u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

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

diagenesis of fossil coral skeletons correlation between trace elements textures and 234 u 238 u a comparative study of pleistocene fossil coral skeletons and of modern coral skeletons was carried out using petrographie and trace element analyses on a suite of pleistocene samples that had previously been studied for 234 u 230 th and u 230 th ages chen et al 1991 evidence of a range of diagenetic changes can be recognized by optical om and scanning electron microscopy sem the normal texture exhibited by modern corals under om consists of fine needles of aragonite forming a radial fibrous pattern around a central dark line center of calcification this pattern can also be seen in many fossil corals in most cases the central dark line partially disappears during diagenesis the radialfibrous pattern is obscured and there is a distinct coarsening of the radial fabric of aragonite to unoriented platy or equant aragonite crystals sem images show diagenetic textures ranging from dense structureless images of the coralline matrix with sharp boundaries at the septa walls to the development of 1 a patchy distribution of dissolution micropores partially filled with aragonite fibers in the matrix 2 aragonite needles coming from selvages in the septa walls which radiate into the septa voids using an electron microprobe and sem concentrations of na s sr and mg were measured no other trace elements were detected na s and mg contents of the matrix the fibrous micropores and radiating needles are highly variable and well correlated high concentrations of na s and mg were found in modern living corals with lower concentrations in fossil corals and fibrous micropores and the lowest value in the radiating needles the reason for the correlations of na s and mg and crystal chemistry and the response to diagenesis of these trace elements is not understood the average concentrations of na s and mg for each sample when plotted against the whole coral initial 234 u are generally correlated chen et al 1991 as all these diagenetic changes involve the recrystallization and deposition of aragonite we infer that the geologic site of diagenesis both for forming the secondary aragonitic phases and for the enhancement of the 234 u content in the fossil corals was the marine environment it is possible that the textural and na s and mg trace element contents of fossil corals be used to ascertain the reliability of fossil coral skeletons for u 230 th dating the basic problem of identifying a priori unaltered coral skeletons for 230 th dating is not yet resolved

tims u series dating and stable isotopes of the last interglacial event in papua new guinea the extensive flight of uplifted reef terraces which occurs along the vitiaz strait on the northern flank of the huon peninsula in png papua new guinea contains a particularly good record of sea level changes in the last 250 ky the huon terraces were the target of an international expedition which took place in july august 1988 in particular we searched for suitable samples for u series dating in a reef complex designated as vii which is correlated with the last interglacial episode and high sea level stand this complex is composed of a barrier reef viib a lagoon and a fringing reef viia twelve corals from these terraces and two corals from the older reef complex viii were selected for analysis the petrography oxygen and carbon isotope compositions and magnesium and strontium concentrations were determined along with the concentrations and isotopic compositions of uranium and thorium 230 th 234 u ages of the corals with 99 aragonite having primary textures and which show u sr ratios around 0 4 10 3 and initial 234 u values close to that of present seawater appear to be reliable the most reliable ages from complex vii corals fall in two tight groups centered at 118 ky and 134 ky corals with 234 u t values higher than 160 and u sr ratios substantially lower than seawater are assumed to have undergone diagenetic alteration which appears to be common in this area the simplest model for sea level height for terrace vii is a continuous rise between 134 and 118 ky alternatively there may have been two periods of rapid sea level rise in contrast in the bahamas there is evidence that sea level remained rather constant over the time interval 132 to 120 ky the absence of ages between 132 and 120 ky in png could be the result of changes in the local tectonic uplift rates during that time or erosion that disrupted the continuous record in any event we find no basis for accepting a single brief time for the age of the last interglacial and applying this age as a precise chronometer for worldwide correlation or as a test of climatic models the older ages reported here precede the milankovitch solar insolation peak at 128 ky and the younger ages are 10 ky after this peak if the present high precision data are correct then it will be necessary to reassess the validity of the milankovitch theory of climatic changes the fundamental issue which must now be resolved is a means of identifying coral samples that have not been disturbed by diagenetic processes

