first significant glacial incursions of subarctic front surface waters above site u1313 did not occur until 2 6 ma at no time during our study interval was sub surface reorganization in the midlatitude north atlantic analogous to the lgm our findings suggest that lgm like processes sensu stricto cannot be invoked to explain interglacial glacial cycle amplification during inhg they also imply that increased glacial productivity at site u1313 during inhg was not only driven by southward deflections of the subarctic front we suggest that nutrient injection from cold core eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the midlatitude north atlantic from 2 7 ma

relative paleointensity rpi and oxygen isotope stratigraphy at iodp site u1308 north atlantic rpi stack for 1 2 2 2 ma narpi 2200 and age of the olduvai subchron 2015 elsevier ltd integrated ocean drilling program iodp site u1308 49 53 n 24 14 w water depth 3871 m provides a record of relative paleointensity rpi and benthic stable isotope stratigraphy back to 3 2 ma the record since 1 5 ma was published previously and here we present the interval from 1 5 ma to 3 2 ma early pleistocene late pliocene the benthic oxygen isotope record in this interval is correlated to marine isotope stage mis 51 to km2 with an apparent hiatus that removed part of the interval spanning mis 104 g2 2 6 2 65 ma at the gauss matuyama boundary the mean sedimentation rate for the 1 5 3 2 ma period is 8 5 cm kyr the age model was built by correlation of the benthic oxygen isotope record to a global stack lr04 apart from the expected polarity reversals three magnetic excursions are recorded punaruu in mis 31 32 at 1092 ka gilsa in mis 54 55 at 1584 ka and a newly recognized excursion labeled porcupine after the nearby porcupine abyssal plain in mis g6 g7 at 2737 ka the ages of polarity reversals at site u1308 on the lr04 time scale are consistent with the current geomagnetic polarity timescale gpts with the exception of the base of the olduvai subchron that occurred in mis 73 corresponding to 1925 ka on the lr04 time scale 25 kyr younger than in the current gpts the rpi record at site u1308 is calibrated using the oxygen isotope age model and combined with four other north atlantic records to obtain a north atlantic rpi stack for 1 2 2 2 ma narpi 2200 that is compared with published rpi stacks epapis sint 2000 and padm2m for 2 2 3 2 ma the site u1308 rpi record is compared with a rpi record from north atlantic iodp site u1314 and with the pacific epapis stack the mean sedimentation rates of the north atlantic sites in narpi 2200 are greater by about an order of magnitude than most of the records incorporated in other stacks the comparison of epapis and narpi 2200 yields an apparent lag for narpi 2200 relative to epapis attributed the epapis age model constructed by correlation of magnetic concentration parameters a proxy for carbonate percentage to a calibrated oxygen isotope record the long rpi record from site u1308 yields a very similar mean value for the brunhes and matuyama virtual axial dipole moments 7 05 1022 am2 implying no polarity bias in the strength of the main geomagnetic dipole in contrast to interpretations from sint 2000 and padm2m the results strengthen the case that rpi can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters kyr

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

sea level changes at the lgm from ice dynamic reconstructions of the greenland and antarctic ice sheets during the glacial cycles abstract new experiments were performed with three dimensional thermomechanical models of the greenland and antarctic ice sheets to simulate their behaviour during the glacial cycles to reconstruct their thickness and extent at the last glacial maximum lgm and to estimate their glacio eustatic contribution to the global sea level stand the calculations used improved ice dynamic and isostatic treatments updated datasets on higher grid resolutions and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations results are discussed from a reference run with standard parameters that is compared with available glacial geological observations and from a series of sensitivity experiments focusing on isostatic adjustment thermomechanical coupling climatic forcing mass balance changes and basal melting rates and viscosity changes of antarctic ice shelves for the antarctic ice sheet we find that volume changes are closely linked with grounding line changes of the west antarctic ice sheet at the lgm the grounding line extended close to the continental shelf break almost everywhere ice over central east antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations for the greenland ice sheet melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the eemian at the lgm the greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas for a plausible range of parameters the experiments indicate that at the time of maximum sea level depression 21 kyr bp the antarctic ice sheet contributed 14 18 m to the sea level lowering and the greenland ice sheet 2 3 m significantly less than the older climap reconstructions whereas both ice sheets were at 21 kyr bp close to their maximum extent the experiments also indicate that their maximum volumes were reached only by 16 5 kyr bp greenland and 10 kyr bp antarctica equal to an additional sea level lowering of respectively 0 4 and 3 7 m holocene retreat was essentially complete by 5 kyr bp in greenland but is found to still continue today in west antarctica before reversing to growth during the next millenium the models were found to reproduce gross features of the ice sheet s history since the lgm in reasonably good agreement with available glacial geological data although observational control on ice thickness changes remains very limited

