did antarctica initiate the ice age cycles at the end of the pliocene epoch about 2 6 million years ago a sustained period of global cooling coincided with the growth of continental ice sheets over europe and north america since then these ice sheets have periodically grown and collapsed more than 50 times driving global sea level fluctuations of more than 100 m what caused this bipolar glacial world on page 847 of this issue woodard et al 1 show that the ice sheets began to grow gradually before 2 7 million years ago this gradual buildup led to a more efficient heat transport between the atlantic and pacific abyssal oceans thus resulting in an atlantic cooling

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

co2 over the past 5 million years continuous simulation and new δ11b based proxy data during the past five million yrs benthic 18o records indicate a large range of climates from warmer than today during the pliocene warm period to considerably colder during glacials antarctic ice cores have revealed pleistocene glacial interglacial co2 variability of 60 100 ppm while sea level fluctuations of typically 125 m are documented by proxy data however in the pre ice core period co2 and sea level proxy data are scarce and there is disagreement between different proxies and different records of the same proxy this hampers comprehensive understanding of the long term relations between co2 sea level and climate here we drive a coupled climate ice sheet model over the past five million years inversely forced by a stacked benthic 18o record we obtain continuous simulations of benthic 18o sea level and co2 that are mutually consistent our model shows co2 concentrations of 300 to 470 ppm during the early pliocene furthermore we simulate strong co2 variability during the pliocene and early pleistocene these features are broadly supported by existing and new 11b based proxy co2 data but less by alkenone based records the simulated concentrations and variations therein are larger than expected from global mean temperature changes our findings thus suggest a smaller earth system sensitivity than previously thought this is explained by a more restricted role of land ice variability in the pliocene the largest uncertainty in our simulation arises from the mass balance formulation of east antarctica which governs the variability in sea level but only modestly affects the modeled co2 concentrations

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

geology of the wilkes land sub basin and stability of the east antarctic ice sheet insights from rock magnetism at iodp site u1361 abstract iodp expedition 318 drilled site u1361 on the continental rise offshore of adelie land and the wilkes subglacial basin the objective was to reconstruct the stability of the east antarctic ice sheet eais during neogene warm periods such as the late miocene and the early pliocene the sedimentary record tells a complex story of compaction and erosion thus hiatuses teasing out the paleoenvironmental implications is essential for understanding the evolution of the eais anisotropy of magnetic susceptibility ams is sensitive to differential compaction and other rock magnetic parameters like isothermal remanence and anhysteretic remanence are very sensitive to changes in the terrestrial source region in general highly anisotropic layers correspond with laminated clay rich units while more isotropic layers are bioturbated and have less clay layers enriched in diatoms are associated with the latter which also have higher ba al ratios consistent with higher productivity higher anisotropy layers have lower porosity and moisture contents and have fine grained magnetic mineralogy dominated by maghemite the more oxidized form of iron oxide while the lower anisotropy layers have magnetic mineralogies dominated by magnetite the different magnetic mineralogies support the suggestion based on isotopic signatures by cook et al 2013 of different source regions during low productivity cooler and high productivity warmer times these two facies were tied to the coastal outcrops of the lower paleozoic granitic terranes and the ferrar large igneous province in the more inland wilkes subglacial basin respectively here we present evidence for a third geological unit one eroded at the boundaries between the high and low clay zone with a hard mostly hematite dominated magnetic mineralogy this unit likely outcrops in the wilkes subglacial basin and could be hydrothermally altered beacon sandstone similar to that detected by craw and findlay 1984 in taylor valley or the equivalent to the elatina formation in the adelaide geosyncline in southern australia schmidt and williams 2013 correlation of the hard events with global oxygen isotope stacks of zachos et al 2001 and lisiecki and raymo 2005 suggest that the source region was eroded during times with higher global ice volume

orbital forcing of the east antarctic ice sheet during the pliocene and early pleistocene the pliocene and early pleistocene between 5 3 and 0 8 million years ago span a transition from a global climate state that was 2 3 c warmer than present with limited ice sheets in the northern hemisphere to one that was characterized by continental scale glaciations at both poles growth and decay of these ice sheets was paced by variations in the earth s orbit around the sun however the nature of the influence of orbital forcing on the ice sheets is unclear particularly in light of the absence of a strong 20 000 year precession signal in geologic records of global ice volume and sea level here we present a record of the rate of accumulation of iceberg rafted debris oshore from the east antarctic ice sheet adjacent to the wilkes subglacial basin between 4 3 and 2 2 million years ago we infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice sheet margin retreat in the warmer part of the record between 4 3 and 3 5 million years ago spectral analyses show a dominant periodicity of about 40 000 years subsequently the powers of the 100 000 year and 20 000 year signals strengthen we suggest that as the southern ocean cooled between 3 5 and 2 5 million years ago the development of a perennial sea ice field limited the oceanic forcing of the ice sheet after this threshold was crossed substantial retreat of the east antarctic ice sheet occurred only during austral summer insolation maxima as controlled by the precession cycle

constraints on the amplitude of late pliocene eustatic sea level fluctuations new evidence from the new zealand shallow marine sediment record since 2 5 ma global eustatic sea level fluctuations have driven recurrent transgressions and regressions of the shoreline across the world9s continental shelves the resulting shallow marine sedimentary record is cyclothemic each cyclothem corresponding to a single milankovitch climatic or sea level cycle wanganui basin new zealand contains one of the most complete late neogene shallow marine stratigraphic records in the world in the form of a continuous cyclostratigraphy representing every 41 k y and 100 k y sea level cycle since oxygen isotope stage 104 ca 2 6 ma a eustatic sea level curve is derived for oxygen isotope stages 100 74 from high resolution faunal paleobathymetric subsidence and stratigraphic analyses of 12 superposed shallow marine cyclothems in the rangitikei river section wanganui basin between 2 6 and 2 0 ma minimum amplitudes of eustatic sea level fluctuations ranged from 110 20 m stages 100 99 to 25 10 m stages 76 75 these independently derived fluctuations are 20 larger than previous estimates and imply greater climatic variability during the onset of major northern hemisphere ice ages

oxygen isotope mass balance constraints on pliocene sea level and east antarctic ice sheet stability the mid pliocene warm period mpwp 3 3 2 9 ma with reconstructed atmospheric p co2 of 350 450 ppm represents a potential analogue for climate change in the near future current highly cited estimates place mpwp maximum global mean sea level gmsl at 21 10 m above modern requiring total loss of the greenland and marine west antarctic ice sheets and a substantial loss of the east antarctic ice sheet with only a concurrent 2 3 c rise in global temperature many estimates of pliocene gmsl are based on the partitioning of oxygen isotope records from benthic foraminifera 18ob into changes in deep sea temperatures and terrestrial ice sheets these isotopic budgets are underpinned by the assumption that the 18o of antarctic ice 18oi was the same in the pliocene as it is today and while the sensitivity of 18ob to changing meltwater 18o has been previously considered these analyses neglect conservation of 18o 16o in the ocean ice system using well calibrated 18o temperature relationships for antarctic precipitation along with estimates of pliocene antarctic surface temperatures we argue that the 18oi of the pliocene antarctic ice sheet was at minimum 1 4 higher than present assuming conservation of 18o 16o in the ocean ice system this requires lower pliocene seawater 18o without a corresponding change in ice sheet mass this effect alone accounts for 5 20 of the 18ob difference between the mpwp interglacials and the modern with this amended isotope budget we present a new pliocene gmsl estimate of 9 13 5 m above modern which suggests that the east antarctic ice sheet is less sensitive to radiative forcing than previously inferred from the geologic record