234u 238u mass spectrometry of corals how accurate is the uth age of the last interglacial period direct measurement of u and th by mass spectrometry recently provided a spectacular improvement in the precision of coral dating by the uth disequilibrium method 1 mass spectrometric data also provide a much better resolution for the examination of subtle diagenetic effects revealed by small variations of the 234u 238u ratio such perturbations may strongly affect the accuracy of the uth chronometer a compilation of all the corals analyzed to date by mass spectrometry shows that most of the corals from terraces of the last interglacial have initial 234u 238u ratios higher than present day seawater in contrast to modern holocene and last glacial corals some samples that have very high 234u 238u initial ratios up to 1 2 and high u concentrations up to 4 ppm were probably contaminated by continental groundwaters however even apparently pristine samples have 234u 238u initial ratios which are still slightly higher than present day seawater mean value 1 160 compared to 1 140 1 150 2 with little overlap between the two distributions this difference in the u initial ratio raises some uncertainty about the accuracy of the uth age determinations of these corals in spite of the fact that the 234u230th ages cluster in a narrow range between 122 and 133 kyr the data could also be interpreted as resulting from slight contamination of corals that are significantly older than 125 kyr two possible explanations may explain these data 1 all these samples may have been diagenetically altered since they all come from surface outcrops which have been directly exposed to precipitations or soil waters for 125 kyr in this case the true age of these corals remains uncertain depending on the timing of the alteration process i e initial late or continuous 2 the second possibility is that some of the differences in 234u 238u ratios measured in 125 kyr cold corals compared to modern seawater may be due to a higher 234u 238u ratio in seawater 125 kyr ago this could result from temporal variations in the weathering regimes of continental land masses

was there an abrupt cold climatic event in the middle eemian pollen record from a palaeolake at the hieronimowo site ne poland abstract seventy samples of lacustrine sediments from a palaeolake at the hieronimowo site ne poland were investigated by pollen analysis method the obtained results indicate that the examined sequence spans the whole eemian interglacial mis 5e the beginning of the early vistulian weichselian mis 5d and some undefined period of the plenivistulian middle weichselian mis 2 4 the specific feature of the studied profile is the great thickness of deposits representing the hornbeam phase of the eemian interglacial e5 r paz which was the younger part of the climatic optimum of this interglacial and the very well developed pollen record of this phase that is absent in other profiles in ne poland due to this our study allowed for the first time in ne poland the detailed reconstruction of changes in the vegetation and in the mean january and july temperature during the middle part of the eemian interglacial this reconstruction unequivocally rules out the existence of an abrupt short lasting cold event at that time only a gradual slight increase in temperature was apparent during the older part of the hornbeam phase to 21 c for july and to 0 c for january and gradual decrease during its younger part to 17 c for july and to 5 c and

multi stage reef development on barbados during the last interglaciation by mapping the vertical and lateral distribution of reefal facies on the west and south coast of barbados we have produced a revised model of reef development for the last interglaciation we find that reef architecture around barbados has significant complexity including evidence for wave exposure related variations in reef geometry and at least 3 stages of reef development that were controlled by variations in sea level during the main stage of development an acropora palmata dominated reef crest aggraded 22 m in response to a minimum sea level rise of 20 m during stage 2 a sea cave was cut 3 4 m above the fossil reef crest possibly indicating that reef growth was terminated before sea level reached the highstand similar sequences elsewhere in the caribbean indicate that this early reef demise may not be a local phenomenon several reefs apparently stopped growing between 2 and 4 m and only in sheltered areas did they reach the highstand at 6 m as recorded by intertidal notches this pattern of reef demise has previously been related to rapid sea level rise at the end of the interglacial but stratigraphic data are equivocal the final stage of reef development on barbados occurred when sea level began to fall this fall was rapid leaving a thin but widespread veneer of reef crest deposits over the proximal reef front and discontinuous intertidal and shallow subtidal deposits capping the distal reef front although further dating is required to differentiate these three stages our only reliable u th tims date indicates that almost 50 of the exposed reef had accreted by 129 ka giving an estimate of 15 ka for the main aggradational stage furthermore reports of relict reef crests buried beneath these exposed deposits indicate that our revised model is incomplete and that earlier stages of reef growth occurred during the last interglaciation these earlier stages imply that sea level was at an interglacial level for as long as 20 ka supporting the devils hole record of interglacial duration unfortunately these estimates could not be verified directly because most of our u th data show major stratigraphic age reversals attributed to diagenesis this pattern is also evident in all other well dated reefal units in the caribbean and leads us to conclude that only diagenetically screened precise stratigraphically consistent coral dates can be used to directly estimate the duration of the last interglaciation

last glacial sea level change deduced from uplifted coral terraces of huon peninsula papua new guinea we have dated corals sampled from the uplifted terraces of huon peninsula papua new guinea that grew during the marine isotope stage 3 to reconstruct sea levels of the last glacial period from 30 to 55 ka kiloannum mass spectrometric u series dating methods resulted in high precision dates and could also be used to recognize diagenetically altered samples the only quantitative test of open systembehaviour of both uraniumand thoriumisotopes involves the com parison of 234 u 238 u ratios at the time of coral growth with present sea water values additional tests included checks for systematic variations in stable isotopes x ray diffraction to detect calcification and petrographic examination sea levels were corrected for glacio hydro isostatic variations and also for the depth range of coral growth habitat sea levels from30 to 55 ka were approxim ately 80 mlower than present superimposed on this general trend four periodic sea level high stands were found at 6 8 ka intervals approximately at 30 38 44 and 52 ka that appear to be synchronous with rapid climate variations previously observed in ice cores and in deep sea sediments r 2001 elsevier science ltd and inqua all rights reserved

