impact of strong deep ocean stratification on the glacial carbon cycle 1 during the last glacial maximum the climate was substantially colder and the carbon cycle was clearly different from the late holocene according to proxy data deep oceanic 13c was very low and the atmospheric co2 concentration also reduced several mechanisms have been proposed to explain these changes but none can fully explain the data especially the very low deep ocean 13c values oceanic core data show that the deep ocean was very cold and salty which would lead to enhanced deep ocean stratification we show that such an enhanced stratification in the coupled climate model climber 2 helps get very low deep oceanic 13c values indeed the simulated 13c reaches values as low as 0 8 in line with proxy data evidences moreover it increases the oceanic carbon reservoir leading to a small yet robust atmospheric co2 drop of approximately 10 ppm

approaches to the study of cheniers along the coastline of the soviet union abstract with the very extensive coastline in the north and northeast and the relatively shorter coastlines in the south cheniers in the ussr can occur in a great variety of climatological conditions ranging from subarctic to subtropical cheniers in the ussr have been studied since approximately 1900 the investigations being mainly concerned with the palaeogeographical aspects since the 1960 s investigations have focussed on contemporary morphodynamics chenier formation appears to depend largely on the relative influence that marine and fluvial factors have on the formation of marginal deltaic plains research in this field is briefly reviewed

origin of peralkaline granites of saudi arabia small volumes of peralkaline granites were generated as the final phase of a pan african calc alkaline igneous event which built the arabian peninsula the peralkaline granites are closely associated with trends or sutures related to ophiolites peralkaline rocks are chemically heterogeneous with anomalous abundances of zr average 2 150 ppm 2 600 1 y 200 190 and nb 105 100 representing up to ten fold enrichments of these elements relative to abundances in calc alkaline granite counterparts large enrichments of some rare earth elements and fluorine are also present the peralkaline granites have scattered whole rock 18o values averaging 8 7 0 6 in the hadb aldyaheen complex and 10 7 1 in the jabal sayid complex quartz albite fractionations of 0 5 to 1 5 signify that the heavier whole rock values probably represent the oxygen isotope composition of the peralkaline magma small variable enrichments of 18o in conjunction with slightly elevated 87sr 86sr initial ratios relative to broadly contemporaneous calc alkaline granites are both suggestive of a small degree of involvement of crustal or crustal derived material in the peralkaline magmas it is proposed that the peculiar magma genesis is associated with a relaxation event which followed continental collision and underthrusting of salt rich sediments

changing influence of antarctic and greenlandic temperature records on sea level over the last glacial cycle we use a simple model to analyse the relationship between ice core temperature proxy data and global ice volume eustatic sea level data over the last glacial cycle lgc by allowing the temperature forcing to be a mix of greenlandic and antarctic signals we optimise the proportion of this mixing to fit sea level data we find that sea level forcing is best represented by a mix of antarctic and greenlandic temperature signals through the whole glacial cycle we suggest that a distinct bipolar switch occurs which links eustatic sea level more closely with the antarctic like variability during the glacial period mis 4 3 and 2 and more closely to the greenland like variability during the last termination ti and the interglacial periods holocene and mis 5 this switch may be caused by the spatio temporal distribution of ice sheet collapse perhaps linked to glacial to interglacial changes in deep water distribution in the ocean which in turn drive changes in pole ward heat and moisture transport

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

the dole effect over the last two glacial interglacial cycles detailed measurements of 18 o of atmospheric oxygen performed on air trapped in the vostok ice cores antarctica are used to extend the record of the dole effect over two climatic cycles back to 240 kyr b p except for glacial terminations i and ii and for an unexpected minimum occurring around 175 kyr the dole effect shows small variations adole within 0 5 these small variations however show a well marked 23 kyr precessional periodicity thus confirming the results obtained by bender et al 1994a for the first climatic cycle to explain the minimum value reached around 175 kyr we invoke the possibility of a peak in the oceanic productivity linked to climatic events induced at low latitudes under glacial conditions

evidence for stratigraphic distortion in the greenland ice core project grip ice core during event 5e1 120 kyr bp from gas isotopes 1 the disturbed stratigraphy of the ice in the lowest 10 of the greenland grip ice core has been previously demonstrated using gas measurements 18o of o2 and ch4 on a few meters depth scale however rapid ice isotopic variations on the scale of 20 cm are experienced in the bottom of the grip ice core with complex chemical signatures that make them difficult to reconcile with a disturbed stratigraphy of the ice this is the case for event 5e1 first described as a dramatic cooling 120 kyr bp we analyzed at a 5 cm resolution the isotopic composition of the air from 2 m of the grip bottom ice core covering event 5e1 the 15n measurements combined with a basic firn modeling lead to the solid conclusion that the rapid event 5e1 is not a climatic event rapid variations of 18o of o2 18oatm are in agreement with a disturbed ice stratigraphy however the double peak shape of the 18oatm recalling chemical data at the same depth requires processes of diffusion after the mixing or even postcoring placing limits to the interpretation of some classical paleoclimatic proxies in small scale mixed ice 1 m

summit of the east antarctic ice sheet underlain by thick ice crystal fabric layers linked to glacial interglacial environmental change ice cores in antarctica and greenland reveal ice crystal fabrics that can be softer under simple shear compared with isotropic ice owing to the sparseness of ice cores in regions away from the ice divide we currently lack information about the spatial distribution of ice fabrics and its association with ice flow radio wave reflections are influenced by ice crystal alignments allowing them to be tracked provided reflections are recorded simultaneously in orthogonal orientations polarimetric measurements here we image spatial variations in the thickness and extent of ice fabric across dome a in east antarctica by interpreting polarimetric radar data we identify four prominent fabric units each several hundred metres thick extending over hundreds of square kilometres by tracing internal ice sheet layering to the vostok ice core we are able to determine the approximate depth age profile at dome a the fabric units correlate with glacial interglacial cycles most noticeably revealing crystal alignment contrasts between the eemian and the glacial episodes before and after the anisotropy within these fabric layers has a spatial pattern determined by ice flow over subglacial topography

