towards radiocarbon calibration beyond 28 ka using speleothems from the bahamas we present a new speleothem record of atmospheric 14c between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period the record is based on a comprehensive suite of ams 14c ages using new low blank protocols and u th ages using high precision mc icpms procedures atmospheric 14c was calculated by correcting 14c ages with a constant dead carbon fraction dcf of 22 7 5 9 based on a comparison of stalagmite 14c ages with the intcal04 reimer et al 2004 calibration curve between 15 and 11 ka the new 14c speleothem record shows similar structure and amplitude to that derived from cariaco basin foraminifera hughen et al 2004 2006 and the match is further improved if the latter is tied to the most recent greenland ice core chronology svensson et al 2008 these data are however in conflict with a previously published 14c data set for a stalagmite record from the bahamas gb 89 24 1 beck et al 2001 which likely suffered from 14c analytical blank subtraction issues in the older part of the record the new bahamas speleothem 14c data do not show the extreme shifts between 44 and 40 ka reported in the previous study beck et al 2001 causes for the observed structure in derived atmospheric 14c variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity data model comparison indicates that major fluctuations in atmospheric 14c during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity although ocean atmosphere system reorganisation also played a supporting role

decoupled fresh saline groundwater circulation of a coastal carbonate aquifer spatial patterns of temperature and specific electrical conductivity summary the coastal carbonate aquifer of the eastern yucatan peninsula discharges groundwaters to the caribbean sea temperature and specific electrical conductance sec are used as natural tracers to gain new insight into the fresh and saline groundwater circulation along an 80 km section of the caribbean coastline the aquifer is density stratified with a cooler freshwater lens overlying a warmer saline water zone non conduit sites generally have lower temperatures and sec in the freshwater lens than conduit sites in conduits 4 km inland within the shallow saline water zone temperature decreases exponentially with distance from the coast with near equilibrium with the fresh waters reached at 10 km inland a distance coincident with the known limit of conduit development this pattern is indicative of the progressive cooling of warm seawater moving inland from the coast a flow direction opposite to that of both the conventional freshwater flow entrainment and geothermal convection models of coastal aquifer circulation

record of mis 5 sea level highstands based on u th dated coral terraces of haiti abstract new geomorphologic investigations and new u th series dates from haiti northwestern peninsula confirm the age of coral reef terraces assigned to mis 5 5 130 ka mis 5 3 107 ka and mis 5 1 83 ka sea level peaks they also provide evidence for a second high sea level occurring some thousand years before 118 ka and indicate a second mis 5 1 sea level stand at about 76 ka these results are in agreement with the raised terraces of barbados although the staircase of haiti consists of four steps compared to eight the haitian sequence can be compared with the maximal number of distinct mis 5 sea level highstands recorded in the world from coral reef tracts and their relative height above or below present sea level three mis 5 5 sea level changes have been recognized with sea level oscillating above or near the present level until 122 ka only dropping then rising to 11 m below present sea level at 120 ka three high frequency sea level oscillations occurred during mis 5 3 and a fourth during mis 5 3 5 2 two or three events may have occurred during mis 5 l according to whether the 73 ka event is considered to belong to mis 5 1

assessment of the garnet clinopyroxene fe mg exchange thermometer using new experimental data a detailed high pressure experimental study of two mafic xenoliths in which coexisting garnet and clinopyroxene plagioclase spinel and olivine were crystallized over a p t range of 10 30 kbar and 950 1200 c has revealed significant differences in temperatures from those estimated for coexisting garnets and clinopyroxenes using the ellis green fe mg exchange thermometer the results show perfect matching at 30 kbar 1150 1200 c but increasing deviation at lower pressure and lower temperature with the ellis green calibration reaching a t overestimate of c 145 c at 10 12 kbar and 950 c the grossular content of the garnet increases from c 21 mol at 10 kbar to 26 31 mol at 30 kbar these results confirm other recent experimental studies that show that the pressure correction and possibly to a lesser extent the correction for grossular content applied by ellis green are not appropriate for lower pressure conditions and give estimated temperatures that are significantly high when applied to granulitic terranes formed at c 10 kbar the new reconnaissance results allow a graphical interpolation of a garnet clinopyroxene geothermometer based on the fe mg exchange reaction which should be applicable to assemblages formed under lower crustal conditions

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

paleoclimatic evidence for future ice sheet instability and rapid sea level rise sea level rise from melting of polar ice sheets is one of the largest potential threats of future climate change polar warming by the year 2100 may reach levels similar to those of 130 000 to 127 000 years ago that were associated with sea levels several meters above modern levels both the greenland ice sheet and portions of the antarctic ice sheet may be vulnerable the record of past ice sheet melting indicates that the rate of future melting and related sea level rise could be faster than widely thought

reconciliation of sea level observations in the western north atlantic during the last glacial cycle abstract a south to north gradient of increasing marine isotope substage mis 5a 80 ka bp sea level has been recorded across the caribbean and surrounding region relative to present mis 5a sea levels range from 19 m to more than 3 m between barbados haiti the bahamas florida bermuda and the us atlantic coast in contrast no gradient in sea level is observed for the last interglacial period mis 5e 128 118 ka bp at tectonically stable localities in the same region with deposits generally lying several metres above present we demonstrate here that these controversial observations are reconciled by taking into account the isostatic response of the earth to glacial loading and unloading a fundamental effect that is commonly overlooked in the interpretation of sea level observations from different locations to define a global sea level curve furthermore the observed gradient can be used to place constraints on earth rheology and is an important indicator of the behaviour of the north american ice sheets during the last glacial cycle