234u 238u ratios and230th ages for hateruma atoll corals implications for coral diagenesis and seawater234u 238u ratios published results for corals that are more than ca 50 ka old from for example barbados and vanuata often yield initial 234u 238u activity ratios that are significantly greater than 1 144 0 004 the value for modern seawater this study reports results for corals from hateruma atoll japan and investigates the effects of diagenesis on the initial 234u 238u ratios of the corals hateruma consists of over 95 reef material of less than 500 ka in age because groundwaters associated with recent carbonates tend not to have elevated 234u 238u ratios the scope for increasing the 234u 238u ratios of hateruma corals through groundwater interaction should be minimal the corals examined range from those which show no petrographic or x ray evidence for diagenetic alteration and are pristine to those containing secondary cements of either aragonite or high or low mg calcite these various phases have been mechanically separated and analysed in agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples it is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial 234u 238u ratios of the six pristine corals three have anomalous 230th 238u ratios requiring u loss and or230th addition the remaining fifteen of the eighteen total analyses reported here yield ages from 1 6 ka to 260 ka no evidence for an increase in 234u 238u ratios in past seawater from this period has been found the best estimates for 234u 238u ratios are close to the current seawater value

high precision u series dating of corals from western australia and implications for the timing and duration of the last interglacial abstract u series ages using methods of thermal ionisation mass spectrometry tims are reported for last interglacial fossil reefs along the stable coastal margin of western australia thorium isotope ratios were measured with superior precision using methods of charge collection high levels of precision in the measurement of both uranium and thorium isotopes has reduced the age uncertainty due to analytical errors excluding the uncertainty in the decay constants by a factor of four over the precisions reported by many earlier tims workers uncertainties in 234u t determined from both 230th 238u and 234u 238u are also significantly smaller than previously reported allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified strict criteria were adopted to screen the new western australian data reliable ages range from 127 to 122 ka published tims observations from other localities have been assessed using the same strict criteria when these are combined with glacio hydro isostatic sea level models they indicate that the last interglacial period occurred from at least 130 to 117 ka however these age constraints are largely determined from single data points and need to be verified with additional ages before considering them to be robust estimates for the timing of onset and termination of the last interglacial globally the main episode of reef growth appears to be confined to a narrow interval occurring from 127 to 122 ka in direct agreement with the narrow range in ages obtained from the western australian sites this may indicate that the last interglacial was of short duration extending from 127 to 122 ka only alternatively this interval may reflect a major reef building event in the middle of a longer duration 130 117 ka interglacial interval

mass spectrometric 230th 234u 238u dating of the devils hole calcite vein the devils hole calcite vein contains a long term climatic record but requires accurate chronologic control for its interpretation mass spectrometric u series ages for samples from core dh 11 yielded 230 th ages with precisions ranging from less than 1 000 years 2 for samples younger than 140 ka thousands of years ago to less than 50 000 years for the oldest samples 566 ka the 234 u 238 u ages could be determined to a precision of 20 000 years for all ages calcite accumulated continuously from 566 ka until 60 ka at an average rate of 0 7 millimeter per 10 3 years the precise agreement between replicte analyses and the concordance of the 230 th 238 u 234 u 238 u ages for the oldest samples indicate that the dh 11 samples were closed systems and validate the dating technique in general