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

geochemical constraints on the regolith hypothesis for the middle pleistocene transition the transition from 41 to 100 kyr glacial cycles and concomitant increase in global ice volume 1 ma remain an enigmatic feature of late cenozoic climate here we examine the petrology mineralogy and geochemistry of the silicate fraction of tills spanning the past 2 ma from the north central united states to evaluate the hypothesis that this so called middle pleistocene transition mpt occurred by erosion of regolith and subsequent exposure of underlying canadian shield bedrock by the laurentide ice sheet these data indicate that late pliocene tills are depleted in crystalline lithologies unstable minerals and major element oxides derived from plagioclase and ferromagnesians and are enriched in kaolinite quartz iron oxides tio2bearing resistates and meteoric 10 be in contrast early and middle pleistocene tills show enrichment in crystalline lithologies stable minerals and major oxides derived from plagioclase and ferromagnesians and depletion in meteoric 10 be whereas late pleistocene tills show major element concentrations that are most similar to that of fresh shield bedrock marine isotope records of sr os and hf show significant changes around the mpt that are consistent with the removal of a regolith and the exhumation of fresh silicate bedrock these results indicate that ice sheets initially expanded on highly weathered bedrock and progressively exhumed a fresher rock source thereby supporting the hypothesis that a change in the composition of the substrate underlying ice sheets best explains the origin of the mpt d 2004 elsevier b v all rights reserved

high frequency climate linkages between the north atlantic and the mediterranean during marine oxygen isotope stage 100 mis100 high resolution records of mediterranean and north atlantic deep sea sediments indicate that rapid changes in hydrology and climate occurred during marine oxygen isotope stage 100 mis100 at 2 52 ma which exhibits characteristics similar to late pleistocene dansgaard oeschger bond cycles and heinrich events as in the late pleistocene north atlantic oceanographic and atmospheric changes were probably transmitted into the mediterranean by some combination of surface water inflow and atlantic mediterranean atmospheric pressure gradients our data suggest that the mechanism s responsible for sub milankovitch and millennial scale climate oscillations were the same over at least the past 2 6 ma notwithstanding the transition from the 41 kyr dominated glacial cycles of the late pliocene to the 100 kyr cycles of the late pleistocene

elastic dislocation modeling of wrinkle ridges on mars wrinkle ridges are one of the most common landforms on mars although it is generally agreed that they are compressional tectonic features formed by folding and thrust faulting there is no consensus on the number of faults involved the geometry of the faults or the maximum fault depth the topography of martian wrinkle ridges in solis planum and lunae planum has been studied using mola data as determined in previous studies the topography shows that most wrinkle ridges are a composite of two landforms a broad low relief arch and a superimposed ridge constrained by mola topographic profiles the geometry and parameters of the faults associated with wrinkle ridges have been modeled the best fits are obtained with a blind listric thrust fault that flattens into a decollement the listric fault geometry is approximated by a series of linear connecting segments with varying dips the major morphologic elements of wrinkle ridges can be matched by varying the displacement on the different fault segments modeling of large scale wrinkle ridges indicates that the maximum depth of faulting or depth to the decollement is about 4 5 km this may correspond to the depth of the contact between the ridged plains volcanic sequence and the underlying megabreccia the results suggest that wrinkle ridge thrust faults are shallow rooted and reflect thin skinned deformation

the accuracy of mid pliocene δ 18 o based ice volume and sea level reconstructions abstract understanding the sensitivity of the polar ice caps to a modest global warming 2 3 c above preindustrial is of paramount importance if we are to accurately predict future sea level change knowledge that will inform both social and economic policy in the coming years however decades of study of the pliocene 2 6 5 3 ma an epoch in recent earth history characterized by atmospheric co2 levels similar to today have so far failed to provide definitive sea level and ice volume estimates for that time here we review the sources of uncertainty in the paired mg ca 18o methodology used to estimate past sea level ice volume and ocean temperature as well as discuss common assumptions that may bias our interpretation of ocean geochemical records including the lr04 benthic 18o stack a global compilation of 57 oxygen isotope records that forms the standard template of climate change history for the last 5 3 million years

the first glacial maximum in north america despite marine evidence for at least 50 pliocene pleistocene ice sheet advances only the most recent one has been accurately reconstructed from terrestrial evidence because there are few techniques for dating older glacial deposits here we show that the cosmic ray produced nuclides beryllium 10 and aluminum 26 can be used to date tills that overlie paleosols