sea level during the penultimate interglacial period based on a submerged stalagmite from argentarola cave italy accurate constraints are presented for the absolute age duration and sea level for the highstand corresponding to marine isotope stage mis 7 1 our work is based on a stalagmite collected in a currently submerged cave from italy argentarola cave flooding of this coastal cave is clearly marked within the stalagmite by a thick marine overgrowth of serpulid worms precise uranium thorium u th ages measured by thermal ionization mass spectrometry suggest that the stalagmite growth varied in phase with climate during mis 7 2 and mis 6 the penultimate glacial period in addition the period of marine transgression is bracketed between 202 and 190 kyr bp defining a mis 7 1 duration of 11 2 kyr comparison with previous studies provides a new constraint on the sea level during mis 7 1 that has approximately remained between 318 and 39 m relative to present sea level the timing of the mis 7 1 highstand is in full agreement with the specmap chronology which contrasts with the growing body of evidence showing a significant phase difference for mis 5 5 a tempting conclusion is that second order sea level highstands such as mis 7 1 may be purely driven by astronomical changes in contrast with major terminations such as termination ii atmospheric co2 levels may partly explain this contrast since the two sea level transitions mis 7 2 7 1 and mis 6 5 5 are characterized by very different co2 rises 20 vs 100 ppm fl 2002 elsevier science b v all rights reserved

suborbital period sea level oscillations during marine isotope substages 5a and 5c the frequency of oscillations in global ice volume as determined by dating of coral reef deposits provides an important test of the milankovitch model of orbital climate forcing the timing of two episodes of high sea level during marine isotope substages mis 5a and 5c here determined to have occurred at 84 and 101 ka bp are broadly consistent with the milankovitch model however new high precision u series dating of uplifted morphologically distinct coral reef terraces at barbados indicate that mis 5a was both longer and more complex than previously established with an additional sea level highstand occurring at 77 ka bp the u series analysis of a large number of samples for each coral reef deposit reveals a well defined correlation between measured age and initial 234u this correlation is evident even within the uncertainty band of 8 commonly used to exclude diagenetically altered samples and allows a more precise and accurate constraint of the age of these deposits by evaluating where the trend line intersects the modern 234u value other proxy climate records also indicate suborbital period variability during mis 5a and 5c and together imply that as for the last ice age orbital forcing alone cannot account for the observed changes in climate

an end to the last interglacial highstand before 120 ka relative sea level evidence from infreschi cave southern italy abstract the timing duration and evolution of sea level during the marine isotope stage 5e mis 5e highstand is a subject of intense debate a major problem in resolving this debate is the difficulty of chronologically constraining the sea level fall that followed the peak of the highstand this was mainly controlled by ice sheet dynamics the understanding of which is relevant for assessing future sea level behavior due to global warming here we use stratigraphical and geochoronological u th dating and tephra fingerprinting evidence from the infreschi archaeological cave marina di camerota southern italy to constrain relative sea level rsl evolution during the mis 5e highstand and younger stages uranium thorium dating of speleothem deposition phases places the maximum highstand rsl at 8 90 0 6 m a s l as indicated by the near horizontal upper limit of lithophaga boreholes measured for along a 3 5 km coastal cliff section geochronological data show that rsl fell more than 6 m before 120 ka suggesting a duration of the last interglacial highstand significantly shorter than proposed in some previous studies modelling shows that the rsl trend predicted by the ice 5g and ice 6g ice sheet simulations is consistent with our data but requires an additional significant reduction of both greenland and antarctic ice sheets to match the height of the local maximum highstand if no correction for tectonics is applied reconciling field data and models requires an earlier and likely shorter duration of the mis 5e highstand this suggests that our new data can constrain global ice volume variations during the penultimate deglaciation as well as glacial inception at the end of the last interglacial according to our chronology there is no local evidence of higher than present day sea levels after 120 ka

speleothem constraints on marine isotope stage mis 5 relative sea levels yucatan peninsula mexico rates of sea level fall at the termination of the last interglacial are poorly defined and archives from which sea level elevations are constrained during marine isotope stage mis 5 in the western north atlantic caribbean region are restricted spatially to a few key sites here growth periods of presently submerged but subaerially deposited speleothems from the yucatan peninsula south east mexico are dated using the 230 th 234 u multi collector inductively coupled plasma mass spectrometric method the growth periods used to constrain maximum elevations of relative sea level are in agreement with glacio isostatic adjustment models for the near to intermediate region of the former north american ice sheets furthermore our data provide additional constraints on the timing of peak relative sea levels during mis 5a and 5c and the timing of the regression following the last interglacial highstand combining our data with coral archives of minimum relative sea level from the same region provides a novel approach to calculating the rate of relative sea level fall although initial estimates are poorly constrained because of the wide range in ages observed for the most suitable corals copyright 2013 john wiley sons ltd

an open system model for u series age determinations of fossil corals the source of excess 234u in fossil corals and its relationship to u series age determinations has been an outstanding problem in geochronology for more than 20 years with increasing numbers of u series isotope measurements in corals and significant improvements in analytical precision through mass spectrometry it is increasingly apparent that a substantial fraction of observed isotope ratios cannot be reasonably explained by closed system decay moreover observations of a positive correlation between 234u 238u and 230th 238u ratios in corals from the same terrace are difficult to explain however the decay of dissolved uranium and recoil mobilization of uranium daughters produce particle reactive 234th and 230th and the coupled addition of these th isotopes could simultaneously increase coral 234u 238u and 230th 238u here we present a quantitative model based on decay dependent redistribution of 234th and 230th permitting calculation of open system coral ages these equations provide a general solution to the recoil redistribution problem applicable to any alpha decay series while measured isotope ratios of corals from the three youngest stratigraphically defined barbados terraces are inconsistent with closed system decay they fall in broadly linear arrays agreeing with model predictions isotopic arrays of older barbados corals and corals from terraces around the world are also consistent with model predictions suggesting the open system model is generally applicable corals with extreme isotopic compositions that are impossible to produce by closed system decay are consistent with the limited range of isotopic compositions predicted by the model at ages older than 600 ka for corals from a single terrace 234th and 230th redistribution appears to be a source of systematic conventional age error even for corals with slightly elevated 234u however open system ages are consistent even for corals with extremely elevated 234u for the youngest three barbados terraces mean open system terrace ages are consistent with mean conventional terrace ages calculated from pristine samples if the most accurate conventional ages are from corals with an initial 234u 238u identical to modern seawater then the open system model will improve the accuracy of coral u series age determinations and dramatically increase the number of reliable ages