glacial induced closure of the panamanian gateway during marine isotope stages mis 95 100 2 5 ma the final phase of the closure of the panamanian gateway and the intensification of northern hemisphere glaciation nhg both occurred during the late pliocene glacial interglacial g ig variations in sea level might therefore have had a significant impact on the remaining connections between the east pacific and the caribbean here we present combined foraminiferal mg ca and 18o measurements from ocean drilling program odp site 1241 from the east pacific and odp site 999 from the caribbean the studied time interval covers the first three major g ig marine isotope stages mis 95 100 2 5 ma 2 5 ma after the intensification of nhg analyses were performed on the planktonic foraminifera neogloboquadrina dutertrei and globigerinoides sacculifer representing water mass properties in the thermocline and the mixed layer respectively changes in sea water temperature relative salinity and water column stratification strongly suggest that the panamanian gateway temporarily closed during glacial mis 98 and 100 as a result of changes in ice volume equivalent to a drop in sea level of 60 90 m reconstructed sea surface temperatures sst from g sacculifer show a glacial decrease of 2 5 c at site 1241 but increases of up to 3 c at site 999 during glacial mis 98 and 100 suggesting that the panamanian gateway closed during these glacial periods the mg ca temperatures of n dutertrei remain relatively stable in the east pacific but do show a 3 c warming in the caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification we infer that the glacial closure of the gateway allowed the western atlantic warm pool to extend into the southern caribbean increasing sst g sacculifer and deepening the thermocline n dutertrei additionally ice volume appears to have become large enough during mis 100 to survive the relatively short lasting interglacial mis 99 so that the gateway remained closed towards the end of mis 98 during mis 97 and into mis 96 temperatures on both sides are mostly similar suggesting water masses exchanged again additionally caribbean variations in sst and 18owater follow a precession like cyclicity rather than the obliquity controlled variations characteristic of the east pacific and many other tropical areas suggesting that regional atmospheric processes related to the trade winds and the intertropical convergence zone itcz had a dominant impact in the caribbean

amplitude of late miocene sea level fluctuations from karst development in reef slope deposits se spain abstract a prograding late miocene carbonate platform in southern spain revealing different sea level pinning points was analysed with the aim to increase the accuracy of reconstruction of past sea level changes these pinning points are distinct diagenetic zones dz and the position of reef framework deposits dz1 is defined by the dissolution of bioclastic components and dz2 by calcitic cement precipitation in dissolution pores calcite cements are granular and radiaxial fibrous and are of meteoric origin as deduced from cathodoluminescence edx spectroscopy as well as from 13c and 18o isotope analyses dz3 has moldic porosity after aragonitic bioclasts with minor granular calcitic cements dz1 and dz2 indicate karstification and the development of a coastal palaeoaquifer during a sea level lowstand dz3 diagenetic features are related to the final subaerial exposure of the section during the messinian salinity crisis facies and diagenetic data reveal a complete cycle of sea level fall 23 1 m and rise 31 1 m a robust age model based on magneto and cyclostratigraphy for these deposits places this cycle between 5 89 and 5 87 ma therefore for the first time this work allows a direct comparison of an outcrop with a pelagic marine proxy record of a specific neogene sea level fluctuation

constraints on global mean sea level during pliocene warmth reconstructing the evolution of sea level during past warmer epochs such as the pliocene provides insight into the response of sea level and ice sheets to prolonged warming1 although estimates of the global mean sea level gmsl during this time do exist they vary by several tens of metres2 4 hindering the assessment of past and future ice sheet stability here we show that during the mid piacenzian warm period which was on average two to three degrees celsius warmer than the pre industrial period5 the gmsl was about 16 2 metres higher than today owing to global ice volume changes and around 17 4 metres when thermal expansion of the oceans is included during the even warmer pliocene climatic optimum about four degrees celsius warmer than pre industrial levels 6 our results show that the gmsl was 23 5 metres above the present level with an additional 1 6 metres from thermal expansion we provide six gmsl data points ranging from 4 39 to 3 27 million years ago that are based on phreatic overgrowths on speleothems from the western mediterranean mallorca spain this record is unique owing to its clear relationship to sea level its reliable u pb ages and its long timespan which allows us to quantify uncertainties on potential uplift our data indicate that ice sheets are very sensitive to warming and provide important calibration targets for future ice sheet models7 using phreatic overgrowths on speleothems sea level during the mid piacenzian warm period which was about two to three degrees celsius warmer than the pre industrial period is shown to have been about 16 metres higher than today

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

antarctic bedrock topography uncertainty and ice sheet stability antarctic bedrock elevation estimates have uncertainties exceeding 1 km in certain regions bedrock elevation particularly where the bedrock is below sea level and bordering the ocean can have a large impact on ice sheet stability we investigate how present day bedrock elevation uncertainty affects ice sheet model simulations for a generic past warm period based on the mid pliocene although these uncertainties are also relevant to present day and future ice sheet stability we perform an ensemble of simulations with random topographic noise added with various length scales and with amplitudes tuned to the uncertainty of the bedmap2 data set total antarctic ice sheet retreat in these simulations varies between 12 6 and 17 9 m equivalent sea level rise after 3 kyrs of warm climate forcing this study highlights the sensitivity of ice sheet models to existing uncertainties in bedrock elevation and the ongoing need for new data acquisition

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

east asian winter monsoon evolution since the late pliocene based on a pollen record from lake xingkai northeast asia a 328 58 m drill core xk12 was recovered from lacustrine alluvial sediments in the xingkai basin northeast china with the aim of obtaining a high resolution pollen record of east asian winter monsoon eawm evolution since 3 6 ma an index based on the pollen record of thermophilous trees and terrestrial herbs is used as an indicator of winter temperature conditions controlled by the eawm at the glacial interglacial scale primary age control was established based on lithostratigraphy and magnetostratigraphy and then the pollen index was correlated to the lr04 global benthic 18 o record and finally tuned to earth orbital obliquity to produce a high resolution astronomical time scale the pollen record indicates that the eawm underwent two stepwise enhancements at 2 8 and 1 6 ma these events are consistent with paleoclimatic records of mean quartz grain size from the chinese loess plateau and they are also in accord with the initiation and intensification of northern hemisphere glaciation our findings suggest that the variability of the eawm since 3 6 ma was primarily controlled by changes in global ice volume and climatic cooling

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

east antarctic deglaciation and the link to global cooling during the quaternary evidence from glacial geomorphology and 10be surface exposure dating of the sor rondane mountains dronning maud land abstract reconstructing past variability of the antarctic ice sheets is essential to understand their stability and to anticipate their contribution to sea level change as a result of future climate change recent studies have reported a significant decrease in thickness of the east antarctic ice sheet eais during the last several million years however the geographical extent of this decrease and subsequent isostatic rebound remain uncertain in this study we reconstruct the magnitude and timing of ice sheet retreat at the sor rondane mountains in dronning maud land east antarctica based on detailed geomorphological survey cosmogenic exposure dating and glacial isostatic adjustment modeling three distinct deglaciation phases are identified for this sector during the quaternary based on rock weathering and 10 be surface exposure data we estimate that the ice sheet thinned by at least 500 m during the pleistocene this thinning is attributed to the reorganization of southern ocean circulation associated with global cooling into the pleistocene which reduced the transport of moisture from the southern ocean to the interior of eais the data also show that since the last glacial maximum the ice surface has lowered less than ca 50 m and that this lowering probably started after ca 14 ka this suggests that the eais in dronning maud land is unlikely to have been a major contributor to postglacial sea level rise and meltwater pulse 1a

potential antarctic ice sheet retreat driven by hydrofracturing and ice cliff failure abstract geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last 25 million years at times reaching 20 m or more above modern if correct this implies substantial variations in the size of the east antarctic ice sheet eais however most climate and ice sheet models have not been able to simulate significant eais retreat from continental size given that atmospheric co2 levels were relatively low throughout this period here we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model data conflict in response to atmospheric and ocean temperatures typical of past warm periods floating ice shelves may be drastically reduced or removed completely by increased oceanic melting and by hydrofracturing due to surface melt draining into crevasses ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing and may fail structurally if stresses exceed the ice yield strength producing rapid retreat incorporating these mechanisms in our ice sheet model accelerates the expected collapse of the west antarctic ice sheet to decadal time scales and also causes retreat into major east antarctic subglacial basins producing 17 m global sea level rise within a few thousand years the mechanisms are highly parameterized and should be tested by further process studies but if accurate they offer one explanation for past sea level high stands and suggest that antarctica may be more vulnerable to warm climates than in most previous studies