late pleistocene and holocene sea level change along the australian coast abstract tectonically the australian continent is relatively stable and as such it provides a good platform for studying late pleistocene and holocene sea level change the observations indicate that present sea level was reached at about 6000 years ago and that since then level has remained constant to within a few metres considerable spatial variability in the amplitude of the emergence and in the time at which sea levels first reached their present values have been observed spatial variability has also been observed in the sea level during the last glacial maximum and during the late phase of the holocene transgression much of this variaiblity is the result of the earth s adjustment to the glacial melting in the late pleistocene early holocene time and the concomitant distribution of this meltwater into the oceans conclusions that are drawn from matching observations with this glacio hydro isostatic model include the following 1 the mantle viscosity increases with depth the average upper mantle viscosity is about 2 3 10 20 pa s and the average lower mantle defined as below 670 km depth viscosity is about 10 22 pa s the average lithospheric thickness for the coastal and offshore region is about 70 80 km lateral variations in these mantle parameters are indicated 2 the addition of melwater into the oceans did not cease 6000 years ago but continued at a reduced rate up to more recent times adding an amount of water equivalent to a 3 m sea level rise in this interval 3 the amplitude of the holocene emergence is a function inter alia of coastal geometry and significant variations occur over distances of a few hundred kilometres and more holocene highstands of 1 2 m are generally well developed at the continental margins but are less well developed or do not developed at all at offshore islands and reefs 4 variations in the time of maximum emergence also occur being earlier at upstream tidal river sites than at coastal sites at offshore reefs or islands the sea level curve lags the coastal curves by 1000 years or more 5 considerable spatial variability occurs in the sea levels at the time of the last glacial maximum with variations of up to 30 m occurring across the continental shelves 6 there is generally no need to invoke tectonic movements to explain the sea level data along the australian coast but possible exceptions occur for the perth region and for tasmania

measurements of natural uranium concentration and isotopic composition with permil level precision by inductively coupled plasma quadrupole mass spectrometry a new analytical technique using inductively coupled plasma quadrupole mass spectrometry icp qms has been developed that produces permil level precision in the measurement of uranium concentration u and isotopic composition 234u in natural materials a 233u 236u double spike method was used to correct for mass fractionation during analysis to correct for ratio drifting samples were bracketed by uranium standard measurements a sensitivity of 6 7 108 cps ppm was generated with a sample solution uptake rate of 30 l min with a measurement time of 15 20 min standards of 30 ng uranium produced a within run precision better than 3 2 r s d for 234u and better than 2 for u replicate measurements made on standards show that a between run reproducibility of 3 5 for 234u and 2 for u can be achieved icp qms data of 234u and u in seawater coral and speleothem materials are consistent with the data measured by other icp ms and tims techniques advantages of the icp qms method include low cost easy maintenance simple instrumental operation and few sample preparation steps sample size requirements are small such as 10 14 mg of coral material the results demonstrate that this technique can be applied to natural samples with various matrices

milankovitch forcing of the last interglacial sea level during the last interglacial sea level was as high as present 4000 to 6000 years before peak northern hemisphere insolation receipt 126 000 years ago the sea level results are shown to be consistent with climate models which simulate a 3 to 4 c july temperature increase from 140 000 to 130 000 years ago in high latitudes with all northern hemisphere land areas being warmer than present by 130 000 years ago the early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred these results indicate that a fuller understanding of the milankovitch climate connection requires consideration of fields other than just insolation forcing at 65 n

hydro isostasy and the sea level isobase of 5500 b p in north queensland australia abstract previous studies of holocene sea level in north queensland have been based on a variety of sea level related deposits with interpretations of mid holocene levels ranging from near zero up to 4 m above present we report data from 8 carefully controlled new sites located from the palm group northwards and extending into the gulf of carpentaria field evidence is from coral reef flats and prograded coastal deposits the highest sea level on inner shelf islands and mainland coast occurred 5500 yrs ago the results of this and of certain previous studies are reduced to a common reference surface or isobase which varies systematically in elevation across the region the isobase correlates strongly with predicted hydro isostatic deformation caused by postglacial sea level rise

geomorphological evidence for late quaternary tectonic deformation of the cape region coastal west central australia abstract a late pleistocene marine isotope stage 5e emergent marine sequence fringes the coastline of the cape region of coastal west central australia and provides elevation and age control to characterize the locations and rates of crustal deformation there is a systematic measurable change in relative paleo sea level elevations across the cape region high precision leveling of modern and pleistocene shoreline features indicates the minimum elevation range of mis 5e shoreline features along the coast is 10 4 m this compares with the 2 5 m elevation range for observed modern shoreline analogs the lack of continuity of mis 5e shoreline elevations along 300 km of coastline demonstrates continuing tectonic deformation along coastal anticlines in the cape region topographic expression of mis 5e features indicates tectonic uplift consistent with late neogene to quaternary deformation on the cape cuvier and cape range anticlines post mis 5e tectonic uplift rates are up to 0 054 0 035 mm yr at fold axial locations estimated subsidence rates are 0 013 0 034 mm yr on fold limbs while the estimated vertical tectonic deformation is small and the rates are low the geomorphological data also demonstrate tectonic activity not stability