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

the anatomy of interglacial sea levels the relationship between sea levels and ice volumes during the last interglacial abstract the elevations and chronology of interglacial shorelines and other sea level indicators provide information on ice volumes for these earlier periods compared with today but as for the holocene the relationship between sea levels and ice volumes for earlier interglacials is not simple because of the planet s deformational gravitational and rotational response to changes in ice water loads glacio hydro isostasy in particular the pattern of global sea level for a particular interglacial will be a function of the earth and ocean response to ice loads applied before during and after the interglacial in question this paper examines the role of glacio hydro isostasy during these glacial cycles to make three key points the first is to demonstrate why interglacial sea levels cannot be interpreted directly in terms of ice volume the second is to illustrate the spatial variability that can be expected in interglacial sea levels because of the earth s isostatic response to changing ice and water loads and to demonstrate why observations from different localities should not be combined into a single sea level function without first correcting for differential isostatic effects the third addresses the question whether in the absence of perfect knowledge of the ice sheets and earth rheology inferences can be made about ice volumes during an interglacial we conclude that if these isostatic factors are ignored interpretations of interglacial sea levels can lead to serious errors in the inferences about ice volumes during the interglacials

sea level oscillations during the last interglacial highstand recorded by bahamas corals whether sea level was stable during the last interglacial remains a subject of debate an analysis of the u th ages of coral reefs in the bahamas corrected for open system behaviour confirms the presence of at least one oscillation within the sea level highstand

pleistocene sea levels from raised coral reefs of haiti the elevations and ages of a sequence of three uplifted pleistocene coral reefs on the northwest peninsula of haiti have been determined with the assignment of a sea level of 6 meters relative to the present day at 130 000 years before present and constant uplift of the reefs the data indicate that sea level stood 10 and 13 meters at 108 000 and 81 000 years before present respectively these results are in substantial agreement with those reported for barbados and new guinea and support the hypothesis of constant uplift for each area sea level data from raised reefs indicate that the interglacial marine oxygen isotope oscillations during oxygen isotope stage 5 are a result of 30 percent ice volume effects and 70 percent temperature effects

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

the distribution style and intensity of alleghanian metamorphism in south central new england petrologic evidence from the pelham and willimantic domes abstract alleghanian metamorphism in south central new england is characterized by late pennsylvanian documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm kyanite mathrm muscovite mathrm staurolite end document grade heterogeneous reconstitution of migmatitic documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepack

how precise are u series coral ages abstract u series dating of fossil reef corals is a well established and widely applied technique in paleoclimate research many fossil corals however show evidence for post depositional diagenetic alteration and it is generally accepted that the accuracy of u series coral ages is more limited due to coral diagenesis than analytical precision in recent years three models have been published that try to correct the effects of diagenesis and allow the calculation of model ages thompson w g spiegelmann m w goldstein s l and speed r c 2003 an open system model for u series age determinations of fossil corals earth and planetary science letters 210 365 381 villemant b and feuillet n 2003 dating open systems by the 238u 234u 230th method application to quaternary reef terraces earth and planetary science letters 210 105 118 scholz d mangini a and felis t 2004 u series dating of diagenetically altered fossil reef corals earth and planetary science letters 218 163 178 here we assess the age variability of both conventional 230th u dating and the three models by application to different sub samples of individual coral specimens the age variability estimated as the 2 standard deviation on the individual ages is compared with the errors quoted by the different methods our results show that the errors of conventional 230th u dating as well as those of the method of thompson et al 2003 do not account for the true age variability the age variability of both methods is in the range of the errors given by the models of villemant and feuillet 2003 and scholz et al 2004 furthermore we show that the widely used reliability criteria are not sufficient to identify all diagenetically altered corals in contrast analysis of different sub samples of one coral specimen allows i to estimate the real age variability ii to test if the assumptions of the models are fulfilled and iii to investigate the diagenetic processes in more detail thus this method should generally be applied to obtain more reliable u series coral ages and errors

determination of time integrated metamorphic fluid fluxes from the reaction progress of multivariant assemblages an expression is derived for the calculation of time integrated metamorphic fluid fluxes in two or more dimensions in rocks undergoing multivariant reactions under conditions of varying pressure temperature and angle of flow this calcuation requires knowledge of mineral assemblages modes and compositions which are obtained from isobaric t xco2 pseudosections constructed using the program thermocalc and compared with those observed in east central vermont thermocalc is capable of reproducing peak mineral assemblages modes compositions and the observed reaction sequences within the system kcanafmasch for two kyanite grade pelitic carbonate rocks from a barrovian style regional metamorphic terrain in east central vermont u s a calculation of fluid fluxes for decarbonation reactions under conditions of horizontal layer parallel flow produces time integrated fluid flux figures of the order of 108 moles m 2 allowance for possible cross layer flow from adjacent dehydrating pelites reduces this figure significantly with episodic cross layer fluxes of the order of 105 moles m 2 being capable of driving the observed decarbonation chlorite bearing carbonate protoliths would have initially dehydrated with increasing temperature a process requiring down temperature fluid flow to produce the assemblages currently observed

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

sea level history of the past two interglacial periods new evidence from u series dating of reef corals from south florida abstract as a future warm climate analog much attention has been directed to studies of the last interglacial period or marine isotope substage mis 5 5 which occurred 120 000 years ago nevertheless there are still uncertainties with respect to its duration warmth and magnitude of sea level rise here we present new data from tectonically stable peninsular florida and the florida keys that provide estimates of the timing and magnitude of sea level rise during the last interglacial period the last interglacial high sea stand in south florida is recorded by the key largo limestone a fossil reef complex and the miami limestone an oolitic marine sediment thirty five new high precision uranium series ages of fossil corals from the key largo limestone indicate that sea level was significantly above present for at least 9000 years during the last interglacial period and possibly longer ooids from the miami limestone show open system histories with respect to u series dating but show a clear linear trend toward an age of 120 ka correlating this unit with the last interglacial corals of the key largo limestone older fossil reefs at three localities in the florida keys have ages of 200 ka and probably correlate to mis 7 these reefs imply sea level near or slightly above present during the penultimate interglacial period elevation measurements of both the key largo limestone and the miami limestone indicate that local relative sea level was at least 6 6 m and possibly as much as 8 3 m higher than present during the last interglacial period