low frequency pliocene climate variability in the eastern nordic seas the pliocene 5 3 2 6 ma is often described as a relatively stable climatic period with warm temperatures characterizing high latitudes new suborbital resolved stable isotope records from ocean drilling program hole 642b in the eastern nordic seas document that the pliocene was not a stable period characterized by one climate rather seven distinct climate phases each lasting between 150 000 and 400 000 years are identified and characterized in the time interval 5 1 3 1 ma four of the transitions between the defined climate phases occurred close to an eccentricity minimum and a minimum in amplitude of change for northern hemisphere summer insolation while two occurred around an eccentricity maximum and a maximum in amplitude in insolation change hence a low frequency response of the nordic seas to insolation forcing is indicated in addition paleogeographic and related paleoceanographic changes expansion of the arctic sea ice cover and onset of northern hemisphere glaciation were important factors behind the evolving pliocene low frequency variability in the eastern nordic seas it is likely that the identified climate phases and transitions are important beyond the nordic seas due to their association with changes to both insolation and paleogeography however a strong and variable degree of diagenetic calcite overgrowth is documented for the planktic foraminifera especially influencing the planktic 18o results the absolute values and amplitude of change cannot be taken at face value

palaeoclimate east antarctica s achilles heel the east antarctic ice sheet is believed to be earth s most stable ice sheet changes in geochemical composition of offshore sediments suggest that its margin repeatedly retreated by at least 350 550 kilometres inland between 5 3 and 3 3 million years ago

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

late quaternary sea level history of saipan commonwealth of the northern mariana islands usa a test of tectonic uplift and glacial isostatic adjustment models

mid pliocene shorelines of the us atlantic coastal plain an improved elevation database with comparison to earth model predictions abstract for nearly a century the atlantic coastal plain acp of the united states has been the focus of studies investigating pliocene and pleistocene shorelines however the mapping of paleoshorelines was primarily done by using elevation contours on topographic maps here we review published geologic maps and compare them to paleoshoreline locations obtained through geomorphometric classification and satellite data we furthermore present the results of an extensive field campaign that measured the mid pliocene 3 3 2 9 ma shorelines of the atlantic coastal plain using high accuracy gps and digital elevation models we compare our new dataset to positions and elevations extracted from published maps and find that the extracted site information from earlier studies is prone to significant error both in the location and more severely in the elevation of the paleoshoreline we also investigate using geophysical modeling the origin of post depositional displacement of the shoreline from georgia to virginia in particular we correct the elevation of our shoreline for glacial isostatic adjustment gia and then compare the corrected elevation to predictions of mantle flow induced dynamic topography dt while a subset of these models does reconcile the general trends in the observed elevation of the mid pliocene shoreline local discrepancies persist these discrepancies suggests that either i the dt and gia models presented here do not capture the full range of uncertainty in the input parameters and or ii other influences such as sediment loading and unloading or local fault driven tectonics may have contributed to post depositional deformation of the mid pliocene shoreline that are not captured in the above models in this context our field measurements represent an important observational dataset with which to compare future generations of geodynamic models improvements in models for dt gia and other relevant processes together with an expanded geographically distributed set of shoreline records will ultimately be the key to obtaining more accurate estimates of eustatic sea level not only in the mid pliocene but also earlier in the cenozoic

on the identification of a pliocene time slice for data model comparison the characteristics of the mid pliocene warm period mpwp 3 264 3 025 ma bp have been examined using geological proxies and climate models while there is agreement between models and data details of regional climate differ uncertainties in prescribed forcings and in proxy data limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models this uncertainty comes in part from the reconstruction of a time slab rather than a time slice where forcings required by climate models can be more adequately constrained here we describe the rationale and approach for identifying a time slice s for pliocene environmental reconstruction a time slice centred on 3 205 ma bp 3 204 3 207 ma bp has been identified as a priority for investigation it is a warm interval characterized by a negative benthic oxygen isotope excursion 0 21 0 23 centred on marine isotope stage km5c km5 3 it occurred during a period of orbital forcing that was very similar to present day climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice with the north atlantic potentially being an important exception

planktic foraminifera shell chemistry response to seawater chemistry pliocene pleistocene seawater mg ca temperature and sea level change abstract foraminifera mg ca paleothermometry forms the basis of a substantial portion of ocean temperature reconstruction over the last 5 ma furthermore coupled mg ca oxygen isotope 18o measurements of benthic foraminifera can constrain eustatic sea level esl independent of paleo shoreline derived approaches however this technique suffers from uncertainty regarding the secular variation of the mg ca seawater ratio mg casw on timescales of millions of years here we present coupled seawater test mg ca temperature laboratory calibrations of globigerinoides ruber in order to test the widely held assumptions that 1 seawater test mg ca co vary linearly and 2 the mg ca temperature sensitivity remains constant with changing mg casw we find a nonlinear mg catest mg casw relationship and a lowering of the mg ca temperature sensitivity at lower than modern mg casw from 9 0 c 1 at mg casw 5 2 mol mol 1 to 7 5 0 9 c 1 at 3 4 mol mol 1 using our calibrations to more accurately calculate the offset between mg ca and biomarker derived paleotemperatures for four sites we derive a pliocene mg casw ratio of 4 3 mol mol 1 this mg casw implies pliocene ocean temperature 0 9 1 9 c higher than previously reported and by extension esl 30 m lower compared to when one assumes that pliocene mg casw is the same as at present correcting existing benthic foraminifera datasets for mg casw indicates that deep water source composition must have changed through time therefore seawater oxygen isotope reconstructions relative to present day cannot be used to directly reconstruct pliocene esl

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

sea level rise due to polar ice sheet mass loss during past warm periods background although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level gmsl rise over the last century mass loss from the greenland and antarctic ice sheets is expected to exceed other contributions to gmsl rise under future warming to better constrain polarice sheetresponse to warmer temperatures we draw on evidence from in terglacial periods in the geologic record that ex perienced warmer polar temperatures and higher gmsls than present coastal records of sea level from these previous warm periods dem onstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales inferring gmsl and ice volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models advances interdisciplinary studies of geo logic archives have ushered in a new era of deciphering magnitudes rates and sources of sea level rise advances in our understanding of polar ice sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea level reconstructions better ice sheet constraints and the recognition that several geophysical processes cause spatially complex patterns in sea level in particular accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea level records and has reconciled a number of site specific sea level reconstructions for warm periods that have oc curred within the past several hundred thou sand years this enables us to infer that during recent interglacial periods small increases in

limited retreat of the wilkes basin ice sheet during the last interglacial the response of the east antarctic ice sheet to global warming represents a major source of uncertainty in sea level projections thinning of the east antarctic george v and sabrina coast ice cover is currently taking place and regional ice sheet instability episodes might have been triggered in past warm climates however the magnitude of ice retreat in the past can not yet be quantitatively derived from paleo proxy records alone we propose that a runaway retreat of the george v coast grounding line and subsequent instability of the wilkes basin ice sheet would either leave a clear imprint on the water isotope composition in the talos dome region or prohibit a talos dome ice core record from the last interglacial altogether testing this hypothesis our ice sheet model simulations suggest that wilkes basin ice sheet retreat remained relatively limited during the last interglacial and provide a constraint on last interglacial east antarctic grounding line stability