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

constraints on the age and duration of the last interglacial period and on sea level variations the relation between height and age of shorelines formed during the last interglacial period as revealed by coral reefs cannot be related directly to changes in ocean volume because of the effect of isostatic uplift in response to changes in ice sheet loading sea level changes at sites near the melting ice sheet such as bermuda and the caribbean islands differ from those along the australian margin modelling of these differences constrains the times of onset and termination of the last interglacial which are at variance with those deduced from oxygen isotope studies of deep sea cores

mis 5a and mis 3 relatively high sea level stands on the hatay samandag coast eastern mediterranean turkey abstract the coastal belt of hatay samandag in the east mediterranean is marked by the intersection of the african arabian and eurasian anatolian platelet plates where several quaternary shorelines related to relative sea level changes can be seen above the current sea level in this study the most common and best preserved high sea level markers of the marine isotope stage mis 5 and mis 3 shorelines were dated for the first time using the mollusc based electron spin resonance esr method as a result of this research the age of the late mis 5 and mis 3 sea level highstands in the eastern mediterranean the elevation of the corresponding shoreline at samandag coast and the vertical component of the late quaternary tectonic movements which has an impact on shoreline were determined the shorelines at 48 43 m elevations between cevlik and samandag at 58 6 m in tekebasi and at 21 m at keldag have been dated to approximately 72 ka and therefore are correlated with mis 5a the shoreline at 40 39 m elevations between cevlik and samandag has been dated to approximately 53 ka and therefore is correlated with mis 3 according to the position of the mis 5a shorelines the uplift rate over the last 72 ka was 0 88 mm y between cevlik and samandag 1 08 mm y in tekebasi and 0 56 mm y in keldag yielding a 0 84 mm y average this rather fast uplift appears to be related to the vertical component of the strike slip active faults in the samandag antakya fault zone

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

precise chronology of the last interglacial period 234u 230th data from fossil coral reefs in the bahamas a detailed study of 238 u 234 u 230 th ages was made for different coral species from two bahamian reefs to determine the time scale of the sea level high during the last interglacial period using recently developed mass spectrometric techniques for the measurement of u and th isotopes thirty seven coral samples were analyzed in replicate typical errors at 125 ky are 1 5 ky 2 and 3 ky time intervals appear to be well resolved this high precision permits detailed chronologic study with time resolution adequate to define stages of the reef s history these data demonstrate that the time between transgression and regression of the ocean in the last interglacial was about 12 ky after which sea level fell rapidly at more than 2 m ky the high sea level stand began possibly by 132 ky and certainly by 129 ky ago when sea level reached 6 m above present mean low sea level high sea level was sustained until 120 ky and then fell rapidly this time period covers the milankovitch insolation peak at 65 n but is not sharply defined and the sea level high lasted from about 4 ky before the insolation peak to 8 ky after it we find no evidence for a double peak of sea level rise in the last interglacial episode that is high stands at both 125 and 142 ky there appears to be some discrepancy between this precise chronology for a coral reef on a tectonically stable platform and the chronology assigned to deep sea sediments the present results show that the duration of the last interglacial led to a 12 ky period of high sea level stand which is much longer than the insolation peak the study area consists of two sizeable bank barrier coral reefs of sangamon age that crop out along the coast northwest of cockburn town on san salvador island and at devil s point on great inagua island the initial stage of reef development is not revealed at either site but the main parts of both reefs are well preserved at cockburn town the beginning of the reef was marked by colonization of acropora palmata on hardground areas and possibly other corals at 132 ky ago patch reefs at the southeastern flank of the developing reef were growing by 129 to 126 ky ago by 126 to 123 ky ago the crest of the reef was formed by the frame building coral a palmata and associated patch reefs flourished along its flanks a palmata coral heads grew upward to a mean low sea level 6 m above the present one the reef began to decline as sea level dropped at about 123 to 120 ky ago near two measured profiles at devil s point the top of a rubblestone dominated by a cervicornis and patch reef corals preserved in growth position have been beveled off and represent an ancient wave cut surface 230 th ages on corals below and above this surface indicate that it was cut at about 125 1 ky ago

