cenozoic global ice volume and temperature simulations with 1 d ice sheet models forced by benthic δ18o records variations in global ice volume and temperature over the cenozoic era have been investigated with a set of one dimensional 1 d ice sheet models simulations include three ice sheets representing glaciation in the northern hemisphere i e in eurasia north america and greenland and two separate ice sheets for antarctic glaciation the continental mean northern hemisphere surface air temperature has been derived through an inverse procedure from observed benthic 18o records these data have yielded a mutually consistent and continuous record of temperature global ice volume and benthic 18o over the past 35ma the simple 1 d model shows good agreement with a comprehensive 3 d ice sheet model for the past 3 ma on average differences are only 1 0 c for temperature and 6 2m for sea level most notably over the 35ma period the reconstructed ice volume temperature sensitivity shows a transition from a climate controlled by southern hemisphere ice sheets to one controlled by northern hemisphere ice sheets although the transient behaviour is important equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric providing limited evidence for hysteresis furthermore the results show a good comparison with other simulations of antarctic ice volume and observed sea level

correcting the cenozoic δ18o deep sea temperature record for antarctic ice volume abstract the oxygen isotope signal in benthic foraminifera from deep sea cores is mainly determined by deep ocean temperature and land ice volume separating the temperature and ice volume signals is a key step in understanding the evolution of cenozoic climate except for the last few million years fluctuations in land ice volume were determined mainly by the size of the antarctic ice sheet here a simplified antarctic ice sheet model and composite deep sea oxygen isotope records are used to derive a deep sea temperature history for the cenozoic the ice sheet model is forced with the oxygen isotope record which is instantaneously corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent the temperature record of lear et al science 287 2000 269 derived from the mg ca ratio in benthic calcite is also used to force the ice sheet model the resulting ice volume does not agree well with the ice volume history inferred by lear et al from a comparison of mg ca and 18 o records the most important points emerging from this study are the cenozoic 18 o record from benthic forams is a truly mixed signal ice volume and deep sea temperature contribute equally to the variance for the period of 45 to 30 ma ago 18 o temperatures are significantly lower than mg ca temperatures rapid nonlinear build up of a continental scale ice sheet on the antarctic continent can easily occur for a linear cooling rate it is unlikely that the method of lear et al provides a reliable measure of ice volume the cooling rate at the beginning of the pliocene is much larger in the 18 o temperature curves than in the mg ca temperature curve

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

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

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

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

miocene pollen record of kc 1 core in the qaidam basin ne tibetan plateau and implications for evolution of the east asian monsoon abstract thick cenozoic deposits in the qaidam basin provide great potential for understanding the tectonic history paleoclimatic changes and evolution of the east asian monsoon this study examines the pollen record from the kc 1 core for the interval covering the later early to late miocene 18 5 ma thermophilic taxa percentages are high between 18 and 14 ma and decrease after this time a pattern which fits well with the middle miocene climatic optimum mmco between 18 and 14 ma and global climatic cooling after 14 ma during the same period xerophytic taxa percentages gradually increase and those of the conifers gradually decrease suggesting an aridification process in the qaidam region driven by the gradual strengthening of the east asian winter monsoon eawm and weakening of the east asian summer monsoon easm the global climate cooling process appears to have driven the climatic development of the qaidam basin region throughout the miocene but the uplift of the tibetan plateau also contributed

areal distribution of the oxygen isotope ratio in greenland mean values of the oxygen isotope ratio relative to standard mean ocean water 8 180 in 0 reported for 46 sites on the greenland ice sheet are compiled together with data on mean annual surface temperature latitude 8180 elevation and mean annual shor test distance to the open ocean denoted by the 10 sea ice concentration boundary stepwise regression analyses with 8180 as the dependent variable define two robust models in the forward mode at the 99 9 confidence level only temperature enters the model in the backward mode at the 95 con fidence level only temperature latitude and distance to the open ocean remain in the model inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of b iho two distributions are based on the bivariate model and two on the multivariate modcl the sccond distribution for each model is obtained substituting mean annual surfa ce tempe ratu re values obtained from the nim bus 7 temperature humidity infrared radiometer thir database all four distribu tions are considered valid and differences between them are evaluated using contoured anomaly maps it is suggested that the inversion o the multivariate model using thir data pro ides the more reliable pattern for stu dies of atmospheric advection or for the derivation of ice flow adjustments for 81ho series obt ained from deep core or ablation zone sites