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

mid pliocene global land monsoon from pliomip1 simulations abstract the mid piacenzian pliocene warm period approximately 3 3 3 0 ma monsoon not only provides us with a useful insight into the future monsoon under a warming scenario with high atmospheric co2 concentration but is also hypothesized to play a key role in climate feedback through impact on the carbon cycle on a geological timescale the monsoon evolution over time is one key to test this hypothesis in this sense we examine the mid piacenzian global land monsoon area glma precipitation glmp and glmp intensity glmpi using all available model data from the pliocene model intercomparison project phase 1 pliomip1 relative to the pre industrial period both the glma and glmp increase in the mid piacenzian and by an average of 7 3 and 5 8 respectively on a large scale the increased glmp comes mainly from northern africa asia and northern australia quantitatively it is the variation of glma not of glmpi that makes a major contribution to the glmp change further analysis reveals that anomalous inland water vapor transportation due to the reduced large scale meridional thermal contrast in the mid to upper troposphere together with the variation of vertical moisture advection and evaporation explains most of the global land monsoon changes a model data comparison shows that the simulated monsoon precipitation variations are roughly consistent with the reconstructions in northern africa asia northern australia central america and eastern south america moreover the intensified mid piacenzian asian monsoon which is supported by both simulations and reconstructions or an overall intensified global land monsoon is hypothesized to contribute to the lowering of atmospheric co2 concentration and the subsequent onset of the sustained major northern hemisphere glaciation

on climate and abyssal circulation in the atlantic ocean during late pliocene marine isotope stage m2 3 3 million years ago abstract marine isotope stage mis m2 3 3 ma is an isolated cold stage punctuating the benthic oxygen isotope 18o stratigraphy of the warm piacenzian interval of the late pliocene epoch the prominent 0 65 18o increase that defines mis m2 has prompted debate over the extent to which it signals an early prelude to the rhythmic extensive glaciations of the northern hemisphere that characterise the quaternary and raised questions about the forcing mechanisms responsible recent work suggests that co2 storage in the deep atlantic ocean played an important role in these events but detailed reconstructions of deep ocean chemical stratification are needed to test this idea and competing hypotheses here we present new records of the nd isotope composition of fish debris and 13c and b ca ratios of benthic foraminifera from the northwest and southeast atlantic ocean our novel geochemical data show that in contrast to major quaternary glaciations such as mis 2 21 ka and mis 100 2 52 ma the deep north atlantic ocean was weakly chemically stratified during mis m2 we show that southern component water incursion into the atlantic ocean was limited to the deep south atlantic basin during mis m2 and peaked well before 10 15 kyr the atmospheric co2 minimum our findings imply that the deep atlantic ocean was not the principle sink of co2 sequestered from the atmosphere during mis m2 implicating a different co2 storage deep water reservoir mechanism presumably southern component water incursion into the pacific ocean weak chemical stratification in the deep atlantic ocean during mis m2 relative to mis 100 and 2 suggests comparatively active atlantic meridional overturning circulation that suggestion is consistent with the warmth of the high latitude north atlantic during mis m2 surface water temperatures cooled during m2 but only close to holocene values our findings may help to explain the paucity of evidence for extensive early glaciation of the northern hemisphere during m2 but leave open the possibility of ice sheet advance on antarctica

the mid pliocene sea level conundrum glacial isostasy eustasy and dynamic topography abstract determining eustatic sea level during the mid pliocene warm period 3 3 to 2 9 ma has been a central but elusive goal in the study of past warm climates estimates of eustatic sea level based on geologic data span a broad range variation that we now recognize is due in part to geographically varying post depositional displacement caused by glacial isostatic adjustment and dynamic topography in this study we combine field observations and glacial isostatic adjustment modeling to estimate the dynamic topography signal in three areas that are important to paleo sea level studies of the mid pliocene warm period south africa west australia and southeastern united states we show that dynamic topography played a significant role in the post depositional displacement of pliocene and even younger pleistocene shorelines in this regard we provide a robust paleo sea level elevation data set corrected for glacial isostatic adjustment that can be used to evaluate predictions from mantle flow models of dynamic topography

the prism pliocene palaeoclimate reconstruction time for a paradigm shift global palaeoclimate reconstructions have been invaluable to our understanding of the causes and effects of climate change but single temperature representations of the oceanic mixed layer for dat

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

pliocene deglacial event timelines and the biogeochemical response offshore wilkes subglacial basin east antarctica abstract significantly reduced ice coverage in greenland and west antarctica during the warmer than present pliocene could account for 10 m of global mean sea level rise any sea level increase beyond this would require contributions from the east antarctic ice sheet eais previous studies have presented low resolution geochemical evidence from the geological record suggesting repeated ice advance and retreat in low lying areas of the eais such as the wilkes subglacial basin however the rates and mechanisms of retreat events are less well constrained here we present orbitally resolved marine detrital sediment provenance data paired with ice rafted debris and productivity proxies during three time intervals from the middle to late pliocene at iodp site u1361a offshore of the wilkes subglacial basin our new data reveal that pliocene shifts in sediment provenance were paralleled by increases in marine productivity while the onset of such changes was marked by peaks in ice rafted debris mass accumulation rates the coincidence of sediment provenance and marine productivity change argues against a switch in sediment delivery between ice streams and instead suggests that deglacial warming triggered increased rates of iceberg calving followed by inland retreat of the ice margin timescales from the onset of deglaciation to an inland retreated ice margin within the wilkes subglacial basin are on the order of several thousand years this geological evidence corroborates retreat rates determined from ice sheet modeling and a contribution of 3 to 4 m of equivalent sea level rise from one of the most vulnerable areas of the east antarctic ice sheet during interglacial intervals throughout the middle to late pliocene

modeling the oxygen isotope composition of the antarctic ice sheet and its significance to pliocene sea level recent estimates of global mean sea level based on the oxygen isotope composition of mid pliocene benthic foraminifera vary from 9 to 21 m above present which has differing implications for the past stability of the antarctic ice sheet during an interval with atmospheric co 2 comparable to present here we simulate the oxygen isotope composition of the antarctic ice sheet for a range of configurations using isotope enabled climate and ice sheet models we identify which ice sheet configurations are consistent with the oxygen isotope record and suggest a maximum contribution from antarctica to the mid pliocene sea level highstand of 13 m we also highlight that the relationship between the oxygen isotope record and sea level is not constant when ice is lost from deep marine basins which has important implications for the use of oxygen isotopes as a sea level proxy

technologies for retrieving sediment cores in antarctic subglacial settings accumulations of sediment beneath the antarctic ice sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies this paper briefly reviews the history of sediment sampling in subglacial environments it then outlines some of the technological challenges and constraints in developing the corers being used in sub ice shelf settings e g george vi ice shelf and larsen ice shelf under ice streams e g rutford ice stream at or close to the grounding line e g whillans ice stream and in subglacial lakes deep under the ice sheet e g lake ellsworth the key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures

high tide of the warm pliocene implications of global sea level for antarctic deglaciation we obtained global sea level eustatic estimates with a peak of 22 m higher than present for the pliocene interval 2 7 3 2 ma from backstripping in virginia united states new zealand and enewetak atoll north pacifi c ocean benthic foraminiferal 18 o values and mg ca 18 o estimates statistical analysis indicates that it is likely 68 confi dence interval that peak sea level was 22 5 m higher than modern and extremely likely 95 that it was 22 10 m higher than modern benthic foraminiferal 18 o values appear to require that the peak was 20 21 m our estimates imply loss of the equivalent of the greenland and west antarctic ice sheets and some volume loss from the east antarctic ice sheet and address the longstanding controversy concerning the pliocene stability of the east antarctic ice sheet

the transient response of ice volume to orbital forcing during the warm late pliocene examining the nature of ice sheet and sea level response to past episodes of enhanced greenhouse gas forcing may help constrain future sea level change here for the first time we present the transient nature of ice sheets and sea level during the late pliocene the transient ice sheet predictions are forced by multiple climate snapshots derived from a climate model set up with late pliocene boundary conditions forced with different orbital forcing scenarios appropriate to two marine isotope stages miss mis km5c and k1 our results indicate that during mis km5c both the antarctic and greenland ice sheets contributed to sea level rise relative to present and were relatively stable insolation forcing between the hemispheres was out of phase during mis k1 and led to an asynchronous response of ice volume globally therefore when variations of precession were high inferring the behavior of ice sheets from benthic isotope or sea level records is complex