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

reconciling astrochronological and 40ar 39ar ages for the matuyama brunhes boundary and late matuyama chron when five matuyama brunhes m b boundary records from the north atlantic are placed on isotope age models produced by correlation of the 18o record directly or indirectly to an ice volume model the m b boundary lies consistently at the young end of marine isotope stage 19 with a mean age for the midpoint of the reversal of 773 1 ka standard deviation 0 4 kyr 7 kyr younger than the presently accepted astrochronological age for this polarity reversal 780 781 ka two recently proposed revisions of the age of the 40ar 39ar fish canyon sanidine fcs standard to 28 201 0 046 ma and 28 305 0 036 ma would adjust 40ar 39ar ages applicable to the m b boundary and other reversals and excursions back to 1 2 ma to ages older than the new astrochronological ages by 8 24 kyr the variables used to construct the ice volume models cannot account for the discrepancy the fcs standard age that best fits the astrochronological ages is 27 93 ma which is within the uncertainty associated with the commonly used value of 28 02 0 16 ma but younger than the recently proposed fcs ages the edc2 and edc3 age models in the dome c antarctic ice core yield ages of 771 7 ka and 766 4 ka respectively for the 10be flux peak that denotes the paleointensity minimum at the reversal boundary implying that the edc2 rather than edc3 age model is consistent with the observations from marine sediments at least close to the m b boundary

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

holocene paleo climatic record from the south african namaqualand mudbelt a source to sink approach variations in the sediment input to the namaqualand mudbelt during the holocene are assessed using an integrative terrestrial to marine source to sink approach geochemical and sr and nd isotopic

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

coupling of co2 and ice sheet stability over major climate transitions of the last 20 million years the co2 content of the atmosphere has varied cyclically between 180 and 280 ppmv over the last 800 000 years closely coupled with temperature and sea level for earlier periods in earth s history pco2 is much less certain and the relationship between pco2 and climate remains poorly constrained we use boron calcium ratios in foraminifera to estimate pco2 during major climate transitions of the last 20 million years myr during the middle miocene when temperatures were 3 to 6 c

internal architecture and evolution of bioclastic beach ridges in a megatidal chenier plain field data and wave flume experiment beach ridges in macrotidal environments experience strong multi annual to multi decennial fluctuations of tidal inundation the duration of tide flooding directly controls the duration of sediment reworking by waves and thus the ridge dynamics flume modelling was used to investigate the impact of low frequency tidal cycles on beach ridge evolution and internal architecture the experiment was performed using natural bioclastic sediment constant wave parameters and low frequency variations of the mean water level the morphological response of the beach ridge to water level fluctuations and the preservation of sedimentary structures were monitored by using side view and plan view photographs results were compared with the internal architecture of modern bioclastic beach ridges in a macrotidal chenier plain mont st michel bay france surveyed with ground penetrating radar the experimentally obtained morphologies and internal structures matched those observed in the field and the three ridge development stages identified in ground penetrating radar profiles early transgressive late transgressive and progradational were modelled successfully flume experiments indicate that flat bioclastic shapes play a key role in sediment sorting in the breaker zone and in sediment layering in the beach and washover fans water level controls washover geometry beach ridge evolution and internal structure low water levels allow beach ridge stabilization and sediment accumulation lower on tidal flats during subsequent water level rise accumulated sediment becomes available for deposition of new washover units and for bayward extension of the beach ridges in the field low frequency water level fluctuations are related to the 4 4 year and 18 6 year tidal cycles experimental results suggest that these cycles may represent the underlying factor in the evolution of the macrotidal chenier coast at the multi decadal to centennial time scale

volatile control of contrasting trace element distributions in peralkaline granitic and volcanic rocks anomalous enrichments of zr 500 ppm zn 100 ppm nb 25 ppm y 60 ppm th 20 pm u 5 ppm lree 230 ppm and hree 35ppm and high rb sr 5 characterize peralkaline granites in contrast to their peraluminous and calc alkaline equivalents within the peralkaline suite comenditic and pantelleritic volcanics exhibit two to five fold increases in the concentrations of these trace elements over comagmatic granites these cannot be explained by crystal liquid fractionation processes and require the evolution of a sodium enriched fluid corresponding trace element increases in the granites in areas of alkali metasomatism support this argument and reflect the partial confinement of this volatile phase within the high level magma chambers ree studies in particular might eventually allow an evaluation of the role of cl versus f and co3 complexing in the evolution of the volatile fluid

hydrogen and oxygen isotope geochemistry of a type granites in the continental margins of eastern china hydrogen and oxygen isotope studies of both whole rock and mineral separates were carried out for five representative atype granites in eastern china from north to south the whole rock d d and d 18 o values vary from 2145 to 282 and from 21 2 to 5 0 for nianzishan pluton from 2135 to 2110 and from 1 6 to 6 7 for shanhaiguan pluton and from 2145 to 2111 and from 1 5 to 9 1 for laoshan massif respectively the highest whole rock dd and d 18 o values are observed in suzhou pluton and range from 281 to 259 and from 3 5 to 9 2 respectively homogeneous d d and d 18 o values are found in kuiqi massif ranging from 2113 to 299 and from 5 6 to 8 5 respectively the results show that the large variabilities in the hydrogen and oxygen isotope ratios are mainly related to the diverse processes of magma evolution such as magma degassing fractional crystallization as well as post magmatic alteration by local meteoric water under subsolidus conditions the initial d d and d 18 o values of the a type granites in eastern china are constrained to be about 250 5 and 7 5 1 0 respectively this is consistent with mantle like protoliths for granitoid rocks and thus precludes the possibility that the a type granites is derived from the anatexis of the 18 o rich upper crust however recycling of crustal materials by earlier subduction cannot be excluded in the processes of generating the a type granitic magmas the variation in the ddepletion of the granites with latitude implies that the paleogeographic localities of the a type granites have not changed significantly since the mesozoic q 2000 elsevier science b v all rights reserved

epica dome c record of glacial and interglacial intensities abstract climate models show strong links between antarctic and global temperature both in future and in glacial climate simulations past antarctic temperatures can be estimated from measurements of water stable isotopes along the epica dome c ice core over the past 800 000 years here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the stable isotope profile the consistency between stable isotope derived temperature and other environmental and climatic proxies measured along the edc ice core is analysed at the orbital scale and compared with estimates of global ice volume mis 2 12 and 16 appear as the strongest glacial maxima while mis 5 5 and 11 appear as the warmest interglacial maxima the links between edc temperature global temperature local and global radiative forcings are analysed we show i a strong but changing link between edc temperature and greenhouse gas global radiative forcing in the first and second part of the record ii a large residual signature of obliquity in edc temperature with a 5 ky lag iii the exceptional character of temperature variations within interglacial periods focusing on mis 5 5 the warmest interglacial of edc record we show that orbitally forced coupled climate models only simulate a precession induced shift of the antarctic seasonal cycle of temperature while they do capture annually persistent greenland warmth models fail to capture the warming indicated by antarctic ice core d we suggest that the model data mismatch may result from the lack of feedbacks between ice sheets and climate including both local antarctic effects due to changes in ice sheet topography and global effects due to meltwater thermohaline circulation interplays an mis 5 5 sensitivity study conducted with interactive greenland melt indeed induces a slight antarctic warming we suggest that interglacial edc optima are caused by transient heat transport redistribution comparable with glacial north south seesaw abrupt climatic changes