u th dating living and young fossil corals from the central tropical pacific this study evaluates the accuracy of u th dates for young 6 a few thousand years old reef corals both living and fossil and explores strategies for refining those dates the high precision of the u th method 0 1 2 for dating young corals is well established earlier studies have demonstrated the method s accuracy for select samples of known age however these studies have focused on typical samples that have extremely low 232 th concentrations tens of pg g here we study the dating systematics of young corals that have low but significant amounts of 232 th up to 1000 pg g indicating the presence of small fractions of non radiogenic 230 th i e 230 th not generated by in situ u decay we report u th ages for living and subaerially exposed fossil corals from palmyra island located in the central tropical pacific that range from 50 to 700 yr old the palmyra corals contain varying amounts of 232 th and small fractions of associated non radiogenic 230 th uncertainty associated with the correction for non radiogenic 230 th can lead to significant errors in u th dates we have characterized non radiogenic 230 th 232 th values 230 th 232 th nr a s a means of minimizing this source of error we calculate 230 th 232 th nr values ranging from 0 to 2u10 35 for the palmyra living corals by comparing measured u th dates to absolute dates for the living coral whose chronology is well established for the fossil corals we employ three different approaches to arrive at 230 th 232 th nr estimates first we compare measured u th dates to absolute dates in samples from a young fossil coral that overlaps the living coral next we use the firm relative dating constraints imposed by five overlapping fossil corals from the 14th 15th centuries to calculate 230 th 232 th nr values finally we attempt to anchor the 14th 15th century floating coral chronology to an absolute chronology by correlating the climate signals in the coral records to those in absolutely dated climate proxy records all lines of evidence point to a range of 230 th 232 th nr for fossil corals that overlaps the range determined for the living coral suggesting that most of the thorium is primary or is added while the coral is still alive our work also demonstrates the utility of multiple 230 th 232 th nr estimates most importantly we demonstrate a method by which accurate 0 5 yr u th based chronologies can be obtained for young fossil corals with significant 232 th concentrations

diffusion controlled corona reaction and overstepping of equilibrium in a garnet granulite yenisey ridge siberia diffusion modelling is applied to layered garnet pyroxene quartz coronas formed by a pressure induced reaction between plagioclase and primary pyroxene in a metabasic granulite the reconstructed reaction involves some change in composition of reactant minerals the distribution of minerals between layers is satisfactorily explained by diffusion controlled reaction with local equilibrium in which the diffusion coefficient for al was smaller than those for fe mg and ca by a factor of approximately four diffusion of mg towards plagioclase implies a chemical potential gradient for mgo component in a direction opposite to the changing mg content of garnet this is explained by the influence of al2o3 on the chemical potential of the pyrope end member grain boundary diffusion is suggested to have operated possibly with composition gradients different from those in the bulk minerals chemical potential differences across the corona are estimated from the variation in garnet composition enabling affinity the free energy change driving the reaction to be estimated as 6 9 1 8 kj per 24 oxygen mole of garnet produced this implies that the pressure for equilibrium among the minerals was overstepped by 1 4 0 4 kbar the probable p t conditions of reaction were in the range 650 790 c 8 10 kbar assuming a timescale of reaction between 106 and 108 years estimated diffusion coefficients for fe mg and ca are in the range 9 10 23 to 5 10 20 m2 s 1 these are consistent with experimental values in the literature for solid state diffusion including grain boundary diffusion

experimental investigation of fe mg distribution between olivine and clinopyroxene implications for mixing properties of fe mg in clinopyroxene and garnet clinopyroxene thermometry

hells bells unique speleothems from the yucatan peninsula mexico generated under highly specific subaquatic conditions abstract we here report on a type of meter sized pendant speleothem growing under water in the submerged el zapote sinkhole cenote west of puerto morelos on the mexican yucatan peninsula these conical mantle shaped downward expanding and diverging calcareous structures here termed as hells bells are yet unreported in the scientific literature they are characterized by bell or trumpet shaped longitudinal and circular elliptical or horse shoe like horizontal cross sections hells bells grow downward based on the downward divergence of the structures and the horizontally laminated internal texture of both blade shaped spar calcite and microspar laminae age dating confirms that hells bells are young

bermuda sea level during the last interglacial bermuda is a stable mid oceanic carbonate platform for which a particularly complete record of sea level fluctuation during the period 135 70 kyr has been reconstructed from 230th 234u dating of corals and speleothems amino acid racemization dating of molluscs and a reinterpretation of geological field relations during the past 5 yr bermuda has been the focus of an extensive geochronological programme which has included a detailed re examination of the geology to be reported elsewhere1 3 here we focus only on the latest interglacial sequence we use the stratigraphie nomenclature of land et al 4 but will present new age data and interpretations of geological relationships this information as it relates to the last interglacial period is given in tables 1 and 2 and summarized in fig 1 we show that during the last interglacial period sea level was only above its present level for a few thousand years at about 125 kyr when it stood at 4 to 6m at 105 and 85 kyr sea level rose to between 15 and 20 m as constrained by ages for submerged speleothems and eolianites at 95 kyr sea level in bermuda was at least 15 m below present level

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

uranium series coral ages from the us atlantic coastal plain the 80 ka problem revisited abstract uranium series coral ages for emergent units from the passive continental margin us atlantic coastal plain acp suggest sea level above present levels at the end of marine oxygen isotope stage mis 5 contradicting age elevation relations based on marine isotopic or coral reef models of ice equivalent sea level we have reexamined this problem by obtaining high precision 230th 238u and 231pa 235u thermal ionization mass spectrometric ages for recently collected and carefully cleaned acp corals many in situ we recognize samples that show no evidence for diagenesis on the basis of uranium isotopic composition and age concordance combining new and earlier data among those ages close to or within the age range of mis 5 over 85 cluster between 65 and 85 ka bp of the corals that we have analyzed those that show the least evidence for diagenesis on the basis of uranium isotopic composition and age concordance have ages between 80 and 85 ka bp consistent with a mis 5a correlation the units from which these samples have been collected are all emergent and have elevations within 3 5 m of those few units where early stage 5 125 000 ka bp coral ages have been obtained the acp appears to record an unusual history of relative sea level throughout mis 5 a history that is also apparent in the dated coral record for bermuda we speculate that this history is related to the regional near to intermediate field effects of ancestral laurentide ice sheets on last interglacial shorelines of the western north atlantic