the slanicul de buzau section a unit stratotype for the romanian stage of the dacian basin plio pleistocene eastern paratethys abstract climatic changes cause large paleoenvironmental responses in semi isolated basins we analyze here the sedimentary successions of the dacian basin romania to evaluate late pliocene and early pleistocene paleoenvironmental changes through macro and micropaleontology these changes are dated by creating a magnetostratigraphic time frame for two long and continuous sections with a combined total thickness of 2850 m the studied succession spans the time interval between 4 7 ma and 1 6 ma and records both the mid pliocene warm period 3 3 2 9 ma and the onset of large scale glaciations on the northern hemisphere 2 7 ma due to progressive basin infill the paleoenvironment changes from brackish to fluvio lacustrine with a major extinction event of lymnocardiine bivalves around 4 15 ma rich and dominantly freshwater mollusk and ostracod faunas develop from this moment onwards between 3 2 ma and 2 95 ma the reappearance of lymnocardiines identifies a short moment of higher salinities the previously identified plescoi event in time this correlates closely to the warmest interval of the pliocene and is therefore most likely related to connectivity to the black sea during maximum sea level after the climatic optimum deposition continues in a fluvio deltaic setting with only scarce finds of fauna increasing amounts of coarse grained fluvial sediments show a close relationship with the progressive cooling during the pleistocene

palynological study of paleoclimate and paleoceanographic changes in the eastern south korea plateau east sea during the plio pleistocene climate transition abstract a palynological study was performed using the core obtained from the integrated ocean drilling program iodp expedition 346 site u1430 in the eastern south korea plateau in the east sea to reveal variability of paleoclimate and paleoceanography during the late pliocene to early pleistocene climate transition period 56 0 68 0 meters below sea floor mbsf two pollen and dinocyst zones are established with a boundary at ca 3 0 ma prior to ca 3 0 ma first pollen and dinocyst zone long term oscillation of the east asian winter monsoon eawm is indicated by fluctuations in the abundance of pollen taxa representing cold dry and cool wet climates after ca 3 0 ma second pollen and dinocyst zone an increase in cold dry conifer pollen indicates an enhanced and stable eawm in addition the prevalence of the xerophytic herb artemisia increases markedly after 3 0 ma suggesting open grassland on the exposed south yellow sea shelf during the sea level lowstand under cold dry climate conditions artemisia pollen are interpreted as having been delivered to the coast through fluvial channels in this grassland environment and subsequently transported to the east sea by inflow of a weak tsushima warm current twc through the narrow korea strait the twc intrusion signal is represented by an influx of tuberculodinium vancampoae a warm water dinoflagellate species in the western pacific region the high abundances of cold dry conifer pollen and cold water dinocyst elements after ca 2 8 ma suggest an intensified eawm meanwhile a short term increase in moisture loving tsuga pollen after ca 2 5 ma was likely due to soil moisture derived from snowfall caused by evaporation of heated seawater from the weak twc in the east sea under cold climate conditions the palynological studies reported here help verify the linkages between the eawm twc precipitation and vegetation responses in around the east sea region

hydrological and temperature change in arctic siberia during the intensification of northern hemisphere glaciation abstract the pliocene epoch represents an analog for future climate with atmospheric carbon dioxide concentrations and continental configurations similar to present although the presence of multiple positive feedbacks in polar regions leads to amplified climatic changes conditions in the pliocene terrestrial arctic are poorly characterized high latitude sedimentary records indicate that dramatic glacial advance and decay occurred in the pliocene arctic with attendant effects on global sea level understanding these deposits and their implications for earth s future requires developing a sense of climatic evolution across the pliocene pleistocene transition and during the intensification of northern hemisphere glaciation inhg 2 7 million yr ago ma here we reconstruct arctic terrestrial environmental change from 2 82 2 41 ma marine isotope stages mis g10 95 using the distribution of branched glycerol dialkyl glycerol tetraethers brgdgts and the isotopic composition of plant leaf waxes dwax in a sedimentary archive from lake el gygytgyn northeast russia our records reveal changes in proxy behavior across this interval that we attribute to changing boundary conditions including sea level sea ice vegetation and pco2 during different miss we find that brgdgt temperatures and dwax are decoupled for most of the record although both show an increasing range of glacial interglacial variability following inhg dwax is stable from mis g10 g4 despite changes in vegetation and temperature suggesting different sources or pathways for moisture to lake el gygytgyn during the late pliocene

closing an early miocene astronomical gap with southern ocean δ18o and δ13c records implications for sea level change we present orbital scale resolution 10 kyr benthic foraminiferal 18o and 13c records from the kerguelen plateau ocean drilling program odp sites 751 and 747 from 14 5 20 0 ma spanning the miocene climate optimum mco 15 17 ma our records fill a critical gap from 17 18 ma a time when many other deep sea records are affected by dissolution we tested the fidelity of published magneto biostratigraphic age models for these sites by astronomically tuning to the 405 kyr eccentricity cycle a comparison of spectral estimates between the untuned and tuned records as well as coherency with laskar s 2004 eccentricity solution revealed quasi 100 kyr cyclicity in 18o and 13c there is only a weak signal associated with the 41 kyr obliquity cycle likely due to the 10 kyr sampling limiting resolution the 18o variations point to persistent 405 and quasi 100 kyr modulations of temperature and sea level changes through the early to middle miocene as predicted by astronomical solutions with changing dominance of the 100 and 41 kyr beat comparison of 18o records with early to middle miocene sequences from the new jersey shelf northeast australian margin bahamas and maldives suggests that the dominant sea level period preserved is the 1 2 myr obliquity cycle with sequence boundaries associated with 18o increases or maxima on the new jersey margin higher order sequences reflect the quasi 100 kyr eccentricity cycles as modulated by 405 kyr cycles we suggest that nesting of stratigraphic cycles is a function of 1 pervasive though changing milankovitch forcing of global mean sea level change and 2 preservation that depends on sufficient sediment supply and accommodation

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

composite sequence stratigraphic patterns in alluvial to shallow marine successions examples from the piacenzian of the valdelsa basin central italy abstract the sequence stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record a similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the piacenzian strata of the southern valdelsa basin central italy specifically we integrated facies analysis paleopedology paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic sedimentary and biotic systems to piacenzian multifrequency relative sea level fluctuations this integrated approach resulted in the definition of a composite sequence stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences referred to the 5th to 3rd order cycles of sea level fluctuations respectively a correlation with the piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea level fluctuations associates the cyclic development of fluvial coastal and shallow marine depositional systems to the mid piacenzian warm period and to the subsequent transition to the gelasian thus the glacio eustatic control prevailed on the development of the described multi scale cyclical pattern of sedimentation compared to the role played by the deformation of the northern apennines orogen

mid to late pliocene 3 3 2 6 ma global sea level fluctuations recorded on a continental shelf transect whanganui basin new zealand abstract we present a 900 m thick mid 3 3 3 0 ma to late pliocene 3 0 2 6 ma shallow marine cyclical sedimentary succession from whanganui basin new zealand that identifies paleobathymetric changes during a warmer than present interval of earth history relevant to future climate change our approach applies lithofacies sequence stratigraphy and benthic foraminiferal analyses to two continuously cored drillholes integrated with new and existing outcrop studies we construct a depositional model of orbitally paced global sea level changes on a wave graded continental shelf unlike many previous studies these shelf sediments were not eroded during sea level lowstands and thus provide the potential to reconstruct the full amplitude of glacial interglacial sea level change paleobathymetric interpretations are underpinned by analysis of extant benthic foraminiferal census data and a statistical correlation with the distribution of modern taxa in general water depths derived from foraminiferal modern analogue technique mat are consistent with variability recorded by lithofacies the inferred sea level cycles co vary with a qualitative climate record reconstructed from a census of extant pollen and spores and a modern temperature relationship a high resolution age model is established using magnetostratigraphy constrained by biostratigraphy and the dating and correlation of tephra this integrated chronostratigraphy allows the recognition of 23 individual sedimentary cycles that are correlated across the paleo shelf and a possible one to one relationship is made to deep ocean benthic oxygen isotope 18o records in general water depth changes were paced by 20 kyr duration between 3 3 and 3 0 ma after which cycle duration is 40 kyr during the late pliocene 3 0 2 6 ma this record provides a future opportunity to evaluate the amplitude and frequency of global pliocene glacio eustatic sea level change independent of the global benthic 18o record