high precision u series dating of last interglacial events by mass spectrometry houtman abrolhos islands western australia the houtman abrolhos islands situated at the western passive margin of the australian continent consist of a series of shelf edge coral reefs the central platforms of the reefs are late pleistocene in age and are generally some 3 5 m above present sea level the uppermost part of the last interglacial reefs normally has an upward shallowing sequence consisting of coral framestone coralline algal bindstone and skeletal grainstone to rudstone this sequence represents deposition in water depths of less than 2 m and provides a good indicator of sea level high precision mass spectrometric dates of corals from the abrolhos reefs including dates obtained from drill cores arological isotopic and stratigraphic criteria are established for the selection of suitable samples for dating and for assessing the reliability of dates using the screened dates and the stratigraphic evidence the timing and character of the sea level variations of the last interglacial in the abrolhos region are examined the data show that sea level of the last interglacial in the abrolhos was 4 m below its present height by ca 134 ka bp and probably reached about 2 m above present height at ca 133 ka bp the exact time at which sea level reached its peak 6 m above present sea level cannot be determined from our data but it is clear that the sea level high stand of the last interglacial lasted until ca 116 ka bp and that for much of the last interglacial sea level at the abrolhos was at a height of about 4 m above its present level

the timing of sea level high stands during marine isotope stages 7 5 and 9 constraints from the uranium series dating of fossil corals from henderson island direct dating of fossil coral reefs using the u series chronometer provides an important independent test of the milankovitch orbital forcing theory of climate change however well dated fossil corals pre dating the last interglacial period 130 thousand years ago ka are scarce due to 1 a lack of sampling localities 2 insufficient analytical precision in u series dating methods and 3 diagenesis which acts to violate the assumption of closed system u series isotopic decay in fossil corals here we present 50 new high precision u series age determinations for fossil corals from henderson island an emergent coral atoll in the central south pacific u series age determinations associated with the marine isotope stage mis 9 interglacial and mis 7 5 interstadial periods are reported the fossil corals show relatively little open system u series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle however open system u series behaviour is still evident in most of the dated corals in particular percent level shifts in the 230th 238u act composition are observed leading to conventional u series ages that are significantly younger or older than the true sample age this open system u series behaviour is not accounted for by any of the open system u series models indicating that new models should be derived the new u series ages reported here support and extend earlier findings reported in stirling et al 2001 providing evidence of prolific coral reef development on henderson island at not vert similar320 ka most likely correlated with mis 9 3 and subsequent reef development at not vert similar307 ka during mis 9 1 while relative sea level was potentially not vert similar20 m lower than during mis 9 3 the u series ages for additional well preserved fossil corals are suggestive of minor reef development on henderson island during mis 7 5 245 230 ka at 240 3 0 8 and 234 7 1 3 ka all u series observations are consistent with the milankovitch theory of climate change in terms of the timing of onset and termination of the dated interglacial and interstadial periods the best preserved samples also suggest that the oceanic 234u 238u during mis 9 and mis 7 5 was within five permil of the modern open ocean composition

the information content of pore fluid δ18o and cl abstractpaleoceanographic proxies indicate that the ocean state during the last glacial maximum lgm differed from the modern ocean state depth profiles of ocean sediment pore fluid 18o and cl have been used to reconstruct the 18o and salinity at the lgm here it is investigated whether pore fluid profiles can constrain ocean 18o and salinity at other times and simultaneously their ability to constrain the lgm 18o and salinity an inverse framework is developed that relies on bayesian parameter estimation thus allowing formal separation of prior assumptions from the information in observations synthetic problems are used to explore the information about past ocean tracers that can be recovered from pore fluid profiles it is concluded that prior knowledge of deep ocean mixing time scales is essential to an accurate inverse estimate of lgm ocean salinity and 18o from modern pore fluid profiles the most recent 10 000 years of ocean salinity and 18o and the error in their estimates are bette

topographic influence on baroclinic instability and the mesoscale eddy field in the northern north atlantic ocean and the nordic seas abstracta weak planetary vorticity gradient and weak density stratification in the northern north atlantic and nordic seas lead to time mean currents that are strongly guided by bottom topography

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

a new view on the driving mechanism of milankovitch glaciation cycles abstract dynamical instabilities in the glaciation and deglaciation of the ice sheets can be triggered by pulsations of the rate of change of the orbital and rotational parameters the purpose of this paper is to demonstrate that the milankovitch glaciation cycles are extremely sensitive to the rate of change of the obliquity frequency the first of our three contributions is a pedagogic principle of dynamical instability which provides a scientific basis for the driving mechanism of the glaciation cycles the second contribution is a clarification of the origin and climate significance of the obliquity related 100 kyr cycle in terms of nonlinear coupling between various orbital and rotational parameters finally the fluctuations in the size of the ice sheets are computed using the weertman birchfield watts model of ice sheets it is demonstrated that the growth and decay of the width of the ice sheets are in good agreement with the variations in the continental ice volume as seen in the late pleistocene 18o record