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

ice sheet modelling characteristics in sea level based temperature reconstructions over the last glacial cycle a widely used method for investigating palaeotemperatures is to analyze local proxy records e g ice cores or deep sea sediment cores the interpretation of these records is often not straightforward and global or hemispheric means cannot be deduced from local estimates because of large spatial variability using a different approach temperature changes over the last glacial cycle can be estimated from sea level observations by applying an inverse method to an ice sheet model in order to understand the underlying physical mechanisms we used a 1 d ice sheet model and a 3 d coupled thermodynamic ice sheet ice shelf bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions results show that i temperature reconstructions are sensitive to the employed formulation of mass balance ii excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and iii hysteresis in the non linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets the ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome which tends to be preserved in warming conditions

plio pleistocene climate evolution trends and transitions in glacial cycle dynamics abstract we describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5 3 myr in particular we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic 18 o when the exponential trend in 18 o variance is removed its spectral power exhibits strong proportional responses to amplitude modulations in orbital forcing over most of the plio pleistocene precession responses correlate with modulations in forcing for the last 5 myr but 41 kyr response is sensitive to obliquity modulation only before 1 4 myr where responses are sensitive to modulations in forcing we demonstrate that glacial cycles are orbitally forced rather than being self sustained or paced by orbital changes the shapes of glacial cycles have several nonlinear properties which may be indicative of glacial interglacial differences in climate sensitivity or response time the saw tooth asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation and the relative duration of interglacial stages decreases at 1 4 myr collectively trends in the shape of glacial cycles and the sensitivity of 18 o to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2 5 and 1 4 myr but show no significant change associated with the appearance of strong 100 kyr cycles during the mid pleistocene transition

marine terrace development on reefless volcanic islands new insights from high resolution marine geophysical data offshore santa maria island azores archipelago abstract submerged marine terraces are relict coastal erosional landforms now underwater due to rising sea level and or land subsidence using as case study the shelf around santa maria island north atlantic ocean we intend to advance our knowledge on the formation and preservation of these features on reefless volcanic islands santa maria is an ideal place to study their combined generation since it displays a sequence of subaerial and submerged marine terraces the latter not studied before distributed between 7 230 m in elevation and 40 140 m in depth respectively based on some geological constraints we investigated a possible correlation between the formation of the different terraces with known sea level changes our results suggest that the spatial distribution of marine terraces at santa maria depends on the complex interplay between glacio eustatic sea level fluctuations the island s vertical motion trends the morphology of the shelf and the intensity of marine erosion subaerial terraces probably developed from 3 5 ma to 1 ma following a fortuitous conjugation of optimal exposure to energetic waves and a suitable arrangement lithology of the stratigraphic units promoting easier erosion their preservation was likely promoted by the uplift trend the island experienced in the last 3 5 ma which was rapid enough to prevent their destruction by subsequent highstands the submerged terraces presumably all younger than 1 ma were largely influenced by shelf gradient leading to more developed and preserved terraces in wider and low gradient sectors displacement by active faults also conditioned the formation and further development of both subaerial and submerged terraces with tectonic activity documented for the 0 693 ma 2 7 ma period

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

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

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

a new method to estimate ice age temperatures on glacial time scales the waxing and waning of the eurasian and north american ice sheets depend largely on variations in atmospheric temperature as global sea level is primarily determined by the volume of these ice sheets there is a direct yet complex relation between global sea level and the northern hemispheric nh temperature this relation is essentially represented by a model of the nh ice sheets we use a thermomechanical ice sheet ice shelf bedrock model in conjunction with an inverse method to deduce a time series of nh temperature from 120 kyr bp until present that is consistent with the observed global sea level record the advantage of this method is that it provides the annual mean surface air temperature averaged over the nh continents north of 40 n the results reveal that ice age temperatures were 4 10 c lower than today which agrees with other temperature reconstructions however reconstructed temperatures are comparitively low during the early stages of the glacial a feature that is consistent with the rapid growth of the ice sheets the sensitivity of the results for uncertainties in precipitation rate in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature during the glacial period 120 15 kyr bp surface air temperatures in the nh north of 40 n were 7 2 1 5 c lower than today s interglacial temperatures