coastal barriers fresh look at origins nomenclature and classification issues abstract based on numerous publications and field work on the northern gulf of mexico coast u s and other coastal areas the present objective is to meet the need for an improved system of the definition and classification of barriers and their components this topic includes morphological and functional interrelationships between beach ridges barriers and similar landforms the term beach ridge was applied to a plethora of sub and supratidal ridge types in contrast the presently proposed definition restricts the term to relict berm and foredune ridges composed of sand or gravel and stabilized after isolation from shore zone of active processes barriers sustain paralic hydrology sediment biotic and nutrient condition in the coastal realm in combination with adjacent lagoons and river deltas these landforms represent physical barriers that lessen marine and related influences in brackish paralic coastal environments benefiting from historic evolution of concepts and nomenclature the task also involves the correction of misattributions rooted in early publications island spit and mainland barriers thus maintain lower salinities reduce wave erosion protect nutrient rich paralic deposits and mitigate storm induced inundation fetch limited lagoonal barrier islands are considered valid barriers only in lagoons where they face inlet transmitted full marine conditions mainland barriers of several subcategories often are important sediment archives of past sea levels hydroclimate climate and tectonic isostatic changes they consist mostly of ridgeplains at the start firmly attached or later migrated and welded to the mainland shore in addition to local hydrodynamic and topographic influences formation conditions may reflect overall paleogeographic conditions including fluvial impact in progradational regressive island settings barriers consist mainly of strandplains that laterally may alternate with narrow spit like sectors they include only single marine respectively lagoon side shore ridges with secondary dune fields sandwiched between them field observations and drillcore studies of microfossil and sediment based depositional facies suggest that most barrier islands originated by the often underestimated shoal aggradation mode two additional genetic models are recognizable a fourth remains hypothetical remotely sensed images indicate that post hurricane regeneration of the largest deltaic barrier chain in the gulf of mexico stalled in recent years late pleistocene barriers significantly influenced present coastal landforms in two extensive regions dramatic changes in past decades indicate that sea level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non deltaic barrier islands

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

shelly cheniers on a modern macrotidal flat mont saint michel bay france internal architecture revealed by ground penetrating radar abstract the relationship between short term morphodynamics and internal structure of shelly chenier ridges is investigated using ground penetrating radar and core x ray analysis complemented with a comparison of aerial photographs these cheniers are located on the uppermost part of a macrotidal flat in mont saint michel bay north western france they actively migrate landward over the salt marshes by washover processes when they are submerged during the coincidence of spring tides and enhanced wave activity the architecture of the cheniers is imaged using high frequency radar antennas 400 mhz to 2 6 ghz three types of cheniers are recognized featuring differences in morphology and internal structure the altitude of the banks on the tidal flat relative to the level of tidal flooding as well as local sediment supply seem to be important forcing parameters in chenier development and stages of evolution on a multi annual time scale evolution of this chenier system is influenced by a combination of the 18 year and the 4 year tidal cycles superimposed on wave activity during minima of the 18 year cycle spring tide level is globally lower on the tidal flat allowing salt marsh progradation and chenier ridge development during peak periods of the tidal cycle former barriers are reworked by wave action and experience onshore migration associated with salt marsh erosion the 4 year tidal cycle coupled with enhanced wave activity is probably responsible for the deposition of large washover units observed in gpr reflection profiles

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

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

the local insolation signature of air content in antarctic ice a new step toward an absolute dating of ice records an accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate a new domain of research in this area has been stimulated by the work of m bender linking the record of n2 o2 ratio in the air trapped in the ice with the local insolation here we investigate the potential of the air content of polar ice v as another and complementary ice proxy of local insolation we propose that the long term changes in air content recorded in ice from the high antarctic plateau is dominantly imprinted by the local summer insolation the v measurements covering the last 440 000 yr and obtained along the epica dc edc ice core are presented 86 of the variance observed in the v record can be explained neither by air pressure nor by temperature changes and then should reflect properties influencing the porosity at close off other than temperature a wavelet analysis indicates a dominant obliquity period around 41 ka over the last 440 ka we propose a mechanism which can account for the observed anti correlation between local insolation and v and explain how the local insolation via the integrated summer insolation can affect the near surface snow structure and consequently the porosity at close off the v and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago the phase difference may reflect the difference between the edc2 chronology based on an inverse dating method and an accurately dated insolation curve our work by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo record

the mid pleistocene transition in the tropical pacific a sea surface temperature sst record based on planktonic foraminiferal magnesium calcium ratios from a site in the western equatorial pacific warm pool reveals that glacial interglacial oscillations in sst shifted from a period of 41 000 to 100 000 years at the mid pleistocene transition 950 000 years before the present sst changes at both periodicities were synchronous with eastern pacific cold tongue ssts but preceded changes in continental ice volume the timing and nature of tropical pacific sst changes over the mid pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time

what drives the millennial and orbital variations of δ18oatm abstract the isotopic composition of atmospheric oxygen 18oatm is a complex marker that integrates changes in global sea level water cycle and biosphere productivity a strong signature of orbital precession has been identified leading to the use of low resolution measurements of 18oatm to date ice core records however the drivers of these 18oatm variations are still poorly known here we combine records of millennial and orbital scale variations on the northgrip vostok and epica dome c edc ice cores to explore the origin of 18oatm variations we show that superimposed on the dominant precession signal millennial 18oatm variations record systematic decreases during warm phases of the dansgaard oeschger events and systematic increases during the cold phases we show that at both timescales 18oatm is strongly related to the monsoon activity itself influenced by precessional and millennial shifts in intertropical convergence zone itcz then we show that despite its simplicity the dole effect defined as the difference between 18oatm and 18o of global sea level enables one to remove the obliquity signal within the 18oatm record and is a good indicator of hydrological cycle and biosphere productivity finally we compare the 18oatm records to past changes in atmospheric composition recorded in ice cores and conclude that 18oatm responds much more than ch4 to precession signal in contrast with earlier views similarities observed at orbital timescales between co2 and 18oatm reveal a stronger coupling than previously thought between the carbon and the oxygen cycles