timing and duration of the last interglacial evidence for a restricted interval of widespread coral reef growth abstract we report new mass spectrometric u series ages for eight last interglacial fossil reefs along the continental margin of western australia corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on last interglacial sea levels without requiring corrections for tectonic movements in addition we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs uranium and thorium isotopes were measured with high levels of precision leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded these data supplement our previous results for rottnest island and leander point leading to more than seventy mass spectrometric u series ages from which constraints can be placed on the timing duration and character of the last interglacial sea level highstand reliable ages show that reef growth started contemporaneously at 128 1 ka along the entire western australian coastline while relative sea levels were at least 3 m above the present level because western australia is located far from the former penultimate glacial maximum ice sheets and are not significantly effected by glacial unloading these data constrain the timing of onset of the last interglacial period to 128 1 ka assuming reef growth started soon after sea level approached interglacial levels a unique regressive reef sequence at mangrove bay constrains the timing of termination of the last interglacial period to 116 1 ka the major episode of reef building however both globally and locally along the western australian coast is restricted to a very narrow interval occurring from 128 ka and 121 ka suggesting that global ocean surface temperatures were warm and or sea levels were stable enough to allow prolific reef growth only during the earlier part of the last interglacial

reassessment of the garnet clinopyroxene fe mg exchange thermometer i evaluation of the pattison and newton 1989 experiments this is part 1 of a two part study on the garnet grt clinopyroxene cpx fe mg exchange equilibrium widely used in geothermometry of amphibolites granulites and eclogites the experimental data set previously published by pattison and newton pn on this equilibrium comprises potentially the largest source of data used for extraction of thermodynamic properties for grt and cpx and for formulation of a new thermometer expression part 2 of this study however the experiments suggested unusual grt and cpx solution properties and resulted in a geothermometer expression that generally returns low temperatures for granulites to verify the reliability of the experiments and to test the experimental technique of grt buffering used in the pn study 69 of the 125 pn runs were reanalysed using wavelength dispersive spectroscopic analysis guided by backscattered electron images special attention was given to analysis of compositional changes in grt in addition to cpx with minor exceptions the reanalysis supports the analytical results of the original pn study the mechanism of equilibration in the runs was a multicomponent solution precipitation process involving dissolution of metastable grt and cpx starting materials and precipitation of newly formed cpx and grt the latter assumed to represent equilibrim compositions the experiments cannot be regarded either as reversed or as strictly bracketing nevertheless cpx compositional parameters including mg na ca and al show the same smooth variations with temperature pressure and composition as found by pn suggestive of a close approach to equilibrium grt in run products retained the moderate heterogeneity of the starting grt although there are subtle compositional trends indicating small changes in grt mg consistent with mass balance constraints these results uphold the essential validity of the technique of grt buffering used in the experiments nevertheless it is possible that the final grt compositional may not coincide with the nominal starting grt compositions requiring assignment of compositional uncertainties to grt for purposes of thermodynamic modelling of the data cpx analyses also require assignment of non zero compositional uncertainties

ice volume and sea level during the last interglacial during the last interglacial period 125 000 years ago sea level was at least several meters higher than at present with substantial variability observed for peak sea level at geographically diverse sites speculation that the west antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice sheet dynamics during this time interval we provide an internally consistent database of coral u th ages to assess last interglacial sea level observations in the context of isostatic modeling and stratigraphic evidence these data indicate that global eustatic sea level peaked 5 5 to 9 meters above present sea level requiring smaller ice sheets in both greenland and antarctica relative to today and indicating strong sea level sensitivity to small changes in radiative forcing

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

two phase nickeliferous monosulfide solid solution mss in megacrysts from mount shasta california a natural laboratory for nickel copper sulfides

tectonostratigraphic evolution of cenozoic marginal basin and continental margin successions in the bone mountains southwest sulawesi indonesia abstract the bone mountains located in southwest sulawesi along the se margin of sundaland are composed of oligocene to possibly lower miocene marginal basin successions bone group that are juxtaposed against continental margin assemblages of eocene miocene age salokalupang group three distinct units make up the latter i middle upper eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part matajang formation reflecting a period of arc volcanism and carbonate development along the sundaland margin ii a well bedded series of oligocene calc arenites karopa formation deposited in a passive margin environment following cessation of volcanic activity and iii a series of lower middle miocene sedimentary rocks in part turbiditic which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity baco formation formed in an extensional regime without subduction the bone group consists of morb like volcanics showing weak to moderate subduction signatures kalamiseng formation and a series of interbedded hemipelagic mudstones and volcanics deko formation the deko volcanics are in part subduction related and in part formed from melting of a basaltic precursor in the overriding crust we postulate that the bone group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west sundaland and by a newly initiated westerly dipping subduction zone on its eastern side around 14 13 ma an extensional tectonic event began in sw sulawesi characterized by widespread block faulting and the onset of potassic volcanism it reached its peak about 1 ma year later with the juxtaposition of the bone group against the salokalupang group along a major strike slip fault walanae fault zone the latter group was sliced up in variously sized fragments tilted and locally folded potassic volcanism continued up to the end of the pliocene and locally into the quaternary