pliocene pleistocene oxygen isotope record site 586 ontong java plateau abstract oceanographic changes in the western equatorial pacific during the past 6 ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from ontong java plateau dsdp site 586 the taxa areglobigerinoides sacculifer pulleniatina cibicidoides wuellerstorfi andoridorsalis umbonatus cooling and ice buildup are indicated by an18o enrichment of 0 3 in the planktic species near 3 4 ma this shift apparently is compensated in the benthic data by a warming of the deep waters by between 1 and 2 c we suggest that the dominant source of upper deep water supply to the pacific changed from antarctic to north atlantic at that time the north atlantic derived water being warmer near 2 8 ma approximately the planktic foraminifera again record an enrichment in18o 18o 0 25 we suggest ice buildup in the northern hemisphere as the cause because of subsequent sharp increase in fluctuations of the 18o signal that is instability the enrichment is magnified in the benthic foraminifera 18o 0 5 by a cooling of the deep water by 1 5 at the time presumably signalling a glacial type reduction of north atlantic deep water nadw production episodic divergence between the signals ofg sacculifer andpulleniatina in the pleistocene apparently reflects periods of increased upwelling in the western equatorial pacific the amplitude of ice volume fluctuations cannot be reconstructed from 18o data alone unless there are constraints on temperature variations the increase in amplitude of fluctuation of the benthic and planktic signals during the pleistocene may be attributed either to an increase in maximum ice volume or to an increase in the fractionation of continental ice or a combination of both causes

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

coupled southern ocean cooling and antarctic ice sheet expansion during the middle miocene the middle miocene climate transition 14 million years ago was characterized by a dramatic increase in the volume of the antarctic ice sheet the driving mechanism of this transition remains under discussion with hypotheses including circulation changes declining carbon dioxide in the atmosphere and orbital forcing southern ocean records of planktic foraminiferal mg ca have previously been interpreted to indicate a cooling of 6 7 c and a decrease in salinity that preceded antarctic cryosphere expansion by up to 300 000 years this interpretation has led to the hypothesis that changes in meridional heat and vapour transport along with an early thermal isolation of antarctica from extrapolar climates played a fundamental role in triggering ice growth here we revisit the middle miocene southern ocean temperature evolution using clumped isotope and lipid biomarker temperature proxies our records indicate that the southern ocean cooling and the associated salinity decrease occurred in phase with the expansion of the antarctic ice sheet we demonstrate that the timing and magnitude of the southern ocean temperature change seen in previous reconstructions can be explained if we consider ph as an additional non thermal control on foraminiferal mg ca ratios therefore our new dataset challenges the view of a thermal isolation of antarctica preceding ice sheet expansion and suggests a strong coupling between southern ocean conditions and antarctic ice volume in times of declining atmospheric carbon dioxide antarctic ice volume expansion in the middle miocene coincides with southern ocean cooling according to biomarker and clumped isotope temperature records from south of tasmania

meta gabbro weathering in the georgia piedmont usa implications for global silicate weathering rates abstract the mineral assemblages in a vertical weathering profile developed over a meta gabbro terrain were studied for their stoichiometry and relative abundances the site is located in the piedmont province in the southeast portion of the appalachians orogenic belt in a forested residual landscape and a temperate climate the soil is classified as a fine mixed thermic ultic hapludalf and defined by distinct a b and c horizons with thicknesses of 17 62 and 250 cm respectively the primary mineral assemblage consists of 44 wt andesine 40 hornblende 6 quartz 4 biotite 3 ilmenite titanomagntite rutile sphene grains and 3 epidote quantitative xrd detailed xrd clay mineralogy and thin section petrography revealed the incipient breakdown of the primary minerals to vermiculite after biotite oxidation randomly ordered mixed layer mica vermiculite smectite as grain coatings kaolin group minerals after mafic silicate dissolution goethite and hematite vermiculite after biotite expandable clay coatings and all the primary minerals with exception to quartz are dissolved away from the a horizon hydroxy interlayered vermiculite and minor amounts of gibbsite occur as tertiary phases in the a horizon using mineral stoichiometries and average abundances for the parent rock and c b and a horizon estimates of primary mineral mass loss were determined the bicarbonate to silica ratio expected from the mineral loss reactions is 6 times higher than the ratio observed in average groundwater of the georgia piedmont this suggests that although weathering of mafic terrains is important to the long term process of transferring co 2 to the oceans the present day contribution of silicate weathering in temperate climates may be more largely influenced by the weathering of felsic terrain