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

orbital tuning chronology for the vostok climate record supported by trapped gas composition abstract we present data on the o2 n2 ratios of trapped gas samples for the entire length of the vostok climate record as in other cores o2 n2 ratios in these samples are less than the atmospheric ratio by a small and variable amount because o2 is selectively excluded during the gas trapping process and because o2 is also preferentially lost in poorly preserved core samples samples younger than 150 ka have large and variable o2 depletions samples older than 200 ka have o2 n2 ratios that replicate well and vary smoothly with depth we plot o2 n2 ratios of well replicated samples older than 160 ka using a chronology derived by matching the 18o of paleoatmospheric o2 18oatm to northern hemisphere june insolation on this timescale o2 n2 varies coherently with local 78 s summertime insolation based on time series analysis of the o2 n2 record and the dynamics of snow metamorphism at the surface we conclude that summertime insolation influences physical properties of ice grains that control the degree of o2 exclusion during bubble closeoff o2 n2 in vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core we show that the 18oatm chronology supported by the coincidence of o2 n2 ratios with insolation is also compatible with recent radiometric dating of corals from high sea stands we further successfully test the 18oatm tuning chronology by showing that it predicts a chronology for the gisp2 core which is essentially indistinguishable from the standard gisp2 chronology and therefore in excellent agreement with the radiometric chronology of hulu cave china an accurate chronology for the vostok ice core is now in place

tertiary anorogenic granites of the western border of the yemen plateau north yemen y a r was affected from 30 to 20 ma ago by intense magmatic activity trap series contemporary with the main tensional tectonic phases of the afro arabian plate in the trap activity two main phases have been recognized the former mainly basaltic between 30 and 26 ma and the second mainly acidic between 23 and 20 ma during the latter period of activity a basaltic dyke swarm and stock like bodies and dykes granophyres were emplaced along the escarpment and coastal plain some granitic bodies intruded the trap series towards the end of the first phase and during the second one on the basis of geochemical and petrological data the tertiary granites of yemen belong to alkaline or peralkaline associations of a type the textural characteristics indicate that the granites are either hypersolvus or subsolvus the mafic mineral assemblages allow three main types of granites to be distinguished by their different environments of crystallization as regards the origin of these kinds of granites several hypotheses account for the peculiarities observed the lack of crustal xenoliths the preliminary data on the sr isotopic ratio the data on major and trace elements point to a direct origin by fractional crystallization without substantial crustal interaction this agrees well with the strong tensile tectonics linked with the uplift of the afro arabian dome and with the lithosphere thinning which provide a minimal opportunity for interaction of the magmas with the crust

the timing of linear dune activity in the strzelecki and tirari deserts australia abstract linear dunes occupy more than one third of the australian continent but the timing of their formation is poorly understood in this study we collected 82 samples from 26 sites across the strzelecki and tirari deserts in the driest part of central australia to provide an optically stimulated luminescence chronology for these dunefields the dunes preserve up to four stratigraphic horizons bounded by palaeosols which represent evidence for multiple periods of reactivation punctuated by episodes of increased environmental stability dune activity took place in episodes around 73 66 35 32 22 18 and 14 10 ka intermittent partial mobilisation persisted at other times throughout the last 75 ka and dune activity appears to have intensified during the late holocene dune construction occurred when sediment was available for aeolian transport in the strzelecki and tirari deserts this coincided with cold arid conditions during marine isotope stage mis 4 late mis 3 and mis 2 and the warm dry climates of the late pleistocene holocene transition period and late holocene localised influxes of sediment on active floodplains and lake floors during the relatively more humid periods of mis 5 also resulted in dune formation the timing of widespread dune reactivation coincided with glaciation in southeastern australia along with cooler temperatures in the adjacent oceans and antarctica

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

expansion of subarctic water masses in the north atlantic and pacific oceans and implications for mid pleistocene ice sheet growth 1 past surface ocean circulation changes associated with the mid pleistocene transition 0 9 0 6 ma were reconstructed in the northern north atlantic odp 983 and the northwest pacific odp 882 using proxies for subarctic subpolar water mass distributions c37 4 alkenone and sea surface temperature u37 both sites experienced a secular expansion of subarctic waters from 1 15 ma spanning both glacial and interglacial intervals after 0 9 ma low c37 4 at site 983 records a northward retreat of subarctic waters during interglacials in the atlantic while continued high glacial c37 4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late pleistocene ice sheets in contrast a secular decline in c37 4 occurred at site 882 from 0 9 to 0 5 ma marking a more gradual retreat of subarctic conditions in the pacific it is proposed that the expansion of subarctic waters between 1 15 and 0 9 ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere ocean circulation changes associated with the mid pleistocene transition that began as early as 1 2 ma

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

using radar sounding data to identify the distribution and sources of subglacial water application to dome c east antarctica basal radar reflectivity is the most important measurement for the detection of subglacial water however dielectric loss in the overlying ice column complicates the determination of basal reflectivity dielectric attenuation is a function of ice temperature and impurity concentration temperature distribution is a function of climate history basal heat flow and vertical strain rate all of which can be partially inferred from the structure of dated internal layers using 11 dated layers isotope records from dome c east antarctica and a model of the spatial variation of geothermal flux we calculate the vertical strain rate and accumulation rate history allowing identification of areas where the basal melt rate exceeds 1 5 mm a 1 the accumulation rate history and vertical strain rates are then used as inputs for a transient temperature model the model outputs for the present day temperature distribution are then combined with depth dependent ionic concentrations to model dielectric loss and infer basal reflectivity the resulting reflection coefficients are consistent 5 db across a variety of subglacial water bodies we also identify a high reflectivity 15 db in concordia trench and along suspected subglacial water flow routes in vincennes basin highland areas tend to have highly variable reflection coefficients near 30 db consistent with an ice bedrock interface this combined model also identifies three areas of enhanced basal melting along concordia ridge concordia subglacial lake and vincennes basin melt at concordia subglacial lake exceeds 5 mm a 1 the inferred basal melt at these locations is not possible without enhanced geothermal flux we demonstrate how radar sounding data can provide both input and verification for a self consistent model of vertical strain vertical temperature distribution and meltwater distribution