petrographic and geochemical features of sinkhole filling deposits associated with an erosional unconformity on grand cayman abstract on grand cayman exposures of dolostones belonging to the cayman formation miocene represent an erosional unconformity that has been developing since the late pliocene 3 6 ma sinkholes that developed during this time have remained open or become partly to fully filled with various combinations of rootcrete breccias loose limestone and dolostone lithoclasts and white red and orange limestones these sinkhole filling deposits have different geochemical attributes to the neogene and pleistocene marine carbonates that form the bedrock of the island the deposits in the sinkholes formed in response to the variations of sea level climate exposure and vegetation that developed during the period when the erosional unconformity was developing the rootcrete oncoids red and orange limestones are terrestrial in origin whereas the limestone and dolostone lithoclasts and white limestones are derived from marine deposits on the erosional unconformity intense root activity led to the formation of rootcrete and terrestrial oncoids but also selectively blackening reworked marine carbonates the red and orange limestone matrices which formed under more arid conditions contrast with the other sinkhole filling deposits that formed during periods when the climate was semi arid to humid the distinctive ree signatures of the sinkhole filling deposits which are different from those of the bedrock limestones and dolostones can probably be attributed to trace amount of terra rossa and or airborne saharan derived dust that are present in those deposits

global budget of water isotopes inferred from polar ice sheets 1 water isotope ratios in ice cores and marine sediments are a key indicator of past temperature and global ice volume quantitative interpretation of these ratios requires understanding of the storage capacity and exchanges among the ocean atmosphere and cryosphere we combine numerical models of ice dynamics and tracer transport to predict bulk ice properties by simulating the fine layering of ice sheets locally validated at ice core sites the 18o 16o content of ice sheets is found to vary between the present and 20 kyr ago from 34 to 37 for greenland from 41 to 42 5 for west antarctica and always remained near 56 5 for east antarctica their combined effect on sea water 18o 16o is a 0 08 0 12 increase 20 kyr ago a 1 11 decrease if ice sheets were to vanish we confirm that ice volume changes in antarctica and greenland linearly affect ocean composition though at different rates

reductions in midlatitude upwelling favorable winds implied by weaker large scale pliocene sst gradients the early to mid pliocene 3 5 3 ma is the most recent geologic period of significant global warmth proxy records of pliocene sea surface temperature sst indicate significant and still unexplained warm anomalies of 3 c 9 c in midlatitude eastern boundary currents where present day cool temperatures are maintained by wind driven upwelling here we quantify the effect of large scale pliocene like sst patterns on the surface wind stress around the california humboldt canary and benguela midlatitude coastal upwelling sites a high resolution atmosphere model forced with pliocene sst simulates changes in surface winds that imply reductions of 10 to 50 in both coastal upwelling driven by alongshore wind stress and offshore upwelling driven by wind stress curl these changes result primarily from a reduced meridional temperature gradient which weakens the subtropical highs and a reduction in zonal land sea temperature contrast which weakens geostrophic alongshore winds these results suggest that pliocene coastal warm anomalies may result in part from atmospheric circulation changes which reduce upwelling intensity the coastal wind stress and offshore wind stress curl are shown to respond differently to incremental changes in sst topography and land surface anomalies significant decreases in simulated cloud fraction within the subtropical highs suggest that a weaker land sea temperature contrast could be maintained by cloud radiative feedbacks

brittle origins for disseminated gold mineralization in mylonite gaocun gold deposit hetai goldfield guangdong proince south china gold mineralization in the hetai goldfield in south china is almost entirely confined to a series of steeply dipping ductile shear zones generated during hercynian indosinian orogenesis of sinian host rocks approximately half of the mineralization is in the form of disseminations in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in einlets and as sulfide cement to brecciated mesoscopic quartz eins heaily influenced by the presence of disseminated mineralization all publications on hetai determine a major role for ductile deformation in the introduction of gold into the deposit the brittle deformation is typically regarded as redistributing within the host structures the gold initially introduced as a result of ductile deformation mechanisms howeer textures of the sulfides associated with the gold indicate an entirely postductile deformation timing as they display none of the features attributed to ductile deformation during the eident brittle deformation phase competence contrasts at the microscopic scale allowed fracturing to focus on the quartz sericite domain boundaries of the mylonite foliation thus permitting the introduction of auriferous fluid into the mylonite to create disseminated mineralization the control exerted by preexisting structures is further reflected in the restriction of disseminated mineralization to the quartz domains presumably because the sericite domains accommodated the deformation in a more distributed fashion seeral other lines of eidence support an origin of the hetai deposit in an upper crustal regime a similar style of disseminated mineralization to that seen in the mylonite surrounds microeinlet terminations in the brecciated quartz eins as well as oerprinting pseudotachylite which is associated with cataclasite there are also large olumes of unmineralized mylonite indicating no connection between the intensity of strain and gold grade we conclude that in structurally controlled deposits the textural category of disseminated gold mineralization can be generated either under entirely ductile or entirely brittle conditions and that microtextural eidence has to be carefully analyzed to determine the mode of formation of a deposit

high eustatic sea level during the middle pliocene evidence from the southeastern u s atlantic coastal plain the middle pliocene approximately 3 5 2 5 ma was a period of global warmth preceding the growth of major northern hemisphere ice sheets the authors report on eustatic sea level for the middle pliocene based on microspaleontologic study of marine deposits of the duplin formation of south carolina and north carolina the duplin was deposited during a middle pliocene marine transgression that formed the orangeburg scarp a prominent wave cut geomorphic paleoshoreline of the southeastern u s atlantic coastal plain they concluded that 1 the scarp in south carolina was formed mostly during the middle pliocene 3 5 3 0 ma 2 eustatic sea level was about 35 plus minus 18 m higher than modern sea level the scarp has been uplifted about 50 65 m since the middle pliocene and 3 ocean water temperatures along eastern north america were warmer when the scarp was formed that they are at present

constraints on the amplitude of mid pliocene 3 6 2 4 ma eustatic sea level fluctuations from the new zealand shallow marine sediment record ice volume calibrations of the deep ocean foraminiferal delta18o record imply orbitally influenced sea level fluctuations of up to 30m amplitude during the mid pliocene and up to 30 per cent loss of the present day mass of the east antarctic ice sheet eais assuming complete deglaciation of the west antarctic ice sheet wais and greenland these sea level oscillations have driven recurrent transgressions and regressions across the world s continental shelves wanganui basin new zealand contains the most complete shallow marine late neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100ka sea level cycle since ca 3 6ma this paper presents a synthesis of faunally derived palaeobathymetric data for shallow marine sedimentary cycles corresponding to marine isotope stages m2 100 ca 3 4 2 4ma our approach estimates the eustatic sea level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation the sea level estimates are consistent with those from delta18o curves and numerical ice sheet models and imply a significant sensitivity of the wais and the coastal margins of the eais to orbital oscillations in insolation during the mid pliocene period of relative global warmth sea level oscillations of 10 30m were paced by obliquity