geometry and dynamics of an east antarctic ice sheet outlet glacier under past and present climates 1 the behavior of east antarctic ice sheet eais outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics and also with regard to epoch scale ice sheet stability during plio pleistocene climate transitions here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate ferrar glacier first under present day environmental conditions and subsequently under both colder and warmer climate regimes representing the last glacial maximum lgm and mid pliocene peak warmth respectively using airborne radar profiles insar derived surface velocities ice core and geological data for empirical constraint we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics our model suggests that the glacier is largely cold based under present conditions flows predominantly by way of internal deformation and cascades over bedrock ridges due to the combined action of changes in cross sectional valley geometry local steepening of the glacier surface and the non local effects of longitudinal coupling time dependent evolutionary simulation of a lower profile glacier under a colder drier lgm climate predicts flow velocities lower than present with minimal bedrock erosion or basal till flux conversely the warmer than present mid pliocene climate produces a more dynamic glacier that is warm based and sliding along much of its bed we propose that eais outlet glaciers such as the ferrar respond dynamically along their length in response to changing environmental forcings with most significant changes taking place in their lower reaches adjustment to perturbations in upper catchments is more muted

modelling the effect of pliocene quaternary changes in sea level on stable and tectonically active land masses a mathematical model was used to examine the effect of pliocene and quaternary changes in sea level on the development of tectonically active and inactive rock coasts the model calculated rates of mechanical wave erosion according to such factors as the deep water wave regime bottom topography and surface roughness and the resistance of the rocks subaerial terraces were truncated or eliminated by subsequent terrace formation at lower elevations especially on steeply sloping landmasses experiencing slow rates of uplift submarine terraces formed during glacial stillstands were best preserved when rapid subsidence quickly carried them below the level of wave action on slowly subsiding landmasses submarine terraces formed during interglacials and glacial periods experienced repeated erosional modification during subsequent periods of rising and falling sea level and were generally less distinctive on rapidly rising or subsiding 5 mm yr 1 landmasses terraces that formed during interglacial stages alternated above and below present sea level with terraces formed during glacial stages despite some differences in terrace occurrence and elevational distribution it may be difficult to distinguish profiles cut during accelerating or decelerating uplift the amount of erosion during sea level oscillations increases with oscillation amplitude and the larger oscillations in the middle to late quaternary were therefore more conducive to erosion than the smaller oscillations of the pliocene and early quaternary the effect of oscillation amplitude may have been countered during the earlier stages of profile development however by steeper submarine gradients and reduced rates of wave attenuation copyright 2014 john wiley sons ltd

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

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

methodology for use of isotopic climate forcings in ice sheet models in ice sheet models an internally consistent calculation of climatic temperature forcing from ice core isotopic records requires that corrections be made for an ice core site s elevation changes such corrections can be important for two reasons first elevation change at an ice divide can be large compared to elevation change at the migrating ice margin resulting in erroneous estimates of marginal melt rate second the of precipitation at an ice divide responds less to regional climatic temperature changes than to local temperature changes of the same magnitude that are caused by elevation changes significant elevation change corrections may also be necessary for inferring the relationships used to calculate climatic temperature from a simple methodology incorporating both of these elevational effects is presented here further i recommend that the to temperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and time series rather than from spatial correlations and justify this recommendation based on current understanding of the atmospheric isotopic distillation system