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

application of airborne gamma ray imagery to assist soil survey a case study from thailand abstract airborne gamma ray imagery agri provides coarse resolution approximately 400 400 m pixel spatial information on gamma ray emitting elements i e potassium k thorium th and uranium u in the upper half meter of the soil these radioelements are a potential information source for soil mapping since their abundance is related to soil geochemistry specifically the chemical composition of parent materials and their weathering products resulting from geomorphic and pedogenic processes the aim of this study was to evaluate the potential of agri for improving digital soil survey process in two phases 1 a preliminary phase where hypotheses of soil landscape relationships are developed and 2 a phase where soil map unit boundaries are placed or revised the study also evaluated the match between agri and existing lithologic geopedologic and soil series maps the study was conducted in a well characterized complex soil landscape the 560 km2 upper pa sak watershed in petchaboon province thailand the relationship between gamma ray data and geological units was examined with box and whisker plots and confirmed by rock and soil samples rock and soil sample classifications were compared with the gamma ray image and to typical radioelement responses found in the literature to interpret agri data in terms of regolith and soil genesis we compared agri to two existing soil maps geopedologic and soil series maps first the geopedologic map was split into four maps according to the geopedologic hierarchy landscape lithology relief and landform at the latter lowest level soil units are also associated secondly soil series and geopedologic soil units were used to examine the distribution of radioelement response to selected soil characteristics parent material texture mineralogy and thickness the interpretations from best correlation in both soil maps were described in terms of the radioelement changes during pedogenic and geomorphic processes based on a review of literature and supported by soil samples in the hypotheses generating stage agri provided useful information in three forms single signal ratio and ternary images enhanced with a hill shaded dem by relating these to lithology material transport and internal pedogenetic processes agri correlated well with the classes of the geopedologic map 1 50 000 at the two higher levels landscape and lithology but to a lesser degree at the two lower levels relief and landform in geopedologic approach in the mapping stage agri showed deficiencies in the soil series map 1 50 000 made by conventional aerial photo analysis and limited field surveys especially in inaccessible areas but also in low relief terraces and flood plains which provided a basis for future field sampling to correct these deficiencies agri suggested new boundaries differentiating topsoil properties and the presence of plinthite despite its coarse resolution clustering of gamma ray and elevation data dem was carried out using fuzzy logic to generate various classification layers final map was produced using total weighted inverse distance of all the classes in a 3 by 3 window class label was assigned to the one with the largest total inverse distance over the entire set of fuzzy classification bands the result shows relatively higher classification accuracy for soil parent material differentiation overall accuracy of 72 as compared to the classification for soil types 67

how well known are the thermodynamics of fe mg ca garnet evidence from experimentally determined exchange equilibria many thermodynamic calculations relating to metamorphic rocks hinge on the thermodynamic parameters of garnet though some models are widely used it is not clear whether their underlying premise is correct that a single set of equations can be written for the activities of the end members of garnet covering the whole compositional range a voluminous body of data can be used to constrain the thermodynamics of garnet namely fe mg exchange experimental data involving garnet and another mineral particularly clinopyroxene orthopyroxene and olivine however examination of these data reveals inconsistencies apparently stemming from differences between the thermodynamics of low ca and high ca garnets with a boundary of about xgca 0 15 in the two regions for the high p t of the experimental data the thermodynamics follow the regular model with values for the interaction parameters in the low ca region of about wgfemg 50r and wafe wgmgca 1300r in which r is the gas constant and in the high ca region of about wgfemg 1100r and wgcafe wgmgca 2200r using the subregular rather than the regular model does not remove the discrepancy the cause of the discrepancy needs to be identified if reliable calculations on rocks are to be made

comparison of conventional and garnet aluminosilicate quartz o isotope thermometry insights for mineral equilibration in metamorphic rocks oxygen isotope thermometry based on fractionations among quartz garnet kyanite sillimanite and potassium feldspar in amphibolite to granulite facies schists and gneisses was compared to thermometry based on mineral equilibria conventional thermometry the former approach takes advantage of the exchange between quartz and more refractory minerals such as garnet and the aluminosilicates and their potential for preserving peak oxygen isotopic fractionations although isotopic thermometry using these phases is potentially an approach for circumventing the problem in slowly cooled rocks of retrograde oxygen isotopic exchange with micas and feldspars and of fe and mg exchange between garnet and biotite the results are accurate or geologically meaningful in only certain settings in most cases the results of isotopic thermometry must be evaluated with the aid of quantitative forward models for calculating the amount of retrograde diffusive exchange among micas feldspars and quartz two models used here predict quartz isotopic compositions that differ by only 0 1 per mil and in most cases reproduce to within 0 2 per mil the measured isotopic composition of quartz excellent agreement between isotopic and conventional thermometry is obtained for mid to upper amphibolite facies rocks that have experienced one period of recrystallization and mineral growth and if they are coarse grained or cooled in the absence of a hydrous fluid phase isotopic temperatures of 850 degrees c are in excellent agreement with conventional thermometry in migmatitic granulite facies metapelites if cooling occurred under anhydrous conditions in other cases isotopic temperatures in granulite facies rocks are higher than conventional temperatures a reasonable result in view of the tendency for retrograde cation exchange between garnet and biotite in samples that have undergone multiple periods of recrystallization or metamorphism isotopic temperatures from coexisting quartz garnet and aluminosilicates may be modified by diffusional exchange of quartz with micas and feldspars aided by recrystallization by retrograde reactions involving the latter phases or by open system interaction with externally derived fluids external fluid infiltration combined with recrystallization of quartz and aluminosilicate may result in isotopic reversals between garnet and matrix phases conventional thermobarometry in such complex rocks based in large part on mineral equilibria involving garnet may be erroneously assigned geological significance in the absence of insights provided by oxygen isotope analysis

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

maximum sea levels for the last glacial period from u series ages of submerged speleothems pleistocene sea levels reflect changes in the surface distribution of land sea and ice which in turn significantly influence the earth s climate1 the most complete record of sea levels for the last glacial cycle has come from raised coral reef terraces of the huon peninsula papua new guinea2 4 but interpretation of this record is hampered by relatively large age uncertainties and the possibility of variation in the rate of tectonic uplift subaerial speleothems stalagmites stalactites and flowstones from submerged caves in tetonically stable areas provide an alternative source of data5 8 as their growth stops when rising sea levels flood the caves previous studies of speleothems have been limited by dating precision5 6 and sample availability5 7 here we present high precision thermal ionization mass spectrometric 230th ages9 11 for a comprehensive suite of speleothem samples from the bahamas our results provide a record of maximum elevation of sea levels for the period from 80 to 10 kyr before the present for much of which sea levels are poorly known we also find that regional palaeoclimatic change can be an important factor in the termination of speleothem growth