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

a coupled climate ice sheet modeling approach to the early cenozoic history of the antarctic ice sheet abstract the sudden widespread glaciation of antarctica and the associated shift toward colder temperatures near the eocene oligocene boundary 34 ma represents one of the most fundamental reorganizations of the global climate system recognized in the geologic record this glacial inception and the subsequent evolution of the early east antarctic ice sheet eais are simulated using a new coupled global climate dynamical ice sheet model accounting for the paleogeography greenhouse gas concentrations changing orbital parameters and varying ocean heat transport suites of long 105 yr climate ice sheet simulations are used to investigate the effects of declining atmospheric co2 compared to those of the tectonic opening of southern ocean gateways and the timing of mountain uplift in the antarctic interior in contrast to the established paradigm for the glaciation of antarctica which centers on the opening of the southern ocean gateways and the thermal isolation of the continent our results show that declining cenozoic pco2 may have played the dominant role first small isolated ice caps formed on the highest antarctic plateaus then as a co2 threshold between 3 and 2 pre industrial level pal was crossed height mass balance feedbacks were initiated during orbital periods with cold austral summers triggering much larger highly dynamic terrestrial ice sheets as co2 continued to decline these isolated ice caps eventually merged into a permanent continental scale eais in our model neither the opening of the southern ocean gateways nor mountain uplift significantly affected the timing of the major ice sheet transition given a scenario of gradually declining co2 from 4 to 2 pal over 10 million years around the eocene oligocene boundary

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

fluvial tidal and storm sedimentation in the chilhowee group lower cambrian northeastern tennessee u s a the lower cambrian chilhowee group of northeastern tennessee consists of the unicoi hampton and erwin formations and is divided into four facies the conglomerate facies occurs only within the lower 200 m of measured section the unicoi formation and consists of fine grained to pebbly quartz wacke with rare thin beds of laminated siltstone low angle to horizontally laminated fine grained sandstone with laminae and lenses of granules and pebbles represents upper flow regime overbank deposition within a braided stream system that was close to a coastline medium scale planar tabular cross stratified conglomerate in which megaripple bedforms are preserved is interpreted as representing deposition in interbar pools of braided channels as flood stage waned and larger bedforms ceased to migrate large scale planar tabular cross stratified conglomerate beds represent migration of large transverse bars within a broad braided stream channel during high flood stage the sandstone facies occurs throughout the chilhowee group and is therefore interbedded with all other facies it consists of mainly medium to very coarse grained subarkosic to arkosic arenite thinly interbedded laminated siltstone and sandstone which may exhibit wavy or lenticular bedding represents deposition during slack water periods between ebb and flood tides large scale planar tabular and trough cross stratification reflects deposition within the deepest areas of subtidal channels whereas medium scale cross stratification represents deposition in shallower water on shoals separating channels fining and thinning upward sequences most likely resulted from the longshore migration of channels and shoals the hummocky facies occurs only in the erwin formation and consists of horizontally laminated to hummocky stratified fine grained arkosic to subarkosic arenite interbedded with equal amounts of bioturbated mudstone it represents deposition between storm and fairweather wave base by combined flow storm currents the quartz arenite facies is characterized by an absence of fine grained units and lithologically consists of a super mature medium to coarse grained quartz arenite large scale planar tabular cross stratification and abundant low angle cross stratification with rare symmetrical ripples lower quartz arenite facies occurs interbedded with the braided fluvial conglomerate facies and was deposited within either a ridge and runnel system or a system of nearshore bars large scale planar tabular cross stratification upper quartz arenite facies which forms the top of two 40 m thick coarsening upward sequences of the type hummocky faciessandstone faciesquartz arenite facies probably represents deposition on sand ridges that formed on a sand starved shelf as transgression caused the detachment and reworking of shoreface channel shoal couplets palaeocurrent data for the chilhowee group are unimodal but widely dispersed from 0 to 180 and exhibit a minor mode to the west the data are interpreted to reflect the influence of longshore tidal and storm currents the ichnofossil assemblage changes upsection from one characterized only by paleophycus to a skolithos ichnofacies and finally to a cruziana ichnofacies the facies sequence biogenic and palaeocurrent data reflect the interaction through time of i non marine and marine processes and 2 transgression coupled with shoreline progradation the chilhowee group represents an overall deepening from terrestrial deposition to a marine shoreface that experienced both longshore and tidal currents and finally to a storm shelf environment that periodically shoaled upward

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

atmospheric carbon dioxide concentration across the mid pleistocene transition the dominant period of pleistocene glacial cycles changed during the mid pleistocene from 40 000 years to 100 000 years for as yet unknown reasons here we present a 2 1 million year record of sea surface partial pressure of co2 pco2 based on boron isotopes in planktic foraminifer shells which suggests that the atmospheric partial pressure of co2 pco2 was relatively stable before the mid pleistocene climate transition glacial pco2 was approximately 31 microatmospheres higher before the transition more than 1 million years ago but interglacial pco2 was similar to that of late pleistocene interglacial cycles 450 000 years ago these estimates are consistent with a close linkage between atmospheric co2 concentration and global climate but the lack of a gradual decrease in interglacial pco2 does not support the suggestion that a long term drawdown of atmospheric co2 was the main cause of the climate transition