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

the dole effect and its variations during the last 130 000 years as measured in the vostok ice core we review the current understanding of the dole effect the observed difference between the delta sup 18 o of atmospheric o sub 2 and that of seawater and its causes extended the record of variations in the dole effect back to 130 kyr before present using data on the delta sup 18 o of o sub 2 obtained from studying the vostok ice core and discuss the significance of temporal variations the dole effect reflects oxygen isotope fractionation during photosynthesis respiration and hydrologic processes evaporation precipitation and evapotranspiration our best prediction of the present day dole effect 20 8 per thousand is considerably lower than the observed value 23 5 per thousand and we discuss possible causes of this discrepancy during the past 130 kyr the dole effect has been 0 05 per thousand lower than the present value on average the standard deviation of the dole effect from the mean has been only per thousand and the dole effect is nearly unchanged between glacial maxima and interglacial periods the small variability in the dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant most periodic variability in the dole effect is in the precession band suggesting that changes in this global biogeochemical termmore reflects variations in low latitude land hydrology and productivity or possibly variability in low latitude oceanic productivity 65 refs 4 figs 3 tabs less

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

antarctic subglacial conditions inferred from a hybrid ice sheet ice stream model abstract subglacial conditions of large polar ice sheets remain poorly understood despite recent advances in satellite observation major uncertainties related to basal conditions such as the temperature field are due to an insufficient knowledge of geothermal heat flow here a hybrid method is presented that combines numerical modeling of the ice sheet thermodynamics with a priori information using a simple assimilation technique additional data are essentially vertical temperature profiles measured in the ice sheet at selected spots as well as the distribution of subglacial lakes in this way geothermal heat flow datasets are improved to yield calculated temperatures in accord with observations in areas where information is available results of the sensitivity experiments show that 55 of the grounded part of the antarctic ice sheet is at pressure melting point calculated basal melt rates are approximately 65 gt year 1 which is 3 of the total surface accumulation although these sensitivity experiments exhibit small variations in basal melt rates the impact on the ice age of basal layers is quite important in areas that are characterized by relatively low melt rates this may lead to standard deviations up to 50 in a model run over a period of 10 6 years subglacial water flow is concentrated underneath the large outlet glaciers of antarctica the larger subglacial lakes are perched at the head of these subglacial water systems an exception however is the lake system of the recovery ice stream catchment that receives a substantial amount of subglacial melt water from the upstream catchment

pleistocene glacial terminations triggered by synchronous changes in southern and northern hemisphere insolation the insolation canon hypothesis throughout the last 900 kyr the late pleistocene earth has experienced periods of cold glacial climate punctuated by seven abrupt transitions to warm interglacials the so called terminations although most of glacial ice is located in the northern hemisphere nh the southern hemisphere sh seems to play a crucial role in deglaciation variation in the seasonal distribution of solar insolation is one candidate for the cause of these climatic shifts but so far no simple mechanism has been identified here we present a mathematical analysis of variations in midsummer insolation in both hemispheres at 65 latitude applying this analysis to the entire pleistocene the last 2 myr we find that prior to each termination the insolation in both hemispheres increases in concert with a sh lead introducing time and energy thresholds to these overlaps calculated times for the onsets of the seven terminations by this insolation canon exceptional overlaps meeting the two threshold prerequisites are 23 139 253 345 419 546 and 632 kyr bp perfectly matching the geologic record the timing originates from the interplay between the two orbital parameters obliquity and precession explaining why terminations occur at integer multiple of the precessional cycle there is no such constellation between 1 and 2 myr bp the early pleistocene in agreement with earth s climate at that time this change in orbital forcing coincides with the mid pleistocene revolution separating the late from the early pleistocene therefore we hypothesize that the insolation canon is the trigger for glacial terminations

palaeoclimate global warmth with little extra co 2 most climate models consider only short term processes such as cloud and sea ice formation when assessing earth s sensitivity to greenhouse gas forcing mounting evidence indicates that the response could be stronger if boundary conditions change drastically

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

transient nature of late pleistocene climate variability the past three million years have seen dramatic climate fluctuation with conditions swinging between cold glacial and warm interglacial extremes these changes are usually interpreted as nonlinear responses of the climate system to subtle cyclical changes in earth s orbit or gradual reduction in the earth s background co2 level thomas crowley and william hyde offer an alternative view proposing that these increasingly pronounced fluctuations though driven by orbital variations are indicative of transient behaviour of a system approaching a branching point that is a point at which the system will undergo a transition to a new stable climate state of permanent midlatitude northern hemisphere glaciation modelling results predict that such a transition could occur in the geologically near future 10 000 100 000 years but only in the unlikely event that background atmospheric co2 falls to levels lower than at during the past 10 000 years climate in the early pleistocene1 varied with a period of 41 kyr and was related to variations in earth s obliquity about 900 kyr ago variability increased and oscillated primarily at a period of 100 kyr suggesting that the link was then with the eccentricity of earth s orbit this transition has often2 3 4 5 been attributed to a nonlinear response to small changes in external boundary conditions here we propose that increasing variablility within the past million years may indicate that the climate system was approaching a second climate bifurcation point after which it would transition again to a new stable state characterized by permanent mid latitude northern hemisphere glaciation from this perspective the past million years can be viewed as a transient interval in the evolution of earth s climate we support our hypothesis using a coupled energy balance ice sheet model which furthermore predicts that the future transition would involve a large expansion of the eurasian ice sheet the process responsible for the abrupt change seems to be the albedo discontinuity at the snow ice edge the best fit model run which explains almost 60 of the variance in global ice volume6 during the past 400 kyr predicts a rapid transition in the geologically near future to the proposed glacial state should it be attained this state would be more symmetric than the present climate with comparable areas of ice sea ice cover in each hemisphere and would represent the culmination of 50 million years of evolution from bipolar nonglacial climates to bipolar glacial climates

a paleoclimatic enigma major glaciations began in the northern hemisphere around 2 75 million years ago after a long prior interval of climatic cooling numerous observations reveal how climate cooled before glacial onset but our understanding of the driving forces behind the cooling remains incomplete

the prerifting stage in the evolution of continental rift zones abstract with the unique red sea rift zone as a basic example the concept of the relation of riftogenesis to prerifting geological evolution is theoretically substantiated new aspects of endogenic regimes and continental crust destruction are defined and a pattern of multistage riftogenesis is outlined the process of riftogenesis is predetermined by long term recurrent thermal mantle activation within well defined linear zones the concept of inheritance of riftogenesis is worked out and the double nature of riftogenesis shown viz its inheritance and autonomy the prerifting stage is characterized by multifocal mantle activation whereas the riftogenesis stage is accompanied by a rise of mantle diapirs the regularities discussed in this paper are typical of the so called active type rifts