speleothem evidence for mis 5c and 5a sea level above modern level at bermuda the history of sea level in regions impacted by glacio isostasy provides constraints on past ice sheet distribution and on the characteristics of deformation of the planet in response to loading the western north atlantic caribbean region and bermuda in particular is strongly affected by the glacial forebulge that forms as a result of the laurentide ice sheet present during glacial periods the timing of growth of speleothems at elevations close to sea level can provide records of minimum relative sea level rsl in this study we used u th dating to precisely date growth periods of speleothems from bermuda which were found close to modern day sea level results suggest that rsl at this location was above modern during mis5e mis5c and mis5a these data support controversial previous indications that bermudian rsl was significantly higher than rsl at other locations during mis 5c and mis 5a we confirm that it is possible to explain a wide range of mis5c a relative sea levels observed across the western north atlantic caribbean in glacial isostatic adjustment models but only with a limited range of mantle deformation constants this study demonstrates the particular power of bermuda as a gauge for response of the forebulge to glacial loading and demonstrates the potential for highstands at this location to be significantly higher than in other regions helping to explain the high sea levels observed for bermuda from earlier highstands

comparison of esr and tims u th dating of marine isotope stage mis 5e 5c and 5a coral from barbados implications for palaeo sea level changes in the caribbean abstract electron spin resonance esr dating of coral has become an efficient geochronological tool in supporting morphostratigraphic studies carried out on barbados during the last 10 years the newly developed approach for de determination de dmax plot procedure improves the precision of esr dating of pleistocene coral and therefore permits differentiation between the main marine isotope stages mis 5 7 9 and 11 and also between sub stages 5e c and a this study compares results of esr and tims uranium series dating u th of emergent last interglacial coral reef terraces from barbados and presents some implications for the timing and extent of sea level changes during marine isotope stages mis 5e c and a both dating methods indicate a distinct formation of up to three coral reef terraces during mis 5e at approximately 132 ka esr to 128 ka u th at c 128 ka esr and at c 120 ka u th to 118 ka esr it is also highly probable that three reef terraces were developed during mis 5c between c 103 ka u th and 105 ka esr the formation of two separate coral reefs during mis 5a is recognized for the first time on barbados with an age estimate for the older mis 5a 2 reef of 85 ka esr or 84 ka u th and an age estimate for the younger mis 5a 1 reef terraces of 74 ka esr or 77 ka u th assuming a constant uplift rate of 0 276 m ka at the south coast of barbados sea level reached its maximum during mis 5e 3 and mis 5e 2 between 132 and 128 ka ago after this sea level declined reaching a level of c 11 m below present sea level approx 118 120 ka ago mis 5e 1 during the substage 5c sea level was generally lower than in substage 5e it reached relative maxima at c 13 20 and 25 m during mis 5c approx 105 ka and formed three distinct coral reef terraces probably in relative short time intervals for the first time a double sea level oscillation is recognized on barbados during mis 5a an early mis 5a 2 c 85 ka with a sea level places at approx 21 m and a late mis 5a 1 sub stage c 74 or 77 ka with a sea level at approx 19 m below present sea level

rapid sea level fall and deep ocean temperature change since the last interglacial period we have dated huon peninsula papua new guinea and barbados corals that formed at times since the last interglacial period applying both 230 th and 231 pa dating techniques as a test of age accuracy we show that marine isotope stage mis 5e ended prior to 113 1 8 0 7 kyr when sea level was 319 m during mis 5b sea level was 357 m at 92 6 8 0 5 kyr having dropped about 40 m in approximately 10 kyr during the mis 5c 5b transition sea level then rose more than 40 m during the mis 5b 5a transition also in about 10 kyr mis 5a lasted until at least 76 2 8 0 4 kyr at a level of 324 m at that time combined with earlier data that places mis 4 sea level at 381 m at 70 8 kyr our late mis 5a data indicate that sea level fell almost 60 m in less than 6 kyr 10 6 m kyr during the mis 5 4 transition the magnitude of the drop is half that of the glacial interglacial amplitude and approximatelyequivalent to the volume of the present dayantarctic ice sheet during this interval the minimum average rate of net continental ice accumulation was 18 cm yr likely facilitated by efficient moisture transport from lower latitudes at three specific times 60 6 8 0 3 50 8 8 0 3 and 36 8 0 2 kyr during mis 3 sea level was between 385 and 374 m sea level then dropped to 3107 m at 23 7 8 0 1 kyr early in mis 2 before dropping further to last glacial maximum lgm values and then rising to present values during the last deglaciation times of rapid sea level drop correspond to times of high winter insolation at low northern latitudes and high winter latitudinal gradients in northern hemisphere insolation supporting the idea that these factors mayhave resulted in high water vapor pressure in moisture sources and efficient moisture transport to high latitude glaciers therebycontributing to glacial buildup we combined our sea level results with deep sea n 18 o records as a means of estimating the temperature and ice volume components in the marine n 18 o record this analysis confirms large deep ocean temperature shifts following mis 5e and during termination i deep ocean temperatures changed bymuch smaller amounts between mis 5c and 2 maximum temperature shift in the deep pacific is about 2 whereas the shift at a site in the atlantic is 4 under glacial conditions temperatures at both sites are near the freezing point the shift in the atlantic is likelycaused bya combination of changing proportions of northern and southern source waters as well as changing temperature at the sites where these deep waters form

pedogenic carbonate crusts calcretes in karstic landscapes as archives for paleoenvironmental reconstructions a case study from yucatan peninsula mexico abstract in the northeastern margin of the yucatan peninsula which is located in southeastern mexico three levels of compact carbonate crusts calcretes interlayered with indurated coastal calcareous sediments calcarenites are discernible since both the calcretes and calcarenites form a continuous carbonate sequence a combined methodology macro and micromorphology geochemistry and mineralogy is used to differentiate them additionally the calcrete layers are dated using the uranium thorium method in order to establish a chronological framework the carbonate differentiation and chronology are then used to establish the paleoenvironmental conditions that prevailed during calcrete formation as well as to reconstruct the coastal landscape evolution and its relation to pleistocene sea level changes during marine isotope stages mis 6 and 5 samples of calcrete layers and calcarenites were taken from two sections in the cancun tulum corridor the lowest level of calcrete underlies a sequence of calcarenites and the two younger levels cap the sequence in calcretes the micromorphology provides evidence of the presence of a relict soil with subangular blocky microstructure root traces and needle fiber calcite associated with soil fungi interactions in contrast the micromorphology of the calcarenites shows ooids and bioclasts typical of a coastal environment geochemically calcretes are depleted in 13c compared to calcarenite with values ranging between 2 and 10 and they have a lower proportion of rare earth elements calcrete mineralogy consists mainly of calcite over aragonite with a low proportion of mg calcite u th dating indicates that the oldest calcrete was formed during the penultimate glacial maximum pgm in mis 6 and the two younger calcretes correspond to the last interglacial period in mis 5c the calcarenite formation occurred earlier also during mis 5 soil formation strong karstification and soil erosion have occurred on younger calcretes this study suggests that these processes developed between mis 4 to mis 1