quantification of vertical movement of low elevation topography combining a new compilation of global sea level curves and scattered marine deposits armorican massif western france a wide range of methods are available to quantify earth s surface vertical movements but most of these methods cannot track low amplitude 5 ma e g cosmogenic isotope studies vertical movements characteristic of plate interiors the difference between the present day elevation of ancient sea level markers deduced from well dated marine deposits corrected from their bathymetry of deposition and a global sea level gsl curve are sometimes used to estimate these intraplate vertical movements here we formalized this method by re assessing the reliability of published gsl curves to build a composite curve that combines the most reliable ones at each stage based on the potential bias and uncertainties inherent to each curve we suggest i that curves which reflect ocean basin volume changes are suitable for the ca 100 to 35 ma greenhouse period ii whereas curves that reflects ocean water volume changes are better suited for the ca 35 to 0 ma icehouse interval and iii that for these respective periods the fit is best when using curves that accounts for both volume changes we used this composite gsl curve to investigate the poorly constrained paleogene to neogene vertical motions of the armorican massif western france it is characterized by a low elevation topography a variscan basement with numerous well dated cenozoic marine deposits scattered upon it using our method we identify low amplitude vertical movements ranging from 66 m of subsidence to 89 m of uplift over that time period their spatial distribution argues for a preferred scale of deformation at medium wavelengths i e order 100 km which we relate to the deformation history of northwestern european lithosphere in three distinct episodes i a phase of no deformation between 38 and 34 ma that has been previously recognized at the scale of northwestern europe ii a phase of low subsidence between 30 and 3 6 ma possibly related to buckling of the lithosphere and iii a phase of more pronounced uplift between 2 6 ma and present which we relate to the acceleration of the africa apulia convergence or to enhanced erosion in the rapidly cooling climate of the pleistocene

departures from eustasy in pliocene sea level records estimates for sea level three million years ago a period with similar atmospheric co2 levels to today vary from 10 to 40 m above present glacial isostatic adjustment modelling suggests that variations in the height of palaeoshorelines result from the residual adjustment of continental flexure following recent glaciations

vertical sorting and the morphodynamics of bed form dominated rivers a sorting evolution model existing sediment continuity models for nonuniform sediment suffer from a number of shortcomings as they fail to describe vertical sorting fluxes other than through net aggradation or degradation of the bed and are based on a discrete representation of the bed material interacting with the flow we present a new type of sediment continuity model that is based on a stochastic description of the bed surface rather than discrete bed layers the model is aimed at conditions dominated by bed load transport wherein the river bed is fully covered by river dunes application of the model should be limited to spatial scales covering a significant number of bed forms the resulting model i e the sorting evolution model is suitable for unsteady conditions as it takes into account the time evolution of for instance vertical sorting in modeling net aggradation or degradation of the river bed the present paper lists the various submodels of a morphodynamic model system to which the sorting evolution model is applied we compare the results of the morphodynamic model system to measured data from two flume experiments the new model shows reasonable results for the predicted time evolution of the vertical sorting profile as well as the time evolution of the grain size distribution of the bed load transport yet the model does not properly include sorting mechanisms associated with partial transport and the winnowing of fines from the trough surface and subsurface the model serves as a basis for a future simplification of the model into a new stochastics based bed layer type sediment continuity model in which vertical sediment fluxes are included in a parameterized way

impact effects and regional tectonic insights backstripping the chesapeake bay impact structure the chesapeake bay impact structure is a ca 35 4 ma crater located on the eastern sea board of north america deposition returned to normal shortly after impact resulting in a unique record of both impact related and subsequent passive margin sedimentation we use backstripping to show that the impact strongly affected sedimentation for 7 m y through impact derived crustal scale tectonics dominated by the effects of sediment compaction and the introduction and subsequent removal of a negative thermal anomaly instead of the expected positive thermal anomaly after this the area was dominated by passive margin thermal sub sidence overprinted by periods of regional scale vertical tectonic events on the order of tens of meters loading due to prograding sediment bodies may have generated these events

geomorphology denudation rates and stream channel profiles reveal patterns of mountain building adjacent to the san andreas fault in northern california usa relative horizontal motion along strike slip faults can build mountains when motion is oblique to the trend of the strike slip boundary the resulting contraction and uplift pose off fault seismic hazards which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges sparse geomorphic markers topographic analyses and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern san andreas fault between jenner and mendocino california emergent marine terraces found southwest of the san andreas fault record late pleistocene uplift rates between 0 20 and 0 45 mm yr 1 along much of the coast however on the northeast side of the san andreas fault a zone of rapid uplift 0 6 1 0 mm yr 1 exists adjacent to the san andreas fault but rates decay northeastward as the coast becomes more distant from the san andreas fault a newly dated 4 5 ma shallow marine deposit located at 500 m above sea level masl adjacent to the san andreas fault is warped down to just 150 masl 15 km northeast of the san andreas fault and it is exposed at just 60 110 masl to the west of the fault landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of and adjacent to the san andreas fault are 0 16 0 29 mm yr 1 but they are only 0 03 0 07 mm yr 1 west of the fault basin average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties the lower elevation areas of this landscape that show high channel steepness and hence calibrated erosion rate are distinct from higher elevation areas with systematically lower channel steepness and denudation rates these two areas do not appear to be coincident with lithologic contacts assuming that changes in rock uplift rates are manifest in channel steepness values as an upstream propagating kinematic wave that separates high and low channel steepness values the distance that this transition has migrated vertically provides an estimate of the timing of rock uplift rate increase this analysis suggests that rock uplift rates along the coast changed from 0 3 to 0 75 mm yr 1 between 450 and 350 ka this zone of recent relatively rapid crustal deformation along the plate boundary may be a result of the impingement of relatively strong crust underlying the gualala block into the thinner weaker oceanic crust left at the western margin of the north american plate by the westward migration of the subduction zone prior to establishment of the current transform plate boundary the warped pliocene marine deposits and the presence of a topographic ridge support the patterns indicated by the channel steepness analyses and further indicate that the zone of rapid uplift may herald elevated off fault seismic hazard if this uplift is created by periodic stick slip motion on contractional structures

the relationship between neogene dinoflagellate cysts and global climate dynamics abstract the neogene period 23 03 2 58 ma underwent a long term relatively gradual cooling trend culminating in the glacial interglacial climate of the quaternary palaeoclimate studies on the neogene have provided important information for understanding how modern patterns of atmospheric and oceanic circulation developed and how they may relate to wider environmental change here we use a newly created global database of neogene dinoflagellate cysts the tertiary oceanic parameters information system topis to investigate how dinoflagellate cysts recorded the cooling of neogene surface marine waters on a global scale species with warm and cold water preferences were determined from previously published literature and extracted from the database percentages of cold water species were calculated relative to the total number of species with known temperature preferences from each site and compared throughout the neogene at differing latitudes overall the percentage of cold water species increases gradually through the neogene this trend indicates a gradual global cooling that is comparable to that reported from other marine and terrestrial proxies this also demonstrates the use of dinoflagellate cysts in determining temperature change on both extended temporal and wide geographical scales the increase in the percentage of cold water species of dinoflagellate cysts recorded worldwide from the early and middle miocene to the late pliocene indicates a global scale forcing agent on neogene climate such as co2

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

dynamic antarctic ice sheet during the early to mid miocene geological data indicate that there were major variations in antarctic ice sheet volume and extent during the early to mid miocene simulating such large scale changes is problematic because of a strong hysteresis effect which results in stability once the ice sheets have reached continental size a relatively narrow range of atmospheric co2 concentrations indicated by proxy records exacerbates this problem here we are able to simulate large scale variability of the early to mid miocene antarctic ice sheet because of three developments in our modeling approach i we use a climate ice sheet coupling method utilizing a high resolution atmospheric component to account for ice sheet climate feedbacks ii the ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice cliff failure and ice shelf hydrofracture iii we account for changes in the oxygen isotopic composition of the ice sheet by using isotope enabled climate and ice sheet models we compare our modeling results with ice proximal records emerging from a sedimentological drill core from the ross sea andrill 2a that is presented in a companion article the variability in antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0 52 0 66 or a sea level equivalent change of 30 36 m for a range of atmospheric co2 between 280 and 500 ppm and a changing astronomical configuration this result represents a substantial advance in resolving the long standing model data conflict of miocene antarctic ice sheet and sea level variability