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

holocene sea level highstand and its implications for the vertical stability of panglao island southwest bohol philippines abstract emerged tidal notches in panglao island southwest bohol central philippines were used to investigate relative sea level changes during the holocene the elevation and profile of a laterally continuous notch were surveyed at 22 sites around panglao island the tidal notch documents higher than present mean sea level pmsl consistent with regional field observations and predictions for mid holocene time the reconstructed paleo shoreline elevations range from 0 to 1 6 m above pmsl exhibiting a general increase to the northeast the more protected part of the coast this lateral variation in the holocene paleo mean sea level msl along with changes in notch depth and profile suggests tilting of the island best explained by differential land movement last interglacial msl estimates by previous workers also show tilting to the southwest moreover the holocene notch data suggest segmentation of the island into several blocks that tilt consistently to the southwest suggesting the presence of faults lineations in aerial photographs trending northeast southwest confirm the presence of these faults these data indicate differential land movements during the holocene and late pleistocene calculated rates of uplift are 0 3 and 0 06 mm yr for the holocene and for the late pleistocene respectively these values relative to the high uplift rates from tectonically active regions imply that panglao is relatively vertically stable after accounting for tectonic tilting mid holocene sea level is estimated at approximately 0 3 0 6 m

transferring radiometric dating of the last interglacial sea level high stand to marine and ice core records in order to derive a radiometric age marker for the end of the penultimate glacial interglacial transition we compiled published u series isotope measurements on corals from the period extending from stage 6 to the middle of the last interglacial and computed the corresponding open system ages using thompson et al model thompson w g spiegelman m w goldstein s l speed r c an open system model for u series age determinations of fossil corals earth planet sci lett 210 2003 365 381 we obtain a global mean age of 126 calendar kyr bp ka 1 7kyr 2 for the beginning of the last interglacial sea level high stand after showing that the phase relationships observed between changes in sea level north atlantic benthic and planktonic foraminifera oxygen isotopic records and atmospheric methane over the last deglaciation were likely also valid over the penultimate deglaciation we derive an age of 131 2ka 2kyr 2 for the abrupt increase in atmospheric ch4 and north atlantic surface temperature marking the end of the penultimate glacial interglacial transition this age is consistent with u th dates of the penultimate glacial interglacial transition recorded in speleothems from sites where speleothems isotopic records are synchronous with north atlantic temperature records over the last deglaciation finally we show that the phase obtained between the climatic response and northern hemisphere summer insolation is not constant from termination ii to termination i implying that northern hemisphere summer insolation alone cannot explain the timing of terminations

a large drop in atmospheric 14c 12c and reduced melting in the younger dryas documented with 230th ages of corals paired carbon 14 14 c and thorium 230 230 th ages were determined on fossil corals from the huon peninsula papua new guinea the ages were used to calibrate part of the 14 c time scale and to estimate rates of sea level rise during the last deglaciation an abrupt offset between the 14 c and 230 th ages suggests that the atmospheric 14 c 12 c ratio dropped by 15 percent during the latter part of and after the younger dryas yd this prominent drop coincides with greatly reduced rates of sea level rise reduction of melting because of cooler conditions during the yd may have caused an increase in the rate of ocean ventilation which caused the atmospheric 14 c 12 c ratio to fall the record of sea level rise also shows that globally averaged rates of melting were relatively high at the beginning of the yd thus these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the mississippi to the st lawrence river triggered the yd event

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

pleistocene sea levels and tectonic uplift based on dating of corals from sumba island indonesia we collected and dated fossil corals from the uplifted reef tracts of sumba island mass spectrometry tims and ams was used to obtain reliable and precise radiochronological results it is possible to identify outcrops corresponding to major sea level high stands isotope stage 1 starting at 7 1 kyr bp 5a c a 86 kyr bp 5c c a 105 kyr bp 5e between 119 and 132 kyr bp and 9 c a 305 kyr bp the radiochronological data are thus broadly consistent with the timing of sea level fluctuations predicted by the astronomical theory of paleoclimates comparison with similar data from other terrace sequences and from benthic 18o records indicates that the average tectonic uplift rate at cape laundi sumba is on the order of 0 2 0 5m kyr the lowest values 0 3m kyr lead to the build up of polycyclic topographic terraces in which it is possible to find corals grown during different interstadial or even interglacial times