a century of climate variability in central dronning maud land east antarctica and its relation to southern annular mode and el nino southern oscillation stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core retrieved from the central dronning maud land east antarctica in order to reconstruct the coastal antarctic climate variability during the last century and its relation to the southern annular mode sam and el nino southern oscillation enso the 18 o records showed a significant relation to the sam with a dominant 4 years variability except during specific periods 1918 1927 19381947 1989 2005 when enso teleconnection was established through the in phase relation between sam and southern oscillation index soi the combined influence of enso and sam was seen on surface air temperatures in this region mainly during the austral summer season from 1989 to 2005 further a significant relationship between 18 o and sam was observed on a decadal scale which overrides the intermittent influence of enso major shifts in the deuterium excess record were observed during periods of enso teleconnections which support a shift in moisture source regions during the periods of stronger enso teleconnections surface air temperatures estimated using the 18 o t spatial slope for this region depicted a significant warming of 1 c for the past century the study reveals that throughout the last century sam was the dominant mode of climatic variability in the coastal region of central dronning maud land on a decadal scale

onset of pacific style deep sea sedimentary carbonate cycles at the mid pleistocene transition the calcium carbonate caco3 content of deep sea sediments in the pacific ocean increases during glacials of the late pleistocene in comparison to interglacials whereas records of sedimentary caco3 in the atlantic ocean show an anticorrelated pattern across glacial interglacial cycles here we show that this anticorrelation in inter ocean caco3 cycles arose comparatively recently at 1 10 million years ago ma during the mid pleistocene transition before this time we show that the caco3 content of pacific and atlantic ocean sediments experienced in phase cyclicity both having atlantic style phasing with respect to glacial interglacial cycles the onset of anticorrelated cyclicity at 1 10 ma involved a twofold switch in the pacific s caco3 cycles glacial caco3 preservation became consistently better while interglacial preservation became consistently worse we demonstrate that the cause of this glacial interglacial mirror imaging of pacific caco3 dissolution cyclicity at 1 10 ma was a switching over of the relative ventilation state of abyssal south pacific waters between glacials and interglacials specifically we suggest that a consistent strengthening of deep water ventilation within the pacific sector of the southern ocean during glacials drove glacial pacific caco3 dissolution to diminish while a contemporaneous weakening of very well ventilated upstream north atlantic deep water during interglacials drove interglacial pacific caco3 dissolution downstream to intensify we propose that the increased mean alkalinity of the global deep ocean driven by the geographically and bathymetrically vast pacific ocean during glacials after 1 10 ma may explain part of the drawdown in glacial atmospheric co2 levels hypothesised to have been linked to the increased severity of these late pleistocene glacials

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

holocene climate and vegetation dynamics on nightingale island south atlantic an apparent interglacial bipolar seesaw in action abstract high resolution analyses of a sediment sequence from an in filled lake on nightingale island at 37 s in the south atlantic have revealed hydrological variations during the last 10 700 cal yr bp which are linked to shifts in the southern hemisphere westerlies and the meridional overturning circulation moc in the atlantic the lowermost part of the sequence 10 700 8600 cal yr bp consists of peat the peat is overlaid by gyttja which continues up to the final overgrowing of the basin around 500 years ago the transition from peat to gyttja at 8600 cal yr bp implies a significant increase in effective humidity probably caused by a northward shift of the southern hemisphere westerlies after the end of the antarctic thermal optimum recurring phases of increased erosion with high deposition of minerogenic particles terrestrial organic matter high c n ratios and pollen grains from plant taxa growing in more distal parts of the catchment indicate periods with higher precipitation these high precipitation periods correspond to periods of southward shifted southern hemisphere westerlies inferred from south america and with periods of weaker moc in the north atlantic therefore we conclude that these periods also characterized by decreased influence from marine aerosols were not caused by the stronger westerlies but by weaker moc and less heat transport from the south to the north atlantic causing warmer sea surface temperatures ssts and increased precipitation in the south atlantic this is the expression of the bipolar seesaw mechanism and implies that it may have been operational also during interglacial conditions

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years 1 we measured 17 o and 18 o in recent antarctic snow and down the vostok ice core and calculated the excess of 17 o with respect to vsmow the magnitude of the 17 o excess in the holocene and the last interglacial is 45 per meg and it remains constant in a transect from the coast to the continental interior analysis of the transect data shows that the 17 o excess is not sensitive to temperature variations over the continent there are significant shifts in 70 excess from low values in glacial to high values in interglacial times the observed shifts suggest higher normalized relative humidity and or wind speeds over the source oceanic regions in glacial times

on the mid pleistocene transition to 100 kyr glacial cycles and the asymmetry between glaciation and deglaciation times 1 a mechanism is proposed for the mid pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations the same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41 kyr oscillations prior to the transition these features arise naturally within the framework of the sea ice switch glacial cycle mechanism of gildor and tziperman 2000 as a result of the gradual cooling of the deep ocean during the pleistocene this cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets it is this latter change that leads to the activation of the sea ice switch and therefore to the initiation of the 100 kyr oscillations the gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods this proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid pleistocene gradual cooling of the deep ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 1620 global change climate dynamics 3309 1640 global change remote sensing 4267 oceanography general paleoceanography keywords climate dynamics glacial cycles mid pleistocene transition 100 kyr 41 kyr