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

antarctic ice sheet response to sudden and sustained ice shelf collapse abumip author s sun s pattyn f simon eg albrecht t cornford s calov r dumas c gillet chaulet f goelzer h golledge nr greve r hoffman mj humbert a kazmierczak e kleiner t leguy gr lipscomb wh martin d morlighem m nowicki s pollard d price s quiquet a seroussi h schlemm t sutter j van de wal rsw winkelmann r zhang t abstract copyright the author s 2020 antarctica s ice shelves modulate the grounded ice flow and weakening of ice shelves due to climate forcing will decrease their buttressing effect causing a response in the grounded ice while the processes governing ice shelf weakening are complex uncertainties in the response of the grounded ice sheet are also difficult to assess the antarctic buttressing model intercomparison project abumip compares ice sheet model responses to decrease in buttressing by investigating the end member scenario of total and sustained loss of ice shelves although unrealistic this scenario enables gauging the sensitivity of an ensemble of 15 ice sheet models to a total loss of buttressing hence exhibiting the full potential of marine ice sheet instability all models predict that this scenario leads to multi metre 1 12 m sea level rise over 500 years from present day west antarctic ice sheet collapse alone leads to a 1 91 5 08 m sea level rise due to the marine ice sheet instability mass loss rates are a strong function of the sliding friction law with plastic laws cause a further destabilization of the aurora and wilkes subglacial basins east antarctica improvements to marine ice sheet models have greatly reduced variability between modelled ice sheet responses to extreme ice shelf loss e g compared to the searise assessments

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

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

the amplitude and origin of sea level variability during the pliocene epoch earth is heading towards a climate that last existed more than three million years ago ma during the mid pliocene warm period 1 when atmospheric carbon dioxide concentrations were about 400 parts per million global sea level oscillated in response to orbital forcing2 3 and peak global mean sea level gmsl may have reached about 20 metres above the present day value4 5 for sea level rise of this magnitude extensive retreat or collapse of the greenland west antarctic and marine based sectors of the east antarctic ice sheets is required yet the relative amplitude of sea level variations within glacial interglacial cycles remains poorly constrained to address this we calibrate a theoretical relationship between modern sediment transport by waves and water depth and then apply the technique to grain size in a continuous 800 metre thick pliocene sequence of shallow marine sediments from whanganui basin new zealand water depth variations obtained in this way after corrections for tectonic subsidence yield cyclic relative sea level rsl variations here we show that sea level varied on average by 13 5 metres over glacial interglacial cycles during the middle to late pliocene about 3 3 2 5 ma the resulting record is independent of the global ice volume proxy3 as derived from the deep ocean oxygen isotope record and sea level cycles are in phase with 20 thousand year kyr periodic changes in insolation over antarctica paced by eccentricity modulated orbital precession6 between 3 3 and 2 7 ma thereafter sea level fluctuations are paced by the 41 kyr period of cycles in earth s axial tilt as ice sheets stabilize on antarctica and intensify in the northern hemisphere3 6 strictly we provide the amplitude of rsl change rather than absolute gmsl change however simulations of rsl change based on glacio isostatic adjustment show that our record approximates eustatic sea level defined here as gmsl unregistered to the centre of the earth nonetheless under conservative assumptions our estimates limit maximum pliocene sea level rise to less than 25 metres and provide new constraints on polar ice volume variability under the climate conditions predicted for this century sea level varied by 13 5 metres on average but up to 25 metres over glacial interglacial cycles during the pliocene epoch due to partial collapses of antarctic ice sheets

a temperate former west antarctic ice sheet suggested by an extensive zone of subglacial meltwater channels several recent studies predict that the west antarctic ice sheet will become increasingly unstable under warmer conditions insights on such change can be assisted through investigations of the subglacial landscape which contains imprints of former ice sheet behavior here we present radio echo sounding data and satellite imagery revealing a series of ancient large sub parallel subglacial bed channels preserved in the region between the moller and foundation ice streams west antarctica we suggest that these newly recognized channels were formed by significant meltwater routed along the icesheet bed the volume of water required is likely substantial and can most easily be explained by water generated at the ice surface the greenland ice sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing for west antarctica the pliocene 2 6 5 3 ma represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present day greenland we propose therefore that a temperate ice sheet covered this location during pliocene warm periods

modeling oxygen isotopes in the pliocene large scale features over the land and ocean the first isotope enabled general circulation model gcm simulations of the pliocene are used to discuss the interpretation of 18o measurements for a warm climate the model suggests that spatial patterns of pliocene ocean surface 18o 18osw were similar to those of the preindustrial period however arctic and coastal regions were relatively depleted while south atlantic and mediterranean regions were relatively enriched modeled 18osw anomalies are closely related to modeled salinity anomalies which supports using 18osw as a paleosalinity proxy modeled pliocene precipitation 18o 18op was enriched relative to the preindustrial values but with depletion of 2 over some tropical regions while usually modest 4 the enrichment can reach 25 over ice sheet regions in the tropics 18op anomalies are related to precipitation amount anomalies although there is usually a spatial offset between the two this offset suggests that the location of precipitation change is more uncertain than the amplitude when interpreting 18op at high latitudes 18op anomalies relate to temperature anomalies however the relationship is neither linear nor spatially coincident a large 18op signal does not always translate to a large temperature signal these results suggest that isotope modeling can lead to enhanced synergy between climate models and climate proxy data the model can relate proxy data to climate in a physically based way even when the relationship is complex and nonlocal the 18o climate relationships identified here from a gcm could not be determined from transfer functions or simple models

icebergs in the nordic seas throughout the late pliocene the arctic cryosphere is changing and making a significant contribution to sea level rise the late pliocene had similar co2 levels to the present and a warming comparable to model predictions for the end of this century however the state of the arctic cryosphere during the pliocene remains poorly constrained for the first time we combine outputs from a climate model with a thermodynamic iceberg model to simulate likely source regions for ice rafted debris ird found in the nordic seas from marine isotope stage m2 to the mid piacenzian warm period and what this implies about the nature of the arctic cryosphere at this time we compare the fraction of melt given by the model scenarios with ird data from four ocean drilling program sites in the nordic seas sites 911a 909c and 907a show a persistent occurrence of ird that model results suggest is consistent with permanent ice on svalbard our results indicate that icebergs sourced from the east coast of greenland do not reach the nordic seas sites during the warm late pliocene but instead travel south into the north atlantic in conclusion we suggest a continuous occurrence of marine terminating glaciers on svalbard and on east greenland due to the elevation of the east greenland mountains during the late pliocene the study has highlighted the usefulness of coupled climate model iceberg trajectory modeling for understanding ice sheet behavior when proximal geological records for pliocene ice presence or absence are absent or are inconclusive

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

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

revisiting antarctic ice loss due to marine ice cliff instability predictions for sea level rise this century due to melt from antarctica range from zero to more than one metre the highest predictions are driven by the controversial marine ice cliff instability mici hypothesis which assumes that coastal ice cliffs can rapidly collapse after ice shelves disintegrate as a result of surface and sub shelf melting caused by global warming but mici has not been observed in the modern era and it remains unclear whether it is required to reproduce sea level variations in the geological past here we quantify ice sheet modelling uncertainties for the original mici study and show that the probability distributions are skewed towards lower values under very high greenhouse gas concentrations the most likely value is 45 centimetres however mici is not required to reproduce sea level changes due to antarctic ice loss in the mid pliocene epoch the last interglacial period or 1992 2017 without it we find that the projections agree with previous studies all 95th percentiles are less than 43 centimetres we conclude that previous interpretations of these mici projections over estimate sea level rise this century because the mici hypothesis is not well constrained confidence in projections with mici would require a greater range of observationally constrained models of ice shelf vulnerability and ice cliff collapse by better quantifying uncertainties for marine ice cliff instability future antarctic ice loss is predicted to be much lower than previously estimated

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years