dating earthquakes with high precision thorium 230 ages of very young corals mass spectrometric techniques have recently yielded significant increases in precision and sensitivity over previous methods for measuring 230 th abundance in corals to assess the accuracy of 230 th ages three corals from vanuatu whose ages were known from counting annual growth bands were analyzed for each sample the date of growth determined by 230 th analysis a d 1969 3 1932 5 and1806 5 2 uncertainties based on analytical error was indistinguishable from the date determined by counting bands a d 1971 1973 1935 1937 and 1804 1810 indicating that the 230 th dates are accurate 230 th dates were also determined for two adjacent emerged heads from santo is vanuatu which were thought to have died when they were raised above sea level during coseismic uplift the dates a d 1864 4 1866 4 were the same indicating that the heads died at the same time and consistent with the idea that they were killed by coseismic emergence around a d 1865 the difference between this date and the date of the only major historically documented earthquake that caused uplift a d 1973 m s 7 5 suggests a seismic recurrence interval of108 4y for santo analogous emerged corals from malekula is vanuatu yielded 230 th dates that were similar to each other a d 1729 3 1718 5 and are inferred to have died during coseismic emergence around a d 1729 in conjunction with the date of the only large historically documented earthquake that caused uplift a d 1965 m s 7 5 the recurrence interval for malekula is236 3y if similar emerged corals can be found this appraoch may be extended back in time and to other localities because it appears that such features can now be dated both accurately and precisely

late quaternary evolution of coral reefs on a cool water carbonate margin the abrolhos carbonate platforms southwest australia late quaternary coral reefs have developed on the southwestern australian margin which has otherwise been characterised by cool water carbonates since the eocene the houtman abrolhos coral reefs are at the limits of existence extending with the assistance of the leeuwin current a poleward flowing warm water stream into a region dominated by more temperate communities coring in the easter group reefs supported by high precision dating by both view the mathml source tims and 14 c methods has shown vigorous coral growth with reefs over 26 m thick in the holocene and over 15 m thick in the last interglacial each of the three abrolhos platforms consists of a central platform composed of last interglacial reefs about which windward and leeward holocene reefs developed asymmetrically reef peritidal and eolian facies comprise the emergent last interglacial limestones which are extensively calcretized with reef facies up to 5 m above msl the last interglacial high stand lasted for at least 10 ka from 130 to 120 ka and possibly 15 ka from 132 to 117 ka holocene reef facies are also emergent by 0 5 m and are overlain by peritidal and storm ridge facies in an upward shallowing sequence windward 10 m thick and leeward 26 m thick holocene reefs in the easter group show contrasting lithofacies the wave exposed windward reefs consist of a slow growing association of coralline algal bindstones and coral framestones whereas fast growing coral framestones dominate the more protected leeward reefs the leeward reefs commenced growth 10 000 years ago and grew to the present sea level by 6500 years ago generating holocene constructional topography consisting of blue hole terrain in the leeward parts of the platforms

last interglacial coastal environments in the mediterranean saharan transition zone abstract the coast of tunisia stretches from the western mediterranean climate belt in the north to the saharan desert climate belt in the south the sediments of this coastal strip provide a record of sea level change if an accurate chronology of the coastal deposits is available we have here surveyed and analysed coastal sites and established a chronology based on optical dating techniques the optical ages range from 156 ka to 62 ka 2 level and cluster around the last interglacial period 125 75 ka our study shows that sea level rose after termination ii for about 25 ka leading to a transgressive deposit at 120 ka a disconformity shown by some deposits suggests a brief drop of sea level during this transgressional phase subsequently for around 40 ka the coastal area became covered by soils colluvia and aeolian sediments indicating a slowly falling sea level while the composition of sediments at the north coast did not change the deposits at the central and south coast experienced a drastic change from a quartz to a carbonate dominated sedimentation sometime during the last interglacial littoral sedimentation ceased at 70 ka when the coast became sediment starved in the course of the falling sea level

relative paleointensity of the earth s magnetic field from marine sedimentary records a global perspective abstract to assess the potential of marine sediments as a source of relative paleointensity information we have undertaken an investigation of selected box cores stored in the scripps core repository we present here new results from two north atlantic box cores magnetic remanence in the sediments is carried by magnetite and is univectorial during alternating field and thermal demagnetization the median destructive field is 25 30 mt normalization by anhysteretic remanent magnetization yields relative paleointensity data that are highly concordant within and between cores age control provided by oxygen isotope data from both cores allows comparison of these relative paleointensity data with contemporaneous archeomagnetic data from czechoslavakia both data sets indicate a peak in paleofield intensity at around 8 10 ka this peak is less prominent in box core data from the western pacific and global averages of archeomagnetic and lava flow data however the peak is evident in data estimating changes in production of radiocarbon which is controlled in part by changes in the dipole moment of the geomagnetic field the excellent agreement between production variations predicted by the changes in dipole moment and those observed suggests that long term variations in atmospheric radiocarbon are dominated by geomagnetic field variations