plateau uplift forcing climate change around 8 6 ma on the northeastern tibetan plateau evidence from an integrated sedimentary sr record abstract the uplift of the northern tibetan plateau tp has long been regarded as one of major factors accounting for both the enhanced process of aridification recorded in central asia and the shifts in the asian monsoonal circulations that are known to have occurred at approximately 8 ma until now there have been few sedimentary records reported on which can directly and in an integrated fashion shed light on the region s tectonic and climate regimes this can be largely attributed to the fact that the influence exerted by the presence of source materials and subsequent sedimentary sorting in this tectonically active region would be likely to bias significantly any paleoclimatic interpretation of silicate derived proxies based on detailed investigations of strontium sr distributions revealed by multi step leaching in a fluvial sequence from the linxia basin which includes paleosols we reconstructed the long term late miocene regional climatic and environmental changes likely to have occurred on the northeastern tp from 12 1 to 5 2 ma we investigated sr related proxies in two typical paleosol profiles to constrain sr mobility in paleosol weathering and thus to further prompt the interpretation of sr related proxies along the whole section we would suggest that carbonate derived sr concentrations and sr ca ratios are suitable proxies for tracing regional climate change associated with weathering and pedogenesis together they exhibit weakened chemical weathering intensity and pedogenesis at 8 6 ma the concomitant appearance of immature sediments through poor sedimentary sorting revealed by silicate derived rb sr 87 sr 86 sr and eu anomaly eu eu alongside a sharp increase in sedimentation rates noted at this time suggests that it was indeed tectonic uplift that principally controlled the dramatic climatic and environmental changes this multi proxy record of concomitant tectonic uplift and climate change in the linxia basin provides direct geological evidence for uplift driven climate change in the northeastern tp region

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

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

antarctic ice volume and deep sea temperature during the last 50 myr a model study a simple quasi analytical model is used to study the sensitivity of the antarctic ice sheet to climate change the model is axisymmetrical and has a profile that only depends on the ice sheet radius the climatic conditions are represented by three parameters the altitude of the runoff line the accumulation rate above the runoff line and the balance gradient below the runoff line the ice sheet may extend into the sea at the grounding line the ice velocity is assumed to be proportional to the water depth for this set up an explicit algebraic expression for the total mass budget of the ice sheet can be derived after calibration of the model with respect to the present day ice sheet equilibrium states are studied for a wide range of temperatures the model predicts a maximum ice volume 3 4 for a temperature that is 2 5 k above the present value for a temperature increase of 7 k mass loss by runoff and calving are about the same in this case the ice volume is about 82 of the current value the ice sheet model is used to correct the cenozoic deep sea temperature record 18o record from benthic foraminifera in ocean sediments for antarctic ice volume the model is forced with the oxygen isotope record which is then corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent it is concluded that for the last 35 106 years the 18o record truly is a mixed temperature ice volume record in which the contributions from these parameters have the same order of magnitude

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

late cenozoic sporopollen records in the yangtze river delta east china and implications for east asian summer monsoon evolution abstract the late cenozoic east asian summer monsoon easm is generally linked with the tibetan plateau uplift and or global cooling in this study four cores zk004 zk005 sz03 and sz04 consisting of fluvial lacustrine deposits spanning the period of 8 0 0 ma were obtained from the yangtze river delta east china for sporopollen analysis to investigate trends in the easm evolution and its driving forces the results show that high percentages of arboreal taxa such as fagaceae ulmaceae juglandaceae taxaceae taxodiaceae liquidambar anacardiaceae rutaceae etc represent a relatively warm and humid climate between 8 0 and 2 6 ma the herb dominated vegetation poceae asteraceae cyperaceae etc is linked with a relatively cold and dry climate after 2 6 ma the compiled thermophilic percentages and ap arbors nap non arbors ratios of these four cores which show that the long term cooling and drying trends are similar to the global cooling since 8 0 ma imply that the easm experienced long term weakening coincident with the global cooling however over this super long time scale the thermophilic percentages and ap nap ratios have remained at roughly stable levels since 2 6 ma possibly due to the effects of the tibetan plateau uplifts