quaternary tectonic stability of the bahamian archipelago evidence from fossil coral reefs and flank margin caves abstract throughout the islands of the bahamian archipelago fossil coral reefs are found from current sea level up to a maximum elevation of 4 m 234 u 230 th radiometric dates obtained from in situ corals from these reefs by both alpha count and mass spectrometric techniques indicates that they were all formed during oxygen isotope substage 5e ca 125 000 years ago those data are consistent with a maximum sea level highstand of 6 m during substage 5e and either no vertical motion of the bahamas or possible isostatic subsidence of up to 2 m during the past 120 000 years no older in situ fossil corals or other subtidal deposits have been found subaerially exposed anywhere in the bahamas that finding suggests that late quaternary at least the past 300 000 years isostatic subsidence has occurred at a rate of 1 2 m per hundred thousand years and or no pre 5e highstands were above modern sea level an independent corroboration of the conclusions drawn about sea level amplitude and tectonic stability of the bahamas from the coral reef data is available from examination of abundant flank margin caves horizontal phreatic dissolution caves found above modern sea level throughout the bahamas these horizontally extensive air filled caves have dissolutional ceilings with elevations that are restricted to 1 to 7 m which is consistent with formation at the margin of a thin freshwater lens elevated by a past 6 m sea level highstand the restricted cave elevations and the lack of stalagmites in these caves that are older than 100 000 years are also consistent with cave formation during substage 5e and possible subsequent isostatic subsidence of a few metres the subsurface geology of the southeastern bahamas contains a long term record millions of years that has been attributed to past tectonic activity along the north american caribbean plate boundary while that record suggests differential subsidence across the bahamas in the tertiary period the data from fossil coral reefs and subtidal deposits and flank margin caves indicate that all bahamian banks on which there are islands have been tectonically stable and behaving similarly for at least the past several hundred thousand years

rapid sea level changes at the close of the last interglacial substage 5e recorded in bahamian island geology rapid and abrupt relative sea level changes within the last interglacial substage 5e are recorded in the island geology of the tectonically stable bahamas from 132 to 118 ka reef growth reached a maximum elevation near 2 m as indicated by fossil reef elevation across the platform whereas bioeroded notches are incised in coastal cliffs as high as 6 m the end of the interval is characterized by voluminous eolianites exhibiting palm tree and frond impressions it is inferred that sea level for most of the interval remained near 2 m restraining reef growth and that the notch at 6 m represents a rapid and brief excursion just before the close of the substage the subsequent fall must have been rapid in order to leave the notch profile intact and mobilize windward lagoon ooids into dunes before cementation could anchor them in order to explain the rapid rise to 6 m glacial surging is invoked the subsequent fall also rapid may be a consequence of the surge flooding high latitudes and providing enough moisture to initiate reglaciation and drawdown

timing and warmth of the last interglacial period new u series evidence from hawaii and bermuda and a new fossil compilation for north america abstract the timing and duration of the last interglacial period have been controversial with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing new high precison thermal ionization mass spectrometric tims u series ages of last interglacial corals from hawaii and bermuda test these competing hypotheses waimanalo formation corals from slowly uplifting oahu hawaii range in age from 134 to 113 ka with most ages between 125 and 115 ka combined with published u series ages from nearby lanai the data suggest a long last interglacial period that may have occurred from 136 to at least 115 ka the results indicate that orbital forcing may not have been the only control on ice sheet growth and decay because sea level would have been high at times of relatively low northern hemisphere summer insolation on tectonically stable bermuda deposits from the 200 ka penultimate interglacial period 120 ka peak last interglacial period and 80 ka late last interglacial period high sea stands have been newly dated fossil corals on bermuda are derived from patch reefs that likely were catch up responses to sea level rise it is expected that u series ages of last interglacial corals on bermuda should overlap with but not be as old as the range of corals on oahu last interglacial corals on bermuda give a range of 125 113 ka which supports this hypothesis a large number of emergent marine deposits on hawaii bermuda and along coastal north america have now been dated to the last interglacial period both oahu and bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks suggesting warmer than present waters during the last interglacial period warmer waters are also suggested for last interglacial localities around most of north america from florida to canada and greenland and baja california to alaska these observations are consistent with similar warm water faunas of last interglacial age reported from japan the mediterranean basin and western australia it is likely that significant changes in ocean currents took place during the last interglacial period with a movement of relatively warm waters to higher latitudes than is the case today

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

characterizing the eemian weichselian transition in northwestern europe with three multiproxy speleothem archives from the belgian han sur lesse and remouchamps cave systems abstract interglacial to glacial transitions represent the most drastic turnovers in the quaternary climate system yet millennial scaled climate variability and stochastic internal variability that result in inter glacial transitions remain poorly understood here three speleothems from two different cave systems in belgium are investigated to characterize the eemian to early weichselian transition the speleothems show high reproducibility for 13c interpreted as a proxy for past vegetation activity controlled by type of vegetation above the cave all three speleothems show a drastic increase in 13c between 118 and 117 ka reflecting a rapid change in vegetation from last interglacial temperate tree species towards glacial open grass vegetation this transition shows a strong affinity with the late eemian aridity pulse leap at 118 1 ka previously identified in pollen records from western germany an age of 117 7 0 5 ka is determined for the start of this transition in the belgian speleothems the speleothem records show a distinct transition in the proxies between eemian optimum conditions and increased variability during the glacial inception and therefore the eemian weichselian transition is set at 117 7 0 5 ka in the speleothem records high resolution trace element analysis shows that the transition is initiated by a cooling pulse followed by a decrease in precipitation through comparison with other archives including north atlantic sedimentary records it is proposed that the transition at 117 7 ka constitutes an internal climate response caused by a substantial input of freshwater from degraded ice sheets by the end of the eemian 120 118 ka