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

cheniers and chenier plains a general introduction abstract cheniers and chenier plains have been studied in many coastal regions throughout the world an inventory of the investigations currently being carried out is presented in this and accompanying papers cheniers and chenier plains are azonal features their distribution ranges from tropical to the subarctic regions and they show a variety of features progradational shorelines where mud accretion is temporarily interrupted favour the development of these features in addition to the concept of otvos and price who define cheniers and chenier plains as being formed exclusively in relation to littoral progradational environments it is suggested here that chenier formation in deltaic progradational environments should also be included genetically two types of cheniers can be distinguished depending on the origin of the related sediments cheniers developing due to wave winnowing of the muddy sediments and the subsequent concentration of the coarser particles to form a longshore bar or ridge which is driven shoreward and cheniers built by littoral drift in both cases they can be recognised by their sedimentary structures when cheniers arrive onshore they will migrate further landward due to washover processes under extreme hydrodynamical conditions e g spring tides storm surges etc to summarise the information concerning the episodic development of chenier plains in order to produce a or a few universal model s appears to be very difficult owing to the numerous factors that influence their formation these include river mouth shifting sealevel changes climatic changes storm frequency mortality of shellfish and bay geometry owing to this sensitivity to environmental changes during their formation cheniers are considered to be very important geomorphological features they provide a relatively accurate record of sealevel and environmental changes which can be dated with high resolution

deep ice cores the need for going back in time abstract after the success of epica the european project for ice coring in antarctica which at dome c east antarctica has provided access to climate and environmental records covering the last 800 ka thousands of years the ice core community is now engaged in the challenge to obtain older records obtaining a 1 5 million year ma record of climate and greenhouse gases is one of the priorities of the international partnerships in ice core sciences ipics largely motivated by the yet unexplained shift in climate cyclicity around the mid pleistocene transition mpt around 1 2 ma ago from epica results and recently published articles we further examine how such a 1 5 ma old ice core will help and is indeed indispensable to depict and understand this transition

glacial and deglacial climatic patterns in australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near shore proxy data abstract this study forms part of a wider investigation of late quaternary environments in the southern hemisphere we here review the terrestrial and near shore proxy data from australia indonesia papua new guinea png new zealand and surrounding oceans during 35 10 ka an interval spanning the lead up to the last glacial maximum lgm the lgm proper 21 2 ka and the ensuing deglaciation sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval a stratigraphically consistent chronology and one or more sources of proxy climatic data tropical australia indonesia and png had lgm mean annual temperatures 3 7 c below present values and summer precipitation reduced by at least 30 consistent with a weaker summer monsoon and a northward displacement of the intertropical convergence zone the summer monsoon was re established in northwest australia by 14 ka precipitation in northeast australia was reduced to less than 50 of present values until warmer and wetter conditions resumed at 17 16 ka followed by a second warmer wetter phase at 15 14 ka lgm temperatures were up to 8 c lower than today in mainland southeast australia and up to 4 c cooler in tasmania winter rainfall was much reduced throughout much of southern australia although periodic extreme flood events are evident in the fluvial record glacial advances in southeast australia are dated to 32 2 5 19 1 1 6 and 16 8 1 4 ka with periglacial activity concentrated towards 23 16 ka deglaciation was rapid in the snowy mountains which were ice free by 15 8 ka minimum effective precipitation in southern australia was from 14 to 12 ka in new zealand the glacial advances date to 28 21 5 and 19 ka with the onset of major cooling at 28 ka or well before the lgm there is no convincing evidence for a younger dryas cooling event in or around new zealand but there are signs of the antarctic cold reversal in and around new zealand and off southern australia there remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of new zealand sites one explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids sea surface temperatures ssts were up to 5 c cooler during the lgm with rapid warming after 20 ka to attain present values by 15 ka the increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation warmer ssts and steeper thermal gradients between land and sea the postglacial increase in winter rainfall in southern australia is probably related to the southward displacement of the westerlies as ssts around antarctica became warmer and the winter pack ice and antarctic convergence zone retreated to the south

extensive mis 3 glaciation in southernmost patagonia revealed by cosmogenic nuclide dating of outwash sediments abstract the timing and extent of former glacial advances can demonstrate leads and lags during periods of climatic change and their forcing but this requires robust glacial chronologies in parts of southernmost patagonia dating pre global last glacial maximum glgm ice limits has proven difficult due to post deposition processes affecting the build up of cosmogenic nuclides in moraine boulders here we provide ages for the rio cullen and san sebastian glacial limits of the former bahia inutil san sebastian bi ssb ice lobe on tierra del fuego 53 54 s previously hypothesised to represent advances during marine isotope stages mis 12 and 10 respectively our approach uses cosmogenic 10be and 26al exposure dating but targets glacial outwash associated with these limits and uses depth profiles and surface cobble samples thereby accounting for surface deflation and inheritance the data reveal that the limits formed more recently than previously thought giving ages of 45 6 ka 139 9 14 3 for the rio cullen and 30 1 ka 45 6 23 1 for the san sebastian limits these dates indicate extensive glaciation in southern patagonia during mis 3 prior to the well constrained but much less extensive mis 2 glgm limit this suggests the pattern of ice advances in the region was different to northern patagonia with the terrestrial limits relating to the last glacial cycle rather than progressively less extensive glaciations over hundreds of thousands of years however the dates are consistent with mis 3 glaciation elsewhere in the southern mid latitudes and the combination of cooler summers and warmer winters with increased precipitation may have caused extensive glaciation prior to the glgm

consistent dating for antarctic and greenland ice cores we are hereby presenting a new dating method based on inverse techniques which aims at calculating consistent gas and ice chronologies for several ice cores the proposed method yields new dating scenarios simultaneously for several cores by making a compromise between the chronological information brought by glaciological modeling i e ice flow model firn densification model accumulation rate model and by gas and ice stratigraphic constraints this method enables us to gather widespread chronological information and to use regional or global markers i e methane volcanic sulfate beryllium 10 tephra layers etc to link the core chronologies stratigraphically confidence intervals of the new dating scenarios can be calculated thanks to the probabilistic formulation of the new method which takes into account both modeling and data uncertainties we apply this method simultaneously to one greenland ngrip and three antarctic epica dome c epica dronning maud land and vostok ices cores and refine existent chronologies our results show that consistent ice and gas chronologies can be derived for depth intervals that are well constrained by relevant glaciological data in particular we propose new and consistent dating of the last deglaciation for greenland and antarctic ice and gas records

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the role of southern ocean processes in orbital and millennial co2 variations a synthesis abstract recent progress in the reconstruction of atmospheric co 2 records from antarctic ice cores has allowed for the documentation of natural co 2 variations on orbital time scales over the last up to 800 000 years and for the resolution of millennial co 2 variations during the last glacial cycle in unprecedented detail this has shown that atmospheric co 2 varied within natural bounds of approximately 170 300 ppmv but never reached recent co 2 concentrations caused by anthropogenic co 2 emissions in addition the natural atmospheric co 2 concentrations show an extraordinary correlation with southern ocean climate changes pointing to a significant direct or indirect influence of climatic and environmental changes in the southern ocean region on atmospheric co 2 concentrations here we compile recent ice core and marine sediment records of atmospheric co 2 temperature and environmental changes in the southern ocean region as well as carbon cycle model experiments in order to quantify the effect of potential southern ocean processes on atmospheric co 2 related to these orbital and millennial changes this shows that physical and biological changes in the so are able to explain substantial parts of the glacial interglacial co 2 change but that none of the single processes is able to explain this change by itself in particular changes in the southern ocean related to changes in the surface buoyancy flux which in return is controlled by the waxing and waning of sea ice may favorably explain the high correlation of co 2 and antarctic temperature on orbital and millennial time scales in contrast the changes of the position and strength of the westerly wind field were most likely too small to explain the observed changes in atmospheric co 2 or may even have increased atmospheric co 2 in the glacial also iron fertilization of the marine biota in the southern ocean contributes to a glacial drawdown of co 2 but turns out to be limited by other factors than the total dust input such as bioavailability of iron or macronutrient supply

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

modelling northern hemisphere ice volume over the last 3 ma the northern hemisphere ice sheet volumes over the last 3 ma were simulated using the lln 2 d model the forcings were both insolation and co2 concentration different atmospheric co2 scenarios were used because of a lack of co2 reconstruction over this remote past with constant co2 concentrations the simulated ice volume does not show any gradual increase as recorded in the marine sediments moreover its spectrum changes according to the chosen value of co2 when co2 is fixed at 220 ppmv the simulated ice volume is dominated by the similar to 100 ka period if a pre industrial co2 concentration of 280 ppmv is used the simulation is dominated by the similar to 41 ka period by using a linearly decreasing co2 concentration going from 320 ppmv at 3 ma bp to 200 ppmv at present the simulated changes in the power spectrum are in agreement with those obtained from the sedimentary records roughly before 1 ma bp the dominating period is similar to 41 ka afterwards the similar to 100 ka period becomes dominant this transition is accompanied by a gradual increase of the ice volume potential mechanisms for this transition are discussed using cyclic co2 fluctuations over the last 0 6 ma does not change significantly the spectral characteristics of the simulated ice volume but amplifies the amplitude of its variations c 1998 elsevier science ltd all rights reserved

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

tropical ocean temperatures over the past 3 5 million years determining the timing and amplitude of tropical sea surface temperature sst change is an important part of solving the puzzle of the plio pleistocene ice ages alkenone based tropical sst records from the major ocean basins show coherent glacial interglacial temperature changes of 1 to 3 c that align with but slightly lead global changes in ice volume and deep ocean temperature over the past 3 5 million years tropical temperatures became tightly coupled with benthic 18o and orbital forcing after 2 7 million years we interpret the similarity of tropical sst changes in dynamically dissimilar regions to reflect top down forcing through the atmosphere the inception of a strong carbon dioxide greenhouse gas feedback and amplification of orbital forcing at 2 7 million years ago connected the fate of northern hemisphere ice sheets with global ocean temperatures since that time

southern ocean dust climate coupling over the past four million years dust plays a central part in ocean biogeochemical cycles by supplying iron and other essential micronutrients to regions where marine productivity is limited by the availability of iron martinez garcia et al present a marine record of dust and iron supply to the southern ocean during the past four million years the data derived from leaf waxes establish that previous records of dust flux from antarctic ice cores are broadly representative of a larger area importantly the dust and iron supply rose sharply 1 25 million years ago suggesting that increased dust supply may be a major influence on the more severe swings between the glacial and interglacial climate of the late pleistocene dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean1 2 indeed dust supply to the southern ocean increases during ice ages and iron fertilization of the subantarctic zone may have contributed up to 40 parts per million by volume p p m v of the decrease 80 100 p p m v in atmospheric carbon dioxide observed during late pleistocene glacial cycles3 4 5 6 7 so far however the magnitude of southern ocean dust deposition in earlier times and its role in the development and evolution of pleistocene glacial cycles have remained unclear here we report a high resolution record of dust and iron supply to the southern ocean over the past four million years derived from the analysis of marine sediments from odp site 1090 located in the atlantic sector of the subantarctic zone the close correspondence of our dust and iron deposition records with antarctic ice core reconstructions of dust flux covering the past 800 000 years refs 8 9 indicates that both of these archives record large scale deposition changes that should apply to most of the southern ocean validating previous interpretations of the ice core data the extension of the record beyond the interval covered by the antarctic ice cores reveals that in contrast to the relatively gradual intensification of glacial cycles over the past three million years southern ocean dust and iron flux rose sharply at the mid pleistocene climatic transition around 1 25 million years ago this finding complements previous observations over late pleistocene glacial cycles5 8 9 providing new evidence of a tight connection between high dust input to the southern ocean and the emergence of the deep glaciations that characterize the past one million years of earth history

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

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

the response of atmospheric nitrous oxide to climate variations during the last glacial period detailed insight into natural variations of the greenhouse gas nitrous oxide n2o in response to changes in the earth s climate system is provided by new measurements along the ice core of the north greenland ice core project ngrip the presented record reaches from the early holocene back into the previous interglacial with a mean time resolution of about 75 years between 11 and 120 kyr bp atmospheric n2o concentrations react substantially to the last glacial interglacial transition termination 1 and millennial time scale climate variations of the last glacial period for long lasting dansgaard oeschger do events the n2o increase precedes greenland temperature change by several hundred years with an increase rate of about 0 8 1 3 ppbv century which accelerates to about 3 8 10 7 ppbv century at the time of the rapid warming in greenland within each bundle of do events the new record further reveals particularly low n2o concentrations at the approximate time of heinrich events this suggests that the response of marine and or terrestrial n2o emissions on a global scale are different for stadials with and without heinrich events

sg06 a fully continuous and varved sediment core from lake suigetsu japan stratigraphy and potential for improving the radiocarbon calibration model and understanding of late quaternary climate changes abstract the high potential of the varved sediments of lake suigetsu central japan to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades however this potential has not been fully realised since the only available long sediment core from the lake sg93 was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections in the summer of 2006 a new sediment core sg06 was recovered from the lake four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely without gaps between segments this new record provides the ability to test existing atmospheric radiocarbon calibration models as well as to assess the scale of inter regional leads and lags in palaeoclimatic changes over the last glacial interglacial cycle multi disciplinary analyses from sg06 are still ongoing but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released thereby allowing fully informed critical evaluation of all subsequent releases of data based on the sg06 record in this paper we report key litho stratigraphic information concerning the sg06 sediment core highlighting changes in the clarity of annual laminations varves with depth and possible implications for the mechanism of the climate change we also discuss the potential of the sg06 record to meet the fundamental goals of the inqua intimate project